Home > NRC Library > Document Collections > Generic Communications > Information Notices > 1987 > IN 87-16
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 Attachment: List of Recently Issued IE Information Notices .
Page Last Reviewed/Updated Tuesday, November 12, 2013