05000277/LER-1979-011, Forwards LER 79-011/01T-0

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Forwards LER 79-011/01T-0
ML19289F306
Person / Time
Site: Peach Bottom  Constellation icon.png
Issue date: 03/29/1979
From: Cooney M
PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To: Grier B
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19289F307 List:
References
NUDOCS 7906070210
Download: ML19289F306 (4)
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LER-1979-011, Forwards LER 79-011/01T-0
Event date:
Report date:
2771979011R00 - NRC Website
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text

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PHILADELPHIA ELECTRIC COMPAMY 2301 MARKET STREET PHILADELPHI A. PA.19101 215:841-400o March 29, 1979 Mr. Boyce H.

Grier, Director Office of Inspection and Enforcement hu31on I United States Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406 Dear Mr. Griez.

SUBJECT:

Licensee Event Repo r,t_,Na r r a t iv e Description The following occurrence was reported to Mr. Greenman, Region I, Office of Inspection and Enforcement initially on March 2, 1979 with supplemental notification on March 15, 1979.

Reference?

Docket Numbers 50-277 & 50-278 Report No:

LER 2-79-11/IT Report Da:e March 29, 1979 Occurrence Date:

March 2, 1979 Facility:

Peach Bottom Atomic Power Station Units 2 and 3 R.D.

1, Delta, PA 17314 Te_chnical Specification Reference'.

Technical Specification 6.9.2.a.(9) requires reporting "perforaance of structures, systems, or components that requires remedial action or corrective measures to prevent operation in a manner less conservative than assumed in the accident analyses in the safety analysis report..."

Description of the Event'.

An engineering review of the containment ventilation system isolation valves determined that the valves (butterfly valves) would not close from the fully open (90 degree) position when subjected to post-LOCA conditions.

Post-LOCA conditions are defined in the FSAR in Figure 14.6-10.

Valve manufacturer preliminary calculations indicated that the valves would close o

Mr. Boyce II. Grier Page 2 March 29, 1979 LER 79-11/1T under post-LOCA conditions if restricted to a maximum of 35 to 40 degrees open.

Subsequent analysis confirmed this valve to be 37 degrees open.

The valve mangfacturer confirmed that the valve body, disc and operator meet heismic requirements.

Further investigation, in;1uding inspection of the valve installation by a re p re s e n t a t ive of PECo Mechanical Engineering Division and members of the :ite Engineering Group (3/3/79), analysis by our Architect Engineer, and subsequent installation inspection by a seismic expert employed by our Architect Engineer, indicated that in some areas the valve control system could not be certified as seismically qualified.

Specifically, one component of the contro) system, a booster relay, could not be certified.

Also the analyses and inspections indicated that soue of the piping and components required additional strapping.

As a result of the initial inspection on 3/3/79, th re e valves A0 2519 (Unit 2 6 inch nitrogen inlet to drywell or torus), A0 3519 (Unit 3 6 inch nitrogen inlet to drywell or torus) and A0 3507 (Unit 3 18 inch exhaust from drywell to standby gas treatment outboard isolation valve) were found with their inflatable seal not inflated.

In each case redundant valves in the respective lines were closed with seals pressurized.

Adjustments were immediately made to the actuating bolt which operates the 2-way seal chamber p ressurizing valve.

This energized the inflatable seal and returned the valve to a fully operational closed position.

Consequences of E v e n t.'

The containment ventilation isolation valves are normally maintained in a closed position during power operation.

The only time both valves are normally opened is during inertment and de-inertment of the containment during startup and just prior to shutdown.

The probability of a LOCA occurring during these short time intervals is considered minimal.

The Technical Specifications provide for these valves to be open (aring the inerting and de-inerting op e ra t i on.

Failure of the accumulator or control components in the valve control system during a seismic event can result in depressurizing the inflatable. seal on the valve disc.

This would cause significant leakage.

I.f the control system on both the inner and outer valve f ailed 'du ring a seismic event, a containnent leak would result.

In order for this occu rre nce to have significant safety implication, a LOCA coupled with a low probability seismic event and failure of the control air system for both isolation valves in a flow path nust occur.

2233 041

M r.

Boyce H.

Grier Page 3 March 29, 1979 LER 79-ll/lT

Cause of Event

In the orig:.nal design of the plant the containment isolation valves were assumed to be in the closed position during reactor operation.

The valves were designed and built to remain closed against post-Loca p re s s u re s.

However, subsequent licensing activities resulted in the requirement for inertment of the containment and the need ts use the isolation valves during reactor operation both for inertment, and maintenance of tne Tech Spec requirement of less than 4% oxygen.

The lack of seismic certification of the cont rol air system was due to a design oversight.

The valves do not require air pressure to close (i.e.,

they are spring to close).

However, the fact that air pressure is required to maintain a leak tight pressure boundary during a seismic event was apparently overlooked during the design of the cont rol air system.

The three uninflated seals were caused by misadjustment of the linkage between the valve stem and the 2-way seal chamber p re s s u riz ing valve.

Correcti_ve Action:

Upon discovery of the inability of the valves to close from a full open position against post-LOCA conditions the valves were blocked in a closed position.

Authorization by the Station Superintendent or his alternate was, and still is, required for opening of these valves during operating conditions when primary containment is required.

Openings of these valves under such conditions are restricted to 30 degrees.

The supply pressure to the valves has been adjusted so that the valves will only open to 30 degrees.

These operations 'are addressed in a System Procedure.

Upon discovery of the seismic concern regarding the valve seal air supply a seismically designed system was installed on the containment ventilation isolation valves.

An ar.ound-the-clock effort resulted in the modification being completed by midnight March 16, 1979 on Unit 2 and by March 19, 1979 on Unit 3 (Unit 3 being shutdown for maintenance at this time).

This modification included installation of a ni t ro ge n supply bottle and related piping and valves to supply air to each valve seal.

While the system as presently modified will provide containment isolation as required, it does hamper operational flexibility.

Further modifications, designed to restore the operational flexibility are being implemented expeditiously and are expected to be completed by May 31, 1979.

The system presently includes an alarm which annunciates the valve open (i.e.

valve not fully closed position).

The modification will include revision of this alarm circuit to include a pressure switch monitoring inflatable 2233 042

Mr. Boyce H.

Grier Page 4

  • March 29, 1979 LER 79-11/1T seal pressure so that the alarm will annunciate both the valve not fully closed position and improper seal pressure.

In addition a positive mechanical stop will be installed to further insure limiting the valves to 37 degrees open.

Yours truly,

/ bb 1.

( Cooney S 2erintende t Generation Division-Nuclear Attachment cc:

Director, NRC - Office of Inspection and Enforcement Mr. Norman M.

Haller, NRC - Office of >lanagement &

Program Analysis 2233 043

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