Replacement of hydrazine in closed cooling systems using 3-step treatment system

Ringhals unit 1(BWR) has taken measures to reduce or even stop the use of hydrazine in closed cooling water systems, this because hydrazine's classification as harmful to the environment as well as staff during operation and maintenance. Today, Ringhals has to apply for a licence every three years for the continual use of hydrazine. A system to replace the use of hydrazine in closed cooling systems was installed in 2007 and includes three major steps of treatment. The first is to ensure low oxygen levels in the water using gas transfer membrane technology (GTM). The second is to control pH in the water by injecting potassium hydroxide and finally, a mixed resin bed is used to clean up the anion and cation impurities in the water. The system has been connected to one of the turbine closed cooling system, earlier treated only with hydrazine. The gas transfer membrane system could connect to seven different closed cooling systems. If the GTM system works out fine, three more closed cooling systems are going to be connected to it in the future. Possible material impacts from the new water environment have been evaluated using an autoclave system with coupons of relevant material. To this date, all three steps have worked out successfully and the autoclave material coupons show preliminary no or low general corrosion as expected due to the alternative water environment. The tests will continue to the end of 2014, with the aim that the result could support a decision to fully remove hydrazine from the closed cooling water systems in Ringhals unit 1. The paper describes the function of the 3-step treatment system and presents the results from the tests with conclusion that it could be an excellent alternative to hydrazine in closed cooling water systems in the future. (author)