ML17266A106

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LER 79-030/01T-0:on 790921,discovered as-built Design Specs for Steam Generator Were Not Used by NSSS Vendor to Establish Instrument Span for Measuring Steam Generator Level.No Cause Given.Low Level Trip Setpoint Raised to 39%
ML17266A106
Person / Time
Site: Saint Lucie NextEra Energy icon.png
Issue date: 10/05/1979
From: Schoppman M
FLORIDA POWER & LIGHT CO.
To:
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML17207A480 List:
References
LER-79-030-01T, LER-79-30-1T, NUDOCS 7910190346
Download: ML17266A106 (3)


Text

lfl Reportab le Occurre 335-79-30 Licensee Event Report Page two

'ADDITIONAL EVENT DESCRIPTION AND PROBABLE CONSE UENCES During an evaluation of steam generator level sensing inst'rumentation conducted as part of compliance with NRC I & E Bulletin 79-21, it was noted that the design specifications of the steam generator had been used by the NSSS vendor to establish the instrument span for measuring steam generator level. In actuality, the as-built dimensions should have been employed for this determination.

The FSAR analysis assumes a reactor trip during a loss of feedwater accident to occur when steam generator water level drops 50 inches below the normal water level. As a result of using the design (instead of as-built) steam generator dimensions, the low level trip setpoint of 37K is in error (non-conservative) by approximately 2X (4 inches) in comparison with the FSAR criteria.

The FSAR analysis does, however, also assume an instrument error of 10 inches in analyzing the loss of feedwater accident.

Confirmation was received from the NSSS vendor that past operation with the setpoint error did not have an effect on the safety analysis and did not affect the health and safety of the public.

This was the first occurrence of this type.

ADDITIONAL CAUSE DESCRIPTION AND CORRECTIVE ACTION Use of wrong dimensions in establishing the steam generator level sensing instrument span resulted in a 2X error in the steam generator low level trip setpoint.

Immediate corrective action was to instruct the control center operators that, in the event of a low steam generator level condition, the reactor was to be manually tripped upon reaching 395 level.

After receipt of NSSS confirmation of the plant staff's evaluation of the proper instrument span, the Reactor Protective System steam generator low level trip setpoint was raised to 39$ .