Techical findings document for generic issue 51: Improving the reliability of open-cycle service-water systems

This report summarizes information needed to prepare a fouling surveillance and control program for a nuclear power plant. The safety significance of bivalve and other fouling is reviewed. Many safety-related systems are cooled either directly by the open-cycle water system or indirectly through intermediate cooling loops. Residual heat-removal heat exchangers, containment cooling units, diesel-generator coolers, fire-protection systems, and safety-related equipment coolers have been fouled by bivalves, sediment, or corrosion. The biological characteristics of bivalves enhance their ability to foul service-water systems. The design of the service-water system provides areas where sediments can accumulate and where bivalves can settle and grow. Surveillance and control systems are available to reduce the occurrence of bivalve, sediment, and corrosion fouling. No one technique seems to provide the best answer. A workable surveillance and control program requires using several surveillance and control alternatives. Utility experience has shown that continuous low-level chlorination of the service-water system is one of the most effective means of minimizing the safety significance of macrofouling