INTERACTION BETWEEN BWR FUEL CLADDING AND FUEL COMPONENTS IN EARLY PHASE OF SEVERE ACCIDENT

抄録

The interaction between the BWR fuel cladding and fuel components was examined to estimate the conditions of fuel failure (temperature and location) in the early phase of Fukushima Dai-ichi Nuclear Power Plant (FDNP) accident. In the first series of tests, four types of specimens were fabricated using commercial fuel cladding and fuel components and heated up with or without high temperature steam to simulate the interaction at each location where the fuel cladding and fuel components would be in contact. In the second series of tests, two types of specimens with encapsulated helium gas were heated up in argon gas to examine the effect of internal pressure on the fuel failure at the plenum and the spacer locations in the steam starvation condition. In both series of tests, some of fuel claddings were pre-oxidized to examine the effect of surface oxide layer formed in the normal operating condition.

The first series of tests demonstrated that apparent eutectic reactions first started near Ni-based fuel components such as rod-spring and ferrule-spring at around 1400 K in the steam starvation condition but this temperature increased with steam supply increased. Barrier effect of oxide layer of fuel cladding was also found. In the second series of tests, mechanical failure and wall-through eutectic reaction occurred competitively at the spacer location, while only mechanical failure was observed at the plenum location.