05000338/LER-1981-001-03, /03L:on 810318 & 19,nitrogen Supply Tank Pressure for Associated Pressure Operated Relief Valves Dropped Below Min Required to Operate Valves for Low Temp RCS Overpressurization Protection.Caused by Leaks in Tanks

/03L:on 810318 & 19,nitrogen Supply Tank Pressure for Associated Pressure Operated Relief Valves Dropped Below Min Required to Operate Valves for Low Temp RCS Overpressurization Protection.Caused by Leaks in Tanks

ML20003E914
Person / Time
Site:	North Anna
Issue date:	04/13/1981
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20003E909	List: 05000338/LER-1981-001, Forwards LER 81-001/03L-0 05000338/LER-1981-001-03, /03L:on 810318 & 19,nitrogen Supply Tank Pressure for Associated Pressure Operated Relief Valves Dropped Below Min Required to Operate Valves for Low Temp RCS Overpressurization Protection.Caused by Leaks in Tanks
References
LER-81-001-03L-02, LER-81-1-3L-2, NUDOCS 8104170491
Download: ML20003E914 (3)

LER-1981-001, /03L:on 810318 & 19,nitrogen Supply Tank Pressure for Associated Pressure Operated Relief Valves Dropped Below Min Required to Operate Valves for Low Temp RCS Overpressurization Protection.Caused by Leaks in Tanks

Event date:
Report date:
3381981001R03 - NRC Website

text

.....-.-.

- s

.m_:..-_,_

.' O i

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT CONTROL BLOCK / / / / / / / (1)

(PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION)

(~'1_1[

/V/A/N/A/S/1/ (2)

/0/0/-/0/0/0/0/0/-/0/0/ (3)

/4/1/1/1/1/ (4)

/ / / (5) 1 V

LICENSEE CODE LICENSE NUMBER LICENSE TYPE CAT

/0/1/

E/(6)

/0/5/0/0/0/3/3/8/

(7)

/0/3/1/8/8/1/ (8) /o/4/1/3/s/1/ (9)

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

/0/2/

/

On March 18, 1981, with Unit 1 in Cold Shutdown, a pressurizer PORV nitrogen /

/0/3/

/

supply tank pressure dropped below the minimum required to operate its

/

/0/4/

/

associated PORV for low temperature RCS overpressurization protection. On

/

/0/5/

/

March 19, 1981, the remaining pressurizer PORV became inoperable for the same /

/0/6/

/

reason. The action statement of the LCO was met. The public health and

/

/0/7/

/

safety were not affected.

/

/0/8/

/__

/

SYSTEM

CAUSE

CAUSE COMP.

VALVE CODE CODE SUBCODE COMPONENT CODE SUBCODE SUBCODE

/0/9/

/S/H/ (11) /E/ (12) /B/ (13) /V/A/L/V/0/P/ (14) /D/ (15)

/Z/ (16)

SEQUENTIAL OCCURRENCE REPORT REVISION LER/R0 EVENT YEAR REPORT NO.

CODE TYPE NO.

(17) REPORT NUMBER

/8/1/

/-/ /0/0/1/ '/\\/

/0/3/

/L/

/-/

[0/

ACTION FUTURE EFFECT SHUTDOWN ATTACHMENT NPRD-4 PRIME COMP. COMPONENT n TAKEN ACTION ON PLANT METHOD HOURS SUBMITTED FORM SUB. SUPPLIER MANUFACTURER

/X/ (18) /X/ (19) /Z/ (20) /Z/ (21) /0/0/0/0/ (22) /Y/ (23) /N/ (24) /A/ (25) /S/4/2/0/ (26)

CAUSE DESCRIPTION AND CORRECTIVE ACTIONS (27)

/1/0/

/

Leaks in both PORV nitrogen low temperature RCS overpressurization systems

/

/1/1/

/

caused the nitrogen tanks to depressurize. Both PORV's were aligned to an

/

/1/2/

/

alternate nitrogen source and operability restored. The RCS was depresssurized/

l

/1/3/

/

and vented on March 20 and both PORV nitrogen low temperature

/

/1/4/

/

overpressurization systems repaired.

/

FACILITY METHOD OF DISCOVERY DESCRIPTION (32)

/ (30) DISCOVERY STATUS

% POWER OTHER STATUS

/A/ (31)

/

OPERATOR OBSERVATION

/

/1/5/

/G/ (28)

/0/0/0/ (29) /

NA ACTIVITY CONTENT RELEASED OF RELEASE AMOUNT OF ACTIVITY (35)

LOCATION OF RELEASE (36) l

/1/6/

/Z/ (33)

/Z/ (34) /

NA

/

/

NA

/

i PERSONNEL EXPOSURES NUMBER TYPE DESCRIPTION (39)

/1/7/ /0/0/0/ (37) /Z/ (38) /

NA

/

PERSONNEL IhadRIES NUMBER DESCRIPTION (41)

/1/8/ /0/0/0/ (40) /

NA

/

LOSS OF OR DAMAGL TO FACILITY (43)

TYPE

DESCRIPTION

p/

t 19

/Z/ (42) /

NA

/

s PUBLICITY ISSUED DESCRIPTION (45)

NRC USE ONLY

/2/0/

/N/ (44) /

NA

/////////////

NAME OF PREPARER W. R. CARTWRIGHT PHONE (703) 894-5151

....,....a~

('~}

Virginia Electric and Power Company North Anna Power Station, Unit #1 Attachment: Page 1 of 2 Docket No. 50-338 Report No. LER 81-001/03L-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 to 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 each PORV, is a tank pressure of 1775 psig (50 psig above the minimum required to account for instrumentation error).

On March 18, 1981, with Unit 1 in Cold Shutdown, a pressurizer PORV nitrogen supply tank pressure dropped below 1775 psig rendering one of two pressurizer PORV's inoperable for low temperature RCS overpressurization protection. On March 19, 1981 the second pressurizer PORV nitrogen supply tank pressure 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 Consequences of Occurrence The action statement of the LCO was met.

The public health and safety were not affected.

Cause of Event

The nitrogen lines between the nitrogen tanks and PORV operators were leaking at mechanical joint points and component points. The primary plant nitrogen supply truck had insufficient pressure to provide makeup to the pressurizer PORV nitrogen tanks. Local repressurization of the tanks with nitrogen bottles proved futile; the tanks dropped below their setpoint pressure soon after being repressurized.

l

Immediate Corrective Action

When the first pressurizer PORV (PCV-1455C) became inoperable for low temperature RCS overpressurization protection, attempts were made l

to refill its associated nitrogen tank with bottled nitrogen. After it became apparent that refill attempts were futile, work began to seal all i

leakage points in the PCV-1455C nitrogen system. 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> and 15 minutes after the first PORV (PCV-1455C) became inoperable, the second i

PORV (PCV-1456) became inoperable. 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 15 minutes after f'~/}

PCV-1456 became inoperable, the "C" RCS accumulator was aligned via l

the containment nitrogen header to supply nitrogen to the pressurizer PROV's. This action restored operability to both PORV's; however, l

redundancy was reduced since the PORV's were aligned to a common nitrogen source. On March 20, 1981, the RCS was depressurized and t

i I

_.,. m m.

~ ~.,-- - - - -.

j f)

Immediate Corrective Action (cont)

Attachment: Page 2 of 2 both 1\\RV's blocked open. Both PORV nitrogen systems were reworked and restored to operable status prior to repressurization of the RCS.

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 overpressurization system is currently being evaluated by engineering. Evaluation results will determine the actions that are necessary to prevent recurrence.

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.

l l O O

m.