ML19210E333

Supplements 780818 Final Deficiency Rept Re Pump Suction & Unstable Flow.Pump Suction Mods Acceptable

ML19210E333
Person / Time
Site:	North Anna
Issue date:	11/29/1979
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
References
474A, NUDOCS 7912040349
Download: ML19210E333 (2)

Text

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November 29, 1979 Mr. James P. O'Reilly, Director Serial No. 474A Office of Insoection & Enforcement PSEAC/MGD:mac: wang U. S. Nuclear Regulatory Commission Region II Docket Nos. 50-404 101 Marietta Street, Suite 3100 50-405 Atlanta, Georgia 30303

Dear Mr. O'Reilly:

In accordance with 10CFR50.5M e), we notified the NRC, Region II, on July 28, 1978 that a hydrauli model test of the North Anna Units 3 and 4 recirculation spray pumps and cans had indicated adverse vortex action at the pumo suction and unstable flow into the first stage impeller. We forwarded our final report concerning this matter in our letter Serial No. 474 dated August 18, 1978. Our final recort stated a modification to the pump suction had been developed to alleviate the unstable flow and vortices, and that this modificetion had been completely tested with acceptable results. Our final report briefly described this modification as a cylinder, with four internal straightening vanes, which was bolted to the pump suction bell.

Subsequent to our final report, discussions with the pump vendor indicated the manuf acturing of the pumps and suction modifications could be facilitated by providing a different suction device. This revised modification consisted of a flat plate with four straightening vanes attached to the pump below the suction bell, and a ring or " washer" welded to the can at the pump suction. A variation of this proposed design had been testad during the development of the cylindrical suction device, but was discouraged by the vendor in favor of a device that could be bolted to the suction bell. Further testing of the cylindrical device revealed certain design tolerances of the device that were required for acceotable operation. The vender indicate <' these tolerances would make manufacturing more difficult, so the flat plate device was develooed in order to avoid the anticipated manufacturing difficulties of the cylindrical device.

The flat plate device was constructed by LaSalle Hydraulic Laboratory, installed on the model and thoroughly tested with acceptable results. Results of the model testing of this modification are available.

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//o 7912040

-2 Both pump suction modifications are acceptable. Due to the more desirable construction aspects of the flat plate suction design, a device of t'11s type will be provided on the recirculation spray pumos/ cans.

If you have any questions, please contact th's office.

Vgr .truly yours, /

..Ii!}Br,own,[$u'l>

S am' C.

Jr. /

Senior Vice President - Power Station Engineering and Construction cc: Mr. Victor Stello, Director Offi e of Inspection L Enforcemuit

..r. Harold R. Denton, Director Office of Nuclear Reactor Regulation bbdb 302 ;59