Document: NRC Regulatory Guide
Document ID: 8e45dce1-e1e7-4415-b1dd-7e2a610e545b
Document Type: regulatory_guide
Title: Fire Protection for Nuclear Power Plants (Rev. 4)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2023/ML20231A835.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.189
CFR Part: 
CFR Title: 

Content:
al expert PIRT panel, given the absence of secondary fires or any other fire precursors and the unique combination of low-probability events needed for their occurrence, concluded that secondary fires resulting from open-circuited CT installations up to and including 15-kilovolt (kV) primary circuit voltage are incredible. The panel recommended no further consideration of secondary fires as a result of CT failures for low- and medium-voltage applications (up to and including 15-kV primary voltage). 5.3.5 Shorting Switch In response to MSO concerns, several licensees have proposed the use of shorting switches as a design feature to protect against hot short-induced spurious operations caused by fire damage. The shorting switch functions to prevent spurious operation of a component by placing a short across a coil in the circuit of concern when the circuit is in its “standby” state. When the component is desired to be operated, the motion of the hand switch removes the short before energizing the coil to actuate the component. Any circuit using a shorting switch should have this feature of removing the short provided by the shorting switch prior to energizing the coil (i.e., break-before-make). An NEI task force was formed to develop generic guidance on the design, use, and implementation of shorting switches to protect against the spurious operation concerns. The NUREG/CR-7150, Volume 3, electrical expert PIRT panel subsequently reviewed the proposed NEI guidance and provided supplemental technical information to form a comprehensive set of design considerations and recommendations for the reliable use and application of shorting switches. The guidelines, including the revisions and additions from NUREG/CR-7150, were then included in NEI 00-01, Revision 4, Appendix I. The design considerations for shorting switches outlined in Appendix I to NEI 00-01, Revision 4, provide an acceptable methodology for shorting switch applications when applied in conjunction with