ML19327B561

LER 89-030-00:on 890714,visual Insp Revealed 3/4 Inch Open Conduit Connection Which Would Have Prevented Successful Leak Test.Cause Unknown.Connection Removed & Hole Sealed. W/891026 Ltr

ML19327B561
Person / Time
Site:	McGuire
Issue date:	10/26/1989
From:	Mcconnell T, Sipe A DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-030, LER-89-30, NUDOCS 8911020040
Download: ML19327B561 (8)

Text

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,. Duke Ibu'er Company ' '(704) 875-4000 '

McGuire Nudear Station c

?O Bar488 Cornelius, NC 28a11-0488 DUKEPOWER October 26, 1989 l

i U.S. Nuclear Regulatory Commission '!

. Document Control Desk  !

Washington,-D.C. 20555

Subject:

McGuire Nuclear Station Units 1,and 2 Docket No. 50-369 Licensee Event Report 369/89-30 ,

Gentlemen: t Pursuant to 10 CFR 50.73 Sections (a)(1) and-(d), attached is Licensee' Event ,

Report 369/89-30 concerning an open conduit connection that~ rendered-the' Control- -

Room Ventilation System inoperabic. This report is being submitted in accordance -

with 10 CFR 50.73(a)(2)(1). This event is considered to be of no significance ~-

with respect to the health and safety of the public.

Very truly yours, T.L. cConnell DVE/ADJ/cbl Attachment xc: Mr. S.D. Ebneter American Nuclear Insurers l Administrator, Region II -c/o Dottie Sherman, ANI Library l U.S. Nuclear Regulatory Commission The Exchange, Suit 245. j

l. 101 Marietta St.. NW, Suite 2900 270 Farmington Avenue 2 Atlanta, GA 30323 Farmington, CT 06032 l INPO Records Center Mr. Darl Hood Suite 1500 U.S. Nuclear Regulatory Commission 1100 Circle 75 Parkway Office of Nuclear. Reactor Regulation Atlanta, GA 30339 Washington, D.C. 20555 M&M Nuclear Consultants Mr. P.K. Van Doorn 1 1221 Avenue of the Americas NRC Resident Inspector

-New York, NY 10020 McGuire Nuclear Station 1 9

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R.L. Gill

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R.M. Glover (CNS) >-

T.D. Curtis (ONS)

P.R. Herran i S.S. Kilborn (W)

S.E. LeRoy

-R.E. Lopez-Ibanez J.J. Maher R.O. Sharpe (MNS)

G.B. Swindlehurst-K.D. Thomas L.E. Weaver R.L. Weber

• J.D. Wylie (PSD)

-J.W. Willis QA Tech. Services NRC Coordinator (EC 12/55)

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''' The Control Room Ventilation System Was Technically Inoperable Due To An Open Conduit Connection Because Of Unknown Reasons i EVENT DATE (Si LER NUMSER tel REPORT DATE (7) OTHER F ACILITIES INVOLVED (8) I MONTM DAY YEAR YEAR SE (ouv,6, MONTM DAY YEAR F ACILity hawis DOCKET NUMBEmisi (A L McGuire, Unit 2 o 9 5,o ; o g o i 3,7;0 j i

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OPE st ATING THit REPORT 18 $USMITTED PURSUANT TO THE RtOUIREMENTS OF 10 CPR { (Ched eae er more 8' f** fodo*'ael (118 MOOE m 1 to 73teH210,1 73.71tel 20 402ttil 20 406ts) 20 406teH110) 60 34WH11 50.730eH2 Het 73.711:1 20 406teH1Het 50.38isH2) 50.73teH2Hvu) O ME aec Py Aast ett i 4101 l l ,

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, NAME TELEPHONE NUMBER ARE A CODE Alan Sipe, Chairman, McGuire Safety Review Group 7,0,4 8;7, 5, ,4,,1,8,3 COMPLETE ONE LINE FOR E ACH COMPONENT F AILURE DESCRIBED IN TH18 REPORT (131 CAUSE SYSTEM COMPONENT M' C' "fg Oy"p,"fg'I I

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On July 14, 1989, Bahnson personnel were preparing to perform a visual inspection and a leak test (pressure test) on the modified Train B Outside Air Pressure Filter Train (OAPFT) filter housing of the Control Room Ventilation (VC) system. The visual inspection revealed a 3/4 inch open conduit connection which would have prevented a successful leak test. The Train B OAPFT filter housing was successfully leak tested after the conduit connection was removed and the hole plugged. The open condait connection allowed an additional inleakage of unfiltered air. This leakage could have resulted in the dose to Control Room personnel to exceed that assumed by the design basis analysis. Design Engineering performed a Past Operability Determination that concluded that, although the VC system was technically inoperable, no danger to the Control Room personnel existed for any credible accident which may have occurred. This event is assigned a cause of l

Unknown because it could not be determined why the open conduit connection was not removed, plugged, and sealed when the filter housing was originally modified.

The best estimate is that the original modification was performed in the third quarter of 1980, which was prior to Unit 1 initial fuel loading. Unit I was in, Mode 1 (Power Operation) at 100 percent power and Unit 2 was in Mode 6 (Refueling) when this event was discovered. Unit 2 had previously operated in Mode 1 at 100 percent I power with these conditions existing.

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EVALUATION:  !

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- 1 Background I J

There are two independent trains of the Control Area Ventilation (VC) system i

[EIIS:VI] which are designed to maintain the habitable environment in,the Control Room (EIIS:NA), Control Room Area and Switchgear Rooms, during normal and. accident .

conditions. Based on these criteria,_the system'is designed as an Engineered Safety Features-(ESF) system with absolute and carbon filtration in the outside air intakes and with equipment redundancies for use as conditions require.

The Control Room (CR) is designed to be maintained at a positive pressure during in accident to prevent entry of contaminants. Prior to implementation of Nuclear _-

Station Modification (NSM) MG-52009, each CR VC filter [EIIS':FLT] train assembly consisted of two 50 percent capacity CR pressurization fans [EIIS: FAN] and one

' filter train. Each filter train consists of a pre-filter, a HEPA filter,.a carbon absorber [EIIS: ABS], controls, ductwork [EIIS: DUCT), isolation dampers [EIIS:DMPl.

and two check dampers (EIIS:UDMP]. All of these components are mounted on a common steel channel [EIIS:CHA] base.

, NSM MG-52009 documented replacing the existing two 50 percent capacity fans that ,

serve each of the two redundant Outside Air Pressure Filter Trains-(OAPFT). The two 50 percent capacity fans were replaced with one nuclear grade 100 percent capacity fan in each train. The new 100 percent capacity CR pressurization fans i_ supply 2000 cubic feet per minute (CFM). The OAPFT is provided to_ filter the outside air used for pressurization of the CR and the recirculated air.

l ANSI N510-1975, Sections 5 and 6 require visual inspection and leak testing i follcwing structural changes to a filter housing.

Technical Specification (TS) 3/4.7.6 addresses the requirement where two independent VC systems shall be operable in all modes. In Mode 1 (Power Operation), Mode 2 (Startup), Mode 3 (Hot Standby), and Mode 4.(Hot Shutdown).

l TS requires that with one train of the VC system inoperable, the inoperable train must be restored to operable status within seven days or be in at least Hot Stana within the next six hours, and in Cold Shutdown within the next_ thirty hours. In Modes 5 (Cold Shutdown), and Mode,6 (Refueling) the TS requires the following:

a. With one VC system train inoperable, restore the inoperable train to Operable status within 7 days or initiate and maintain operation of the remaining operable VC system train in the recirculation mode; and

b. With both VC system trains inoperable or with the oper'able VC system train, required to be in the recirculati m mode by Action a. , not capabl.-

of being powered by an operable emergency power source, suspend all operations involving core alterations or positive reactivity. changes.

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TS 3/4.7.6 applies to both Unit 1 and Unit 2 because the VC system is shared by I both units. Also, TS 3/4.7.6 includes requirements that two independent VC trains shall be demonstrated operable at least once each 18 months by verifying a system ,

flow rate of 2000 CFM +/- 10 percent and a CR positive pressure of >/= 0.125 inches l water gauge, relative to outside atmosphere. l Description of Event On July 14, 1989, at approximately 1000, Bahnson personnel were preparing to perform the visual inspection and leak test"on the modified Train B OAPFT filter housing. Bahnson personnel were using Bahnson procedure SP-MNS-11.002, Leak Test For, Duct Housing NSM MG-11905 and 52009. The visual inspection prior to leak testing revealed a 3/4 inch open electrical conduit connection. This 3/4 inch open conduit connection would have prevented a successful leak test. Work request (WR) 953549 was initiated to remove the electrical conduit connection and plug the hole.

The Train B OAPFT filter housing was successfully leak tested after the 3/4 inch conduit connection was removed and the hole plugged.

The Train A OAPFT filter housing was examined to determine if a similar condition existed. This examination revealed that the conduit connection had been removed, plugged, and sealed.

On September 18, 1989, Design Engineering (DE) personnel completed a Pas

• Operability Determination. DE personnel determined that, although the VC system was technically inoperable, no danger to the CR personnel existed for any credible accident which may have occurred.

Conclusion This event is assigned a cause of Unknown, because it could not be determined during the course of this investigation why the 3/4 inch conduit connection on the Train B OAPFT filter housing was not removed, plugged, and sealed. It was determined that modification to the OAPFT filter housings, which resulted in the open conduit connection, was made prior to Unit 1 initial fuel loading. The best estimate is that the modification was performed in the third quarter of 1980. This time frame is based on a documented revision to the manufacturers manual, MCM 1211.00-1526, dated September 12,1980. This modification invelved welding the filter housing outlet dampers in the open position. Welding these dampers in a fixed position would also have necessitated the disconnection of the damper electric operators which could have resulted in the open conduit connection. This conclusion was supported by reviewing the Project Services computer. print outs, for the three types of Nuclear Production Department requested station modifications; Nuclear Problem Report (NPR), Nuclear Station Modification (NSM), and McGuire Exempt Variation Notice (KEVN). There were a total of 67 modification requests identified involving the VC system comprised of 6 NPRs, 45 NSMs, and 16 MEVNs.

None of these modification requests involved welding of the OAPFT outlet dampers in an open position. The WR computer program data base was also searched for a WR involving the removal of the conduit connection on Train A OAPFT housing. No WRs Ngeoxun.. .u.s. cro, u n - +e

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0l0 0l4 or 0 l6 rexv n . ww. .an=wanc em.amaw nn were identified where the description of vork requested ~or action taken involved removal of a conduit connection.

The leak testing pursuant to section 6 of ANSI N510-1975 is similar to the hydrostatic testing of pressure boundry components to verify structural integrity.

This-test is required on new filter housings or on filter housings that have been structurally modified. The periodic testing by station Performance personnel verifies TS requirements for flow rate versus pressure drop across the filter '

L package and the efficiencies of the HEPA filter bank and the charcoal adsorber l bank. The periodic testing would only identify breaches into the filter housing J l that were new, different then previously tested, and large enough to affect indicated test parameters. The effects of the additional inleakage on previous tests would be in a non-conservative direction, increasing the measured leakage by l approximately 1 to 2 percent of the test value. This effect is considered negligible because previous test results were sufficiently within the test acceptance criteria. This is also supported by the fact that Train A and Train B l '

tested filter efficiencies are similar. A visual examination of the filter housing is. performed under periodic test procedure PT/1,2/A/4450/15A, OAPFT OAPFT-2 Visual Inspection, prior to filter efficiency testing. The procedure specifies checks for structural soundness, missing or loose. fasteners, condition of access doors, etc. This procedure also requires that any abnormalities be identified in the provided comments section. A review of completed visual inspection records revealed that such problems as broken bolts and door latches have been identified and evaluated for effects on filter testing. The key issue here is the fact that the conduit connection was not an abnormality because it was there from the time of system turnover from construction. Also, none of the engineers or technicians that tested the system perceived the conduit connection as an opening or breach of the filter housing. Bahnson personnel had an advantage of recognizing the-conduit connection as an opening because they were working on the inside as well as on the outside of the filter housing.

This investigation revealed that WR 501212 was initiated to remove the conduit connection on September 14, 1988. Discussions with the WR initiator, Maintenance Engineering Services (MES) Specialist A, revealed that this WR was written based axi a housekeeping concern only. The MES Specialist did not recognize the conduit connection as being a breach of the filter housing.

A review of the McGuire LER data base for the past 12 months revealed one event, LER 369/88-37 that involved a TS violation with a root cause or contributing cause of Unknown. LER 369/88-37 involved the Ice Condenser system (EIIS:BC). Therefore, this event is not considered recurring since different systems were involved.

As a result of other events involving the VC system identified in LER 369/89-15 and LER 369/89-26, the problem with operability of the VC system in general is considered to be recurring.

This event is not Nuclear Plant Reliability Data System (NPRDS) reportable.

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~There were no personnel injuries radiation overexposures, or releases of radioactive material as a result of this event.

'I CORRECTIVE ACTIONS: I i

Immediate: I The conduit connection was removed and the hole was sealed.

Subsequent: None Planned: None  !

SAFETY ANALYSIS:

The design requirements of the VC system are to supply filtered air at a controlled  !

temperature and humidity to the CR and to pressurize the CR to prevent inleakage of unfiltered air. The VC system helps ensure that doses to CR personnel are ALARA j and remain below Code of Federal Regulations, Title 10, Part 50 (10CFR50), Appendix 1 A, Criteria 19 (GDC-19) limits.

During"a recent modification inspection and test, areas of possible inleakage to the VC system were discovered which could allow unfiltered air to enter the CR at an estimated maximum rate of 27 cfm. These possible sources of leakage were {

properly corrected.

The design basis analysis of the dose to CR personnel assumes an inleakage of 10 cfm to account for CR doors [EIIS:DR] being opened for personnel access. Using the j very conservative assumptions employed for design basis analysis, with.the 2 additional 27 cfm inleakage, the system would not maintain the CR environment in conformance with GDC-19 criteria. The system was thus inoperable according to design basis analysis.

The consequences of an accident with the VC system operation with 27 cfm inleakage would have been reduced by the following factors.which are not considered in the design basis analysis:

1) Dilution of air leaking into the CR by this path by the Auxilia'ry i Building (VA) system [E,IIS:VF]. .

2) Operation of the VA exhaust filters to remove iodine and particulates i from the air leaving the Auxiliary Building [EIIS:hT] . This .

substantially reduces the dose contribution from assumed Emergency Core Cooling System leakage.

3) Substantially lower iodine releases in realistic accidents than those ,

assumed in the design basis accident.

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4) The iodine removal capability of the Containment Spray (NS) system. l

[EIIS:BE] is much greater than that assumed in the design basis I calculation after recirculation of sump water begins.  ;

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5) The CR dose calculation assumes operation of only one train of AnnMus l Ventilation (VE) system [EIIS:VD] along with failure of one train of the "

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( VC system. This double failure assumption adds conservatism.

6) Respirators are available to CR personnel which would reduce dose during _

periods when contaminated air is being drawn into the CR.

7) The average deposition factor assumed for inleakage is conservative and is assumed to exist for the entire 30 day accident period.

Consideration of these factors would result in CR doses well below GDC-19 limits.

Thus, although the system was technically inoperable, no danger to the CR personnel existed for any credible accident which may have occurred.

This event did not affect the health and safety of the public.

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