05000293/LER-1980-080-01, /01T-0:on 801031,reactor Vessel Relief Valve Rv 203-3A Opened.Caused by Nitrogen Regulator Valve Which Froze in Open Position.Drywell Instruments Will Be Operated by Compressed Air W/Nitrogen Supply Isolated

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/01T-0:on 801031,reactor Vessel Relief Valve Rv 203-3A Opened.Caused by Nitrogen Regulator Valve Which Froze in Open Position.Drywell Instruments Will Be Operated by Compressed Air W/Nitrogen Supply Isolated
ML19339C776
Person / Time
Site: Pilgrim
Issue date: 11/14/1980
From: Mcloughlin M
BOSTON EDISON CO.
To:
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19339C775 List:
References
LER-80-080-01T, LER-80-80-1T, NUDOCS 8011190444
Download: ML19339C776 (2)
v • d • e


LER-1980-080, /01T-0:on 801031,reactor Vessel Relief Valve Rv 203-3A Opened.Caused by Nitrogen Regulator Valve Which Froze in Open Position.Drywell Instruments Will Be Operated by Compressed Air W/Nitrogen Supply Isolated
Event date:
Report date:
2931980080R01 - NRC Website
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NRC FCCM 384 U. S. NUCLEA'1 REGULATOOY COMMISSION

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8 60 61 0o0 JET NUM8ER 68 69 EVENT DATE 74 75 REPORT DATE 80 EVENT OESCRIPTION ANO PROBABLE CONSEQUENCES h l o { 21 10n October 31, 1980 at approximately 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br /> with the reactor at 100 percent steady l (3771 l state power operation, the reactor vessel elief valve RV 203-3A opened. The reactor l

4 1 o 14 l lwas subsequently manually scrammed at 50 percent nower.

Corrective measures to prevent l IOIsI l recurrence were taken and the reactor returned to operation on November 1, 1980 at ap-l 1 O is I I proximately 0317 hours0.00367 days <br />0.0881 hours <br />5.241402e-4 weeks <br />1.206185e-4 months <br /> (Refer to Attachment for additional information).

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i ; o ; l A nitrogen regulator valve manufactured by C. A. Norgren Company of Littleton, Coloradop

,,,, y g model No. 11-002-097 and rated at 400 and 125 psi maximum inlet and outlet pressure is [-

believed to have frozen in the open position.

160 to 165 psi nitrogen pressure was thereby transmitted to the relief valve's solenoid actuttor valve and initiated the j

pneumatic operator of the relief valve.

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PILGRIM NUCLEAR POWER STATION

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DOCKET NO. 50-293 Attachment to LER 80-080/01T-0

Description

At approximately 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br /> on October 31, 1980 with reactor at 100 percent steady state power operation the reactor vessel relief valve RV 203-3A opened.

The relief valve could not be reclosed until reactor pressure dropped to ap-proximately 20 psig. The relief valve's operation was the result of approxi-mately 165 psi nitrogen pressure being fed to the relief valve's ASCO three way, solenoid control valve. Analysis has revealed that the relief valve's setpoint pressure varies inversely to its solenoid actuator's nitrogen pressure above 145 psi. _ A similar event occurred on October 7,1980 and was reported as LER 80-069/01T-0.

The relief valve's solenoid actuator supply was switched from nitrogen to compressed ' air and the reactor returned to criticality on Jovember 1, 1980 at approximately 0317 hours0.00367 days <br />0.0881 hours <br />5.241402e-4 weeks <br />1.206185e-4 months <br />.

Cause and Corrective Action On October 31, 1980 an indepth investigation of the nitrogen. supply system was initiated.

The investigation concluded that liquid nitrogen passing by its ambient air vaporizer froze an in-line regulator. This in-line, blow-down regu-lator froze in the open position. This permitted nitrogen tank pressure main-tained at 180 psi to be transmitted to the relief valve's solenoid actuator.

This regulator, manufactured by C. A. Norgren Company, was installed in parallel to an existing regulator in August, 1980. The existing regulator fails in the closed position so the conditiens resulting from failure of the Norgren regulator could only have occurred since the August installation.

To preclude recurrence of this event the following design changes are being contemplated:

A)

Removal of the " fail open", Norgren, blow-down regulator and its replacement with a " fail close" regulator B)

A reduction of nitrogen tank pressure from 180 psi to less than 135 psi.

C) The addition of a 135 psi relief valve to the nitrogen header down-stream of the regulators.

1 Until these modifications are completed drywell instruments will be operated by compressed air with their nitrogen supply isolated.

These modifications are expected to be completed by December 15, 1980.

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