United States Nuclear Regulatory Commission - Protecting People and the Environment

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 Tuesday, November 12, 2013