ML20085E861
| ML20085E861 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/04/1976 |
| From: | Gilleland J TENNESSEE VALLEY AUTHORITY |
| To: | Knuth D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| Shared Package | |
| ML20085E842 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8308160614 | |
| Download: ML20085E861 (4) | |
Text
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'/re.916 March 1, 1976 4
Dr. Donald F. Knuth, Director Office of Inspection and Enforcement f h, U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Dr. Knuth:
BROWNS FERRY NUCLEAR PLANT UNIT 3 - REPORTABLE DEFICIENCY -
POTENTIAL FOR RHR PUMP OPERATION BEYOND RUNOUT CONDITION Initial report of the subject reportable deficiency was made to H. C. Dance, NRC-IE, Region II, on February 3, 1976. In compliance with paragraph 50.55(e) of 10 CFR Part 50, we submit the enclosed interim report of the deficiency.
Very truly yours,
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< J. E. Gilleland Assistant Manager of Power Enclosure CC (Enclosure):
Mr. Norman C. Moseley, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Region II - Suite 818 230 Peachtree Street, NW.
Atlanta, Georgia 30303 l
i 8308160614 760524 PDR ADOCK 05000296 S
PDR An Equal Opportunity Employer O
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EliCLOSURE baCUIis FER?.T WCLEAR PLV.? UI!IT 3 POTENIIAL FOR RER FUM? O':ZRATIO.'I III I2 CESS OF DESIGIT RUI!OI;T DDR 224 IUTERDI REPORT Descriution of Deficiency A sin;;1e failure analysis of prcposed codifications to the Residual Heat Rc= oval (RER) System for units 1 and 2 identified a potential single
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failure inthe present plant configuration for n11 three units.
Tnic single failure occurring after a loss of coolant accident (LCCA) could result in short-ter= RHR pu=p cperatica in excess of design runout. Tnis was considered an unacceptable ch'llenge to pu=p availability since two PIR pumps are required for long-term contain=ent cooling.
Cause of Deficiency During a 1CCA, the 1cw pressure coolant injection (LPCI) logic for the RER Systes calls for the injectica of water from four P}3 pu=ps through an unbroken recirculation loop to the reactor vessel. A single active cccponent failure in this logic could result in incorrect loop selection and direct all four RER pu=ps to flew to the break. A break in the recir-culation loop discharge line is the limiting situation.
A significant increase in total systes fica above the design condition will result due to the loss of recirculation loop jet pu p ficw resistance (which con-stitutes over 50 percent of the total system flow resistance). Tne resulting flow has been shein by calculations to exceed the runcut capacity of the pu=ps, as determined frcs the pu=p canufacturer's test data. A single failure in the logic could also result in four PJIR pt=ps injecting into both recirculation loops si=ultaneously, with one loop broken.
This is the limiting case.
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Another single failure that was considered, and found to be less lisiting was the case unere the loop selection was perfomed correctly for a recirculation line break, but the recirculation pu=p discharge valve in the unbreken loop fails to close. This results in en additional fic1 path thzough the reciren1? tion pu=p to the reactor vessel. This path is in parallel uith the no=21 one thrcugh the jet pt=ps, but has a much 1cuer flow resistance. This could also result in RER pt=p operation in excess of design rtmont, but it is not the. limiting case.
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[fitfetyImolications Tne R!iR injection code is not needed for short-ter:'. core cooling for either of the two cases discussed. However, the operation of the PliR pu=ps in excess of design runout presents a potential cha.nenge to the availability of the pumps since they are needed for long-tern contM-=t cooling.
A mini =u:s of_ two RER pu=ps and associated heat exchangers cust be operable for long-ters contain=ent cooling.
Descriotion of Corrective Action An orifice will be instaned in the discharge pipin5 of each PER pu=p.
The orifices will be sized so that three p.=:ps will supply adequate flow in the LICI mode to maintain fuel temperature belou established 1L=its.
They vill also provide the necessary flow resistance to prevent the four RHR pu=ps from. exceeding their design ~ runout flo r capability following the worst case single failure.
Confir.atory tests will be conducted with the orifices installed to co= pare the required R'iR systen flow characteristics with the acutal characteristics. Results of the confor:atory testing will be included in a final report.
Means Taken to Prevent a Recurrence The ' addition of pu=p discharge orifices will correct the design deficiency and thus eliminate the possibility of Ri-3 pc=p operation in excess of design runout due to the postulated single failure.
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