Study on design methodology and evaluation criteria for nuclear power plant simplification

Abstract

The objectives of this work are to establish the design methodology aimed at resolving design complexity, and to develop evaluation criteria which can be used as a decision-making tool for design simplification. There is a growing interest in redesign of nuclear power plant, especially in simplification of the present designs. However, there exists no clear methodology or criteria for plant simplification. Therefore, it is essential and valuable to study such problems. In this work, by incorporating most aspects on system design applicable to simplification into general system design process, an approach for design simplification is proposed and the simplicity is defined as evaluation criteria for simplification. Proposed design approach is based on the key concepts of Functional Independence and Information Minimization which have been proposed as axiomatic design decision rules in the manufacturing field. Design methods employed in this design approach are top-down decomposition method and regular structure method, which reflect the two design concepts. Informational entropy concept is adopted as a measure of simplicity, and system entropy evaluation model and its quantification method are developed. Through the case study for verifying the applicability of entropy concept, it is found that physical complexity affected by number of components, interconnections, and configurations can be quantified by the measure of system entropy, and that, in the viewpoint of understandability or system uncertainty, it can also be reduced by improving component or system reliability and installing the status monitoring instrument for component or system. From the results of AFWS case study, it is concluded that the entropy measure is an effective decision-making tool for design simplification. Finally, the proposed design methodology is expected to contribute to the improvement of engineering design process as well as design simplification.