Material issues for design and licensing of MYRRHA ADS system

The deployment of innovative nuclear systems including MYRRHA ADS system relies primarily upon the availability of structural materials able to withstand their harsh operation conditions, in particular with respect to the material compatibility with the coolant under intense irradiation. The materials selection and qualification are critical issues for successful development of such nuclear systems. The selection of structural materials should rely on a number of their intrinsic properties with respect, among others, to thermo-mechanical loading conditions, coolant-material interaction effects, irradiation and their synergetic effects of all previously mentioned. Therefore, it is important to be able to appropriately characterize these materials. However, the behaviour of materials under operation conditions of innovative nuclear systems is not appropriately covered by the available testing and evaluation standards requiring updates of existing standard procedures and sometimes development of new ones. Today, individual laboratories rely on their own experience and on experimental and irradiation facilities available to them. Although it is possible to extract helpful qualitative information, it is difficult to interpret the various data quantitatively. The main goal of materials R and D and qualification programme for MYRRHA candidate materials is to provide reliable material property data for design and licensing of MYRRHA. It also aims to assist with the following activities: a) design of various components; b) fuel development; c) safety analysis; d) coolant technology development; e) elaboration of the surveillance program. At the moment the efforts are distributed over the following four overlapping activities: a) Identification of key material issues for design and licensing of MYRRHA; b) Development of test and evaluation guidelines for structural materials characterisation; c) Assessment of material properties; d) Development of testing infrastructure. The three major material degradation effects that have been identified so far for nuclear systems with lead-bismuth coolant and for MYRRHA in particular are liquid metal corrosion, environmentally assisted cracking and irradiation effects. In this paper we will report on the material R and D approach for MYRRHA and the progress accomplished so far. (author)