Information Notice No. 84-57: Operating Experience Related to Moisture Intrusion in Safety-related Electrical Equipment at Commercial Power Plants
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
July 27, 1984
INFORMATION NOTICE NO. 84-57: OPERATING EXPERIENCE RELATED TO MOISTURE
INTRUSION IN SAFETY-RELATED ELECTRICAL
EQUIPMENT AT COMMERCIAL POWER PLANTS
All holders of a nuclear power reactor operating license (OL) or
construction permit (CP).
This notice is provided to alert licensees and applicants of a potentially
significant problem pertaining to moisture intrusion into safety-related
electrical equipment located in high humidity/high temperature areas of the
power plant. We expect that recipients of this notice will review the
information for applicability to their facilities and consider actions, if
appropriate, to preclude a similar problem from occurring at their
facilities. However, suggestions contained in this information notice do not
constitute NRC requirements and, therefore, no specific action or response
Description of Circumstances:
Numerous occurrences of safety-related equipment failures resulting from
moisture intrusion have been reported to the NRC since IE Bulletin 79-01B
was issued. Most of these failures involved electrical termination boxes,
junction boxes, pressure switches, etc. Recently the NRC Office of Analysis
and Evaluation of Operational Data (AEOD) performed a study on these
operational events with data obtained from 53 reported events that occurred
from July 1980 through February 1984. Most of these events occurred at
boiling water reactor (BWR) plants and involved equipment located outside of
primary containment, such as in the reactor building basement, and in the
high-pressure coolant injection (HPCI), low-pressure coolant injection
(LPCI), and reactor heat removal/reactor core isolation cooling (RHR/RCIC)
pump rooms. Details of the aforementioned study are documented in the
AEOD-C402 report, which is currently being published by the NRC.
Analysis of equipment failures in the AEOD study shows that most of the
electrical components were short-circuited and corroded when failure
occurred. In most cases, the shorting was caused by moisture leaking into
the equipment housing and junction boxes. Contributing factors to this
moisture intrusion inside the equipment housing were:
(1) Installed equipment had lost its environmental protection boundary as a
result of maintenance activities.
July 27, 1984
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(2) Many early designs and installations did not provide adequate
protective boundaries. Unsealed conduits and other possible pathways
were allowed to exist that permitted moisture to leak into the
(3) Moisture and steam may have entered at unsealed conduit ends located at
higher elevations and eventually found their way down to the equipment
housing and junction boxes at lower elevations.
The AEOD study indicates that the licensees had taken several corrective
actions, including cleaning and drying the equipment and, in some cases,
completely replacing components. However, moisture intrusion into electrical
equipment housing remains a recurring problem at nuclear power plants.
To prevent moisture-induced degradation and to maintain integrity of safety
related electrical equipment, the NRC staff recommends that holders of
operating licenses and construction permits consider the following
(1) Provide routine surveillance of areas where equipment is installed to
assure that its environmental parameters are within its designed limits
during normal plant operations.
(2) Ensure that plant maintenance programs include adequate administrative
controls to require restoration of vapor barriers, gaskets, and seals
to equipment after maintenance or testing activities are completed,
(a) providing watertight sealing to all electrical conduit-to-junction
boxes and conduit-to-terminal box connection points for
safety-related equipment located in areas of the reactor building
and areas that are potentially subject to high temperature steam
or water impingement.
(b) ensuring that the existence (or lack) of box drain holes and
equipment interfaces are in conformance with the test setup
established during equipment qualification testing and with the
(3) Provide more details and, when necessary, include pictorial
descriptions in surveillance and/or maintenance procedures that involve
the disassembly/reassembly of equipment housings.
(4) Train personnel working on electrical, electronics, and instrumentation
equipment in installation techniques to prevent the potential of
moisture intrusion into equipment housings.
(5) Provide adequate quality assurance review to ensure that appropriate
instructions are included in the surveillance and maintenance
procedures and to verify that equipment is properly protected against
moisture intrusion when reassembled.
July 27, 1984
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If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC regional office, or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: N. B. Le, IE
M. El-Zeftawy, AEOD
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