ML20085E861

Interim Deficiency Rept Re Potential for RHR Pump Operation Beyond Runout Condition.Initially Reported on 760203.Addl Pump Discharge Orifices Will Correct Design Deficiency

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: ML20085E841 ML20085E850 ML20085E861
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8308160614
Download: ML20085E861 (4)

Text

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OW7'9+ 831 Power Building /

g fly {~ ; TENNESSEE VALLEY AugORITY CH ATTANOOGA, TENNESSEE 374o1

'/re .916 March 14 , 1976 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,

) . ;' i - ,1 j l(? '.fra : 5 .- ..

< 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 -

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w V 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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