United States Nuclear Regulatory Commission - Protecting People and the Environment

Containment Purging and Venting During Normal Operation - Guidelines for Valve Operability (Generic Letter 79-46)


GL79046 

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

                            September 27, 1979 

ALL LIGHT WATER REACTORS 

Gentlemen: 

RE:  Containment Purging and Venting During Normal Operation - Guidelines 
     For Valve Operability 

By letter dated November 28, 1978, the Commission (NRC) requested all 
licensees of operating reactors to respond to generic concerns about 
containment purging and venting during normal plant operation. We are 
continuing our review of responses to those letters. 

As a result of our reviews, 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 pending a re-evaluation which shows satisfactory valve performance 
under the Design Basis Accident - Loss of Coolant Accident (DBA-LOCA) 
condition can be provided. 

We have developed the enclosed guidelines with the aid of our consultants, 
Brookhaven National Laboratory. Valve manufacturers have also teen contacted
and are cognizant of these guidelines. You are requested to initiate action 
on an expedited basis to ensure that containment vent and purge valves at 
your facility meet these guidelines. 

Please inform us within 30 days that you commit to implement a valve 
qualification program on an expedited basis. 

                                   Sincerely, 


                                   Darrell G. Eisenhut, Acting Director 
                                   Division of Operating Reactors 

Enclosure: 
Guidelines for Demonstration 
     of Operability of Purge and 
     Vent Valves 

cc:  w/enclosure 
     See next page 

                                                                 7910220413 
.

                                 ENCLOSURE 
                       GUIDELINES FOR DEMONSTRATION 
                       OF OPERABILITY OF PURGE AND 
                               VENT VALVES  

                               OPERABILITY 

In order to establish operability it must be shown that the valve actuator's
torque capability has sufficient margin to overcome or resist the torques 
and/or forces (i.e., fluid dynamic, bearing, seating, friction) that resist 
closure when stroking from the initial open position to full seated (bubble 
tight) in the time limit specified. This should be predicted on the 
pressure(s) established in the containment following a design basis LOCA. 
Considerations which should be addressed in assuring valve design adequacy 
include: 

1.   Valve closure rate versus time - i.e., constant rate or other. 

2.   Flow direction through valve; P across valve. 

3.   Single valve closure (inside containment or outside containment valve) 
     or simultaneous closure. Establish worst case. 

4.   Containment back pressure effect on closing torque margins of air 
     operated valve which vent pilot air inside containment. 

5.   Adequacy of accumulator (when used) sizing and initial charge for valve
     closure requirements. 

6.   For valve operators using torque limiting devices - are the settings of
     the devices compatible with the torques required to operate the valve 
     during the design basis condition. 

7.   The effect of the piping system (turns, branches) upstream and 
     downstream of all valve installations. 

8.   The effect of butterfly valve disc and shaft orientation to the fluid 
     mixture egressing from the containment. 

                              DEMONSTRATION 

Demonstration of the various aspects of operability of purge and vent valves
may be by analysis, bench testing, insitu testing or a combination of these 
means. 

Purge and vent valve structural elements (valve/actuator assembly) must be 
evaluated to have sufficient stress margins to withstand loads imposed while
valve closes during a design basis accident. Torsional shear, shear, 
bending, tension and compression loads/stresses should be considered. 
Seismic loading should be addressed. 

Once valve closure and structural integrity are assured by analysis, testing
or a suitable combination, a determination of the sealing integrity after 
closure and long term exposure to the containment environment should be 
evaluated. Emphasis should be directed at the effect of radiation and of the
containment spray chemical solutions on seal material. Other aspects such as
the effect on sealing from outside ambient temperatures and debris should be
considered. 
.

                                 - 2 - 

The following considerations apply when testing is chosen as a means for 
demonstrating valve operability: 

Bench Testing 

A.   Bench testing can be used to demonstrate suitability of the in-service 
     valve by reason of its tracibility in design to a test valve. The 
     following factors should be considered when qualifying valves through 
     bench testing. 

     1.   Whether a valve was qualified by testing of an identical valve 
          assembly or by extrapolation of data from a similarly designed 
          valve. 

     2.   Whether measures were taken to assure that piping upstream and 
          downstream and valve orientation are simulated. 

     3.   Whether the following load and environmental factors were 
          considered 

          a.   Simulation of LOCA 
          b.   Seismic loading 
          c.   Temperature soak 
          d.   Radiation exposure 
          e.   Chemical exposure 
          d.   Debris 

B.   Bench testing of installed valves to demonstrate the suitability of the
     specific valve to perform its required function during the postulated 
     design basis accident is acceptable. 

     1.   The factors listed in items A.2 and A.3 should be considered when 
          taking this approach. 

In-Situ Testing 

In-situ testing of purge and vent valves may be performed to confirm the 
suitability of the valve under actual conditions. When performing such 
tests, the conditions (loading, environment) to which the valve(s) will be 
subjected during the test should simulate the design basis accident. 

NOTE:     Post test valve examination should be performed to establish 
          structural integrity of the key valve/actuator components. 
Page Last Reviewed/Updated Wednesday, May 22, 2013