732. 軽水炉における事故時の燃料破損形態と事故後の炉心冷却性

抄録

A study on post-accident core coolability of LWR is in progress based on the practical fuel failure behavior experienced in NSRR, PBF, PNS and others. The fuel failure behavior at LOCA, RIA and PCM conditions are reviewed, and seven types of fuel failure modes are extracted as the basic failure mechanism at accident conditions. Those are; (1) cladding melt or brittle failure, (2) molten UO₂ failure, (3) high temperature cladding burst, (4) low temperature cladding burst, (5) swelling of molten UO₂ and (6) cracks of embrittled cladding for irradiated fuel rods, and (7) TMI-2 core failure. The post-accident core coolability at each failure modes are discussed. The fuel failures caused actual flow blockage problems are only the types of (2), (5) and (7). A characteristic which is common among these three types is that, the fuel rods are in the conditions violated the present safety criteria for accidents, and UO₂ pellets are in melting or near melting hot conditions when the fuel rods failed.