Information Notice No. 89-63: Possible Submergence of Electrical Circuits Located Above the Flood Level Because of Water Intrusion and Lack of Drainage

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                September 5, 1989

                                   CIRCUITS LOCATED ABOVE THE FLOOD LEVEL 
                                   BECAUSE OF WATER INTRUSION AND LACK OF 


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees that electrical 
circuits located above the plant flood level within electrical enclosures may 
become submerged in water because appropriate drainage has not been provided.  
Failure of electrical circuits during service conditions, including postulated 
accidents, can occur due to submergence if water enters these enclosures and 
there is no provision for drainage.  The electrical enclosures addressed by 
this notice include terminal boxes, junction boxes, pull boxes, conduits, 
condulets, and other enclosures for end-use equipment (such as limit switches, 
motor operators, and electrical penetrations), the contents of which may 
include cables, terminal blocks, electrical splices and connectors.  It is 
expected that recipients will review this information for applicability to 
their facilities and consider actions, as appropriate, to avoid similar 
problems.  However, suggestions contained in this information notice do not 
constitute NRC requirements; therefore, no specific action or written response 
is required.

Description of Circumstances:

On March 20, 1989, the Clinton Power Station experienced an unexpected ingress 
of water into the drywell.  About 10 feet of water from the dryer pool drained 
into the reactor cavity pool causing about 4 inches of standing water in the 
drywell.  Following the event, the licensee found evidence of water intrusion 
in several electrical enclosures located above the flood level.  These 
enclosures did not have drain holes.  The licensee corrected the problem by 
drilling holes in all appropriate junction boxes, terminal boxes, pull boxes, 
condulets, and end-use equipment enclosures inside the drywell and the 

The Monticello plant found that a junction box for RHR pump motor leads con-
tained several inches of water (NRC Inspection Report 50-263/87-013-DRS).  The 
box did not have a drain hole.  The licensee initially determined that the as-
sociated conduits were routed through humid areas, which could have resulted 

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in condensation from the conduits accumulating in the box.  However, the 
licensee later postulated that hosing down of equipment in that area may have 
caused water to enter the box through unsealed openings.  In this instance, 
the circuits were found wet but not yet submerged in the accumulating water.  
The licensee drilled weep holes in all appropriate motor-lead junction boxes 
and other enclosures to correct the problem. 

During an inspection performed at Clinton Power Station from August 17 through 
August 21, 1987, NRC inspectors identified a terminal box without drain holes.
The box was required to be environmentally qualified in accordance with the 
requirements of 10 CFR 50.49.  Although the box was located above the 
postulated plant flood level, it was subject to possible water and moisture 
intrusion that could submerge the contents of the box in an accident.  
Subsequently, the licensee identified 156 terminal boxes without drain holes, 
which could affect multiple safety systems.  The licensee drilled drain holes 
in the affected terminal boxes.  During a followup inspection performed from 
February 6 through February 24, 1989, the NRC identified six additional 
junction boxes requiring drain holes.  Several of these boxes contained taped 
electrical splices which the licensee's environmental qualification program 
had not demonstrated to be environmentally qualified to perform their required 
function for the required duration if they became submerged following a 
loss-of-coolant accident (LOCA).  Following this finding, the licensee 
identified numerous other enclosures with taped splices that required drain 


The NRC regulation pertaining to environmental qualification specifically 
regarding submergence is addressed in 10 CFR 50.49(e)(6), which states that 
the electrical equipment qualification program must consider submergence (if 
subject to being submerged).  The regulation also makes reference to two 
guidance documents: "Guidelines for Evaluating Environmental Qualification of 
Class 1E Electrical Equipment in Operating Reactors," November 1979 (DOR 
Guidelines), and NUREG-0588, "Interim Staff Position on Environmental Quali-
fication of Safety-Related Electrical Equipment."  NUREG-0588, 
Paragraph 2.2(5) states that where equipment could be submerged, it should be 
identified and demonstrated to be qualified by test for the duration required.
DOR Guidelines, Section 6, state that particular emphasis should be placed on 
common problems, such as protective enclosures installed upside down with 
drain holes at the top and penetrations in equipment housings for electrical 
connections being left unsealed or susceptible to moisture intrusion through 
stranded conductors.

Water can enter and accumulate in electrical enclosures located above the 
flood level through various unsealed openings, including enclosure covers, 
conduits, and conduit fittings.  Water may enter an enclosure through a run of 
conduit from an upper elevation or by directly impinging on unsealed openings.
Steam and humidity also may enter an enclosure through conduits and unsealed 
openings and then condense and accumulate at the bottom of the enclosure.  The 
content of the enclosure may become submerged as a result.  Proper drain holes 
will prevent this.

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Submergence could occur during service conditions, including accidents such as 
a LOCA or other high-energy line break.  For clarity, a component is 
considered submerged if it is partially or completely immersed in water.  
Submergence of components in electrical enclosures may occur even though the 
enclosures are located above the plant flood level because of inadequate 
drainage in the enclosure.  

Water intrusion also may occur from hosing down the equipment during house-
keeping.  It is important to note that extreme care needs to be taken during 
such activities so that the water does not penetrate unsealed enclosure 
openings and travel through conduits to enclosures at lower elevations.

Information Notice 84-57, "Operating Experience Related to Moisture Intrusion 
on Safety-Related Electrical Equipment at Commercial Power Plants," addressed 
watertight sealing of all electrical conduits to junction boxes and 
conduit-to-terminal box connection points for safety-related equipment located 
in areas of the reactor building as well as for areas that are potentially 
subject to high temperature steam or water impingement.  This notice further 
addressed the importance of ensuring that box drain holes and equipment 
interfaces are in conformance with the test setup established during equipment 
qualification testing and with the vendor's recommendations.

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate NRR project 

                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contacts:  A. S. Gautam, NRR 
                     (301) 492-1376

                     H. Walker, NRR
                     (301) 492-0867

Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment 
                                                            IN 89-63 
                                                            September 5, 1989 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to_________

89-62          Malfunction of Borg-Warner    8/31/89        All holders of OLs
               Pressure Seal Bonnet Check                   or CPs for nuclear
               Valves Caused By Vertical                    power reactors. 
               Misalignment of Disk 

89-61          Failure of Borg-Warner Gate   8/30/89        All holders of OLs
               Valves to Close Against                      or CPs for nuclear
               Differential Pressure                        power reactors. 

88-48,         Licensee Report of Defective  8/22/89        All holders of OLs
Supp. 2        Refurbished Valves                           or CPs for nuclear
                                                            power reactors. 

89-60          Maintenance of Teletherapy    8/18/89        All NRC Medical 
               Units                                        Teletherapy 

89-59          Suppliers of Potentially      8/16/89        All holders of OLs
               Misrepresented Fasteners                     or CPs for nuclear
                                                            power reactors. 

89-58          Disablement of Turbine-Driven 8/3/89         All holders of OLs
               Auxiliary Feedwater Pump Due                 or CPs for PWRs. 
               to Closure of One of the 
               Parallel Steam Supply Valves 

89-57          Unqualified Electrical        7/26/89        All holders of OLs
               Splices in Vendor-Supplied                   or CPs for nuclear
               Environmentally Qualified                    power reactors. 

89-56          Questionable Certification    7/20/89        All holders of OLs
               of Material Supplied to the                  or CPs for nuclear
               Defense Department by Nuclear                power reactors. 

89-45,         Metalclad, Low-Voltage        7/6/89         All holders of OLs
Supp. 1        Power Circuit Breakers                       or CPs for nuclear 
               Refurbished With Substandard                 power reactors. 

89-55          Degradation of Containment    6/30/89        All holders of OLs
               Isolation Capability by a                    or CPs for nuclear
               High-Energy Line Break                       power reactors. 
OL = Operating License
CP = Construction Permit 

Page Last Reviewed/Updated Wednesday, March 24, 2021