ML19345C139
| ML19345C139 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay, Diablo Canyon |
| Issue date: | 11/07/1980 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Crane P PACIFIC GAS & ELECTRIC CO. |
| References | |
| NUDOCS 8012030934 | |
| Download: ML19345C139 (1) | |
Text
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UNITED STATES 3
NUCLEAR REGULATORY COMMISSION O
E REGION V o,
1990 N. CALIFORNIA BOULEVARD. :sC.TSE 10.4 SUITE 202, WALNUT CREEK PLAZAn 5Y b C' o
WALNUT CREEK, CALIFORNIA 94596 November 7,198080 NOV 10 FM 3 II Us NR':
3ERvicES Docket Nos. 50-133, 50-275, 50-323 DThNcH Pacific Gas and Electric Company 77 Beale Street.
-San Francisco, California 94106 AttenMon: Mr. Philio A. Crane, Jr.
Ass 1: tant General Counsel Gentlemen:
This Information Notice is provided as an early notification of a possibly significant matter.
It is expected that recipients will review the information for possible applicability to their facilities. No spucific action or response is recusted at this time.
If further NRC evaluations so indicate, an IE Circular' or Bulletin will be issued to recomend or request roecific licensee actions.
If you have ~ questions regarding this matter, please contact the Director of the appropriate liRC Regional Office.
Sincerely,
^
k[.4 hts $-
Director
Enclosures:
1.
IE Information Notice No. 80-40 2.
List ~of Recently Issued Ir Information Notices cc w/ enclosures:
J. D. Shiffer, PG&E W. Raymond, PG&E E. Weeks, PG&E, Humboldt Bay E. B.-Langley, Jr., PG&E 99030N u
SSIllS tio. : 6835 Accession f!o. :
UlITED STATES 8008220269 NUCLEAR REGULATORY C0mISSIO!!
Ill 80 0FFICE OF It!SPECTI0tl AtID EllFORCEMEilT UASHI!;GT0fi, D.C. 20555 i'ovember 7,1980 IE Information ?!otice lio.: 80-40:
EXCESSIVE iiIROGEt1 SUPPLY PRESSURE ACTUATES SAFETY-RELIEF VALVE OPERATI0fl TO CAUSE REACTOR DEPRESSURIZATION Description of Circumstanc> 3:
On October 7 and 31, 1980, the reactor coolant system was spuriously depres-surized at Boston Edison Company's Pilgrim fluclear Power Station Unit No.1.
The Pilgrim Station Unit 1 uses a GE BWR. The depressurizations resulted when excessive pressure in the nitrogen supply system caused the "A" Target Rock (TR) s-afety-relief valve to open and remain open until the excessive supply pressure could be isolated, pneumatic operator pressure vented and the main steam system depressurized sufficiently to allow the main disk to reseat These two events involved a failure in the pressure regulation of the supp'y nitrogen and nct a failure of the TR safety-relief valve to function as designed.
The safety-relief valves at Pilgrin are designed to be supplied, with other drywell instrumentation, from either the compressed air system or containment atmosphere control system (CACS). The CACS uses ritrogen for containment inerting. The succly for the safety-relief valves is provided from the CACS through an ambient air vaporizer and then througn one of two parallel pressure regulators or a parallel bypass line. Shortly before the time of each event a new supply of licuid nitrogen had been added to the storage tanks.
At the time of the events the two pressure regulators here in service with the bypass closed.
Nitrogen pressure supplying the valves increased to 160 - 165 psi.
This may have been caused by liquid nitrogen reaching the pressure regulators or by a failure in a pressure regulator.
The result was excessive pressure which was sufficient to leak through the solenoid actuator and initiate the pneumatic operator of the safety-relief valve.
'Ine design normal operating pressure of the comoressed air or nitrogen systems supplying the safety-relief valves is90-110 psi. At a pressure of 145 psi the solenoid.alve nay begin to leak since excesshe pressure acts to unseat the disk. The supply pressure must then decrease to 135 psi or less for the solenoid disk to r m eat.
In addition, the design of the safety-relief valve is such that as t*
main steam pressure increasas, less instrument pressure is necessary to initi ce the pneumatic operator. Approximately 3 to 5 psi at the pneumatic operator is sufficient to initiate the safety-relief valve opening.
Such a pressure begins to build with leakage through the solenoid actuator and was reached in the "A" valve at 160 psi supply pressure.
Accord.nq to information from GE and TRC, approximately 180 psi pressure is necessary for all of the safety-relief valves to open as result of supply overpressure.
It would appear that urder such conditions of overpressure that safety-relief valve openings would be Mauential rather than simultaneous.
The particular solenoid actuator valves used with these two-stage safetyrelief valves are manufactured by TRC. Their design is such F.at excessive control pressure tends to unseat the solenoid valve disk. The three-stage TR safety-relief
- valves use either AVC0 (Automatic Valve Company) or iSCO (Automatic Switch Company) solenoid-valves according to information from GE.
The AVCo solenoid
i IN 80-40 November 7, 1980 Page 2 of 2 valve has been tested to 300 psi and found not to leak and the ASCo solenoid valve tends to seat with increasing supply pressure. Therefore, the NRC believes that the tendency for solenoid leakane and hence safety-relief valve opening is confined to the two-stage safety-relief valve installations.
This information is provided as a notification of a possibly significant matter which is still under review by the NRC staff.
It is anticipated that the results of continuing NRC review will culminate in issuance of an IE Bulletin which will recommend or require specific licensee action.
In the interin, we expect that recipients will review the information for possible applicability to their facilities, particularly those with installations of the TR two-stage safety-relief valves.
If you have ouestions regardino this mattet, please contact the Director of the aopropriate NRC Regional Office.
i IN 80-40 November 7, 1980 RECENTLY ISSUED IE INFORMATION NOTICES Information Uate of Notice No.
Subject Issue Issued to 80-39 Malfunctions Of Solenoid 10.51/30 All light water reactor Valves Manufactured By facilities holding Valcor Enaineering Corporation power reactor OLs or cps 80-38 Cracking In Charging Pump 10/30/80 Al' PWR facilities Casing Cladding with an OL or CP 80-37 Contair.nent cooler leaks 10/24/80 All nuclear power and reactor cavity facilities holding ficodinq at Incian Point power reactor OLs Unit 2 or cps 80-36 Failure of Steam 10/10/80 All nuclear power Generator Support Bolting reactor facilities holding power reactor OLs or cps 80-35 Leaking and dislodged 10/10/80 All categories G and Iodine-124 implant. seeds G1 nedical licensees 80-34 Doron dilution of reactor 9/26/20 All pressurized water i
coolant during s teaia reactor facilities generator decontamination holding power reactor OLs 80-33 Determination of teletherapy 9/15/80 All teletherapy timer accuracy (G3) licensees 80-32 Clarification of certain 3/12/80 All NRC and agreement requirenents for Exclu-state licensees sive-use shipments of radioactive materials 80-31 Maloperation of Gould-8/27/80 All light water reactor Brown Boveri Type 480 facilities holding OLs volt type K-600S and or cps K-DON 600S circuit j
breakers
- Operating Licenses or Construction Permits