ML20149B081
| ML20149B081 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 12/04/1978 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20149B054 | List: |
| References | |
| NUDOCS 7812120036 | |
| Download: ML20149B081 (4) | |
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'f ENVIRONMENTAL IMPACT APPRAISAL BY THE DIVISION OF SITE SAFETY AND ENVIRONMENTAL ANALYSIS SUPPORTING AN AMENDMENT RELATING TO THE MODIFICATION OF A CONSTRUCTION PERMIT REQUIREMENT COMANCHE PEAK STEAM ELECTRIC STATION, UNIT NOS. 1 AND 2' (CPPR-126 AND CPPR-127) t TEXAS UTILITIES GENERATING-COMPANY DALLAS POWER AND LIGHT COMPANY TEXAS ELECTRIC SERVICE COMPANY-TEXAS POWER AND LIGHT COMPANY-00CKETS NOS. 50-445 AND 50-446 1.
Description of Proposed Action The action proposed is the issuance of an amendment to the construc-tion permits pertaining to the Comanche Peak Steam Electric Station (CPSES) Unit Nos. 1 and 2.
The proposed modification relates to conditio: 3.E.(7) of'the permits.
This condition requires that the Applicants (Texas Utilities Generating Company, et a1.) design CPSES to control the addition of chlorine'to the circulatTng water system to control biofouling such that the concentration of the total residual chlorine (TRC) at the point of discharge is 0.1 ppm or the minimum prar.e ole level demonstrated by the Applicants as being necessary.
The condition further requires that the Applicants determine:the '
minimum practicable level of chlorination necessary, prior to initia-tion of power operation, through a study program and that the results of the study be submitted as part of the operating license application.
By letter dated June 30,.1978, the Applicants contended that a theo-retical analysis of chlorination needs for CPSES based on conditions at other plants located on other bodies of cooling water is not a practicable procedure.
The Applicants also noted that.the Environ-mental Protection Agency (EPA) Region 6 has issued a draft National Pollutant Discharge. Elimination System (HPDES) permit for CPSES which called for a chlorine minimization study after station startup. ;The Applicants proposed that Condition 3.E.(7) of.the construction. permits be amended to allow the study to be performed after startup of the station.
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Environmental Considerations for the Proposed Action As support for their amendment request the Applicants submitted with their June 30, 1978 letter an Environmental Assessment of the Perform-ance of an Operational Chlorine Minimization Study.
This report was supplemented by additional information furnished in a letter dated September 8, 1978.
The Applicants agreed that there was need to control discharges of chlorine and that a study to establish the minimum level needed was appropriate.
The Applicants stated that use of chlorine during the study would be limited to a maximum level of 0.5 ppm of total residual chlorine (TRC) in the discharge and assessed the potential impacts of discharges at that level.
The Applicants further stated the chlorination would be conducted no more than one-half hour for each unit (two consecutive treatments for two unit operation), repeated every twelve hours.
Comanche Peak Steam Electric Station (CPSES), comprising two 1161 MWe pressurized water reactors, is under construction in Somervell County, Texas approximately 8 kilometers (5 miles) north-northwest of Glen Rose, Texas.
The cooling water source is an offstream cooling impound-ment of 1306 ha (3228 acres), Squaw Creek Reservoir (SCR).
SCR began filling in February 1977 and was approximately one-half full by volume in June 1978.
Each unit will be cooled by four circulating water pumps, each with a capacity of 17 cubic meters per second (275,000 gpm), installed in a circulating water intake structure located in SCR.
Discharge to SCR is through one pipe per unit, each 4.9 meters (16 feet) in diameter.
The top of each discharge pipe is approximately 6.7 meters (22 feet) below the surface of SCR at the normal high water level of 236 meters (775 feet) MSL.
The discharge point is near the head of Panther Branch Arm (PBA), about 1950 meters (6400 feet) from where PBA merges with the main part of the reservoir.
The Applicants' assessment of potential impact on PBA and SCR employed a simulation of the hydrodynamic transport and dissipation of the chbrine in the discharge as it moved down PBA to SCR.
The assessment included effects of chemical reaction rates, temperature, sunlight, l
and variations in number of operating units (1 or 2) and seasons of the year (winter or summer).
Entrainment of aquatic biota into the plume and time-weighted exposures to chlorine were computed.
Compari-sons were noted to an Acute Mortality Threshold.* The Applicants
- Mattice, J.S., " Power Plant Discharges:
Toward More Reasonable Effluent Limitations on Chlorine," Nuclear Safety 18 (6), 802-819 (1977).
Mattice, J.S. and H.E. Zittel, " Site Specific Evaluation of Power Plant Chlorination," Water Pollution Control 48(10), 2284-2308 (1976).
l I found no expected conditions where biota would be exposed in excess of the Acute Mortality Threshold and concluded that there would be no impact resulting from chlorine discharges occurring during the minimization study.
The biota subject to impact are those oostulated to be present after completion of construction and filling of the reservoir, based on biota found in similar reservoirs in Texas.
'l Staff and consultants of the NRC's Division of Site Safety and Environ-mental Analysis (DSE) evaluated the Applicants' assessment and performed their own independent assessment of the effects of chlorination during the minimization study.
DSE staff found some apparent flaws in the Applicants' assessment, though the general approach seemed valid, and concluded that the conclusion of no impact on aquatic biota from chlorine discharges was not supported.
Using the simplifying assumption that chlorine concentrations declined as the discharged water moved down PBA only due to chemical reactions (the dilution flow provided by the bottom inflow layer and the effects of longitudinal dispersion were neglected), an upper limit of effect was calculated by the staff.
The staff also assumed for the purposes of assessing the biological impact that entrainment of aquatic organisms in the chlorine plume will occur along its entire length.
Further, it was assumed that, once entrained into the plume, organisms will not escape, but will be carried along with it and that organisms entrained into the plume in Panther Branch Arm are as sensitive to chlorine toxicity as the most sensitive freshwater organisms in the Mattice-Zittel Acute Mortality Threshold.
The staff assessment led to the finding that about one-half of PBA could l
be affected by potentially lethal TRC concentrations.
PBA accounts for less than 10 percent of the surface area of SCR.
Thus a maximum of the equivalent of about 5 percent of the area of Squaw Creek Reservoir might be adversely affected by TRC during the minimization study.
If biological proiuctivity per unit of surface area in Panther Branch Arm is similar to that in the remainder of Squaw Creek Reservoir (no data indicate otherwise and this seems reasonable), the NRC staff considers the predicted biological impact of the proposed chlorination schedule to be acceptable for the following reasons:
(1) It appears that, even under worst case conditions, the adverse effects of TRC will be limited to portions of Panther Branch Arm.
(2) Although phytoplankton and zooplankton in the upper reaches of Panther Branch Arm may be killed by TRC levels proposed by the Applicants, their high reproductive rates will assure adequate population levels in the remainder of the reservoir.
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-l (3) Ichthyoplankton'may be adversely affected by the proposed chlorination schedule.
While fish species do not have'the short generation times of.phytoplankton and zooplankton, and could-therefore be slower;to recover from perturbations, only a small portion'of Squaw Creek Reservoir could be impacted by chlorine.
1 The staff does not believe that fish populations in Squaw Creek-Reservoir will be significantly affected by chlorine discharges during the minimization study.
(4) Benthic organisms, including macroinvertebrates, fish eggs and larvae, and bottom-dwelling adult fishes, also may'be adversely-affected by chlorination of. Comanche Peak Power Station.
- However, the assessment of' chlorination impact is somewhat different for these organisms than it is for plankton or nekton entrained -into the plume, because it is assumed that benthic biota remain stationary on the bottom of Panther Branch Arm.
Thus, during each chlorination application, they could be exposed to an elevated concentration of chlorine throughout a period of 60 minutes. The Mattice-Zittel Acute Mortality Threshold indi-cates that freshwater organisms can tolerate a maximum concen-tration of about 0.05 ppm TRC for 60 minutes without suffering.
l mortality'from acute chlorino toxicity.
TRC concentrations of 0.05 ppm or less are predicted for distances of 1219 to 1402 m from the discharge, respectively, depending upon the season and operating conditions.
Benthos would be impacted in!approximately the same region of Panther Branch Arm as would plankton.
The staff considers the potential loss of approximately 5 percent of the benthos in Squaw Creek Reserv.oir not-to be significant.
(5) No other impacts, such as to recreational uses of SCR like fishing or swimming, appear likely to occur to any significant degree as a recult of the chlorination study.
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Conclusion and Basis for Negative Declaration On the. basis of the foregoing analysis and the NRC staff evaluation, it is concluded that there will be no significant environmental impacts attributable to the proposed action.
Furthermore, any impacts which do occur will be very small compared to those for the entire i
project as predicted and described in the staff's Final Environmental Statement (Construction Permit) issued in June 1974.
Having made this conclusion, the DSE staff has further concluded that no environ-1 mental impact statement for the proposed action need be prepared and 1
that a negative' declaration to this effect is appropriate.
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Dated:
DEC 4 1978 i
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