Off-Gas Source Estimation for Boiling Water Reactors under Various Operation Conditions

Radioactive fission gases (krypton and xenon) are observed in boiling water reactor (BWR) plants without defective fuel under various operation conditions. The off-gas in a BWR plant without defective fuel arises from fissile impurities within the cladding materials and/or fissile material deposited on the cladding surface. To estimate the off-gas source in operating plants, the source estimation method considering the off-gas transport time from production to measurement was applied to the data collected under various plant operation conditions. This method was verified by the adaptation of three sets of off-gas data groups to the source of cladding impurity and/or deposition actually observed in the plants. The judgment as to whether off-gas derives from a cladding impurity or a deposition was made by analyzing the data of 11 BWRs with different off-gas levels.