Excerpt from Annual Environmental reports issued by Northeast Utilities
Includes information on fish kills from the Millstone Nuclear Reactor
If all three MNPS units had been operating throughout the 1997 larval season, nearly 500 million larvae would have been entrained, about six times larger than the actual annual entrainment estimate (Monitoring Studies, p. 96, 1997).
Abundance of adult winter flounder spawners in the Niantic River has been greatly depressed since 1992. The current size structure of the spawning population is heavily skewed towards larger fish and may be an indication of potential stock collapse (Winter Flounder, p.95).
Atlantic silverside abundance in the shore-zone area showed a decreasing trend during three-unit operation (Fish Ecology, p.125).
The estimated number of cunner (918 million) and tautog (331 million) eggs entrained in
1996 were about six times lower than the average three-unit entrainment (Table 4). In
1996, about 5 million anchovy eggs were entrained.
Larval entrainment estimates of anchovies (25 million) in 1996 and of American sandlance
(3 million) in 1997 were much less than the long-term averages (about 553 and 62,
respectively), including the period prior to three-unit operation (table 5). An
entrainment estimate of 31 million was determined for grubby during 1997. Although
cooling-water flow during the period of grubby entrainment in 1997 was only about 20% of
the long-term average during the three-unit period, the larval entrainment estimate fell
within historical range. Record high densities of larval grubby accounted for the
relatively high entrainment rate despite low cooling-water flow (Table 3). Atlantic
menhaden experienced a sharp increase in entrainment from less that 10 million annually to
216 million during 1989 and , except for 1993, annual losses since then have ranged
between 22 and 58 million. Entrainment of winter flounder larvae totaled 79 million in
1997; this loss is evaluated in the Winter Flounder Studies section of this report (Fish
Ecology, p.117)
Impingement at Unit 2, which does not have a return sluiceway, is routinely monitored by plant operational personnel and impingement counts are only made when a large impingement event occurs (Fish Ecology, p.117).
Indications of plant effluents were observed. Detectable levels of Co-58, and Ag-110m were apparent. The detection of these nuclides throughout the year, as witnessed by positives detected in other aquatic media, corresponds to routine effluents and to the increased curies released due to multiple shutdowns and outages by Millstone Units 1 and 2 (Annual Radiological Environmental Report, 1994 p. 4-5).
4.17.2 Fish-Other (Table 17B)
As in previous years, plant related activity was detected in some 1994 quarry samples
(location 40X). Positive values of C0-60 and Ag-110m were observed.
The quarry location is not accessible to members of the general public and with the
dilution of the Long Island Sound, the levels of radioactivity generally become
undetectable in fish samples outside of the quarry. Using the concentrations measured in
the quarry and diluting them by the near field dilution factor of 3 determined for quarry
discharges into the Sound, doses to the maximum individual can be counted. See Section 5.0
for these results (Annual Radiological Environmental Report 1994, p. 4-6).
4.19. Oysters (Table 19)
All locations except for the quarry discharge utilize stocked oysters, trays are kept at
these sampling areas to guarantee samples and facilitate sample collection. Native oysters
are normally sampled at the quarry discharge (location 40X) which is an extra location.
However, the native population of oysters within the quarry is also being depleted and
trays were used for the last two quarry samples.
Plant related activity was observed in all samples from within the plant discharge area
(locations 32 and 40X). In general, the quarry oysters (typically native oysters except
for those noted above) show the highest levels. Although location 32 is labeled as
vicinity of the discharge, it is actually at the end of the quarry. This activity included
Co-58, Co-60, Zn-65, and Ag-110m. All nuclides detected were seen at levels similar to
those for the last two years. No plant related activity was observed in samples from
beyond the plant discharge area.
The 1994 Zn-65 levels are comparable to those measured for the past four years. The reason
Zn-65 is unique to Unit 1 is because since 1987 zinc has been injected into the reactor
coolant to reduce the plateout of Co-60 on piping walls and hence radiation worker
exposure is reduced.
The only other aquatic media which detected Zn-65 was aquatic flora. The high levels in
oysters is caused by their distinct capacity to accumulate zinc. Studies have shown that
oysters can accumulate as much as 50 times or more the amount of zinc compared to most
other seafoods (Wolfe, 1979). As Figure 4.2 shows, Zn-65 concentration in quarry oysters
has closely followed the amount of curies of Zn-65 discharged in Unit-1 liquid effluents.
Except for the last two quarters in 1994 when native oysters could not be obtained, a
remarkable dependency has existed between the amount of Zn-65 discharged into the
environment and the Zn-65 concentration measured in the native quarry oysters. All efforts
will be made in the future to continue to sample native oysters within the quarry (Annual
Radiological Environmental Report 1994, p. 4-6).
4.20. Clams (Table 20)
GeLi analyses indicated the presence of plant related Co-60, and ag-110m. These levels
correspond to the elevated levels seen in other aquatic samples for the same period. The
dose consequence of radioactivity via this pathway is discussed in Section 5.0 (Annual
Radiological Environmental Report 1994, p.4-8).
If all three units had operated fully during 1997, nearly 500 million larvae would have been entrained, more than six times the actual estimate (viii Monitoring Studies, 1997).
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