High-Burnup BWR Fuel Behavior Under Simulated Reactivity-Initiated Accident Conditions

Thermal Stress Analysis of High-Burnup LWR Fuel Pellet Pulse-Irradiated in Reactivity-Initiated Accident Conditions

“…In fact, PIE observation indicates that the pellet fragments from the rim structure after the rod failure in the NSRR experiment were typically large and long, suggesting that the break did not occur extensively in the rim region. 7) Also, composition analysis of gas released by grain separation during the experiments shows that the origin of the fission gases is not localized on a specific radial position of the pellet. 7,21) However, it is considered that the gas bubble expansion cannot be in a null magnitude.…”

“…7) Also, composition analysis of gas released by grain separation during the experiments shows that the origin of the fission gases is not localized on a specific radial position of the pellet. 7,21) However, it is considered that the gas bubble expansion cannot be in a null magnitude. Then, it should be noted that the compressive stress would be further intensified by the bubble expansion, because the bubble expansion would increase the effective expansion rate of the pellet in a macroscopic scale.…”

“…Given these considerations, the present study performed analyses on the dynamic interactions among pellet temperature profiles, thermal stress, and PCMI under RIA conditions using the fuel code RANNS. [4][5][6] The main purpose is focused on the quantitative evaluation of the process with the target NSRR experiments OI-12 (PWR fuel) 3) and FK-4 (BWR fuel), 7) and particular evaluation is addressed to the contribution of the fission gas bubble expansion to the pellet instantaneous swelling in terms of the thermal stress.…”

Fission Gas Release in BWR Fuel with a Burnup of 56 GWd/t during Simulated Reactivity Initiated Accident (RIA) Condition

“…In fact, this segment fuel rod was irradiated at a relatively high linear heat rate, and the maximum linear heat rates during the first, second, third and fourth cycles were estimated as about 35, 33, 30, and 26 kW/m, respectively. 4,15) From the calculation results obtained using a fuel performance code, 16) it was considered that the maximum temperature at the pellet center reaches 1280, 1240, 1140, and 1060 C during each base irradiation cycle, taking the thermal conductivity degradation of the irradiated fuel pellet 17,18) into account. The temperature levels during the first and second cycles are sufficient to cause the migration of fission gas atoms, and it is also probable that part of the accumulated fission gas was released near the central region of the fuel pellet during base irradiation.…”

“…However, the investigation on the fission gas release behavior during an RIA condition is quite limited compared with that during base irradiation. Nakamura and coworkers 3,4) estimated the fission gas release ratios of irradiated boiling water reactor (BWR) fuels during simulated RIA conditions and compared the fission gas release behavior with that during base irradiation. They assumed that the concentration ratio of xenon (Xe) to krypton (Kr) in puncture gas reflects the radial distribution of the plutonium built up during base irradiation, and they used the (Xe/Kr) ratio for investigating the radial position of fission gas release in fuel pellets.…”