ML20196C942
| ML20196C942 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 12/05/1988 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| GL-85-16, NUDOCS 8812080145 | |
| Download: ML20196C942 (3) | |
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TENNECCEE VALLEY AUTHORITY CH ATTANOOG A. TENNESSEE 37401 f
SW 157B Lookout Place 058 051988 U.S. Nuclear Regulatory Commission ATTN Document Control Desk Washington, D.C.
20555 centlement la the Matter of
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Docket Nos. 50-327 Tennessee Valley Authority
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50-328 SEQUOYAH NUCLEAL PLANT (SQN) - TEMPORARY EXEMPTION FROM ADMINISTNATIVE
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PROVISIONS OF 10 fC.50.46 - REQUEST FOR ADDITIONAL INFORMATION
Reference:
TVA letter to NRC dated November 3, 1988, "Sequoyah Nuclear Plant (SQN) - Temporary Exemption from Administrative Provisions of 10 CFR 50.46" The reference transaltted a request for a temporary exemption from administrative provisLons of 10 CFR 50.46 for cycle 4 operation of SQN units 1 and 2.
The temporary exemption was requested in support of a reduced minimm delivered upper head injection (UMI) water volume.
l To support NRC review of the temporary exemption request, the SQN Project Manager requested that additional information be provided in the following areast 1.
History of UHI development 2.
Magnitude of errors introduced by the sensitivity studies 3.
Benefits of UHI removal 4.
Potentist financial impacts assoclated with performance of the conflematory UMI evaluation model analysis 7
The UHI system was added to the SQW design in 1973 as the result of i
revised Atomic Energy Comission ( AEC) emergency core cooling system l
(ECCS) performance criteria, which required peak clad temperature (PCT) to be less than 2,200 degrees Fahrenheit (F) following a postulated loss
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of coolant accident (LOCA). The primary function of UHI is to provide 1
addLtional core cooling during the blowdown portion of a postulated LOCA caused by a double-ended, cold les break (DECLB).
- 'he UHI system is in addLtion to the ECCS cold-leg accum letors and pumps.
Application of the UHI design was restricted to 4-loop, ice-condenser plants because of their higher power ratings in combination with lower containment back pressure following a postulated LOCA.
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.' ()E6 051988 U.S. Nuc1 car Regulatory Connission The magnitude of errors introduced by the utilizatLon of the sensitivity studies is no more than the errors introduced through the utilization of the UH1 evaluation model computer ' ade. The sensitivities were developed from multiple runs of the UH1 eve. sation model.
The multiple runs were performed to determine the effect a on PCT of varying input parameters such as delivered UHI water volume, heat flux bot channel f actor, and steam generator tube plugging. Therefore, because the sensLtivities were developed directly from the UH1 evaluation model, the error associated wLth them is that which is inherent to the computer code.
The removal of UH1 from the SQN design will result in significant operation / maintenance improvements.
During refueling outages, approx! ately four days of critical path work is required for disassembling, reassembling, and testing of UH1 connectLons to the reactor vessel head.
Deletion of this work would also result in decreased personnel exposure (approximately 59 person-rem each outage).
The removal of UH1 would also provide operation / maintenance improvements by the deletion of the survettlance requirements associated with UNI operability. UH1 removal will also provide a nuclear safety benefit by removing the potentlet for injecting nitrogen into the reactor coolant system. Injected nitrogen could occur only if multiple failure prevented the automatic isolation system from functioning af ter injection.
Injected nitrogen could form volds that might impede natural circulation and core cooling.
As discussed in the reference, TVA contends that the performance of the confirmatory UH1 evaluation model analysis wl11 provide no significant benefit.
It is, therefore, submitted that TVA discretionary resources could be better uttilzed if directed at operation / maintenance improvements. Such discretionary improvements include the deletion of the boron injection tank (BIT) as discussed in Generic Letter 85-16.
TVA is alsu investigating discretionary operation / maintenance improvements associated with the ice condenser. These include reduced ice weight analyses and increased Lee weighing intervals.
The implementation of standardized, improved, and restructured technical specifications at SQN is also categorized as a discretionary operation / maintenance improvement. Many factors affect the availability of funds for discretionary projects; for example, the recent forced outage to repair the SQN unit 1 main generator wlL1 alter the priorities placed on discretionary improvements.
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U.S. Nuclear Regulatory Comission M8 05 M Please direct questions concerning this issue to R. R. Thompson at (615) 843-7470.
Very ttvly yours.
TENNESSEE VALLEY AUTHORITY l
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p R. pCeld ey, Mana Nuclear Licensing and Regulatory Affairs cc:
Ms. S. C. Black, Assistant Dirwetor i
for Projects TVA Projects Division U.S. Nuclear Regulatory Comlanton One White FIlnt, North I'
11555 Rockvitte Pike Rockville, Maryland 20852 Mr. F. R. McCoy, Assistant Director for Inspectlen Programs
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TVA Projects Division l
U.S. Nuclear Regulatory Comission l
Region 11 101 Marietta Street, NW, suite 2900
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Atlanta, Georgia 30323 t
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Sequoyah Resident Inspector l
sequoyah Nuclear Plant j
l 2600 Igou Ferry Road j
Soddy Daley, Tennessee 31379 1
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