International Fusion Materials Irradiation Facility

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The International Fusion Materials Irradiation Facility, also known as IFMIF, is a projected materials test facility in which candidate materials for the use in an energy producing fusion reactor can be fully qualified. IFMIF is an accelerator-based neutron source that produces, using deuterium-lithium nuclear reactions, a large neutron flux with a spectrum similar to that expected at the first wall of a fusion reactor. The IFMIF project was started in 1994 as an international scientific research program, carried out by Japan, the European Union, the United States, and Russia, and managed by the International Energy Agency. Since 2007, it has been pursued by the Japanese Government and EURATOM under the Broader Approach Agreement in the field of fusion energy research, through the IFMIF/EVEDA project, which conducts engineering validation and engineering design activities for IFMIF.

Background[edit]

The deuterium-tritium fusion reaction generates mono-energetic neutrons with an energy of 14.1 MeV. In fusion power plants, neutrons will be present at fluxes in the order of 1018 m−2s−1 and will interact with the material structures of the reactor by which their spectrum will be broadened and softened. A fusion relevant neutron source is an indispensable step towards the successful development of fusion energy. Safe design, construction and licensing of a fusion power facility by the corresponding Nuclear Regulatory agency will require data on the materials degradation under neutron irradiation during the life-time of a fusion reactor. The main source of materials degradation is structural damage which is typically quantified in terms of “displacements per atom” (dpa).[1] Whereas in the currently constructed large fusion experiment, ITER, structural damage in the reactor steels will not exceed 2 dpa at the end of its operational life, damage creation in a fusion power plant is expected to amount to 15 dpa per year of operation.[2]

The need of a relevant fusion source[edit]

Fig. 1. Comparison of the neutron spectra of the helium cooled pebble bed (HCPB) blanket of a fusion DEMO reactor, with different planned or existing neutron sources including IFMIF [6], [7].

None of the most commonly available neutron sources are adequate for fusion materials testing, for various reasons. The accumulation of gas in the material microstructure is intimately related to the energy of the colliding neutrons. For steels, the 54Fe(n,α)51Cr and 54Fe(n,p)54Mn reactions are responsible for most of the protons and α-particles produced, and these have an incident neutron energy threshold at 0.9 MeV and 2.9 MeV respectively. Therefore conventional fission reactors, which produce neutrons with an average energy around 1-2 MeV, cannot adequately match the testing requirements for fusion materials. In fact the leading factor for embrittlement, the generation of α-particles by transmutation, is far from realistic conditions (actually around 0.3 appm He/dpa).[3] Spallation neutron sources with a wide spectrum of energies up to the order of hundreds of MeV leading to a potentially different defect structures, and generating light transmuted nuclei that intrinsically affect the targeted properties of the alloy. Ion implantation facilities offer insufficient irradiation volume (maximum values of a few hundreds µm thick layer) to carry out standardized mechanical property tests. Also the low elastic scattering cross section for light ions makes damage levels above 10 dpa impractical.[4] The d-Li reaction exploited for IFMIF [5] is able to provide an adequate fusion neutron spectrum as shown by the comparison of IFMIF with other available neutron sources,.[6][7] In summary, due to the sensitivity of materials to the specificities in the irradiation conditions, such as α-particle generation/dpa combined with damage levels of above 15 dpa per year of operation under temperature controlled conditions, material tests require the neutron source to be comparable to a fusion reactor environment.

International Fusion Material Irradiation Facility (IFMIF)[edit]

Fig. 2. Artistic bird-eye view of IFMIF. Plant dimensions are 190 x 90 m with 5 floors.

The IFMIF plant consists of five major systems,:[8][9] 1) Accelerator Facility, 2) Li Target Facility, 3)Test Facility, 4)Post-Irradiation Examination (PIE) Facility, and 5)Conventional Facility. The whole plant must comply with international nuclear facility regulations. The energy of the beam (40 MeV) and the current of the parallel accelerators (2 x 125 mA) have been tuned to maximize the neutron flux (1018 m−2 s−1) while creating irradiation conditions comparable to those in the first wall of a fusion reactor. Damage rates >20 dpa per year of operation can be reached in a volume of 0.5 l of its High Flux Test Module that can accommodate around 1000 small specimens.[10] The small specimen testing techniques developed aim at full mechanical characterization (fatigue, fracture toughness, crack growth rate, creep and tensile stress) of candidate materials, and allow, besides a scientific understanding of fusion neutron induced degradation phenomena, the creation of the major elements of a fusion materials database suited for designing, licensing and reliably operating future fusion reactors. The main expected contributions of IFMIF to the nuclear fusion community [11] are to:

  1. provide data for the engineering design for DEMO,
  2. provide information to define performance limits of materials,
  3. contribute to the completion and validation of existing databases,
  4. contribute to the selection or optimization of different alternative fusion materials,
  5. validate the fundamental understanding of the radiation response of materials including benchmarking of irradiation effects modelling at length-scales and time-scales relevant for engineering application,
  6. tests blanket concept and functional materials prior to or complementary to ITER test blanket module testing.

The IFMIF Intermediate Engineering Design[edit]

Fig. 3 Schematics of IFMIF plant including its 5 facilities.

The engineering design of the IFMIF plant is intimately linked with the validation activities, and was conducted during the first phase of the IFMIF/EVEDA project. The IFMIF Intermediate Engineering Design Report was established in June 2013 and adopted by the stakeholders in December 2013. The IFMIF Intermediate Engineering Design defines the major systems in outline. The two accelerator CW deuteron beams of 5 MW each impinge in an overlapping manner at an angle of ±9° with a footprint of 200 mm x 50 mm and a steady time profile on the liquid Li jet, with the Bragg’s peak absorption region at about 20 mm depth.

Fig. 4. Tmax envelope in the beam footprint under nominal conditions at different depths (in green) vs Ts corresponding to the centrifugal pressure in the flowing lithium (in red). 615 K corresponds to the beam line pressure of 0.001 Pa [12].

The Target Facility, which holds the inventory of about 10 m3 of Li, forms and conditions the beam target. The Li screen fulfils two main functions: 1) to react with the deuterons to generate a stable neutron flux in the forward direction and 2) to dissipate the beam power in a continuous manner. The flowing Li (15 m/s; 250 °C) is shaped and accelerated in the proximity of the beam interaction region by a two-stage reducer nozzle forming a concave jet of 25 mm thickness with a minimum radius of curvature of 250 mm in the beam footprint area. The resulting centrifugal pressure raises the boiling point of the flowing Li and thus ensures a stable liquid phase. The beam power absorbed by the Li is evacuated by the heat removal system and the lithium is cooled to 250 °C by a serial of heat exchangers. The control of impurities, essential for the quality of the liquid screen, will be done through a tailored design of cold and hot trap systems, and purities of Li during operation better than 99.9% are expected. On-line monitoring of impurities will detect impurity levels over 50 ppm. Based on numerical analyses carried out in the last three decades, the beam-target interaction is not expected to have a critical impact on jet stability.[12] The Test Facility will provide high, medium and low flux regions ranging from ›20 dpa/full power year (fpy) to ‹1 dpa /fpy with increasingly available irradiating volumes of 0.5 l, 6 l and 8 l that will house different metallic and non-metallic materials potentially subjected to the different irradiation levels in a power plant. More specifically, in the high flux region, fluences of 50 dpa in ‹3.5 years in a region of 0.5 l, together with power plant relevant fluences of ›120 dpa in ‹5 years in a region of 0.2 l, are planned. The high flux region will accommodate about 1000 small specimens assembled in 12 individual capsules independently temperature controlled that will allow not only mechanical characterization of the candidate structural materials tested, but also an understanding of the influence in their degradation with material temperature during irradiation. The Post-Irradiation Examination facility, an essential part of IFMIF, is hosted in a wing of the main building in order to minimize the handling operations of irradiated specimens.[13] It will not only allow testing irradiated specimens out of the different testing modules, but also characterizing metallographically the specimens after destructive testing.

Engineering Validation Activities[edit]

Fig. 5. Layout of LIPAc and its construction sharing.
Fig. 6. The EVEDA Lithum Test Loop in Oarai, Japan.
Fig. 7. LEBT image of the deuteron injector of the Linear IFMIF Accelerator Prototype Accelerator (LIPAc) under installation in Rokkasho, Japan.

To minimise the risks in constructing IFMIF, the IFMIF/EVEDA project has constructed or is constructing prototypes of those systems which face the main technological challenges that have been identified throughout the years of international cooperation in establishing a fusion relevant neutron source,.[14][15] namely 1) the Accelerator Facility, 2) the Target Facility, and 3) the Test Facility,.[16][17] An Accelerator Prototype (LIPAc), designed and constructed mainly in European laboratories and under installation at Rokkasho at JAEA premises, is identical to the IFMIF accelerator design up to its first superconductive accelerating stage (9 MeV energy, 125 mA of D+ in Continuous Wave (CW) current), and will become operational in June 2017.[18] A Li Test Loop (ELTL) at the Oarai premises of JAEA, integrating all elements of the IFMIF Li target facility, was commissioned in February 2011,[19] and is complemented by corrosion experiments performed at a Li loop (Lifus6) in ENEA, Brasimone.[20] A High Flux Test Module (two different designs accommodating either Reduced Activation Ferritic-Martensitic steels (RAFM) or SiC),[21][22] with a prototype of the capsules housing the small specimens to be irradiated in the BR2 fission reactor of SCK/CEN Mol [23] and tested in the cooling helium loop HELOKA of KIT, Karlsruhe,[24] together with a Creep Fatigue Test Module [25] manufactured and tested at full scale at PSI, Villigen. Detailed specific information on the on-going validation activities is being made available in related publications [17]-,[25][26][27][28][29][30],.[31]

References[edit]

  1. ^ M.I. Norgett et al, A proposed method of calculating displacement dose rates, Nuclear Engineering Design 33 (1975) 50-54
  2. ^ M.R.Gilbert et al., An integral model for materials in a fusion power plant: transmutation, gas production, and helium embrittlement under neutron irradiation, Nuclear Fusion 52 (2012)
  3. ^ R.A. Stoller, The role of cascade energy and temperature in primary defect, Journal of Nuclear Materials 276 (2000)
  4. ^ D.J. Mazey, Fundamental aspects of high-energy ion-beam simulation techniques and their relevance to fusion materials studies, Journal of Nuclear Materials 174 (1990)
  5. ^ http://www.ifmif.org
  6. ^ S. Zinkle and A. Moeslang, Evaluation of irradiation facility options for fusion materials research and development, Fusion and Engineering Design 88 (2013) 472-482
  7. ^ P. Vladimirov and A. Moeslang, Comparison of material irradiation conditions for fusion, spallation, stripping, and fission neutron sources, Journal of Nuclear Materials 329-340 (2004) 33
  8. ^ IFMIF International Team, IFMIF Comprehensive Design Report, IEA on-line publication
  9. ^ IFMIF Intermediate Engineering Design Report: IFMIF Plant Design Description document (not available on-line; delivered upon request at ifmif-eveda@ifmif.org)
  10. ^ P. Garin et al., IFMIF specifications from the users point of view, Fusion Engineering and Design 86 (2011) 611
  11. ^ A. Moeslang, Development of a Reference Test Matrix for IFMIF Test Modules, Final report on the EFDA Task TW4-TTMI-003D4, (2006)
  12. ^ J. Knaster et al., Assessment of the beam-target interaction of IFMIF: A state of the art, Fusion Engineering and Design (2014)
  13. ^ E. Wakai et al., Design Status of Post Irradiation Examination Facilities in IFMIF/EVEDA, J. Plasma Fusion Res., Vol. 9 (2010)
  14. ^ E.W. Pottmeyer, Jr., The Fusion Material Irradiation Facility at Handford, Journal of Nuclear Materials, 85 & 86, 463-5 (1979)
  15. ^ T. Kondo, et al., Selective energy neutron source based on the D-Li stripping reaction, Journal of Fusion Energy, 8 229-235, (1989)
  16. ^ P. Garin et al., Main baseline of IFMIF/EVEDA project, Fusion Eng. Design, 84 pp.259-264 (2009)
  17. ^ a b J. Knaster et al., IFMIF: overview of the validation activities, Nuclear Fusion 33 (2013) 116001
  18. ^ P. Cara et al., 2012 Overview and status of the Linear IFMIF Prototype Accelerator (LIPAc), Proc. IAEA Fusion Energy Conf. 2012 (San Diego, CA, 2012)
  19. ^ H. Kondo et al., Completion of IFMIF/EVEDA Li test loop construction, Fus. Eng. Des. 87 (2012) 418
  20. ^ A. Aiello et al., Lifus (Li for Fusion) 6 loop design and construction, Proceedings of SOFT 2012 Liege
  21. ^ F. Arbeiter et al., Overview of results of the first phase of validation activities for the IFMIF High Flux Test Module, Fusion Engineering Design 87 (2012) 1506
  22. ^ T. Abe, et al., SiC/SiC composite heater for IFMIF, Proceedings of SOFT 2012, Liege
  23. ^ P. Gouat et al., Present status of the Belgian contribution to the validation and design activities for the development of the IFMIF radiation-testing modules Fusion Eng. Des. 86
  24. ^ G. Schlindwein et al., Start-up phase of the HELOKA-LP low pressure helium test facility for IFMIF irradiation modules, Fus. Eng. Des. 87 (2012) 737
  25. ^ a b P. Vladimirov et al., Nuclear responses in IFMIF creep-fatigue testing machine, Fusion Eng. Des. 83 1548 (2008)
  26. ^ M. Pérez et al., IFMIF: steps toward realization, Proceedings of SOFE 2013 San Francisco
  27. ^ M. Sugimoto, T. Imai, Y. Okumura, K. Nakayama, S. Suzuki, M. Saigusa, Issues to be verified by IFMIF prototype accelerator for engineering validation, J. Nucl. Mat. 307-311 (2002) 1691-1695
  28. ^ J. Knaster et al., Installation and commissioning of the 1.1 MW deuteron prototype Linac of IFMIF, Proceedings of IPAC 2013, Shanghai
  29. ^ R. Gobin et al., IFMIF Injector acceptance tests at CEA/Saclay: 140 mA/100 keV deuteron beam characterization, Proceedings of ICIS 2013, Chiba
  30. ^ H. Shidara et al., Installation status of deuteron injector of IFMIF prototype accelerator in Japan, Proceedings of IPAC 2013, Shanghai
  31. ^ T. Kondo et al., Observation of the Li target in the EVEDA Li Test Loop, Proceedings of ISFNT 2013, Barcelona