BWR Plants with Low Shutdown Radiation LevelDesign and Construction of Plants and Current Experience with Occupational Exposure of Plants

摘要

Occupational exposure during BWR refueling and annual maintenance periods is determined by radioactive corrosion products, such as 60Co and 58Co deposited on major components and piping of the primary cooling system.The authors have investigated behavior of radioactive corrosion products, e.g. generation, activation and deposition processes, in the primary cooling system, and then expressed the findings as mathematical equations. These provide corrosion product simulation models to predict the amounts of radioactive corrosion products depositing on components and piping.The effects of corrosion product reduction procedures on shutdown dose rate were evaluated using the model. The procedures were incorporated into the Japanese Improvement and Standardization Program. Improvements of operational procedures to control water chemistry, such as Ni/Fe ratio, as well as application of hardware improvements resulted in an extremely low occupational exposure of less than 90 man?rem/yr for currently constructed BWR plants.