United States Nuclear Regulatory Commission - Protecting People and the Environment

Containment Purging and Venting During Normal Operation (Generic Letter 79-54)


GL79054 

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                          WASHINGTON, D. C. 20555 

Docket No. 50-348 

     Mr. Alan R. Barton 
     Senior Vice President 
     Alabama Power Company 
     Post Office Box 2641 
     Birmingham, Alabama 35291 

     Dear Mr. Barton: 

     RE: Containment Purging and Venting During Normal Operation 

     By letter dated November 28, 1978, the Commission (NRC) requested all 
     licensees of operating reactors to respond to generic concerns about 
     containment purging or venting during normal plant operation. The 
     generic concerns were twofold: 

     (1)  Events had occurred where licensees overrode or bypassed the 
          safety actuation isolation signals to the containment isolation 
          valves. These events were determined to be abnormal 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 degrading
          containment integrity during the dynamic loads of a design basis 
          loss of coolant accident (DBA-LOCA). 

     The NRC position of the November 1978 letter requested that licensees 
     take the following positive actions pending completion of the NRC 
     review: (1) prohibit 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 administrative 
     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 hours per year. 
     Licensees were requested to demonstrate (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 Standard Review Plan (SRP) 6.2.4 Revision 1 
     and the associated Branch Technical Position CSB 6-4, which have 
     effectively classed the purge and vent valves as "active" invoking the 
     operability assurance program of SRP 3.9.3. 

     The NRC staff has made site visits to several facilities, has met with 
     licensees at Bethesda, Maryland, and has held telecon conferences with 
     many other licensees and met with some valve manufacturers. During 
     these discussions, the NRC staff has stressed that positive actions 
     must be taken as noted above to assure that containment integrity would 
     be maintained in the event of a DBA-LOCA. 
.

Mr. Alan R. Barton                - 2 -

     As a result of these actions, we have learned from several licensees 
     that at least three valve vendors have reported that their valves may 
     not close against the ascending differential pressure and the resulting
     dynamic loading of the design basis LOCA. All identified licensees who 
     are affected have proposed to maintain the valves in the closed 
     position or to restrict the angular opening of the valves whenever 
     primary containment integrity is required until a re-evaluation is 
     provided which shows satisfactory valve performance under the DBA-LOCA 
     condition. 
     
     Recently, a report under 10 CFR Part 21 was received by the NRC from 
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 during accident conditions. The report discusses 
     the use of an unqualified solenoid valve for a safety-related valve 
     function which requires operation under 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 performance for conditions 
     noted in the previous paragraph must consider the concerns identified 
     in IE Bulletin 79-01A. 
     
     As the NRC review progresses, licensees which might have electrical 
     override circuitry problems are being advised not to use the override 
     and to take compensatory interim measures to minimize the problem. 

     In light of the information gained during our reviews of your 
     submittals dated January 9, February 5, June 20, and August 7, 1979 and 
     the information cited above, we believe an interim commitment from you 
     is required at this time. This is the case, even though you may have 
     proposed Technical Specification changes or other long or short-term 
     measures, which we are reviewing. 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 which could result from the postulated, DBA-LOCA while operating 
     with open purge or vent valves, we believe your prompt response to this 
     letter is required. In accordance with 10 CFR 50.54(f), you are 
     requested 
.

Mr. Alan R. Barton                - 3 -

     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 enable 
     us to determine whether or not your license to operate Farley Nuclear 
     Plant Unit No 1 should be modified, suspended, or revoked. 
     
                                        Sincerely, 



                                        A. Schwencer, Chief 
                                        Operating Reactors Branch #1 
                                        Division of Operating Reactors 

     Enclosure: 
     Interim Position for Containment 
       Purge and Vent Valve Operation 

     cc:  w/enclosure 
          See next page 
.

Mr. Alan R. Barton
Alabama Power Company              - 4 -
 cc:  Ruble A. Thomas, Vice President 
     Southern Services, Inc. 
     Post Office Box 2625 
     Birmingham, Alabama 35202 

     George F. Trowbridge, Esquire 
     Shaw, Pittman, Potts and Trowbridge 
     1800 M Street, N.W. 
     Washington, D. C. 20036 

     John Bingham, Esquire 
     Balch. Bingham, Baker, Hawthorne, 
     Williams and Ward 
     600 North 18th Street 
     Birmingham, Alabama 35202 

     Edward H. Keiler, Esquire 
     Keiler and Buckley 
     9047 Jefferson Highway 
     River Ridge, Louisiana 70723 

     George S. Houston Memorial Library 
     212 W. Burdeshaw Street 
     Dothan, Alabama 36303 
.

                 INTERIM POSITION FOR CONTAINMENT PURGE 

AND VENT VALVE OPERATION PENDING RESOLUTION OF ISOLATION VALVE OPERABILITY 

Once the conditions listed below are met, restrictions on use of the 
containment purge 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 established 
separately for each system. 

1.   Whenever the containment integrity is required, emphasis should be 
     place on operating the containment in a passive mode as much as 
     possible and on limiting all purging and venting times to as low as 
     achievable. To justify venting or purging, there must be an established 
     need to improve working conditions to perform a safety related 
     surveillance or safety related maintenance procedure. (Examples of 
     improved working conditions would include deinerting, reducing 
     temperature*, humidity*, and airborne activity sufficiently to permit 
     efficient performance or to significantly reduce occupational radiation 
     exposures), and 
     
2.   Maintain the containment purge and vent isolation valves closed 
     whenever the reactor is not in the cold shutdown 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 operable 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 butterfly valves may, on an interim basis, be 
          demonstrated by limiting the valve to be no more than 30 to 
          50 open (90 being full open). The maximum opening shall 
          be determined 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 introduced, and 
          
     b.   Modifications, 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 infection actuation 
          signals is uninhibited and operable to initiate valve closure when
          any other isolation signal may be blocked, reset, or overridden. 

* Only where temperature and humidity controls are not in the present 
design. 

Page Last Reviewed/Updated Wednesday, May 22, 2013