JP2002303691A - Solid-cooled reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve inherent safety by preventing a loss of coolant and a loss of cooling function of a core. SOLUTION: A solid cooling block 1 having a fuel loading part 1a for loading nuclear fuel and a heat extraction part 1b for taking out heat for use, a heat exchange means 2 arranged in the heat extraction part 1b and a core 3 having power density never leading to melting of the solid cooling block 1 are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid-cooled nuclear reactor. More specifically, the present invention relates to a reactor which further improves safety by eliminating the occurrence of assumed accident events such as loss of coolant accident, loss of cooling function, and reactivity accident necessary for safety evaluation of a reactor. It is.

[0002]

2. Description of the Related Art In a conventional nuclear reactor, the core is housed in a reactor pressure vessel, and the core heat is taken out of the reactor by a gas or liquid coolant circulating in the reactor pressure vessel to cool the core. I am trying to do it. The coolant taken out of the reactor is cooled again by radiating its heat through a steam generator, a heat exchanger, or the like, and is returned to the reactor pressure vessel. That is, the core is cooled by using a coolant as a fluid and circulating the fluid. Specifically, for example, light water in a light water reactor, heavy water in a heavy water reactor,
Helium gas and carbon dioxide gas were used as coolants in gas furnaces, and liquid metal was used as coolant in fast breeder reactors.

Further, in a conventional nuclear reactor, a coolant that has been heated to a high temperature by cooling the core is used for generating steam or high-temperature gas for rotating a power generation turbine. After cooling the cooling water by raising the
It was circulated again to the core.

On the other hand, as a method of controlling the reactivity of the core, there is a method of inserting and removing a control rod made of a neutron absorbing material into and from the core. Conventionally, control rods are, for example, several centimeters in order to prevent a reactivity accident while taking into account the time required for starting the reactor.
Per second.

[0005]

However, in a nuclear reactor using a gas or a liquid as a coolant, the coolant flows. Therefore, a countermeasure for the loss of the coolant, that is, a countermeasure for the loss of the coolant is separately taken. Had to be kept.

[0006] In a nuclear reactor in which the cooling water, which has been cooled to a high temperature by cooling the core, is cooled by generating steam or a high-temperature gas for power generation and circulated again to the core, for example, a turbine trip or a failure of a circulating pump causes a failure. If steam or high-temperature gas ceases to circulate, the high-temperature coolant cannot be cooled and the cooling function of the core will be lost, so take measures to prevent the loss of the cooling function assuming that case. Needed.

Further, in the safety evaluation of a reactor, it is necessary to assume a reactivity accident due to a control rod jumping out or a change in coolant flow rate. Has been requested.

Further, there is a demand for further improving the safety of the reactor by enabling passive reactivity control with respect to a change in the reactivity of the core. There is also a demand for simplifying the structure by eliminating the need for a reactor pressure vessel.

An object of the present invention is to provide a nuclear reactor which does not lose the cooling function of the coolant and the core. The present invention also structurally prevents reactivity accidents,
An object of the present invention is to provide a nuclear reactor capable of passive reactivity control. It is a further object of the present invention to provide a nuclear reactor that can eliminate the need for a reactor pressure vessel.

[0010]

In order to achieve the above object, a solid-cooled nuclear reactor according to claim 1 includes a fuel element enclosed by a heat-conductive solid-cooling block directly in contact with the fuel element. While the heat of the fuel element is extracted through the fuel element and the fuel element constitutes a core having a power density that does not melt the solid cooling block, the solid cooling block is cooled by natural convection of the surrounding fluid and gradually cooled. I try to heat it.

Therefore, the nuclear fuel loaded in the core is cooled by the solid cooling block, and heat of the core is extracted through the solid cooling block. Extraction of heat transmitted to the solid cooling block may be released from the surface of the solid cooling block to a surrounding fluid, such as air or water or other liquid, or may be a heat extracting means provided inside or on the solid cooling block, for example. It is transmitted to cooling means such as heat exchange means. Since the power density of the core is designed to be smaller than the value that can melt the solid cooling block, that is, the solid cooling block is designed to a value that does not melt due to residual heat or decay heat after the core shuts down. The cooling block does not melt. Moreover, the solid cooling block does not flow unlike a liquid or a gas, so that it is not lost. Also, even if the means for cooling the heat of the core via the solid cooling block loses its ability, the cooling function is not completely lost since it is cooled by natural heat radiation from the surface of the solid cooling block.
The residual heat or decay heat of the core is 1/10 of the reactor operation.
Sufficient heat-reduction capability is sufficient, and cooling can be sufficiently realized by natural heat radiation.

Further, the solid cooling block seals a fuel element filled with nuclear fuel. Therefore, the solid cooling block functions as a reactor vessel, and a pressure vessel required in a reactor using liquid or gas as a coolant is not required.

Here, the solid cooling block is gradually heated by natural convection cooling of the surrounding fluid on its surface, for example, by air cooling or water cooling (including liquids other than water). Therefore, even if it becomes impossible to remove the heat of the solid cooling block by the coolant passing through the solid cooling block, the solid cooling block is cooled by radiating heat from the surface to the surrounding fluid, and the cooling function is completely completed. Will not be lost. In the case of water cooling of the solid cooling block, the solid cooling block is submerged in a sufficient amount of liquid in the pool to remove residual heat and decay heat of the core, and cooled by natural convection of the liquid. Preferably. In this case, since the cooling capacity is much larger than that of air cooling, the heat output of the nuclear reactor can be made larger than that of a natural heat radiation reactor by air cooling. In addition, by storing the liquid in the pool, the fluid is not lost as in the case of a broken pipe. Furthermore, in this case, since the solid cooling block is submerged in the liquid and there is no danger of fire,
Graphite can be used as a solid cooling block.
Graphite has a small thermal neutron absorption cross-section, and the thermal neutron economy is good.

The solid cooling block can be implemented as long as it is a solid material having thermal conductivity. Among them, it is preferable to use metal or graphite. In the case of a graphite block,
It is economical because neutron absorption is small and it is not absorbed wastefully. Further, as the solid cooling block, for example, a metal or the like having excellent heat transfer properties, such as aluminum and copper, may be used. In this case, when the solid-cooled nuclear reactor is a thermal neutron reactor, the absorption cross section of thermal neutrons is The use of small aluminum or the like is preferred. When a metal solid cooling block is used, there is no risk of fire, so that cooling can be performed not only by water cooling but also by air cooling.

The solid-cooled nuclear reactor according to claim 6 is
The solid cooling block is provided with a coolant path that penetrates through the block and circulates a coolant, and the coolant flowing through the path extracts heat of the fuel element, cools the core, and generates heat for power generation and the like. It is designed to be used as a power source. In this case, the heat transmitted to the solid cooling block is transmitted to the coolant flowing in the coolant path passing through the solid cooling block, and is taken out of the solid cooling block as a heat source for power generation or driving. Therefore, the output of the core can be set to a value corresponding to the cooling capacity of the coolant circulating using the coolant path. Even in such a case, even if the circulation of the coolant is stopped for some reason, for example, if the removal of heat from the coolant path, for example, the steam generating pipe due to a turbine trip, is stopped, the decay heat and the residual heat of the core are solid-cooled. Since the heat is cooled by radiating heat from the surface of the block, the cooling function is not completely lost. In such a case, since the reactor is shut down passively, it is not necessary to gradually reduce the heating value of the reactor by 100%, and the residual heat removal capability of the reactor (at most about 10% of the reactor heating value, generally Is less than that).

According to a seventh aspect of the present invention, in the solid-cooled nuclear reactor according to any one of the first to fifth aspects, a thermoelectric conversion element is attached to the solid-state cooling block, and the core is taken out through the solid-state cooling block. The heat is directly used to generate electricity. In this case, the heat of the core taken out through the solid cooling block is transmitted to one pole of the thermoelectric conversion element, and the heat of the fixed cooling block in contact with the other pole is radiated to the surrounding air or water. The cooling causes a temperature difference between the two poles of the thermoelectric conversion element. The heat transmitted to the solid cooling block is transmitted to the thermoelectric conversion element via the solid cooling block, and is released from the surface of the solid cooling block into the surrounding air or water or other liquid. Further, the solid cooling block does not flow unlike a liquid or a gas, so that it is not lost. Further, even if it becomes impossible to remove the heat of the solid cooling block by the thermoelectric conversion element, the solid cooling block is radiated from its surface and cooled, so that the cooling function is not completely lost.

According to an eighth aspect of the present invention, in the solid-cooled nuclear reactor according to the second aspect, a fluid passage is provided for receiving radiation irradiation in a liquid in which the solid cooling block is submerged,
A fluid to be activated or heated flows through the fluid passage. Therefore, the radiation leaked from the core is applied to the fluid passage. When a fluid flows through the fluid passage, the fluid is also irradiated with radiation, and for example, an isotope can be manufactured. Further, the fluid can be heated by irradiation with radiation, and the energy of the radiation can be extracted as heat energy.

According to a ninth aspect of the present invention, there is provided the solid-cooled nuclear reactor according to any one of the first to eighth aspects, further comprising a control rod, and a restricting means for restricting a withdrawal speed of the control rod to a set speed or less. It is like that. Therefore,
Structurally, the control rod cannot be pulled out at a high speed, and a reactivity accident such as control rod jumping out can be prevented.

The invention according to claim 10 is the first invention.
In the solid-cooled reactor according to any one of claims to 9, a passive controller for increasing or decreasing the reactivity according to a temperature change is attached to the solid-cooled block, and the passive controller is a neutron absorber, A driving member connected to the neutron absorber and deformed by a change in temperature, wherein the driving member has a first shape for positioning the neutron absorber outside the core and a second shape for moving the neutron absorber into the core. And when the temperature of the solid cooling block rises above a set temperature, the solid cooling block is deformed from the first shape to the second shape.

In this case, during a normal operation in which the temperature of the solid cooling block does not rise to a temperature at which the driving member deforms to the second shape, the driving member has the first shape, and the neutron absorber is the core. Is located outside. On the other hand, when the temperature of the solid cooling block abnormally rises and reaches a set temperature for deformation, the driving member deforms from the first shape to the second shape and moves the neutron absorber into the core. For this reason, a negative reactivity is inserted into the core, and the power decreases. And
When the temperature of the solid cooling block decreases due to a decrease in output, the shape of the driving member returns from the second shape to the first shape, and the neutron absorber is pulled out of the core. Therefore, the reactivity increases and the output increases. In this way, the reactivity is passively controlled according to the vertical fluctuation of the core temperature.

[0021] Further, the invention according to claim 11 is based on claim 1.
11. The solid-cooled nuclear reactor according to any one of to
A safety rod device that reduces the reactivity according to the temperature rise is attached to the solid cooling block, and the safety rod device is a neutron absorber, and the neutron absorber is magnetically adsorbed and suspended above the reactor core. A supporting magnet body is provided, and the magnet body has a Curie point at a temperature higher than a normal temperature of the solid cooling block during reactor operation and lower than a melting point of the solid cooling block.

In this case, during normal operation in which the temperature of the solid cooling block does not rise to the Curie point of the magnet, the neutron absorber is suspended above the reactor core.
On the other hand, when the temperature of the solid cooling block rises abnormally and reaches the Curie point, the magnet body cannot magnetically attract the neutron absorber, so that the neutron absorber falls into the core. This results in a negative reactivity being inserted into the core, reducing power and possibly shutting down the reactor.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail based on the best mode shown in the drawings.

FIG. 1 conceptually shows an example of an embodiment in which the solid-cooled nuclear reactor according to the present invention is configured as a thermal neutron reactor. The solid-cooled nuclear reactor 5 encloses the fuel element 4 in a heat-conductive solid cooling block 1 that is in direct contact with the fuel element so as to extract heat from the fuel element 4 through the solid cooling block 1. The solid cooling block 1 is cooled by the natural convection of the surrounding fluid and gradually heated. More specifically, the solid-cooled nuclear reactor 5 includes a solid-cooling block 1 having a fuel loading section 1a on which nuclear fuel is loaded and a heat extraction section 1b for extracting heat for use, and a heat extraction section 1b. And a core 3 having a power density that does not melt the solid cooling block 1.

The solid cooling block 1 is made of a metal having excellent heat transfer properties, such as aluminum and copper. However, when the solid-cooled nuclear reactor 5 is a thermal neutron reactor, it is preferable to use aluminum or the like having a small thermal neutron absorption cross section.
Further, a large number of radiating fins 1c are provided on the surface of the solid cooling block 1.

At the center of the solid cooling block 1, for example, a plurality of holes serving as fuel loading portions 1a are formed at predetermined intervals. A fuel element 4 such as a fuel rod filled with nuclear fuel is inserted into the fuel loading section 1a, and the fuel element 4 and the solid cooling block 1 are inserted.
Are brought into direct contact with each other to transfer heat generated by the fuel to the solid cooling block 1 to cool the fuel element 4. After the fuel element 4 is inserted, the hole serving as the fuel loading section 1 a is covered and closed, and the fuel element 4 is sealed in the solid cooling block 1. As a result, the solid cooling block 1 functions as a reactor vessel, and it becomes unnecessary to use a reactor vessel that is required in a reactor using a liquid or a gas that is forcibly circulated as a coolant.

A coolant passage is provided between the solid cooling block 1 and, for example, between the fuel loading portions 1a and through the block 1 to circulate a fluid coolant such as light water to extract heat from the reactor core 3. ing. This coolant path is, for example, a heat extraction unit 1 formed by a plurality of through holes.
b and a steam generating pipe (hereinafter, referred to as a steam generating pipe 2) which is a heat exchange means 2 inserted into the heat extracting portion 1b. That is, the solid cooling block 1 incorporates the steam generating pipe 2 functioning as a steam generator. A fluid such as light water flows in the steam generating pipe 2. In this solid-cooled nuclear reactor 5, since the steam generating pipe 2 is disposed between the fuel elements 4, the light water flowing in the steam generating pipe 2 functions as a moderator, and becomes a thermal neutron reactor. The steam generated in the steam generating pipe 2 is supplied to, for example, a power generation turbine (not shown).

The core 3 has a power density that does not melt the solid cooling block 1. That is, the power density is designed so that the temperature of the solid cooling block 1 does not reach the melting point during the operation of the reactor. In this case, the solid cooling block 1
The heat dissipation from the volume and the surface, the flow rate in the steam generating tube 2 and the like are also taken into consideration. The design of the power density can be obtained by the same method as the design of the power density of light water reactors, experimental reactors, and the like that have been put into practical use, and thus the description thereof is omitted. In this embodiment, the core 3 of the solid cooling block 1 in which the fuel element 4 and the steam generating pipe 2 are arranged is the core 3.

The temperature of the solid cooling block 1 during the operation of the solid cooling reactor 5 is, for example, when aluminum is used as the solid cooling block 1, the melting point of aluminum is 6
It is about 400 ° C. because of 60 ° C., and about 800 ° C. when copper is used as the solid cooling block 1 because the melting point of copper is 1084 ° C. That is, the solid cooling block 1
The power density of the core 3 is designed so that the temperature of the core 3 becomes these temperatures. Therefore, the solid cooling block 1 does not melt.

The power density of the core 3 is designed to a value that does not cause the solid cooling block 1 to be melted by residual heat or decay heat after the core is stopped. Therefore, even after the core is stopped, the solid cooling block 1 does not melt.

The heat generated in the core 3 by the operation of the solid-cooled nuclear reactor 5 is transmitted to the solid-state cooling block 1, whereby the core 3 is cooled. Then, the heat transmitted to the solid cooling block 1 is transmitted to the steam generation pipe 2 of the heat extraction unit 1b, and heats the light water flowing in the steam generation pipe 2 to generate steam. The steam is used to rotate a steam turbine of a generator to generate power. Also, the solid cooling block 1
The heat is also dissipated from the surface. Since a large number of radiating fins 1c are provided on the surface of the solid cooling block 1, heat is efficiently radiated.

Incidentally, an air flow is formed around the solid cooling block 1 by natural convection. With this flow of air, heat radiation from the surface of the solid cooling block 1 can be performed more efficiently. The solid cooling block 1 also functions as a reactor vessel, and a flow of air is formed outside the reactor. Therefore, the solid cooling block 1 is different from a conventional reactor in which a flow of coolant is formed in the reactor vessel. It is easy to form and control the air flow. Further, in the solid-cooled nuclear reactor 5, heat exchange is performed between the solid cooling block 1 and the fluid by passing the steam generating tube 2 through the solid cooling block 1. In this case, the steam generating tube 2 simply passes through the solid cooling block 1. The steam generating pipe 2 is disposed outside the solid cooling block 1 because the fluid does not permeate the inside of the solid cooling block 1. A flow is formed outside. That is, the flow in the steam generating pipe 2 is also formed outside the solid cooling block 1, and compared with the conventional reactor in which the flow of the coolant is formed in the reactor vessel, the flow of the fluid is not formed. Its control is easy.

In the solid-cooled nuclear reactor 5, even when the flow of light water in the steam generating tube 2 is stopped and heat removal from the heat extraction part 1b cannot be expected, the core 3 can be continuously cooled. In other words, the solid cooling block 1 heated by cooling the core 3 radiates heat on its surface, and can continue to cool the core 3 without melting. Also, the solid cooling block 1
Is a metal and has good thermal conductivity, so that the cooling capacity of the core 3 can be sufficiently ensured. Further, since the solid cooling block 1 is solid and does not flow, unlike the liquid or gaseous coolant, the solid cooling block 1 is not lost due to breakage of the piping or the like. Also, since the solid cooling block 1 is made of metal,
There is no fear of fire and good radiation shielding performance. Furthermore, since the solid cooling block 1 is in a lump,
Structurally strong. For these reasons, the safety of the reactor is further improved.

FIG. 2 conceptually shows a case where the solid-cooled nuclear reactor 5 is applied to a fast neutron reactor. The heat extraction portion 1b of the solid cooling block 1 is provided at a position sufficiently distant from the fuel loading portion 1a. Here, the sufficiently distant position means that the light water in the steam generating tube 2 arranged in the heat extraction part 1b has no influence on the deceleration of neutrons contributing to the fission reaction in the reactor core 3, or has no influence. It is a position where the influence is negligible even if it is ignored. By thus separating the heat extraction unit 1b from the fuel loading unit 1a sufficiently, it is possible to prevent the fast neutrons that contribute to the nuclear fission reaction from being decelerated by the light water in the steam generation tube 2. Also,
As the solid cooling block 1, it is preferable to use copper or the like that does not have a large absorption cross section of fast neutrons, has a high heat transfer coefficient, and has a higher melting point than aluminum.

Even in the fast neutron reactor having such a configuration, even if the flow of light water in the steam generating pipe 2 is stopped,
The solid cooling block 1 can continue to cool the core 3 by radiating heat from the surface. Also, the solid cooling block 1
Is not a fluid, it is not lost, there is no need to worry about fire in the solid cooling block 1, the radiation shielding performance by the solid cooling block 1 is good, and the solid cooling block 1 is structurally strong. Point, solid cooling block 1
Functions as a reactor vessel in the same manner as in the case where the solid-cooled reactor 5 is a thermal neutron reactor. For these reasons, the safety of the reactor is further improved as in the case of the thermal neutron reactor. It is.

FIG. 3 conceptually shows an example of an embodiment of a nuclear power plant provided with the solid-cooled nuclear reactor 5. The steam generating pipe 2 constitutes a part of a loop 7 for supplying steam to the power generating turbine 6. The steam generated in the steam generating pipe 2 is supplied to a power generation turbine 6, for example, a steam turbine to rotate it. Thereby, power generation is performed. Then, the steam that has caused the power generation turbine 6 to rotate is returned to a light water state by the condenser 8, and then is pressurized by the pump 9 to be pressed into the steam generating pipe 2.
Supplied to

FIG. 4 shows another embodiment. In this solid-cooled nuclear reactor, instead of taking out the heat of the core taken out through the solid-state cooling block 1 to the outside of the block 1 using a more fluid coolant, a heat exchange means 2 ′ composed of a thermoelectric conversion element is used. And power is generated directly by utilizing the heat of the core 3 taken out through the solid cooling block 1. By providing the thermoelectric conversion element 2 ′ on the surface of the solid cooling block 1 or by burying the thermoelectric conversion element 2 ′, a temperature difference is formed between the two poles of the thermoelectric conversion element 2 ′ to take out the heat of the reactor core 3 in the form of electricity. The heat of the core 3 taken out through the solid cooling block 1 is transmitted to one pole of the thermoelectric conversion element 2 ', and the heat of the fixed cooling block 1' in contact with the other pole is radiated to the surrounding air or water. As a result, a temperature difference is generated between the two poles of the thermoelectric conversion element 2 ′. The heat transmitted to the solid cooling block 1 is transmitted to the thermoelectric conversion element 2 ′ via the solid cooling block 1 and is also released from the surface of the solid cooling block 1 into the surrounding air or into water or other liquid. . Further, the solid cooling block 1 does not flow unlike a liquid or a gas, so that it is not lost. Therefore,
Even if it becomes impossible to remove heat from the core 3 by the thermoelectric conversion element 2 ', the solid cooling block 1 is cooled by radiating heat from the surface thereof, so that the cooling function is not completely lost.
In this case, there is no need to use any fluid that may be lost before the power is generated by the heat of the reactor core 3, and the safety of the reactor is improved in conjunction with the improvement of the safety of the reactor described above. Further improvements can be made, and unmanned operation of the reactor can be achieved.

In the above description, heat is radiated from the surface of the solid cooling block 1 by air cooling. However, the solid cooling block 1 is submerged in a water pool at normal pressure, or water is sprayed on the surface of the solid cooling block 1. It is also possible to perform heat radiation by water cooling by spraying or the like. By performing heat radiation by water cooling, improvement in heat radiation performance from the surface of the solid cooling block 1 can be expected.

In the above description, the heat generated in the reactor core 3 is used for power generation by supplying the steam generated in the steam generating pipe 2 to, for example, the power generation turbine 6, but the invention is not limited to this. For example, heat generated in the core 3 may be used as a heat source for heating or the like.

In the above description, steam is generated by flowing light water into the steam generating pipe 2. However, the present invention is not limited to light water. For example, liquid such as heavy water or gas such as helium gas or carbon dioxide gas is used. There may be. When a gas is allowed to flow in the steam generating pipe 2, a gas turbine is used as the power generation turbine 6 as a matter of course.

Further, the solid-cooled nuclear reactor 5 may be one module (hereinafter, referred to as module 5), and a plurality of modules 5 may be installed in parallel. FIG. 5 shows the concept in this case. Each module 5 is installed in a reactor containment vessel 10 and is further covered with a shield 11. Shield 1
An air flow is formed inside the solid cooling block 1 to remove heat released from the surface of the solid cooling block 1. The steam generating tubes 2 of each module 5 are connected to the same power generating turbine 6. That is, the number of turbines 6 for power generation is one, and the steam generated in each module 5 is supplied to the turbine 6 for power generation and used for power generation. After rotating the power generation turbine 6, the light water returned to a liquid state by a condenser (not shown) is pressurized by a pump 9 and supplied to the steam generation pipe 2 of each module 5. Reference numeral 12 denotes a crane for loading or unloading the module 5. By making the solid-cooled nuclear reactor 5 into a module, the modules 5 may be installed in a number corresponding to the power generation scale and the like. By doing so, the number of the modules 5 and the power generation turbines 6 and the like can be kept to a minimum and the power generation cost can be reduced. Further, the number of power generation turbines 6 and pumps 9 may be increased according to the number of modules 5 installed.

FIG. 15 shows another embodiment of the present invention in which the solid-cooled nuclear reactor is configured as a multipurpose reactor for generating heat for heating, for example. This solid-cooled nuclear reactor
The fuel element 4 is sealed in a heat-conducting solid cooling block 1 that is in direct contact with the fuel element 4, and the heat of the fuel element 4 is extracted through the solid cooling block 1.
The heat of the fuel element 4 taken out by the solid cooling block 1 is cooled by the natural convection of the fluid around the solid cooling block 1 and gradually heated, and the heat is used for heating and seawater desalination in chemical processes and the like. It was done. In this case, the heat generated in the core 3 is not radiated from the surface (including the radiation fins) of the solid cooling block 1 but has no cooling means, but the power density of the core melts the solid cooling block 1. Since the core 3 having no scale is constructed, there is no fear of melting during operation. Note that a large number of heat radiation fins 1c are provided on the surface of the solid cooling block 1.

Next, FIGS. 16 to 19 conceptually show an embodiment of a water-cooled solid-cooled nuclear reactor according to the present invention. In this embodiment, the solid-cooled nuclear reactor is, for example, a boiling water reactor (BWR).

The solid-cooled reactor 45 includes a solid-cooling block 41 having a fuel loading section 41a into which nuclear fuel is loaded, a heat extraction section 41b for extracting heat for use, and a heat-exchange section disposed in the heat extraction section 41b. It is provided with an exchange means 42 and a core 43 having a power density that does not melt the solid cooling block 41 and is submerged in the liquid.

The solid cooling block 41 is, for example, graphite. In the solid-cooled nuclear reactor 45, the solid-cooled block 41
Is submerged in the liquid and there is no risk of fire. Therefore, graphite can be used as the solid cooling block 41. Graphite has a small thermal neutron absorption cross-section, and the thermal neutron economy is good. However, the solid cooling block 41 may be made of a metal having excellent heat transfer properties, such as aluminum or copper. In this case, when the solid cooling reactor 45 is a thermal neutron reactor, the absorption of thermal neutrons is cut off. It is preferable to use aluminum or the like having a small area.

For example, the fuel loading section 4 of the solid cooling block 1
Between 1a, there is provided a coolant path which passes through the block 41 and circulates a fluid coolant such as light water to extract heat from the core 43. This coolant path is, for example, a heat extraction portion 4 formed by a plurality of through holes.
1b, and a cooling pipe (hereinafter, referred to as a cooling pipe 42) which is a heat exchange means 42 inserted into the heat extraction portion 41b. That is, in the solid cooling block 41, a large number of holes serving as the fuel loading portion 41a are formed at predetermined intervals. As shown in FIG. 18, for example, each of the fuel loading portions 41a is formed in an area 46 outside the solid cooling block 41 (an area outside the imaginary line A in FIG. 18). Fuel elements 4 such as fuel rods in which the fuel loading section 41a is filled with nuclear fuel
4 is inserted, and the fuel element 44 is brought into direct contact with the solid cooling block 41 to transfer heat generated by the fuel to the solid cooling block 41 to cool the core 43. For example, a low-enriched uranium oxide fuel is used as the nuclear fuel, and a zircaloy alloy, which has been used, for example, is used as the cladding tube.
The loading of the fuel element 44 is performed simultaneously with the manufacture of the fuel unit 47. After the fuel element 44 is inserted, the hole serving as the fuel loading portion 41 a is covered and closed, and the fuel element 44 is sealed in the solid cooling block 41. Thus, the solid cooling block 41 functions as a reactor pressure vessel, and the reactor pressure vessel, which is a generally required component, can be eliminated. For this reason, the structure of the nuclear reactor is simplified, and the construction cost can be reduced.

The outer region 4 of the solid cooling block 41
A large number of through holes serving as heat extraction portions 41b are formed between the fuel loading portions 41a and the inside region (the region inside the outside region 46) 48. The cooling pipe 42 is inserted into the heat extraction part 41b. The lower end of the cooling pipe 42 in the outer region 46 communicates with an inlet chamber 50 connected to a cooling water inflow pipe 49. The lower end of the cooling pipe 42 in the inner region 48 communicates with an outlet chamber 52 connected to the steam outlet pipe 51. The upper end of the cooling pipe 42 in the outer area 46 and the upper end of the cooling pipe 42 in the inner area 48 communicate with each other through the upper chamber 53. A fluid such as light water flows through the cooling pipe 42.
The steam is heated while moving up the cooling pipes 42 in the outer area 46 and becomes steam, and is superheated (superheated) while moving down the cooling pipes 42 in the inner area 48. Light water can be used as a moderator by flowing light water into the cooling pipe 42 in the outer region 46 in which the fuel element 44 is provided. On the other hand, steam having inferior performance as a moderator is supplied to the inner side where the fuel element 44 is not provided. It is made to flow to the cooling pipe 42 in the area 48.

The inside of the fuel element 44 has a higher pressure than its surroundings, and its cladding swells and the solid cooling block 4
Close the gap between 1. For this reason, the fuel element 44 and the solid cooling block 41 are in good contact, and heat transfer is performed well. Further, the inside of the cooling pipe 42 has a higher pressure than the surroundings, and the cooling pipe 42 expands to close a gap between the cooling pipe 42 and the solid cooling block 41. For this reason, the cooling pipe 42 and the solid cooling block 41 are in good contact with each other, and heat transfer is performed well.

The solid-cooled nuclear reactor 45 has, for example, a plurality of fuel units 47. The number of fuel units 47 installed is determined according to the output scale of the solid-cooled nuclear reactor 45, and conversely, the output scale can be determined based on the number of installed fuel units 47. When the solid-cooled nuclear reactor 45 is used for power generation, for example, a number of fuel units 47 according to the power generation scale are installed. If the solid-cooled nuclear reactor 45 is small, one fuel unit 47 may be used.
In the present embodiment, for example, 16 fuel units 47 are
They are arranged side by side in four columns and four columns. It should be noted that a control rod having a cross-shaped cross section is inserted between the fuel units 47.

Below the row of fuel units 47, a cooling water inflow pipe 49 and a steam outflow pipe 51 are arranged one by one. Four mounting flanges 54 are fixed to the cooling water inflow pipe 49 and the steam outflow pipe 51 at predetermined intervals. Each of the fuel units 47 can be fixed on the cooling water inflow pipe 49 and the steam outflow pipe 51 by overlapping and fixing the flanges 55 fixed to the bottom surface of the fuel unit 47 on these mounting flanges 54. The cooling water inlet pipe 49 and the inlet chamber 50 can be connected, and the steam outlet pipe 51 and the outlet chamber 52 can be connected. At the time of refueling or the like, the flange 55 is removed from the mounting flange 54 and the fuel is replaced together with the fuel unit 47. The cooling water inflow pipe 49 and the steam outflow pipe 51 are sequentially bundled, respectively, and are finally collected into one cooling water inflow pipe 49 and the steam outflow pipe 51, respectively, and led to the power generation facility 56.

The core 43 has a power density that does not melt the solid cooling block 41. That is, the power density is designed so that the temperature of the solid cooling block 41 does not reach the melting point during the operation of the nuclear reactor. In this case, the volume of the solid cooling block 41, heat radiation from the surface, the flow rate in the cooling pipe 42, and the like are also taken into consideration. The design of the power density can be obtained by the same method as the design of the power density of light water reactors, experimental reactors, and the like that have been put into practical use, and thus the description thereof is omitted. In this embodiment, the fuel element 44 of the fuel unit 47 is
The part where the cooling pipes 42 are arranged is a core 43.

The power density of the core 43 is designed to a value that does not melt the solid cooling block 41 due to residual heat or decay heat after the core is stopped. Therefore, the solid cooling block 41 does not melt during operation of the reactor or after shutdown.

The fuel unit 47 is submerged in the liquid in the reactor pool 57. The liquid stored in the reactor pool 57 is, for example, water. However, it is needless to say that it is not limited to water. Water is stored in the reactor pool 57 at normal pressure.

The reactor pool 57 is formed in a so-called semi-underground structure. That is, the reactor pool 57 has a structure for storing water in a large hole, and does not have a structure for storing water in a space surrounded by a wall. Therefore, it is possible to prevent water from flowing out of the reactor pool 57 due to damage to the wall. During the normal operation of the solid-cooled reactor 45, several percent of the heat is transferred from the solid-cooled block 41 to the reactor pool 57. Therefore, a small heat exchanger 58 is installed in the reactor pool 57 and the water in the reactor pool 57 is retained. Temperature of, for example, up to 60
It is cooled to about ℃.

When the cooling water is lost due to breakage of the cooling water inflow pipe 49 and the steam outflow pipe 51 or the cooling capacity of the cooling medium such as a turbine trip or a shaft fixation of the steam pump is lost, the cooling pipe 42 of the fuel unit 47 is removed. The void increases, the reactivity of the reactor decreases due to a negative void coefficient or the like, and the reactor shuts down. Even if the nuclear reactor stops, decay heat is generated in the core 43, and this decay heat is transmitted from the fuel element 44 to the solid cooling block 41, and the solid cooling block 41
Is naturally radiated from the surface of the reactor pool to the water in the reactor pool 57. Therefore, the temperature of the fuel element 44, the fuel unit 47, and the like does not become abnormally high, and their soundness is maintained. That is, there is no possibility that an accident such as melting of the core, which may have a great effect on the public, will occur, and it is not necessary to design the nuclear reactor on the assumption of such an accident.

The amount of water retained in the reactor pool 57 is sufficient for removing decay heat when the reactor is stopped. Therefore, even if the cooling function of the small heat exchanger 58 in the reactor pool 57 does not work for some reason, the decay heat of the core 43 can be received. The area around the reactor pool 57
For example, it is hardened with concrete. A liner made of, for example, stainless steel is provided on the inner surface of the reactor pool 57 to prevent seepage of retained water.

During the operation of the reactor, the reactor pool 57 is closed by a reactor cover 59 made of steel, thereby preventing leakage of radioactive substances. Further, the control rod 60 is driven by a control rod driving mechanism 61 installed above the reactor cover 59. The control rod drive mechanism 61 is installed above the reactor lid 59, so that maintenance and inspection of the control rod drive mechanism 61 is possible even during operation of the reactor, and the work is easy. The control rod 60 is connected to the control rod drive mechanism 61 by, for example, an electromagnet. When the power is turned off, the control rod 60 drops by gravity and is inserted into the nuclear reactor.

A spent fuel pool 62 is provided adjacent to the reactor pool 57, and the spent fuel is cooled and stored together with the fuel unit 47. Spent fuel pool 62
A transfer gate 64 is provided on a partition wall 63 between the reactor pool 57 and the transfer gate 64. The transfer gate 64 is opened to transfer the spent fuel together with the fuel unit 47. During operation of the reactor, the transfer gate 64 is closed and the reactor pool 5 is closed.
7 is sealed. The spent fuel unit 47 having spent fuel is transferred from the reactor pool 57 to the spent fuel pool 62 by a crane 66 provided on the ceiling of the reactor building 65. Since the spent fuel unit 47 is transferred by the crane 66, it can be transferred by remote control. Further, the transfer gate 64 is provided on the partition wall 63.
Is provided to transfer the spent fuel unit 47 underwater, so that the water in the reactor pool 57 and the spent fuel pool 62 serves as a radiation shield, and radiation protection is achieved. The spent fuel pool 62 may not be provided next to the reactor pool 57. The reference numeral 67 in FIG. 16 denotes a gate for carrying in and out the fuel unit 47 and the like.

The heat generated in the fuel element 44 by the operation of the solid-cooled nuclear reactor 45 is transmitted to the solid-cooled block 41.
Thereby, the fuel element 44 is cooled. Then, the heat transmitted to the solid cooling block 41 is transmitted to the cooling pipe 42 of the heat extraction section 41b, and heats the light water flowing in the cooling pipe 42 to generate steam, and superheats the generated steam. Further, heat is also radiated from the surface of the solid cooling block 41. Thus, the core 43 is cooled.

The steam generated in the cooling pipes 42 of the fuel units 47 is guided to the steam turbine of the power generation facility 56 by the steam outlet pipe 51 and returned to the water state by the condenser, and then cooled by the main steam pump. The fuel is supplied to each fuel unit 47 through a water inflow pipe 49. The solid-cooled nuclear reactor 45 of this embodiment is a BWR type light water reactor that allows generation of steam in the reactor core 43, but has a track record of commercial operation.
The recirculation system that is required for a light water reactor is unnecessary. This is because all the light water supplied to the fuel unit 47 is changed into steam in the fuel unit 47.

In the solid-cooled nuclear reactor 45, the cooling pipe 42
As in the case of the solid-cooled nuclear reactor 5 described above, the core 43 can be continuously cooled even when the flow of light water in the reactor is stopped and heat removal from the heat extraction unit 41b cannot be expected. In addition, since the solid cooling block 41 is submerged in the reactor pool 57 and the solid cooling block 41 can be water-cooled, the solid cooling block 41 can be efficiently cooled, and the reactor can be enlarged accordingly. it can. If a plurality of fuel units 47 are installed, the heat output of the reactor can be reduced, for example, by 10
It can be designed as large as about 00 MW.

In the solid-cooled nuclear reactor 45, the control rod 6
Since 0 is a gravity drop type, the inherent safety is high. Further, the inside of the reactor pool 57 is at normal pressure, the control rod 60 is not structurally pushed out by the pressure, and the inherent safety is further improved. Need to be designed.

The solid cooling block 41 is connected to the fuel element 4
4 is sealed, and the solid cooling block 41 functions as a reactor pressure vessel. Further, in the solid-cooled nuclear reactor 45, heat is exchanged with light water by passing the cooling pipe 42 through the solid cooling block 41. In this case, the cooling pipe 42 merely passes through the solid cooling block 41. However, since light water does not permeate the solid cooling block 41, the cooling pipe 42 is disposed outside the solid cooling block 41. That is, the flow in the cooling pipe 42 is generated by the solid cooling block 4 functioning as a reactor pressure vessel.
1 is formed outside. For this reason, the formation and control of the fluid flow are easier and the structure of the reactor can be simplified as compared with the conventional reactor in which the coolant flow is formed in the reactor pressure vessel. .

Since the pressure in the reactor pool 57 is normal pressure and the pressure in the cooling pipe 42 of the fuel unit 47 is higher,
Even if the cooling pipe 42 is damaged, it is considered that water in the reactor pool 57 does not flow into the cooling pipe 42.
Therefore, it is considered that the void in the cooling pipe 42 is reduced by the inflow of the water in the reactor pool 57, and the positive reactivity is not applied. Even if the water in the reactor pool 57 flows into the cooling pipe 42 and a positive reactivity is applied, the reactivity is designed by designing the absolute value of the negative void coefficient in an appropriate range. It is sufficiently possible to prevent a reactivity accident such as breakage of the fuel unit 47 even when the voltage is applied.

As described above, the solid-cooled reactor 45 is structurally prevented from causing an accident, and has a very high intrinsic safety which does not require a quick operation by an operator. The solid-cooled reactor 45 has a heat output of 1000M.
W, electric power of 1000 MW can be ensured sufficiently in the range of a small reactor with an electric output of about 300 MW.
Economic efficiency comparable to that of a large-scale power reactor can be achieved.

In order to evaluate the heat transfer performance of the solid-cooled nuclear reactor 45, the temperature distribution of the solid-cooled block 41 was analyzed. The result is shown in FIG. In this calculation example, the solid cooling block 41 has a cross section of about 40 cm × 40 c.
Use a graphite block with a rectangular shape of m.
A total of 81 fuel elements 44 in nine rows are stored, and the temperature distribution is shown diagonally from the center of the graphite block. The linear output of the fuel element 44 was set to 20 kW / m, which is the same as that of a BWR-type reactor having a track record of commercial operation. In addition, a gap layer is provided on the surface of the graphite block to control natural heat radiation to the reactor pool 57. As shown in FIG.
Although the temperature exceeds 000 ° C, the temperature of the graphite part is up to 417
° C. When the heat is not removed from the cooling pipe 42 due to the loss of the coolant or the like, the reactor naturally stops due to a negative void coefficient or the like, and the residual heat (decay heat) is reduced from the surface of the solid cooling block 41 to the reactor. The heat is naturally radiated to the pool 57. FIG. 19 also shows the temperature distribution in the graphite block when the residual heat is 5% of the normal output (about 15 seconds after shutdown of the reactor). The temperature of the graphite portion reaches a maximum of 542 ° C., and the soundness of the graphite block and the fuel element 44 is ensured. Immediately after the loss of the coolant, the temperature rise is suppressed by the heat capacity of the solid cooling block 41 such as graphite.

The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, as shown in FIG.
A fluid passage 68 for receiving radiation irradiation may be provided in the liquid in which 1 is submerged, and a fluid to be activated or heated may flow through the fluid passage 68. The fluid passage 68 is, for example, a pipe, in the vicinity of the fuel unit 47, for example, 10 cm.
Are arranged at intervals. The fluid flowing in the fluid passage 68 is, for example, a liquid or a gas. Fuel unit 4
By irradiating the fluid in the fluid passage 68 with neutrons and γ-rays leaking from the fluid 7, for example, it is possible to produce an isotope.

Also, by using tungsten or the like as the pipe material of the fluid passage 68, the fluid can be heated by γ heating from γ rays from the fuel unit 47. The fluid passage 68 is completely independent of the fuel unit 47, and is independent of the temperature of the core 43.
The temperature inside can be set. In other words, the maximum temperature of the core 43, which is subject to restrictions such as fuel melting, is limited, but the temperature in the fluid passage 68 is not subject to such restrictions. Therefore, for example, heat of about 1000 ° C. can be generated, and such high-temperature heat can be used as it is in industry and the like, and hydrogen can be produced using the heat. become. Thus, the fluid passage 68 can be used for multiple purposes.

This solid-cooled nuclear reactor 45 is suitable for installing a fluid passage 68. That is, a reactor pressure vessel is necessary for a reactor having a track record of commercial operation, and it is necessary to make a hole in the reactor pressure vessel in order to install the fluid passage 68. It is generally not desirable to drill holes in the reactor pressure vessel, which makes the installation of the fluid passage 68 difficult.
On the other hand, the solid-cooled reactor 45 does not require a reactor pressure vessel, and the installation of the fluid passage 68 is easy. That is,
For example, despite being a large nuclear reactor that can be used in a power plant, it is suitable for setting the fluid passage 68,
For example, radiation irradiation, heat utilization, hydrogen production, and the like can be performed while generating power.

In the above description, the reactor pool 57
The liquid for cooling the fuel unit 47 is, of course, not limited to water.

In the above description, the heat generated in the core 43 is used for power generation by supplying the steam generated in the cooling pipe 42 to the power generation facility 56, for example. However, the present invention is not limited to this. The heat generated in 43 may be used as a heat source for heating or the like.

In the above description, light water is supplied as cooling water into the cooling pipe 42. However, the present invention is not limited to light water. For example, liquid water such as heavy water or gas such as helium gas or carbon dioxide gas may be used. Is also good. When a gas is allowed to flow through the cooling pipe 42, a gas turbine is used as a power generation turbine.

In the above description, the solid-cooled nuclear reactor 4
Although the reactor 5 is a BWR-type reactor, the cooling system may be divided into a primary loop and a secondary loop, and the primary loop may be pressurized to suppress the generation of steam, thereby forming a PWR-type reactor.

Further, as a nuclear fuel used for the fuel element 44, a coated particle fuel for a high temperature gas reactor can be used.

[0075]

6 and 7 show a solid-cooled nuclear reactor 5 according to the present invention.
Here is an example in which is replaced with a thermal neutron reactor.

As the nuclear fuel to be filled in the cladding tube of the fuel element 4, for example, a low-enriched uranium oxide fuel which has been used in a light water reactor is used. As a material of the cladding tube, for example, a zircaloy alloy or an aluminum alloy which has been used is used. The fuel rods 4 filled with nuclear fuel are loaded into the solid-state cooling block 1 at the time of manufacturing the solid-cooled nuclear reactor 5, and after the fuel rods 4 are loaded, the fuel rods 4 are covered with the upper lid 14 and sealed. In this solid-cooled nuclear reactor 5, the spent fuel is taken out of the reactor core 3 at the time of decommissioning, and it is not assumed that the nuclear fuel is replaced during the operation. For example, at the time of decommissioning, the entirety of the reactor 5 is transported to a dedicated handling facility (not shown) while the fuel rods 4 are kept sealed in the solid cooling block 1, and the upper lid is closed underwater using a remote device such as a magic hand. Remove 14 and take out spent fuel.

The solid-cooled nuclear reactor 5 is, for example, 2
It is operated without refueling for a period of about 0 to 60 years. In light water reactors that have already been operated, about 4% of nuclear fuel (uranium) is burned in about 5 years.
Since the solid-cooled reactor 5 is designed so that the power density is 1/10 to 1/100 or less of that of the light water reactor which has already been operated, the operation can be performed for about 20 to 60 years. The power density of the core 3 is designed to be, for example, about 10 MW / m ³ per unit volume of the fuel part.

In the solid-cooled nuclear reactor 5, the core 3
Of the steam generating tube 2
Each of these is passed through a plurality of heat extraction portions 1b. For example, one steam generating pipe 2 is passed through three heat extraction portions 1b. In this case, it is preferable that the first pass 2 a that first passes through the solid cooling block 1 is disposed near the center of the core 3. This is because the light water in the first pass 2a has a lower temperature and the lowest void rate than the light water in the second pass 2b and the third pass 2c, so that neutrons can be decelerated most efficiently. This is because even if light water having a low temperature is injected into the steam generating tube 2 for some reason, the change in the temperature of the light water can be minimized and the change in the reactivity of the reactor core 3 can be minimized. Although only one steam generating tube 2 is shown in FIG. 6, this is a conceptual view of the configuration, and in actuality, an appropriate number of Needless to say, the steam generating pipe 2 is installed.

The solid-cooled nuclear reactor 5 is provided with a passive controller 15 for increasing or decreasing the reactivity of the reactor core 3 in accordance with a change in the temperature of the solid-cooled block 1. For example, by forming a hole in the solid cooling block 1 and forming a through-hole in the upper lid 14, and inserting a passive control device 15 from the hole 11 a formed in the shield 11 into these hole and the through-hole, The mechanical control device 15 is attached to the solid cooling block 1.

FIG. 8 shows the passive control device 15. The passive control device 15 includes a neutron absorber 16 and the neutron absorber 1
6, a driving member 17 that is deformed by a temperature change. The driving member 17 moves the neutron absorber 16 into the core 3 in a first shape for moving the neutron absorber 16 out of the core 3. It has a second shape, and when the temperature of the solid cooling block 1 rises above the set temperature T, it is transformed from the first shape to the second shape.

The neutron absorber 16 is made of, for example, B ₄ C, Ag
-In-Cd or the like. The neutron absorber 16 is formed, for example, in a rod shape, and is housed in a sleeve 18. A support rod 19 is attached to the neutron absorber 16, and the support rod 19 passes through a second plate 20 and a third plate 21 fixed in the sleeve 18. A first plate 22 is disposed between the second plate 20 and the third plate 21, and the first plate 22 is fixed in the middle of the support rod 19. That is, the first plate 2
2 is movable integrally with the support rod 1 in the sleeve 18.

The driving member 17 is made of, for example, Ni-Ti-Pb
A coil spring made of alloy shape memory alloy,
It is arranged between the second plate 20 and the first plate 22. The transformation temperature (set temperature T) of the shape memory alloy can be set by adjusting its composition. The transformation temperature T is set, for example, higher than the temperature of the solid cooling block 1 during normal operation of the solid cooling reactor 5 and lower than the melting point of the solid cooling block 1. The transformation temperature T is
For example, it is 810 ° C.

When the temperature of the driving member 17 rises due to the temperature rise of the core 3 and exceeds the transformation temperature T, the driving member 17 is deformed from the contracted first shape to the extended second shape. . When the driving member 17 has the first shape, as shown by a solid line in FIG.
The neutron absorber 16 is lifted by a coil spring 23 disposed between the neutron absorber 16 and the third plate 21, so that the neutron absorber 16 is disposed outside the reactor core 3. On the other hand, the driving member 17
8, the neutron absorber 16 is lowered by compressing and retracting the coil spring 23, and the neutron absorber 16 is inserted into the reactor core 3 as shown by a two-dot chain line in FIG.

For example, when the driving member 17 is a coil spring having a length of about 30 cm, by compressing the driving member 17 to a length of about 5 cm, when the transformation temperature T is exceeded, the length of the driving member 17 is reduced. Will extend about 25 cm. For example, a solid-cooled nuclear reactor 5 having a height of about 100 cm
In the case of, the position where the height is 20 cm to 80 cm at the center is the place that most affects the reactivity. For this reason, if the neutron absorber 16 connected to the driving member 17 is previously set at a position of about 90 cm at the height of the solid-cooled nuclear reactor 5,
When the temperature of the driving member 17 exceeds the transformation temperature T, the height of the neutron absorber 16 drops to a position of 65 cm, and
It is possible to shut down the reactor 5.

Further, a safety rod device 24 for reducing the reactivity in accordance with the temperature rise of the solid cooling block 1 may be provided in the solid cooling nuclear reactor 5. For example, a hole is formed in the solid cooling block 1 and a through-hole is formed in the upper lid 14, and the hole 1 formed in the shield 11 is formed in these holes and the through-hole.
The safety rod device 24 is attached to the solid cooling block 1 by inserting the safety rod device 24 from 1b.

FIG. 9 shows the safety rod device 24. The safety rod device 24 includes a neutron absorber 16 and a magnet body 2 that magnetically attracts the neutron absorber 16 and supports the neutron absorber 16 in a state of being suspended above the core 3.
The magnet body 25 has a Curie point at a temperature higher than the normal temperature of the solid cooling block 1 during the reactor operation and lower than the melting point of the solid cooling block 1. In this embodiment, the iron piece 26 is attached to the neutron absorber 16, and the iron piece 26 is attracted by the magnet 25. However, when the neutron absorber 16 itself is adsorbed to the magnet, the neutron absorber 16 may be directly adsorbed by the magnet 25 as a matter of course.

The magnet body 25 is attached to the inner peripheral surface of the sleeve 28 by the bracket 27. In this embodiment, for example, the solid cooling block 1 has a melting point of 660 ° C.
Is used, and the temperature of the solid cooling block 1 during operation of the reactor is usually about 300 to 400 ° C., so a Ba ferrite magnet having a Curie point of 460 ° C. is used as the magnet body 25.

The neutron absorber 16 is made of, for example, B ₄ C, Ag
-In-Cd or the like. The neutron absorber 16 is the sleeve 2
8, and as shown by the solid line in FIG.
It is adsorbed and suspended by. When the temperature of the magnet body 25 exceeds the Curie point due to a rise in the temperature of the solid cooling block 1, the neutron absorber 16 falls due to gravity as shown by a two-dot chain line in FIG. Since the safety rod device 24 using the magnet 25 has a structure in which the neutron absorber 16 is dropped using gravity, if the neutron absorber 16 is dropped once, the reactivity decreases, and the reactor core 3 is dropped. Even if the temperature decreases, the neutron absorber 16 is not automatically extracted from the core 3, and the reactor is stopped until the neutron absorber 16 is extracted from the core 3 by an operator.

The solid-cooled reactor 5 is provided with a control rod 29 for an operator to start, stop, and control the power of the reactor, and a limiting means 30 for restricting the withdrawal speed of the control rod 29 to a set speed or less. I have. FIG. 10 shows the control rod 29 and FIG. 11 shows the control means 30. A small annular step motor 32 is installed in the sleeve 31, and when the annular step motor 32 rotates, the screw rod 33 moves up and down. An electromagnet 34 is attached to the lower end of the screw rod 33. The electromagnet 34 is attached to the iron piece 2 attached to the neutron absorber 16.
6 is magnetically attracted.

The limiting means 30 is, for example, an electric control mechanism for limiting the maximum rotation speed of the annular step motor 32, and is provided between the annular step motor 32 and the controller 35 for controlling the annular step motor 32. ing. Therefore, even if the controller 35 attempts to rotate the annular step motor 32 at a speed higher than the predetermined speed, the limiting means 30 limits the speed to the predetermined speed,
The moving speed of the neutron absorber 16 is limited. However, the restricting means 30 is not limited to an electric control mechanism, and may be, for example, a computer program for controlling the annular step motor 32. The computer program sets an upper limit of the rotational speed of the annular step motor 32. May be.

The limiter 30 limits the maximum rotation speed of the annular step motor 32 so that the control rod 29 can be pulled out at the highest speed, for example, about several cm / min. Control rod 2
By limiting the maximum value of the withdrawal speed of 9 to several cm / min, it takes, for example, one day or more to start up the solid-cooled reactor 5, but the change in reactivity is made as slow as possible to further enhance safety. It is a design philosophy that a long-time startup is allowed to realize the performance. Incidentally, in a typical light water reactor that has been in operation, the pull-out speed of the control rod is about several cm / sec, and even at this speed, safety is sufficiently ensured. Since it is not assumed, the number of times of stopping and restarting the reactor is small, and it is easy to realize the above design concept.

The operator moves the neutron absorber 16 up and down by operating the annular step motor 32 for starting, stopping, and controlling the reactivity of the solid-cooled nuclear reactor 5. Since the moving speed of the neutron absorber 16 in this case is extremely low,
The reactivity of the reactor core 3 changes very slowly. On the other hand, when the reactor such as the scram is stopped, the neutron absorber 16 can be instantaneously dropped into the reactor core 3 by cutting off the current of the electromagnet 34. The reactor 5 is stopped by dropping the neutron absorber 16. In the event of an abnormality such as a loss of power at a power plant, the current of the electromagnet 34 is cut off, and the neutron absorber 16 is dropped instantaneously.

In order to operate the solid-cooled nuclear reactor 5 having such a configuration for 20 to 60 years without refueling, it is necessary to compensate for a decrease in reactivity due to a long-term lack of fuel combustion. For this reason, in the solid-cooled nuclear reactor 5, the moderator tube 36 is installed near the reactor core 3 according to the prediction of the decrease in the reactivity. FIG. 12 shows the moderator tube 36. A moderator 38 such as light water is sealed in the cladding tube 37. By inserting the moderator tube 36 into the core 3, the ability to decelerate the neutrons of the core 3 is improved, the proportion of thermal neutrons is increased, and a decrease in reactivity due to fuel combustion deficiency is compensated. The moderator tube 36 is inserted into the vicinity of the reactor core 3 when the reactor 5 is stopped by periodic inspection or the like, thereby preventing occurrence of a reactivity accident. Further, the moderator 38 sealed in the cladding tube 37 is not limited to light water, but may be a liquid such as heavy water or a solid such as ZrH.

An air flow is formed between the solid-state cooling block 1 of the solid-state cooling reactor 5 and the shield 11 to promote heat radiation from the surface of the solid-state cooling block 1. Since the solid cooling block 1 seals the fuel rods 4 and functions as a pressure vessel in a reactor vessel, that is, a light water reactor, the flow of air is formed outside of the one that functions as a pressure vessel. By doing so, compared to the case where a flow is formed inside the pressure vessel,
The formation and control of the air flow are easy, and the confirmation of the air flow is also easy. That is, in a reactor that has been operating, a coolant flow is formed inside the pressure vessel,
In the solid-cooled nuclear reactor 5, since the air flow is formed outside the solid cooling block 1 functioning as a pressure vessel, it is easy to form and control the air flow, Confirmation is easy, safety is easy to understand, and safety can be further enhanced.

The heat generated in the core 3 by the operation of the solid-cooled nuclear reactor 5 is transmitted to the solid-state cooling block 1, whereby the core 3 is cooled. Then, the heat transmitted to the solid cooling block 1 is transmitted to the steam generating pipe 2 and heats the light water flowing in the steam generating pipe 2 to generate steam. Further, heat is also radiated from the surface of the solid cooling block 1. Steam generating pipe 2
The steam generated therein is supplied to, for example, a power generation turbine 6.

In the solid-cooled nuclear reactor 5, when the temperature of the solid-cooled block 1 rises during operation and the temperature of light water functioning as a moderator in the steam generating tube 2 also rises, the void fraction increases, so that The rate at which neutrons are decelerated to thermal neutrons decreases, and the reactivity of the core 3 decreases. That is, self-control works. On the other hand, even when the temperature of the solid cooling block 1 increases during operation, when the flow rate in the steam generating pipe 2 increases, the temperature of the light water that functions as a moderator does not increase significantly as a result. For this reason, self-controllability due to the above-mentioned moderator mode temperature rise cannot be expected much, but in this case, the passive control device 15 is activated by the temperature rise of the solid cooling block 1 and the neutron absorber 16 is moved to the core 3. , It is possible to impart a negative reactivity to the core 3. In addition, since the solid cooling block 1 thermally expands, leakage of fast neutrons from the core by the solid cooling block 1 increases, and the reactivity is further reduced. That is, also in this case, self-controllability works. Then, when the reactivity decreases and the temperature of the solid cooling block 1 returns to a normal value,
The shape of the driving member 17 of the passive control device 15 returns from the second shape to the first shape, and the neutron absorber 16 is withdrawn from the core 3. Therefore, the reactivity of the core 3 increases, and the reactor 5 is operated at the target output. That is, the reactivity of the reactor core 3 is automatically controlled according to the temperature of the reactor core 3, and the automatic operation of the reactor becomes possible. In addition, since the reactivity decreases due to the Doppler effect due to the temperature rise of the nuclear fuel, self-controllability due to this is expected.

Further, by designing the reactor to be stopped by moving the neutron absorber 16 of the passive control device 15 to the reactor core 3, when the temperature of the solid cooling block 1 rises to a predetermined temperature. In the meantime, the solid-cooled nuclear reactor 5 can be automatically stopped by the passive control device 15. Therefore, the safety of the solid-cooled nuclear reactor 5 is further improved.

When the safety rod device 24 is provided, the temperature of the solid cooling block 1 rises and the safety rod device 2
When the temperature of the magnet body 25 reaches the Curie point of 460 ° C., the neutron absorber 16 magnetically attracted by the magnet body 25 falls into the reactor core 3 and a negative reactivity is inserted to stop the reactor. As described above, by providing the safety rod device 24 of a different system from the passive control device 15, safety is further improved. In the safety rod device 24 using the magnet 25, once the neutron absorber 16 is inserted into the core 3, the neutron absorber 16 is automatically extracted from the core 3 even if the temperature of the solid cooling block 1 decreases. And the reactor 5 remains stopped until operated by an operator.

In the solid-cooled nuclear reactor 5, even if the flow of light water in the steam generating tube 2 is stopped or lost, and it is not possible to expect the removal of heat from the heat extraction section 1b, heat is radiated on the surface of the solid-cooled block 1. , The core 3 can be kept cooled. That is, the solid cooling block 1 that has been heated by cooling the core 3 radiates heat on its surface, so that the core 3 can be continuously cooled without melting. Solid cooling block 1
Are provided with a large number of radiating fins 1c on the surface thereof, so that the natural air cooling capacity is improved. Further, the heat is radiated to the outside of the solid cooling block 1 functioning as a pressure vessel, and the radiated heat can be controlled from outside the solid cooling block 1 by forming a flow of air around the solid cooling block 1. , Its control is easy. Further, since the solid cooling block 1 is made of metal and has good heat conductivity, the cooling capacity of the core 3 can be sufficiently ensured. If it is impossible to remove heat from the solid cooling block 1 with light water in the steam generating pipe 2 due to a turbine trip or the like, the reactor is stopped by the passive control device 15 or the like. As long as it has the ability to remove the decay heat (less than about 10% of the calorific value during normal operation of the reactor).
It is not necessary to have the ability to remove 100% of the calorific value of the core 3 during normal operation.

FIGS. 13 and 14 show examples in which the solid-cooled nuclear reactor 5 of the present invention is a fast neutron reactor.

As in the liquid sodium-cooled fast breeder reactor,
A fuel rod 4 in which a U-Pu mixed oxide fuel is filled in a stainless steel cladding tube is used. However, such fuel rod 4
However, the invention is not limited to this. For example, a nitride fuel or a metal fuel may be used as the nuclear fuel, and zircaloy or the like may be used as the material of the cladding tube. When a metal fuel is used, a liquid layer forming phenomenon may occur in which the metal uranium or plutonium of the fuel and iron or Ni in the stainless steel of the cladding tube form an alloy at a temperature of about 650 ° C. or higher and melt. Therefore, it is necessary to prevent this by using a cladding tube made of zirconium, zircaloy, or the like that does not contain iron, Ni, or the like.

The loading and unloading of the fuel rods 4 is not carried out at the power plant site as in the case of the above-described thermal neutron reactor, but is loaded at the time of manufacturing the solid-cooled nuclear reactor 5.
After the operation period of about 60 years to 60 years, the solid-cooled reactor 5
The whole is transported to a special handling facility where the fuel rods 4 are taken out.

Fuel loading section 1 of solid cooling block 1 made of copper
A hole serving as the heat extraction portion 1b is made at a position sufficiently distant from a, and the steam generating tube 2 is inserted. This prevents light water in the steam generating pipe 2 from affecting the reactivity of the reactor core 3.
However, in this case, since the steam generating pipe 2 is arranged at a position sufficiently distant from the core 3, the solid cooling block 1
It is not possible to expect the self-controllability of the reactor due to void generation when the temperature of the reactor becomes high. However, in this case, it is not necessary to consider the influence of the application of the reactivity when the low-temperature water enters the steam generating tube 2. Instead of using light water as the fluid in the steam generating pipe 2, a gas such as He gas may be used. Since gas is inferior to light water in its ability to decelerate fast neutrons to thermal neutrons, when gas is used as the fluid in the steam generation tube 2, the steam generation tube 2 can be installed at a position close to the reactor core 3. Become. Therefore, the degree of freedom in designing the reactor is improved.

In this embodiment, the passive control device 15 is provided even when the solid-cooled nuclear reactor 5 is a fast neutron reactor. Therefore, the reactivity can be automatically controlled according to the temperature change of the core 3 as in the case of the thermal neutron reactor. Also, the neutron absorber 16 of the passive control device 15
When the reactor 5 is designed to be stopped by inserting it into the core 3, the steam
Since the heat removal of the solid cooling block 1 by the fluid in the inside cannot be expected and the temperature of the solid cooling block 1 rises,
The neutron absorber 16 of the passive control device 15 can move to the core 3 and automatically shut down the reactor 5.

The passive control device 15 and the safety rod device 2
And 4 may be provided. During operation of the fast neutron reactor, the temperature of the solid cooling block 1 is usually about 600 ° C. to 800 ° C., and the melting point of copper used as the solid cooling block 1 is 1
Since the temperature is 084 ° C., for example, an alnico magnet having a Curie point of 850 ° C. is used as the magnet 25 of the safety rod device 24. When the temperature of the solid cooling block 1 rises and the temperature of the magnet body 25 of the safety rod device 24 reaches the Curie point of 850 ° C., the neutron absorber 16 magnetically attracted by the magnet body 25 falls and becomes negative in the reactor core 3. The reactor is shut down by inserting the reactivity. Thus, the passive control device 15
By installing a safety rod device 24 of a different system from that of the above, safety is further improved.

Also, when the solid-cooled nuclear reactor 5 is a fast neutron reactor, the control rods 29 are used similarly to the case of the thermal neutron reactor.
It is a matter of course that the restricting means 30 may be provided in the.

In order to operate this solid-cooled nuclear reactor 5 for 20 to 60 years without refueling,
It is necessary to compensate for the decrease in reactivity due to long-term combustion loss of fuel. In the case of a fast neutron reactor, plutonium can be propagated in the reactor, so it is possible to design the reactor to minimize the decrease in reactivity due to combustion deficiency. The neutron absorber 39 is periodically removed little by little at intervals of several years to several tens of years as needed to compensate for reactivity due to fuel deficiency. In addition, as the neutron absorber 39 previously installed in the reactor core 3, for example, iron or the like can be used.

A large number of radiating fins 1c are also provided on the surface of the solid cooling block 1 to improve the natural air cooling capacity, similarly to the thermal neutron reactor.

In the above description, the passive control device 1
Although the safety rod device 5 and the safety rod device 24 are provided side by side, both need not necessarily be provided together, and only one of them may be provided.

[0110]

As described above, according to the solid-cooled nuclear reactor of the first aspect, the core is cooled by the solid-state cooling block, the heat generated in the core is utilized through the solid-state cooling block, and the solid-state cooling block is used. The surface is cooled by a fluid by natural convection, so that no loss of coolant occurs and even if heat is not taken out from the solid cooling block on the heat utilization side, the solid cooling block is Since heat is radiated on the surface, the cooling function is not completely lost, and the core can be continuously cooled. That is, it is possible to further improve the intrinsic safety of the reactor without losing the coolant or the cooling function of the core. In addition, emergency core cooling system (ECC
Safety facilities such as S) and a residual heat removal system are not required, so that the equipment of the nuclear reactor can be simplified and the cost can be reduced.

Further, since the solid cooling block seals the fuel element filled with the nuclear fuel, the solid cooling block can function as a pressure vessel. For this reason, a pressure vessel becomes unnecessary, and the structure of the nuclear reactor can be simplified.

Further, according to the solid-cooled nuclear reactor according to the second or third aspect, even if it becomes impossible to remove heat from the solid-cooled block by the coolant passing through the solid-cooled block, the solid-cooled block cannot be removed. Since the heat is released from the surface to the surrounding fluid to be cooled, the cooling function is not completely lost. In addition, since cooling is performed by natural convection, devices such as a pump and a fan for circulating a cooling fluid are not required, and further safety devices provided when these are stopped due to a power failure or the like are not required.

In particular, according to the solid-cooled nuclear reactor of the second aspect, the cooling capacity is much larger than that of the air-cooled reactor, so that the heat output of the reactor can be made larger than that of the natural-cooled nuclear reactor by the air-cooled reactor. Moreover, by storing the liquid in the pool,
There is no loss of fluid like a pipe break. Furthermore, in this case, since the solid cooling block is submerged in the liquid and there is no risk of fire, graphite can be used as the solid cooling block. Graphite has a small thermal neutron absorption cross section,
Good economics of thermal neutrons. In addition, when using a solid cooling block made of metal, there is no risk of fire.
It can be cooled not only by water cooling but also by air cooling.

According to the solid-cooled nuclear reactor of the sixth aspect, the heat transmitted to the solid-cooled block is transmitted to the coolant flowing in the coolant path to be used as a heat source for power generation or driving. Therefore, the power of the core can be set to a value corresponding to the cooling capacity of the coolant circulating using the coolant path. That is, it can be a high-power reactor. Moreover, even in this case, when the circulation of the coolant is stopped for some reason, for example, even if the removal of heat from the coolant path, for example, the steam generating pipe due to a turbine trip or the like is lost, the decay heat and the residual heat of the core are not reduced. Sufficient gradual heating can be achieved by cooling by heat radiation from the surface of the solid cooling block.

Further, according to the solid-cooled nuclear reactor according to the seventh aspect, power can be generated by directly using the heat of the core taken out through the solid-cooled block. Moreover, even if it becomes impossible to remove the heat of the solid cooling block by the thermoelectric conversion element,
Since the solid cooling block is cooled by radiating heat from its surface, the cooling function is not completely lost.

According to the solid-cooled nuclear reactor of the eighth aspect, the fluid flowing through the fluid passage in the pool is irradiated with the radiation utilizing the radiation leaked from the reactor core, for example, to produce a radioisotope, The fluid can be heated to use the heat, or hydrogen can be produced.

Further, according to the solid-cooled nuclear reactor of the ninth aspect, it is possible to prevent a sudden change in reactivity due to the insertion and removal of the control rod, and to structurally prevent a reactivity accident.

According to the solid-cooled nuclear reactor of the tenth aspect, when the temperature of the solid-cooled block rises abnormally and reaches a set temperature for deformation, the drive member changes from the first shape to the second shape. Since the neutron absorber is deformed and moved into the core, a negative reactivity is inserted into the core, and the power is reduced.
Then, when the temperature of the solid cooling block decreases due to the decrease in output, the shape of the driving member returns from the second shape to the first shape, the neutron absorber is pulled out of the reactor core, the reactivity is increased, and the output is increased. In this way, the reactivity is passively controlled according to the vertical fluctuation of the core temperature.

According to the solid-cooled nuclear reactor of the eleventh aspect, during a normal operation in which the temperature of the solid-cooled block does not rise to the Curie point of the magnet, the neutron absorber is suspended above the core. However, when the temperature of the core rises abnormally, the magnet that magnetically attracts the neutron absorber loses magnetism, so that the reactor can be shut down by dropping the neutron absorber into the core.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of a solid-cooled nuclear reactor to which the present invention is applied, and is a conceptual diagram in a case where the reactor is a thermal neutron reactor.

FIG. 2 is a conceptual diagram showing a second embodiment of a solid-cooled nuclear reactor to which the present invention is applied, in which the reactor is a fast neutron reactor.

FIG. 3 is a conceptual diagram showing a first embodiment of a nuclear power plant to which the present invention is applied.

FIG. 4 is a conceptual diagram illustrating a third embodiment of a solid-cooled nuclear reactor to which the present invention is applied, in which a thermoelectric conversion element is used as a heat exchange unit.

FIG. 5 is a conceptual diagram showing a second embodiment of a nuclear power plant to which the present invention is applied, in which a solid-cooled nuclear reactor is modularized and a plurality of modules are installed.

FIG. 6 is a conceptual diagram showing an example in which the solid-cooled nuclear reactor of the present invention is a thermal neutron reactor.

FIG. 7 is a conceptual diagram showing an arrangement relationship of fuel rods, steam generating tubes, and the like of the thermal neutron reactor of FIG.

FIG. 8 is a longitudinal sectional view showing a passive control device.

FIG. 9 is a longitudinal sectional view showing a safety rod device.

FIG. 10 is a longitudinal sectional view showing a control rod.

FIG. 11 is a conceptual diagram showing a limiting unit.

FIG. 12 is a longitudinal sectional view showing a moderator tube for compensating the reactivity.

FIG. 13 is a conceptual diagram showing an example in which the solid-cooled nuclear reactor of the present invention is a fast neutron reactor.

FIG. 14 is a conceptual diagram showing an arrangement relationship of fuel rods, steam generating tubes, and the like of the fast neutron reactor of FIG.

FIG. 15 is a conceptual diagram showing an embodiment in which the solid-cooled nuclear reactor of the present invention is configured as a multipurpose reactor that can be used as a heating heat source or the like.

FIG. 16 shows a fourth embodiment of a solid-cooled nuclear reactor to which the present invention is applied, and is a conceptual diagram of a nuclear power plant provided with the solid-cooled nuclear reactor.

FIG. 17 is a longitudinal sectional view showing a fuel unit when the solid-cooled nuclear reactor is a BWR.

FIG. 18 is a cross-sectional view showing a fuel unit when the solid-cooled nuclear reactor is a BWR.

FIG. 19 is a conceptual diagram showing the arrangement of fuel units when the solid-cooled nuclear reactor is a BWR.

FIG. 20 is a diagram showing a temperature distribution in the fuel unit at normal time and after decay heat removal.

FIG. 21 is a conceptual diagram showing a fifth embodiment of a solid-cooled nuclear reactor according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid cooling block 1a Fuel loading part 1b Heat extraction part 2 Heat exchange means 3 Core 4 Fuel rod (fuel element) filled with nuclear fuel 15 Passive control device 16 Neutron absorber 17 Drive member 24 Safety rod device 25 Magnet 29 Control Rod 30 Limiting means 41 Solid cooling block 41a Fuel loading part 41b Heat extraction part 42 Heat exchange means 43 Core 44 Fuel rod filled with nuclear fuel 45 Solid cooling reactor 57 Reactor pool 68 Fluid passage to be irradiated

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G21C 9/02 G21C 15/04 S 15/04 G21D 7/04 G21D 7/04 G21C 9/02 M

Claims (11)

[Claims] 1. A fuel element is enclosed by a heat-conductive solid cooling block which is in direct contact with the fuel element, and heat of the fuel element is extracted through the solid cooling block. A solid-cooled nuclear reactor comprising a core having a power density that does not melt the solid-cooled block and cooling the solid-cooled block by natural convection of the surrounding fluid to gradually heat the solid-cooled block. 2. The solid cooling block is submerged in a sufficient amount of liquid in a pool to remove residual heat and decay heat of the core, and cooled by natural convection of the liquid. A solid-cooled nuclear reactor as described. 3. The solid-cooled nuclear reactor according to claim 1, wherein said solid-cooled block is air-cooled by natural convection on its surface. 4. The solid-cooled nuclear reactor according to claim 2, wherein said solid-cooled block is made of metal. 5. The solid-cooled nuclear reactor according to claim 2, wherein said solid-cooled block is graphite. 6. The solid cooling block is provided with a coolant path that penetrates through the block and circulates a coolant, and the coolant flowing in the path extracts heat of the fuel element and cools the core. The solid-cooled nuclear reactor according to any one of claims 1 to 5, wherein the extracted heat is used as power generation, a power source, and the like. 7. The solid-state cooling block according to claim 1, wherein a thermoelectric conversion element is attached to said solid-state cooling block, and power is generated by directly utilizing heat of said core taken out through said solid-state cooling block. A solid-cooled nuclear reactor according to any one of the above. 8. The solid cooling device according to claim 2, wherein a fluid passage for receiving radiation is provided in the liquid in which the solid cooling block is submerged, and a fluid to be activated or heated flows through the fluid passage. Reactor. 9. The solid-cooled nuclear reactor according to claim 1, further comprising a control rod, and a restricting means for restricting a drawing speed of the control rod to a set speed or less. 10. The solid cooling block is provided with a passive control device for increasing or decreasing the reactivity in response to a temperature change, wherein the passive control device is connected to the neutron absorber and the neutron absorber. A driving member that is deformed by a change in temperature, the driving member having a first shape for positioning the neutron absorber outside the core, and a second shape for moving the neutron absorber into the core. The solid-cooled nuclear reactor according to any one of claims 1 to 9, wherein when the temperature of the solid metal coolant rises above a set temperature, the solid-metal coolant is deformed from the first shape to the second shape. 11. A safety rod device for reducing the reactivity in response to a rise in temperature is attached to the solid cooling block. The safety rod device includes a neutron absorber and a magnetic adsorption of the neutron absorber. A magnet body supported in a state of being suspended above the core, wherein the magnet body has a temperature higher than a normal temperature of the solid metal coolant during a reactor operation and lower than a melting point of the solid metal coolant. The solid-cooled nuclear reactor according to any one of claims 1 to 10, wherein the reactor has a Curie point.