Modernization of Technical Requirements for Licensing of Advanced Non-Light Water Reactors: Selection and Evaluation of Licensing Basis Events

Abstract

This report, "Modernization of Technical Requirements for Licensing of Advanced Non-Light Water Reactors: Selection and Evaluation of Licensing Basis Events," represents a key element in the development of a methodology for the efficient licensing of advanced non-light water reactors (non-LWRs). It is the result of a Licensing Modernization Project (LMP) led by Southern Company and cost-shared by the U.S. Department of Energy (DOE). The LMP will result in detailed proposals for establishing licensing technical requirements to facilitate riskinformed and performance-based design and licensing of advanced non-LWRs. Such a methodology acknowledges enhancements in safety achievable with advanced designs and reflects more recent states of knowledge regarding safety and design innovation, creating an opportunity for reduced regulatory complexity with increased levels of safety. The project builds on best practices as well as previous activities through DOE and industry-sponsored advanced reactor licensing initiatives. The LMP objective is to assist the Nuclear Regulatory Commission (NRC) in developing regulatory guidance for licensing advanced non-LWR plants. This report presents a modern, technology-inclusive, risk-informed, and performance-based (TI-RIPB) approach to identifying Licensing Basis Events (LBEs), which cover a spectrum of events considered in the design and licensing of a nuclear power plant. A key licensing outcome of this approach is the structured selection of Design Basis Accidents (DBAs) that are traditionally analyzed in Chapter 15 of the license application.

A Limited-Scope Probabilistic Risk Assessment Study to Risk-Inform the Design of a Fuel Storage System for Spent Pebble-Filled Dry Casks

“…IE is the first disturbance to a normal operation of the NPP, thus, the IE selection is not only the primary step to accomplish the accurate and complete PRA model [35] but also to determine the analysis scope. The advanced non-LWR PRA standard suggests a plant or design-specified systematic approach to ascertain IEs, such as master logic diagram (MLD), failure modes and effort analysis (FMEA), heat balance fault tree (HBFT), or hazard and operability analysis (HAZOP) as a process hazards analysis (PHA) [27,31]. In this paper, the methods for IE identification are briefly introduced and compared, with the most appropriate being employed for the pebble bed-filled dry cask PRA.…”

“…Historically, VHTR PRA was performed by similar methods to those used for the LWR, however, in company with the evolution of the coated particle fuel, the VHTR PRA techniques have grown with the evolution of reactor design and licensing issues [23][24][25][26][27]. The licensing modernization project (LMP) established risk-informed and performance-based licensing technical requirements for advanced non-LWRs through the evaluation of a licensing basis event (LBE) and structures, systems, and components (SSC) performance [27][28][29]. For severe accident progression, source term, and consequence analysis from the LBE and the SSC performance, U.S. NRC plans to improve the capabilities of the existing computational simulation code, including MELCOR, MACCS, and SCALE [30].…”

“…Heat Balance Fault Tree HBFT aims to identify the IE by detecting a deviation from the thermal balance in the system [27]. Since the HBFT is a fault tree combined with technical considerations for heat/energy balance, it is useful to notice where and why the heat/energy imbalance occurs by tracking the cause and effect.…”

A Critical Look at the Need for Performing Multi-Hazard Probabilistic Risk Assessment for Nuclear Power Plants

“…Core Damage Frequency (CDF), Large Early Release Frequency (LERF), or Conditional Containment Failure Probability (CCFP) are the surrogates for the Quantitative Health Objectives (QHO) for currently operating LWRs [48]. However, for advanced non-LRWs, a set of frequency-consequence criteria called F-C Target is used [15].…”

“…This new concept needs a unique perspective in terms of PRA since the three levels approach for LWRs is no longer appropriate since some of the Generation IV reactor designs have no concept of core damage. To address this gap, the Licensing Modernization Project (LMP) [15] aimed to develop a framework to support designers in developing a more reasonable licensing basis and to support the NRC in developing regulations for advanced non-LWR plants. The LMP methodology is technology-inclusive, risk-informed, and performance-based (TI-RIPB).…”