Biofouling has been long recognized as a potential cause of ineffi- 

 ciency and eventual failure of cooling water systems. For ocean sited 

 thermal power plants, the major types of fouling are: 1) slime formation 

 in the condenser tubes, reducing heat transfer efficiency and enhancing 

 corrosion, and 2) macro invertebrate growth (particularly mussels) through- 

 out the cooling water system, causing reduced water flow, blockage, 

 erosion, and subsequent leakage. 



Prior to construction of Millstone Unit I, biofouling was anticipated 

 to be a problem, and provisions were made for anti-fouling procedures. 

 Intake structures were designed to minimize regions of stagnant water, 

 and protective coatings were applied where necessary. Equipment was 

 installed to inject chlorine into the intake bays, intermittently for 

 most of the year, and continuously during the presumed mussel spawning 

 season (when ambient water temperatures ranged between 45 and 55 F) . 

 Condenser cross-connect valves were also installed, to allow thermal 

 back-flushing of condenser tubes and circulating water pump bays. 

 Similar systems were incorporated in the design for Unit II. 



The chlorination program for Unit I was initiated in August of 

 1970, and the diffuser system was redesigned in Spring of 1976. For 

 Unit II, chlorination began in November of 1974, and the diff users 

 modified in Summer of 1978. At both Units, the modifications were 

 designed to allow more even diffusion of chlorine along the walls and 

 floors of the intake bays. Unit I chlorinates circulating and service 

 water systems simultaneously, at a rate of 2,500 lbs/day; Unit II has 

 separate systems for circulating and service water, injecting at a rate 

 of 1,600 lbs/day into the former, and 200 lbs/day into the latter. The 

 duration and cycle frequency vary betweeen Units. Since no significant 



