Modernization of Technical Requirements for Licensing of Advanced Non-Light Water Reactors: Safety Classification and Performance Criteria for Structures, Systems, and Components

Abstract

A companion report described the LMP approach to selecting and evaluating licensing basis events and for identifying structures, systems, and components (SSCs) that are classified as Safety-Related. The current document outlines the approach to performing the following additional tasks that impact the development SSC design performance targets: • Complete the process of SSC safety classification by subdividing non-safety-related SSCs into subcategories to identify additional safety-significant SSCs that require special treatment • Describe the LMP approach to the definition of risk significant SSCs • Describe the LMP approach for defining safety-significant SSCs in terms of their risk significance and role in supporting defense-in-depth (DID) adequacy * As used in this report, the term "PRA safety function" is defined as any function modeled in the PRA that protects one or more radionuclide barriers, or otherwise prevents or mitigates a release of radioactive material to the environment. Those safety functions that are relied on in the design to prevent or mitigate a design basis accident within 10 CFR 50.34 dose limits are referred to as required safety functions.

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

“…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].…”