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Harmonisation of Design Codes and Standards in Nuclear Industry by Professor Nawal Prinja on 5th March 2012

Overview

After more than 50 years of development, the civil nuclear power industry is now ready for standardised reactor designs which will enable the reactor designs from one country to be built in another country. Such standardisation will help nuclear power to contribute to the clean energy needs and lead to safer and more reliable use of nuclear power around the world. One of the areas where the nuclear industry has taken initiative is to harmonise industry codes and standards. This presentation describes the first pilot project being run by an International Task Force set up by the World Nuclear Association under their Cooperation in Reactor Design Evaluation and Licensing (CORDEL) group to harmonisation codes and standards.

The first step towards harmonisation of pressure boundary codes and standards has been completed by the Code Comparison Project which has been managed by the ASME Standards Technology LLC. Six Standards Development Organisations (SDOs) namely ASME (USA), AFCEN(France), KEA (Korea), JSME (Japan), NIKIET (Russia) and CSA (Canada) had participated in the project. The scope of the code comparison project was restricted to Class 1 components only including pressure vessels, piping, valves and pumps. The objective was to identify the significant differences that would have an impact on designing and manufacturing a component in one country and using it in another country. The code comparison project has highlighted various reasons which have resulted in the differences in national codes and standards. It is recognised that all differences cannot be resolved but some progress towards convergence and mutual recognition could be achieved in the short- to medium-term. Therefore, as a start, the proposed Pilot Project will be focused on design codes and standards only in the two areas – technical design and personnel qualifications. It should be clarified that the need to harmonise does not imply non-compliance but should be considered as achieving equivalent status in other countries.

There are two basic approaches to the design of engineering components and structures: design by rule and design by analysis. In the design by rule approach, rules and limitations set by a design standard are adhered to. The design by analysis approach requires either analytical or computational effort to predict stress levels and this is where computational techniques like the Finite Element Analysis (FEA) is increasingly being used in the industry. The commercially available FEA software packages are already harmonised as they are based on common mathematical principles, however, their application in design is not. The methodology and nomenclature of design codes are different from those used in numerical techniques like the FEA. Since an FEA can produce a lot of detailed stress information, it is important to appreciate the importance of various classes of stresses and their respective limits. Before finalising the design, an analyst has to demonstrate that the structural design meets the requirements set down in the design code agreed between the supplier and the buyer. He or she has to assess the data from the finite element analysis in accordance with the rules set in the design code. Such design assessments not only require analysis expertise but also good knowledge of the design rules and their interpretation.

Harmonisation of allowable stress limits is the most important aspect as they influence the methodology used to justify the design, furthermore, these stress limits which are imposed to prevent certain failure modes must be based on common scientific principles. With advanced analysis and structural reliability methods it should be possible to have common technical rules and avoid any inconsistencies in the codes and standards. It is proposed to focus on the harmonisation of allowable stress limits for this pilot project.
Further details regarding the webinar can be found at http://www.nafems.org/events/nafems/2012/harmonisation/.

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