An Improved Model for Assessing the Effectiveness of Hydrogen Water Chemistry in Boiling Water Reactors

For nearly two decades, hydrogen water chemistry (HWC) has been used as a remedial measure to protect boiling water reactor (BWR) structural components against intergranular stress corrosion cracking (IGSCC). In this paper, computer modeling is used to evaluate the effectiveness of HWC for BWRs. The DEMACE computer code, equipped with an updated chemical reaction set, G values, and a Sherwood number, is adopted to predict the chemical species concentration and electrochemical corrosion potential (ECP) responses to HWC in the primary heat transport circuit of a typical BWR. In addition, plant-specific neutron and gamma dose rate profiles are reported. DEMACE is calibrated against the data of oxygen concentration variation as a function of feedwater hydrogen concentration in the recirculation system of the Chinshan Unit 2 BWR.

The determinant result for assessing the effectiveness of HWC is the ECP. For a typical BWR/4-type reactor such as Chinshan Unit 2, it is found that protecting the core channel and the lower plenum outlet is quite difficult even though the feedwater hydrogen concentration is as high as 2 ppm, based on the predicted species concentration and ECP data. However, for regions other than those mentioned earlier, a moderate amount of hydrogen added to the feedwater (0.9 ppm) is enough to achieve the desired protection against IGSCC.