Material attractiveness evaluation of actinides in Pyroprocessing Facility for partitioning and transmutation cycle

分離変換サイクルにおける乾式再処理施設内のアクチノイド核種の不正利用価値評価

大泉 昭人   ; 相楽 洋*

Oizumi, Akito; Sagara, Hiroshi*

使用済燃料に含まれる高レベル放射性廃棄物処分の負担軽減のために、商業サイクルから分離したマイナーアクチノイドを加速器駆動システム(ADS)により核変換させる、分離変換サイクルの研究開発が進められている。扱われる燃料の化学形態や組成が既往サイクルとは異なるため、分離変換サイクルに要求される保障措置(SG)の検認精度や核物質防護(PP)のレベルについて検討する必要がある。本研究では、乾式再処理施設で扱われるCd陰極と窒化物の粉について、SGの検認目標やPPの設計レベルの検討に資する物質の不正利用価値が評価された。さらに、一般的な沸騰型軽水炉(BWR)のMOX燃料集合体(新燃料及び使用済燃料)の同評価結果と比較された。その結果、Cd陰極,窒化物の粉のいずれにおいても、崩壊熱の大きいPuのPu同位体割合が多い影響で、Puの核爆発装置当たりの発熱量が大きくなるため、BWRのMOX燃料集合体(新燃料及び使用済み燃料)よりも物質の不正利用価値が低いということが明らかとなった。

Research and development of partitioning and transmutation (P&T) cycle with accelerator-drive systems (ADSs) transmuting minor actinides (MAs) separated from the commercial cycles has been continuously conducted to reduce the high-level radioactive waste (HLW) contained in spent fuel discharged from nuclear power plants. The Japan Atomic Energy Agency has proposed a pyrochemical process for reprocessing ADS spent fuel with high decay heat and radioactivity due to the large amount of MA. Since the chemical form and composition of the fuels are different from those of the current commercial cycles, it is necessary to examine the inspection goal of the safeguards (SGs) and the design level of physical protections (PPs) which are required for the P&T cycle. In this study, the material attractiveness was evaluated assuming the diversion of the Cd cathode and the nitride powder from the pyroprocessing in terms of non-proliferation. Additionally, they were compared with the material attractiveness of the MOX fuel assemblies (fresh and spent fuels) for a conventional boiling water reactor (BWR). The Cd cathode used to recover actinides from ADS spent fuel by molten salt electrolysis in the pyroprocessing facility of P&T cycle was less attractive than the MOX fuel assembly for the BWR because the Cd cathode included Pu having high decay heat. The nitride powder electrorefined from the ADS spent fuel was also less attractiveness than the MOX fuel assembly for the BWR because of the same reasons of the Cd cathode.