COMPUTER MODELING FOR BOILING WATER REACTORS ON RADIOLYSIS, ECP, AND CRACK GROWTH RATES

摘要

The limited accessibility of boiling water reactors (BWRs) has made it difficult or sometimes impossible to monitor the development of material damage inside these reactors. Material damage in BWRs usually occurs in the form of intergranular stress corrosion cracking (IGSCC) and irradiation assisted stress corrosion cracking (IASCC), due to the presence of strongly oxidizing species, such as oxygen and hydrogen peroxide. These species are produced in or near the reactor core by the irradiation of water by neutrons and gamma photons. By calculating the concentrations of the radiolysis species, which in turn determine the ECP and the crack growth rate in the heat transport circuits (HTCs) of BWRs, we are able to predict the rate at which damage develops throughout the entire HTCs of BWRs. A computer code has been developed for modeling tie development of material damage in the BWRs. The algorithm of the code contains facilities for estimating the concentrations of radiolysis products (in particular O_2, H_2, and H_2O_2), the electrochemical corrosion potential (ECP), and the kinetics of growth of a reference crack in sensitized Type 304SS around the HTCs. After calibrating the model against plant data from Dresden-2, the code is able to successfully account for the oxygen concentration and the ECP in the recalculation system of Duane Arnold. This computer code is a useful tool for assessing the performances of materials in the HTCs of BWRs under normal water chemistry, hydrogen water chemistry, and noble metal coatings.