ML20012F518

LER 90-010-00:on 900305,actuation of Control Room Emergency Air Cleanup & Filtration Subsystem Occurred.Caused by Moisture in Detector Housing.Air Intake Monitors Cleaned & Desiccant Placed in housing.W/900404 Ltr

ML20012F518
Person / Time
Site:	Seabrook
Issue date:	04/04/1990
From:	Belanger R, Feigenbaum T PUBLIC SERVICE CO. OF NEW HAMPSHIRE
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-010, LER-90-10, NYN-90087, NUDOCS 9004160063
Download: ML20012F518 (5)

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Seer V,ce Preside nt and l Chief Opwating OHkw j i

L NYN-90087 I

(- , April 4, 1990 United States Nuclear Regulatory Commission Washington, DC 20555 l I

Attention: Document Control Desk I

References (a) Facility Operating License NPF-67. Docket No. 50 443  !

H (b) Facility Operating License NPF-86 Docket No. 50-443 l l

Subjects Licensee Event Report (LER) No. 90 010 00: Actuation of j

, Control Room Emergency Air Cleanup and Filtration Subsystem i due to Failed Radiation Monitor t Gentlemen: r Enclosed please find Licensee Event Report (LER) No.90-010 00 for i Seabrook Station. This submittal documents an event which occurred on ,

. March 5, 1990, and is being reported pursuant to 10CFR50.73(a)(2)(iv). I

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t Should you require further information regarding this matter, please  !

contact Mr. Richard R. Belanger at (603) 474 9521, extension A048 r i

Ver truly yours, crc / (2n k[ V Ted C. Feige M ,

Enclosures NRC Forms 366, 366A i

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9004160063 9004o4

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

• Seabrook, NH 03874

• Telephone (603) 474 9521

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United States Nuclear Regulatory Commission April 4. 1990 Attention Document Control Desk Page two l

l cca Mr. Thomas T. Martin I Regional Administrator  !

c United States Nuclear Regulatory Commission Region I l 475 Allendale Road -

King of Prussia. PA 19406 Mr. Victor Neroes. Project Manager

([k 1 . Project Directorate 1 3 }

United States Nuclear Regulatory Commissio.1 Division of Reactor Projects Washington, DC 20555 '

t Mr. Noel Dudley NRC Senior Resident Inspector  ;

P.O. Box 1149  !

Seabrook, NH 03874 INPO ,

Records Center  !

1100 circle 75 Parkway  ;

Atlanta, GA 30339 t

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t On March 5, 1990. at 9842 a.m., a Control Room Emergency Air Cleanup and Filtration Subsystem (CBA) automatic recirculation signal was received after one of the east air intake radiation monitors. RH-6506B. spiked into a high ,

alarm condition.

The root cauce of this event has been determined to be moisture in the detector housing. This moisture condensed on the Geiger-Huller (GM) tube 4 leads when exposed to cold process air and resulted in a spike. The spike l caused the monitor to enter a high alarm condition which in turn caused the transfer of CBA to its recirculation / filtration mode.

Both east air intake monitors have been cleaned and desiccant has been placed i in the housings to keep them dry. A long term corrective action that is presently being evaluated is to move the east intake monitors into the Diesel Generator Building. Redundant CBA actuation logic is als6 being evaluated.

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. ,

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On March 5. 1990, at 9:42 a.m. EST, the train B east air intake radiation r, monitor. RM-65063. spiked, causing a high alarm condition. This condition

" initiated the Control Room Emergency Air Closaup and Filtration Subsystem L (CBA) (VI) and the subsequent transfer of the system to its recticulation/

filtration mode.

ROOT CAUSE Upon investigation it was determined that moisture had accumulated within the detector assembly. This caused a direct connection between the two lead wires of the Geiger-Muller (GM) tube. This simulated a detector saturation condition and caused the monitor to spike.

The root cause of the spike was the entrapment of moist air within the detector assembly during maintenance. This moist air was then exposed to cold process air which caused the moisture to condense. It was this

- condensation on the GM tube leads which caused the spike, and caused the monitor to enter the high alarm condition and subsequent CBA actuation.

CORRECTIVE ACTION RM-6506B was dried and returned to service. The train A east air intake monitor. RM-6506A. was checked and found to also have moisture within the housing. It was also dried and returned to service. Desiccant packs have been placed in both monitor housings to remove moisture.

For long term corrective action. New Hampshire Yankee is evaluating a Design Coordination Report (DCR) to relocate the east air intake monitors to the Diesel Generator Building. This will allow the monitors to experience warmer T process air conditions. Prcsently these monitors are located close to the air inlet while their counterpart west air intake monitors are located in the Diesel Generator Building over 400 feet away from the inlet. This would place the east intake monitors in approximately the same conditions as the west air intake radiation monitors which have a history of more reliable performance.

. Currently CBA is actuated by any one signal from either the train A or B,

[ east or west air intake radiation monitor. This is one of one actuation logic. A redundant actuation logic or other appropriate modifications for the air intake radiation monitors are being evaluated. The intent of f modifications being considered will be to reduce spurious initiations of CBA

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while assuring continued reliability of the system.

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There were no adverse safety consequences as a result of this event. All equipment other than the monitor functioned as designed, fulfilling the L Engineered Safety Features (EST) function. The failure of the monitor in l this manner does not impair the ESF function of the Control Room Emergency l Air Cleanup and Filtration Subsystem and automatically places the CBA system  !

in the cuafiguration required by Seabrook Station Technical Specification L 3.3.3.1. ,

PREVIOUS OCCURRENCES Previous occurrences of Engineered Safety Features (ESP) actuations involving {

f ailed radiation monitors were reported vik Seabrook Station 1,ERs 90 007 00.  ;

9%006-01, 90 005 00. 89 003 00, 69 00100 and 87 00100.

f At the time of this event. Seabrook Station was in MODE 3. Hot Standby, with i a Reactor Coolant System temperature of 557'F and pressure of 2235 psi.

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