E. Wakai

IFMIF: overview of the validation activities

The Engineering Validation and Engineering Design Activities (EVEDA) for the International Fusion Materials Irradiation Facility (IFMIF), an international collaboration under the Broader Approach Agreement between Japan Government and EURATOM, aims at allowing a rapid construction phase of IFMIF in due time with an understanding of the cost involved. The three main facilities of IFMIF (1) the Accelerator Facility, (2) the Target Facility and (3) the Test Facility are the subject of validation activities that include the construction of either full scale prototypes or smartly devised scaled down facilities that will allow a straightforward extrapolation to IFMIF needs. By July 2013, the engineering design activities of IFMIF matured with the delivery of an Intermediate IFMIF Engineering Design Report (IIEDR) supported by experimental results. The installation of a Linac of 1.125 MW (125 mA and 9 MeV) of deuterons started in March 2013 in Rokkasho (Japan). The worlds largest liquid Li test loop is running in Oarai (Japan) with an ambitious experimental programme for the years ahead. A full scale high flux test module that will house ~1000 small specimens developed jointly in Europe and Japan for the Fusion programme has been constructed by KIT (Karlsruhe) together with its He gas cooling loop. A full scale medium flux test module to carry out on-line creep measurement has been validated by CRPP (Villigen).

Swelling behavior of F82H steel irradiated by triple/dual ion beams

Abstract Irradiations for spallation target vessels and structural materials of fusion reactors were simulated using simultaneous triple/dual ion beams consisting of Fe 3+ , He + and H + ions or Fe 3+ and He + ions at temperatures between 470 and 600 °C to 50 dpa. The swelling of F82H (Fe–8Cr–2W–0.2V–0.04Ta–0.1C) martensitic steel was enhanced by a synergistic effect of displacement damage and the implantation of helium and hydrogen. The maximum swelling of F82H steel was 3.2% at 470 °C under a simulation of structural materials of fusion reactors, and was higher than 1.2%, which applied to a simulation of spallation target vessel. The swelling under a simulation of fusion reactor decreased with increasing irradiation temperature, however the swelling under a simulation of spallation target vessel was again increased at 600 °C by the high helium concentration. From the microstructural analysis of taking account of cavity growth process, the cause of the enhancement of swelling under a simulation of fusion reactor is thought to be gas pressure of hydrogen and helium in cavities during irradiation. The effects of 50% cold-working and carbon implantation on swelling behavior were also examined. The swelling was reduced from 3.2% to 1.4% by 50% cold-working, and to 0.5% by carbon implantation.

The accomplishment of the Engineering Design Activities of IFMIF/EVEDA: The European-Japanese project towards a Li(d,xn) fusion relevant neutron source

The International Fusion Materials Irradiation Facility (IFMIF), presently in its Engineering Validation and Engineering Design Activities (EVEDA) phase under the frame of the Broader Approach Agreement between Europe and Japan, accomplished in summer 2013, on schedule, its EDA phase with the release of the engineering design report of the IFMIF plant, which is here described. Many improvements of the design from former phases are implemented, particularly a reduction of beam losses and operational costs thanks to the superconducting accelerator concept, the re-location of the quench tank outside the test cell (TC) with a reduction of tritium inventory and a simplification on its replacement in case of failure, the separation of the irradiation modules from the shielding block gaining irradiation flexibility and enhancement of the remote handling equipment reliability and cost reduction, and the water cooling of the liner and biological shielding of the TC, enhancing the efficiency and economy of the related sub-systems. In addition, the maintenance strategy has been modified to allow a shorter yearly stop of the irradiation operations and a more careful management of the irradiated samples. The design of the IFMIF plant is intimately linked with the EVA phase carried out since the entry into force of IFMIF/EVEDA in June 2007. These last activities and their on-going accomplishment have been thoroughly described elsewhere (Knaster J et al [19]), which, combined with the present paper, allows a clear understanding of the maturity of the European–Japanese international efforts. This released IFMIF Intermediate Engineering Design Report (IIEDR), which could be complemented if required concurrently with the outcome of the on-going EVA, will allow decision making on its construction and/or serve as the basis for the definition of the next step, aligned with the evolving needs of our fusion community.

Effect of triple ion beams in ferritic/martensitic steel on swelling behavior

Abstract The synergistic effects of displacement damage and atomic hydrogen and helium on swelling of the ferritic/martensitic steel, F82H, has been investigated. The irradiation was performed at temperatures between 470 and 600 °C to 50 dpa (displacement per atoms) under conditions of simultaneous ion beams consisting of Fe3+, He+ and H+ ions or Fe3+ and He+ ions. The swelling of F82H steel under triple beams with 18 appm He/dpa and 70 appm H/dpa was larger than that under dual beams with 18 appm He/dpa. The swelling in F82H under triple beams increased with decreasing irradiation temperature from 0.1% to 3.2%, while swelling under dual beams was between 0.04% and 0.08%. On the other hand, in the case of triple beam irradiation with a high ratio of gas/dpa, the swelling tended to increase with irradiation temperature. The swelling in ferritic/martensitic steels is significantly enhanced by the synergistic effect of displacement damage, hydrogen and helium atoms.

IFMIF/EVEDA lithium test loop: design and fabrication technology of target assembly as a key component

The engineering validation and engineering design activity (EVEDA) for the International Fusion Materials Irradiation Facility (IFMIF) is proceeding as one of the ITER broader approach activities. In the concept of the IFMIF, two 40 MeV deuteron beams are injected into a liquid Li stream (Li target) flowing at a velocity of 15 m s−1. The EVEDA Li test loop (ELTL) is aimed at validating the hydraulic stability of the Li target at a velocity up to 20 m s−1 under a vacuum condition of 10−3 Pa as the most important issue. Construction of the ELTL, which is the largest liquid metal loop possessing 5.0 m3 Li for the fusion research ever, was completed in the O-arai Research & Development Center in the Japan Atomic Energy Agency on 22 November 2010. This paper presents the design and fabrication technology of a target assembly called integrated target assembly, in which the Li target is produced by a contraction nozzle along a concave channel. There are two concepts regarding the target assembly: the integrated target assembly and the bayonet target assembly. Both target assemblies are outlined in this paper, and then the newly proposed design of the integrated target assembly for the ELTL and its fabrication technology are given. The integrated target assembly was processed by a five-axis milling machine and the processing accuracy was measured by 3D measurement tools. Finally, methods applied for the validation of the stability of the Li target are introduced in this paper.

Corrosion–erosion test of SS316 in flowing Pb–Bi

Abstract Corrosion tests of austenitic stainless tube were done under flowing Pb–Bi conditions for 3000 h at 450 °C. Specimens were 316SS produced as a tubing form with 13.8 mm outer diameter, 2 mm thickness and 40 cm length. During operation, maximum temperature, temperature difference and flow velocity of Pb–Bi at the specimen were kept at 450, 50 °C, and 1 m/s, respectively. After the test, specimen and components of the loop were cut and examined by optical microscope, SEM, EDX, WDX and X-ray diffraction. Pb–Bi adhered on the surface of the specimen even after Pb–Bi was drained out to the storage tank from the circulating loop. Results differed from a stagnant corrosion test in that the specimen surface became rough and the corrosion rate was maximally 0.1 mm/3000 h. Mass transfer from the high temperature to the lower temperature area was observed: crystals of Fe–Cr were found on the tube surface in the low-temperature region. The sizes of crystals varied from 0.1 to 0.2 mm. The depositing crystals were ferrite grains and the chemical composition ratio (mass%) of Fe to Cr was 9:1.

Microstructural study of irradiated isotopically tailored F82H steel

Abstract The synergistic effect of displacement damage and hydrogen or helium atoms on microstructures in F82H steel irradiated at 250–400 °C to 2.8–51 dpa in HFIR has been examined using isotopes of 54 Fe or 10 B . Hydrogen atoms increased slightly the formation of dislocation loops and changed the Burgers vector for some parts of dislocation loops, and they also affected on the formation of cavity at 250 °C to 2.8 dpa. Helium atoms also influenced them at around 300 °C, and the effect of helium atoms was enhanced at 400 °C. Furthermore, the relations between microstructures and radiation-hardening or ductile to brittle transition temperature (DBTT) shift in F82H steel were discussed. The cause of the shift increase of DBTT is thought to be due to the hardening of dislocation loops and the formation of α′-precipitates on dislocation loops.

Swelling behavior of TIG-welded F82H IEA heat

Tungsten-inert-gas weld joints prepared from the IEA heat of F82H were irradiated with 10.5 MeV Fe ions and 1.05 MeV He ions at 450 °C. Transmission electron microscopy observation revealed a marked cavity growth up to 30 nm at 50 dpa in the over-tempered portion of the heat-affected zone (HAZ), while cavities in the quenched portion of HAZ remained smaller (up to 10 nm). Base metal results also showed that a specimen tempered at 780 °C contained larger cavities than those tempered at 750 °C. Cavities in cold-worked specimens were the smallest. Initial dislocation densities in F82H, which are affected by heat treatment and/or mechanical treatment, dominate the cavity growth.

Effect of simultaneous ion irradiation on microstructural change of SiC/SiC composites at high temperature

Abstract The effect of simultaneous triple ion irradiation of He, H and Si on microstructural evolution of two kinds of SiC/SiC composites (HNS composite (using Hi-Nicalon type S SiC fiber) and TSA composite (using Tyranno SA SiC fiber)) at 1000 °C has been investigated. The microstructure observations of SiC/SiC composites irradiated to 10 dpa were examined by transmission electron microscopy. He bubbles were hardly formed in matrix of TSA composite, but many helium bubbles and some cracks were observed at grain boundaries of matrix of HNS composite. He bubbles and cracks were not, on the other hand, observed in the both fiber fabrics of HNS and TSA composites. Debonding between fiber and carbon layer following irradiation region was not observed in the both composites. Under these irradiation conditions, TSA composite showed the better microstructural stability against ion beams irradiation than one of HNS composite.

Swelling of F82H irradiated at 673 K up to 51 dpa in HFIR

Abstract Reduced-activation ferritic/martensitic steel, F82H (8Cr–2W–0.2V–0.04Ta–0.1C), and variants doped with isotopically tailored boron were irradiated at 673 K up to 51 dpa in the high flux isotope reactor (HFIR). The concentrations of 10B in these alloys were 4, 62, and 325 appm during HFIR irradiation which resulted in the production of 4, 62 and 325 appm He, respectively. After irradiation, transmission electron microscopy (TEM) was carried out. The number density of cavities increased and the average diameter of cavities decreased with increasing amounts of 10B. The number density decreased and the average diameter increased with increasing displacement damage. Swelling increased as a function of displacement damage and He concentration.