H. Takatsu

Optimization of HIP bonding conditions for ITER shielding blanket/first wall made from austenitic stainless steel and dispersion strengthened copper alloy

Abstract Optimum bonding conditions were studied on the Hot Isostatic Pressing (HIP) bonded joints of type 316L austenitic stainless steel and Dispersion Strengthened Copper alloy (DSCu) for application to the ITER shielding blanket / first wall. HIP bonded joints were fabricated at temperatures in a 980–1050°C range, and a series of mechanical tests and metallurgical observations were conducted on the joints. Also, bondability of two grades of DSCu (Glidcop Al-25 ® and Al-15 ® ) with SS316L was examined in terms of mechanical properties of the HIP bonded joints. From those studies it was concluded that the HIP temperature of 1050°C was an optimal condition for obtaining higher ductility, impact values and fatigue strength. Also, SS316L/Al-15 joints showed better results in terms of ductility and impact values compared with SS316L/Al-25 joints.

Mechanical properties of HIP bonded joints of austenitic stainless steel and Cu-alloy for fusion experimental reactor blanket

Abstract Tensile, fatigue and impact properties have been measured for hot isostatic pressing (HIP) bonded joints of type 316 austenitic stainless steel (SS316)/SS316, and of SS316/Al2O3 dispersion strengthened copper (DSCu). The HIP bonded joints of SS316/SS316 had almost the same tensile and fatigue properties as those of the base metal. The HIP bonded joints of SS316/DSCu had also almost the same tensile properties as those of the base metal of the DSCu, though total elongation and fatigue strength were slightly lower than those of the DSCu base metal. Further data accumulation, even with further optimization of fabrication conditions, is required, especially for HIP bonded SS316/DSCu joints, to confirm above data and reflect to blanket/first wall design.

Development of ceramic breeder blankets in Japan

Ceramic breeding blankets are the main options for DEMO reactor designs in JAERI, and large efforts have been made in the area of related materials development, engineering-scaled R&D, as well as design development. A long-term R&D program was launched in 1996 to provide an engineering database and fabrication technologies for the DEMO blanket and its performances by means of in-pile and out-of-pile mock-up tests, aiming at module tests in ITER as a near-term target. A variety of fundamental researches have also been carried out, mainly in universities, to support the above project-oriented R&D, laying emphasis on tritium-release characteristics from the ceramic breeding materials. The present paper overviews the current status of the ceramic breeding DEMO blanket design and related R&D in Japan, and outlines the long-term development program.

High heat flux testing of a HIP bonded first wall panel with built-in circular cooling tubes

Abstract A HIP bonded DS-Cu/SS first wall (FW) with built-in circular cooling tubes was fabricated under the optimized HIP conditions. High heat flux testing of the panel was carried out on electron beam facility, JEBIS , at JAERI. The objective of this test is to examine the thermomechanical performance of the panel, including the integrity of the HIP bonded interfaces and also to examine the relation between the design fatigue curve and experimental results. Test conditions applied during these tests were 5.0–7.0 MW/m 2 in average, much higher than the ITER normal operation condition of 0.5 MW/m 2 , to accelerate the fatigue test with a repetition cycle up to 2500 cycles in total. High heat flux tests consisted of two test campaigns. Throughout these tests, no damages such as cracks were observed and no degradation in heat removal performance was also observed from temperature responses measured with thermocouples embedded within the panel. Thermomechanical integrity of the panel was confirmed within the parameter tests and the fatigue lifetime of the panel was found to be much longer than the design fatigue curve of this material, or even beyond the raw fatigue data.

Development of joining technology for Be/Cu-alloy and Be/SS by HIP

Joining of Be/DSCu and Be/SS by using HIP technique with and without various interlayers were investigated as a screening test for selecting optimum joining method and conditions. Metallurgical observation and shearing tests were performed for basic characterization of the bonded joints. For Be/DSCu, the use of Ag interlayer with 700°C HIP temperature would be a prime candidate if Cd formation under neutron irradiation would not seriously affect plasma operation and joint performance. Other than the Ag interlayer, a Cr/Cu interlayer gave relatively high joint strength in the present screening test. The lower HIP temperature, 550°C, for this joint contributes to prevent sensitization of stainless steel (SS) structural material. As for Be/SS, the highest joint strength was obtained with a Ti interlayer. The HIP temperature of 800°C or a little higher would be applied for this joint to avoid SS sensitization.

Development of high conductive C/C composite tiles for plasma facing armor

C/C composites with high thermal conductivity were developed in unidirectional, two-dimensional and felt types, and were fabricated as full-scale armor tile. Their thermal conductivity in the direction perpendicular to the plasma-side surface is 250 – 550 W/m°C, that is comparable to that of pyrolytic graphite. It was shown by heat load tests that the C/C composites have low surface erosion characteristics and high thermal shock resistance. Various kinds of C/C composites were successfully bonded to metal substrate, and their mechanical strength and thermal shock resistance were tested.

Application of HIP bonding to first wall panel fabrication made from reduced activation ferritic steel F82H

Abstract As a course of fabrication technology development of DEMO breeding blankets, fabrication of small-scaled first wall panels made from reduced activation ferritic steel F82H has been attempted by applying HIP (Hot Isostatic Pressing) method. By applying the conditions identified in the previous studies, two flat panels with ten cooling channels each have been fabricated. One of the fabricated panels was destructively tested to examine metallurgically sound HIP bonding and to characterize the change of the micro-structure of the F82H steel due to the HIP process. Destructive examination has confirmed sound bonding for all of the HIP interfaces and satisfactory dimensional tolerance, and applicability of HIP bonding to the complex component made from this steel has been demonstrated.

Performance of JT-60 divertor plates

Abstract Operational experiences on the performance and material behavior of the JT-60 divertor plates are presented. The outside X-point operation using TiC-coated Mo (TiC/Mo) plates was performed with absorbed power up to 20 MW and duration of 1 s without degradation of the plasma performance by sweeping the separatrix to control the surface temperature below the melting point. The use of graphite divertor plates extended the absorbed power up to 25 MW with duration of 4 s in the lower X-point operation. However, the graphite was eroded and redeposited on the divertor plates and the carbon content in the plasma was increased compared to the outer X-point operation with carbon tiles. A few lower graphite tiles were seriously damaged and radioactivated. Improvements in thermal shock resistance and erosion characteristics of the graphite are necessary. High heat concentration at tile edges and disruption-induced heat loads should be avoided in the future devices.

High heat flux experiments at JAERI

Recent R&D results on high-heat flux components are presented, including construction of a new test stand. The test stand can extract an electron beam of 4.1 at 100 keV. E-folding divergence of the beam is 1.7 mrad, and the latest beam performance is also described. At the original test stand, which can produce hydrogen-ion beams of 50 A at 100 keV for 10 s, high-Z divertor armors, were tested. Tungsten plates brazed on copper blocks have been proven to have enough durability against heat flux under 10 MW/m/sup 2/. Carbon-fiber-carbon (CFC) composites were tested at the new electron-beam test stand and an electron-beam welding machine. Under disruption-simulation conditions, evaporation weight loss of CFC was lower than that of isotropic graphite.<<ETX>>

Operation experiences of the JT-60 first walls during high-power additional heating experiments

JT-60 started its operation in May 1985 with TiC-coated molybdenum or Inconel 625 first walls. They provided very clean surfaces as well as superior plasma characteristics during Joule heating discharges. Though 20 μm-thick TiC coatings showed good adhesion characteristics, melting of the TiC coating and also the molybdenum or Inconel 625 substrate was observed at some specific spots, and an influx of heavy metals to the main plasma was inevitable during discharges. Initial results of the additional heating experiments showed degrading effects of locally melted TiC-coated molybdenum or Inconel 625 on plasma operation. Therefore, about a half of the TiC-coated first walls were removed and new graphite first walls were installed during the venting period from April to May 1987. The start-up of the discharge conditioning after installation of a significant number of graphite tiles was very rapid. Flexibility in plasma operation was increased, and JT-60 extended the operation region beyond its original specifications. The graphite first walls of the main chamber performed admirably and maintained their integrity under the conditions of plasma current and additional heating power up to 3.2 MA and 30 MW, respectively. On the other hand, the number of damaged divertor plates was much larger than that expected. The reason of unexpected failure is now under examination.