UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001

September 26, 2003

NRC INFORMATION NOTICE 2003-18: GENERAL ELECTRIC TYPE SBM CONTROL

SWITCHES WITH DEFECTIVE CAM

FOLLOWERS

Addressees

All holders of operating licenses for nuclear power reactors, except those who have

permanently ceased operations and have certified that fuel has been permanently removed

from the reactor vessel.

Purpose

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

addressees of recent and long-term operational experience with control switches and relays

incorporating a polycarbonate plastic material manufactured by General Electric known as

Lexan®. 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 January 5, 2003, at Calvert Cliffs Unit 1, an emergency diesel generator (EDG) output

breaker failed to close on demand. The licensee found that a single block module (SBM) type

auxiliary switch on the General Electric (GE) Magne-Blast type breaker had a broken cam

follower. The cam follower consists of a steel pivot pin centered in clear Lexan®. The pin had

sheared and fallen to the bottom of the switch. At the pin location, the Lexan® was cracked

with some pieces missing. Because the cam follower was broken, contact 152/b in the closing

coil circuit failed open, preventing the completion of the logic permitting closure of the breaker.

The licensee inspected individual breaker components affected by this deficiency. Of the 24

breakers inspected, 5 had defective SBM switches. At Unit 1, the defective switches were on

the EDG output breaker discussed above and a service water pump breaker; at Unit 2, a

service water pump breaker, a high-pressure injection system breaker, and an EDG output

breaker. All these switches had noticeably cracked Lexan® but were not in as bad a condition

as the switch on the Unit 1 EDG output breaker. The licensee replaced these switches with GE

Type SB-12 switches. Both SBM and SB-12 switches contain Lexan® cam followers but the

SB-12 switch was fabricated with Lexan® not exposed to hydrocarbons, a potential failure

mechanism discussed in Information Notice 80-13, ?General Electric Type SBM Control

Switches with Defective Cam Followers.”

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Background

In 1976, GE recognized this problem (GE Service Information Letter [SIL] No. 155). The SIL

stated that the material used for the cam followers prior to July 1972 was an acetyl resin

composition called Delrin®. Delrin® is easily distinguishable by its milky opaque appearance

from the clear Lexan®. The SIL recommends replacement of the SBM switches in safety

applications. GE replaced Lexan® in these switches with Valox®, which has a white opaque

appearance similar to Delrin®.

No failures of SBM switches have been reported attributable to cam followers made of Delrin®

or Valox®. However, properties of these or related materials have been discussed in NRC

generic communications, as noted below.

The cause of the Lexan® failures was believed to be exposure of the switches to hydrocarbon

chemicals during manufacture or maintenance. With respect to the manufacturing process,

switches made between July 1972 and May 1975 were believed to be suspect. GE SIL No. 155

provided date codes to aid in the identification of suspect switches.

The Maine Yankee licensee had previously (in 1972) experienced failures of SBM switches

during maintenance when using contact cleaner and discontinued use of any type of contact

cleaner on SBM switches. 

In 1976, GE supplemented SIL No. 155, adding a recommendation to inspect all SBM switches

that have polycarbonate cam followers and to replace those found to have severely cracked

cam followers.

In 1979, GE again supplemented SIL No. 155, reminding BWR operators of the need to inspect

the SBM switches according to Supplement 1 and discussing manufacturing changes made

since January 1976: discontinuing use of nonvirgin Lexan® materials, discontinuing use of

hydrocarbons, and reducing stress during roll pin insertion.

In 1980, NRC issued Information Notice 80-13 to describe the SBM switch cam follower defects

found at Cooper and Diablo Canyon Unit 1. These switches are used broadly and thus

represent a potential common-mode failure affecting multiple safety-related systems. At

Cooper, SBM switches are used primarily as hand control switches in the control room. At

Diablo Canyon Unit 1, they provide auxiliary contacts in three switch applications on 4 kV and

12 kV Magne-Blast breakers: a breaker-mounted auxiliary switch, a cell-mounted auxiliary

switch, and a cell interlock switch. These defects were described as severe cracking with a

rock salt appearance that could ultimately progress to mechanical failure.

Additional, more recent operating experience may be cited. In 1998, the Perry licensee

mistakenly determined that IN 80-13 and SIL No. 155 did not apply to local control switches on

installed ABB HK breakers. The licensee committed to reevaluate the applicability and take

appropriate corrective action.

In 1996, the LaSalle licensee experienced problems while downshifting the recirculation pump. 

The licensee failed to take appropriate corrective action for safety-related SBM switch

degradation concerns identified in 1979, 1990, and 1995.
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Also in 1996, the Turkey Point licensee observed that a 4 kV bus clearing relay failed to actuate

in test. An intake cooling water system pump motor breaker stationary switch failed to operate

its contacts as required. The licensee found a cracked internal cam follower on this switch. 

The licensee also observed that all four 4 kV buses contained SBM switches but concluded that

all four 4KV buses were operable, characterizing the problem as an isolated random failure and

noting the manufacturer's assessment that the switches would function 45,000 cycles with

existing cracks and the licensee’s plans to replace the switches at the next opportunity.

In 1995, the Maine Yankee licensee found three broken cam followers in SBM switches on

medium-voltage breakers. Two did not prevent switch function and the third affected only a

spare contact. The licensee did not identify a safety concern but did identify a need for more

effective communications with GE, including obtaining an index of all GE service letters to

evaluate against the affected components in the plant.

Also in 1995, the Pilgrim licensee encountered an SBM switch cam follower failure of the highpressure coolant injection system suction valve from the torus. A similar failure occurred in

1992. The NRC cited the licensee for not promptly correcting the 1992 failure and noted that

the 1995 failure was corrected satisfactorily. Previous similar failures at this plant can be cited

as well: a core spray inboard injection valve in 1988, and a hydrogen analyzer sample flow line

in 1993. 

In 1994, the Cooper licensee inspected 130 SBM switches and found cracking, opaqueness,

and missing pieces of cam followers on 34 of them.

In 1992, the Fort Calhoun licensee experienced a failed switch for a raw water pump because

of a cracked cam follower. At the time, the licensee was replacing switches with open cracks or

missing pieces.

Discussion

Though failure of SBM switches because of cracked or broken cam followers was noted some

30 years ago, problems persist. Guidance on avoiding the problem is available.

Licensees have found SBM switches with degraded Lexan® cam followers of the affected date

codes among their stored components in addition to those installed in the plant. In addition to

replacing the affected switches in service, licensees have determined that eliminating affected

switches, whether degraded or not, from the stored components effectively prevents inadvertent

use of such defective switches.

Other operating experience that differs from the above in one or more respects might

nevertheless apply to the general problem of degradation of plastic materials used in nuclear

power plants. Degradation of Delrin®-related materials in applications different from control

switches is described in NRC Information Notices 83-45 and 92-85. Thermal properties of

Valox® or related material are discussed in NRC Bulletin 78-01. 

In 2003, NRC inspectors at the Surry plant learned of degradation of zippertubing, a plastic

product of Zippertubing Company, used to bundle electric cable inside the safety injection

cabinets at both Units 1 and 2. This product was qualified and delivered as part of the original 
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equipment during plant construction. Zippertubing sold the product as ZIP-31 at that time,

discontinued its manufacture 10-12 years ago, and now markets a similar product as ZIP-41. 

The Surry licensee removed this covering. This operating experience relates to NRC

Information Notice 91-20 ?Electrical Wire Insulation Degradation Caused Failure in a SafetyRelated Motor Control Center.”

In 2002, the San Onofre licensee reported degradation of contacts due to excessive use of

Inhibisol, a cleaning solvent based on trichloroethane (TCE). The cleaning solvent caused the

plastic housing for the contacts to break down. Over time, small amounts of the plastic came

loose and interfered with the contacts, resulting in linestarter degradation and the failure of

safety-related valves. The NRC issued Information Notice 2003-06, ?Failure of Safety-Related

Linestarter Relays at San Onofre Nuclear Generating Station.” Information Notice 93-76,

?Inadequate Control of Paint and Cleaners for Safety-Related Equipment,” may also apply.

In 1995, the Browns Ferry licensee reported GE Type HFA 51 Series AC relay failures involving

shorting of coil wire insulation made of nylon or Lexan®. After its review, the licensee replaced

308 such relays at Unit 3. The NRC issued Information Notice 81-01, ?Possible Failures of

General Electric Type HFA Relays” and Bulletin 84-02, ?Failures of General Electric Type HFA

Relays in Use in Class 1E Safety Systems.”

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

questions about this notice, contact one of the persons listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

/RA/

William D. Beckner, Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Technical Contacts: Vernon Hodge, NRR Joe O'Hara, Region I

 301-415-1861 410-495-4669

 E-mail: cvh@nrc.gov E-mail: jmo@nrc.gov

Stephen Alexander, NRR

301-415-2995

E-mail: sda@nrc.gov

Attachment: List of Recently Issued NRC Information Notices
____________________________________________________________________________________

OL = Operating License

CP = Construction Permit

Attachment 1

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LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

____________________________________________________________________________________

Information Date of 

Notice No. Subject Issuance Issued to

____________________________________________________________________________________

2003-17 Reduced Service Life of

Automatic Switch Company

(ASCO) Solenoid Valves With

Buna-N Material

09/29/2003 All holders of operating licenses

for nuclear power reactors.

2003-16 Icing Conditions Between

Bottom of Dry Storage System

and Storage Pad

Pending All 10 CFR Part 72 licensees and

certificate holders.

2003-15 Importance of Followup

Activities in Resolving

Maintenance Issues

09/05/2003 All holders of operating licenses

for nuclear power reactors except

those who have permanently

ceased operation and have

certified that fuel has been

permanently removed from the

reactor vessel.

2003-14 Potential Vulnerability of Plant

Computer Network to Worm

Infection

08/29/2003 All holders of operating licenses

for nuclear power reactors,

except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor vessel. 

2003-13 Steam Generator Tube

Degradation at Diablo Canyon

08/28/2003 All holders of operating licenses

for pressurized-water reactors

(PWRs), except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor.

Note: NRC generic communications may be received in electronic format shortly after they are

issued by subscribing to the NRC listserver as follows:

To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the following

command in the message portion:

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