ML20212A826
| ML20212A826 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 09/08/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20212A815 | List: |
| References | |
| NUDOCS 9909170135 | |
| Download: ML20212A826 (6) | |
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UNITED STATES g
j NUCLEAR REGULATORY COMMISSION e
WASHINGTON, D.C. 2065Hooi i
49.....
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.103 TO FACILITY OPERATING LICENSE NO. NPF-72 AND AMENDMENT NO.103 TO FACILITY OPERATlNG LICENSE NO. NPF-77 COMMONWEALTH EDISON COMPANY BRAIDWOOD STATION. UNIT NOS.1 AND 2 DOCKET NOS. STN 50-456 AND STN 50-457
1.0 INTRODUCTION
By letter dated July 30,1999, Commonwealth Edison Company (Comed, the licensee) proposed changes to the technical specifications (TSs) for Braidwood Station, Units 1 and 2, to change the upper temperature of the ultimate heat sink (UHS) from 98 degrees Fahrenheit to 100 degrees Fahrenheit. The licensee requested that the change remain in effect until September 30,1999. The licensee also requested an exigent review because prolonged hot weather and little precipitation resulted in elevated UHS temperatures at Braidwood. The licensee foresaw that the UHS temperature could approach or exceed 98 degrees Fahrenheit if there was a continuance of the conditions or a recurrence of similar conditions later in the summer. Exceeding a UHS temperature of 98 degrees Fahrenheit would require that both plants be shut down.
2.0 EVALUATION 2.1 Basis for the UHS TS The two principal safety functions of the UHS are to dissipate heat following a reactor shutdown l
and to dissipate the residual heat generated during accident conditions. The maximum heat l
load on the UHS consists of one unit's undergoing post-Loss-of Coolant Accident (LOCA) cooldown concurrent with loss of offsite power, and the unaffected unit's undergoing a safe non-accident shutdown. Both units are assumed to be at full power operation prior to the l
shutdown. This condition represents the UHS maximum heat load. To perform the principal l
functions, the UHS must contain sufficient volume of water at or below the maximum temperature to allow the Essential Service Water (SX) System to operate for at least 30 days following the design basis LOCA without the loss of Net Positive' Suction Head (NPSH), and without exceeding the maximum design temperature of the equipment served by the SX system.
Mitigation of non-LOCA accidents is not dependent on UHS temperature.
I 9909170135 990908 PDR ADOCK 05000456 p
. k 2.2 Evaluation of Prooggi, Chance
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For the LOCA analysis, the temperature of the UHS is one of the parameters used to calculate
- the performance of the residual heat removal (RHR) heat exchangers. The licensee had assumed a ' 'HS temperature of 100 degrees Fahrenheit in the original heat removal
. calculations. Jonsequently, there is no change to the calculated peak cladding temperature during a LOCA.
For containment response analyses, the UHS temperature affects the assumptions for the RHR heat exchanger and the Reactor Containment Fan Cooler (RCFC). A Component Cooling (CC) water temperature of 120 degrees Fahrenheit was previously assumed based on an SX temperature of 100 degrees Fahrenheit. An SX temperature of 100 degrees Fahrenheit was already assumed for the inlet temperature to the RCFC. Therefore, the proposed temperature has already been determined to be acceptable by these analyses. The peak containment temperature and pressure and long-term containment temperature profile used in
' Environmental Qualification remain unchanged.
Additional specific analyses done by the licensee support a maximum SX temperature of 100 degrees Fahrenheit. These analyses evaluated the operation of and the components needed to support operation of the CC water closed loop system, the Auxiliary Feedwater pumps, the Emergency Core Cooling System pumps, the Containment Spray pumps, the SX pumps (including SX pump NPSH), the Control Room chillers, the Emergency Diesel Generators, and the RCFCs. The support equipment includes oil coolers, room cubicle coolers, and jacket water cooling systems.
The licensee completed an analysis of the UHS and verified that the UHS is capable of providing sufficient cooling for normal shutdown of one unit and accident conditions in the other unit. The meteorological conditions chosen for the Braidwood Station UHS analysis utilized a l
synthetic 36-day period consisting of the most severe 5 days, most severe 1 day, and the most i
severe 30 days based on Braidwood's licensing basis meteorological data. Heat sink temperatures for these weather periods were evaluated using a model of the UHS. The licensee's analysis considered two cases with different numbers of SX pumps operating. For i
the case with three SX pumps operating, the UHS temperature remained below 100 degrees i
Fahrenheit. For the other case, with four SX pumps operating, the UHS temperature reached about 100.8 degrees Fahrenheit for a period of approximately 1-hour. Even though the UHS temperature was above 100 degrees Fahrenheit, the licensee concluded that the components would continue to perform their safety function for the following reasons:
l A.
. The UHS temperature peak is of short duration at approxi,mately 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> into the accident scenario, which is past the time period where the maximum residual heat load from containment will occur.
B.
The assumption in the desigh basis analysis of a constant SX temperature of
.100 degrees Fahrenheit is conservative with respect to the calculated SX temperature profile over the duration of the event.
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The magnitude and duration of the peak is not sufficient to cause adverse effects on the equipment and components, l
The increase in risk is judged to be minimal for the period remaining until September 30,1999 l.
- (the point at which the TS UHS value reverts back to 98 degrees Fahrenheit). Because the l
licensee has determined that the proposed temperature is acceptable for the LOCA and containmer,i pressure response analyses, there is no increase in risk associated with these elements of the accident analysis. In addition, specific component analyses conducted by the licensee demonstrate acceptable component operation at the proposed temperature.
increasing the UHS temperature could influence the loss of condenser vacuum initiating event frequency through an increase in the circulating water temperature. However, the licensee has determined that condenser vacuum is reduced only slightly at the higher UHS temperature, and there is still sufficient margin to condenser operating limits. Therefore, it was concluded that the change in loss of condenser vacuum initiating event frequency was negligible. No other adverse influences on risk were identified by the licensee through examination of the Probabilistic Risk Analysis (PRA) model for the plant.
2.3 Summary In considering the minimalimpact of operating Braidwood with a maximum allowable UHS temperature of 100 degrees Fahrenheit, and the short time duration in which such operation would be permitted, the staff concludes that the proposed change is acceptable.
3.0 EXIGENT CIRCUMSTANCES
The Commission's regulations,10 CFR 50.91, contain provisions for issuance of amendments when the usual 30 day public notice period can not be met. One such provision concerns exigencies. ' An exigency is a case where the staff and the licensee need to act promptly, but
. failure to act promptly does not necessarily involve a plant shutdown, derating, or delay in start-
.up. The exigency case usually represents an amendment involving a safety enhancement to t.
the plant.
Under such circumstances, the Commission notifies the public in one of two ways: by issuing a Federal Reaister notice providing an opportunity for hearing and allowing at least two weeks for prior public comments, or by issuing a press release discussing the proposed changes, using l
the local media. In this case, the Commission used the first approach.
' The licensee submitted the request for amendment on July 30,1999, it was noticed in the Federal Register on August 18,1999 (64 FR 44962), at which tirne the staff proposed a no significant hazards consideration determination. Comed requested that the proposed temporary change be reviewed on an exigent basis. The licensee stated, "The prolonged hot L
weather in the area during the month of July resulted in sustained elevated UHS temperatures.
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The average temperature of the UHS peaked above 96 degrees Fahrenheit during the last several days of the hot period." The licensee further stated that continued hot weather conditions might result in the temperature exceeding 98 degrees Fahrenheit before the 30-day
. public comment period provided by 10 CFR 50.91(a) expired. Without the amendment, UHS c
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temperatures exceeding 98 degrees Fahrenheit would have resulted in both Braidwood units having to be shut down.
Therefore the staff is issuing the amendment under exigent circumstances. The licensee requested that the higher UHS temperature be in effect until September 30,1999, in case additional periods of extended hot weather occurred in August or September. Using the normal 30-day comment period would have reduced the amount of time available to the licensee to take advantage of the higher temperature limit on a non-emergency basis.
4.0 '
FINAL NO SIGNIFICANT HAZARDS CONSIDERATION DETERMINATION The Commission's regulations in 10 CFR 50.92 state that the Commission may make a final determination that a license amendment involves no significant hazards considerations if operation of the facility in accordance with the amendment would not: (1) involve a significant increase in the probability of consequences of an accident previously evaluated; or (2) create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety.
Operation of the facility in accordance with the proposed amendment will not involve a significant increase in the probability or consequences of an accident previously evaluated.
Analyzed accidents are assumed to be initiated by the failure of plant structures, systems or components. An inoperable UHS is not considered as an initiator of any analyzed events. The analyses for Braidwood assume a UHS temperature of 100 degrees Fahrenheit. The proposed change does not involve any physical alteration of plant systems, structures or components. A UHS temperature of up to 100 degrees Fahrenheit does not increase the failure rate of systems, structures or components because the systems, structures or components are rated and analyzed for operation with SX temperatures of 100 degrees Fahrenheit and the design allows for higher temperatures than at which they presently operate.
The basis provided in Regulatory Guide (RG) 1.27, " Ultimate Heat Sink for Nuclear Power Plants," Revision 2, dated January 1976, was employed for the temperature analysis of the Braidwood Station UHS to implement General Design Criteria 44 and 2 of Appendix A to 10 CFR Part 50. This RG was employed for both the original design / licensing basis of the Braidwood Station UHS and a subsequent evaluation that investigated the potential for increasing the average water temperature of the UHS from s 98 degrees Fahrenheit to s 100 degrees Fahrenheit. The meteorological conditions chosen for the Braidwood Station UHS analysis utilized a synthetic 36-day period consisting of the most severe 5 days, most severe 1 day, and the most severe 30 days based on historical data. The heat loads selected for the UHS analysis considered one Braidwood Unit in a LOCA condition concurrent with a loss-of-Offsite Power (LOOP) and the remaining Braidwood unit undergoing a normal plant shutdown. In the analysis, the heat loads are removed by the UHS using only SX pumps. The main condenser cooling pond is conservatively assumed not to be available at the start of the event. The analysis showed that with an initial UHS temperature of 100 degrees Fahrenheit, the required heat loads can be met for 30 days while maintaining essential service water temperatures at acceptable values. Based on the aforementioned, the staff concludes that the increase of the initial UHS temperature from s 98 degrees Fahrenheit to s 100 degrees
3 Fahrenheit at the start of the design basis event will result in the continued ability of the equipment and components supported by the SX system to perform their safety functions.
Operation of the facility in accordance with the proposed amendment will not create the possibility of a new or different kind of accident from any accident previously evaluated. The proposed action does not involve a physical alteration of the units. There is no change being made to the parameters within which the units are operated that is not bounded by the analyses. There are no setpoints at which protective or mitigative actions are initiated that are affected by this proposed action. The proposed action will not alter the manner in which equipment operation is initiated, nor will the function demands on credited equipment be
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changed. No alteration in the procedures that ensure the units remain within analyzed limits, is
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proposed, and no change is being made to procedures relied upon to respond to an off-normal event. As such, no new failure modes are being introduced. The proposed action does not alter assumptions made in the safety analysis.
Operation of the facility in accordance with the amendment will not involve a significant reduction in a margin of safety. The proposed action allows operation with the UHS temperature s 100 degrees Fahrenheit until September 30,1999. The margin defined by the difference in the assumed steady state SX temperature and the calculated SX temperature profile integrated over the duration of the event is not significantly impacted. The margin of safety is determined by the design and qualification of the plant equipment, the operation of the plant within analyzed limits, and the point at which protective or mitigative actions are initiated.
The proposed action does not impact these factors. There are no required design changes or equipment performance parameter changes associated with this change. No protection setpoints are affected as a result of this change. This temperature increase will not change the operational characteristics of the design of any equipment or system. All accident analysis assumptions and conditions will continue to be met.
Therefore, the Commission determinates that the amendment involves no significant hazards consideration.
5.0 STATE CONSULTATION
in accordance with the Commission's regulations, the lilinois State official was notified of the proposed issuance of the amendments. The State official had no comments.
6.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in. individual or cumulative occupational radiation exposure. The Commission has made a final finding that the amendments involve no significant hazards consideration. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).. Pursuant to 10 CFR 51.22(b), no environmental
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,r - impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
7.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: G. Dick Date: September 8,1999 1
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