Risk informed technical specifications

Plant Technical Specifications (TS) are issued to reactor licensees by the United States Nuclear Regulatory Commission (U.S. NRC) as Appendix A to the Operating License. The TS ensure that nuclear power plant reactor safety is maintained by compliance with the deterministic assumptions contained in the plant Safety Analysis Report (SAR). These assumptions are the initial conditions associated with plant operating parameters, as well as structures, systems, and components (SSCs) that are used in the safety analysis. This ensures that the resultant consequences to the health and safety of the public of any event evaluated in the SAR will be within analyzed bounds. Since the TS are based on design basis analyses and not on operational basis events, this can result in SSCs that are not important to safety being over-regulated. In addition, the TS Actions were developed without risk insights, and may not result in the lowest risk plant state or mode. This causes the licensees and the NRC to expend significant resources on issues that are not important to safety, and potentially overlooking issues that are more important to safety. TS have evolved over time starting as custom, individualized, TS whose content varied with each set issued by the NRC for each plant that was licensed. The custom TS evolved to Standard Technical Specifications (STSs), and ultimately, the Improved Standard Technical Specifications (ISTSs). These improvements were primarily deterministic, focusing on achieving a consistent format and content, and addressing inconsistent interpretation. Risk insights were only used in two applications in the development of the ISTS for Westinghouse NSSS plants. The first was in the confirmation that any Limiting Condition of Operation (LCO) that did not satisfy any of the three criteria for Technical Specification content that was proposed to be relocated out of the Technical Specifications was not a significant risk contributor on a dominant risk sequence. The second was the incorporation of a generic Westinghouse Owners Group (WOG) program relaxing Reactor Trip System (RTS) and Engineered Safety Features Actuation System (ESFAS) instrumentation test times, Completion Times (CTs), and Surveillance Frequencies. The Nuclear Steam Supply System (NSSS) Owners Groups (OGs), along with the Nuclear Energy Institute, identified several RITS improvement initiatives in 1998. This paper reviews and discusses these RITS initiatives and their status. (authors)