Balancing material selection and inspection requirements in structural design of fast breeder reactors based on “System Based Code” concept

The System Based Code concept proposed by Asada et al. [Asada, Y., Tashimo, M., Ueta, M., 2002a. System Based Code—Principal Concept. Proc. ICONE10, 22730; Asada, Y., Tashimo, M., Ueta, M., 2002b. System Based Code—Basic Structure. Proc. ICONE10, 22731] intends to realize margin exchange, in order to optimize design. This paper presents preliminary calculation of margin exchange between material strength and the accuracy and frequency of inservice inspection (ISI), taking a reactor vessel of a fast breeder reactor, of which dominant failure mode is creep-fatigue, as an example. The original design is a structure of forged rings of 316FR, material with superior creep strength. Alternative designs use either Type 304 stainless steel or welded structure of 316FR plates, leading to increased failure probability compared to the original design. The accuracy and frequency necessary to compensate this increase of failure probability was estimated. Results envisioned margin exchange between material strength and ISI under practical conditions. Sophistication of the procedure to calculate failure probability will ensure the application of the concept of margin exchange to practical design.