Application of In-Service Temperature Lowering to Reduce Radioactivity Corrosion Product Deposition on Carbon Steel Piping of BWR Residual Heat Removal System

• Published in: Journal of nuclear science and technology 2002-10, Vol.39 (10), p.1051-1059
• Main Authors: AIZAWA, Motohiro, CHIBA, Yoshinori, OHSUMI, Katsumi, UCHIDA, Shunsuke, TAKAHASHI, Toshihiko, SAITOH, Takeshi
• Format: Article
• Language: English
• Subjects: Applied sciences; BWR type reactors; carbon steels; cobalt 60; corrosion products; dehydration; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Installations for energy generation and conversion: thermal and electrical energy; lower temperature shutdown cooling method; nuclear power plants; occupational exposure; piping; radioactivity; RHR systems
• ISSN: 0022-3131; 1881-1248
• DOI: 10.1080/18811248.2002.9715293

Assessment of plant data and experiments on deposition of ion species on carbon steel were carried out in order to develop suitable countermeasures to reduce RHR (residual heat removal) piping dose rate. It was thought that radioactivity deposits on the RHR piping were mainly from radioactive ion species in the coolant and they were enhanced by the dehydration reaction of corrosion products on the piping. From an evaluation for temperature dependence of the dehydration reaction, it was proposed to lower the start-up temperature of RHR operation as a way to reduce radioactivity deposition. Feasibility studies of improved RHR operation were conducted and test operations were carried out in the Shika Nuclear Power Station Unit 1. Application of the improved RHR operation resulted in a temperature reduction from 150°C to 110°C, and a radioactivity deposition reduction on the RHR piping to one-fifth ofthat in conventional RHR operation. The improved RHR operation has now been applied to more than fifteen Japanese BWRs and significant suppression effects of radioactivity deposition have been observed.