ML19340C849
| ML19340C849 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 11/07/1980 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Millen C PUBLIC SERVICE CO. OF COLORADO |
| References | |
| NUDOCS 8012170802 | |
| Download: ML19340C849 (1) | |
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$114Y AN 8LAZA ORIVE. SulTE t000 A AUNoroN. TEXAS 75C11
$ TATE Novemcer 7, 1350 Occket No. 50-267 Puclic Service Comcany of Colorado ATTN:
Mr. C. K. Millen Senior Vice Presicent P. O. Box 340 Cenver, Coloraco 30201 Gentlemen:
This IE Information Notice is ;:roviced as an early notification of a possibly significant matter.
I-is expected nat recicients will review -he information for possible acclicacility to their facility.
.No s::ecific action or resconse is requestec at this time.
If further NRC evaluations so incicate, an IE Circular or Sulietin will be issued :a recommenc or reques specific licensee actions.
If you have cuestions regarding this matter, please c:ntac ne Director of the apcropriate NRC Regional Office.
Sincerely,.
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Enclosures:
1.
IE Information Notice No. 30 40 2.
Lis: of Recently 'ssueo II Information Notices
- 0. W. Waremcourg, Nuclear ?recuc: ion Manager
. or St. Vrain Nuclear Station
?. O. Box 268 l
?lattaville, Colorado 30651 L. 3 rey, Manager, Quality Assurance l
80121
-Q 70
SSIh5 No..
6835 Accession No.:
3008220269 UNITED STATES NUCLEAR REGULATORY CCMMISSION Q" b 0FFICE OF INSPECTION AND ENFORCEMENT
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WASHINGTON, D.C. 20555 IE Information Notice No. 30-40 Date:
November 7, 1980 Page 1 of 2 EXCESSIVE NIROGEN SUPPLY PRES 5URE ACTUATE 5 SAFETY-RELIEF VALVE OPERATION TO CAUSE REACTOR DEPRESSURIZATION Description of Circumstances:
On Octooer 7 and 31, 1980, the reactor coolant system was spuriously depres-surized at Boston Edison Comoany's Pilgrim Nuclear Power Station Unit No. 1.
The Pilgrim Station Unit No. 1 uses a GE SWR. The cepressurizations resulted when excessive pressure in the nitrogen sucoly system caused the "A" Target Rock (TR) safety-relief valve to open and remain open until the excessive suoply pressure could be isolated, oneumatic 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 cressure regulation of the supply nitrogen and not a failure of the TR safety-relief valve to function as designed.
The safety-reli' valves at Pilgrim are designed to be supplied, with other drywell instrumentation, from either tne comoressed air system or containment atmosphere control system (CACS).
The CACS uses nitrogen for containment inerting.
The supply for the safety-relief valves is provided from the CACS through an amoient air vaporizer and then through one of two parallel pressure regulators or a pars 1'lel bypass line.
Shortly before the time of each event a new supoly of liquid nitrogen had been added to the storage tanks.
At the time of the events the two pressure regulators were in service with the bypass closed.
Nitrogen pressure suoplying the valves increased to 160-165 psi.
This may have been caused by licuid nitrogen reaching tne pressure regulators or by a failure in a pressure regulator.
The result was excessive pressure wnich was sufficient to leak through the solenoid actuator and initiate the pneumatic operator of the safety-relief valve.
The design normal coerating pressure of the comoresseo air or nitrogen systems sucolying the safety-relief valves is90-110 psi.
At a pressure of 145 psi the solenoid valve may begin to leak since excessive pressure acts to unseat the disk.
The supply cressure must then decrease to 135 psi or less for the solenoid disk to reseat.
In addition, the design of the safety-relief valve is sucn that as tne main steam pressure increases, less instrument pressure is necessary to initiate the pneumatic operator.
Approximately 3 to 5 psi at the pneumatic operator is sufficient to initiate the safety-relief valve opening.
IE Information Notice No.:
30-40 Novemoer 7, 1080 Page 2 of 2 Sucn a pressure begins to build with leakage througn the solenoic actuator and was reacned in the "A" valve at 160 osi sucoly pressure.
Accorcing to information from GE and TRC, accroximately 180 osi cressure is necessary for all of the safety-relief valves to coen as result of supply overpressure.
It would appear that under sucn concitions of overpressure that safety-relief valve openings would ce sequential rather than simultaneous.
The particular solenoid actuator valves used with these two-stage safety-relief valves are manufactured by TRC.
Their design is sucn that excessive control pressure tends to unseat the solenoid valve disk.
The three-stage TR safety-relief valves use either AVC0 (Automatic Valve Comoany) or ASCO (Automatic Switch Company) solenoid valves according to information from GE.
The AVC0 solenoic valve nas 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 l
believes that the tendency for solenoid leakage and nence 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 whicn 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 Sulletin wnien will recommend or require specific licensee action.
In the interim, we expect that recipients will review the information for possible applicability to their facilities, carticularly those with installations of the TR two-stage safety-relief valves.
If you have ouestions regarding this matter, please contact the Director of tne appropriate NRC Regional Office.
J IE Information Notice No. 30-40 Novemoer 7, 1980 LISTING OF RECENTLY 155UE0 IE INFORMATION NOTICES Information Suoject Date Issued To Notice No.
Issued 30-33 Determination of Tele-9/15/80 All teletheracy l
theracy Timer Accuracy (G3) licensees 30-34 Boron Oilution of Reactor 9/26/80 All Pressuri:ed Coolant Ouring Steam Water Reactor Generator Decontamination Facilities holding power reactor Operating Licenses (OLs) 30-35 Leaking and Dislodged 10/10/80 All categories G anc Iodine-124 Imolant Seeds G1 medical licensees 50-36 Failure of Steam 10/10/80 All nuclear power t
Generator Support Bolting reactor facilities holding Operating Licensees (OLs) or Construction Permits (cps) 30-37 Containment Cooler Leaks 10/24/80 All nuclear power and Reactor Cavity facili+'es holding Flooding at Indian Point power ceactor Operating Unit 2 Lice'aes (OLs) or j
Construction Permits (cps) 80-38 Cracking in Charging 10/30/80 All Pressurized Water Reactor Facilities i
holding power reactor l
Operating Licenses (OLs) l and Construction Permits (cps)
I 30-39 Malfunctions Of Solenoid 10/31/80 All lignt water reactor Valves Manufactured By facilities holcing i
l Val' ar Engineering Corporation power reactor OLs or cps l
l Enclosure l
l i
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