Harmonizing mechanical codes and standards for innovative reactors

The Cooperation in Reactor Design Evaluation and Licensing Working Group (CORDEL) of the World Nuclear Association (WNA) promotes the development of a worldwide nuclear environment where internationally accepted standardized reactor designs can be deployed without major design changes. As reactor designs are standardized at a high level through IAEA SSR-2/1, CORDEL worked to identify the most influential requirements within this safety standard and align their interpretations by national regulators. Engineering design rules (Requirement 18) are a key requirement and their application heavily influences reactor designs via applicable codes and standards (C&S) in a given country. The CORDEL Mechanical Codes and Standards Task Force (MCSTF) was set up in 2011 to promote the harmonization of these C&S. The MCSTF proposed harmonized approaches for several topics within international C&S. These approaches have their foundations in industrial best practice and are informed by experts who have contributed to MCSTF reports. A standardized methodology has been employed across the topics which initially compares the requirements and scopes of C&S to determine where areas of equivalence already exist, where discrepancies lie and gaps where scopes do not overlap. Following the comparison, benchmarking exercises are undertaken to determine the differences in outcomes for the application of the various codes on standard class 1 nuclear components. The results of the benchmarking exercises were used to propose recommendations for harmonized practices. To date, the MCSTF has completed work on several key topics: - The certification of non-destructive examination personnel. The MCSTF compared existing requirements across nuclear and non-nuclear codes and proposed a recommendation for convergence in certification requirements for fabrication. - A comparison of welding qualification and welding quality assurance across six international C&S. - Proposed harmonized practices for non-linear analysis design rules, based upon code comparisons and benchmarking exercises. - A comparison of requirements in C&S for fatigue life analysis design rules. - Highlighting the challenges faced by the nuclear industry in introducing advanced manufacturing techniques with regards to regulation and C&S. This paper presents an overview of the MCSTF's work and methodologies with a focus on its recent publications; the Non-Linear Analysis Design Rules Series and the Advanced Manufacturing paper. The first of these is a three part study on existing mechanical design C&S with the aim of proposing identifying a more harmonized approach in using non-linear analysis methods. An initial comparison showed that many different approaches are currently used within the industry, this gives rise to discrepancies. The impact of choices made by analysts in setting up simulations and assessing their outcomes was a notable source of divergence highlighted in the report. The MCSTF therefore proposed best practices and recommended that standards developing organizations should seek to include them in their C&S. The paper on nuclear advanced manufacturing techniques presents current initiatives in the domain by WNA members and pathways to overcome current regulatory challenges. Regulatory acceptance of these techniques and design approaches will be key in enabling the licensing and deployment of innovative reactors over the next decade. (author)