Functions of Ion Exchange Resins in Japanese BWRs

Major functions of ion exchange resins in the BWR condensate demineralizer (CD) are deionization and CRUD removal. Particularly CRUD removal is very important technology for reducing radiation source. Authors found that CRUD removal efficiency of CD resins increased with time in long-term operation. Aging has the effect of changing water retention capacity and surface area of cation exchange resins so as to forward the adsorption, dissolution and diffusion process for amorphous CRUD. Swelling and attrition during long-term use could change the resin properties, and swelling results from oxidative breaking for crosslinking. Thus low crosslinking resins whose properties are similar to those of the aged resins have been developed, and one of them showed fairly good performance for CRUD removal. Nowadays BWR primary coolant requires much purer water containing extremely less impurities, not only CRUD but also organic compounds and silica. From now on various requirements will arise concerning BWR primary coolant. Ion exchange resins would have to meet the requirements.