ML20042E178

LER 90-006-01:on 900206,control Room Ventilation Sys Train a Radiation Monitor Went Into High Alarm Condition.Caused by Mechanical Binding of Check source.Geiger-Muller Tube Replaced & Monitor Returned to svc.W/900406 Ltr

ML20042E178
Person / Time
Site:	Seabrook
Issue date:	04/06/1990
From:	Belanger R, Feigenbaum T PUBLIC SERVICE CO. OF NEW HAMPSHIRE
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-006, LER-90-6, NYN-90089, NUDOCS 9004200349
Download: ML20042E178 (5)

Text

. i 1New Hampshire

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l Senior Vice President and Chief Operating CWicer NYN-90089-April 6, 1990 United States Nuclear Regulatory Commission Washington, DC 20555 Attention Document Control Desk-

Reference:

'( a ) . Facility Operating License NPF-67. Docket No. 50-443' (b) Facility Operating License NPF-86, Docket No. 50-443

Subject:

Licensee Event Report (LER) No. 90-006-01: Actuation of

• Control Room Emergency Air Cleanup and Filtration Subsystem due to Failed Radiation Monitor Gentlemen:

Enclosed please find Licensee Event' Report (LER)'No. 90-006-01 for Seabrook. Station. This submittal supplements LER 90-006-00, which documented an event which occurred on February 6, 1990. It also addresses issues of Seabrook Station LERs 90-005-00 and 90-007-00, which reported similiar events that-occurred on February.3, 1990, and February 8, 1990, respectively. This event is being reported pursuant to 10CFR50.73(a)(2)(iv).  ;

Should you require further information regarding this matter, please contact Mr. Richard R. Belanger at (603) 474-9521, extension 4048.

Very t ly.yours,

1. d/ d2k' f Ted . Feig um Enclosures NRC Forms 366, 366A i

9004200349 900406 PDR ADOCK 05000443 k -

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.t New Hampshire Yankee Division of Public Service Company of New Hampshire P.O. Box 300

• Seobrook, NH 03874

• Telephone (603) 474 9521

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' Unite'd State's Nuclear Regulatory Commission April 6, 1990 'i Attention Document Control' Desk Page two.

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cci Mr. Thomas T. Martin-

• l Regional Administrator f United' States Nuclear Regulatory Commission l' Region'I-

• 475 A11endale Road' King of Prussia, PA. 19406 i

'Mr. Victor Nerses, Project Manager' Project l Directorate I-3 United States Nuclear Regulatory Commission Division'of Reactor Projects Washington,'DC 20555

-Mr. Noel Dudley NRC Senior Resident' Inspector P.O. Box 1149'

'Seabrook, NH 03874 INPO Records Center 1100 circle 75 Parkway Atlanta, GA 30339

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l On February 6, 1990 at 6:22 pm EST, following a source check, the control room ventilation system Train A radiation monitor (RM-6506A) went into a high alar:n condition. The monitor is located within the east air intake structure. The alarm condition resulted in the actuation of the Control l

Room Emergency Air Cleanup and Filtration Subsystem (CEA) (VI) and the transfer of the system to its recirculation / filtration mode. The radiation monitor check source became mechanically bound in front of the Geiger-Muller (GM) tube window, causing the monitor to enter into a high alarm condition.

This problem was resolved by smoothing the walls of the guide slots and increasing the tension on the solenoid return spring. However, during this I repair the GM tube became detached from the detector assembly plate. The GM tube was remounted, and a retest of the monitor was unsuccessful because of l damage from the assembly being detached and remounted. The GM tube was replaced, and the monitor was returned to service at 3:54 pm on February 7, 1990. There were no adverse safety consequences as a result of this event.  !

All equipment other than the monitor functioned as designed, fulfilling the Engineered Safety Features (ESP) function.

Previous events involving ESF actuations resulting from failed radiation monitors were reported via Seabrook Station LERs 90-005-00,89-003 00, t 89-001-00 and 87-001-00.

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On February 6, 1990 at 6:22 pm EST, following a cource check the control room _l t

ventilation system Train A radiation monitor (RM-6506A)'went into a high alarm-condition. The monitor is located within the east air intake' structure. The alarm condition resulted in the actuation of the Control Room Emergency Air

• Cleanup'and Filtration Subsystem (CBA) [VI) and the transfer of the system to its recirculation / filtration mode. The event occurred following~an automatic

__ check source test. This check source test:is automatically performed every 24 l hours.

CORRECTIVE ACTIONS l

It appears the radiation monitor check: source became mechanically bound, . such that the check source rod was binding against its guide-slots, resulting in the source remaining po::itioned in front of the GM tube window longer than normal. This caused the monitor'to enter the high alarm condition. The walls of the guide slots were smoothed with emery cloth.and the tension of the solenoid return spring was increased to prevent the binding from recurring.

However, during these activities-the GM tube became detached from the detector assembly plate. The GM tube was remounted, and after a retest of the monitor was unsuccessful because of damage from the assembly being detached and remounted, the GM tube was replaced. The monitor was returned to service at:

3:54 pm on February 7,'1990.

Due to repetitive problems with the east air intake monitors,'RM-6506A&B, '

(see Seabrook Station LERs 90-007-00 and 90-005-00), the west intake monitors, RM-6507A&B, were also checked for rod binding problems. There appeared to be no problems with these monitors. <

To prevent recurrence of this event, a note vill be incorporated'into the surveillance procedures for these monitors to look for.and remove any burre on the check sources rod, to adjust spring tension, if necessary, and to visually verify smoothness of operation. In addition, the routine perfonnance i monitoring and trend analysis activities that have' been it.:plemented will continue to track and evaluate future failures of a similar nature. For long term corrective action, New Hampshire Yankee is evaluating a Design t Coordination Report (DCR) which will address redundant.CBA actuation logic or other appropriate modifications to increase'the reliability of the air intake radiation monitors. -

ROOT CAUSE The root cause'of the monitor failure has been determined to be mechanical binding of the check source. The check source assembly consists of a check source, drive rod and a spring return rotary actuator. The rod / actuator mechanical linkage translates the rotary motion into a rod linear motion.

The drive rod is guided by a long hollow tube. With the requirement for i

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s check source movement the potential exists for. check source misalignment and ' '

2 binding. The binding results in the check source remaining positioned-in M- front of the detector window longer than the automatic test circuit allows, l T' causing the monitor to go into a high alarm condition.. This-results in  !

initiation of the Control Room Emergency. Air Cleanup and Filtration Subsystem .!

V: transferring to its recirculation / filtration mode.  !

3; ~ A review of the- history of the four intake air radiation monitors (RM-6506A&B and RM6507AEB) has been completed. Since 1986, three out of the four intake '

o monitors have had one event each involving a check source binding. The intake-monitors.use a Model RD-7 detector. There are a total.of thirteen RD-7. '

detectors at Seabrook Station. .In over 15,000 check source actuatione'with .

the RD-7 detector since-1986, there have been only eight check source binding-events.

SAFETY CONSEOUENCES

' There were no. adverse safety consequences as a result of this event. . 'All equipment other than the detector check source linkage functioned as designed, fulfilling the Engineered Safety Features (ESP) function. The. failure of the monitor in this manner does not impair the ESF function of the Control Room g Emergency Air Cleanup and Filtration Subsystem and. automatically-places the CBA system in the configuration required.by Seabrook Station Technical

_ Specification 3.3.3.1'.

t PREVIOUS OCCURRENCES L A previous occurrence of an ESF actuation resulting from a radiation monitor d check source binding was reported via Seabrook Station: LER 90-005-0,0.

i Additionally, events involving ESF actuations resulting from failed radiation g monitors were reported via Seabrook Station LERs 89 003-00, 89-001-00~and 4 I

i 87-001-00 however, these events did not result from check source binding. .

Since 1986 there have been only eight check source binding events with the RD -7 detectors , however not all of these resulted in an ESF actuation.

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aw f At the time of this event, Seabrook Station was in Mode 5 cold shutdown.

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