Search

The current status and the progress of research and development (R&D) activities for a Fusion DEMO reactor in the National Institutes for Quantum and Radiological Science and Technology (QST) Rokka...

Reduced activation ferritic/martensitic steels (RAFMs) have been developed for the structural material of fusion reactor blanket. Extensive researches were conducted using transmission electron microscopy (TEM) to define the precipitation behavior of MX (M: Metallic elements, X: C and/or N) precipitates such as vanadium and tantalum carbides and/or nitrides, since they strongly affect material properties. However, it is not completely defined yet. TEM can obtain detailed information, but the observable volume is limited and it needs a long time to obtain representative and statistically reliable microstructural information. It is fruitful to complement TEM results applying other characterization techniques together. In this work, we studied the precipitation behavior of MX in the RAFM, F82H, through the application of various techniques with larger observable volumes and compared with TEM past results. We additionally tried to find sub-nanometric MX precipitates that can be hardly observed through TEM. From the result, the TaX (X: C and/or N) phase surely varied depending on the chemical composition of alloy and heat treatment; some TaX precipitates were unstable during tempering, MX precipitates were intergranular, and sub-nanometric MX were not found in the matrix. These obtained results were helpful to define the precipitation behavior of MX in F82H.

Several key components, such as superconducting coils, remote handling equipment, heating systems, have been designed and manufactured by JADA (Japan Domestic Agency). These activities have been carried out in accordance with the agreed schedule; in collaboration with the ITER organization and other domestic agencies. As a significant technical program using ITER, to design and to manufacture the TBS (Test blanket system), some R&D and design activities have also been conducted in Japan. Under the IFERC (the International Fusion Energy Research Center) projects of BA (Broader Approach) activities, design and R&D activities on fusion DEMO reactor have been carried out. For the DEMO R&D activity, five basic R&D subjects for a DEMO blanket system have been selected, and been studies under close collaborations between EU and JA: structure materials (RAFM steels and SiC/SiC composites), functional materials (tritium breeders and neutron multipliers), and tritium technology. From 2007, the above project...

To improve the fatigue properties evaluation of the joint region of the fusion reactor blanket, the effect of the non-uniform distribution of the microstructure and strength on the fatigue properti...

The diameter of pressurized tubes of F82H and B-doped F82H irradiated up to ~6 dpa have been measured by a non-contacting laser profilometer. The irradiation creep strains of F82H irradiated at 573...

When fusion welding is conducted on the dissimilar materials between a reduced activation ferritic/martensitic steel F82H steel and an austenite stainless steel SUS 316 steel, δ ferrite is generally formed and inevitably deteriorates the weld properties. In this study, dissimilar welding of F82H to SUS 316 steel was successfully achieved by friction stir lap welding technique. It revealed that the shape and microstructure of the joint interface can be controlled by controlling the welding temperature, in another word, by changing the applied load. By controlling the welding temperature at ∼710°C, a sound dissimilar joint can be obtained with a smooth joint interface and no mixed microstructure, despite the relative overlapping position of the steel plates. All the dissimilar joints showed high shear tensile strength and fracture in the base metal of F82H steel plate, which has lower strength than the SUS 316 steel plate at room temperature.

A toughness-improved type of F82H steel called F82H mod3 has been developed, and the material properties and irradiation behavior have been examined. The significant modification of the chemical co...

The effect of specimen size and shape on the fatigue life of reduced activation ferritic/martensitic steel “F82H IEA-heat” was investigated to develop a fatigue life evaluation method using a small specimen for testing neutron-irradiated materials. The fatigue test was carried out at room temperature in air using three kinds of round-bar specimen (minimum diameter cross sections of 1, 4, and 7 mm) and one hourglass specimen (minimum diameter cross section of 1.25 mm). The effect of specimen size on fatigue life from a level of 103 to 104 cycles was almost negligible for the round-bar specimens. The shorter fatigue life at the total strain range below 0.6% and the slightly longer fatigue life at the total strain range above 0.8% of the hourglass specimen relative to that of the standard specimen were observed from a level of 102 to 104 cycles.

The effect of specimen shape on the low cycle fatigue life of reduced activationferritic/martensitic steel, F82H IEA-heat, was investigated to develop a reliable smallspecimen test technique (SSTT) for fatigue. The low cycle fatigue test was carried out at room temperature in air at a total strain range of 0.8–3.0%. One round-bar-type and three kinds of hourglass-type miniature fatigue specimens were used. The relationship between total strain range (δet) and number of cycles to failure (Nf) in one of the hourglasstype specimens, which is the current standard miniature fatigue specimen in Japan, was represented by the Manson-Coffin-type regression formula (δϵt = 376N 0.84 f + 2.16N −0.16 f ). The effect of specimen shape on the lowcycle fatigue life and fracture mode was almost negligible among the four specimen types, and their fatigue lives were almost the same. Similar stress distributions at the minimum cross sections of these specimens were shown above the total strain range of 0.8% by elasto-plastic...

Dissimilar metal electron beam welding with reduced activation ferritic/martensitic steel, F82H IEA heat, and SUS316L austenitic stainless steel was studied. Mechanical property evaluation at room ...

A detailed study was conducted on the first wall fabrication process using the reduced activation ferritic/martensitic steel that will be used to fabricate ITER test blanket modules. The effects of the tube-drawing process on microstructural and mechanical properties of F82H is one of the most important issues for fabrication of the module. Square tubes with all mm x 1.5 T (thickness) mm x 3500 L (length) mm have been developed by a cold-rolling method. This tube is long enough to fabricate the first wall without any joint in the cooling path. Its surface roughness (Rz) and outer curvature are less than 1 μm and 1.4 mm, respectively. Dimensions were accurate enough to reduce the assembly gap for a Hot Isostatic Pressing (HIP) joint. Although the rolling process introduced an elongated microstructure containing dense precipitates, this anisotropic microstructure was successfully recovered by heat treatments corresponding to that used in the HIP process. This work demonstrated that the drawing process could be applicable to a fabrication process for the breeding-blanket component.

In order to determine the contributions of different microstructural features to strength and to deformation mode, microstructure of deformed flat tensile specimens of irradiated reduced activation F82H (IEA heat) base metal (BM) and its tungsten inert-gas (TIG) weldments (weld metal and weld joint) were investigated by transmission electron microscopy (TEM), following fracture surface examination by scanning electron microscopy (SEM). After irradiation, the fracture surfaces of F82H BM and TIG weldment showed a martensitic mixed quasi-cleavage and ductile-dimple fracture. The microstructure of the deformed region of irradiated F82H BM contained dislocation channels. This suggests that dislocation channeling could be the dominant deformation mechanism in this steel, resulting in the loss of strain-hardening capacity. While, the necked region of the irradiated F82H TIG, where showed less hardening than F82H BM, showed deformation bands only. From these results, it is suggested that the pre-irradiation microstructure, especially the dislocation density, could affect the post-irradiation deformation mode.

Previous work reported that a TIG weld joint of F82H exhibited low irradiation hardening in a tensile test, compared to the base metal. Microhardness tests and microstructure observation on the neutron-irradiated TIG weld joint of F82H revealed that the over-tempered zone in the heat-affected zone (HAZ) exhibited this good performance. The region in the HAZ where the prior austenite grain size became very fine during welding also exhibited lower irradiation hardening. Hypotheses for these low-hardening mechanisms were proposed based on the phase diagram and grain size.

The effects of irradiation up to 20 dpa on the Charpy impact properties of reduced-activation ferritic/martensitic steels (RAFs) were investigated. The ductile-brittle transition temperature (DBTT)...