United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-16: Degradation of Static "O" Ring Pressure

                                                        SSINS No.: 6835 
                                                             IN 87-16 

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

                                April 2, 1987

Information Notice No. 87-16:   DEGRADATION OF STATIC "O" RING PRESSURE 
                                   SWITCHES 

Addressees: 

All light-water reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

This notice is to alert addressees to the potential for degradation of 
certain Static "Q" Ring (SOR) pressure switches with Kapton diaphragms 
caused by exposure to ammonia and other chemicals that may be present in the 
process medium. It is expected that recipients will review the information 
for applicability to their facilities and consider actions, if appropriate, 
to preclude similar problems 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: 

A number of SOR pressure switches (Model N.o. 6TA-B4-NX-JJTTX6) were 
declared inoperable at the Davis-Besse Nuclear Power Plant between January 7 
and 12, 1987, when results of a routine surveillance indicated that the 
pressure switch set points had drifted outside of technical specification 
tolerances. The SOR switches that were declared inoperable are located on 
the lines supplying steam to the auxiliary feedwater (AFW) pump turbines and 
are used to detect a low steam pressure and isolate the affected AFW pump in 
the event of a steam line break. 

Subsequent investigation by the licensee, Toledo Edison, and SOR revealed 
that ammonia present in the steam lines had interacted with the Kapton 
diaphragm of the pressure switch, permeated it, and formed a bubble between 
the laminations of the Kapton diaphragm (fluorinated silicone membrane). It 
is believed that the formation of this bubble between the diaphragm layers 
caused the set point of the switch to shift. 

At Davis-Besse, ammonia is added to the feedwater system to help control 
chemistry--primarily pH. Hydrazine, which is regularly added to coolant 
systems to help control chemistry and to scavenge oxygen, also is a source 
of ammonia because hydrazine reacts with oxygen to form ammonia. SQR has 
stated that qualified pressure switch models beginning with 1, 4, 5, 6, 8, 
9, 12, and 54 may be affected if ammonia is present in the process medium. 

8703310090
.

                                                            IN 87-16     
                                                            April 2, 1987 
                                                            Page 2 of 3

Discussion: 

SOR generally uses Kapton as the primary diaphragm material in their Class 
1E qualified switches. Toledo Edison had recently installed the 
environmentally qualified switches as part of a system upgrade. Earlier 
model commercial grade SOR pressure switches at Davis-Besse used BUNA-N 
diaphragms. In 1979, the BUNA-N diaphragms were replaced with 316 stainless 
steel diaphragms. Because there have been no reported malfunctions of 
pressure switches using stainless steel diaphragms and because stainless 
steel is impermeable to ammonia, the pressure switches using Kapton 
diaphragms were replaced with pressure switches using stainless steel 
diaphragms. 

When Toledo Edison ordered the Class 1E switches from SOR, the environmental 
conditions that the switches would be subjected to during normal operation 
were not specified. Thus, the ability of the switch to perform its required 
function in response to an accident was degraded because the procurement 
documents did not specify the normal process medium. 

The instrument drift condition can go undetected for a considerable period 
of time. At Davis-Besse, the switches are tested for operability during 
bimonthly surveillance. The calibration of the set point is verified during 
each refueling outage. Therefore, even though the switch may demonstrate 
operability, setpoint drift exceeding the specified limits may not be 
detected until refueling outage calibrations. 

Another factor contributing to the instrument drift at Davis-Besse is that 
the set point for the pressure switches (20 psig) was on the lower end of 
the adjustable range (10-85 psig). The instrument drift condition caused by 
the formation of an ammonia bubble between the diaphragm layers may not be 
significant on switches used in high pressure applications. 

Additionally, NRC has learned from DuPont, the manufacturer of Kapton, that 
certain concentrations of chemicals such as ammonium hydroxide, sodium 
hydroxide, and potassium hydroxide will cause Kapton to degrade. When 
determining the suitability of an SOR pressure switch using a Kapton 
diaphragm to a particular application, it may be desirable to examine the 
resistance of Kapton to chemicals present in the application environment. 
For further information on Kapton properties call: 

                         DuPont Company 
                         Electronics Department
                         High Performance Films Division
                         1-800-527-2601
.

                                                            IN 87-16
                                                            April 2, 1987 
                                                            Page 3 of 3  

If you have any no specific or written response is required by this notice. 
If you have any questions regarding this matter, please contact the Regional 
Administrator of the appropriate regional office or this office. 




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


Technical Contact:  K. R. Naidu, IE
                    (301) 492-4179

                    J. G.  Giitter, IE
                    (301) 492-4043

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