Cladding Performance under Power Oscillations in BWRs

Stability has been the main concern in the development stage of BWRs in history. Although stability studies of BWRs have a long history and there is extensive literature available, the literature on fuel performance under unstable power oscillations is very limited. It is very desirable to investigate the fuel integrity in BWR power oscillation conditions. This goal of this work is to examine the cladding performance under the power oscillations. The calculations of fuel deformation were first conducted by using the FRAPTRAN code to simulate the Japanese FK11 test and power oscillation under normal BWR operating conditions. Then, based on the results of FRAPTRAN, the cladding fatigue analysis was conducted. Based on the analysis, it could be concluded that: 1 FRAPTRAN code could be used to analyze fuel performance under BWR power oscillations. The FRAPTRAN code results were in good agreement with FK-11 test in Japan. 2The fuel deformation was mainly caused by PCMI and was roughly proportional to the fuel enthalpy. Enhanced cladding deformation due to ratcheting was not found. 3The cladding could satisfy the design criterion in ASME Code under power oscillation conditions, which means it could maintain the fuel integrity. 4Cladding thermal fatigue is not an issue under power oscillations, unless dryout takes place.