TABLE 1. The total number of panels used in comparisons for the time periods of 'before' (B = 

 panels collected from May 1979 to May 1986) versus 'after' (A = panels collected from August 1986 to 

 August 1987) three-unit operation at the Millstone Nuclear Power Station, nominally 

 6 panels/exposure period/year. 



Some panels lost, attributed to Hurricane Gloria (Sept. 1985). 



One panel lost from frame and rack assembly. 



Panels inadvertently exposed for 3 months or 9 months excluded from analyses. 



Percentage of wood lost from panels in 1979 

 was based on visual assessments made while split- 

 ting the panels in search of shipworms. From 

 1980 to 1987 wood-loss was based on percentages 

 derived from radiographs, which correlated well 

 (r^ = 0.98) with panel weight loss data (NUSCo 

 1987). 



Results 

 Seawater Temperatures 



Each of the four exposure periods was charac- 

 terized by a different water temperature regime 

 (Fig. 3). The seawater temperatures during the 

 Feb-Aug and Aug-Feb exposure periods are best 

 described by their ranges because temperatures 



continually increase and decrease, respectively. 

 Feb-Aug began when ambient water temperatures 

 (measured at MNPS intakes) were coldest 

 ( < 3 °C) and ended when water temperatures 

 were warmest ( > 20 °C). Its converse, the Aug- 

 Feb period started with warm temperatures and 

 ended with cold. Seawater temperatures during 

 the May- Nov and Nov-May exposure periods are 

 more appropriately described by average values 

 because they are composed of the warmest (av- 

 erage = approx. 16 °C) and coldest (average = 

 approx. 7 "C) months of the year, respectively. 

 Panels at the effluent sites (EB, ES) were exposed 

 to undiluted thermal effluent; since 1978, effluent 

 temperatures have averaged 9-11 °C above ambi- 

 ent, and maximum AT's were in the range of 



Exposure Panel Program 231 



