JPS62479B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to boiling water nuclear reactors, and particularly to in-reactor neutron instrumentation (Local Power Range Monitor; hereinafter referred to as
It is called LPRM. ) related to abnormality diagnosis technology.

LPRM measures the neutron flux inside the reactor core, and the measured value is input into a process computer, which is an important basic input used for calculating the power distribution, burnup distribution, etc. in the core in so-called core performance calculations. However
The performance of LPRM changes over time due to the adverse environment such as radiation and high temperature inside the reactor.

Among LPRM performance changes, changes in performance due to U ²³⁵ deterioration can be corrected by calculation, but changes in performance due to other causes are generally slow and do not require operator intervention since they are not obvious failures such as disconnections. Until now, it has been difficult to determine whether there is an abnormality.

FIG. 1 shows an example of the count value RP of LPRM. Figure 1A shows an example of a healthy LPRM, in which it monotonically decreases with time t due to the deterioration of U ²³⁵ in the LPRM. 1st
Figure B is an example of an unhealthy LPRM, in which the calculated value RP increases with time t despite the deterioration of U ²³⁵ , so it can be determined that the LPRM is abnormal. The problem is that these changes occur slowly over time, on the order of days or weeks, making it difficult to judge.

The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to immediately discover and determine the abnormality when the LPRM changes abnormally over time, and issue a warning to the operator.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is an explanatory diagram showing the configuration of the neutron instrumentation abnormality diagnosis apparatus of the present invention, and arrows indicate input flows.

Normally, about 100 LPRM2 are arranged in the core 1. The counted values of LPRM2 are input into the core performance calculation device 3 along with plant data such as temperature and pressure.
The burnup calculated by the core performance calculation device is LPRM.
The signal is input to the deterioration correction device 4. Further, the count value of the LPRM2 is corrected by the LPRM deterioration correction device 4, normalized by the output standardization device 5, and inputted to the LPRM count storage device 6 at appropriate time intervals. after that,
The LPRM count averaging device 7 calculates the rate of change over time of the count value, and the rate of change determining device 8 determines the rate of change. If the rate of change is positive or negative, the alarm device 9 is activated.

The LPRM deterioration correction device 4 corrects the decrease in the count value RP due to the deterioration of U ²³⁵ of the LPRM 2 using the burnup E calculated by the core performance calculation device 3 as follows.

With a as a constant, the sensitivity S of LPRM is S=e ^-aE
Therefore, when the reactor output is constant, the corrected count value RC becomes RC=RP/S.

If the reactor output changes, the output standardization device 5
to compensate for fluctuations in reactor output. In other words, if the output at time 0 is normalized to 1.0 and the reactor output at any time is CTP, then the count value RC
becomes RC=RP/S×CTP.

Due to the physical (nuclear) properties of LPRM, RC is constant with respect to time t, as shown in FIG.

The RC value calculated as described above is stored in the LPRM count storage device 6 at appropriate time intervals. It is desirable to memorize this interval, usually every hour, for a few seconds.

FIG. 4 shows the count value RC and the number N of stored count value data. Next, the LPRM count averaging device 7 determines the change in RC over time. The method is to obtain the data shown in Figure 4 using the least squares method using a linear straight line RC = at + b (a, b, constant, t: time), and if the coefficient a is 0 or 0.
It is determined whether the value is small or close to . For example, in the case of the LPRM count value as shown in FIG.

As explained above, according to the neutron instrumentation abnormality diagnosis device of the present invention, by selecting time-varying LPRM data, LPRM can be reliably and easily performed.
It is possible to discover abnormalities in nuclear reactors, judge them, and report them to operators, improving the safety of nuclear reactors.

[Brief explanation of the drawing]

Figure 1A is an explanatory diagram showing the relationship between the count value and time of a healthy LPRM, B is an abnormal LPRM, Figure 2 is an explanatory diagram showing the configuration of the neutron instrumentation abnormality diagnosis device of the present invention, and Figure 3 is an explanatory diagram showing the relationship between the count value and time of an abnormal LPRM. FIG. 4 is an explanatory diagram showing the relationship between the coefficient value RC and time t. FIG. 4 is an explanatory diagram showing the relationship between the count value RC and the number N of data stored in the LPRM count storage device. 1... Core, 2... LPRM, 3... Core performance calculation device, 4... LPRM deterioration correction device, 5... Output standardization device, 6... LPRM coefficient storage device, 7...
LPRM count averaging device, 8...change rate determination device,
9...Alarm device.

Claims (1)

[Claims] 1 In a boiling water reactor, input the LPRM count value into the core performance calculation device to determine burnup, input the burnup and LPRM count value into the LPRM deterioration correction device, and standardize the corrected LPRM count value for output. The output data of the output standardization device is stored in the LPRM count storage device at appropriate time intervals, the rate of change of the LPRM count value is calculated from this data by the LPRM count averaging device, and the rate of change determination device calculates the rate of change of the LPRM count value from this data. A neutron instrumentation abnormality diagnostic device characterized by determining an abnormality in an LPRM and notifying the abnormality of the LPRM by an alarm device.