ML19345C029
| ML19345C029 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 11/07/1980 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Counsil W CONNECTICUT YANKEE ATOMIC POWER CO. |
| References | |
| NUDOCS 8012030771 | |
| Download: ML19345C029 (1) | |
Text
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CEN Md( ?AS e.a uq#o, UNITED STATES
' 7, NUCLEAR REGULATORY COMMISSION REGION I 0,
631 PARK AVENUE g,e KING op PRUSSIA, PENNSYLVANIA 19406 November 7,1980 Docket No. 50-213
. Connecticut Yankee Atomic Power Company ATTN:
Mr. W. G. Counsil Vice President - Nuclear Engineering and Operations P. O. Box 270 Hartford, Connecticut 06101 1
.1 Gentlemen:
The enclosed IE Information Notice No. 80-40, " Excessive Nitrogen Supply Pressure Actuates Safety-Relief Valve Operation to Cause Reactor Depressurization,"
is fonvarded to you for information.
No written response is requirad.
If you desire additional-information regarding this matter, please contact this office.
Sincerely, G
Boyce H.' Grier Director
~
Enclosures:
1.
IE Information Notice No. 80-40 2.
List of Recently Issued IE Information Notices l
CONTACT:
D. L. Caphton (215-337-5266) cc w/encis:
R. Graves, Plant Superintendent D. G. Diedrick, Manager of Quality Assurance J. R. Himmelwright, Licensing Safeguards Engineer 8012ogo 771
O SSINS No.:
6835 Accession No.:
UNITED STATES 6008220269 NUCLEAR REGULATORY COMMISSION IN 80-40 0FFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 November 7, 1980 IE Information Notice No. : 80-40:
EXCESSIVE NIROGEN SUPPLY PRESSURE ACTUATES SAFETY-RELIEF VALVE OPERATION TO CAUSE REACTOR DEPRESSURIZATION Description of Circumstances:
On October 7 and 31, 1980, the reactor coolant system was spuriously depres-surized at Boston Edison Company's Pilgrim Nuclear 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) safety-relief valve to open and remain open until the excessive supply pressure could be isolated, pneu.aatic operator pressure vented and the main stcam system depressurized sufficiently to allow the main disk to reseat.
These two events involved a failure in the pressure regulation of the supply nitrogen and not a failure of the TR safety-relief valve to function as designed.
The safety-relief valves at Pilgrim are designed to be supplied, with other drywell instrumentation, from either the compressed 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 ambient air vaporizer.and then through one of two parallel pressure regulators or a parallel bypass line.
Shortly before the time of each event a new supply 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 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.
The design normal operating pressure of the compressed air or nitrogen systems supplying the safety-relief valves is90-110 psf-At a pressure of 145 psi the solenoid valve may begin to leak since excessive pressure acts to unseat the disk.
The supply pressure must then decrease to 135 psi or less for the solenoid disk to reseat.
In addition, the design of the safety-relief valve is such that as the 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 t;he 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.
According to information from GE and Tk, approximately 180 psi pressure is necessary for all of the safety-relief valves to open as result of supply overpressure.
It would appear that under such conditions of overpressure that safety-relief valve openings would be sequential rather than simultaneous.
IN 80-40 Page 2 of 2 The particular solenoid actuator valves used with these two-stage safetyrelief valves are manufactured by TR.
Their design is such that excessive control pressure tends.tc unseat the solenoid valve disk.
The three-stage TR safety-relief valves use either AVC0 (Automatic Valve Company) or ASCO (Automatic Switch Company) solenoid valves according to information from GE.
The AVC0 solenoid 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 leakage 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 recos.nend or require specific licensee action.
In the interim, 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 questions regarding this matter, please contact the Director of the appropriate NRC Regional Office.
t
IE Information Notice No. 80-40 November 7, 1980 RECENTLY ISSUE 0 IE INFORMATION NOTICES Information Subject Date Issued to Notice No.
Issued
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80-39 Malfunctions of 10/31/80 All holders of a Solenoid Valves power reactor OL Manufactured by Valcor or CP Engineering Corporation 80-38 Cracking in Charging 10/30/80 All holders of Pump Casing Cladding a PWR power reactor OL or CP 80-37 Containment Cooler 10/24/80 All holders of a Leaks and Reactor power reactor OL Cavity Flooding at or CP Indian Point Unit 2 80-36 Failure of Steam 10/10/80 All holders of a Generator Support power reactor Bolting OL or CP 80-35 Leaking and Dislodged 10/10/80 All holders of a Iodine-125 Implant Category G or G1 Seeds Medical License 80-34 Baron Oilution of 9/26/80 All holders of a Reactor Coolant During PWR Power Reactor OL Ste m Generator Decontamination 80-33 Determination of 9/15/80 All holders of Teletherapy Timer a teletherapy Accuracy license 80-32 Clarification of 9/12/80 All holders of Certain Requirements an NRC or Agreement for Exclusive-use State License Shipments of Radioactive Materials 80-31 Maloperation of Gould-8/27/80 All holders of Brown Boveri 480V-Type a power reactor K-600S and X-Oon 6005 OL or CP Circuit Breakers 1
.