Abstract
The cladding of fuel elements in the core of a pressurized water reactor nuclear power plant (PWR) is the first barrier to the radioactive material in the reactor. Once the fuel cladding fails, the radioactive fission products or even fissile material in the fuel elements will be released into the primary coolant, thereby challenging the safe operation of the plant. Fuel cladding failures diagnosis is indispensable for PWR as fuel failure is not inevitable and the impact on nuclear safety is significant. Based on the continuous research on fission product generation and release mechanisms for decades, several fuel failure diagnosis methods for PWR have been established and specific nuclides have been selected as indicators of fuel failures. Recent research shows Kr-85 is a good indicator for the diagnosis of the number of failed fuel rods for its insensitivity to the fuel rod defect size and failed fuel burn-up, but it is hard to measure the activity of Kr-85 in the primary coolant due to the interference of other nuclides. However, the activity of Kr-85 inside the waste gas treatment system can be measured where the activity of other nuclides has been significantly reduced by decay. Hence, the fuel failure diagnosis method is improved based on Kr-85 activities inside the waste gas treatment system. The operating data of Chinese in-service nuclear power plants are used to validate the improved fuel failure diagnosis method, and the validation results show that the improved diagnosis method of fuel failures can accurately diagnose the fuel failure and has wider applicability.
