since 1979, have been managed almost exclusively by EPB biologists. 

 Results from the dives are used to determine the need for thermal back- 

 flushes or manual cleaning of trashracks and intake structures; dives 

 after these procedures assessed their effectiveness. We also look for 

 evidence of mechanical failure, e.g., metal fatigue, blockage of chlorine 

 d iff users, inadequate cathodic protection. Additionally, we have estab- 

 lished in situ experiments to study mussel fouling. 



Laboratory experiments were also designed to determine mussel 

 growth rates, settlement patterns, and response to various time/temperature/ 

 chlorine treatments. Much of the information from these studies and 

 from the inspection dives was incorporated into the Millstone Station 

 response to the NRC I & E Bulletin No. 81-03 (Appendix II). One conclusion 

 drawn from the studies was that the thermal back-flushes were effective 

 in controlling mussel growth in the circulating water intake bays, with 

 or without intermittent chlorination. Further, growth studies determined 

 that the frequency of thermal back-flushes (mussel cooks) could be 

 reduced from monthly to six times per year, spaced as far apart as 12 

 weeks in winter and 6 weeks apart in summer, and that the duration of 

 the cooks could be reduced to 20 minutes. Unit I implemented the new 

 schedule in 1981 with savings in excess of $100,000 and no loss of 

 mussel control effectiveness; based on recent cost differences between 

 nuclear and fossil generation, annual savings for Unit II on a 6 vs. 12 

 cook/yr schedule are estimated to be approximately $130,000. John 

 Becker informs us that Unit II adopted the new schedule in 1982. 



Another result of recent studies is a corroboration of earlier 

 ones, that intermittent chlorination, at least with the dosage and 

 frequency used presently, is not effective in controlling mussel growth 



