Containment Purging and Venting During Normal Operation - Guidelines for Valve Operability(Generic Letter 79-46)
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D. C. 20555
September 27, 1979
ALL LIGHT WATER REACTORS
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.
Darrell G. Eisenhut, Acting Director
Division of Operating Reactors
Guidelines for Demonstration
of Operability of Purge and
See next page
GUIDELINES FOR DEMONSTRATION
OF OPERABILITY OF PURGE AND
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
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
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 of the various aspects of operability of purge and vent valves
may be by analysis, bench testing, insitu testing or a combination of these
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
- 2 -
The following considerations apply when testing is chosen as a means for
demonstrating valve operability:
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
1. Whether a valve was qualified by testing of an identical valve
assembly or by extrapolation of data from a similarly designed
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
a. Simulation of LOCA
b. Seismic loading
c. Temperature soak
d. Radiation exposure
e. Chemical exposure
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 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.
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