Technical Basis for ASME Section III Code Case N-940

Abstract Advanced reactor designers are considering probabilistic safety and risk in the plant design process, which results in a significantly different safety basis compared to light-water reactors. Risk-informed safety categorization processes provide a graded approach that generally permits construction of items to industrial codes with appropriate special treatments, commensurate with their contribution to safety or risk. Several advanced reactor designers are considering the use of industrial codes for these items to improve commercial viability due to perceived advantages of the cost and schedule of construction. However, there are reasons why a designer may prefer using nuclear Codes and Standards, such as ASME Section III, for this scope: desirable nuclear design rules, service levels, and quality processes. The ASME Section III Standards Committee identified a strategic initiative to develop alternate rules that recognize the reduced safety and risk contributions of these items. This paper presents the technical basis for the recently approved Code Case N-940, “Alternate Rules for Nondestructive Examination and Testing of Items Commensurate with their Contribution to Safety or Risk, Section III, Division 5.” The technical basis for this approach reviews the existing regulatory framework, the relationship between Service Levels in the ASME Section III design rules and the associated construction rules (i.e., NDE, testing, and materials), and construction requirements permitted in industrial codes.