ML19340B204

LER 80-069/01X-0:on 801007,w/unit at 96% Steady State Power, Reactor Vessel 203-3A Safety Relief Valve Opened.Caused by Excessive Nitrogen Supply Pressure.Pressure Resulted in Leakage Through Solenoid Valve Into Valve Diaphragm

ML19340B204
Person / Time
Site:	Pilgrim
Issue date:	10/10/1980
From:	Mcloughlin M BOSTON EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
LER-80-069-01X, LER-80-69-1X, NUDOCS 8010210647
Download: ML19340B204 (2)

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' BOSTON EDISON COMPANT .

TELECOPY MESSAGE Oct. 10, 1980 73 215-337-5324 .

Date/ Time: 7 Telephone Number Tat Director, Region I - From: Pilgrim Nuclear Power Station Office of Inspection and Enforcement RFD #1 Rocky M11 Road U'. S Ifuelear Regulatory Commission Plymouth, MA 02360 631 Park Avenua King-of_ Prussia, PA 19406 b _

' Subjcet: PROMPT REPORTA3LE OCCURRENCE

. Docket Number 50-293; License DPR-35 .

-Assigned LER Number.

80-069/01X-0 (Reported per Technical Specification 6.9.B.1.1)

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On october 7,1980 at 0403 hours0.00466 days <br />0.112 hours <br />6.66336e-4 weeks <br />1.533415e-4 months <br /> with the reactor at 96 percent steady Even:

Description:

state power' operation, t'he reactor vaissel relief valve RV 203-3A opened. The reactor

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was subsequently manually scrammed and an investigation to determine the cause of the

, relief valve. operation initiated.. .

. . ....-  :, l 160 Causo and. Corrective. Action: Investigation revealed that high nitrogen pressure of psi resulted in leakage past the seat 'of the valve's three way, solenoid control valve into the diaphram of the relief valve causing it to lift. Nitrogen pressure was reduced to 110 psi.

Fccility Status: ~

96 % Thermal MW c) Routina Startup ~

g) Shutdown d) Routs:e Shutdown h) Refueling o) Steady ~ State r -

'i) Other

'f) Load' Changing .

j) No Applicaple A written follow-up report wfTT be sent whhh two weeks. .

Mr. John Johnson Prep'ared by Mr. M. Thomas McLoughlin MRC, person notified -

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fS 3 (2) copies to:

8010.2yo 4 4 7 -

Office of Management Information and Program Control -

U. S. Nuclear Regulatory Commission. ,

[ BOSTON EDISOE COMPANY ,

PILGRIM NUCLEAR POWER STATION '

DOCKET'NO.-50-293' Attachment'to LER 80-069/01X-0 Descrir*'~;

At 04u, .ours on October 7,1980 with the unit in steady state operation at 96% power and' reactor' pressure approximately equal' to 1025 psi Safety Relief Valre (S.R.V.) 203-3A opened. ,

4 Station procedures.were followed and unit taken off line. All indications are that the valve remained open until the. vessel depressurized. Ope. rations per-sonnel tried many times during the pressure reductiot:, to cycle the valve using controls on control panel 903.

'1 Unit was taken to cold shutdown, the drywell inerted, and an entry made at ap-proximately 1700. hours the same . day. l j Cause and Corrective Action Investigation revealed that the inadvertent opening of the S.R.V. was caused by excessive Nitrogen supply pressure. Nitrogen pressure at the time of ' the event was approximately 160-165 psi instead of the 110' psf indicated in the design

specification.-

This excessive pressure resulted in some leakage through .the solenoid valve into the diaphram of the S.R.V.

The design of the S.R.V... is such. that the air pressure on the diaphram needed to cause the S.R.V.- to open reduces as the main steam pressure increases. This I explains why the-valve did not open until this particular reactor pressure level I was realized.

The analysis indicates that the S.R.V. should have closed as the main steam pressure decreased as long as the leakage through the- solenoid control valve ]

rammined constant. However, operating practices dictate that whenever a S.R.V.  !

'does open or is caused to open, . attempts will be .made to . close it via controls '  ;

on panel 903. This was done. repeatedly during the time the vessel was de- i pressurizing.' W'nen the control for "A" S.R.V. was -placed first in the "open" j i position and then in the "close" position, the solenoid control valve energized l 2nd opened. The . design of the control valva is such that it cantat close. with either air or nitrogen pressure greater than 135 psi. The ,160 psi Nitrogen j

pressure therefore, resulted in the control valve staying in the open position which prevented-the S.R.V. from closing. )

1 j Until a' permanent redesign of the N2 supply system can be' implemented,- the fol - l j'. lowing corrective measures hcve been -initiated: I

11. ' N2 : supply pressure will be maintained at 110 psi as indicated at PI 4339.

2. . : Station procedure No. 2.1.15 " Daily Surveillance Log" will be- revised to I require an operator-verification check of nitrogen pressure once/shif t. -1 f

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