4 Fusion Reactor and Fusion Reactor Materials

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1 4 Fusion Reactor and Fusion Reactor Materials 4.1 Overview of research activities in Fusion Reactor and Materials Division Fusion Reactor Materials Division Abstract: Big progresses were made on each research programs in the Fusion Reactor and Materials Division in Chinese Helium-cooled Ceramic Breeder TBM design was improved. Manufacturing a sub-module was investigated with the success in Be pebble fabrication and the measurement of thermal conductivity of Li4SiO4 pebbles. Blanket design was done for CFETR reactor. For Divertor technology and the related materials, an EB high heat flux test facility (EMS-60) has been put into use. Small scale of ITER grade W and several alloys were made, while thick tungsten coating and W/CuCrZr brazing technologies were successfully developed. In addition, an innovation MHD concept for liquid divertor was addressed. For low activation structural materials, several batches of 1000kg scale CLF-1 steel were produced with high temperature mechanical properties, weldability and the effect of strong magnetic field evaluated. Carbides dispersion strengthening vanadium alloys were developed, and the combination strengthening of V-4Cr-4Ti alloy (SWIP-30) by cold-work and thermal aging was evaluated. Final design of ITER shielding blanket and magnet supporting structure was completed, a series of key equipment were built for manufacturing and testing. With efficient development of related technologies a SB FSP was manufactured. HIP joining and TIG welding technologies were developed and improved for FW and magnet supporting structure, respectively. Key words: TBM;DEMO;Fusion reactor 1 Reactor Design and TBM Program 1.1 HCCB TBM modification design Chinese HCCB (Helium- cooled Ceramic Breeder) TBM design is improved based on such new requirements: Cross-section is changed to 464 mm 1670 mm, weight of structural material (only RAFMs) should be lower than 1.3 tons, design value of surface heat flux is reduced to 0.35 MW m -2, getting new ideas by checking the rules and criteria, trying to meet requirements from other components or systems such as pipe forest and helium coolant system (design pressure is changed from 8 to 9 MPa). Updated design for CH HCCB TBM holds 4 submodules arrayed along the poloidal direction with a 10mm gap. Sub- modules are welded on TBM s back plate. Except that coolant He into first wall pipes is distributed by back-plate, other parts of sub- modules are cooled by helium distributed by sub-modules themselves. Middle plate is used to strengthen the structure of Box of a sub-module to meet criteria level D. On both sides of middle plate are two- layer U- shaped cooling plates. Breeding material Li 4SiO 4 pebbles are in the two layer plates outside which is Be pebbles. Neutronics analyses show that tritium production rate (TPR) is mg/fpd. Thermal calculations show that the maximum Temp. is 799 o C at the front part of Li 4SiO 4 in two-layer U-shaped structure, while that in Be zone, is 530, 489 and 533 o C in middle plate and in first wall, respectively. In back plate, many cavities are planned to distribute or collect coolant. More design activities including calculations and analyses are ongoing. 1.2 HCCB TBM mock-up On former finished CH HCCB TBM design with 12 submodules arrayed in 2 6, a TBM mockup is designed to explore the manufacturing processes and procedures. The mock- up with the dimension of 592 (P) 484(T) 675 mm(r) has one sub-module similar with that in TBM while the other three are replacements to fulfill coolant circuit. There are three steps of developing process for the mockup: machining and welding studies on CLF-1 steel, R&D for key components and study for integration techniques. Welding methods include Tungsten Inert Gas (TIG), electron- beam welding (EBW), vacuum diffusion welding (VDW) and laser beam welding (LBW). Some key structures of the mockup have been trial-manufactured and analyzed. Fig.2. Cooling plates of trial-manufactured sub-modules by VDM. Fig.1. Structures of CH HCCB TBM and its sub-module. 1.3 Fusion reactor design study An interface code was developed to suit burn- up calculation of fusion- fission hybrid reactor with casing structure. The burn- up calculations have been carried out for the fusion- fis- 141

2 sion hybrid reactor design based on the plasma parameter of ITER and casing structure arrangement of fuel. The changes of the key reactor parameters such as K eff, M and TBR with operating time were obtained. The accumulation of fissile nuclide, neutron poison, and actinide in blankets was also investigated. Preliminary fuel management was considered according to the characteristic of burn- up of hybrid reactor design. The design and hydraulic analysis of first wall were performed to achieve a reasonable cooling arrangement. The selection and optimization of plasma parameters of CFETR have been performed for the case of normal magnet. Blanket design and analysis have been investigated for CFETR reactor with both superconductor and copper magnet. The lifetime of magnet was estimated in terms of radiation fluence level. In addition, the key parameters such as TBR, energy deposition, neutron wall loading, were calculated and analyzed. For tritium self- sufficiency, the calculated value of TBR was discussed. The modules of helium- cooled blanket were designed according to the CFETR requirements and the preliminary analyses were carried out. 1.4 R&D on TBM breeder materials The helium cooled ceramic breeder blanket is a promising concept for the fusion blanket, where layers of lithium ceramic pebble bed are arranged between cooling plates. These pebble Fig.4. Electron beam Material testing Scenario (EMS-60). beds are subjected to nuclear heating caused by the fusion neutrons; therefore, heat is transferred from the hot pebble beds to the coolant. The thermal properties of the lithium ceramic pebble beds have a significant impact on the blanket s temperature profile and the heat extraction process. For the thermo-mechanical design of the ceramic breeder blanket, the effective thermal conductivity of pebble beds is an important design parameter. The effective thermal conductivity of Li 4SiO 4 pebble beds was investigated. The Li 4SiO 4 pebble bed is single size with a packing fraction of 61%. Helium at the atmospheric pressure was used as a cover gas. The effective conductivity was measured as a function of temperature. The experimental results showed that the effective thermal conductivity increases with increasing average bed temperature. In order to improve the tritium breeder ratio, Beryllium is selected as the neutron multiplier. The Rotating Electrode Process (REP) has been adopted to produce beryllium pebble for impurity control and mass production. The beryllium pebbles by REP have been developed and successfully realized. The beryllium pebbles of different sizes have been fabricated by controlling the arc current and velocity of the rotating electrode. The test results indicate that REP method have excellent prospects for the fabrication of beryllium pebbles and the attractiveness of their properties. Fig.3. Thermal conductivity of Li4SiO4 pebble bed. 2 Divertor related materials, mockups and component technologies 2.1 EMS-60 electron beam material testing scenario An electron beam material testing scenario (EMS- 60, Fig. 4) was designed by SWIP and manufactured by PTR Company in Germany. This facility passed the final acceptance tests in the middle of 2012, and then the auxiliary cooling system and diagnostic equipment were deployed, finally the operation of this scenario began at the end of EMS- Fig.5. Brazed W/CuCrZr testing mockup and its thermal fatigue test results at 7.2 MW m -2 heat flux. 142

3 60 adopts a 60 kw welding gun with 150 kev accelerate voltage, like Judith-1 of FZJ in Germany, can simulate the transient and steady wall loads of plasma facing materials and small scale plasma facing components in fusion devices, in this way it can evaluate their high heat flux performances. The successful operation of EMS -60 indicates the top level heat load facility can be available in China. The main features of EMS-60 are as follows: Main power:60 kw;frequency: 30 khz;scanning area: mm 2 ;Pulse duration:³1ms;main chamber:10-4 Pa;Base temperature of test sample: RT-800 C. 2.2 Pure tungsten and tungsten alloys ITER grade tungsten, pure tungsten with grain refinement, tungsten alloys, such as W-La 2O 3, W-TiC and W-K alloy,were developed by domestic cooperation. It is found that W with appropriate amount of TiC alloy can increase the re- crystallization temperature up to 1700 o C. Thermal shock tests indicate the threshold of crack initiates at much high energy densities compared with traditional PM-W. In addition, fast chemical vapor deposition (CVD) tungsten coating on CuCrZr alloy and carbon material substrates was developed. The deposition rate of tungsten can reach up to 0.3~0.4 mm.h - 1 with good coating quality. CVD- W/CuCrZr mockups with gradient W-Cu interlayer can endure 1000 cycles at 11 MW m -2 steady heat flux. 2.3 Brazed W/CuCrZr moc-kup First one kind of low activation filler Cu-Mn alloy with multiple crystalline features was developed and the brazing joining technology of W to CuCrZr alloy was optimized. Up to now the brazed W/CuCrZr mockup manufacturing technique was finalized and series mockups of small size to mediate size (for instance mm) were manufactured, which shows the advantage of technology simplicity and quality controllability. Cyclic tests of brazed W/CuCrZr mockups indicated good thermal fatigue properties and they can withstand 1000 cycles at a steady heat flux of at least 7 MW m -2 without visible damages as shown in Fig. 5. Furthermore, steady thermal fatigue and transient thermal shock tests are simulated by ANSYS code and good conformity was achieved. Nowadays the brazed mockups with artificial defects are being manufactured and they will be used for high heat flux tests and ultrasonic tests with purpose of establishing the acceptable criteria for series production. Fig.6. Schematic of a guidable liquid metal free curve surface flow. 2.4 Advanced liquid metal divertor Advanced liquid metal divertor/limiter is facing many technological challenges, especially, it is needed to solve two major MHD engineering feasibility issues at present, or to avoid magnetic field enhancing rivet flow and MHD spraying due to the induce current in the flow. In 2012, Liquid-metal MHD group addressed an innovation concept of guidable liquid metal free curve surface flow (Fig 6), finished the investigation both theoretically and experimentally. The results indicatethat a guidable liquid metal free curve surface flow can well avoid rivet flow under the flow in a gradient transversal magnetic field (Fig 7). Fig.7. Comparison of the experimental results of normal liquid metal free curve surface flow (left) and a guidable free curve surface flow (right) in a gradient transversal magnetic field. 3 Structural materials for fusion applications 3.1 Reduced activation ferritic/martensitic steels (RAFMs) CLF-1 Several 1000 kg heats of CLF-1 steel were produced and manufactured into different product forms including plates, bars, tubes and wires in accordance with the design of the CN HCCB TBM. The microstructure and properties evolution of the CLF- 1 steel during thermo- mechanical process were studied using a thermal mechanical simulator. The obtained results on the stress-strain curves and relationship between thermo-mechanical parameters and microstructure can be useful to get finer grain size microstructure and better mechanical properties of CLF-1 steel in the fabrication mock-up of CN HCCB TBM. High temperature performances of creep resistance of the CLF- 1 steel were studied. Long- term thermal creep properties tests were carried out at different stresses at 773 K, 823 K and 873 K. Some of the tests have been carried out for up to 5000 h, and is still in progress. The CLF- 1 steel shows adequate creep rupture level with low minimum creep rate and long rupture time. The low cycle fatigue test of CLF-1 steel was carried out. The fatigue life of JLF-1 steel at 773 K was slightly lower than that at 573 K and room temperature, which indicates that the effect of test temperature on fatigue property of CLF-1 steel is insignificant. For the fabrication of CN HCCB TBM, different joining technologies will be required. Plates and tubes of CLF-1 143

4 steel with different sizes are used for the study of the joining technologies. Results show that a post- welding heat treatment is essential to improve the mechanical properties of the joints. Currently these joining technologies are being studied on the different size plates and on the joining for the plates and pipes to make the joining techniques applicable for TBM manufacturing. A series of other researches on the CLF-1 steel were carried out and some fruitful results have been obtained, including the effect of high temperature and magnetic field on microstructure and vacuum characteristic, but also the thermal ageing effect on the evolution of microstructure and properties. 3.2 Vanadium alloy Recent efforts in the development of vanadium alloys focused on the mechanical alloying. In the past year, a Ti 3SiC 2 dispersion strengthened V-4Cr-4Ti alloy with Y addition was fabricated. The study started from the investigation of refining mechanism of the V-4Cr-4Ti-1.8YH 2 powder mixture. A minimum milling time for complete mechanical alloying was found. After that, some small V- 4Cr- 4Ti alloys with different contents of Ti 3SiC 2 have been fabricated using the optimized milling parameters and with Spark Plasma Sintering (SPS) along with Hot iso- static pressing (HIP). Tensile tests show Ti 3SiC 2 can improve the strength and the ductility of V-4Cr-4Ti alloy. This improvement is most remarkable when the Ti 3SiC 2 content is 0.2~0.6 wt% and the annealing temperature is above 1000 o C, for which the yield strength is 855 MPa, ultimate strength is 1108MPa and the total elongation is about 17%, respectively. Grain size refining and dispersion strengthening are the main mechanisms for this improvement. Transmission Electron Microscopy (TEM) observation shows most of the grain sizes vary from 0.5 μm to 1.5 μm. Y 2O 3 and Ti 3SiC 2 are the main nanoparticles, for which, the size of Y 2O 3 is about 30 nm, while the size of Ti 3SiC 2 is about 10 nm. In order to supply more samples for further research, cooperation has been carried out between SWIP and domestic university to fabricate 2 kg Ti 3SiC 2 dispersion strengthened V- 4Cr- 4Ti alloy via mechanical alloying. For SWIP-30, which is a melted V-4Cr-4Ti alloy, the microstructures after different heat treatments were observed and RT fatigue tests were applied on this alloy. Diffraction pattern and Energy Dispersive Spectrometer (EDS) analysis have been carried out for the spheral precipitates. The results show that besides Ti-(C,O,N), which is usually observed in previous work, some other precipitates such as TiCr (Im- 3m(229), bcc structure, similar to W) and TiCr 2 (Fd-3m(227), fcc structure, similar to Cu 2Mg) are observed. The fatigue experiments used standard heat treatment (STD) and cold working followed by aging (SACWA) treatment to prepare the fatigue specimens. By comparing the equivalent cyclic constitutive curve and the tensile constitutive curve, a conclusion was obtained, which is that below the controlled strain amplitude, SACWA exhibits cyclic softening characteristics, while the STD exhibits cyclic hardening characteristics, respectively. 4 Shielding blanket The R&D of ITER shielding blanket (SB) procurement task obtained great progress in The final design and analysis of the blanket module were finished on schedule, and all the design criteria issued by ITER IO have been met. In the research on fabrication technology for the first wall (FW), two important issues were solved, which are: (1) Bonding of Be/SS during the HIP joining Be/Cu for FW component; (2) TIG deformation of the HV channel. A couple of eligible enhancedthermal-loading modules (5 MW.m -2 ) were fabricated, and both results of hydraulic pressure test and helium leak test met the criteria issued by ITER. Worth noting, the helium leak rate at RT is lower than Pa.m 3 s - 1. Moreover, a series of key facilities, such as high temperature vacuum furnace, curved surface ultrasonic test equipment for Be/Cu interface inspection, high temperature vacuum mechanical test machine and 400kW electron beam platform for thermal fatigue evaluation and so on have been built or under construction. As to the R&D activities for SB fabrication technologies, cooperation with Dongfang (Guangzhou) heavy machinery Co., Ltd and Aerospace Xinli Casting and Forging Co., Ltd had been promoted to design and fabricate the full- scale prototype (FSP). All properties of the produced large 316L(N)-IG forging peace( mm)have met the ITER material acceptance criteria. In detail, the grain size is smaller than that classified as Grade 3, and the total ferrite content is less than 1%. Tests on deep drilling(deeper than 1m), deep cutting and welding cover plate were performed to choose appropriate processing parameters that can result in good dimension tolerance as required. TIG welding procedure qualification was done and successful with the IO accepting the data package. Fig. 9 shows Fig.8. Tensile curves for Ti3SiC2 dispersion strengthened V- 4Cr- 4Ti after annealing at different temperatures. Fig.9. of ITER SB prototype. Cooling channels and holes locating in the front face 144

5 the full- scale prototype of SB module finished before the end of 2012, the straightness and position of the drilling is better than 0.5 mm, the roughness of inner surface is better than Ra6.3 with a global accuracy of the FSP of less than 0.5mm, which supplied a strong support for the qualification of the SB manufacturing. 5 R&D activities of the magnet support procurement task Great progress has been achieved in the ITER Magnet Supports project. In respect to qualification test, GS mock- up multidimensional test platform has been designed and manufactured. The results of static analysis, dynamic analysis and life cycle calculation have proved its feasibility, based upon which the platform is approved by ITER experts. The test platform which successfully passed the pre- acceptance can be claimed as the first large and complex multidimensional test platform Fig.10. GS mock-up multidimensional test platform. that enjoys the independent intellectual property rights. It is conducive to a good preparation for the final qualification of GS prototype manufacturing. In addition, the design, manufacturing and debugging of liquid helium temperature multi- sample automatic changing tensile machine have been accomplished. The results of the crosscheck performed by labs both at home and abroad prove to be reliable and valid. Moreover, 100 KN liquid nitrogen friction-abrasion testing machine and 2000 KN liquid nitrogen fatigue machine have been calibrated and accepted, enabling a sufficient preliminary preparation for the material qualification and prototype testing. As for the welding, argon arc welding has been adopted to fabricate the TF, PF and CC thermal anchor attachment prototypes, on which dimension measurement, visual test, thermal shock test, metallographic inspection, leak detection, peeling test and heat exchange test have been conducted. The test results indicate that argon arc welding can fully fulfill the ITER requirements. Besides, the TIG automatic welding machine has been installed and debugged With regard to the quality management, a relatively comprehensive quality management system has been established to thoroughly implement the quality assurance concept. Based on its own characteristics, procedures for document and record control, etc. have been drawn up and improved to ensure the traceability and regularity of the management. Furthermore, no non-conformity was found during the two quality audits led by CN DA and IO who affirmed and highly praised the current management mode and performance. 145