United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-52: Conductor Insulation Degradation on Foxboro Model E Controllers

                                                           SSINS NO.:  6835 
                                                           IN 86-52        

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                                June 26, 1986

Information Notice No. 86-52:   CONDUCTOR INSULATION DEGRADATION ON 
                                   FOXBORO MODEL E CONTROLLERS 

Addressees: 

All nuclear power reactors holding an operating license or a construction 
permit. 

Purpose: 

This notice is to alert recipients to a potentially generic problem with 
conductor insulation degradation on 15 conductor/24 gage interconnection 
coil-cord cable sets (cable sets) supplied by the Foxboro Company (TFC) for 
use with Foxboro model E electronic controllers. Degradation of the 
insulation could result in a common mode failure in that wiring of the same 
age in various controllers may fail in certain circumstances, such as a 
seismic event. Recipients are expected to review the information for 
applicability to their facilities and consider actions, if appropriate, to 
preclude a similar problem from occurring at their facilities. However, 
suggestions contained in this information notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.

Description of Circumstances: 

While performing routine surveillance on the reactor protection system (RPS)
instrumentation at the Haddam Neck Nuclear Plant in October 1984, 
Connecticut Yankee Atomic Power Company (CY) found that the conductor 
insulation on a cable set for a Foxboro model E electronic controller in the 
control room RPS logic cabinet was in a degraded condition after more than 
10 years of service. The degradation consisted of embrittlement of the 
insulation on the conductors within the cable set. CY determined that 
handling could cause the wire insulation to disintegrate with the potential 
for unanalyzed short circuits occurring. Further inspections determined that 
21 similar Foxboro cable sets in the RPS exhibited the same degradation. 
Normal CY maintenance activities did not require access to the terminal 
block portion of the cable set, so it is not clear how long this condition 
may have existed. CY issued a licensee event report (LER 50-213/84-017 dated 
11/01/84) in which it stated that the cause of the degradation was aging and 
that the insulation had poor stability. 





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TFC has been aware of this problem since the fall of 1978, and concluded in 
a 1979 internal report that the failures seemed to be occurring after about 
15 years in the field and were due to oxidation aging. Additionally, the 
report stated that sometime after 10 years the insulation of the individual 
wires will deteriorate and wires may contact each other and that all model E 
controllers 10 years or older should be examined for insulation 
deterioration at least annually. Due to inadequacies in TFC's Part 21 
evaluation and reporting procedure, TFC failed to make notification to 
either their customers or the NRC (reference violation 85-01-01 in VPB 
inspection report 99900225/85-01). 

Discussion: 

An NRC inspection at the Foxboro Company (reference VPB inspection report 
99900225/85-01) and discussions with the cable manufacturers have determined
that: 

1.   The Foxboro Company recommends that all cable sets for Foxboro model E 
     controllers should be examined for insulation degradation at least 
     annually, regardless of when they were purchased since these cable sets
     may have been in stock at The Foxboro Company warehouse for several 
     years. 

2.   Foxboro has disposed of all of the remaining coil-cord cable sets in 
     stock to prevent recurrence of the insulation degradation condition. 

3.   The cable manufacturers typically had a 1-year warranty for the 
     coil-cord cable sets. The life expectancy of the cable sets under mild 
     service conditions and environment is under 10 years. 

In addition, the Institute of Materials Science (IMS) of the University of 
Connecticut performed an analysis of two of the defective cable sets for CY.
The IMS analysis concluded that the insulation degradation of some 
production batches was due to poor stability of the insulation material. 

Foxboro model E electronic controller numbers 61, 62, and 67 have been 
identified as utilizing the coil-cord type of cable sets. A subsequent 
Foxboro electronic controller model line has similar numbers 61 H, 62 H, and
67 H but they are not affected. Foxboro cannot determine which nuclear 
facilities have installed model E electronic controllers in safety-related 
systems. Foxboro issued a letter on October 18, 1985 which discussed "end of
life" components. However, this letter may not have been effective at 
notifying end users of the problem. Therefore, Foxboro issued a second 
letter to all nuclear power plants on June 4, 1986. Foxboro stopped 
manufacturing the model E electronic controllers in 1970 and withdrew model 
E product line support in 1984. Coil-cord cable sets were available for 
replacement from Foxboro until 1984. However, the cable sets that Foxboro 
had in stock were several years old. In the June 4, 1986 letter, TFC 
committed to supporting nuclear power plant control system needs. 
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No specific action or written response to this information notice is 
required. If you have any questions regarding this matter, please contact 
this office or the appropriate Regional Administrator. 



                              Edward L. Jordan, Director 
                              Division of Emergency Preparedness 
                                and Engineering Response 
                              Office of Inspection and Enforcement 

Technical Contact:  J. J. Petrosino 
                    (301) 492-4513 

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