Estimation of Shutdown Dose Rate around Recirculation Pipes during Operating Life of Boiling Water Reactors

Abstract

A calculation model was developed to predict shutdown dose rate around the recirculation pipes and components in boiling water reactors (BWRs) by simulating the generation, transport, activation and deposition of corrosion products in the primary cooling water. The model is characterized by separating cobalt species in the water into soluble and insoluble materials and then calculating the deposits on the pipe wall for each species using the following considerations: 1. Soluble cobalt (designated as ionic cobalt) is taken into a spinel structure on the surface after diffusing into the oxide layers.2. Insoluble cobalt (designated as crud cobalt) deposits on the oxide layers.3. A part of the ionic cobalt released from the crud on the oxide layers is taken into a spinel structure like (1). The calculated results agree satisfactorily with measurements in two BWR plants. The shutdown dose rate around the recirculation pipes during the entire operating life was calculated to evaluate the effects of the radiation reduction procedures.