05000339/LER-1981-051-03, /03L-0:on 810620,pressurizer Power Operated Relief Valve Nitrogen Supply Tank Pressure Dropped Below Required Min for Low Temp RCS Overpressurization Protection.Caused by Sys Leaks.Tanks Floated on Primary Nitrogen Supply Tr

/03L-0:on 810620,pressurizer Power Operated Relief Valve Nitrogen Supply Tank Pressure Dropped Below Required Min for Low Temp RCS Overpressurization Protection.Caused by Sys Leaks.Tanks Floated on Primary Nitrogen Supply Truck

ML20009E705
Person / Time
Site:	North Anna
Issue date:	07/15/1981
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20009E684	List: 05000339/LER-1981-051, Forwards LER 81-051/03L-0 05000339/LER-1981-051-03, /03L-0:on 810620,pressurizer Power Operated Relief Valve Nitrogen Supply Tank Pressure Dropped Below Required Min for Low Temp RCS Overpressurization Protection.Caused by Sys Leaks.Tanks Floated on Primary Nitrogen Supply Tr
References
LER-81-051-03L, LER-81-51-3L, NUDOCS 8107280375
Download: ML20009E705 (3)

LER-1981-051, /03L-0:on 810620,pressurizer Power Operated Relief Valve Nitrogen Supply Tank Pressure Dropped Below Required Min for Low Temp RCS Overpressurization Protection.Caused by Sys Leaks.Tanks Floated on Primary Nitrogen Supply Truck

Event date:
Report date:
3391981051R03 - NRC Website

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r U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVEF REPORT i

4 CONTROL BLOCK / / / / / / / (1)

(PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION)

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LICENSEE CODE LICENSE NUMBER LICENSE TYPE CAT

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DOCKET NUMBER EVENT DATE REPORT DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES (10)

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/ On June 20, 1981, with Unit 2 in Hot Shutdown, pressure in both pressurizer PORV /

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/ nitrogen supply tanks dropped below the minimum required to operate the pressuri-/

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/ zer PORV's in a mannec consistent with the design basis (120 minimum available

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/ valve cycles) for low temperature RCS overpressurization protection.

This event /

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/ is reportable pursuant to T.S. 6.9.1.9.b.

The action statement of the LCO (T.S. /

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/ 3.4.9.3) was met.

The public health and safety were not affected.

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COMP.

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SYSTEM

CAUSE

CAUSE CODE CODE SUBCODE COMPONENT CODE SUBCODE SUBCODE

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ACTION FUTURE EFFECT SHUTDOWN ATTACHMENT NPRD-4 PRIME COMP.

COMPONENT TAKEN ACTION ON PLANT METHOD HOURS SUBMITTED FORM SUB. SUPPLIER MANUFACTURER

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CAUSE DESCRIPTTON AND CORRECTIVE ACTIONS (27)

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/ Leaks in both pressurizer PORV nitrogen low temperature RCS overpressurization

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/ systems caused the nitrogen tanks to depressurize. The tanks were floated on the/

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/ the primary plant nitrogen supply bottle truck to maintain adequate pressure.

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/ Repairs to reduce leakage have been made.

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FACILITY METHOD OF STATUS

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Operator Observation

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LOCATION OF RELEASE (36)

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PERSONNEL EXPOSURES NUMBER TYPE DESCRIPTION (39)

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LOSS OF OR DAMAGE TO FACILITY (43)

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PUBLICITY ISSUED DESCRIPTION (45)

NRC USE ONLY

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9107290375 s10715

'ER W. R. CARTWRIGHT PHONE (703) 894-5151 PDR ADOCK 05000339

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PDR

r Virginia Electric and Power Company North Anna Power Station, Unit #2

Attachment:

Page 1 of 2 Docket No. 50-339 Report No. LER 81-051/03L-0

Description of Event

Low temperature RCS overpressurization protection is provided by two pressurizer PORV's.

When the pressurizer PORV's are operated in " low temperature RCS overpressurization protection mode" each PORV receives its motive power from-its own nitrogen tank via step down regulators and a control solenoid operated valve.

In order to provide 120 valve cycles (to meet no operator action for 10 minutes with 5 seconds per valve cycle design criteria), each tank must be pressurized 'o 1725 psig. Alarms are provided in the Control Room which are operated by a pressure switch on each nitrogen tank.

Tank pressure indication is not provided in the Control Room, but is provided locally in the containment.

The setpoint for the alarm pressure switches and an operability criteria for low temperature RCS overpressurization protection as provided by eacb PORV, is a tank pressure of 1775 psig (50 psig above the minimum required to account for instrumentation error).

On June 20, 1981, at approximately 1945, with Unit 2 in Hot Shutdown, the pressure in one of the pressurizer PORV nitrogen supply tanks dropped below 1775 psig rendering one of the pressurizer PORV's inoperable.

At 2145 on June 20, 1981, the pressure in the remaining pressurizer PORV nitrogen supply tank dropped below 1775 psig rendering the remaining pressurizer PORV inoperable for low temperature RCS overpressurization protection.

This event is reportable pursuant to T.S. 6.9.1.9.b.

Probable Ce ces of Occurrence The ability of the low temperature RCS.overpressurization pro-tection system to provide extended overpressurization protection was reduced. The action statement of the LCO (T.S. 3.4.9.3) was met.

The public health and safety were not affected.

Cause of Event

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~

Nitrogen leakage from the low temperature RCS overpressurization protection system caused the tank pressures to drop.

The primary plant nitrogen supply tube truck had insufficient pressure to clear the low level alarm (reset point at approximately 1835 psig).

Immediate Corrective Action

Seven hours and forty-five minutes after both pressurizer PORV's were declared inoperable, operability was restored by floating the pressurizer PORV nitrogen bottles on the primary plant tube truck. Although the low pressure alarms did not r2 set (reset at approximately 1835 psig), pressurizer PORV tank pressures were observed within the operable range at 1800 psig on local pressure gages.

Primary plant bottle truck pressure was closely monitored until 1330 on June 21, 1981 to insure operablility of the pressurizer PORV's for RCS overpressurization protection.

At 1330 on June 21, 1981 the pressurizer PORV's were blocked open providing an RCS vent path which precluded an overpressurization event.

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Attachment:

Page 2 of 2 After blocking open the pressurizer PORV's, a leaking pressurizer l

PORV nitrogen supply relief valve was reworked and all pressure fitting j

tightened.

Scheduled Corrective Action Future corrective actions are pending completion of an on going engineering study of the pressurizer PORV nitrogen low temperature RCS overpressurization system.

Actions Taken to Prevent Recurrence The pressurizer PORV nitrogen low temperature RCS overpre',surization system is currently being evaluated by engineering.

Evaluation results will determine the actions that are necessaty to prevent recurrence.

I Generic Implications The pressurizer PORV nitrogen low temperature RCS overpressurization system was custom built and designed.

Other systems of similar designs might experience similar leakage problems. North Anna Units 1 and 2 have had chrcnic pressurizer PORV nitrogen leakage problems.

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