In previous articles we saw that the formidable energy radiated by stars —and the Sun is one of them— is a consequence of fusion reactions that take place in its core. We also know that reproducing and controlling these reactions on our planet is a difficult challenge for science, technology and industry. Nevertheless, humanity is taking on this enormous challenge because nuclear fusion will provide future generations with very safe and practically unlimited energy with very little environmental impact.
To recreate on Earth the extreme temperatures and pressures that prevail on the Sun, temperatures higher than 150 MK must be reached. Under these conditions, to withstand the very intense high-energy neutron bombardment that will occur in the first generation of future fusion reactors, robust and advanced materials will be needed. This is one of the main technological requirements for fusion reactions in a steady and continuous way. IFMIF, which is essentially a neutron source, arises precisely to understand the mechanical degradation of materials under the high neutron flux.
Therefore, the purposes of IFMIF are:
- To provide data to design the engineering of future fusion plants.
- To select and optimize the most suitable materials for fusion facilities.
- To provide data on the performance of these materials and of the different systems, with a view to DEMO and the fusion reactors that, on that model, will be built later.
IFMIF is thus a key step in building efficient and viable fusion power plants.
WHAT IS IFMIF/EVEDA?
In 1994 the fusion science community in Japan, European Union, United States and Russia agreed to work on the IFMIF conceptual design as part of an international collaboration coordinated by the International Energy Agency. Since 2007, this work has been addressed in the International Fusion Materials Irradiation Facility/Engineering Design and Engineering Validation Activities (IFMIF/EVEDA) project, which is one of the activities of the Broader Approach Agreement, an agreement between the EU and Japan aimed at complementing the ITER project and accelerating fusion development.
The IFMIF/EVEDA project consists of four subprojects:
- IFMIF engineering design.
- Validation of the sample irradiation area systems.
- Validation of the lithium loop system.
- Validation of the accelerator system.
The first three subprojects were successfully completed, but the one involving the accelerator system, which consists of the construction and commissioning of a prototype accelerator similar to those of IFMIF (known as LIPAc, which stands for Linear IFMIF Prototype Accelerator), is still active.
Thus, after crowning the first stage of IFMIF/EVEDA, the EU and Japan signed a Joint Declaration extending the Broader Approach Agreement in March 2020. In this second phase IFMIF/EVEDA will therefore focus on improving the functioning of LIPAc.
We will now discuss in more detail the validation subprojects in the systems of both the sample irradiation area and the lithium loop, leaving the details of the LIPAc facility for future articles.
The design and validation of test facilities was developed in the EU, with KIT (Karlsruhe, Germany) as the leading laboratory, supported by CIEMAT (Madrid, Spain), SCK-CEN (Mol, Belgium) and CRPP (Lausanne, Switzerland).
The design of test facilities was carried out in parallel with the prototyping of the High Flux Testing Module (HFTM) and of the equipment for the examination of small irradiated specimens and for the on-line creep test in the Medium Flux Testing Module (CFTM). The engineering progress was also made on an HFTM alternative design to allow irradiation at very high temperatures, suitable for irradiation testing of silicon carbide.
In 2011, a lithium test loop similar to the one at the IFMIF plant, but with a smaller lithium target width, was built and commissioned at the JAEA Research and Development Center (Oarai, Japan). The target was designed based on a single piece of stainless steel. However, ENEA (Italy) built a more ambitious design in Brasimone, with a removable backplate.
The tasks related to the validation of the lithium target installation involved four activities, which were carried out jointly by JAEA and ENEA:
- Construction and commissioning of the loop, including purification systems.
- Lithium target diagnostics.
- Erosion/corrosion testing of the loop structural materials.
- Remote manipulation of the assembly.
ELTL flow validation and purification systems
The IFMIF/EVEDA lithium test loop (ELTL) began operating in February 2011. This loop, about 20 m high, consists of three floors and a pit (in which the discharge tank was placed).
It should be noted that, following the damage caused by the Great East Japan Earthquake, the lithium loop was recommissioned in September 2012. During its repair, tests were conducted to obtain decisive data on the geometrical stability of the lithium flow and the performance of the flow guidance structure up to a flow velocity of 20 m/s, evidencing that it is possible to control the lithium flow stably over long periods of time.
The lithium reservoir could store 2,500 kg of lithium. Its commissioning was particularly complex as air and humidity contamination had to be avoided (values below 25 ppm were guaranteed).
During the first EVEDA phase, multiple validation activities on the scale experimental facilities, various component tests and several laboratory experiments for the Lithium Target Facility were completed.
Such activities have provided valuable feedback on the design processes both in the engineering phase itself and in the subsequent development stages of IFMIF. In other words, not only has the practical maturity of the technologies involved been proven, but the lessons learned ensure that IFMIF will be a feasible, efficient and safe facility for testing materials, a vital stepping stone to fusion energy.
Lithium target diagnostics
This diagnosis is of crucial importance, since a lithium screen sufficient to absorb the beam energy must be ensured. For this purpose, a device has been developed that does not appear to generate visible disturbances. Its adaptation to ELTL and the high radiation environment of IFMIF remains to be seen.
Specific corrosion/erosion tests were planned at ENEA-Brasimone (Italy), but certain drawbacks in the validation activities led to the construction, in 2010, of a new liquid lithium test facility. The experimental program foresaw up to 8,000 hours of corrosion/erosion testing, which started in 2013 and were successfully concluded.
Validation of remote manipulation
JAEA developed a specific orbital laser welding machine for remote welding and cutting of steel lipseal flanges. The validation process, using a mock-up of the IFMIF inlet duct, was carried out in collaboration with Osaka University. One of the main objectives was to develop quality standards applicable to remote procedures.
On the other hand, ENEA built a mock-up to simulate remote sample replacement using a removable backplate based on the bayonet concept. The tests, which mimicked the geometrical constraints of the test cell, used a remote manipulation system similar to the one planned for IFMIF.
 Within the EU fusion program, advanced structural materials are being investigated for use in DEMO and future fusion reactors. These materials, mainly special steels, tungsten and silicon carbide composites, are expected to exhibit “low activation” and “radiation resistance” to high neutron flux and to be tritium compatible. IFMIF was created for the certification of these materials.
IFMIF: Acronym for International Fusion Materials Irradiation Facility.
DEMO: Acronym for DEMOnstration Power Plant. It is a reactor that will apply the scientific and technological advances learned in ITER, perfecting them and giving rise to the precursor pattern of commercial fusion reactors.
EVEDA: Acronym for Engineering Design and Engineering Validation Activities.
Broader Approach Agreement: This is the bilateral agreement on broadening the approach to fusion technology signed between the EU and Japan on the basis of several major research projects to be carried out in Japan, the purpose of which is to complement ITER by pooling scientific and technical efforts and interests to make fusion energy a reality.
LIPAc: Acronym for Linear IFMIF Prototype Accelerator.
KIT: Acronym for Karlsruher Institut für Technologie (Karlsruhe Institute of Technology). It is one of the largest and most prestigious German scientific research institutions.
SCK-CEN: Acronym for Studiecentrum voor Kernenergie-Centre d’Étude de l’énergie Nucléaire (Center for Nuclear Studies). It is the main Belgian nuclear research center.
CRPP: Acronym for Center for Research in Plasma Physics, an organization within the Swiss Federal Institute of Technology in Lausanne, which is one of the most prestigious Swiss universities in Europe.
JAEA: Acronym for Japan Atomic Energy Agency (its Japanese transliteration is Nihon genshiryoku kenkyū kaihatsu kikō). It is one of Japan’s leading independent public institutions, dedicated to nuclear research.
ENEA: Acronym for Agenzia nazionale per le nuove tecnologie, l’energia e lo sviluppo economico sostenibile (National Agency for New Technologies, Energy and Sustainable Economic Development). It is the second largest Italian public research organization and is focused on energy research, particularly nuclear research.