MDEP Technical Report TR-CSWG-02. Technical Report on Lessons Learnt on Achieving Harmonisation of Codes and Standards for Pressure Boundary Components in Nuclear Power Plants

This report was prepared by the Multinational Design Evaluation Program's (MDEP's) Codes and Standards Working Group (CSWG). The primary, long-term goal of MDEP's CSWG is to achieve international harmonisation of codes and standards for pressure-boundary components in nuclear power plants. The CSWG recognised early on that the first step to achieving harmonisation is to understand the extent of similarities and differences amongst the pressure-boundary codes and standards used in various countries. To assist the CSWG in its long-term goals, several standards developing organisations (SDOs) from various countries performed a comparison of their pressure-boundary codes and standards to identify the extent of similarities and differences in code requirements and the reasons for their differences. The results of the code-comparison project provided the CSWG with valuable insights in developing the subsequent actions to take with SDOs and the nuclear industry to pursue harmonisation of codes and standards. The results enabled the CSWG to understand from a global perspective how each country's pressure-boundary code or standard evolved into its current form and content. The CSWG recognised the important fact that each country's pressure-boundary code or standard is a comprehensive, living document that is continually being updated and improved to reflect changing technology and common industry practices unique to each country. The rules in the pressure-boundary codes and standards include comprehensive requirements for the design and construction of nuclear power plant components including design, materials selection, fabrication, examination, testing and overpressure protection. The rules also contain programmatic and administrative requirements such as quality assurance; conformity assessment (e.g., third-party inspection); qualification of welders, welding equipment and welding procedures; non-destructive examination (NDE) practices and qualification of NDE personnel. In the course of reviewing the results of the SDO's code-comparison project, the CSWG found that the similarities and differences between each county's code and standard varied considerably amongst different countries. For example, one country's code was almost identical to another country's code in technical areas while others contained vastly different requirements. Regardless of the similarities and differences, the CSWG found that each pressure-boundary code has been determined by each country to result in a component with an acceptable level of quality and safety. It should be recognised that the rules for component design is just one aspect of the entire component design and construction process addressed by a pressure-boundary code. In addition, there are also philosophical and cultural factors involved that play a major role in the overall quality of the design and construction of a pressure-boundary component. In other words, the implementation of the code requirements alone does not always provide a true representation of the component's quality and safety without consideration of these philosophical and cultural factors. Mixing different country's codes and standards requirements might be detrimental and should be carefully evaluated when attempted. A collaborative evaluation by knowledgeable experts in each code or standard is one approach that may enable the use of different countries' code requirements. Overall, the CSWG concludes that each country's pressure-boundary code provides the necessary design and construction requirements to produce components with an acceptable level of quality and safety when (1) the code is used in conjunction with its country's standard industry practice, (2) the code is supplemented with industry and regulatory guidance documents, and (3) the code is implemented in a manner consistent with its cultural and philosophical factors. Furthermore, the CSWG concludes that harmonisation of pressure boundary codes is a long-term goal that will require the cooperation and coordination of SDOs, nuclear industry (e.g., vendors, designers, manufacturers, and owners) and regulators on an international scale. It is achievable if one acknowledges that code harmonisation is a continual process - not an end product unto itself