United States Nuclear Regulatory Commission - Protecting People and the Environment

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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