ML20050B703

Ro:On 820324,w/reactor in Mode 5,unplanned Dilution Occurred While Filling RCS Water Storage Tank from Refueling Water Storage Tank

ML20050B703
Person / Time
Site:	San Onofre
Issue date:	03/26/1982
From:	Ray H SOUTHERN CALIFORNIA EDISON CO.
To:	Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
NUDOCS 8204070253
Download: ML20050B703 (2)

Text

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gm g 44 Southern California Edison Company 9 t; S AN ONOPRE NUCLE AR GENER A TING S T A TION P .O. B O X 128 S Ata C LEMEN T E C A LIFOR NI A 92472 H. B FI A Y istgpwong ST ATION M AN AGER 1714)492-7700 March 26, 1982 U.S. Nuclear Regulatory Commission ss Office of Inspection and Enforcement @\ ,

Region V N

.D 1450 Maria Lane, Suite 210 G 73 16 Walnut Creek, California 94596-5368 s 9fc,0 Docket No. 50-361 k pd g Z San Onofre, Unit 2 g f.sg 9 Attention: Mr. R. H. Engelken, Regioni Administrator #

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Dear Sir:

This letter describes a reportable occurrence involving an unplanned dilution of the Reactor Coolant System (RCS) in excess of 0.5% Delta K/K. This submittal is in accordance with the reporting requirements of Section 6.9.1.12.d of Appenoix A to Facility Operating License NPF-10.

With the reactor in Mode 5 on March 24, 1982, a filling operation of the Reactor Coolant System commenced fraat the Refueling Water Storage Tank (RWST). A planned dilution of approximately 75 ppm was cxpected at completion. However, sampling of the RCS during a pause in the filling operation indicated that this dilution (i.e. from 1974 ppm to 1899 ppm) resulted when reactor vessel water level was raised from the middle of the hotleg nozzel to the top. Based on the volume addition, a dilution at this point of only 30 ppm was expected. Thus, an unplanned dilution of 0.7% Delta K/K (equivalent to 45 ppm) had occurred, even though the intended total dilution (75 ppm) was not exceeded.

Shutdown margin during this event decreased to a minimum of about -C6N 19% Delta K/K. In accordance with Technical Specification 3.1.1.2 a rj minimum shutdown margin of 2", Delta K/K is required for Mode 5. Thus //6 there was no significant reduction in plant safety margin as a result of this event.

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March 26,1982 Mr. R. H. Engelken, Regional Administrator U.S. Nuclear Regulatory Commission Our investigation into this incident is continuing and the result

, of our review will be forwarded to you with our 14 day report.

cc: U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Office of Management Information & Program Control Director, Records Center - INP0 A. E. Chaffee (USNRC Resident Inspector - San Onofre Unit 2) a I

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