PWR secondary water chemistry guidelines in Japan - Purpose and technical background

Highlights: • Framework of PWR secondary water chemistry guidelines in Japan are presented. • Guideline necessity, definitions, philosophy and technical background are mentioned. • Some guideline settings for control conditioning and diagnostic parameters and recommendations are explaines. • Chemistry strategy is also mentioned. -- Abstract: In the more than 40 years of operational history of pressurized water reactors (PWRs) in Japan, sustainable development of water chemistry technologies has resulted in the world's highest secondary system component integrity; additionally, secondary system components, especially steam generator (SG) tubing, with excellent material integrity have been developed to prevent leakage of radioactive contamination from the primary to the secondary system and to maintain the heat removal function of the secondary system. Although reasonable control and diagnostic parameters for water chemistry are utilized by each PWR owner, the specific values are not shared. To ensure reliable PWR operation and to achieve the highest safety level, relevant members of the Standards Committee and the related committee organized by the Atomic Energy Society of Japan (AESJ) decided to establish water chemistry guidelines for PWRs. The Japanese PWR secondary water chemistry guidelines provide strategies for improving material integrity and the heat removal function. The guidelines also provide reasonable "action levels" for control parameters and "control values" and "diagnostic values" for multiple parameters, and they stipulate the responses when these levels are exceeded. Specifically, "conditioning parameters" are adopted in the guidelines. Good operational practice conditions are also discussed with reference to long-term experience. This paper introduces the purpose, technical background and framework of preliminary secondary water chemistry guidelines for Japanese PWRs. Addition, the differences in bases of parameter settings between the Japanese and overseas guidelines are discussed.