Risk-Informed Margin Management (RIMM) Industry Applications IA1 - Integrated Cladding ECCS/LOCA Performance Analysis - Problem Statement

Abstract

The U. S. NRC is currently proposing rulemaking designated as "10 CFR 50.46c" to revise the lossof-coolant-accident (LOCA)/emergency core cooling system (ECCS) acceptance criteria to include the effects of higher burnup on cladding performance as well as to address other technical issues. The NRC is also currently resolving the public comments with the final rule expected to be issued in April 2016. The impact of the final 50.46c rule on the industry may involve updating of fuel vendor LOCA evaluation models, NRC review and approval, and licensee submittal of new LOCA evaluations or re-analyses and associated technical specification revisions for NRC review and approval. The rule implementation process, both industry and NRC activities, is expected to take 4-6 years following the rule effective date. As motivated by the new rule, the need to use advanced cladding designs may be a result. A loss of operational margin may result due to the more restrictive cladding embrittlement criteria. Initial and future compliance with the rule may significantly increase vendor workload and licensee cost as a spectrum of fuel rod initial burnup states may need to be analyzed to demonstrate compliance. Consequently, there will be an increased focus on licensee decision making related to LOCA analysis to minimize cost and impact, and to manage margin.The proposed rule would apply to a light water reactor and to all cladding types. The key points of the new rule are as follows:Cladding performance cannot be evaluated in isolation. Cladding performance and ECCS performance need to be considered in a coupled way. Models for cladding performance even within the design basis will need to be updated for regulatory purposes.Effort needs to be expended in searching regulatory issue space for the limiting case ("ECCS performance must be demonstrated for a range of postulated loss-of-coolant accidents of different sizes, locations, and other properties, sufficient to provide assurance that the most severe postulated loss-of-coolant accidents have been identified. ECCS performance must be demonstrated for the accident, and the post-accident recovery and recirculation period." SECY-12-0034).In the remainder of this report, we address the technical issues and approaches we will use to investigate this Industry Application within the Risk-Informed Safety Margin Characterization (RISMC) Pathway. Specifically, in Section 2 we review the RISMC vision, and discuss the industry application concept and its implementation strategy. In Section 3 we define the Risk-Informed Margin Management (RIMM) Industry Application #1 (IA1), Integrated Cladding ECCS/LOCA Performance Analysis, aiming to develop and demonstrate an advanced methodology and tool for industry to apply to large-break LOCA issue evaluation, decision making, and margin management. Sections 4, 5, and 6 introduce the subsequent phases of the IA1 project, and Section 7 proposes a schedule and budget for all phases of the project.