Progress and current status in water radiolysis calculation for BWR primary circuit

In order to assess the material integrity of the BWR primary components from the viewpoint of material degradation, it has been widely recognized that the radiolysis modeling and the corrosion potential modeling are of vital use for the environmental evaluation of the BWR primary systems. At the last Workshop on LWR Coolant Water Radiolysis and Electrochemistry, summary papers on both modeling discussions were presented. The Hydrogen Water Chemistry Task Team of the Atomic Energy Society of Japan is now discussing standard evaluation procedures of hydrogen water chemistry to guarantee mitigating corrosive conditions for core internals in aged BWRs. This time the progress and current status on the procedures are reported. The radiolysis model should include G-values and reaction rate constants as essential parameters and also deal with plant related parameters such as radiation dose rates. A kind of a sensitivity analysis was performed and the key parameters have been identified. It has been rather a consensus that the radiolysis modeling technique has been well acknowledged as a useful tool. The mixed potential model has been widely used to predict the electrochemical corrosion potential as an important index to evaluate the SCC susceptibility of the materials. In this model the corrosion potential is calculated based on the concentrations of the water radiolysis products and other fluid dynamics parameters as flow velocity, equivalent diameter, etc. Since ECPs at all the necessary points in the BWR primary system are not available, the model calculation is regarded as a necessary tool to predict the effectiveness of environmental mitigation measures such as hydrogen water chemistry. Therefore it is necessary to establish a standard procedure for the evaluation of radiolysis product and the ECP. Recently AECL has issued a data base on the rate constants and G-values. The adoption of those data will be discussed and the comparison of the results to the previous ones will be provided.