ML19209B116

Forwards IE Bulletin 79-21, Temp Effects on Level Measurements. Action Required

ML19209B116
Person / Time
Site:	Prairie Island
Issue date:	08/13/1979
From:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:	Wachter L NORTHERN STATES POWER CO.
References
NUDOCS 7910090191
Download: ML19209B116 (1)

Text

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%..** o Docket No. 50-282 AUG 131979 Docket No. 50-306 Northern States Power Company AITN:

Mr. Leo Wachter Vice President Power Production and System Operation 414 Nicollet Hall Minneapolis, MN 55401 Gentlemer.

Enclosed is IE Bu11eti2 No. 79-21 which requires action by you with regard to your PWR power reactor facilities with an operating license.

Should you have acy questions regarding this Bulletin or the actions required by you, please contact this office.

Sincerely, b.

ames G. Keppler Director

Enclosures:

1.

IE Bulletin No. 79-21 2.

List of IE Eulletins Issued in the Last 6 Months cc w/encls:

Mr. F. P. Tierney, Jr.

Plant Manager Central Files Director, NRR/DPM Director, NRR/ DOR PDR Local PDR NSIC TIC John W. Ferman, Ph.D.,

Nuclear Engineer, MPCA

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Accession No: 7908090103 SSINS No:

6820 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.

20555 August 13, 1979 IE Bulletin No. 79-21 TEMPERATURE EFFECTS ON LEVEL MEASUREMENTS Description of Circumstances:

On June 22, 1979, Westinghouse Electric Corporation reported, to NRC, a potential substantial safety hazard under 10 CFR 21.

The report, Enclosure No. 1, addresses the effect of increased containment temperature on the reference leg water column and the resultant effect on the indicated steam generator water level.

This effect would cause the indicated steam generator level to be higher than the actual level and could delay or prevent protection signals and could, also, provide erroneous information during post-accident monitoring.

Enclosure No. I addresses only a Westinghouse steam generator reference leg water column; however, safety related liquid level measuring systems utilized on other steam generators and reactor coolant systems could be affected in a similar manner.

Actions To Be Taken By Licensees:

s For all pressurized water power reactor facilities with an operating license:*

1.

Review the liquid level measuring systems within containment to determine if the signals are used tc initiate safety actions or are used to provide post-accident monitoring information.

Provide a description of systems that are so employed; a description of the type of reference leg shall be included, i.e., open column or sealed reference leg.

2.

On those systems described in Item 1 above, evaluate the effect of post-accident ambient temperatures on the indicated water level to determine any change in indicated level relative to actual water level.

This evaluation must include other sources of error including the effects of varying fluid pressure and flashing of reference leg to steam on the water level measurements.

The results of this evaluation should be presented in a tabular form similar to Tables 1 and 2 of Enclosure 1.

3.

Review all safety and control setpoints derived from level signals to verify that the setpoints will initiate the action re utred b the lan analyses throughout the range of ambi instrumentation, including accident t these setpoints.

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June 22,1979 NS-TMA-2104 Mr. Victor E ello Director Ofrice of Inspection and Enforcerent U.S. Nuclear Regulatory Comission East West Towers Building 4350 East Wes_t Highway Bethesda, Maryland 20014

Subject:

Steam Generator Water Level This is to (.onfirm my telephene conversation of June 21, 1979 with Mr.

Norman C. Moseley, Director, Divisio, of Reactor Operation and Inseec-tion and Mr. Samuel E. Bryan, Assistant Director for Field Coordination.

In that conversation, I reported that Westinghouse had informed its utility customers of corrections that should ',e applied to indicated steam generdtor water level and recomended that they incorporate those ccrre:tiens in the steam generator low water level protection system setpoints and emergency operati,ng procedures for operating plants as appropriate.

High energy line breaks inside containment can result in heatup of the steam generator level measurement reference leg.

Increased reference leg water column temperature will result in a decrease of the water column density with a consequent apparent increase in the indicated steam generator water level (i.e., apparent level exceeding actual level). 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.

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).

The following is a list of backup signals available in those Westinghouse plants which take credit in their Final Safety Analysis Reports for steam generator water level trip with an adverse containment environment:

overtemperature delta T; high

' pressurizer pressure; containment pressure and safety injection.

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