Bulletin 76-06: Diaphragm Failures in Air Operated Auxiliary Actuators for Safety/Relief Valves

                          WASHINGTON, D. C. 20555 

                                                  IE Bulletin No. 76-06 
                                                  DATE: July 21, 1976 
                                                  Page 1 of 3 



On July 8, 1976, Vermont Yankee reported that during a scheduled refueling 
outage surveillance test on their Target Rock valves, the auxiliary air 
actuator was found to be inoperable on three of the four valves. 

The licensee reported that investigation disclosed that the actuator 
diaphragms, composed of dacron fabric reinforced silicone rubber, had been 
degraded by excessive heat. The excessive heat is attributed to the fact 
that, contrary to the valve manufacturer's installation instructions, 
thermal insulation had been applied to the pneumatic actuator. The licensee 
further reported that the valve in which the diaphragm was found not to be 
degraded, was installed in the direct path of cooling air discharge from the
ventilation system, thus receiving supplementary cooling. 

Elastomeric materials such as the subject diaphragms are known to have 
finite service life and to be degraded by excessive temperatures; however, 
this is the first reported instance of degradation of this component. This 
event has particular safety significance, since failure of the diaphragms 
defeats the function of the Automatic Depressurization System. In 
recognition of this situation, the NRR Division of Operating Reactors 
conducted a telephone survey on July 16, 1976, of selected BWR operating 

                                                  IE Bulletin No. 76-06  
                                                  DATE: July 21, 1976  
                                                  Page 2 of 3 


All operators of BWR and PWR reactor facilities with operating licenses are 
to take the following action: 

     1.   Determine that the insulation installed on safety related 
          diaphragm operated relief valves in high temperature fluid systems 
          is in accordance with the current recommendations of the valve 
          vendor i.e. that there is no thermal insulation on the upper part 
          of the valve, including the air actuator. 

     2.   Ensure that the procedures used for the disassembly and inspection
          of these valves, as required by the Technical Specifications, 
          specifically include inspection of the subject diaphragms to 
          determine that no significant deterioration of the diaphragm 
          material has occurred. 

     3.   Ensure that the vendor's recommended service life and shelf life 
          for the diaphragms is not exceeded for the environmental 
          conditions to which the material is exposed.  

     4.   A report of your plans and schedules for accomplishing the above 
          actions should be submitted within 10 days after receipt of this 
          Bulletin. For facilities already surveyed by NRR: DOR, this report
          should confirm information reported orally. 

     5.   The NRC Regional Office should be promptly informed, within 24 
          hours, of any adverse findings resulting from your inspection 
          and/or review of the subject diaphragms or their application. 

     6.   Within 20 days after completion of the actions described in Item 
          4 above, report the results, including for any valves found to 
          have degradation of diaphragms, the make, type, size, diaphragm 
          material, and service (system) application. 

                                                  IE Bulletin No. 76-06 
                                                  DATE: July 21, 1976  
                                                  Page 3 of 3 

Reports should be submitted to the Director of the NRC Regional Office and a 
copy should be forwarded to the NRC Office of Inspection and Enforcement, 
Division of Reactor Inspection Programs, Washington, D. C. 20555. 

Approval of NRC requirements for reports concerning possible generic 
problems has been obtained under 44 U.S.C 3152 from the U. S. General 
Accounting Office. (GAO Approval B-180255(R0072), expires 7/31/77). 

Page Last Reviewed/Updated Tuesday, September 01, 2015