ML19260B586
| ML19260B586 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 10/30/1979 |
| From: | Schwencer A Office of Nuclear Reactor Regulation |
| To: | Proffitt W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| References | |
| NUDOCS 7912100411 | |
| Download: ML19260B586 (5) | |
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'o UNITED STATES l'
, ~,,g NUCLEAR REGULATORY COMMISSION c
WASHINGTON, O. C. 20555 k...../
October 30, 1979 1
Docket No. 50-338
.Hr. W. L. Proffitt i
Senior Vice President - Power i
Virginia Electric and Pcwer Company l
Post Office Box 26666 Richmond, Virginia 23261
Dear Mr. Proffitt:
RE: Containment Purging and Venting During Nomal Operation By letter dated December 11, 1978, the Commission (NRC) requested all licensees of operating reactors to respond to generic concerns about containment purging or venting during nomal plant operation. The generic concerns were twofold:
(l) Events had occurred where licensees overrode or bypassed the safety actuation isolation signals to the containment isolation valves.
These events were determined to be abnomal occurrences and reported to Congress in January 1979.
(2) Recent licensing reviews have required tests or analyses to show that containment purge or vent valves would shut without deguding con-tainment integrity during the dynamic leads of a design basis loss of coolant accident (DBA-LOCA).
The NRC position of the Novemoer 1978 letter requested that licensees
- take the following positive actions pending canpletion of the NRC review:
(1) pronibit the override or bypass of any safety actuation signal which would affect another safety actuation signal, the NRC Office of Inspection and Enforcement would verify that aaministrative controls prevent improper manual defeat of safety actuation signals, and (2) cease purging (or venting) of containment or limit purging (or venting) to an absolute minimum, not to exceed 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year. Licensees were requested to demonstrata (by test or by test and analysis) that containment isolation valves would shut under postulated DBA-LOCA condition.' The NRC positions were amplified by citation (and an attached copy) of our Standart! Review Plan (SRP) 6.2.4 Revision 1 and the associated Branch Technical Fasition CSB 6-4, which have effectively classed the purge and vent valves as
" active" invoking tne operability assurance program of SRP 3.9.3.
y The NRC staff has made site visits to several facilities, has cet with licensees at Bethesda, Maryland, and nas held telecon conferences with many otner licensees anc met with scme valve manufacturers. During these ciscussions, the NRC staf# nas stressed that positive actions must be taken as noted above to assure :nat containment integrity would be maintained in tne event of~a CSA-LCCA.
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Mr. W. L. Proffitt Virginia Electric and Power Co. October 30, 1979 As a result of these actions, we have learned from several licensees tnat at least three valve vendors have reported that their valves may not close against the ascending differential pressare and the resulting dynamic loading of the design basis LOCA. All identified licensees who are affected have proposed to maintain the valves in the cicsed position or to restrict the angular cpening of the valves whenever primary containment integrity is required until a re-evaluation is provided which shows. satisfactory valve perfomance under the DBA-LOCA condition.
Recently, a report under 10 CFR Part 21 was received by the NRC fran the manufacturer of butterfly valves which are installed in the primary containment at the Three Mile Island Unit 2 Nuclear Station. These butterfly valves are used for purge and exhaust purposes and are required to operate ouring accident conditions. The report discusses the use of an unqualified solenoid valve for a safety-related valve function which requires operation uncer accident conditions. The solenoid valve is used to pilot control the pneumatic valve actuators which are installed on the containment ventilation butterfly valves at this facility. Your re-evaluation of valve perfomance for conditions noted in the previous paragraph must consicer the concerns identified in IE Bulletin 79-01A.
As the NRC review progresses, licensees which might have electrical override circuitry problems are seing advised not to use the override and to take cmpensatory interim measures to minimize the problem.
In light of the infomation gained during our review of your submittal dated January 17, 1979 and the information cited above, we believe an interim commitment from you is required at this time. This is the case, even though your Technical Specifications restrict purging above 350*F. Our interim requirements in Enclosure 1 do not appear to be met for all conditions other than cold shutdown. For your use, we have provided as an attachment an interim NRC staff position. In addition, our recently developed " Guidelines for Demonstration of Operability of Purge and Vent Valves" were provided by separate letter to licensees of each operating reactor. This letter in no way relaxes any existing licensing requirements for your facility.
Because of the potential adverse effects on the public health and safety whien could result fran the postulated, D8A-LOCA while operating with open purge or vent valves, we believe your pranpt response to this letter is required.
In accordance with 10 CFR 50.54(f), you are requested 1521 171
Mr. W. L. Proffi.tt Virginia Electric and' Power Co. October 30, 1979 to inform us in writing within 45 days of receipt of this letter of your commitment to operate in conformance with the enclosed interim position and to provide us with information which demonstrates that you have initiated the purge and vent valve operability verification on an expedited basis. The information provided in your response.will enaole us to determine whether or not your license to operate North Anna Power Station, Unit No. I should be modified, suspended, or revoked.
Sincere ~,
A. Schwencer, Chief Operating Reactors Branch il Division of Operating Reactors
. Encl osure:
Interim Position for Containment Purge ano Vent Valve Operation cc: w/ encl osure See next page IS21 i72
Mr. W. L. Proffi tt Virginia Electric and Power Company October 30, 1979 cc: Mr. Michael W. Maupin Hunton and Williams Post Office Box 1535 Richmond, Virginia 23213 Swem Library College of William and Mary Williamsburg, Virginia 23185 Donald J. Surke U. S. Nuclear Regulatory Commission Region II Office of Inspection and Enforcement 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 T
1521 i73
INTERIM PdSITICA 70R'CONTAINM$NT'PORGE MD VENT VALVE OPERATION PENDING RESOLUT!0N 6F'tSOLATION VALVE OPERABILITY
~
Unce the conditions listed oelow are met, restrictions on use of the containment purse and vent system isolation valves will be revised based on our review of your responses to the November 1978 letter justifying your proposed operational mode. The revised restrictions can be gstablished separately for each system.
1.
Whenever the containment integrity is required, emphasis should be placed on operating the containment in a passive mode as much as possible end on limiting all purgir.g and venting times to as icw as achievable.
To justify venting or purging, tnere must be an established need to improve working conditions to cerfom a safety related surveillance or safety related maintenance procedure.
(Examples of improved working concitions would incluce deinerting, reducing temperature *, humidity *,
anc airoorne activity sufficiently to pemit efficient perfomance or to significantly reduce occupational radiation exposures), and 2.
heintain the containment purge and vent isolation valves closed whenever the reactor is not in tne cold shutcown or refueling mode until such time as you can show that:
a.
All isolation valves greater than 3" nominal diameter used for
[
containment purge and venting operations are operaole under the most severe design basis accident flow condition loading and can close within the time limit stated in your Technical Specifications, design criteria or operating procedures. The operability of butter-fly valves may, on an interim basis, be demonstrated by limiting the valve to ce no more than 30* to 50* open (90* being full open). The maximum opening shall be detemined in consultation with the valve supplier. The valve opening must be such that the critical valve parts will not be damaged by DBA-LOCA loads and that the valve will tend to close when the fluid dynamic forces are introcuced, and b.
Mocifications, as necessary, have been made to segregate the containment ventilation isolation signals to ensure that, as a minimum, at least one of the automatic safety injection actuation signals is uninhibited anc operaole to initiate valve closure when any other isolation signal may oe blockeo, reset, or overridden.
- Only wnere temperature and humidity controls are not in the present design.
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