United States Nuclear Regulatory Commission - Protecting People and the Environment

LICENSEE: ROCHESTER GAS & ELECTRIC CORP.
SITE: GINNA 1 EN NUMBER:35392
DOCKET:
EVENT DATE: 02-22-99
RX TYPE: PWR EVENT TIME: 15:40
VENDORS: W-2-LP NOTIFY DATE: 02-22-99
EMERGENCY CLASS: N/A REGION: 1 STATE: NY TIME: 16:27
OPS OFFICER: FANGIE JONES
10 CFR SECTION: AOUT OUTSIDE DESIGN BASIS
UNIT SCRAM CODE RX CRIT INIT PWR INITIAL MODE CURR PWR CURRENT MODE
1 N Y 75 Power Operation 75 Power Operation

DISCOVERY OF MODELING ERRORS IN THE MAIN STEAM LINE BREAK ANALYSIS

The following text is a portion of a facsimile received from the licensee:

"Ginna Station was notified by its NSSS vendor, Westinghouse Electric Company, of two modeling errors in the analysis for a main steam line break (MSLB) with an assumed single failure of a feed water control valve. The first error was not taking into account the full amount of energy released to containment by the flashing of high temperature feed water downstream of the motor operated isolation valves after feed water flow is isolated. The second error was a mistake in the assumed time of feed water isolation. Isolation should have occurred at 85 seconds but incorrectly occurred at 15 seconds.

"Preliminary analyses show that in the past, under the postulated conditions of a MSLB coincident with a feed water regulating valve failure, the containment pressure design limit may have been exceeded and that Ginna Station may have been in a condition outside the design basis of the plant. This condition is also being evaluated for the criteria of l0CFR2l. However, a recently performed analysis for the current operating cycle using more realistic modeling assumptions, accounting for cycle specific shutdown margin values and crediting current heat sink temperatures showed that acceptable results (less than 60 psig) were obtained. Thus there is no concern for continued plant operation through the end of the current cycle (March 1, 1999) based on these results."

Further analyses will be performed prior to the plant restarting after the next refueling.

The licensee notified the NRC Resident Inspector.

Page Last Reviewed/Updated Thursday, March 29, 2012