Fusion Materials Development Research Articles

RAMI analysis of DONES Lithium systems updated to the last design modifications

IFMIF-DONES project is aimed at building a neutron source facility for fusion materials development and qualification. This facility will provide a database of materials exposed to similar irradiation conditions as in DEMO. Neutrons are obtained by means of a deuteron beam impacting onto a liquid lithium film target provided by the Lithium System (LS). An important aspect of the project design activities is to assess the system reliability at all phases of the facility life-cycle to support a reliability growth during the ongoing design phase and to monitor the compliance with the stated availability goals. Following RAMI methodology, first a Failure Mode Effect Analysis (FMEA) is done in order to point out all the relevant unavailability conditions in the Lithium Systems (e.g. main loop and related heat removal systems, impurity control system, target system, etc.). Then, RBDs (Reliability Block Diagram) are derived from FMEA by implementing a reliability-wise representation of system component behavior and simulate the system performance under due operating conditions. Finally, a Phase Diagram (PD) is defined to have into account all the different states of the LS (e.g. normal opeation, corective maintenance (CM) and preventive maintenance (PM)) during two years of operation, a cycle that is repeating for 20 years of operation. The current design detail level and functioning logic is taken into account also considering the foreseen Local Instrumentation & Control System. The compliance with the availability target of 94% attributed to the Lithium System during its operation time is verified.

Combinatorial discovery of irradiation damage tolerant nano-structured W-based alloys

One of the challenges in fusion reactors is the discovery of plasma facing materials capable of withstanding extreme conditions, such as radiation damage and high heat flux. Development of fusion materials can be a daunting task since vast combinations of microstructures and compositions need to be explored, each of which requires trial-and-error based irradiation experiments and materials characterizations. Here, we utilize combinatorial experiments that allow rapid and systematic characterizations of composition-microstructure dependent irradiation damage behaviors of nanostructured tungsten alloys. The combinatorial materials library of W-Re-Ta alloys was synthesized, followed by the high-throughput experiments for probing irradiation damages to the mechanical, thermal, and structural properties of the alloys. This highly efficient technique allows rapid identification of composition ranges with excellent damage tolerance. We find that the distribution of implanted He clusters can be significantly altered by the addition of Ta and Re, which play a critical role in determining property changes upon irradiation.

The TechnoFusion Consortium of Spanish institutions and facilities towards the development of fusion materials and related technologies in Europe

With the objective of contributing to the European development of materials, technologies and facilities for the demonstration of the thermonuclear fusion, the construction of the unique TechnoFusión facility was planned in 2009. The TechnoFusión consortium, formed by selected Spanish research groups and laboratories located in Madrid, has jointly advanced in the search for solutions to the remaining technological issues of nuclear fusion by magnetic and inertial confinement. In addition, the foundation of the TechnoFusión partnership has been essential to create a network of collaborations, and also to expand and specialize human resources, by training scientists and technical staff in the use of high-tech tools.Supported by the TechnoFusión_Comunidad Madrid (III) regional programme, the consortium is focused on providing support for the construction of medium-­sized, relevant facilities in Madrid (Spain). Regarding magnetic and inertial fusion issues, the programme is structured in several key experiments and infrastructures, which combine the development of materials, of cutting-edge technologies and the construction of associated facilities, with the progress in simulation and application of computational neutronics:

High-dose ion irradiation damage in Fe28Ni28Mn26Cr18 characterised by TEM and depth-sensing nanoindentation

One of the key challenges for the development of high-performance fusion materials is to design materials capable of maintaining mechanical and structural integrity under the extreme levels of displacement damage, high temperature and transmutation rates. High-entropy alloys (HEAs) and other concentrated alloys have attracted attention with regards to their performance under fusion conditions. In recent years, a number of investigations of the irradiation responses of HEAs have peaked the community’s interest in them, such as the work of Kumar et al. (2016), who examined Fe27Ni28Mn27Cr18 at doses as high as 10 dpa. In this work, we study Fe28Ni28Mn26Cr18 concentrated multicomponent alloy with irradiation doses as high as 20 dpa. We find the presence of Cr rich bcc precipitates in both the un-irradiated and in the irradiated condition, and the presence of dislocation loops only in the irradiated state. We correlate the features found with irradiation hardening by the continuous stiffness method (CSM) depth-sensing nanoindentation technique and see that the change in the bulk hardness increases significantly at 20 dpa for temperatures 450 °C. These results indicate that the alloy is neither stable as a single phase after annealing at 900 °C, nor particularly resistant to irradiation hardening.

Fusion Materials Development at Forschungszentrum Jülich

Material issues pose a significant challenge for the design of future fusion reactors. From a historic point of view, the material mix used for the first wall of a fusion reactor has continually evolved, from original steel vessels to carbon and other low‐Z materials such as beryllium to tungsten as the primary candidate for a reactor's first wall armor and divertor material. For materials considered for fusion applications, a highly integrated approach is necessary. Resilience against neutron damage, good power exhaust, and oxidation resistance during accidental air ingress are design relevant issues while deciding on new materials or improving upon baseline materials. Neutron‐induced effects, e.g., transmutation adding to embrittlement, retention, and changes to thermomechanical properties, are crucial to material performance. In this contribution, the recent progress (2013–2019) in fusion materials development for current and future fusion devices, at Forschungszentrum Jülich GmbH, with activities focussing on advanced materials and their characterization is given. It is a continuation and extension of the work given by Coenen et al.

Transition from ductilizing to hardening in tungsten: The dependence on rhenium distribution

Mechanical responses of tungsten (W) and its alloys are strongly controlled by the properties of 1/2<111> screw dislocations. Rhenium (Re), as a typical alloying and transmutation element in W, can substantially modify the properties of the dislocations, thus the plasticity of the materials. In this study, we investigate the interaction of Re and Re clusters with the screw dislocations in W by first-principles calculations in combination with theoretical models. Specifically, we propose two competing and Re-distribution dependent mechanisms, i.e. “ductilizing effect” and “hardening effect”; both are crucial to the mechanical properties of W. For the ductilizing effect, dispersed Re atoms weaken the surrounding interatomic interaction and reduce the shear resistance, thus facilitating the motion of the dislocation. In contrast, for the hardening effect, Re clusters formed by aggregated Re atoms due to irradiation can increase the Peierls stress and energy, thus hindering the motion of the dislocations. The proposed mechanisms shed light on the experimental observations that there is a Re-induced transition from ductilizing to hardening due to irradiation. The current work provides a theoretical guidance to the development of W-based future fusion materials in search of ductilizing alloying elements.

Transition from Ductilizing to Hardening in Tungsten: The Dependence on Rhenium Distribution

Mechanical responses of tungsten (W) and its alloys are strongly controlled by the properties of 1/2 screw dislocations. Rhenium (Re), as a typical alloying and transmutation element in W, can substantially modify the properties of the dislocations,thus the plasticity of the materials. In this study, we investigate the interaction of Re and Re clusters with the screw dislocations in W by first-principles calculations in combination with theoretical models. Specifically, we propose two competing and Re-distribution dependent mechanisms, i.e., “ductilizing effect” and “hardening effect;” both are crucial to the mechanical properties of W. For the ductilizing effect, dispersed Re atoms weaken the surrounding interatomic interaction and reduce the shear resistance, thus facilitating the motion of the dislocation. In contrast, for the hardening effect, Reclusters formed by aggregated Re atoms due to irradiation can increase the Peierls stress and energy, thus hindering the motion of the dislocations. The proposed mechanisms shed light on the experimental observations that there is a Re-induced transition from ductilizing to hardening due to irradiation. The current work provides a theoretical guidance to the development of W-based future fusion materials in search of ductilizing alloying elements.

Synchronized fusion development considering physics, materials and heat transfer

Significant achievements have been made in the last 60 years in the development of fusion energy with the tokamak configuration. Based on the accumulated knowledge, the world is embarking on the construction and operation of ITER (International Thermonuclear Experimental Reactor) with a production of 500 MWf fusion power and the demonstration of physics Q = 10. ITER will demonstrate D–T burn physics for a duration of a few hundred seconds to prepare for the next long-burn or steady state nuclear testing tokamak operating at much higher neutron fluence. With the evolution into a steady state nuclear device, such as the China Fusion Engineering Test Reactor (CFETR), it is necessary to examine the boundary conditions imposed by the combined development of tokamak physics, fusion materials and fusion technology for a reactor. The development of ferritic steel alloys as the structural material suitable for use at high neutron fluence leads to the use of helium as the most likely reactor coolant. This points to the fundamental technology limitation on the removal of chamber wall maximum heat flux at around 1 MW m−2 and an average heat flux of 0.1 MW m−2 for the next test reactor. Future reactor performance will then depend on the control of spatial and temporal edge heat flux peaking in order to increase the average heat flux to the chamber wall. With these severe material and technological limitations, system studies were used to scope out a few robust steady state synchronized fusion reactor (SFR) designs. As an example, a low fusion power design at 131.6 MWf, which can satisfy steady state design requirements, would have a major radius of 5.5 m and minor radius of 1.6 m. Such a design with even more advanced structural materials like Wf/W composite could allow higher performance and provide a net electrical production of 62 MWe. These can be incorporated into the CFETR program.

Japanese Fusion Materials Development Path to DEMO

This paper reports Japanese strategy for developing blanket structural materials for DEMO. In the Japanese program, the candidate materials are categorized into Primary Option (RAFM) and Advanced Options (V-alloy, SiC/SiC, ODS-RAFM etc.). A staged development is planned corresponding to the three decision-making points (DPs), DP1: Intermediate check and review (C&R), DP2: Decision of transition of research and development (R&D) focus to DEMO, and DP3: Decision of DEMO construction. The near-term D-Li neutron source (A-FNS) and IFMIF are regarded as key facilities for the development. The strategy emphasizes “standardization” as an important step toward DEMO design qualification and licensing. The procedure to standard materials specifications by way of establishing structural design criteria and materials property requirements, and the procedure’s interaction with the schedule of irradiation data acquisition are discussed.

Three Game Changing Discoveries: A Simpler Fusion Concept?

This paper encourages exploration of a broad range of magnetic fusion concepts in parallel with mainline tokamak development. Such exploration will certainly lead to increased understanding of fusion science and possibly to an attractive fusion energy concept. As an example, this paper describes three discoveries which greatly increase the attractiveness of the magnetic mirror plasma confinement concept. The mirror concept is thought to have three unattractive characteristics. The magnets are complex, the plasma is plagued with micro-instabilities and the electron temperature would never approach required keV levels. Persistent research on the gas dynamic trap device at the Budker Institute of Nuclear Physics in Russia and elsewhere have overcome these three deficiencies. Stable high energy density plasma can be confined with simple circular magnets, micro-instabilities can be tamed, and electron temperatures reaching a keV have been measured. These three accomplishments provide a basis to reconsider the mirror concept as a neutron source for medical applications, fusion materials development, nuclear fuel production, and fusion energy production.

Developing structural, high-heat flux and plasma facing materials for a near-term DEMO fusion power plant: The EU assessment

The findings of the EU ‘Materials Assessment Group’ (MAG), within the 2012 EU Fusion Roadmap exercise, are discussed. MAG analysed the technological readiness of structural, plasma facing and high heat flux materials for a DEMO concept to be constructed in the early 2030s, proposing a coherent strategy for R&D up to a DEMO construction decision.A DEMO phase I with a ‘Starter Blanket’ and ‘Starter Divertor’ is foreseen: the blanket being capable of withstanding ⩾2MWyrm−2 fusion neutron fluence (∼20dpa in the front-wall steel). A second phase ensues for DEMO with ⩾5MWyrm−2 first wall neutron fluence. Technical consequences for the materials required and the development, testing and modelling programmes, are analysed using: a systems engineering approach, considering reactor operational cycles, efficient maintenance and inspection requirements, and interaction with functional materials/coolants; and a project-based risk analysis, with R&D to mitigate risks from material shortcomings including development of specific risk mitigation materials. The DEMO balance of plant constrains the blanket and divertor coolants to remain unchanged between the two phases. The blanket coolant choices (He gas or pressurised water) put technical constraints on the blanket steels, either to have high strength at higher temperatures than current baseline variants (above 650°C for high thermodynamic efficiency from He-gas coolant), or superior radiation-embrittlement properties at lower temperatures (∼290–320°C), for construction of water-cooled blankets. Risk mitigation proposed would develop these options in parallel, and computational and modelling techniques to shorten the cycle-time of new steel development will be important to achieve tight R&D timescales. The superior power handling of a water-cooled divertor target suggests a substructure temperature operating window (∼200–350°C) that could be realised, as a baseline-concept, using tungsten on a copper-alloy substructure. The difficulty of establishing design codes for brittle tungsten puts great urgency on the development of a range of advanced ductile or strengthened tungsten and copper compounds.Lessons learned from Fission reactor material development have been included, especially in safety and licensing, fabrication/joining techniques and designing for in-vessel inspection. The technical basis of using the ITER licensing experience to refine the issues in nuclear testing of materials is discussed.Testing with 14MeV neutrons is essential to Fusion Materials development, and the Roadmap requires acquisition of ⩾30dpa (steels) 14MeV test data by 2026. The value and limits of pre-screening testing with fission neutrons on isotopically- or chemically-doped steels and with ion-beams are evaluated to help determine the minimum14MeV testing programme requirements.

Multimodal options for materials research to advance the basis for fusion energy in the ITER era

Well-coordinated international fusion materials research on multiple fundamental feasibility issues can serve an important role during the next ten years. Due to differences in national timelines and fusion device concepts, a parallel-track (multimodal) approach is currently being used for developing fusion energy. An overview is given of the current state-of-the-art of major candidate materials systems for next-step fusion reactors, including a summary of existing knowledge regarding operating temperature and neutron irradiation fluence limits due to high-temperature strength and radiation damage considerations, coolant compatibility information, and current industrial manufacturing capabilities. There are two inter-related overarching objectives of fusion materials research to be performed in the next decade: (1) understanding materials science phenomena in the demanding DT fusion energy environment, and (2) application of this knowledge to develop and qualify materials to provide the basis for next-step facility construction authorization by funding agencies and public safety licensing authorities. The critical issues and prospects for development of high-performance fusion materials are discussed along with recent research results and planned activities of the international materials research community.

Advanced materials characterization and modeling using synchrotron, neutron, TEM, and novel micro-mechanical techniques—A European effort to accelerate fusion materials development

For the realization of fusion as an energy source, the development of suitable materials is one of the most critical issues. The required material properties are in many aspects unique compared to the existing solutions, particularly the need for necessary resistance to irradiation with neutrons having energies up to 14MeV. In addition to withstanding the effects of neutrons, the mechanical stability of structural materials has to be maintained up to high temperatures. Plasma-exposed materials must be compatible with the fusion plasma, both with regard to the generation of impurities injected into the plasma and resistance to erosion and hydrogen isotope retention. The development of materials fulfilling these and other criteria is a large-scale and long-term activity which involves basic materials science, materials development, characterization under both loading conditions and off-line, as well as testing under neutron flux-induced conditions. For the realization of a DEMO power plant, the materials solutions must be available in time. The European initiative FEMaS-CA – Fusion Energy Materials Science – Coordination Action – aims at accelerating materials development by integrating advanced materials characterization techniques, among them the efficient use of neutron and synchrotron-based techniques, into the fusion materials community. Further, high-end transmission electron microscopy and mechanical characterization (also on a microscopic level in order to facilitate tests of small material volumes, such as from neutron irradiation campaigns) are to be more extensively applied in fusion materials research. Finally, irradiation facilities for neutron damage benchmarking are contributing to the understanding of radiation effects. This overview demonstrates by means of a few examples the recent advancements in fusion materials research, e.g. by applying synchrotron X-ray and neutron tomography to novel materials and components. Deeper understanding of radiation effects is achieved by in situ TEM of materials under irradiation. Modeling of irradiation effects is closely linked to activities at irradiation facilities. Finally, new developments in mechanical testing on micro- and nano-scales are addressed.

Evaluation of irradiation facility options for fusion materials research and development

Successful development of fusion energy will require the design of high-performance structural materials that exhibit dimensional stability and good resistance to fusion neutron degradation of mechanical and physical properties. The high levels of gaseous (H, He) transmutation products associated with deuterium–tritium (D–T) fusion neutron transmutation reactions, along with displacement damage dose requirements up to 50–200displacements per atom (dpa) for a fusion demonstration reactor (DEMO), pose an extraordinary challenge. One or more intense neutron source(s) are needed to address two complementary missions: (1) scientific investigations of radiation degradation phenomena and microstructural evolution under fusion-relevant irradiation conditions (to provide the foundation for designing improved radiation resistant materials), and (2) engineering database development for design and licensing of next-step fusion energy machines such as a fusion DEMO.A wide variety of irradiation facilities have been proposed to investigate materials science phenomena and to test and qualify materials for a DEMO reactor. Some of the key technical considerations for selecting the most appropriate fusion materials irradiation source are summarized. Currently available and proposed facilities include fission reactors (including isotopic and spectral tailoring techniques to modify the rate of H and He production per dpa), dual- and triple-ion accelerator irradiation facilities that enable greatly accelerated irradiation studies with fusion-relevant H and He production rates per dpa within microscopic volumes, D–Li stripping reaction and spallation neutron sources, and plasma-based sources.The advantages and limitations of the main proposed fusion materials irradiation facility options are reviewed. Evaluation parameters include irradiation volume, potential for performing accelerated irradiation studies, capital and operating costs, similarity of neutron irradiation spectrum to fusion reactor conditions, temperature and irradiation flux stability/control, ability to perform multiple-effect tests (e.g., irradiation in the presence of a flowing coolant, or in the presence of complex applied stress fields), and technical maturity/risk of the concept. Ultimately, it is anticipated that heavy utilization of ion beam and fission neutron irradiation facilities along with sophisticated materials models, in addition to a dedicated fusion-relevant neutron irradiation facility, will be necessary to provide a comprehensive and cost-effective understanding of anticipated materials evolution in a fusion DEMO and to therefore provide a timely and robust materials database.

Deuteron-Induced Cross Section Calculations of Some Structural Fusion Materials

The development of fusion materials for the safety of fusion power systems and understanding nuclear properties is important. The reaction cross-section data have a critical importance on fusion reactors and development for fusion reactor technology. In this study, the theoretical cross sections of some structural fusion materials such as Cr, V, Fe, Ni, Zr and Ta in deuteron-induced reactions have been investigated. The new calculations on the excitation functions of 50Cr(d, α)48V, 51V(d, 2n)51Cr, 51V(d, 4n)49Cr, 54Fe(d, α)52Mn, 54Fe(d, n)55Co, 58Ni(d, α)56Co, 96Zr(d, n)97Nb, 96Zr(d, 2n)96Nb and 181Ta(d, 2n)181W reactions have been carried out up to 90 MeV incident deuteron energies. In these calculations, the pre-equilibrium and equilibrium effects have been investigated. The pre-equilibrium calculations involve the geometry dependent hybrid model and hybrid model. Equilibrium effects have been calculated according to the Weisskopf–Ewing model. The ALICE/ASH computer code has been used in all calculations. The calculated results have been compared with the experimental data existing in EXFOR database and found to be in good agreement.

Summary of the International Workshop on Magnetic Fusion Energy (MFE) Roadmapping in the ITER Era; 7–10 September 2011, Princeton, NJ, USA

With the ITER project now well under way, the countries engaged in fusion research are planning, with renewed intensity, the research and major facilities needed to develop the science and technology for harnessing fusion energy. The Workshop on MFE Roadmapping in the ITER Era was organized to provide a timely forum for an international exchange of technical information and strategic perspectives on how best to tackle the remaining challenges leading to a magnetic fusion DEMO, a nuclear fusion device or devices with a level of physics and technology integration necessary to cover the essential elements of a commercial fusion power plant. Presentations addressed issues under four topics: (1) Perspectives on DEMO and the roadmap to DEMO; (2) Technology; (3) Physics-Technology integration and optimization; and (4) Major facilities on the path to DEMO. Participants identified a set of technical issues of high strategic importance, where the development strategy strongly influences the overall roadmap, and where there are divergent understandings in the world community, namely (1) the assumptions used in fusion design codes, (2) the strategy for fusion materials development, (3) the strategy for blanket development, (4) the strategy for plasma exhaust solution development and (5) the requirements and state of readiness for next-step facility options. It was concluded that there is a need to continue and to focus the international discussion concerning the scientific and technical issues that determine the fusion roadmap, and it was suggested that an international activity be organized under appropriate auspices to foster international cooperation on these issues.

The materials production and processing facility at the Spanish National Centre for fusion technologies (TechnoFusión)

In response to the urgent request from the EU Fusion Program, a new facility (TechnoFusión) for research and development of fusion materials has been planned with support from the Regional Government of Madrid and the Ministry of Science and Innovation of Spain. TechnoFusión, the National Centre for Fusion Technologies, aims screening different technologies relevant for ITER and DEMO environments while promoting the contribution of international companies and research groups into the Fusion Programme. For this purpose, the centre will be provided with a large number of unique facilities for the manufacture, testing (a triple-beam multi-ion irradiation, a plasma–wall interaction device, a remote handling for under ionizing radiation testing) and analysis of critical fusion materials. Particularly, the objectives, semi-industrial scale capabilities and present status of the TechnoFusión Materials Production and Processing (MPP) facility are presented. Previous studies revealed that the MPP facility will be a very promising infrastructure for the development of new materials and prototypes demanded by the fusion technology and therefore some of them will be here briefly summarized.

Present status of refurbishment and irradiation technologies in JMTR

The Japan Materials Testing Reactor (JMTR) of the Japan Atomic Energy Agency is a testing reactor for various neutron irradiation tests on nuclear fuels and materials, as well as for radioisotope production. The operation of JMTR stopped temporarily in August 2006 for refurbishment and improvement. The renewed JMTR will resume operation in Japanese fiscal year 2011. The renewal of aged reactor components, the preparation of new irradiation facilities, and the development of irradiation technologies have been carried out for the resumption of the new JMTR. The new JMTR with the new irradiation facilities and the irradiation technologies will be utilized for the research and development of fission and fusion reactor fuels and materials. This paper describes the present status of the refurbishment and the irradiation technologies focused on instrumentation such as the multi-paired thermocouple which is applicable to irradiation temperature control and a ceramic oxygen sensor in JMTR.

Extrapolation of GDT Results to a Neutron Source for Fusion Materials Testing

The achievement of 60% beta and near classical confinement in the Russian Gas Dynamic Trap (GDT) provides a basis for extrapolating to a 2 MW neutron source with 2 MW m-2 of 14 MeV neutron flux over an area of ~1 m2. Such a source is needed for fusion materials development and qualification. We consider two axisymmetric configurations: a single mirror cell Deuterium-Tritium Dynamic-Trap Neutron Source (DTNS) and a Tandem-mirror Neutron Source (TNS). Compared to earlier US neutron source concepts, neither configuration utilizes complex minimum-B magnets or thermal barriers. In this paper we describe extrapolations from GDT with the same physical size, and the same dimensionless plasma parameters, but with higher magnetic field as well as higher neutral beam energy and power.

An Investigation for Ground State Features of Some Structural Fusion Materials

Environmental concerns associated with fossil fuels are creating increased interest in alternative non-fossil energy sources. Nuclear fusion can be one of the most attractive sources of energy from the viewpoint of safety and minimal environmental impact. When considered in all energy systems, the requirements for performance of structural materials in a fusion reactor first wall, blanket or diverter, are arguably more demanding or difficult than for other energy system. The development of fusion materials for the safety of fusion power systems and understanding nuclear properties is important. In this paper, ground state properties for some structural fusion materials as 27Al, 51V, 52Cr, 55Mn, and 56Fe are investigated using Skyrme–Hartree–Fock method. The obtained results have been discussed and compared with the available experimental data.