This paper introduces a methodology for the determination of a complete set of safety factors that maintains consistency between design code and fitness-for-service code of nuclear components. The purpose of the work is to materialize the System Based Code concept, which is indispensable for the development of next generation nuclear reactors. The methodology consists of three principles proposed by the author which should be the basis of code development for new next generation reactors. The principles are; 1) Design to target reliability, 2) Continuous reliability evaluation from design to fitness-for-service, 3) Update of reliability evaluation based on information obtained during construction and operation. Effectiveness of the methodology is demonstrated using a simple example problem. The problem deals with pipe subjected to internal pressure under conditions which is typical in light water reactors. Following the reliability evaluation of current situation which meets the provisions of design code and fitness-for-serve code published from Japan Society of Mechanical Engineers, the three principles are applied step-by-step and safety factors and reliability indices are newly derived. It is shown that a complete application of the three principles could lead to a set of safety factors that assures consistency in terms of reliability in design and fitness-for-service, and improves allowable stresses as well. Technologies to be developed and issues to be discussed for application of the methodology to more complicated and practical situations are described as well.
Mechanics-based statistics of failure risk of quasibrittle structures and size effect on safety factors