United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-09: Isolation Transfer Switches and Post-fire Shutdown Capability

                                                            SSINS No.: 6835 
                                                            IN 85-09       

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

                              January 31, 1985

Information Notice No. 85-09:   ISOLATION TRANSFER SWITCHES AND POST-FIRE
                                   SHUTDOWN CAPABILITY 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP). 

Purpose: 

This information notice is to alert recipients of potential deficiencies in 
the electrical design of isolation transfer switches installed outside the 
control room at many nuclear power plants. The transfer switches provide 
electrical isolation of certain shutdown circuits from the control room and 
other essential fire areas during post-fire accident conditions. It is 
expected that recipients will review the information for applicability to 
their facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities. However, suggestions contained in 
this notice do not constitute NRC requirements; therefore, no specific 
action or written response is required. 

Description of Circumstances: 

During a recent NRC fire protection inspection at the Wolf Creek facility, 
it was discovered that a fire in the control room could disable the 
operation of the plant's alternate shutdown system. Isolation transfer 
switches of certain hot shutdown systems would have to be transferred to the 
alternate or isolated position before fire damage occurred to the control 
power circuits of several essential pumps and motor-operated valves at this 
facility. If the fire damage occurred before the switchover, fuses might 
blow at the motor control centers or local panels and require replacements 
to make the affected systems/components operable. This situation existed 
because the transfer scheme depended on the existing set of fuses in the 
affected circuit and did not include redundant fuses in all of the alternate 
shutdown system circuits. For most of the transfer switches, the situation 
would not cause a problem because the desired effect after isolation is the 
deenergization of power. In instances where the system/component has to be 
operable or where operation might be required to override a spurious 
actuation of a component (such as a motor-operated valve), replacement of 
fuses may have become necessary. In such cases, troubleshooting/repair would 
be required to achieve or maintain hot shutdown. 



8501300138
.

                                                          IN 85-09        
                                                          January 31, 1985 
                                                          Page 2 of 2     

Discussion: 

At the Wolf Creek facility, where the concern was discovered, the transfer 
switches at the remote shutdown panel had redundant fusing. The only 
transfer switches identified as a concern were those at other local stations 
that mainly involve support systems operability or correction of spurious 
operations. The facility is either modifying existing switches or installing
new switches for certain components so that redundant fusing will exist with
a new (different) set of fuses switched into the circuit when the switch is 
placed in the isolated mode. Alternate shutdown procedures also are being 
revised so that shutdown could be achieved under fire conditions which 
result in immediate evacuation of the control room and control room circuit 
damage that causes maloperation of equipment prior to isolation outside the 
control room. 

This situation may exist at other facilities and may involve the shutdown 
panel and other local stations that are needed for alternate shutdown 
capability. This could include the switches and other circuits on the 
alternate/remote shutdown panel. Operability of the hot shutdown systems, 
including the ability to overcome a fire or fire suppressant induced 
maloperation of hot shutdown equipment and the plant's power distribution 
system, must exist without repairs, including replacement of fuses. Section 
III.G.1 of Appendix R to 10 CFR 50 addresses fire protection of safe 
shutdown capability. Meeting this requirement for the affected circuits will 
ensure that redundant fuses are part of the transfer schemes. 

No specific action or written response is required by this information 
notice. However, if you have any questions regarding this notice, please 
contact the Regional Administrator of the appropriate NRC regional office or
the technical contact listed below. 


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

Technical Contact:  W. T. LeFave, NRR
                    (301) 492-9470

                    V. D. Thomas, IE
                    (301) 492-4755

Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, November 12, 2013