Information Notice No. 86-13, Supplement 1: Standby Liquid Control Squib Valves Failure to Fire
SSINS No: 6835
IN 86-13, Supplement 1
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
August 5, 1986
Information Notice No. NO 86-13, SUPPLEMENT 1: STANDBY LIQUID CONTROL
SQUIB VALVES FAILURE TO
FIRE
Addressees:
All boiling water reactor facilities holding an operating license or a
construction permit
Purpose:
This notice is to alert addressees to additional information regarding the
causes of a generic problem with squib valves used in the standby liquid
control system Recipients are expected to 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:
Information Notice 86-13 stated that failure of the squibs to fire at
Vermont Yankee was caused by two problems: a plant wiring change in the
terminal box and incorrect wiring of the connector supplied with the squib
valve primer charge However the latest information regarding the event
shows that the principal cause for the squib valve failures and the loss of
the standby liquid control (SLC) system function was the incorrect wiring in
the primer chamber supplied by the vendor in 1983 and initially installed in
July 1984
A secondary cause for the event was the failure to detect the manufacturing
defect before using the parts in the plant Although a squib valve from the
vendor's same manufacturing lot was "bench" tested in the plant maintenance
shop before installation, the bench test only verified the adequacy of the
explosive material, but did not test the electrical wiring configuration If
a test had been conducted for a representative sample of the chambers
installed in the SLC system in 1984, the loss of SLC system function could
have been prevented The error was identified by the licensee's staff in
February 1986 while testing the installed valves at the end of the operating
cycle
The electrical wiring configuration in the plant gave an indication of
circuit continuity in the control room but was incapable of firing the squib
valves
8608010284
IN 86-13, Supplement 1
August 5, 1986
Page 2 of 2
NRC inspection also found irregularities in the plant wiring in that the
as-found firing circuit wiring differed from the design drawings The
differences occurred following a design change to the firing circuits in
1977 when difficulties encountered during the installation resulted in a
needed field modification for the firing circuit The adequacy of the
modified circuit was demonstrated by the successful completion of the annual
surveillance tests from 1977 to 1984 with primer chambers of the type
supplied in 1977 The field modification did not go through the normal
review process and therefore was not reflected in a change to the as-built
drawing of the firing circuit However, if the field modification had been
reviewed in 1977 it would have been approved Thus the primary cause for the
SLC system failure remains the primer manufacturing error and the secondary
cause is the failure to detect the error
Discussion:
According to the NRC staff's understanding, there are two important lessons
from the experience gained as a result of this event
Bench testing of squib valves is not an absolute indication that the valves
will function in the plant circuit Testing in the plant circuit provides an
added confidence that the plant circuit is capable of firing the valves
Control room indication of circuit continuity may be achieved by an
electrical pathway that is not the pathway of the firing circuit Therefore,
control room indication of SLC system continuity is not an absolute
indication of the circuit's ability to fire the squib charge and activate
the SLC system
No specific action or written response is required by this information,
notice If you have questions about this matter, please contact the Regional
Administrator of the appropriate NRC regional office or this office
Edward L Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Eric Weiss, IE
(301) 492-9005
Attachment: List of Recently Issued Information Notice No.
Page Last Reviewed/Updated Friday, May 22, 2015