Cooling system and heat exchange essentials

The RHR system heat exchangers are also available to supplement the fuel pool cooling heat exchangers. RHR system heat exchangers are not normally required but may be needed if more than the normal number of spent fuel assemblies is stored in the pool. The system pumps and heat exchangers are located in the fuel building below the normal fuel pool water level. Heat exchangers are cooled by essential plant service water. 

Essentially all industrial metals are susceptible to SCC in some specific environment. Of the metals commonly used in cooling water systems, copper-based alloys and stainless steels are most frequently affected. Common specific corrodents causing SCC in these and other heat exchanger metals are listed in Table 9.1. 

Nevertheless, and despite all the operational problems, during a 6-month period, the cooling system remained essentially free of slime growth. The bacteria levels were held to 1 x 105, no heat exchangers were taken out of service for cleaning, and the carbon steel Corrosometer corrosion rates were reduced to 1 to 3 mpy, with 5 to 8 mpy recorded from carbon steel coupons. Copper was 0.2 mpy. 

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