Bulletin 78-04: Environmental Qualification of Certain Stem Mounted Limit Switches Inside Reactor Containment
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
February 21, 1978
IE Bulletin No. 78-04
ENVIRONMENTAL QUALIFICATION OF CERTAIN STEM MOUNTED LIMIT SWITCHES INSIDE
REACTOR CONTAINMENT
Description of Circumstances:
As a result of a recent review by Westinghouse of the seismic and
environmental qualifications of the electrical circuitry used for valve
operation, certain stem mounted limit switches (SMLS) associated with
various safety related valves were found not to be environmentally qualified
for loss of coolant accident (LOCA) conditions. The switches in question are
installed on certain motor operated valves and certain air-operated valves
located in primary containment. The functions of these valves provide either
containment isolation or emergency core cooling system (ECCS) alignment
during accident conditions.
Westinghouse has stated that for air operated valves the SMLS function is to
provide "latch-in" capability to the actuation control circuitry of the
valve. It therefore is designated as safety-related and must receive seismic
and environmental qualification.
The concern arises if the SMLS contacts short circuit during LOCA
conditions. If this occurs and if the valve control switch is in the "AUTO"
position (and control air is available to the valve operator), the valve
will move from its post accident position to the normal operating position
when either the safety injection or containment isolation signal is reset. A
limited number of the switches are also used in safety related motor
operated valve circuits in Westinghouse designed plants.
The attached Westinghouse Technical Bulletin, NSD-TB-77-13 issued on
September 30, 1977, further describes the problem and provides suggestions
for correcting the problem in air-operated valve actuation circuitry. One of
the corrective actions considered by Westinghouse involves replacement of
the switch with a switch that is environmentally qualified. An alternative
corrective action utilizes a circuit modification to the "latch-in" feature
associated with the air-operated valve circuitry so that no adverse affect
on valve operation can occur during
1 of 3
.
IE Bulletin No. 78-04 February 21, 1978
post accident conditions. For example, VEPCO has initiated a modification to
the valve control circuitry at North Anna to remove the SMLS contacts from
the valve operation circuitry.
The SMLS in question is identified as NAMCO Model D2400X or EA-170-302 SNAP
LOCK. NAMCO can provide qualified switches to replace unqualified ones upon
request from the user. Because all NAMCO SNAP LOCK type switches have been
seismically qualified by tests, only environmental qualification is a
concern in this issue. This problem ma be generic for all power reactor
facilities with an operating license or a construction permit.
Action to be Taken by Licensees and Permit Holders:
For all power reactor facilities with an operating license or a construction
permit:
1. Determine if your facility utilizes or plans to utilize NAMCO D2400X or
EA-170--302 SNAP LOCK switches in any safety related equipment in the
primary containment, including the valve control circuitry previously
discussed.
2. If any such applications are identified, review these applications to
determine the adequacy or qualification testing for these switches and
submit the qualification documentation or references to NRC for review.
3. If evidence is not available to support a conclusion of adequacy,
submit your plans and programs, including schedules, for corrective
action.
4. Provide your response in writing within 30 days for facilities holding
an operating license and within 60 days for those facilities with a
construction permit. Reports should be submitted to the Director of the
appropriate NRC Regional Office and a copy should s be forwarded to the
U. S. Nuclear Regulatory Commission, Office of Inspection and
Enforcement, Division of Reactor Operations Inspection, Washington,
D.C. 20555.
2 of 3
.
IE Bulletin No. 78-04 February 21, 1978
Approved by GAO, B180225 (R0072); clearance expires 7/31/80. Approval was
given under a blanket clearance specifically for identified generic
problems.
Attachment:
W Technical Bulletin
NSD-TB-77-13
3 of 3
Page Last Reviewed/Updated Tuesday, March 09, 2021