Essential service water and charging system modifications

Slovenia's Krsko nuclear power plant (632 MWe Westinghouse, 2 loop PWR), which went into commercial operation in 1982, has recently completed two modifications that have solved some longstanding plant operational problems. The first modification was the installation, in June, 1994, of three self-cleaning strainers in the safety related essential service water system. The second modification was the replacement, in May, 1995, of the charging flow control valve. Because the valve had been improperly sized in the initial design, loss of automatic flow control had been a recurring plant problem, and the plug and trim had been replaced four times. This paper describes the problems leading to the decisions to make the modifications, and the design, installation, and testing that was done to perform and prove the modifications