PNO-V-88-013A, on 880114,reactor Bldg Overpressurization Occurred.Investigation Revealed That High/Low Pressure Trip Circuit for Train 'B' Fan Trip Circuit Inoperable.Licensee Continuing Investigation to Determine Root Cause

PNO-V-88-013A:on 880114,reactor Bldg Overpressurization Occurred.Investigation Revealed That High/Low Pressure Trip Circuit for Train 'B' Fan Trip Circuit Inoperable.Licensee Continuing Investigation to Determine Root Cause

ML20147B072
Person / Time
Site:	North Carolina State University
Issue date:	02/19/1988
From:	Bosted C, Johnson P NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
To:
References
PNO-V-88-013A, PNO-V-88-13A, NUDOCS 8803010438
Download: ML20147B072 (2)

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d I PRELIMINARY NOTIFICATION OF EGi 3 UNUSUAL OCCURRENCE--PNO-V-88-13A Date 02/19/88 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information presented is as initially received without verification or evaluation and is basically all that is known by Region V staff on this -

data.

FACILITY: Washington Public Power Supply System Emergency Classification WNP-2 Notification of Unusual Event DOCKET NO. 50-297 Alert Richland, Washington ' Site Area Errergency General Emergency XX Not Applicable

SUBJECT:

UPDATE ON FAILURE OF SECONDARY CONTAINMENT The plant is~ currently in Mode 4 (cold shutdown). The licensee continued their evaluation of the reactor building overpressurization which occurred on January 14, 1988, to determine the sequence and root cause of the event. As of February 18, 1988, the licensee had detennined the following:

o An inspection (per NRC Bulletin 88-01) was completed on the 480 VAC breakers for the reactor building air supply and exhaust fans. The breaker for supply fan ROA-FN-1A was the last to be completed, o' The equipment operator (EO) was instructed to "rack in" the breaker for fan ROA-FN-1A.

He racked.in the breaker and installed the fuse blocks for the closing and trip circuit control power, but failed to verify that the position indicating light on the breaker was indicat';ng that the breaker was open (indication powered from trip circuit; light would have indicated trip circtit energized),

o At approximately(9:40 room supervisor CRS) top.m. thenonnal restart reactorRaactor operator (RO) ventilation.

Building was instructed by the control In preparation, the R0 moved the remote control switch for fan ROA-FN-1A from PULL TO LOCK to NORMAL.

The RO noted before doing so, that the breakee position light was not lighted, but he thought that the bulb had burned out. Fan ROA-FN-IA apparently autostarted when the control switch was placed in NORMAL. The autostart feature is provided to start the opposite fan when (1) the breaker is closed (closes the "a" contact in the opposite fan control circuit) and, (2) a low DP exists across the fans. These conditions vere met which caused fan ROA-FN-1A to start. Although, this was not imediately indicated to the RO. A system overpressure trip at +4" H,0 apparently functioned, but did not result in a trip of the fan because the trip tircuit was deenergized.

I a After moving the switch, the RO checked the light bulb and determined that the bulb l was satisfactory. The control switch was then returned to the PULL TO LOCK position.

o The R0 and the CRS noticed that the Reactor Building pressure had exceeded full l scale (later determined to be approximately 13" by extrapolation) and then decreased l to about 1.6', The presst.re decrease to 1.6", apparently resulted from the opening l created in the building roof by overpressure. The recorder trace indicated that the fan ran for approximately 2 minutes before the roof failed. The E0 and the shift support supervisor (SSS) verified that the fuse blocks were correctly installed and Itcally tripped the fan breaker. By this time, the fan had been running for a total of approximately 9 minutes.

PY f "O PNO-V-88-013A PDR b #

o .The CRS directed the E0 to bring both the open and close fuse blocks to the control room. All fuses were replaced. These fuses were later tested as good; but, one of

-the fuse blocks was determined to have a loose fit on one end of one fuse. This can'd have made an intermittent connection, o- When the fuses were reinstalled, the RO took fan ROA-FN-1A control switch from PULL TO LOCK to NORMAL; the fan started without the R0 going to the start

. position on the switch. The RO then started the exhaust fan. <

o At approximately 11:30 pm, the oncoming E0 identified that a large number of nuts and bolts were scattered on the refueling floor. Shortly after, the shift manager (SM) determined that the roof was damaged and declared the secondary containment inoperable.

Additional Comments o Subsequent investigation also revealed that the high/ low pressure trip circuit for the Train "B" fans. trip function has.been inoperable (not a factor in this event). The "a" contacts in the closing circuits for both Trains were found to be bypassed, o The roof and walls were installed with shear bolts, which were designed to shear at about 14". Burns & Roe apparently intended the roof to relieve first (possible concern about personnel liability due to wall panels falling off).

The licensee is continuing their investigation to determine the root cause and contributing factors to the event. The resident inspectors and Region V personnel are continuing to  ;

cvaluate the licensee's progress on this matter.  ;

This information is current as of 4:30 pm (PST) February 18, 1988.  ;

CONTACT: P. Johnson C. Bosted .

FTS 463-3745 (509) 377-2627 l

91STRIBUTION MADE BY 5520 T0: FAX TO: .

Date Time Date Time Chairman Zech EDO RI INPO //;JG Comm. Roberts AEOD RII NSAC //: 2J' Comm. Bernthal PA0 RIII LICENSEE Comm. Carr SLITF RIV RESIDENT INSPECTOR ///ft? .

Comm. Rogers. NRR PQS. OPERATIONS OFFICER //.'le?

SFCv NMSS CA~ ARM MAIL TO: '

POR O! DCS (Original)

OGC OIA DOT:(Trans.Only.ApplicableState)

ACRS RES GPA RV FORM 211 Revised: 8/19/87 l I

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