Information Notice 2002-12, Submerged Safety-Related Electrical Cables
| ML020790238 | |
| Person / Time | |
|---|---|
| Issue date: | 03/21/2002 |
| From: | Beckner W NRC/NRR/DRIP/RORP |
| To: | |
| Hodge, CV, NRR/DRIP/REXB, (415-1861) | |
| References | |
| IN-02-012 | |
| Download: ML020790238 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 March 21, 2002 NRC INFORMATION NOTICE 2002-12: SUBMERGED SAFETY-RELATED ELECTRICAL
CABLES
Addressees
All holders of operating licenses or construction permits for nuclear power reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform
addressees of observed protracted submergence in water of electrical cables that feed safety- related equipment. It is expected that recipients will review the information for applicability to
their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances
On November 11, 2001, at the Oyster Creek Nuclear Power Plant, a 4160-Vac cable failure
deenergized a unit substation for the 480-Vac system, prompting unit shutdown. The licensee
replaced the faulted Anaconda Unishield cable with a Cablec cable and conducted a root cause
evaluation. On the basis of that evaluation, the licensee concluded that the cable failure
resulted from a localized delamination of the cable jacket aggravated by water intrusion into the
underground cable conduit, subsequent cable drying, and corona degradation of the insulation
[Licensee Event Report 50-219/2001-01, dated January 7, 2002].
NRC inspectors reviewed similar concerns at Pilgrim Nuclear Power Station (Inspection Report
50-293/01-05), Millstone Nuclear Power Station Unit 2 (no inspection report generated), and
Beaver Valley Power Station (Inspection Report 50-334/01-09). At Pilgrim, the inspectors
identified one issue of very low safety significance (Green), finding that safety-related cables
located inside manholes were submerged in water for an extended period of time. Although not
a specific violation of NRC requirements, this was a notable weakness given that the licensee
did not have a routine monitoring and inspection program for these underground cables. At
both Millstone Unit 2 and Beaver Valley, the inspectors observed submerged safety-related
cables, but learned that the cables were designed to withstand such submergence.
On August 30, 2000, at the Brunswick Steam Electric Plant, NRC inspectors toured a system of
underground manholes and found safety-related electrical cables, including electrical splices, submerged in water. In addition, the inspectors observed leaking ductbanks, corroded and
broken cable supports, cable jacket tears, inoperable sump pumps, and inoperable level control
circuits. Prior to that inspection, on January 21, 1999, the Brunswick licensee inspected one of
the manholes in this system, found adverse conditions, and classified the entire system of 57 manholes in Maintenance Rule (MR) a(1) status. That classification refers to Title 10 of the
Code of Federal Regulations (10 CFR), Section 50.65(a)(1), which requires monitoring of the
performance or condition of a system against licensee-established goals to reasonably ensure
that the system can satisfy its intended function (NRC Inspection Report 50-325/2000-04, dated
October 27, 2000).
On October 2, 1999, at Davis-Besse, a component cooling water pump tripped as a result of a
phase-to-ground fault on a medium-voltage 3-phase power cable. The specific cable in
question was installed in a 4-inch polyvinyl chloride (PVC) conduit, which runs partially
underground, and had been in service for 23 years.
Discussion
Oyster Creek Nuclear Power Plant
The licensee determined that the safety significance of this event was minimal because the
redundant electrical power source remained operable and because no functional failure of any
safety system occurred. After replacing the failed portion of the cable and making necessary
repairs, the licensee brought the plant back up to power. In the long term, the licensee is
evaluating replacement cables that are extruded and manufactured with modern techniques
and the use of above-ground cable trays for its medium voltage electrical distribution system.
Brunswick Steam Electric Plant
The licensee established a manhole restoration project to restore the material condition of the
electrical manholes, including those with cabling addressed by the Maintenance Rule. Using
risk assessment techniques to schedule the restorations, the licensee restored 52 manholes to
varying degrees over a period of more than one year, satisfying the goals of (1) inspecting and
repairing degraded cable and (2) minimizing water leakage into plant structures and manholes
to prevent corrosion of cable supports and components.
Licensee corrective actions included (1) identifying and repairing degraded protective cable
jackets, (2) cleaning or coating corroded cable supports or components, (3) addressing leakage
of rainwater or groundwater by replacing the seals of duct banks entering manholes or plant
structures and installing plastic inserts under manhole covers to divert accumulating rainwater
away from the manholes, (4) replacing sump pumps and switch mechanisms as needed, and
(5) adding check valves to sump pump discharge piping to prevent rainwater from backing up
into manholes.
The licensee is currently evaluating the effectiveness of this project. To date, the licensee has
not identified water leakage from manholes in plant buildings. Davis-Besse Nuclear Power Station
In determining the root cause of the medium-voltage cable failure, the licensee theorized that
water in the conduit gradually penetrated the outer neoprene cable jacket, migrated through the
cloth binder tape just inside the jacket and through the various layers of the cable construction, and finally penetrated the ethylene propylene rubber (EPR) insulation by osmosis. The water
seeping into the cable layers likely contained impurities that precipitated in the outer region of
the EPR. Because the conductor was off-centered, precipitation of these impurities presumably
disturbed the electric field in the jacket material. The accompanying observed cracking and
conversion of the jacket material to carbon may have released additional impurities that would
have further degraded the cable. Breakdown of the insulation would be most concentrated in
the regions of the highest electric field intensity produced by the current in the conductor.
However, this scenario has not been confirmed.
The licensee successfully tested the cables of the other two component cooling water pumps
and the associated makeup pumps. On the basis of these tests, the licensee concluded that
the ground was an isolated fault.
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 project manager from the NRCs Office of Nuclear Reactor
Regulation (NRR).
/RA/
William D. Beckner, Program Director
Operating Reactor Improvements Program
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical contacts: V. Hodge, NRR Paul Shemanski, NRR
301-415-1861 301-415-1377 E-mail: cvh@nrc.gov E-mail: pcs@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
Document Name: G:\REXB\cvh\event reviews\submcabl inf 20109.wpd
OFFICE RE:OES:RORP: DE:EEIB TECH EDITOR (A)SC:RORP:D PD:RORP:DRIP
DRIP RIP
NAME CVHodge PCShemanski TKoshy WDBeckner
DATE 03/18/2002 03/18/2002 03/18/2002 03/20/2002 03/21/2002
Attachment 1 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
_____________________________________________________________________________________
2002-11 Recent Experience with 03/12/2002 All holders of operating licenses
Degradation of Reactor for pressurized-water reactors
Pressure Vessel Head (PWRs), except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
2002-10 Nonconservative Water Level 03/07/2002 All holders of operating licenses
Setpoints on Steam for nuclear power reactors, Generators except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
2002-09 Potential for Top Nozzle 02/13/2002 All holders of operating licenses
Separation and Dropping of for nuclear power reactors, and
Certain Type of Westinghouse non-power reactors and holders
Fuel Assembly of licenses for permanently
shutdown facilities with fuel
onsite.
2002-08 Pump Shaft Damage Due to 01/30/2002 All holders of operating licenses
Excessive Hardness of Shaft for nuclear power reactors, Sleeve except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
2002-07 Use of Sodium Hypochlorite for 01/28/2002 All holders of operating licenses
Cleaning Diesel Fuel Oil for nuclear power except those
Supply Tanks who have ceased operations and
have certified that fuel has been
permanently removed from the
reactor vessel.
2002-06 Design Vulnerability in BWR 01/18/2002 All holders of operating licenses
Reactor Vessel Level or construction permits for boiling
Instrumentation Backfill water reactors (BWRs).
Modification
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit