Information Notice 2002-12, Submerged Safety-Related Electrical Cables

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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