Bulletin 76-06: Diaphragm Failures in Air Operated Auxiliary Actuators for Safety/Relief Valves
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
IE Bulletin No. 76-06
DATE: July 21, 1976
Page 1 of 3
DIAPHRAGM FAILURES IN AIR OPERATED AUXILIARY ACTUATORS FOR SAFETY/RELIEF
VALVES.
DESCRIPTION OF CIRCUMSTANCES:
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
facilities.
.
IE Bulletin No. 76-06
DATE: July 21, 1976
Page 2 of 3
ACTION TO BE TAKEN BY LICENSEE:
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).
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