ML20046A425
| ML20046A425 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 02/28/1993 |
| From: | NORTHEAST UTILITIES SERVICE CO. |
| To: | |
| Shared Package | |
| ML20046A417 | List: |
| References | |
| D06229, D6229, NUDOCS 9307280073 | |
| Download: ML20046A425 (4) | |
Text
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' Enclosure to Letter No. D06229 i
O SCOPE OF STUDY FOR THE IMPACT OF MACROFOULING CONTROL PRACTICES ON NIANTIC BAY NEAR MILLSTONE POINT 1
I NORTHEAST NUCLEAR ENERGY COMPANY.
MILLSTONE NUCLEAR POWER STATION.
NPDES PERMIT CT0003263 i
Northeast Utilities Service Company PO Box 270 Hartford, Connecticut 06141-0270 February 1993 3
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6 INTRODUCTION Northeast Nuclear Energy Company (NNECO) operates Millstone Nuclear Power Station (MNPS) in Waterford, Connecticut. The Station consists of three plants: Unit 1 is a 660 MWe boiling water reactor, Unit 2 is an 870 MWe pressurized water reactor, and Unit 3 is an 1150 MWe pressurized water reactor. All three Units use seawater from Niantic Bay for once-through condenser cooling (circulating water) and for auxiliary heat exchanger cooling -
(service water). Combined circulating and service water flow from each Unit is released, through separate discharge structures, into the north end of an abandoned granite quarry (ca. 350 m long,100 m wide,30 m maximum depth), and ultimately into Long Island Sound via two channels (cuts) at the south end of the quarry (Fig.1).
Both circulating and service water systems are vulnerable to biofouling. Macrofouling (attachment and growth of large organisms; in our area, mostly barnacles, hydroids, and particularly, blue mussels) can reduce flow through piping, or if shells become lodged in condensers or heat exchangers, they can cause erosion / corrosion, and through-wall pitting of the tubes. Microfouling (development of a microbial ' slime' on wetted surfaces) can reduce heat transfer efficiency, and by altering the electro-chemical environment, can lead to microbiologically influenced corrosion (MIC).
At MNPS, sodium hypochlorite is used to control biofouling in service water systems at all three Units, and to control microfouling in the circulating water systems (macrofouling in circulating water is controlled by periodic thermal backwashes of the condensers, or ' mussel cooks'). Sodium hypochlorite is continuously injected into the service water systems, to produce a discharge concentration of less than 0.25 ppm free available chlorine (FAC); the process of sodium hypochlorite injection is generically termed ' chlorination'. Chlorination of the circulating water systems is intermittent; the pump bays are dosed sequentially, for a total of two hours per Unit, to produce a discharge concentration ofless than 0.25 ppm FAC. Although the Millstone NPDES permit would allow chlorination regimes of two hours per Unit per day, by present operating procedures, chlorination is performed twice per week at each Unit: on Sunday and Thursday at Unit 1, on Tuesday and Friday at Unit 2, and on Wednesday and Saturday at Unit 3.
Combined service water flows are only about 4% of the total cooling water flow at MNPS; therefore, any chlorine residuals in the service water are diluted by a factor of 25 when they enter the quarry, except during the period when a Unit's circulating water is being chlorinated. We will investigate the impacts of MNPS chlorination under these extreme conditions, even though the bulk of chlorine is used for microfouling, rather than macrofouling, control. Since Unit 3 is scheduled to begin a refueling outage of July 31,1993,
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we plan to conduct the study in early summer of 1993.
Impact Analysis Study Page 1 of 3
SCOPE OF STUDY The proposed study consists of two parts: 1) determination of chlorine levels in the effluent quarry, including at the quarry cuts (as the quarry is enclosed, this will be essentially independent of tidal stage, and related entirely to the power plant's chlorination regime),
and 2) if detectable chlorine levels are found at the quarry cuts, determination of the mixing characteristics of the chlorinated effluent with the receiving waters (this will depend on tidal stage, as the effluent plume is strongly affected by tidal currents, once it leaves the quarry).
To conduct the first part of the study, samples will be taken on three different days,.
encompassing each Unit's circulating water chlorination regime. Each sample run will consist of samples collected from each Unit's discharge, at representative locations along the length of the quarry, and a' the southern quarry cut, where the discharge enters Long Island Sound. Sample runs will be conducted prior to the start of circulating water chlorination, during the chlorination period, and for a sufficient period of time after cessation of the circulating water chlorination to determine the duration of detectable chlorine in the quarry (residence time in the quarry, under three-Unit operating conditions,is less than one-half hour). Total residual chlorine will be measured to the nearest 0.01 ppm above a threshold detection limit of 0.05 ppm, using a Hach Pocket Colorimeter test kit, which uses the N,N-Diethyl-p-Phenylenediamine (DPD) reagents (Method 330.5 in EPA Publication 600/4 020). Water temperature will be measured at each sample point.
If, based on results from the first part of the study,it is determined that detectable levels of chlorine are leaving the quarry, the second part of the study will be conducted, to determine the fate of discharged chlorine in the effluent plume. Characteristics of the MNPS effluent plume are well documented (e.g., NUSCO 1988); samples will be collected at approximately 25 m intervals along the centerline of the plume until residual chlorine concentrations fall below detectable levels. Sam}iles will be collected during both maximum flood and maximum ebb tidal stages; if necessary, the plant's chlorination schedule will be adjusted to ensure that treatment of circulating water occurs during the tidal stage of interest.
All results of the study will be included in a comprehensive report to the DEP, and submitted on or before November 30,1993.
REFERENCE CITED Northeast Utilities Service Company (NUSCO).1988. Hydrothermal Studies. Pages 322-355 in Monitoring the marine environment of Imng Island Sound at Millstone Nuclear Power Station, Waterford, Connecticut. Three-Unit Operational Studies, 1986-87.
Impact Analysis Study Page 2 of 3
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Figure 1.
Site map of Millstone Nuclear Power Station, showing area to be sampled during the proposed Macrofouling Control Practices Impact Analysis Study (approximate locations of sample points are indicated by 'x').
4 Impact Analysis Study Page 3 of 3
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