Plymouth, Massachusetts (Fig. 1). The Pilgrim nuc- 

 lear unit is a direct cycle boiling water reactor with 

 a design power rating of 1998 MWt and a net power 

 output of 655 MWe. The station uses once-through 

 cooling with an open channel surface jet discharge 

 system. Water used for condenser cooling is drawn 

 from Cape Cod* Bay at a normal rate of about 

 310,000 gpm which removes about 4.5 x 10 9 Btu/hr 

 of heat from the condenser resulting m a water 

 temperature increase of about 29°F above the water 

 temperature at the intake. The cooling water is 

 returned to Cape Cod Bay via a 900-ft discharge 

 channel at velocities varying from about 2 fps 

 (MHW) to 8 fps (MLW). The general configuration 

 of the intake, discharge channel and breakwater 

 jetties is shown in Fig. 1. 



MENHADEN MORTALITY 



Following a several-day station outage, the Pil- 

 grim reactor was restarted and the generator phased 

 to grid on April 6, 1973. During startup operation 

 and until full power level was achieved, the tem- 

 perature of the discharge water increased an aver- 

 age 0.5°F/hr above that at the intake. Small num- 

 bers of live menhaden were seen in the discharge 



channel by Pilgrim Station personnel on April 6, 

 1973. It was not until April 8, 1973, however, that 

 Pilgrim personnel began to observe several mori- 

 bund menhaden in the discharge effluent. By 

 April 9, 1973, the number of menhaden observed in 

 the discharge channel dying and exhibiting signs of 

 stress characterized primarily by erratic and unco- 

 ordinated movements had increased substantially, 

 and as a result the Massachusetts Division of Marine 

 Fisheries was notified that a fish kill was in progress 

 at Pilgrim Station. With the exception of two adult 

 menhaden collected on the station's intake screens 

 on March 15, 1973, no menhaden had been recorded 

 prior to April 6, 1973, in the vicinity of the station 

 during routine biological sampling conducted by 

 the Massachusetts Division of Marine Fisheries 

 throughout the winter months. Menhaden do not 

 usually appear in the Cape Cod Bay region until 

 May and generally depart by November. 



Based on visual observations it was estimated 

 that several thousand menhaden were in the dis- 

 charge channel and an additional 75,000 to 100,000 

 were schooling immediately off the discharge chan- 

 nel in the thermal plume where water temperatures 

 ranged between 50°F and 62°F. The fish were 



BREAKWATER 

 JETTY 



FIG. 1 Pilgrim Nuclear Power Station Unit 1 site plan. Arabic numerals indicate water sampling stations. 



76 Marcello, Fairbanks 



