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Resolution of Generic Safety Issues: Issue 48: LCO for Class 1E Vital Instrument Buses in Operating Reactors (Rev. 1) ( NUREG-0933, Main Report with Supplements 1–35 )


An AEOD memorandum302 to NRR on July 15, 1980, identified the concern that some operating nuclear power plants do not have technical specifications or Administrative controls governing operational restrictions for Class 1E 120 VAC vital instrument buses and associated inverters. Without such restrictions, these power sources could be out of service indefinitely and thereby may place certain

safety systems in a situation where they could not meet the single failure criterion.302 NRR concurred with the AEOD recommendation that LCOs should be applied to those operating reactors not presently having LCOs specifically addressing the loss of Class 1E 120V AC vital instrument buses.303 The LCOs should be similar to those identified in the Standard Technical Specifications concerning such systems. DL was instructed to implement appropriate technical specifications covering these systems.303

DL's work was undertaken as MPA B-71. A technical evaluation by LLNL, undertaken in support of MPA B-71, supports a 72-hour/year outage limit as a proposed LCO. The LLNL technical evaluation report304 has been accepted by NRC and is in the process of being formally issued to NRC by LLNL; DL's work of establishing an appropriate technical specification change is nearing completion, subject to NRR and CRGR review.317 The LLNL work scope was limited to PWRs. Consideration of application to BWRs is part of the ongoing DL work.


A proposed resolution for PWRs is available304 and is in final evaluation by NRR to determine whether the proposed resolution is necessary and appropriate for BWRs as well.317 However, in November 1986, this issue was integrated into the resolution of Issue 128.1001


0302.Memorandum for H. Denton from C. Michelson, "Operational Restrictions for Class IE 120 VAC Vital Instrument Buses," July 15, 1980. [8210120114]
0303.Memorandum for C. Michelson from H. Denton, "LCO for Class IE Vital Instrument Buses in Operating Reactors," September 29, 1980. [8010220035]
0304.UCID-19469, "120 VAC Vital Instrument Buses and Inverter Technical Specifications," Lawrence Livermore National Laboratory, October 28, 1982. [8405180177]
0317.Memorandum for G. Lainas from F. Miraglia, "CRGR Package for MPA B-71, 120 VAC Vital Instrument Buses and Inverter Technical Specifications," November 23, 1982. [8212160596]
1001.Memorandum for H. Denton from T. Speis, "Integration of Electrical Power Issues into Proposed Generic Issue 128, `Electrical Power Reliability,'" November 28, 1986. [8612080528]