Project Objectives

The main objective of GEMMA is to address those remaining key areas concerning materials behaviour under GenIV reactor conditions where R&D is required to approach technological maturity.
Consistently, four strategic objectives are pursued:

Advance in the qualification of currently available materials under conditions of relevance for GenIV reactors, by focusing on those currently chosen as candidate for structural core components, including welds, and by selecting conditions of specific interest for the different ESNII prototypes, in order to derive or improve correlations of use for their design
Advance the predictive capabilities of models describing the modifications experienced by materials in operation when subjected to irradiation or exposed to corrosive environments, by adopting a physicsbased approach validated on bespoke experiments on both technological and model materials
Explore and identify mitigation strategies to reduce the degradation of materials in operation and therefore enhance the safety and efficiency of the systems, based both on the improved understanding of the physical mechanisms and processes leading to the changes of the properties of materials and on the adoption of measures of protection (specifically surface engineering solutions against aggressive environments), considering also the development of innovative materials
Ensure a continuous dialogue and exchange with the system designers, in order to guarantee the relevance of the results obtained and the transfer of results and approaches to the end-users, paving the way whenever possible for the updating of design codes such as RCC-MRx, while setting in place a strategy for the widest dissemination possible of the results, including open access and measures aimed at attracting young researchers to the field of nuclear materials

In this framework, five specific technical objectives have been identified:

The qualification of welds of existing selected structural materials obtained in compliance with the requirements of existing design codes, including assessment of residual stresses
The full experimental qualification of structural materials and their welds exposed to liquid lead and LBE at relevant temperatures and for relevant times, including the development of related numerical models
The experimental screening of structural materials and their welds exposed to gas (helium) up to very high temperature
The development and testing of mitigation strategies against corrosion/erosion/dissolution due to liquid metal and gas (helium), following two strategies: (i) application of different surface engineering techniques and (ii) development of alumina forming austenitic steels (AFA-steels)
The numerical modelling and experimental assessment of the changes produced on structural materials by irradiation, with specific focus on void swelling, which is one the main limiting factors to high burnup in cladding materials

The selection of the materials to be qualified through experiments and models is based on the observation that all four system prototypes plan to use the same class of materials for the cladding of the fuel, namely cold worked Ti-stabilised austenitic steel, and that most reactor core structural components in all systems are planned to be fabricated using AISI 316L(N) austenitic steel (this material is considered also in GFR, for the vessel, although in this system most components will have to use refractory materials). The inclusion of welded joints in the qualification matrix is especially important, because failures take place almost invariably there and currently hardly any data are available for welds, especially qualified welds. A large amount of experimental data will be generated and such data will be transformed into design correlations of use for system and component designers. Ultimate goal is to consider their possible inclusion, whenever possible, in the Design Rules of the RCC-MRx code, or at least their translation into practical quantitative recommendations for designers.