IE Circular 77-11, Leakage of Containment Isolation Valves with Resilient Seats
CR77011
September 2, 1977
MEMORANDUM FOR: B. H. Grier, Director, Region I
J. P. O'Reilly, Director, Region II
J. G. Keppler, Director, Region III
E. M. Howard, Director, Region IV
R. H. Engelken, Director, Region V
FROM: H. D. Thornburg, Director, Division of Reactor
Operations Inspection, IE
SUBJECT: IE CIRCULAR 77-11, LEAKAGE OF CONTAINMENT ISOLATION
VALVES WITH RESILIENT SEATS
The subject document is transmitted for issuance on September 6, 1977. The
Circular should be issued to all holders of Reactor Operating Licenses and
Construction Permits. Also enclosed is a draft copy of the transmittal
letter.
H. D. Thornburg, Director
Division of Reactor Operations
Inspection
Office of Inspection and
Enforcement
Enclosures:
1. Circular 77-11
2. Draft Transmittal Letter
CONTACT: R. E. Shewmaker, IE
49-27751
.
Transmitted letter for Circular 77- 11 to each holder of an NRC Operating
Licensee.
Addressee:
The enclosed Circular 77-11 is forwarded to you for information. If there
are any questions related to your understanding of the suggested actions,
please contact this office.
Signature
(Regional Director)
Enclosure:
IE Circular 77-11
.
IE Circular 77-11
Date: September 6, 1977
Page 1 of 2
LEAKAGE OF CONTAINMENT ISOLATION VALVES WITH RESILIENT SEATS
DESCRIPTION OF CIRCUMSTANCES:
Several licensees have reported difficulty in satisfying leakage test
requirements on containment Isolation valves with resilient valve seats. The
seat materials have been identified as neoprene and ethylene propylene. The
licensees reporting difficulty in satisfying the testing requirements had
either a 36-inch or 42-inch butterfly valve manufactured by the Henry Pratt
Company with neoprene seats or a 24-inch butterfly valve manufactured by the
Allis Chalmers Company with ethylene propylene seats.
The cause of the excessive leakage has been determined to be either general
degradation of the resiliency characteristics of the seal, cold temperatures
and the associated "hardening" of the seal, or a combination of the two.
Testing of these isolation valves is required under 10 CFR 50, Appendix J on
an interval defined as each reactor shutdown for refueling, but in no case
at an interval greater than 2 years. In all except one of these several
cases described herein it was the required testing which defined the leakage
path.
In these cases an examination of the resilient valve seat material indicated
that the material had hardened and lost some resiliency and showed signs of
wear due to valve cycling. Exposure to various environmental conditions such
as humidity and temperature have also, in some cases, apparently accelerated
the degradation or changed the performance characteristics of the seating
material.
In one case, the valve was continuously pressurized as part of a penetration
pressurization system and it was determined that the valve leakage was
cycling with the outside air temperatures. When the air temperature dropped
at night, the valve seat would contract away from the valve and leakage
would begin. As temperature increased, the reverse would occur. If this
isolation valve had not been under constant pressure monitoring this
phenomenon would not have been observed unless a Type C local leak rate test
had been performed to check the leakage under both temperature conditions.
.
IE Circular 77-11
Date: September 6, 1977
Page 2 of 2
The valves involved have been those associated with containment purge and
ventilation systems. Preliminary information seems to indicate that for the
service these valves see, a life expectancy of the resilient seats is at
best about 3 years and may be less, dependent upon specific conditions to
which they are subjected.
Actions by the licensees have consisted of several different approaches to
assure the continued nearly leak-tight behavior of these large, butterfly
isolation valves. Seats are being replaced, seat materials are being tested
for resiliency, local testing frequency has been increased, and for the
facility where leakage was associated with temperature extremes, an external
heat source has been provided.
All holders of operating licenses or construction permits should be aware of
the possible limited useful life of the resilient valve seats for use on
large, butterfly valves. Certain steps can be taken to minimize the
possibility of excessive valve leakage and measures can be taken to quickly
detect the leaks if they occur.
These actions may be implemented through the following considerations.
1. Based on available data or manufacturers recommendations, assess the
acceptability of testing frequency and maintenance schedules for
existing valves of the type described. If results of the review
indicate the need for replacement, schedules for the replacement of
resilient seat materials should be developed.
2. Review of expected service conditions to provide assurance that
temperature extremes will not adversely affect the leakage rates. The
need for shortened intervals of testing should also be considered.
3. For those licensees who have plants under construction, applicants
should re-examine the specifications for the design and purchase of
similar valves so that their characteristics in service are anticipated
and the future maintenance program is considered prior to plant
completion.
No written response to this Circular is required; however, as needs or
experience indicate there may be further follow-up action. If such follow-up
is required the individual licensees will be contacted. If you require
additional information regarding this subJect, contact the Director of the
appropriate NRC Regional office.
Enclosure:
List of IE Circulars
Issued in 1977
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