Morphology change of rock-like oxide fuels in reactivity-initiated-accident simulation tests

反応度事故模擬実験での岩石燃料の組織変化

中村 武彦 ; 笹島 栄夫 ; 山下 利之; 上塚 寛

Nakamura, Takehiko; Sasajima, Hideo; Yamashita, Toshiyuki; Uetsuka, Hiroshi

3種類の未照射の岩石(ROX)燃料の反応度事故(RIA)時挙動を調べるための試験を実施した。すなわちイットリア安定型ジルコニア(YSZ)単相型,YSZ/スピネル混合型及びスピネル中YSZ粒子分散型ROX燃料をNSRRでパルス照射し、RIA時の燃料破損モード,破損しきい値及びこの影響を調べた。燃料破損は、多量の燃料溶融を伴った破裂破損であった。破損モードの違いにもかかわらず、ROX燃料のしきい値は約10GJmとUO燃料と同程度であった。しかし、ROX燃料の場合溶融燃料の分散が低いエンタルピで発生するため、破損の影響はUO燃料と大きく異なるものであった。過渡加熱条件での燃料構造の変化と材料間の反応について、光学及び電子顕微鏡を用いた観察と分析を行った。

Pulse irradiation tests under simulated RIA conditions were performed with three types of ROX fuels. Single phase YSZ, homogeneous mixture of YSZ/spinel and YSZ particle dispersed in spinel type ROX fuels were pulse irradiated in the Nuclear Safety Research Reactor (NSRR). Mode and threshold of the fuel failure including its consequences were investigated under the RIA conditions. The fuel failure occurred in a burst type mode in all the three types of ROX fuel tests with considerable fuel melting. Even though the mode was quite different from those of UO fuel, failure threshold enthalpies of the ROX fuels were close to that of UO fuel at about 10 GJ m. The consequence of the failure of the ROX fuels was different from the one of UO fuel, because molten fuel dispersal occurred at lower enthalpies in the ROX fuel tests. Change of the fuel structure and material interaction in the transient heating conditions were examined through optical and secondary electron microscopy, and electron probe micro analysis.