ML20214U566
| ML20214U566 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 12/01/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20214U539 | List: |
| References | |
| NUDOCS 8612090310 | |
| Download: ML20214U566 (3) | |
Text
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'k UNITED STATES 8 '~
NUCLEAR REGULATORY COMMISSION n
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WASHINGTON, D. C. 20555
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SAFETY EVAltlATION RY THE OFrICE OF NUCLEAR REACTOR REGULATION RELATED TO AMEN 0 MENT NO.50TO FACILITY OPERATING LICENSE OPR-77 AND AMENDMENT NO.4270 FACTLITY OPERATING LICENSE DPD-79 TENNESSEE VALLEY AUTHORITY INTRODUCTION In a letter dated August 8,1986, the Tennessee Valley Authority (TVA or licensee) requested changes to the Technical Specifications for Segunyah Nuclear Plant linits 1 and 2.
The changes would modify the flow balance surveillance requirements for the safety injection pumps and the centri-fugal charging pumps. The changes pemit greater imbalance between the flow injected into the four loops than was previously allowed.
Flow balancing is important since in loss of coolant accident analyses the loop receiving the greatest ECCS flow is assumed to be broken and to spill its portion of the injected coolant. The Technical Specifications therefore specify the minimum flow to the three lowest flow loops.
The licensee also proposes to remove the automatic closure signal from the low flow protection (miniflow) lines for the centrifugal charging pumps.
Removal of the autoclosure feature provides greater protection from pump overheating at high discharge pressures but acts to reduce ECCS flow. The total requested reduction in safety injection and centrifugal charging pump flow is approximately 6% for the surveillance test which is at low pressure. The effect of not isolating the miniflow lines would be more significant at higher discharge pressures such as would occur during a small break LOCA.
EVALUATION The licensee evaluated the effect of reduced safety iniection and centrifugal charging pump flow on small break LOCAs. A sensitivity study of small break LOCA in WCAP-9600 indicates that for each percentage decrease in ECCS ' low, the calculated peak cladding ternperature will increase by 15 F.
During the time of core uncovery for the most severe small break LOCA the reactor system pressure would be approximately 600 psia. At that pressure the open miniflow lines protecting the centrifugal charging pumps would bypass a greater # rec-tion of the flow so that the total reduction in flow from the FSAR value would be 10%. Based on the WCAP-9600 sensitivity study of the effect of ECCS flow reduction on small break LOCA a 10% ECCS finw reduction would result in a 150"F increase in peak cladding temperature. Since the UFSAR analyses of small break LOCA predict peak cladding temperatures of less than 1500 F, the staff concludes that the 2?00 F limit of 10 CFR 50.46 will not be exceeded.
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-p-The licensee perfomed additional large break LOCA calculations with the lower flows from the safety injection and centrifugal charging pumps.
For the most severe large break LOCA the peak cledding temperature was calculated to be 2113 F which is below the limit of 2000"F.
This calculation was performed in October 1983 using the 1981 version of the Vestinahouse UHI ECCS Evaluation Model. The calculation conservatively assumed 10% steam generator tube plugging and is documented in the UFSAR.
Since October 1983 Westinghouse made a correction in the SATAN-VI code that is a part of the 1981 UHI Eval-uation model. The correction wculd increase the peak cladding temperature by less than 4"F.
Westinghouse also informed the staff of a potential non-conservatism in the WREFLOOD code that is also part of the 1981 UHI Evaluation Model. Modification of the WREFLOOD code to correct the cotential non-conservatism could increase the peak cladding temperature by 6 to 12 F.
In consideration of the margin in the licensee's calculation of peak cladding temperature for large break LOCA and the small magnitude of the nonconserv-atisms in the computer codes, the staff concludes that the 2200*F limit on peak cladding temperature will not be exceeded and that the Sequoyah ECCS perfomance remains acceptable.
To aid in meeting the new minimum ficw limits for the three injection lines with the lowest flow, the licensee requests that the maximum total safety injection pump flow be increased to 675 gpm from 660 gpm. This will reduce the need for throttling the pump discharce. The maximum flow is limited by NPSH concerns for the pump at high flows since the required NPSH increases with increased flow. The licensee verified that adequate NPSH would be available at the higher flow rate using pump test curves from the manufacturer. The staff concludes that this change is acceptable.
ENVIRONMENTAL CONSIDERATION These amendments involve changes in use of facility components located within the restricted a'ea as defined in 10 CFR Part 20 and changes in surveillance r
requirements. The staff has determined that the amendments involve no signi-ficant 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 in-crease in indivioual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that these amendments involve no significant hazards consideration, and there has been no public corrent on such finding. Accordingly, the amendments meet the eligibilfty criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environroental impact statement or envircrrental assess-ment need be prepared in connection with the issuance of the amendments.
CONCLUSION The Commission made a proposed determination that the amendments involve no significant hazards consideration which was publisted in the Federal Register on September 2a, 1986 (51 FR 33958) and consulted with the state of Tennessee, t'o public cumments were received, and the state of Tennessee did not have any ccoments.
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We have concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety cf the public will not be endangered by operation in the proposed manner, and (2) such activities will be cenaccted in compliance with the Conrission's regulations and the issuance of these an+ndaents will not be inimical to the corren defense and security or to the health and safety of the rublic.
Principal Contributors:
Carl R. Stahle, PWR#4, DPWR-A Joe Holenich, PWR#4, DPWR-A W. Jensen, PARS Dated: December 1, 1986 e
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