Information Notice 2002-04, Wire Degradation at Breaker Cubicle Door Hinges

Wire Degradation at Breaker Cubicle Door Hinges

ML013510387
Person / Time
Site:	Diablo Canyon
Issue date:	01/10/2002
From:	Beckner W Division of Regulatory Improvement Programs
To:
Thomas Koshy, NRR-DRIP, 301-415-1176
References
TAC MB3369 IN-02-004
Download: ML013510387 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 January 10, 2002 NRC INFORMATION NOTICE 2002-04: WIRE DEGRADATION AT BREAKER CUBICLE

DOOR HINGES

Addressees

All holders of licenses for nuclear power reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform

addressees of degraded breaker cubicle wires found at the Diablo Canyon nuclear power plant.

These wires connect electrical equipment mounted on cubicle doors to equipment inside the

breaker cubicles. Over time, the wires degraded due to cold-working and aging. 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 actions or written response is required.

Description of Circumstances

On March 14, 2001, at Diablo Canyon, Unit 2, functional testing of relays associated with

containment spray (CS) pump 2-2 indicated that the overcurrent relay would not trip the pump

breaker. Troubleshooting revealed a broken wire between the CS pump 2-2 breaker cubicle

swingout door and the main 4kV cubicle. The pump was returned to operable status after the

broken wire was replaced and other cubicle wires were inspected.

The broken wire was analyzed, and it was determined that a number of wire strands had been

broken for some period of time based on the presence of corrosion at the end of the broken

strands. After reviewing the finding for potential generic implications, the licensee determined

that a 10% sample of 4kV breaker cubicles would be inspected for wire degradation. On

March 21-22, 2001, the first three 4kV breaker cubicles from the sample were inspected. Two

of the breaker cubicles showed no wire damage, but the third breaker cubicle contained two

degraded, but not broken, wires. This breaker cubicle is associated with Unit 1, CS pump 1-1.

On March 23, 2001, it was decided that an inspection of all 4kV breaker cubicles was needed, except where an inspection would be risky with the reactors at power (e.g., 4kV-to-480V feeder

breakers and startup crosstie breakers). Subsequent inspections during March 23-28, 2001, revealed four more cubicles with degraded wires, resulting in a total of six cubicles containing

degraded wires. Table 1, identifies the cubicle, the type of wire damage, and the effect on the

vital 4kV electrical system.

TABLE 1. DESCRIPTION OF BREAKER CUBICLE WIRE DEGRADATION

Breaker Cubicle

Description

Equipment

Containment spray The overcurrent relay had one completely broken wire.

pump 2-2 Containment spray One wire used for overcurrent protection had exposed and broken

pump 1-1 strands. A second spare wire had damaged insulation.

Safety injection A wire associated with overcurrent protection for one of the three

pump 2-2 phases had broken strands.

Unit 2, bus H Two wires associated with load shedding of residual heat removal

auxiliary feeder (RHR) pump 2-2 and CS pump 2-2 had broken strands.

breaker

Unit 1, bus F A wire connecting the ammeter select switch and test cut-out switch

auxiliary feeder had damage to the outer cloth jacket of the insulation.

breaker

Diesel generator 1- Two wires associated with the ground sensor auxiliary relay and alarm

3 feeder breaker had broken strands. A third abandoned wire also had broken strands.

Component cooling A wire providing power to an indicating lamp had damaged outer

water pump 2-1 insulation, although the inner insulation was still intact.

Of the degraded wires found in the six cubicles, only the broken wire associated with CS pump

2-2 was found to impact the 4kV electrical distribution system. If an overcurrent condition

occurred on CS pump 2-2, the broken wire would prevent the overcurrent relay from opening

the breaker, resulting in potential damage to the pump motor and/or loss of the associated vital

4kV bus. Submitting the other degraded wires to a 5-ampere current for one minute proved

them able to carry out their respective functions. A 5-ampere current is the maximum current

expected for any of the degraded wires.

Discussion

Breaker Cubicle Arrangement and Wire Type

The broken wire removed from CS pump 2-2 breaker cubicle was AWG #12, Type TA

insulation, National Electrical Manufacturers Association (NEMA) Class K (high strand) copper

wire. This wire has an inner rubber-type jacket and an outer fibrous jacket. The degraded

wires found in the other breaker cubicles were of similar type, but some were of a different

gauge. The breaker cubicles and the components inside them, including the wires, were

bought from General Electric and installed circa early 1970s during plant construction. The vital Class 1E 4kV breaker cubicles are General Electric Type M-26 breaker cubicles that

have two swingout doors. The bottom swingout door accesses the breaker and the top

swingout door accesses the breaker controls. Various relays, controls, and indications are

mounted on the top swing-out door. The number and type of equipment mounted on the top

swingout door depend on the type of plant equipment powered through the breaker. The

number of pieces and type of equipment mounted on the top swingout door also determines the

number of wires connecting the door-mounted equipment with terminals inside the cubicle

(typically 40 to 100 wires.)

The wires connecting the door-mounted equipment with terminals inside the cubicle are

supported by two vertical wire braces (also called wire looms) as shown in Attachment 1. The

purpose of the wire looms is to prevent the wires from becoming pinched in the door hinge

when the breaker is opened and closed. One wire loom is mounted on the swingout door

approximately 6 inches off the door surface and 2 inches from the door hinge. The other wire

loom is mounted inside the cubicle approximately 10 inches from the door hinge and

approximately 2 inches off the inner cubicle wall. The figure shows the construction and the

location of the wire loom in relation to the door, door hinge, and other breaker components.

When the door is fully opened, there is approximately 2 to 10 inches of wire slack between the

two wire braces.

Root Cause

The licensee has performed a formal evaluation to determine the cause of the breaker cubicle

wire degradation. The evaluation indicates that cold working and aging of the wires are the

causes.

(1) Cold Working

In a wire loom layout, in certain cases the wires are forced into the side of the breaker

cubicle when the cubicle door is closed. This can force the wire on the inside of the

bend to exceed the minimum bend radius for a dynamic bend, resulting in cold-working

of the strands. Subsequent cycling of the door eventually results in wire failure.

(2) Age-related degradation of the wires

Over time, the plasticizer leaches out of the PVC insulation, resulting in embrittlement.

Flexing of the wire causes the insulation to break. The loss of the mechanical support

provided by the insulation focuses the bending at the break, speeding the cold working

of the wire strands and causing eventual failure.

Corrective Actions

All degraded wires that have been identified have been replaced, and a continuity test has been

performed to ensure that the wires are connected to the correct terminals and functional. The

licensee is currently planning to inspect other wires in the plant that are susceptible to cold

working and age-related degradation using a risk-informed work schedule. Specifically, the

licensee is carrying out the following modifications. (1) Redesign the breaker cubicle wire looms and/or wire loom supports to eliminate

excessive bending at the door hinge area.

(2) Replace the wires that span the breaker cubicle hinge areas with standing class K or S

wire that uses contemporary insulation (non-PVC).

This information notice requires no specific action or written response. If you have any

questions regarding the information notice, please contact the technical contacts listed below or

the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

/RA/

William D. Beckner, Program Director

Operating Reactor Improvements Program

Division of Regulatory Improvement Programs

Office of Nuclear Reactor Regulation

Technical contacts: T. Jackson, Region IV Paul Shemanski, NRR

(805) 595-2354 301-415-1377 E-mail: twj@nrc.gov E-mail: pcs@nrc.gov

Attachments:

1. Breaker Cubicle Interior

2. List of Recently Issued NRC Information Notices

ML013510387 Template: NRR-052

• See previous concurrence

OFFICE RORP TECH ED DE:EEIB (A) SC:RORP PD:RORP

NAME TKoshy PKleene* JCalvo* TKoshy* WBeckner*

DATE 01/09/02 12/04/01 01/10/02 01/10/02 01/10/02

IN 2002-04 Attachment 1 Breaker Cubicle Interior

Attachment 2 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

______________________________________________________________________________________

Information Date of

Notice No. Subject Issuance Issued to

______________________________________________________________________________________

2002-03 Highly Radioactive Particle 1/10/2002 All holders of operating licenses

Control Problems During Spent for nuclear power reactors, Fuel Pool Cleanout holders of licenses for

permanently shutdown facilities

with fuel onsite, and holders of

licenses for non-power reactors.

2002-02 Recent Experience with 01/08/2002 All holders of operating licenses

Plugged Steam Generator for pressurized-water reactors

Tubes (PWRs), except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor.

2002-01 Metalclad Switchgear Failures 01/08/2002 All holders of licenses for nuclear

and Consequent Losses of power reactors.

Offsite Power

2001-19 Improper Maintenance and 12/17/2001 All holders of operating licenses

Reassembly of Automatic Oil for nuclear power reactors, Bubblers except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor vessel.

2001-18 Degraded or Failed Automated 12/14/2001 All uranium fuel conversion, Electronic Monitoring, Control, enrichment, and fabrication

Alarming, Response, and licensees and certificate holders

Communications Needed for authorized to receive safeguards

Safety and/or Safeguards information. Information notice is

not available to the public

because it contains safeguards

information.

______________________________________________________________________________________

OL = Operating License

CP = Construction Permit