Information Notice No. 89-63: Possible Submergence of Electrical Circuits Located Above the Flood Level Because of Water Intrusion and Lack of Drainage
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
September 5, 1989
Information Notice No. 89-63: POSSIBLE SUBMERGENCE OF ELECTRICAL
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
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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September 5, 1989
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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
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
H. Walker, NRR
Attachment: List of Recently Issued NRC Information Notices
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
89-60 Maintenance of Teletherapy 8/18/89 All NRC Medical
89-59 Suppliers of Potentially 8/16/89 All holders of OLs
Misrepresented Fasteners or CPs for nuclear
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
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