Intake Water Tunnels

Intake water tunnels are generally made from concrete, and absorption of water by concrete is the main reason for corrosion in reinforcement. In intake structures the problems are due to concrete failure from salts penetrating into the concrete and corroding the rebar. Hard, dense concrete with ample cover to reinforcement and without cracks and porosity has good resistance to corrosion against seawater. In Indian nuclear power plants, the experience with concrete intake tunnels with respect to corrosion behavior is not bad except that special care is required for protection against algae, clams, mussels, etc. which attach to the tunnel surface. 

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Salt water intake tunnels, particularly along the southern coast, are subjected to biofouling. A class of toxic coatings known as organotins utilizes compounds of tin oxides and fluorides to retard the formation of barnacles, algae, etc. These coatings look quite promising. 

Seawater supply is from an intake 20 m below the water surface, about 1.5 km offshore and 2.2 km from the RO plant. The supply tunnel is about 70 m below the ground surface. The pre-treatment train includes chlorination, polyelectrolyte and ferrous sulphate coagulation/flocculation, acid dosage, dual-media filtration, anti-sealant addition, acid, cartridge filtration and sodium metabisulphite (e.g. see Figures 3.31 and 3.32]. The RO system is a two-pass unit. Post-treatment includes CO2 and lime treatment and chlorination with sodium hypochlorite. The desalinated product water TDS is 220 mg/1 with maximum boron concentration of 1 mg/1. 

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