ML19327B151

LER 89-026-00:on 890720,both Trains of Control Area Ventilation Sys Inoperable.Caused by Design Deficiency Because of Unanticipated Interaction of Components.Original Check Damper Reinstalled in Fan on Train B.W/891019 Ltr

ML19327B151
Person / Time
Site:	McGuire
Issue date:	10/19/1989
From:	Mcconnell T, Sipe A DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-026-01, LER-89-26-1, NUDOCS 8910250328
Download: ML19327B151 (11)

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. Dukeher Com;>any ' M4)!M McGuirr Nuclear Station

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.L DUKEPOWER October 19, 1989 i

U.S. Nuclear Regulatory Comenission

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Subject:

M Guire Nuclear Station Units 1 and 2 i

Docket No. 50-369 5 p Licensee Event Report 369/89-26 j

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Gentlemen: '

Pursuant to 10 CFR 50.73 Sections (a)(1) and (d), attached is Licensee Event i Report 369/89-26 concerning both trains of the Control Area Ventilation System t being inoperable because of Design Deficiency. This report'is being submitted in  !

accordance with 10 CFR 50.73(a)(2)(i). This event is considered to be of no significance with respect to the health and safety of the public.  ;

Very truly yours,  !

-b) do k ksAf T.L. McConnell '

DVE/ADJ/cb1 Attachment

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Mr. S.D; Ebneter American Nuclear lnsurers

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Administrator, Region II c/o Dottie Sherman, ANI Library  !

U.S. Nuclear Regulatory Comission The Exchange, Suit 245  ;

101 Marietta St. NW, Suite 2900 270 Farmington Avenue 't 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 ,

1221 Avenue of the Americas NRC Resident Inspector New York, NY 10020 [

McGuire Nuclear Station 8910250328 891019 PDR ADOCK 05000369 79-  ;

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" Cover Letter Page 2 bact B.W. Bline A.S. Daughtridge y- R.C. Futrell R.L. Gill R.M. Glover (CNS) 7.D. Curtis (ONS).

P.R. Herran S.S. Kilborn ()[)

S.E. LeRoy R.E. Lopez-Ibanez J.J. Maher R.O. Sharpe (MNS) s 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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"'t Both Train's Of The Control Area Ventilation System Were Inoperable Enemune Of A Damien Deficiency That Deleted A check D=-ar tve=1 n i ua muus . ici atro.1 ti n iti or tn enciut n inve6vte ei

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, M eSD4eH1Hel M ?SteH2Het to.?3isitt Hal OctNett coast.ct von tugt Lam etti NAt itLtPMONE kvwsta amt.copt Alan Sipe, Chairman, McGuire Safety Review Group 7, O i 4 8,7 i 5, ,4 ,1,8,3 C0eePLtil CN4 UNE SOR I.CN COMPONENT f.4Lupt patcmesp sN tMis atPoet tsp 8vstle Coup 0 Nth? n}P0g,1,ag,l gaygg g y gg g, egy,oggg, p.Ngg.C n4Pog,1,agg p

t C.WSt "'"${.C- o I I I I l i I I I i 1 l l I l l l I i l l I I I I I l l MONin p. . tam SuPPLlutNT.L mtPont IRPictID ttei vtS 199 von remeen $KpfCTfD $VOttl5SION De tti %Q l l l t . .ct ,o~, ,e .. .e. . ,w . ,s . e..,-. . ,, , . - , n.1 On July 20, 1989, Performance personnel began Post Modification Testing (PMT) to functionally verify the operation of the Outside Air Pressure Filter Train (OAPFT) fan on Train B of the Control Area Ventilation (VC) system. The OAPFT was originally designed with two 50 percent capacity fans. Because of maintenance anst reliability problems and space limitations, a Nuclear Station Modification (NSM) was written to change these fans to one 100 percent capacity fan. While performing the PMT, Performance personnel determined that both VC system Trains A and B may have been inoperable becaur,e the NSM deleted a check damper on Train B. With this check damper removed and the VC system in certain operating modes, a condition could exist where more air could be recirculated through the failed OAPFT rather than air being pulled in f rom outside. This would decrease the ability of the operating OAPFT fan to pressurire the Control Room. On September 19, 1989, Design Engineering (DE) personnel confirmed that the VC system Train A could not be justified operable with the check damper removed and isolation dampers open on Train B. Unit I was in Mode 1 (Power Operation) at 100 percent power and Unit 2 was in No Mode (Core Unloaded) at the time this event was discovered. This event is assigned a cause of Design Deficiency because of an unanticipated interaction of components ano a mechanical functional design deficiency. The original check damper was reinstalled in OAPFT fan on Train B. ,

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EVALUATION:

Background

l There are two independent trains of the Control Area Ventilation [EIIS:VI) (VC)  !

system which are designed to maintain the habitable environment in the Control Room l

[EIIS:NA), Control Room Area, and Switchgear Rooms, during normal end accident conditions. Based on these criteria, the system is designed as an Engineered i Safety Features (EST) (EIIS JE] system with absolute and carbon filtration in the  ;

outside air intakes and with equipment redundancies for use as conditions require.

The Control Room is designed to be maintained at a positive pressure during an i accident to prevent entry of contaminants. Prior to implementation of NSM MG-52009 each VC filter [EIIS:FLT] train assembly consisted of two 50 percent capacity  ;

Control Room pressurization fans [EIIS FAN} and one filter train. Each filter  !

train consisted of a pre-filter, a HEPA filter, a carbon absorber [EIIS: ABS), i controls, ductwork [EIIS DUCT), isolation dampers [EIIS:DMP), and two check dampers

[EIIS:UDMP] (see drawing on page 8 of 9). 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 bought l from Brad-McClung-Pace, Inc. that serve each of the two redundant OAPFTs. The i frames for the 50 percent capacity fans were weakening from stress cracks, and  ;

bearing replacements were common. Based on the fact that the fans saw limited run l

time and had preventative maintenance performed on them but still failed '

frequently, the fans were considered unreliable. Therefore, two commercial grade 50 percent capacity fans were replaced wit _h one nuclear grade 100 percent capacity fan. This modification also deleted the check damper mounted at the discharge of each OAPFT fan. The new 100 percent capacity Control Room pressurization fans supply 2000 cubic feet per minute (CFM) each, one per train. The OAPFT is provided .

to filter the outside air used for pressurization of the Control Room and the air .

l recirculated from the Control Room before being returned through the Control Room Ventalation fans (see drawing on page 9 of 9).  ;

l Technical Specification (TS) 3/4.7.6 addresses the requirement where two , '

independent VC systems shall be operable in all modes. In Mode 1, Mode 2  ;

(Startup), Mode 3 (Hot Standby), and Mode 4 (Hot Shutdown), the 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 Standby.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 recirculation mode; and

b. With both VC system trains inoperable or with the operable VC system train, required to be in the recirculation mode by Action a., not capable of being powered by an operable emergency power source, suspend all operations involving core alterations or positive reactivity changes.

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. s== =ac w ana w on TS 3/4.7.6 applies to both Unit 1 and Unit 2 because the VC system is shared by 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 Control Room positive pressure of >/=

0.125 inches water gauge, rel4tive to outside atmosphere.

On May 12, 1989, the NRC issued Amendment Number 95 to Facility opera' ting License NPF-9 and Amendment Number 77 to Facility Operating License NPF-17 for the McGuire Nuclear Station (MNS) Unit 1 and Unit 2. These amendments changed the TSs to authorize a one time extension of the allowed outage time for the VC system to provide for system modification. The allowed outage time extension was 21 days for each train, with one train inoperable at a time and one of the two MNS units in a re-fueling outage with no transport of toxic gas containers on site.

Description of Event On July 6, 1989, the VC system Train A was tested satisfactorily in accordance with procedure pT/0/A/4450/080, Control Area Ventilation Performance Test. This allowed Train B to be taken out of service for implementation of modifications. On July 10, 1989, work request 96690 was signed by Operations (OPS) personnel for NSM MG-52009 to be implemented on Train B. Train B was declared inoperable on July 9, 1989 at 1900. During implementation of the NSM, Trains A and B of the VC system were isolated from each other. On July 14, 1989, the NSM work on Train B was completed by the Bahnson Service Company. VC Trains A and B were then unisolated from each other. Unit 2 was in Mode 6 from July 14, 1989 until July 19, 1989. On July 19, 1989, Unit 2 entered No Mode.

On July 20, 1989 at 0600, Performance personnel began PMT for the Train B OAPFT fan as required by procedure TT/0/A/9100/334, Post-Modification Testing of CRA-0APFT-2 After Implementation Of NSM MG-11905, Revision 0 and NSM MG-52009, Revision 0. At 0730, the VC system had trouble maintaining the Control Room pressure in accordance with the requirements of the test procedure. At 0845, Performance personnel began 1 troubleshooting to determine if any alignment existed for which enough outside air could be pulled in to pressurize the Control Room. With Train A.OAPFT fans not operating and isolation dampers failed open, DP measurements were taken on Train A ]

OAPFT package with both check dampers closed and while holding both check dampers open. With the Train B fan operating, Performance personnel observed reverse flow through the Train A filter package.

This reverse flow is a flow path of lower j resistance as compared to the outside intakes. Initial reverse flow through the i filter Train A with the check damper closed was approximately 200 CFM and reverso l flow with the check damper open was approximately 675 CFM. Performance personnel  !

reviewed this data with Station Management and DE personnel. Performance personnel emphasized their concern of operability which may arise if the modification is continued and irrplemented on Train A with deletion of the check damper on Train A.

With the NSM complete on Train B, the new fan without the check damper was capable of pressurizing the Control Room; however, in the condition where one OAPFT fan was operating and the other OAPFT fan had a pneumatic or power failure, the condition existed with the check damper deleted where there would not be enough outside air pulled in to pressurize the Control Room. During PMT on VC Train B, the Train B check damper was deleted; however, Train A check dampers remained installed.

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On July 20, 1989, at 2200, OPS personnel were notified by Performance personnel {

that a possible condition on the Train A OAPFT, the operable train at the time, '

existed where reverse flow through Train B OAPFT could occur. Therefore, at 2315, the manual volume dampers were positioned to ensure the operability of VC Train A  :

would be maintained while Train B was still inoperable. The red tags associated l with Removal and Restoration (R&R) number 09-876 were added to the VC Train B work '

request to ensure that when Train B was completely checked out the manual volume i dampers would be restored to their proper operable status. '

Construction and Maintenance Department (CMD) personnel initiated a Variation Notice MC-2145 on July 21, 1989, to re-install the original check damper in the VC Train B OAPTT fan. At 2030, the check damper was re-installed and checkout was completed by Instrumentation and Electrical personnel. At 2210, OPS personnel cleared the red tags and repositioned the manual volume dampers according to R&R 09-876, thereby ensuring VC Train A operability. VC Train B check damper was then ,

able to limit backflow through Trein B OAPFT if Train A OAPFT was operating. On July 23, 1989, at 0914 VC Train B was declared operable thereby allowing the modifications to begin on VC Train A.

DE personnel completed their evaluation of this condition on September 19, 1989 and determined that Train A VC could not be justified operable with the check damper removed and the isolation dampers opened or Train b VC. Therefore, it was determined that TS 3.7.6 had been violated because both VC trains were inoperable from July 14, 1989 to July 20, 1989.

Conclusion This event is assigned a cause of Design Deficiency because of an unanticipated interaction of components and a mechanical functional design deficiency. DE personnel deleted the check dampers because of an oversight. The review by DE personnel of the deletion of the two 50 percent capacity fans on each OAPFT and the replacement of one 100 percent capacity fan on each OAPFT determined that the check dampers were unnecessary. The check damper's original design criteria was twofold

- to prevent air from shott-cycling between the two 50 percent fans, and to prevent reverse flow through the filter train.

Cycling between the 50 percent fans could only occur when the adjoining fan had failed. In this case, only one fan providing 1000 CFM of air was available. This amount of air was not adequate to maintain the habitability of the Control Ro e.

The station had always considered a filter train inoperable if one of two associated 50 percent fans had failed. Because the NSM replaced the two 50 percent fans with one 100 percent fan, a check damper would not be needed to prevent short-cycling.

The second check damper design criteria was to prevent reverse flow through the OAPFT. When an OAPFT was not in operation, isolation dampers located at the OAPFT inlet and at each fan discharge prevented flow through the train. During normal plant operation, the filter train was not operated and the isolation dampers were closed. Upon fan start, the isolation dampers automatically opened. The isolation dampers " fail safe" position is open, to allow filtered air into the Control Room.

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0l 0 0 [5 Only during an emergency condition concurrent with a fan mechanical failure or power failure would the check dampers be required to prevent reverse flow through the failed filter train. With the modification, this condition was not known to exist until the PMT was performed.

The decision made by DE personnel to delete the check dampers on NSM MG-52009 was based on damper construction, damper quality, and pressure restriction through the filter. The check dampers are Ruskin model CBS4. They are of lightweight  ;

construction, and have no internal seals. The check dampers only restrict reverse flow through the filter train, not the recirculation from the Control Room duct.

With a flow of 2000 CFM, the pressure drop through the filter train varies from 3  !

to 4.5 inches of water. Because of this pressure restriction, DE personnel stated that recirculation through the inoperable VC train recirculation duct would occur more easily than flow through the failed filter train (with or without the check damper (s)). This configuration with the manual volume dampers in the recirculation duct open, had been previously tested satisfactorily. The decision to delete the check dampers took all of these points into consideration.

If this problem had not been discovered and NSM MG-52009 was completed as designed dampers on both Train A and Train B would have been deleted. If a VC OAPFT fan was operating because of an EST actuation and the other VC OAPTT fan had a mechanical ,

failure with the isolation dampers in a fail-safe open position, this would have '

caused a condition to exist where there would be reverse flow t.? tough the failed OAPFT fan. This would have degraded the ability of the operating OAPFT fan to maintain the required Control Room pressurization of + 0.125 inches of water gauge or greater.

The original check dampers were re-installed in both OAPFT fans for Trains A and B according to Variation Notices written under NSM MG-52009.

Also, NSM MG-52282 was initiated for DE personnel to replace the check dampers with new check dampers with blade or jamb seals or both, and suitable frame and blade construction. These new check dampers would leak less than the existing dampers, thereby aiding system balancing. The amount of outside air provided to the Control Room will increase as recirculation air decreases and thereby increase the margin to maintain the positive pressure in the Control Room.

A review of McGuire Licensee Event Reports (LERs) for the past 12 months revealed two TS violation events on ventilation systems, LER 369/88-19 and LER 369/89-15, with a root cause or contributing cause of Design Oversight. Therefore, this event is considered recurring. LER 369/88-19 documented an event concerning the Hydrogen Skimmer System dampern. Corrective actions as a result of this event would not have prevented this event from occurring. LER 369/89-15 documented an event on the VC system and was discovered during the same PMT testing of NSM MG-52009 as was this event. The corrective actions as a result of LER 369/89-15 would not have prevented this current event from occurring.

LERs 369/89-06 documented a misplaced solenoid [EIIS: SOL] arrangement of valve

[EIIS:V] 1NV-459, Main Letdown Orifice Isolation, because of a Design Deficiency.

LER 369/88-28 documented misplaced solenoid valves on the Main Steam [EIIS:SB) l l

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0l 0 0l 6 or 0l9 Isolation valves [EIIS:ISV) because of incorrect instrument detail drawings. LER 369/89-07 documented misplaced solenoid valves on the Chilled Water system

[EIIS:KM] and the Nuclear Service Water system [EIIS:BI] because of a Design Deficiency because Design Engineering personnel approved unqualified material for installation. LER 369/88-36 documented a deficiency functional design of the I'1esel Generator Starting Air [EIIS:LC] and Instrument Air [EIIS:LD] systems because of a Design Deficiency. LER 369/89-27 documented a Design Deficiency because the wrong setpoint for a DP switch in the Annulus Ventilation System

[EIJS VD) was selected. Events caused by Design Deficiencies are considered recurring problem's.

As a result of other events involving Ventilation System problems caused by Design Deficiencies, the problem of TS violations caused by Desigr. Deficiencies in general is considered to be recurring.

DE personnel are documenting the Design Bases of Safety Related Systems which included ventilation systems. This has enabled DE personnel to identify, evaluate and correct Design Deficiencies.

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

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

CORRECTIVE ACTIONS:

Immediate: OPS personnel positioned dampers to ensure operability of VC Train A.

Subsequent: 1) CMD personnel reinstalled the original check damper in OAPFT  !

fan on Train B according to Variation Notice MC-2145 ,

2) OPS personnel repositioned the dampers on VC Train B and maintained VC Train A operable.

3) CMD personnel reinstalled the original' check damper l'n OAPFT fan on Train A according to McGuire Nuclear Production Variation Notice, MPVN-999. .

Planned: 1) According to NSM MG-52282, DE will purchase check dampers with blade or jamb seals or both, and suitable frame and blade construction which will meet required specifications.

2)- Project Services personnel will ensure the new check dampers will be installed.

SAFETY ANALYSIS:

The function of the OAPFT fans is to maintain a positive pressure in the Control Room to prevent in-leakage of potentially contaminated (unfiltered) air. The OAPM OUshe $ $ '? ' '

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0l2l6 0l0 0l7 or 0 l9 vent en . .e - aac e amm on fans provide outside air (required for pressutization) through the Control Room filter package. {

During an accident requiring pressurization of the Control Room, both trains of OAPFT receive an automatic start signal. The VC system is designed to pressurize ,

the Control Room with either train operating. The post modification testing was  ;

designed to verify the proper operation of the VC system af ter modifying the i system. The post modification test determined that one OAPFT fan would not fully pressurize the Control Room with the check dampers removed. Therefore, the B train '

check damper was reinstalled prior to returning Train B 0/.PFT to service.

During the time that Train B OAPFT was being tested, no design basis events i occurred. Had a design basis event occurred, Train A OAPFT would have been available to provide air to the Control Room for pressurization. It is unknown whether Train A OAPFT would have fully pressurized the Control Room with Train B OAPFT check damper removed. However, had a design basis event occurred while Train B OAPFT was being tested. Train B OAPFT could have been made available for ,

operation, in which case the removed check damper would not have had any impact on  ;

either train's performance. ,

The principle contaminant in air leaking into the Control Room is assumed to be ,

iodine which is very conservatively modeled in dose calculations. Very low amounts of iodine would be expected to reach the area around the Control Room since this required passage through either Auxiliary or Turbine Building ventilation systems ,

or passageways.

Control Room Operator dose would be further reduced by operation of the Auxiliary .

Building Ventilation system which is not safety related, but has been maintained to safety standards.  ?

In the event that Control Room atmosphere became unbreathable, self contained breathing apparatus respirators provided in the Control Room area could be employed. Radiation monitors in the Control Room would alert Control Room personnel of high radiation levels.

Had a design basis accident occurred during the post modification testing of Train  !

B OAPFT, the dose to Control Room personnel would have been well within 10CFR100 limits.

The health and safety of the public were not affected by this event.

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