Information Notice No. 84-57: Operating Experience Related to Moisture Intrusion in Safety-related Electrical Equipment at Commercial Power Plants

                                                            SSINS No.: 6835 
                                                            IN 84-57       

                                UNITED STATES
                            WASHINGTON, DC 20555

                                July 27, 1984

                              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 
is required. 

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. 

                                                             IN 84-57     
                                                             July 27, 1984 
                                                             Page 2 of 3  

(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 
     equipment housing. 

(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 
preventive actions: 

(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, 
     such as: 

     (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 
          vendor's recommendations. 

(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. 

                                                             IN 84-57     
                                                             July 27, 1984 
                                                             Page 3 of 3  

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
                    (301) 492-9673

                    M. El-Zeftawy, AEOD
                    (301) 492-4434

List of Recently Issued IE Information Notices

Page Last Reviewed/Updated Wednesday, March 24, 2021