Issue 48: LCO for Class 1E Vital Instrument Buses in Operating Reactors

DESCRIPTION

An AEOD memorandum[1]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.[2]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.[3]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.[4]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 report[5]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.[6]The LLNL work scope was limited to PWRs. Consideration of application to BWRs is part of the ongoing DL work.

CONCLUSION

A proposed resolution for PWRs is available[7]and is in final evaluation by NRR to determine whether the proposed resolution is necessary and appropriate for BWRs as well.[8]However, in November 1986, this issue was integrated into the resolution of Issue 128.[9]