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JP3892864B2 - Method for electrolytic reprocessing of spent salt from spent fuel - Google Patents
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JP3892864B2 - Method for electrolytic reprocessing of spent salt from spent fuel - Google Patents

Method for electrolytic reprocessing of spent salt from spent fuel Download PDF

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JP3892864B2
JP3892864B2 JP2004241254A JP2004241254A JP3892864B2 JP 3892864 B2 JP3892864 B2 JP 3892864B2 JP 2004241254 A JP2004241254 A JP 2004241254A JP 2004241254 A JP2004241254 A JP 2004241254A JP 3892864 B2 JP3892864 B2 JP 3892864B2
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molten salt
cathode
spent
spent fuel
fuel
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JP2004361418A (en
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浩司 水口
裕一 東海林
健一 松丸
尋 鴨志田
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Toshiba Corp
Toshiba Plant Systems and Services Corp
Tokyo Electric Power Co Holdings Inc
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Tokyo Electric Power Co Inc
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies

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Description

本発明は、使用済み燃料の溶融塩電解再処理方法に係わり、さらに詳しくは、原子力発電所で使用済みの燃料を溶融塩電解により再処理する方法に関する。   The present invention relates to a molten salt electrolysis reprocessing method of spent fuel, and more particularly to a method of reprocessing spent fuel in a nuclear power plant by molten salt electrolysis.

従来から、原子力発電所で使用済みの、酸化ウラン、アルカリ金属元素、貴金属元素、希土類元素、および原子炉内で生成したプルトニウム等の超ウラン元素（ＴＲＵ）を含む燃料を再処理するには、せん断し脱被覆した後、ＮａＣｌやＫＣｌのような溶融塩中で、陽極と陰極との間に電圧をかけて電解を行なう溶融塩電解方法が行なわれている。   To reprocess fuel that has traditionally been used in nuclear power plants and contains uranium oxide, alkali metal elements, noble metal elements, rare earth elements, and transuranium elements (TRU) such as plutonium produced in the reactor, A molten salt electrolysis method in which electrolysis is performed by applying a voltage between an anode and a cathode in a molten salt such as NaCl or KCl after shearing and decoating.

この方法においては、陽極で塩の電解により発生した塩素ガスによって、使用済み燃料の各成分が溶融塩中に溶解し、一方陰極で、電気的に還元されて酸化ウラン（ＵＯ２）等が顆粒状酸化物として回収される。そして、この溶解および電解回収工程で残った溶融塩に、塩素と酸素の混合ガスを吹き込むことにより、プルトニウムとネプツニウムのイオンがそれぞれ酸化され、かつ電解によりＰｕＯ２、およびＮｐＯ２が回収されるように構成されている。 In this method, each component of the spent fuel is dissolved in the molten salt by chlorine gas generated by electrolysis of the salt at the anode, while uranium oxide (UO 2 ) and the like are granulated by being electrically reduced at the cathode. It is recovered as a state oxide. Then, a mixed gas of chlorine and oxygen is blown into the molten salt remaining in this dissolution and electrolytic recovery process, so that plutonium and neptunium ions are oxidized, and PuO 2 and NpO 2 are recovered by electrolysis. It is configured.

しかしながら、このような従来からの溶融塩電解再処理方法においては、以下に示すような種々の問題があった。すなわち、
１）陽極溶解工程で、使用済み燃料に含まれている貴金属元素が溶融塩中に溶解するが、これら貴金属イオンが析出する電位（酸化還元電位）がウラニルイオンのそれと極めて近いため、陰極で貴金属元素も同時に析出してしまい、回収したＵＯ２中に貴金属が混入してしまう。
２）パイログラファイトのような電解槽（電解るつぼ）を構成する材料が、ウラニルイオンによって腐食されやすいため、るつぼの寿命が１０００〜２０００時間と短い。
３）ウラナスイオンやプルトナスイオンの酸化処理に時間がかかる。
４）溶融塩から発生する揮発性成分が、電解槽内の各部に付着し、配管等の目詰まりを引き起こしやすい。
などの問題があった。 However, such conventional molten salt electrolytic reprocessing methods have various problems as described below. That is,
1) In the anodic dissolution process, the noble metal element contained in the spent fuel dissolves in the molten salt, but the potential at which these noble metal ions precipitate (oxidation-reduction potential) is very close to that of the uranyl ion, so the noble metal at the cathode Elements are also precipitated at the same time, and noble metals are mixed in the recovered UO 2 .
2) Since the material constituting the electrolytic cell (electrolytic crucible) such as pyrographite is easily corroded by uranyl ions, the life of the crucible is as short as 1000 to 2000 hours.
3) It takes time to oxidize uranas ions and plutonas ions.
4) Volatile components generated from the molten salt adhere to each part in the electrolytic cell and easily cause clogging of piping and the like.
There were problems such as.

本発明は、これらの問題を解決するためになされたもので、使用済み燃料の溶融塩電解による再処理において、貴金属元素等の不純物の混入のない、より高品質の燃料成分を回収することができる溶融塩電解再処理方法を提供することを目的とする。   The present invention has been made to solve these problems, and can recover higher-quality fuel components free from impurities such as precious metal elements in reprocessing of spent fuel by molten salt electrolysis. An object of the present invention is to provide a molten salt electrolytic reprocessing method.

本発明の使用済み燃料の溶融塩電解再処理方法は、導電性るつぼに溶融塩を装荷し、該るつぼを陽極として使用済み燃料の電解を行ない、陽極で溶解するとともに、所要の成分を固体陰極に回収する溶融塩電解再処理方法において、前記固体陰極が断面楕円形の棒状を呈しており、かつこの陰極を軸の回りに自転させながら電解を行なうことを特徴とする。   The method of reprocessing spent salt electrolysis of spent fuel according to the present invention comprises loading molten salt into a conductive crucible, electrolyzing the spent fuel using the crucible as an anode, melting the anode, and dissolving the required components into a solid cathode. In the molten salt electroreprocessing method to be recovered, the solid cathode has a bar shape with an elliptical cross section, and electrolysis is performed while rotating the cathode about its axis.

本発明の再処理方法においては、溶融塩中に溶解したウラン、ウラン・プルトニウム等の酸化物を電解して回収するための陰極として、楕円形の断面を有する棒状の電極が使用され、かつこの陰極を軸の回りに回転（自転）させながら電解が行なわれているので、電解槽底部に沈積した使用済み燃料を舞い上がらせることなく、溶融塩全体が撹拌され、溶解および析出の効率がいずれも向上する。   In the reprocessing method of the present invention, a rod-shaped electrode having an elliptical cross section is used as a cathode for electrolyzing and recovering oxides such as uranium and uranium / plutonium dissolved in a molten salt, and this Since the electrolysis is carried out while rotating (spinning) the cathode around its axis, the entire molten salt is stirred without causing the spent fuel deposited on the bottom of the electrolytic cell to rise, and both the efficiency of dissolution and precipitation is achieved. improves.

そして、回収する燃料中への貴金属元素等の不純物の混入を低減することができ、より高品質の燃料を得ることができる。また、使用済み燃料の陽極側での溶解と核燃料物質の陰極側での析出を同時に効率よく行なうことができ、使用済み燃料の処理効率を向上させることができる。   Further, impurities such as noble metal elements can be reduced in the fuel to be recovered, and a higher quality fuel can be obtained. Moreover, the spent fuel can be efficiently dissolved on the anode side and the nuclear fuel material can be deposited on the cathode side at the same time, and the processing efficiency of the spent fuel can be improved.

以下、本発明の実施例を図面に基づいて説明する。   Embodiments of the present invention will be described below with reference to the drawings.

図１は、本発明の再処理方法の実施例に用いる処理装置を示す断面図である。   FIG. 1 is a sectional view showing a processing apparatus used in an embodiment of the reprocessing method of the present invention.

この処理装置においては、導電性るつぼ１に溶融塩２が収容されており、溶融塩２中には、グラファイトのような導電性材料から形成され、Ａ−Ａ断面が図２に示すように楕円形を有する棒状の陰極３が設けられている。また、この陰極３には回転駆動機構４が連結されており、陰極３と陽極である導電性るつぼ１との間には、電解のための電源５が接続されている。さらに、導電性るつぼ１の周りには、内部の温度を所定温度に保つための電気炉６が設置されている。電解処理に先だって、溶融塩２中に使用済み燃料（粉体もしくは粒体）７が装荷される。   In this processing apparatus, a molten crucible 2 is accommodated in a conductive crucible 1, and the molten salt 2 is formed of a conductive material such as graphite, and the AA cross section is elliptical as shown in FIG. A rod-like cathode 3 having a shape is provided. The cathode 3 is connected to a rotational drive mechanism 4, and a power source 5 for electrolysis is connected between the cathode 3 and the conductive crucible 1 serving as an anode. Further, an electric furnace 6 is installed around the conductive crucible 1 to keep the internal temperature at a predetermined temperature. Prior to the electrolytic treatment, spent fuel (powder or granules) 7 is loaded into the molten salt 2.

このような処理装置において、使用済み燃料７が導電性るつぼ１の底部に沈積した状態で、るつぼ１と回転する陰極３との間に電源５を用いて電流を流すと、るつぼ１底部に接するように沈積した使用済み燃料７が、以下に示す反応機構により溶解する。   In such a processing apparatus, when a current is passed between the crucible 1 and the rotating cathode 3 with the spent fuel 7 deposited on the bottom of the conductive crucible 1, the power source 5 is used to contact the bottom of the crucible 1. The spent fuel 7 deposited in this manner is dissolved by the reaction mechanism shown below.

例えばウラン酸化物について言えば、ウラン酸化物自体が、陽極であるるつぼ１に電子を供給して、ウラニルイオンとなり溶解する反応（（１）式に示す）と、溶融塩中に存在する塩素イオンが陽極であるるつぼ１に電子を供給して塩素ガスとなり、この塩素ガスとウラン酸化物が反応してウラニルイオンとなって溶解する反応（（２）式および（３）式に示す）の２つの反応機構により溶解する。
ＵＯ２→ＵＯ２ ２＋＋２ｅ− ………（１）
２Ｃｌ−→Ｃｌ２＋２ｅ− ………（２）
ＵＯ２＋Ｃｌ２→ＵＯ２ ２＋＋２Ｃｌ ………（３） For example, with respect to uranium oxide, a reaction in which uranium oxide itself supplies electrons to the crucible 1 as an anode and becomes a uranyl ion and dissolves (shown in the formula (1)), and a chlorine ion present in the molten salt. 2 of the reaction (shown in the equations (2) and (3)) in which electrons are supplied to the crucible 1 serving as the anode to form chlorine gas, and the chlorine gas and uranium oxide react to form uranyl ions. It dissolves by two reaction mechanisms.
UO 2 → UO 2 2+ + 2e − (1)
2Cl − → Cl 2 + 2e − (2)
UO 2 + Cl 2 → UO 2 2+ + 2Cl (3)

したがって、使用済み燃料７を効率よく溶解させるには、使用済み燃料７が陽極である導電性るつぼ１にできるだけ接触していることが必要である。   Therefore, in order to dissolve the spent fuel 7 efficiently, it is necessary that the spent fuel 7 is in contact with the conductive crucible 1 as an anode as much as possible.

一方、陰極には、溶融塩中に溶解した核燃料物質が、例えばウランについて言えば、（４）式に示す反応により析出する。
ＵＯ２ ２＋＋２ｅ−→ＵＯ２ ………（４） On the other hand, the nuclear fuel material dissolved in the molten salt is deposited on the cathode by the reaction shown in the formula (4) for uranium, for example.
UO 2 2+ + 2e − → UO 2 (4)

このような陰極での析出を効率よく行なうためには、陽極であるるつぼの近傍で溶融塩中に溶解した核燃料物質のイオンが、陰極近傍に供給される必要がある。   In order to efficiently perform such deposition at the cathode, the nuclear fuel material ions dissolved in the molten salt in the vicinity of the crucible as the anode must be supplied in the vicinity of the cathode.

このように使用済み燃料７の処理を効率よく行なうためには、陽極での溶解と陰極での核燃料物質の析出とを、両方とも効率良く行なう必要がある。そして、前者の要求を満たすには、沈積した燃料粉体が舞い上がるような溶融塩の撹拌は行なわない方が良いが、後者の要求を満たすには、溶融塩中に溶解した核燃料物質にイオン濃度分布ができないように、できるだけ撹拌を行なった方が良く、両者の要求は撹拌の適否について相反することになる。   In order to efficiently process the spent fuel 7 as described above, it is necessary to efficiently perform both dissolution at the anode and deposition of the nuclear fuel material at the cathode. In order to satisfy the former requirement, it is better not to stir the molten salt so that the deposited fuel powder soars, but in order to satisfy the latter requirement, the ion concentration in the nuclear fuel material dissolved in the molten salt It is better to stir as much as possible so that the distribution is not possible, and both requirements conflict with each other regarding the suitability of stirring.

実施例の処理方法によれば、陰極３が楕円形の断面を有する棒状電極であり、これが回転駆動機構４により軸の周りに回転されているので、導電性るつぼ１の底部に沈積した使用済み燃料７を、舞い上がらせることなく、溶融塩２全体を撹拌することが可能であり、陽極での溶解も陰極での析出も両方とも効率良く行なうことができる。   According to the processing method of the embodiment, the cathode 3 is a rod-like electrode having an elliptical cross section, and this is rotated around the axis by the rotary drive mechanism 4, so that it is used deposited on the bottom of the conductive crucible 1. The entire molten salt 2 can be stirred without causing the fuel 7 to rise, and both dissolution at the anode and precipitation at the cathode can be performed efficiently.

本発明の実施例に用いる処理装置を模式的に示す断面図である。It is sectional drawing which shows typically the processing apparatus used for the Example of this invention. 図１のＡ−Ａ矢視断面図である。It is AA arrow sectional drawing of FIG.

符号の説明Explanation of symbols

１…導電性るつぼ、２…溶融塩、３…棒状の陰極、４…回転駆動機構、５…電源、６…電気炉、７…使用済み燃料。   DESCRIPTION OF SYMBOLS 1 ... Conductive crucible, 2 ... Molten salt, 3 ... Rod-shaped cathode, 4 ... Rotation drive mechanism, 5 ... Power supply, 6 ... Electric furnace, 7 ... Used fuel.

Claims (1)

導電性るつぼに溶融塩を装荷し、該るつぼを陽極として使用済み燃料の電解を行ない、陽極で溶解するとともに、所要の成分を固体陰極に回収する溶融塩電解再処理方法において、前記固体陰極が断面楕円形の棒状を呈しており、かつこの陰極を軸の回りに自転させながら電解を行なうことを特徴とする使用済み燃料の溶融塩電解再処理方法。   In a molten salt electrolysis reprocessing method in which a molten salt is loaded into a conductive crucible, and electrolysis of spent fuel is performed using the crucible as an anode, and the required components are recovered in the solid cathode. A molten salt electrolysis reprocessing method for spent fuel, characterized in that it has a bar shape with an elliptical cross section, and electrolysis is performed while rotating the cathode around its axis.
JP2004241254A 2004-08-20 2004-08-20 Method for electrolytic reprocessing of spent salt from spent fuel Expired - Fee Related JP3892864B2 (en)

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