Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
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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
.
