ML19345C141
| ML19345C141 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 11/07/1980 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| References | |
| NUDOCS 8012030936 | |
| Download: ML19345C141 (1) | |
Text
.-
y o,
UNITED STATES y y e ff(,g NUCLEAR REGULATORY COMMISSION 34\\
.f;c c REGION V o, Ih' V U[
1990 N. CALIFORNIA BOULEVARD
' ((,3 o
SUITE 202. WALNUT CREEK PLAZA
-..\\l!
su,*
WALNUT CREEK, CALIFORNIA 94596 i;ovember 7,1980 ::?.) ll,~j g.
g, 3 g.)
~'
Docket tio. 50-312 EivecIs
.an Sacramento Municipal Utility District P. O. Box 15830 Sacramento, California 95813 Attention: Mr. John J. !!attiece Assistant General Manager Gentlemen:
This Information Notice is provideo as an early notification of a possibly significant matter.
It is expecteo tnat recipients will review the information for possible applicability to tne1r facilities. No specific action or response is recuested at unis time.
If furtner NRC evaluations so indicate, an IE Circular or Bulletin will ce issueo to recomend or request specific licensee actions.
If ycu ha'.c questions regaraing tnis matter, please contact the Director of the appropriate iiRC Regional Office.
Sincerely,
/
/h/
R.' H. cn [gelken w,
L77 f
L-Ofrector I
Enclosures:
1.
IE Information !!ctice No. 80-40 2.
List of Recently Issued IE Information flotices cc w/ enclosures:
R. J. Rodriguez, SMUD L. G. Schwieger, SMUD BO 1203 0 93 C O
m W'
9
~
SSINS No.: 6835 Accession t!o. :
UNITED STATES 8008220269 itUCLEAR REGULATORY COMMISSION IN 80 0FFICE OF INSPECTION AND ENFORCEMENT MASHINGTON, D.C. 20555 iovember 7, 1980 IE Information Notice No.: 80 a0: 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 Comoany's Pilgrim Nuclear Power Station Unit No.1.
The Pilgrim Station Unit i uses a GE BWR. The depressurizations resulted wPan excessive pressure in tne nitrocen supoly system caused the "A" Target Rock (TR) sefety-relief valve to open and remain open until the excessive supply pressure could be isolated, pneumatic ocerator pressure vented and the main steam system depressurizea sufficiently to allow tne main disk to reseat.
These two events involved a failure in tne 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, frcm either the compressed air system or containment atmosphere control system (CACS). The CACS uses nitrogen for containment inerting. The supcly for the safety-relief valves is provided from the CACS through an amotent 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 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 psi. 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 pneunatic operator. Approximately 3 to 5 psi at the pneumatic ocerator 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. According 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 under such conditions of overpressure that safety-relief valve openings would be sequential rather than simultaneous.
The particular solenoid actuator _ valves used with these two-stage safetyrelief valves are manufactered by TRC. Their design is such that excessive control i
pressure'tends to 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 AVCo solenoid
IN 80-40 November 7, 1980 Page 2 of 2 valveen tested.to 300 psi and found not to lesk and the ASCo solenoid valveto seat with increasing supply ~ pressure. Therefore, the NRC belie't the tendency for solenoid leakage and hence safety-relief valve openionfined to tne two-stage safety-relief "alve installations.
This tion is provided as a notification of a possibly significant mattei is still under review by the NRC staff.
It is anticipated that the ref continuing NRC review will culminate in issuance of an IE Bulleth will recommend or require specific _ licensee action.
In the intertxpect that recioients will review the information for possible appliu to their: facilities, carticularly those with installations of the TF. age safety-relief valves.
If you have cuestions regardina this matterie contact the. Director of the appropriate NRC Regional Office.
l
IN 80-40 November 7, 1980.
L RECENTLY' ISSUED IE INFORMATICN NOTICES Information Cate of Notice No.
Subject-Issue Issued to 80-39 Malfunctions Of Solenoid 10/31/80 All light water reactor
-Valves Manufactured By facilities holding Valcor Engineering Corocration power reactor OLs or cps 80-38 Cracking In Charging Pump 10/30/80 All PWR facilities Casing Cladding with an OL or CP 80-37 Centainment cooler leaks 10/24/80 All nuclear power and reacter cavity facilities holding flooding at Incian Point power reactor OLs Unit 2 or cps 80-36 Failure of Steam 10/10/80 All nuclear power Generator Suoport 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 medical licensees 80-32 Coren dilution of reacter 3/26/80 All pressurized water ccolant during steam reactor facilities-generator decontamination holding power reactor Ols 80-33 Catermination of teletherapy 9/15/80 All teletherapy timer accuracy (G3) licensees 4
80-32 Clarification of certain
'8/12/80 All NRC and agreement requirements for Exclu-state licensees sive-use shipments of radioactive materials 80-31 Malooeration of-Gould-8/27/80 All light water reactor Brown Boveri Type 480 facilities ' holding OLs volt type K-600S and or cps
~
K-00M 600S circuit breakers
- Operating Licenses or Construction Permits
.,