高速炉によるTRU消滅処理に関する研究(III) -TRU燃料集合耐非均質装荷の検討-

Study on TRU transmutation by LMFBRs(III); Characteristics of heterogeneous TRU-loading core

若林 利男; 山岡 光明

not registered; Yamaoka, Mitsuaki

高レベル廃棄物中に含まれる超ウラン元素(TRU)を高速炉により消滅処理する研究の一環として,TRU混入量の多いターゲット集合体(特殊燃料)を少数体炉心に非均質に装荷する方式について,炉心設計の成立性を検討した。この方式はTRUを含む燃料を少数にできるので,製造上や管理上,メリットをもつ可能性がある。本研究では,まず,TRUを添加することによる燃料物性(融点,熱伝導度)の変化を,今までに公開されている物性データを基に推定し,それを基にしてTRU混入量依存の燃料許容線出力を算出した。この許容線出力を条件として,ターゲット集合体を分散装荷した方式について,核・熱特性を解析検討した。検討の結果,燃料の線出力制限を満足するためにターゲット集合体の燃料ピン径を細く一体あたりのピン本数を多くするとともに,ターゲット集合体の炉心内配置の最適化,流量配分の最適化を図ることにより,ターゲット集合体方式によるTRU消滅が成立可能であることがわかった。

A heterogeneous MA-loading method, where a few number of subassemblies with concentrated MA fuel (target fuel subassemblies) are loaded in the core, can have an advantage in fabricating and managing the MA-loaded fuel since the number of the MA-loaded fuel subassemblies is smaller compared with the method loading MA homogeneously. A study has been carried out on the feasibility of the heterogeneous MA-loading in an oxide-fueled 1000MWe LMFBR core. Based on the experimental data on fuel properties of MA fuel published up to now, it was found that MA loading significantly reduces the linear power limit almost proportionally to the MA loading ratio because of degradation of the thermal conductivity and the melting point. Furthermore, core analyses showed that heterogeneous MA-loading leads to a significant power deformation in the core if the design of target fuel subassemblies is the same as that of the normal fuel subassemblies with no MA fuel loaded. These cause a serious thermal problem. An effort was made so as to make the heterogeneous method feasible. The fuel pin design and the loading pattern of the target fuel subassemblies were studied. It was found that reduction of the fuel pin diameter and the Pu enrichment is essential to reduce the power of MA-loaded fuel. It is concluded that the heterogeneous MA-loading method is feasible by optimizing fuel design, loading pattern and coolant flow of MA-loaded fuel subassemblies.