ML19248D224

LER 79-015/01T-1 on 790621:notifies That High Energy Line Break Inside Containment Could Result in Potential Steam Generator Level Bias.Caused by Heatup of Steam Generator Level Measurement Ref Leg.Tech Spec Change Submitted

ML19248D224
Person / Time
Site:	Beaver Valley
Issue date:	08/01/1979
From:	Werling J DUQUESNE LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19248D204	List: ML19248D203 ML19248D208 ML19248D209 ML19248D217 ML19248D221 ML19248D224 ML19248D226
References
LER-79-015-01T, LER-79-15-1T, NUDOCS 7908130442
Download: ML19248D224 (2)

Text

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EVENT DATC 74 75 REPOHT DATE t;0 EVENT DESCRIPTION AND PROBAOLE CONSEQUENCES h o 2 IThe NSSS vendor has notified BVPS that a high energy line break inside containment  ;

o a lcould result in a potential steam generator level bias due to the heatup of the  ;

o 4  ! steam generator level measurement reference leg. This potential level bias could  ;

o s [ result in delayed protection signals (reactor trip and auxiliary feedwater y o o l initiation) which are based'on low-low steam generator water level. ,

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[il21l During the upcoming refueling outage, the S/G level reference legs will be  ;

i a l insulated. A technical specification change is being submitted to correct the  ;

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Attachment To LER 79-15/0lT-1 Beaver Valley Power Station Duquesne Light Company Docket No. 50-334 The NSSS vendor has notified BVPS that a high energy line break inside containment could result in a potential steam generator level bias due to the heatup of the steam generator level measurement reference leg. This potential level bias could result in delayed protection signals (reactor trip and auxiliary feedwater initiation) which are based on low-low steam generator water level. The high energy line break in containment will result in an increased reference leg water column temperature which in turn results in a decrease of water column density with a consequent apparent increase in the indicated steam generator water level (i.e., apparent level exceeding actual level). In the case of a feedline rupture, this adverse environment could be present and could delay or prevent the primary signal arising from declining steam generator water level (low-low steam generator level). Back-up signals which may be available include the following:

overtemperature delta T, high pressurizer pressure, containment pressure, and safety injection. For other high energy line breaks which could introduce a similar positive bias to the steam generator water level measurement, steam generator level does not provide the primary trip function and the potential bias would not interfere with needed protective system actuation. By way of example, a containment temperature of 180F could result in a 3% bias in steam generator levels. Refering to the attached figures (Figure 14.3-57 and Figure 14.3-58 from the BVPS FSAR for a Hot Leg DER) a containment pressure in excess of 1.5 psig (which in turn actuates safety injection, auxiliary feedwater and reactor trip) occurs prior to the containment atmosphere being heated up to 180F. Thus, the possibility of a greater bias of the steam generator level signal above 180F for this particular case is not relevant to protection system actuation. In correcting the steam generator water level setpoint for this bias, the reference leg bias is additive to the existing setpoint.

Per Westinghouse bulletin, the steam generator low-low level trip will be administratively increased an addition 10 percent which results in 20 percent total. During the upcoming rebeHng outage, the steam generator level reference legs will be insulated. A technical specification change is being submitted to account for the required setpoint with the insulation installed.

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