ML19256E514

Final Interim Deficiency Rept Re RHR Pump Motor Svc Factor. Flow Restrictions Will Be Added to Each RHR Pump Hot Leg & Cold Leg Injection Header to Provide Pressure Drop Necessary to Prevent Pump Motor Overloading

ML19256E514
Person / Time
Site:	Susquehanna
Issue date:	10/17/1979
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19256E512	List: ML19256E511 ML19256E514
References
NUDOCS 7911070555
Download: ML19256E514 (1)

Text

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ENCLOSURE SEQUOYAH NOCLEAR PLANT UNITS 1 AND 2 RHR PUMP MOTOR SERVICE FACTOR NCR NER 79-3 FINAL REPORT

_D_escription of Deficiency During preoperati- 11 testing, the RHR pump motors were found to exceed their allowable service factor of 1.15. This occurred during certain low head operational L) des, such as with one pump discharging to four reactor coolant loops. The problem is related to that of Sequoyah Nuclear Plant NCR CEB 79-4 which partly concerns flow cavitation in certain operational modes caused by excessive pressure drop through th2 conttol valves.

The RHR discharge piping system pressure drop is lower than that specified in the Westinghouse design criteria. This comes, in part, from conservative design calculations made using Crane Technical Paper No. 410, which resulted in calculated line pressure drops that are much greater than what is actually being experienced during system testing. The problem was aggravated by the RHRS pump motors having mar s u,ox reserve horsepower for maximum service con-ditions and by the inability of the RHR throttling valves to throttle under the existing system conditions. Low back pressure in the injection lines allowed cavitetion across the valves when throttling. This situation provides the potential for the pump motors to overload froa pumping exces-sive flow rates and for the other problems noted above to occur.

Safety Implications Overloading of the pumps could result in pump tripout under some service conditions, one cf the worst cases being when the RHR system is furnishing suction to the oIS pumps. This could result in tripout of the RHR pumps and in less of suction to the SIS purps, causing damage and/or requiring operator action to restart the system or the redundant train. This would constitute a reduction in the available redundant safeguards provisions described in the planc FSAR.

Corrective Action Flow restrictions are to be added in each RHR pump hot leg and cold leg injection header to ptavide the pressure drop nccessary to prevent pump motor overloading. The restrictions will be located downstream of t.

control valves and the injection line flow elements, but upstream of e isolation check valves. These restrictions will also be ef fective it.

ameliorating the cavitation problem of NCR CEB 79-4. The restriction design is being developed by Westinghouse, and the piping system modifications will be complete before un.t 1 fuel loading. All TVA design project managers d

are being informed of these problems to prevent recurrence in future plant designs.

. The Watts Bar Nuclear Plant RHRS design is similar to the Sequoyah Nuclear Plant one. Consequently, similar corrections will probably be required at Watts Bar.

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