A four-year IAEA project involving nine research institutes resulted in the preparation of a set of guidelines aimed at standardizing small specimen test techniques (SSTT) for reference structural materials used in fusion energy.
Fission neutrons for materials testing have been available for decades in hundreds of experimental reactors worldwide. An extensive database for irradiated materials is also available. However, experimental fusion reactors for materials testing unfortunately do not exist. Testing facilities with a 14 MeV neutron source for irradiating candidate materials under fusion reactor conditions and offering control of the temperature of the irradiated material have been under development for four decades and have become an urgent need and crucial feature in world fusion roadmaps.
The optimization of the limited testing space makes the use of small specimens indispensable. The limited testing volume with needed neutron fluxes in accelerator driven fusion relevant neutron sources drove the development of small specimens for fusion applications.
This need was already identified in 1983 when the first review of the state of the art of these techniques was done. The development has continued steadily in various laboratories worldwide yielding similar results, but without a standard procedure. Since then, more than 10 specific symposia have taken place, but no harmonization of SSTT has been accomplished. The nuclear industry, and in particular the fusion industry, has found that the lack of common uses in SSTT is preventing them from comparing and exchanging data in an optimal manner.
The IAEA launched in 2017 a coordinated research project (CRP) series, entitled Towards the Standardization of Small Specimen Test Techniques for Fusion Applications, focused on the harmonization of the most relevant five small specimen test techniques. Half of the work was already performed in the first phase of the CRP and the task is expected to be finalized in its second phase, starting in 2022.
Specific Research Objectives
The overall objective of this CRP was to provide a set of guidelines for SSTT based on common agreed best practices on main material test techniques (tensile, creep, low cycle fatigue, fracture toughness, fatigue crack growth) for reference structural fusion materials as first step of a full standardization of the SSTT.
The participants of the CRP were:
- Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Spain;
- Fusion for Energy (F4E), European Union;
- Karlsruher Institut für Technologie (KIT), Germany;
- National Institute for Fusion Science (NIFS), Japan;
- Oak Ridge National Laboratory (ORNL), USA;
- Rokkasho Fusion Institute - National Institutes for Quantum and Radiological Science and Technology (QST), Japan;
- Shanghai Jiao Tong University (SJTU), China;
- Tohoku University, Japan;
- United Kingdom Atomic Energy Authority (UKAEA), UK.
Relevance
The CRP created a pioneering international expert group from China, the European Union (EU), Japan and the United States, as well as materials researchers, and provided a platform for intense efforts towards standardisation of SSTT. Engaging same participants (research units as well as individuals) involved in different test methods has proven to harmonize the scattered expertise.
All experimental campaigns (Round Robin test) in the CRP have been performed with RAFM steels that are the respective reference structural materials in China, the EU and Japan for next generation fusion plants (DEMO) and for ITER test blanket module.
To obtain approvals for fusion material testing and generation of valid mechanical data using SSTT, standardization accepted by an international organization is strictly speaking not “mandatory”, however, it is essential to ease and smoothen the upcoming processes.
