IE Circular 81-06, Potential Deficiency Affecting Certain Foxboro 10 to 50 Milliampere Transmitters

                                                           SSINS No.:  6820 
                                                           Accession No.   
                                                           IEC 81-06       

                               UNITED STATES 
                           WASHINGTON, D.C. 20555 
                               April 14, 1981


Description of Circumstances: 

NRC has been recently advised of two deficiencies in certain E-10 Series 
Foxboro transmitters which could adversely affect their operation during 
accident conditions. The deficiencies involve the improper use of Teflon 
wire insulation and an unsuitable capacitor in the amplifier section of 
these transmitters. The transmitters in question have been identified as 
Foxboro Models N-E11, N-E13, and E-11, E-13 with suffix Codes /MCA, 
/MCA/RRW, and /MCA/RR. These transmitters operate at an output signal level 
of 10 to 50 milliamperes (mA). Similar model number units operating in the 
range of 4 to 20 mA are not a concern in these matters. 

Briefly, the information on the deficiencies was brought to the attention of
the NRC Staff during a recent meeting with several licensees of a "Utility 
Transmitter Qualification (UTQ) Group." This group has been formed to 
develop and implement an acceptable environmental qualification test program 
for safety related electrical equipment in use or planned for use in nuclear
power plants. 

According to Foxboro, the Teflon insulation material in question has 
demonstrated a tendency to embrittle and deteriorate when subjected to an 
integrated radiation dose of 200 megarads. A total integrated dose (TID) of 
200 megarads was called for in the qualification test sponsored by the UTQ 
Group that led to the discovery of the Teflon insulation and capacitor 

With respect to the capacitor problem, the manufacturer determined that the 
capacitor was not hermetically sealed as specified. Unsealed capacitors can 
leak and malfunction under adverse conditions, especially those of heat and 
time. Foxboro determined that the capacitor failed after being subjected to 
high temperatures resulting from gamma heating during the above-mentioned 
qualification test. 

Subsequent to the investigation into the discussed problems, Foxboro issued 
a technical letter dated March 12, 1981 to all licensees, NSSS vendors, 
architect-engineers, and others who have purchased the Foxboro 10 to 50 mA 
transmitters in question. This technical letter further describes the Teflon
and capacitor deficiencies and provides recommendations to identify and 
correct the problems. Foxboro has also provided a copy of master instruction
(MI) booklet, MI-20-145, dated September 1976, on the Foxboro 10 to 50 mA 
transmitters, to recipients of the technical letter. The MI document has 
been specifically marked on pages 5 and 6 to identify the parts of the 
amplifier in question. 

                                                          IEC 81-06       
                                                          April 14, 1981  
                                                          Page 2 of 2     

Enclosed are copies of the technical letter and the master instruction 
document for your use and appropriate action. 

For holders of Licenses of operating facilities including NTOL and SEP 
plants, it should be noted that reporting requirements are specified in the 
NRR/OL safety evaluation report (SER) relating to environmental 
qualification of safety related electrical equipment. These instructions, 
"We request that you provide --- within 90 days," are stated in both the SER 
and the transmittal letter to each utility. 

Recommended Actions to be Taken by All Nuclear Power Facilities Holding an 
Operating Licensee or a Construction Permit: 

1.   Determine if your facility has installed or plans to install Foxboro 10
     to 50 mA transmitters that have model numbers the same as those 
     identified above in safety-related systems located in areas subject to 
     a harsh environment, including those areas where long-term LOCA coolant
     piping is routed. 

2.   Where Foxboro 10 to 50 mA transmitters are identified, it is 
     recommended that you replace the suspect amplifiers in accordance with 
     the recommendations and instructions provided in the enclosed letter 
     and instruction manual. However, if it is determined that a transmitter 
     is installed in an area where the TID is less than 10 megarads, the 
     licensee should assure that the affected transmitter will function as 
     intended under the expected TID resulting from the postulated accident 

3.   We remind you that the equipment qualification SER identified above 
     requires that licensees of operating facilities (including NTOL and SEP
     plants) develop plans and programs including schedules for corrective 
     action and the basis supporting continued operation regarding items 1 
     and 2 above. This information should be incorporated in your submittal 
     to the SER on equipment qualification. 

4.   For Holders of Construction Permits, resolution of these matters should
     be available for review through normal follow-up inspections by the NRC
     Regional Offices. This information will also be considered during the 
     operating license review. 

No written response to this circular is required. If you need additional 
information with regard to this subject, please contact the Director of the 
appropriate NRC Regional Office. 

1.   Foxboro Technical Letter 
       dated March 12, 1981 
2.   Foxboro Master Instruction 
       MI 20-145 dated September 1976 
3.   Recently issued IE Circulars  

                                                 Attachment 1 

                                                  Foxboro, MA 02035 U.S.A. 
The Foxboro Company 
12 March 1981 

Subject:  Potential Deficiency Affecting Foxboro Transmitters, Model Numbers
          N-E11, N-E13 or E11, E13 with suffix Codes /MCA, /MCA/RRW, or 


Our records indicate that you have received one or more of the Foxboro model
numbered transmitters listed above. This letter is to notify you that two 
deficiencies have been discovered in some of these transmitters which may 
exist in the units shipped to you. The transmitters in question operate at a 
signal level of 10-5OmA. Similar model numbered units operating at 4-2OmA 
are not affected. 

The first issue involves the possible use of incorrect insulating sleeving 
on transistor and zener diode lead wires in the amplifier. The second issue 
involves the use of a specific vendor's capacitor which is not hermetically 
sealed (although claimed to be so). As a result, the capacitor electrolyte 
can leak under adverse service conditions, specifically heat and time. The 
failure mode is a decrease in resistance across the capacitor resulting in 
electrical leakage. The transmitter operation can be affected by limiting 
the output to something less than full value which, in time, can degrade to 
no output at all. 

Insulating Sleeving - Radiation resistant sleeving consisting of a silicone 
coated glass fiber braid has been substituted by a teflon sleeving in some 
transmitters. Tests have shown that teflon will become brittle and 
deteriorate with a substantial integrated radiation dose. Foxboro testing 
has demonstrated that the teflon sleeving used in these devices will 
withstand an integrated dose of 10 megarads with no noticeable 
deterioration. Tests to 200 megarads produce the brittle conditions which 
can result in the teflon flaking from the wires. Based on these tests, 
operating plants not expected to exceed an integrated dose of 10 megarads 
have no potential problem and no action is required. 

Where the integrated dose rate could exceed 10 megarads, then units in 
service should be inspected to determine if the proper insulating material 
has been used. This can be accomplished by opening the transmitter in 
accordance with Foxboro Master Instruction MI 20-145. The amplifier cover 
must be removed exposing the amplifier assembly. At one end of the assembly,
a transistor and a zener diode are mounted in the base casting which serves 
as a heat link. The insulating material in question is a sleeving slipped 
over the lead wires from these two components. The proper material is white 
and heavy looking. Positive 


Page 2 
12 March 1981  


identification can be made by inspecting one end of the material to 
establish that the outer material covers an inner braid. Teflon, if used, 
will be a single layer material and could be either clear or white. 

If improper insulation is present, then the corrective action is to replace 
the amplifier (Foxboro P/N N0148PW). Replacement amplifiers can be purchased
from your local Foxboro Sales or Service Representatives. If you prefer to 
have Foxboro Service Personnel inspect the equipment and, if necessary, 
replace the amplifier, this can be arranged at standard service rates. 

Capacitor - The capacitor degradation problem was discovered over time 
through tracking failure situations. Internal corrective action has been 
taken to remove the vendor involved from the qualified vendor list and to 
purge all stock of capacitors from this vendor. Degradation of this 
capacitor is a function of time and service conditions with heat being a 
primary contributor. This phenomenon was observed in recent tests of 
transmitters using these capacitors. The capacitor in question is 
manufactured by Cornell-Duebilier and can be specifically identified by a 
type number in the form TX-65-XXXX as well as a monogram in a box followed 
by a date code, e.g. CDE 0874. It is assigned Foxboro part number N0141MF. 

To determine if this capacitor is present requires a visual inspection of 
the amplifier which can be accomplished as described above for the 
insulating sleeving inspection. The recommended corrective action should the 
above described capacitor be present is to replace the amplifier (Foxboro 
P/N N0148PW) although is possible to replace the capacitor with a Foxboro 
provided substitute. Use of Foxboro Service personnel to perform the 
inspection and replacement, if necessary, can be arranged at standard 
service rates as described above. 

Due to lack of knowledge of specific application, redundancy, and the like, 
Foxboro cannot determine if the NRC reporting requirements of 10CFR Part 21 
are applicable. This determination is the responsibility of the user and any
such reporting would be made by them after completing their evaluation of 
the situation. 

If you have any questions regarding the above, please contact the 
undersigned directly. 

Very truly yours, 

William Calder, Manager 
Corporate Quality Assurance 


Enclosure MI 20-145 


Page Last Reviewed/Updated Tuesday, September 01, 2015