JP4174622B2 - Method for separating alkaline compound of heavy water and heavy water containing alkaline compound - Google Patents
Method for separating alkaline compound of heavy water and heavy water containing alkaline compound Download PDFInfo
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Description
本発明は、重水炉で用いられた劣化重水を精製する過程で廃液として発生するアルカリ含有重水の処理方法に関する。 The present invention relates to a method for treating alkali-containing heavy water generated as waste liquid in the process of refining deteriorated heavy water used in a heavy water reactor.
熱中性子の減速材として重水を用いている重水炉では、重水樹脂交換作業等によって劣化重水が発生する。重水の廃液の処理は、該重水廃液に含まれる不純物（アルカリ性化合物、ガンマ核種など）と重水を分離し、重水を回収するとともに不純物を安全に廃棄することが求められる。このため、劣化重水は、重水精製装置によって重水品位を上げてリサイクルされている。電解法による重水精製装置は、電解助剤としてアルカリを使用しているため、精製を繰り返すと、濃縮されたアルカリ性化合物、トリチウム及びガンマ核種を含む重水廃液が発生する。アルカリ入りの重水廃液には、アルカリ性化合物成分、トリチウム及びガンマ核種が存在する。該重水廃液は、前記不純物と重水を分離し、重水を回収するとともに不純物を安全に廃棄する必要がある。
これまで、該重水廃液の不純物を除去する方法して、該重水廃液に直接炭酸ガスを吹き込み重炭酸塩とした後、蒸発釜で単蒸留、さらに重炭酸塩を熱分解温度以上に加熱して、中和塩中にトリチウムが残留しない様にした処理方法が提案されている（特許文献１）。しかしこの方法では、重炭酸塩の熱分解は２５０℃以上５００℃にまでの高温加熱しているのが実情である。これは、結合水をもつ重炭酸塩は水と炭酸ガスに分解できるが、そのために高温を必要とすることによると考えられる。また、アルカリ金属の水酸化物を溶解した重水に炭酸ガスを吹き込み、ｐＨ１２〜１４の範囲に調整して、アルカリ炭酸塩を形成させた液を蒸発乾固させる方法が提案されている（特許文献２）。しかしこの方法は極めて高アルカリ性で重水液を処置し、蒸発乾固するので、処理対象液の取扱いに注意を要する。また装置の材料に特別の耐アルカリ性の材料を用いなければならず、装置のコスト上難点があった。
Up to now, as a method of removing impurities in the heavy water waste liquid, carbon dioxide is blown directly into the heavy water waste liquid to form bicarbonate, and then simple distillation in an evaporating pot, and further heating the bicarbonate to a thermal decomposition temperature or higher. A treatment method in which tritium does not remain in the neutralized salt has been proposed (Patent Document 1). However, in this method, the thermal decomposition of bicarbonate is actually performed at a high temperature of 250 ° C. to 500 ° C. This is thought to be due to the fact that bicarbonate with bound water can be decomposed into water and carbon dioxide, which requires high temperatures. Further, a method has been proposed in which carbon dioxide gas is blown into heavy water in which alkali metal hydroxide is dissolved, and the pH is adjusted to a range of 12 to 14 to evaporate and dry the liquid in which the alkali carbonate is formed (patent document). 2). However, since this method is extremely highly alkaline and treats a heavy water solution and evaporates to dryness, care must be taken in handling the solution to be treated. Moreover, a special alkali-resistant material has to be used for the material of the apparatus, which has a problem in the cost of the apparatus.
したがって本発明の目的は劣化重水を精製する過程で発生するアルカリ含有重水廃液から不純物と重水を分離し、重水を回収する方法を提供することにある。特に本発明の目的は、上記のアルカリ含有重水廃液からの不純物と重水の分離を緩衝作用を利用して中和により高アルカリ性条件下でなく、中性付近のｐＨ条件下で、且つ、廃液を上記のような高温に昇温せずに実施できる方法を提供することにある。本発明は、上記の目的を容易に且つ安価に処理するプロセスと装置を提供するものである。 Accordingly, an object of the present invention is to provide a method for separating heavy water from impurities and heavy water from an alkali-containing heavy water waste liquid generated in the process of purifying deteriorated heavy water. In particular, the object of the present invention is to separate impurities and heavy water from the above-mentioned alkali-containing heavy water waste liquid by neutralization using buffering action, not under highly alkaline conditions but under neutral pH conditions, An object of the present invention is to provide a method which can be carried out without raising the temperature as described above. The present invention provides a process and apparatus for easily and inexpensively processing the above objects.
本発明の課題は以下の手段によって達成された。
すなわち本発明は、
（１）アルカリ性化合物を含有する重水に予め炭酸ガスを吹き込み重炭酸塩とした後、該重炭酸塩含有の重水を硫酸によって中和し、硫酸塩を含む重水を蒸発乾固することを特徴とするアルカリ性化合物と重水を分離する方法、
（２）アルカリ性化合物を含有する重水を直接蒸留し、残留液に炭酸ガスを吹き込み重炭酸塩とした後、該重炭酸塩含有の重水を硫酸によって中和することを特徴とするアルカリ性化合物と重水を分離する方法、
（３）重水廃液のアルカリ性化合物濃度が１質量％以下であって、かつトリチウム濃度が１×１０ ７ Ｂｑ／ｍｌ以下である場合には、アルカリ性化合物を含有する重水を直接蒸留し、残留液に炭酸ガスを吹き込み重炭酸塩とした後、該重炭酸塩含有の重水を硫酸によって中和し、硫酸塩を含む重水を蒸発乾固する操作を行い、前記以外の濃度である場合には、アルカリ性化合物を含有する重水に予め炭酸ガスを吹き込み重炭酸塩とした後、該重炭酸塩含有の重水を硫酸によって中和し、硫酸塩を含む重水を蒸発乾固する操作を行うことにより、トリチウムの分配を制御するアルカリ性化合物と重水の分離方法、および
（４）前記（１）又は（２）記載のアルカリ性化合物を含む重水もしくは該重水の残留液に炭酸ガスを吹き込み重炭酸塩とした後、該重炭酸塩が硫酸によって中和する際に緩衝作用することを特徴とする前記（１）〜（３）のいずれか１項に記載の方法。
を提供するものである。
The object of the present invention has been achieved by the following means.
That is, the present invention
(1) Carbon dioxide is previously blown into heavy water containing an alkaline compound to form a bicarbonate, and then the bicarbonate-containing heavy water is neutralized with sulfuric acid, and the heavy water containing the sulfate is evaporated to dryness. To separate alkaline compound and heavy water,
(2) Heavy water containing an alkaline compound is directly distilled, carbon dioxide gas is blown into the residual liquid to form a bicarbonate, and then the bicarbonate-containing heavy water is neutralized with sulfuric acid. How to separate,
(3) When the alkaline compound concentration in the heavy water waste liquid is 1% by mass or less and the tritium concentration is 1 × 10 7 Bq / ml or less, the heavy water containing the alkaline compound is directly distilled to form a residual liquid. Carbon dioxide is blown into bicarbonate to neutralize the bicarbonate-containing heavy water with sulfuric acid and evaporate the heavy water containing sulfate to dryness. Carbon dioxide gas is blown into heavy water containing a potassium compound in advance to form a bicarbonate, and then the bicarbonate-containing heavy water is neutralized with sulfuric acid, and the heavy water containing the sulfate is evaporated to dryness . A separation method of alkaline compound and heavy water for controlling the distribution of tritium, and (4) heavy water containing the alkaline compound described in (1) or (2) above or a residual liquid of heavy water by blowing carbon dioxide into bicarbonate. The method according to any one of (1) to (3) above, wherein the bicarbonate acts as a buffer when the bicarbonate is neutralized with sulfuric acid.
Is to provide.
上記のように、不純物の濃度に応じた重水廃液の処理プロセスを所定の順序に替えることにより、迅速に、高温昇温せずに処理を遂行することが可能になるとともに、回収重水中のアルカリ性化合物とガンマ核種の存在量を抑え、且つ回収重水の品位を高く保つことが可能となった。また、アルカリ性化合物は、硫酸によって中和することから、安定な硫酸塩となり、容易に廃棄処分することを実現した。 As described above, by changing the treatment process of the heavy water waste liquid according to the concentration of impurities to a predetermined order, it becomes possible to perform the treatment quickly and without raising the temperature at high temperature, and the alkalinity in the recovered heavy water It became possible to suppress the abundance of compounds and gamma nuclides and to keep the quality of recovered heavy water high. In addition, since the alkaline compound is neutralized with sulfuric acid, it becomes a stable sulfate, and can be easily disposed of.
硫酸塩は、化学的にトリチウムが存在しえない化合物であるので、単蒸留後、乾固することによってトリチウム混入を極力抑えることが可能となった。さらに、これらの一連の処理プロセスは、処理装置への熱的、化学的負荷が少ないことから、処理装置の長期にわたる健全性（耐久性）及び操業の安全性が優れる。 Since sulfate is a compound in which tritium cannot be present chemically, it is possible to minimize tritium contamination by drying after simple distillation. Furthermore, these series of treatment processes are excellent in the long-term soundness (durability) and operational safety of the treatment equipment because the thermal and chemical loads on the treatment equipment are small.
本発明は、重水廃液中に含まれる不純物の量（アルカリ性化合物、トリチウム、ガンマ核種）を予め測定しておき、その不純物濃度にあった次に示す処理プロセスを適用する。 In the present invention, the amount of impurities (alkaline compound, tritium, gamma nuclide) contained in the heavy water waste liquid is measured in advance, and the following treatment process corresponding to the impurity concentration is applied.
アルカリ性化合物とトリチウム濃度がともに低い重水廃液（水酸化カリウムとして、おおよそ１質量％以下、トリチウム濃度が１×１０7Ｂｑ／ｍｌ以下）の場合を、第１の実施態様として、説明すると、単蒸留して殆どのトリチウム含有重水を回収後、蒸留釜に残留した濃縮液を軽水あるいは該重水廃液を用いて溶解し、炭酸ガス通気後硫酸によって中和する。この処理操作によって回収重水の重水品位を低下させず、且つアルカリ性化合物へのトリチウム移行量を十分に抑えることが出来る。なお、回収された重水にはアルカリ性化合物やガンマ核種は、殆ど移行しないことが確認されている。 The case of a heavy water waste solution having a low alkaline compound and tritium concentration (as potassium hydroxide, approximately 1% by mass or less, tritium concentration of 1 × 10 7 Bq / ml or less) will be described as a first embodiment. After most of the tritium-containing heavy water is recovered, the concentrated liquid remaining in the distillation kettle is dissolved using light water or the heavy water waste liquid, neutralized with sulfuric acid after aeration of carbon dioxide gas. By this treatment operation, the heavy water quality of recovered heavy water is not lowered, and the amount of tritium transferred to the alkaline compound can be sufficiently suppressed. It has been confirmed that alkaline compounds and gamma nuclides hardly migrate to the recovered heavy water.
第２の実施態様として、アルカリ性化合物とトリチウム濃度がともに上記第１の実施態様より高い重水廃液の場合は、重水廃液に炭酸ガスを吹き込んで重炭酸塩（重炭酸カリウムなど）とした後に硫酸によって中和し、単蒸留・乾固してトリチウム含有重水を回収する。蒸発釜に残留した硫酸塩は、軽水によって溶解する。この処理操作によって回収重水の重水品位を低下させず、且つ中和された硫酸塩溶液へのトリチウム移行量を十分に抑えることが出来る。 As a second embodiment, in the case of a heavy water waste liquid in which both the alkaline compound and the tritium concentration are higher than those in the first embodiment, carbon dioxide is blown into the heavy water waste liquid to form a bicarbonate (such as potassium bicarbonate), and then sulfuric acid is used. Neutralize, collect simple water and dry to collect tritium-containing heavy water. Sulfate remaining in the evaporation kettle is dissolved by light water. This treatment operation can sufficiently suppress the amount of tritium transferred to the neutralized sulfate solution without reducing the heavy water quality of recovered heavy water.
上記の第１及び第２の実施態様のうち、炭酸ガスを通気した後硫酸によって中和する方法は、炭酸ガスによってアルカリ性化合物（主に炭酸カリウム）を重炭酸塩に変化させて、硫酸中和の際の中和助剤（急激なｐＨ変化を緩衝する役割）として利用する。また、硫酸を中和剤に選定した理由は、中和した後の生成した硫酸塩は、水への溶解度が高くまた、室温において容易に溶解させることが出来ること及び化学的にトリチウムを存在しえない化合物であることによる。 Among the first and second embodiments described above, the method of neutralizing with sulfuric acid after aeration of carbon dioxide gas is to neutralize sulfuric acid by changing an alkaline compound (mainly potassium carbonate) to bicarbonate with carbon dioxide gas. It is used as a neutralization aid (role for buffering sudden pH changes) during the process. In addition, the reason for selecting sulfuric acid as the neutralizing agent is that the sulfate salt produced after neutralization has high solubility in water, can be easily dissolved at room temperature, and chemically contains tritium. This is because it is a compound that cannot be used.
以下、第１及び第２の実施態様を併せて本発明の方法として説明する。
本発明方法においては、重水廃液をそのまま、あるいは濃縮液としたのち、この重水廃液に炭酸ガスをまず吹き込み、それから硫酸で中和する工程を有する。先に強アルカリＫＯＨに対してＣＯ2（弱酸）を吹き込んで中和してから、硫酸（強酸）で中和する。この方法によれば、ｐＨが急激に変化しないため、ｐＨコントロールがしやすくなる。また、硫酸で中和することになり、塩（残留物）がトリチウムを含む水和物を持たないため、常圧であれば１００℃に加熱するだけで、水分を蒸発できる。
Hereinafter, the first and second embodiments will be described together as the method of the present invention.
In the method of the present invention, the heavy water waste liquid is used as it is or as a concentrated liquid, and then carbon dioxide gas is first blown into the heavy water waste liquid and then neutralized with sulfuric acid. First, CO 2 (weak acid) is blown into the strong alkali KOH to neutralize it, and then neutralized with sulfuric acid (strong acid). According to this method, since the pH does not change abruptly, it is easy to control the pH. Moreover, since it will neutralize with a sulfuric acid and a salt (residue) does not have a hydrate containing tritium, if it is normal pressure, a water | moisture content can be evaporated only by heating to 100 degreeC.
本発明の中和反応は、アルカリ化合物としてＫＯＨを例にとると次式によって表すことができる。
ＫＯＨ（強塩基）＋ＣＯ2（弱酸）→ＫＨＣＯ3（弱塩基） （１）
２ＫＨＣＯ3（弱塩基）＋Ｈ2ＳＯ4（強酸）→Ｋ2ＳＯ4↓＋２ＣＯ2↑＋２Ｈ2Ｏ （２）
上記反応式から明らかなように、ＫＯＨ（強塩基）をＣＯ2（弱酸）によってＫＨＣＯ3（弱塩基）とすることで、Ｈ2ＳＯ4（強酸）との中和反応が緩和される。ここでは、ＫＨＣＯ3（弱塩基）が緩衝剤となり、重水廃液に緩衝作用をもたらす。
The neutralization reaction of the present invention can be expressed by the following formula when KOH is taken as an example of the alkali compound.
KOH (strong base) + CO 2 (weak acid) → KHCO 3 (weak base) (1)
2KHCO 3 (weak base) + H 2 SO 4 (strong acid) → K 2 SO 4 ↓ + 2CO 2 ↑ + 2H 2 O (2)
As is clear from the above reaction formula, the neutralization reaction with H 2 SO 4 (strong acid) is alleviated by changing KOH (strong base) to KHCO 3 (weak base) with CO 2 (weak acid). Here, KHCO 3 (weak base) serves as a buffer, and provides a buffering action to the heavy water waste solution.
本発明において重水廃液中のアルカリ性化合物としては、主として重水生成装置から排出されるＫＯＨ、Ｋ2ＣＯ3、ＮａＯＨ、Ｎａ2ＣＯ3等のカリウムやナトリウムを含むアルカリ性化合物である。通常、重水廃液中のアルカリ性化合物の含有量は０．０１〜６０質量％であるが、これに制限されるものではない。また、上記実施態様１の蒸留液の濃縮した重水廃液の場合はアルカリ性化合物の濃度は、ＫＯＨ溶解度６５％（ａｔ２０℃）程度である。
また、炭酸ガスの吹き込み量は、上記式（１）に示すアルカリ化合物の反応が行われるに十分な量であり、通常、重水廃液に含まれるアルカリ性化合物濃度相当品の１１０％である。
また本発明において重炭酸塩を形成したのちに硫酸を添加して廃液を中和する。この硫酸の添加量は、上記式（２）の反応が完結するのに十分な量である。
In the present invention, the alkaline compound in the heavy water waste liquid is an alkaline compound containing potassium and sodium such as KOH, K 2 CO 3 , NaOH, Na 2 CO 3 and the like mainly discharged from the heavy water generator. Usually, the content of the alkaline compound in the heavy water waste liquid is 0.01 to 60% by mass, but is not limited thereto. Moreover, in the case of the heavy water waste liquid which concentrated the distilled liquid of the said Embodiment 1, the density | concentration of an alkaline compound is about 65% of KOH solubility (at20 degreeC).
Further, the amount of carbon dioxide blown is an amount sufficient for the reaction of the alkali compound represented by the above formula (1), and is usually 110% of the alkaline compound concentration equivalent product contained in the heavy water waste liquid.
In the present invention, after forming the bicarbonate, sulfuric acid is added to neutralize the waste liquid. The amount of sulfuric acid added is sufficient to complete the reaction of the above formula (2).
本発明において、硫酸塩を形成されたのち、重水を蒸発乾固させるが、上述のように常圧であれば１００℃に加熱するだけで水分を蒸発できる。生成した塩自体は水に溶解すると中性なので、中和する工程が不要で、そのまま放流が可能である。
一方、従来の方法はＣＯ2を吹き込むだけなので、トリチウムを含む水和物を伴う塩を生じるため、２５０℃まで加熱しなければならなかった（強塩基を加熱するため、材料が高くなる。）。また、塩自体も溶解すると強アルカリとなるため、その後の処理の前に中和する工程が必要であった。
次に本発明の好ましい実施態様を、図面に従って説明する。
In the present invention, after the sulfate is formed, the heavy water is evaporated to dryness. However, as described above, the water can be evaporated only by heating to 100 ° C. under normal pressure. Since the produced salt itself is neutral when dissolved in water, it does not require a neutralization step and can be discharged as it is.
On the other hand, since the conventional method only blows CO 2 , a salt with a hydrate containing tritium is formed, so it has to be heated to 250 ° C. (the material is expensive because a strong base is heated). . Further, since the salt itself becomes a strong alkali when dissolved, a step for neutralization is necessary before the subsequent treatment.
Next, preferred embodiments of the present invention will be described with reference to the drawings.
本発明においては、不純物の濃度に応じた重水廃液の処理プロセスに適用できる図１に示す処理装置を用いる。この処理装置は、重水廃液（被処理液）供給装置１、溶解液（希釈液）供給装置２、緩衝用炭酸ガス供給装置３、槽内攪拌用ガス供給装置４、中和用硫酸供給装置５、重水廃液計量タンク６、蒸発釜７、還流装置８、冷却器９、処理液タンク１０、重水回収タンク１１から構成される。重水廃液（被処理液）は、ポンプによって蒸発釜７へ移送される。
アルカリ性化合物とトリチウム濃度がともに低い重水廃液（アルカリ性化合物濃度がおおよそ１質量％以下）の場合は、該重水廃液を１０５〜１２０℃で単蒸留し、精製された重水が重水回収タンク１１にたまる。蒸発釜７に残留したアルカリ性化合物は、溶解液（希釈液）あるいは該重水廃液（被処理液）を用いて溶解される。その際、槽内攪拌用ガスを用いて高濃度のアルカリ廃液の溶解を容易にする。緩衝用炭酸ガスを用いて重炭酸塩とした後、中和用硫酸によって中和する。中和処理された廃液は、処理液タンク１０へ移送され、一連の操作を終了する。
アルカリ性化合物とトリチウム濃度がともに高い重水廃液（アルカリ性化合物濃度がおおよそ１％質量以上）の場合は、上記の構成要素を用いて重水廃液の単蒸留を行わないで重水廃液計量タンク６から、蒸発釜７に送り炭酸ガスを吹き込んだ後、中和用硫酸供給装置５から硫酸を導入し、重炭酸塩を硫酸塩とする中和を行う。次いで蒸発釜７を好ましくは１０５〜１３０℃に加熱してトリチウムを含有する重水を蒸留し、重水回収タンク１１に集める。一方蒸発釜７の加熱をさらに続け、蒸発残留物である硫酸塩を乾固する。
In the present invention, the treatment apparatus shown in FIG. 1 that can be applied to the treatment process of heavy water waste liquid according to the concentration of impurities is used. This processing apparatus includes a heavy water waste liquid (liquid to be treated) supply device 1, a solution (dilution liquid) supply device 2, a buffer carbon dioxide gas supply device 3, a tank stirring gas supply device 4, and a neutralization sulfuric acid supply device 5. , A heavy water waste liquid measuring tank 6, an evaporation pot 7, a reflux device 8, a cooler 9, a treatment liquid tank 10, and a heavy water recovery tank 11. The heavy water waste liquid (liquid to be treated) is transferred to the evaporation kettle 7 by a pump.
In the case of a heavy water waste liquid having a low alkaline compound and tritium concentration (the alkaline compound concentration is approximately 1% by mass or less), the heavy water waste liquid is simply distilled at 105 to 120 ° C., and purified heavy water is collected in the heavy water recovery tank 11. The alkaline compound remaining in the evaporation kettle 7 is dissolved using a dissolving liquid (diluted liquid) or the heavy water waste liquid (processed liquid). At that time, the high-concentration alkaline waste liquid is easily dissolved by using the gas for stirring in the tank. Bicarbonate is formed using buffer carbon dioxide, and then neutralized with sulfuric acid for neutralization. The neutralized waste liquid is transferred to the treatment liquid tank 10 and the series of operations is completed.
In the case of heavy water waste liquor having a high alkaline compound and tritium concentration (alkaline compound concentration is approximately 1% by mass or more), the evaporating kettle is used from the heavy water waste liquid measuring tank 6 without performing simple distillation of the heavy water waste liquid using the above components. After the carbon dioxide gas is blown into the fuel cell 7, sulfuric acid is introduced from the neutralizing sulfuric acid supply device 5 to neutralize the bicarbonate to sulfate. Next, the evaporation kettle 7 is preferably heated to 105 to 130 ° C. to distill heavy water containing tritium and collect it in the heavy water recovery tank 11. On the other hand, the heating of the evaporation kettle 7 is further continued to evaporate the sulfate as an evaporation residue.
次に本発明を実施例に基づきさらに詳細に説明する。例中、濃度、組成を示す％は質量％である。 Next, the present invention will be described in more detail based on examples. In the examples,% indicating concentration and composition is% by mass.
（実施例１）
アルカリ性化合物とトリチウム濃度がともに低い重水廃液（重水濃度９９％、アルカリ性化合物濃度［ＫＯＨとして］０．５％、トリチウム濃度１×１０7Ｂｑ／ｍｌ、ガンマ核種濃度１．５Ｂｑ／ｍｌを含む重水廃液）を上記に示す装置を用いて次のとおり処理した。
(Example 1)
Heavy water waste liquid with low alkaline compound and tritium concentration (heavy water waste liquid containing 99% heavy water concentration, 0.5% alkaline compound concentration [as KOH], tritium concentration 1 × 10 7 Bq / ml, gamma nuclide concentration 1.5 Bq / ml ) Was processed as follows using the apparatus shown above.
重水廃液は、重水廃液供給装置１を用いて重水廃液計量タンク６へ移送した。重水廃液を１０リットル計量後、その全量を蒸発釜７へ移送した。蒸留釜７および還流装置８を１０５℃で加熱、冷却器９を１０℃で冷却して重水廃液を単蒸留した。重水回収タンク１１には精製された重水が約９．９リットル回収できたことを確認した。この回収重水のカリウム濃度を測定したところ１５ｐｐｍであり、残存廃液として、ガンマ核種は３０Ｂｑ／ｍｌ、トリチウム濃度３５０Ｂｑ／ｍｌであった。蒸留することによって十分に精製されていることがわかった。 The heavy water waste liquid was transferred to the heavy water waste liquid measuring tank 6 using the heavy water waste liquid supply device 1. After measuring 10 liters of the heavy water waste liquid, the entire amount was transferred to the evaporation kettle 7. The distillation kettle 7 and the reflux device 8 were heated at 105 ° C., the cooler 9 was cooled at 10 ° C., and the heavy water waste liquid was simply distilled. It was confirmed that about 9.9 liters of purified heavy water could be recovered in the heavy water recovery tank 11. When the potassium concentration of this recovered heavy water was measured, it was 15 ppm. As the residual waste liquid, the gamma nuclide was 30 Bq / ml and the tritium concentration was 350 Bq / ml. It was found that the product was sufficiently purified by distillation.
溶解液（希釈液）供給装置２から移送された溶解液を用いて、蒸発釜７の残留物を溶解した。その際、槽内攪拌用ガス供給装置４から供給する圧縮空気を用いて、槽内を十分に攪拌した。溶解後、緩衝用炭酸ガス供給装置３を用いて処理水を炭酸ガスで十分にバブリングして重水廃液中アルカリの化学系をすべて重炭酸塩とした。中和用硫酸供給装置５から少量ずつ希硫酸を重水廃液へ滴下し、ｐＨ計を用いてｐＨ７近傍に調節した。重水廃液中に重炭酸塩があるために、それが緩衝剤となって容易にｐＨを調節することができた。処理液は、処理液タンク１０に移送し１０倍量の溶解液で希釈し一連の操作を終了した。処理液中のトリチウム濃度を測定したところ、２×１０4 Ｂｑ／ｍｌとなり、これをさらに希釈すれば液体廃棄物として放出することが可能となる。 The residue in the evaporation kettle 7 was dissolved using the solution transferred from the solution (diluent) supply device 2. At that time, the inside of the tank was sufficiently stirred using compressed air supplied from the tank stirring gas supply device 4. After dissolution, the treated water was sufficiently bubbled with carbon dioxide using the buffer carbon dioxide supply device 3 to make all the alkali chemical system in the heavy water waste liquid into bicarbonate. Dilute sulfuric acid was dripped into the heavy water waste solution little by little from the sulfuric acid supply device 5 for neutralization, and the pH was adjusted to around 7 using a pH meter. Since bicarbonate was present in the heavy water effluent, it became a buffer and could easily adjust the pH. The treatment liquid was transferred to the treatment liquid tank 10 and diluted with 10 times the amount of the dissolution liquid, and the series of operations was completed. When the tritium concentration in the treatment liquid is measured, it becomes 2 × 10 4 Bq / ml, and if this is further diluted, it can be released as liquid waste.
（実施例２）
アルカリ性化合物とトリチウム濃度がともに高い重水廃液（重水濃度９９％、アルカリ性化合物濃度［ＫＯＨとして］２５％、トリチウム濃度１×１０8Ｂｑ／ｍｌ、ガンマ核種濃度３．２Ｂｑ／ｍｌを含む重水廃液）を上記に示す装置を用いて次のとおり処理した。
(Example 2)
Heavy water waste liquid with high alkaline compound and tritium concentration (heavy water waste liquid containing heavy water concentration 99%, alkaline compound concentration [as KOH] 25%, tritium concentration 1 × 10 8 Bq / ml, gamma nuclide concentration 3.2 Bq / ml) It processed as follows using the apparatus shown above.
重水廃液は、重水廃液供給装置１を用いて重水廃液計量タンク６へ移送した。重水廃液を５リットル計量後、その全量を蒸発釜７へ移送した。緩衝用炭酸ガス供給装置３を用いて蒸発釜７へ炭酸ガスを十分にバブリングした後、中和用硫酸供給装置５から少量ずつ希硫酸を重水廃液へ滴下し、ｐＨ計を用いてｐＨ７近傍に調節した。その後蒸発釜７を約１３０℃で加熱してトリチウムを含有する重水を蒸留した。さらに１３０℃で加熱を続け、流出液がなくなるまで蒸留し、蒸発残留物である硫酸塩を乾固した。 The heavy water waste liquid was transferred to the heavy water waste liquid measuring tank 6 using the heavy water waste liquid supply device 1. After measuring 5 liters of the heavy water waste liquid, the whole amount was transferred to the evaporation kettle 7. After sufficiently bubbling carbon dioxide into the evaporation kettle 7 using the buffering carbon dioxide supply device 3, dilute sulfuric acid is dropped little by little from the neutralizing sulfuric acid supply device 5 into the heavy water waste solution, and the pH is brought close to pH 7 using a pH meter. Adjusted. Thereafter, the evaporation kettle 7 was heated at about 130 ° C. to distill heavy water containing tritium. Further, heating was continued at 130 ° C., and distillation was performed until there was no effluent, and the sulfate as an evaporation residue was dried.
次いで、溶解液（希釈液）供給装置２を用いて軽水を蒸発釜７へ注入し、蒸発釜７の残留物を溶解した。その際、槽内攪拌用ガス供給装置４から供給する圧縮空気を用いて、槽内を十分に撹拌した。処理液は、処理液タンク１０に移送し１０倍量の溶解液で希釈し一連の操作を終了した。この試験において回収重水中のカリウム濃度を測定したところ１２ｐｐｍであった。残存廃液として、ガンマ核種７０Ｂｑ／ｍｌ、トリチウム濃度７０Ｂｑ／ｍｌであった。 Next, light water was poured into the evaporation kettle 7 using the dissolving liquid (diluent) supply device 2 to dissolve the residue in the evaporation kettle 7. In that case, the inside of a tank was fully stirred using the compressed air supplied from the gas supply apparatus 4 for stirring in a tank. The treatment liquid was transferred to the treatment liquid tank 10 and diluted with 10 times the amount of the dissolution liquid, and the series of operations was completed. In this test, the potassium concentration in the recovered heavy water was measured and found to be 12 ppm. The remaining waste liquid was a gamma nuclide of 70 Bq / ml and a tritium concentration of 70 Bq / ml.
（比較例１）
実施例１での条件（アルカリ性化合物濃度が低い場合）で炭酸ガスを導入しないで硫酸中和した。その結果、回収重水のカリウム濃度２０ｐｐｍ、処理済み廃液中のガンマ核種３５Ｂｑ／ｍｌ、トリチウム濃度４００Ｂｑ／ｍｌ（定容値は実施例１と同じ）であったが、溶液のｐＨを制御できず、ｐＨが１以下になってしまった。
(Comparative Example 1)
Under the conditions in Example 1 (when the alkaline compound concentration is low), sulfuric acid was neutralized without introducing carbon dioxide. As a result, the potassium concentration of recovered heavy water was 20 ppm, the gamma nuclide in the treated waste liquid was 35 Bq / ml, and the tritium concentration was 400 Bq / ml (the constant volume was the same as in Example 1), but the pH of the solution could not be controlled. The pH has become 1 or less.
（比較例２）
実施例１での条件（アルカリ性化合物濃度が低い場合）で、緩衝工程（炭酸ガス）と中和工程（硫酸）を省いた。その結果、回収重水のカリウム濃度１０ｐｐｍ、処理済み廃液中のガンマ核種５０Ｂｑ／ｍｌ、トリチウム濃度５２０Ｂｑ／ｍｌ（定容値は実施例１と同じ）であった。また、蒸留釜に残った残留物を水で溶解した時の溶解液のｐＨは１４であり、次の工程へ進むには、なんらかで中和しなくてはならない。
(Comparative Example 2)
The buffering step (carbon dioxide gas) and the neutralization step (sulfuric acid) were omitted under the conditions in Example 1 (when the alkaline compound concentration was low). As a result, the potassium concentration of recovered heavy water was 10 ppm, the gamma nuclide in the treated waste liquid was 50 Bq / ml, and the tritium concentration was 520 Bq / ml (the constant volume value is the same as in Example 1). In addition, when the residue remaining in the still is dissolved with water, the pH of the solution is 14. In order to proceed to the next step, it must be neutralized in some way.
（比較例３）
実施例２での条件（アルカリ性化合物濃度が高い場合）で炭酸ガスを導入しないで蒸留し、硫酸中和した。その後再び蒸留乾固した。その結果、比較例１同様に処理液のｐＨが制御できず、ｐＨが１以下となってしまった。その処理液を蒸留したところ、回収重水のカリウム濃度２５ｐｐｍ、ガンマ核種３０Ｂｑ／ｍｌ、トリチウム濃度６０Ｂｑ／ｍｌ（定容値は実施例２と同じ）となったが、二度目の蒸留乾固時、硫酸ミストが回収液側に移行し、回収液のｐＨが２となった。
(Comparative Example 3)
Distillation was performed without introducing carbon dioxide under the conditions in Example 2 (when the concentration of the alkaline compound was high), and the mixture was neutralized with sulfuric acid. Then it was again distilled to dryness. As a result, the pH of the treatment liquid could not be controlled as in Comparative Example 1, and the pH was 1 or less. When the treated liquid was distilled, the recovered heavy water had a potassium concentration of 25 ppm, a gamma nuclide of 30 Bq / ml, and a tritium concentration of 60 Bq / ml (the constant volume was the same as in Example 2). The sulfuric acid mist moved to the recovered liquid side, and the pH of the recovered liquid became 2.
（比較例４）
実施例２での条件（アルカリ性化合物濃度が高い場合）で、緩衝工程（炭酸ガス）と中和工程（硫酸）を省き、１０５〜１２０℃で蒸留した。その結果、回収重水のカリウム濃度５０ｐｐｍ、処理済み廃液中のガンマ核種１５Ｂｑ／ｍｌ、トリチウム濃度６４００Ｂｑ／ｍｌ（定容値は実施例１と同じ）であった。また、蒸留釜に残った残留物を水で溶解した時の溶解液のｐＨは１４であり、次の工程へ進むには、なんらかで中和しなくてはならなかった。
(Comparative Example 4)
Under the conditions in Example 2 (when the alkaline compound concentration is high), the buffering step (carbon dioxide gas) and the neutralization step (sulfuric acid) were omitted, and distillation was performed at 105 to 120 ° C. As a result, the potassium concentration of recovered heavy water was 50 ppm, the gamma nuclide in the treated waste liquid was 15 Bq / ml, and the tritium concentration was 6400 Bq / ml (the constant volume value is the same as in Example 1). Further, when the residue remaining in the still was dissolved with water, the pH of the solution was 14. In order to proceed to the next step, it was necessary to neutralize something.
１ 重水廃液（被処理液）供給装置
２ 溶解液（希釈液）供給装置
３ 緩衝用炭酸ガス供給装置
４ 槽内攪拌用ガス供給装置
５ 中和用硫酸供給装置
６ 重水廃液計量タンク
７ 蒸発釜
８ 還流装置
９ 冷却器
１０ 処理液タンク
１１ 重水回収タンク
DESCRIPTION OF SYMBOLS 1 Heavy water waste liquid (processed liquid) supply apparatus 2 Dissolved liquid (diluent) supply apparatus 3 Buffering carbon dioxide supply apparatus 4 Gas supply apparatus for stirring in tank 5 Neutralization sulfuric acid supply apparatus 6 Heavy water waste liquid measuring tank 7 Evaporation pot 8 Reflux device 9 Cooler 10 Treatment liquid tank 11 Heavy water recovery tank
Claims (4)
3. Carbonic acid gas is blown into heavy water containing the alkaline compound according to claim 1 or 2 to form a bicarbonate, and then the bicarbonate acts as a buffer when neutralizing with sulfuric acid. The method according to claim 1.
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