報告書番号

T97082

タイトル（和文）

ＰＵＲＥＸ再処理条件下における高燃焼度ＵＯ２燃料及びＭＯＸ燃料溶解特性

タイトル（英文）

DISSOLUTION STUDIES ON HIGH BURN-UP UO2 AND MOX FUELS FOR APPLYING TO PUREX REPROCESSING

概要 （図表や脚注は「報告書全文」に掲載しております）

商業用軽水炉で照射された高燃焼度燃料（燃焼度約６５ＭＷｄ／ｋｇＵ）及びＭＯＸ燃料（燃焼度約４５ＭＷｄ／ｋｇＵ）の溶解試験を行い，溶解特性及び，不溶解残渣の特性を調べ，ピュ－レックス法による現在の再処理法が適用可能であるか検討した。１）どちらの燃料も７規定硝酸溶液中では，約４０分で溶解が完了した。これに対し４規定硝酸では，どちらも溶解が完了するまでに２時間以上であった。ふたつの燃料の溶解速度はほぼ同じであることが分かった。２）高燃焼度燃料に関しては，不溶解残渣発生量が燃焼度に対して比例より大きな割合で増加した。ＭＯＸ燃料では，ＵＯ２燃料の測定結果から予想される量に比べて若干増加したが，燃料内に局所的に燃焼度の高いＰｕスポットが観察されており，これらが増加の一因となっていると考えられる。３）不溶解残渣の主成分は，どちらもＭｏ，Ｒｕ，Ｔｃ，Ｒｈ，Ｐｄであり，燃料中の金属性析出物の成分とほぼ一致した。不溶解残渣は増加するものの硝酸濃度等を調節することにより大きな問題は無く溶解し，これまでの再処理法が適用できることが分かった。

概要 （英文）

IN JAPAN, THE BURN-UP OF COMMERCIAL LWR FUELIS INTENDED TO BE INCREASED TO 55MWD/KGU TO REDUCE THE VOLUME OF SPENTFUEL AND THE COST OF THE TOTAL FUEL CYCLE. THE USE OF LWR MOX FUEL FORTHE PU-THERMAL FUEL CYCLE IS ALSO PLANNED IN ORDER TO CONSUME THE PU FROM LWR FUEL REPROCESSING. THE REPROCESSING OF BOTH OF SPENT HIGH BURN-UP UO2 FUEL AND SPENT LWR MOX FUEL IS CURRENTLY PART OF THE NATIONAL STRATEGY FOR THE NUCLEAR FUEL CYCLE FROM THE VIEWPOINT OF TOTAL FUEL CYCLE COST AND SECURITY. THERE HAVE BEEN FEW STUDIES ON THE REPROCESSING OFHIGH BURN-UP UO2 FUEL AND LWR MOX FUEL. THEREFORE, WE ESTIMATED THE APPLICABILITY OF THE PUREX PROCESS, WHICH IS EMPLOYED IN MANY COMMERCIAL REPROCESSING PLANTS, TO HIGH BURN-UP UO2 FUEL AND LWR MOX FUEL. IN PARTICULAR, WE STUDIED THE DISSOLUTION BEHAVIOR OF BOTH FUELS UNDER THE DISSOLUTION CONDITIONS OF PLANNED COMMERCIAL REPROCESSING PLANTS IN JAPAN.THE DISSOLUTION BEHAVIOR OF HIGH BURN-UP UO2 FUEL AND LWR MOX FUEL THAT WERE IRRADIATED IN COMMERCIAL LWRS WAS STUDIED AND THE RESIDUE FROM THE DISSOLUTION PROCESS WAS ANALYZED. BECAUSE 3N 4N NITRIC ACID SOLUTION WILL BE USED IN COMMERCIAL REPROCESSING PLANTS IN JAPAN, BOTH HIGH BURN-UP UO2 FUEL AND LWR MOX FUEL WERE DISSOLVED IN 4N AND 7N NITRIC ACID SOLUTION IN THIS TEST. THE EFFECT OF THE NITRIC ACID CONCENTRATION WAS ESTIMATED. 1)BOTH HIGH BURN-UP UO2 FUEL AND LWR MOX FUEL WERE DISSOLVED COMPLETELY AFTER 40 MINUTES IN THE 7N NITRIC ACID SOLUTION BUT MORE THAN 120 MINUTES WAS REQUIRED TO COMPLETELY DISSOLVE BOTH FUELS IN 4N NITRIC ACID SOLUTION. IT CAN BE CONCLUDED THAT THE DISSOLUTION RATES OF THE HIGH BURN-UP UO2 FUEL(63GWD/TM) AND THE LWR MOX FUEL(43GWD/TM) ARE ALMOST THE SAME. 2)THE AMOUNT OF RESIDUE OF THE HIGH BURN-UP UO2 FUEL WAS LARGER THAN THAT EXPECTED BASED ON THE LINEAR RELATIONSHIP WITH THE BURN-UP THAT WAS ESTABLISHED FROM THE DATA FOR THE LOWER BURN-UP UO2 FUEL.THERE WAS SLIGHTLY MORE RESIDUE FROM THE MOX FUEL THAN FROM UO2 FUELS OF THE SAME BURN-UP. THE PU AGGLOMERA

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