Millstone Nuclear Power Station 



The MNPS complex consists of three nuclear 

 power plants (Fig. 3). Unit 1, a 660-MWe boiling 

 water reactor, first generated electricity on October 

 26, 1970 and began commercial operation No- 

 vember 29, 1970. Unit 2, an 870-MWc pressurized 

 water reactor, first generated electricity on No- 

 vember 7, 1975 and began commercial operation 

 in December 1975. Unit 3, a 1150-MWe pres- 

 surized water reactor, first generated electricity on 

 February 12, 1986, and began commercial oper- 

 ation April 23, 1986. All three units use once- 

 through condenser cooling water systems. The 

 rated circulating flows for Units I, 2 and 3 are 

 26.5, 34.6 and 56.6 m' /s, respectively. Cooling 

 water is drawn from depths greater than 1 m below 

 mean sea level by separate shoreline intakes lo- 

 cated on Niantic Bay (Fig. 3). The intake struc- 

 tures, typical of shoreline installations, have coarse 



bar racks and traveling screens. The cooling water 

 from Units 1, 2, and 3 (noininally heated to a 

 maximum of 13.9, 12.7 and 9.5°C above ambient, 

 respectively) flows from discharge structures and 

 combines in an abandoned granite quarry. The 

 wanned water (about 1 1°C warmer than ambient 

 when all three units arc operating near maximum 

 capacity) exits the quarry at high velocity througli 

 two quarry cuts equipped with fish baniers. Once 

 in LIS the effluent mixes with ambient water so 

 that the surface water temperature of the plume 

 has cooled to 4°C above ambient within about 

 1,100 m of the cuts; the configuration and extent 

 of the thermal plume is highly dynamic and varies 

 with tidal currents (see Ilydrothermal Studies sec- 

 tion of this report). An operational history in- 

 cluding cooling water flow and discharge temper- 

 ature is provided in Figure 4. 



Because the Millstone site has been under de- 

 velopment since the early 1960's, a chronology of 



rig. 3. The MNPS site. Construction of the cofTer dam around the Unit 3 intake structure was completed 

 during March 1976. Its removal began during April 1983 and was completed during September 1983. The 

 second cut was opened in August 1983. 



