Progress of High Heat Flux Component Manufacture and Heat Load Experiments in China

Transcription

1 Progress of High Heat Flux Component Manufacture and Heat Load Experiments in China Xiang Liu 1, Youyun Lian 1, Jiming Chen 1, Zengyu Xu 1, Lei Chen 1, Quanming Wang 1, Xuru Duan 1, Guangnan Luo 2 and Qingzhi Yan 3 1 Southwestern Institute of Physics, P.O. Box 432, Chengdu , Sichuan, China 2 Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei, Anhui , China 3 University of Science & Technology Beijing, No.30 Xueyuan Road, Haidian District, Beijing , China Abstract. High heat flux component manufacture is the critical technology for the current fusion experimental devices and fusion reactors in the future since it will face fusion plasma directly and endure high flux particle irradiation and huge heat deposition from core plasma. Be/CuCuZr/ss, W/CuCrZr and CFC/CuCrZr modules have been selected as the high heat flux components for ITER first wall and divertor chambers, respectively. Different pure tungsten and tungsten alloys are being developed in China for ITER use and the requirements of the domestic fusion devices, meanwhile the joining technology of tungsten with heat sink CuCrZr is being developed, in particular flat structure W/CuCrZr brazed mockups by silver free Cu- Mn solder and monoblock structure W/CuCrZr mockups by pure copper casting and hot iso-static press technique. In order to evaluate the heat load performances of high heat flux materials and components, a 60 kw electron-beam material testing scenario (EMS-60) has been constructed and a 400 kw engineering mockup testing scenario (EMS-400) is being created. Preliminary heat load tests indicated grain refinement PM-W with high purity and W-K alloy have good resistance to transient thermal shocks, while brazed W/CuCrZr and monoblock W/CuCrZr mockups can withstand 1000 cycles under 6-8 MW/m 2 stable heat flux. 1. Introduction High heat flux components for first wall and divertor are the key subassembly of the present fusion experiment apparatus and fusion reactors in the future. They will play important roles of resisting the energetic particle irradiation and huge heat deposition from the core plasma, as well as efficaciously dispelling such energy load. Therefore it is requested the metallurgical bonding among the plasma facing materials (PFMs), heat sink and support materials. Be/CuCuZr/ss, W/CuCrZr and CFC/CuCrZr modules will be used for ITER first wall and divertor chambers, respectively. As to PFMs, ITER grade vacuum hot pressed beryllium CN-G01 was developed in China and has been accepted as the reference material of ITER first wall and will be used for the manufacture of ITER FW modules [1]. Additionally pure tungsten and tungsten alloys, as well as chemical vapor deposition (CVD) W coating are being developed for the aims of ITER divertor application and the demand of domestic fusion devices, and significant progress has been achieved [2, 3], particularly CVD-W coating is expected to play a big role in the modification of the present fusion

2 experiment devices with W operations owing to its rapidity, economical and good compatibility with the present FW and divertor structure [4]. For plasma facing components (PFCs), high heat flux components used for divertor chamber are being studied according to the development program of the fusion experimental reactor of China. Two reference joining techniques of W/Cu mockups for ITER divertor chamber are being developed, one is mono-block structure by pure copper casting of tungsten surface following by hot iso-static press (HIP), and another is flat structure by brazing [5,6]. The brazing material is a silver free Cu-Mn alloy. On the other hand, in order to evaluate the heat load performances of high heat fux materials & components since these are their critical evaluation and acceptance criteria. A 60 kw Electron-beam Material testing Scenario (EMS-60) has been constructed at Southwestern Institute of Physics (SWIP),which is very like JUDITH-1 in Germany and suitable to the material and small scale mockup evaluation. Furthermore, an Engineering Mockup testing Scenario (EMS-400) with 400 kw electron-beam melting gun from Von Ardenne Company (Germany) is under construction and will be available by the middle of next year. After that, China will have the comprehensive capability of high heat load evaluations from PFMs and small-scale mockups to engineering full scale PFCs. In this paper, the developments of high heat flux materials & components are overviewed, in particular focusing on the developments of high purity PM-W with fine grains and W-K alloy since they have proven good resistance to thermal shocks, and brazed flat W/CuCrZr and monoblock W/CuCrZr mockups since they are considered as the mockup elements of ITER divertor. 2. Experimental 2.1 Developments of tungsten and tungsten alloys As you know, tungsten could be the most promising plasma facing material for fusion reactors. The present researches indicate that grain refinement tungsten has better thermal shock resistance and neutron irradiation resistance capability. Meanwhile purity of tungsten generally has a positive effect on heat load capability, thus high purity and fine grain are one of the development directions of tungsten, the other could be alloying, aiming at the improvement of re-crystallization temperature and the reduce of DBTT (ductile-brittle transfer temperature) by alloying and dispersion strengthening by oxides or carbides. Following these directions high purity tungsten with fine grains and tungsten alloys are being developed in China, for example, high purity tungsten with purity of more than 99.99% and grain size of a fraction of 1 m to 10 m has been developed both by means of powder metallurgy and the combination of spark plasma sintering (SPS) and resistance sintering under ultrahigh pressure (RSUHP), W-K alloy and W-La 2 O 3, Y 2 O 3, TiC and H f C dispersion strengthening alloys both by traditional powder metallurgy method and mechanical alloying etc. Here we will concentrate on the performances of grain refinement commercial PM-W by forging and ultra high pure tungsten, as well as W-K and W-La 2 O 3 alloys under transient heat loads. 2.2 Developments of W/CuCrZr mockups

3 For ITER divertor, two kinds of W/CuCrZr module structure are considered, one is flat panels used for dome region, and the manufacture route is silver free brazing bonding, the other is mono-block structure manufactured by pure copper casting following by HIP. According to Chinese fusion development strategy and the requirements of the upgrade and modification of current fusion experimental devices, such as EAST and HL-2A, W/CuCrZr joining both by two methods above is being studied. Cu-Mn solder with Ni addition was developed, small scale W/CuCrZr mockups with size of mm have been prepared by braze technology at 950 C temperature for min., then rapidly cooling to avoid strength loss of CuCrZr alloy, solder is Cu (75wt. %)-Mn (24wt. %)-Ni (1wt. %) alloy foils. Non-crystalline state Cu-Mn solder is also being developed. It is expected for enhancing bonding strength and promoting the thermal fatigue property because it has better homogenous and anti-oxidation capability, as well as wider flexibility of alloying. In addition, small scale W/CuCrZr monoblock mockup with size of mm 3 was prepared by ASIPP (Institute of Plasma Physics, Chinese Academy of Sciences). Both brazed and monoblock W/CuCrZr mockups show perfect metallurgical bonding and good bonding strength (tensile strength ~150 Mpa). Small scale mockups after high heat flux tests were indicated in Fig High heat flux testing facilities and heat load tests Fig.1 Small scale brazed mockup (upper) and monoblock mockup (lower) after high heat load tests Fig.2 Sketch drawing of the EMS 60 apparatus High heat load performances are the critical evaluation criteria of high heat flux materials & components, for this purpose a 60 kw electron beam material testing scenario (EMS-60) has been constructed at SWIP (its sketch drawing was shown in Fig. 2), which adopts a 60kW welding electron beam with maximal 150 kev acceleration voltage, and can scan mm 2 area with maximal frame rate of 30 khz, its pulse duration can change from 1 ms to continue. Generally speaking EMS- 60 is very similar with JUDITH-1 in Germany and suitable to the material and small scale mockup evaluation tests. Furthermore, an engineering mockup testing scenario (EMS-400) with 400 kw electron-beam melting gun from Von Ardenne Company (Germany) is under construction and will be available by the middle of next year. The

4 electron beam can cover m 2 area with scanning frequency up to 10 khz. In addition this facility will have the ability of beryllium handling and C, 4MPa water coolant supply. After that, China will have the comprehensive capability of high heat load evaluations from PFMs and small-scale mockups to engineering full scale PFCs. Different grade tungsten and tungsten alloys were tested in EMS 60 by focusing on the ing and melting initiation, and propagation under transient heat load conditions. In the material evaluation tests, all samples with size of mm 3 are polished mechanically and installed on a movable sample holder with active cooling, the absorbed power density is measured by the current through the testing sample. 5 ms single and multiple s with absorbed energy density of 1-5MJ/m 2 were loaded on different W grade samples to simulate the influence of plasma disruption and ELMs. The test results are concluded in table 1. Table 1 different W grades by single and multiple thermal shocks W grades Characters 1MJ/m 2-1 2MJ/m 2-1 3MJ/m 2-1 4MJ/m 2-1 1MJ/m s 1 MJ/m 2-2MJ/m s s Ultra pure W purity No change No change Melting Melting / / Micro- Grains: 10 m Micro Commercial W Forging, vertical to forging direction Main throughout surface Main throughout surface / / / Commercial W Forging, parallel to forging No change Main ring Main ring melting Main ring melting Surface roughness, / W-La 2 O 3 alloy 0.5 wt.% La 2 O 3 No change No change melting melting / / / W-K alloy 0.08 wt.% K No change No change Main ring Main ring / / plastic deformation The screening and thermal fatigue tests of small scale W/CuCrZr brazed and monoblock mockups were also performed in EMS 60. For brazed W/CuCrZr the sample size is mm 3, in which the thickness of tungsten tile is 10 mm and a cooling channel in diameter of 12 mm is drilled in the CuCrZr heat sink. Before heat load tests, the infrared camera and optical pyrometer are calibrated by thermocouples using the same W calibration tile, and the absorbed energy was measured by means of calorimeter, an approximate energy absorb coefficient of 0.56 for the present tungsten tiles is calculated. The heating and cooling time are 10 seconds and 15 seconds, respectively. The experiment procedure is 3 MW/m 2 by 200 cycles and then 6 MW/m 2 by 1000 cycles, following by 8.5 MW/m 2 for 200 cycles and 11 MW/m 2 for 100 cycles. During the experimental processes coolant is de-ionized water with inlet temperature of 25 C and 800l/h flux. The surface temperature during the testing

5 Surface temperature ( C) FTP/P1-12 processes was measured both by the infrared camera and optical pyrometer. Similar tests were also carried out for monoblock W/CuCrZr mockups. 3. Results and discussions For plasma facing materials, the resistance capability to high heat loads from core plasma is one of the critical issues; especially the transient heat loads come from plasma disruptions, such as hard disruption (HD), ELMs and VDEs, in which ELMs are found to have potential destructivity to PFMs owing to their occurrence with high frequency beyond 1 Hz [7]. In fact, from table 1 we can see that the initiation threshold of and melting for most of tungsten grades is in the range of 1-3 MJ/m 2 for 5 ms single, however, multiple transient loads will induce initiation below this threshold, meanwhile the tungsten surface will appear serious plastic deformations with number increase as shown in Fig. 3. Among all of tungsten grads tested, commercial pure tungsten showed the worst thermal shock resistance capabilities, especially the surface is vertical to the rolling or forging direction although forging process was believed to promote the properties of sintering W by densification and grain refinement, therefore the ITER grade tungsten was specified that the W surface shall be parallel to rolling or forging direction. High pure tungsten (purity of 99.99%) with smaller grain of about 10 m compared to commercial W (approximately 30 m grain size) and W-K alloy have better thermal shock resistance capabilities, the initiate at about 3MJ/m 2. For the former the reason might be owing 10 m Fig.3 Surface morphology of K doped W by 2MJ/m 2 pulsed heat flux for 100 cycles Cycles Fig.4 High heat load tests of brazed W/Cu mockup to better thermo-mechanical properties of ultra-purity tungsten and higher grain boundary strength by grain refinement. For the latter, the reason could result from better plastics and K element dispersion strengthening of K doped tungsten, thus suppressing the occurrence but causing serious plastic deformation as shown in Fig. 3. Considering that tungsten as PFMs will have to face higher heat loads in the future fusion reactors, therefore the efforts to restrain ELMs by plasma confinement and control and to enhance tungsten performances by purification and alloying are strongly requested.

6 For plasma facing components, more concerns are their thermal fatigue properties besides the compatibility of armor tiles with fusion plasma since the failure of PFCs will induce the issue of plasma safe operation. Fig. 4 shows the surface temperature change of brazed W/CuCrZr mockups under cyclic heat load tests. No off-normal surface temperature change was observed. After heat load testing, the sample was cut for interface inspection, no were found at the interface region. It indicated that brazed W/CuCrZr mockups could withstand over 6 MW/m 2 stable heat flux for at least 1000 cycles. Similarly heat load tests of monoblock W/CuCrZr mockup can survive 8.4 MW/m 2 heat flux for 1000 cycles, where the surface temperature of tungsten tiles is about 1150 C as shown in Fig. 5. A modification of enhanced coolant supply is being conducted, and it will be available to carry out the thermal fatigue tests at higher heat load conditions next experimental campaign, in this way the surface temperature of tungsten armor can be kept lower than the re-crystallization temperature to avoid the possible failure owing to re-crystallization brittleness. 4. Conclusions Different grade tungsten materials and W/CuCrZr mockups were developed, and the high heat load evaluation facilities were constructed, which will make the evaluation tests of high heat flux materials & components up to engineering scale available in China soon. The present experiment results indicate that ultra-high pure tungsten with fine grains has better thermal shock resistance ability compared with commercial tungsten, and W-K alloy has better capability to suppress initiation and propagation but easily deformation. W/CuCrZr mockups fast brazed by silver free Cu- Mn alloy can endure at least 6 MW/m 2 stable heat flux by 1000 cycles without any damage, and W/CuCrZr monoblock mockups made by pure copper casting and following hot iso-static press can survive 1000 cycles under 8 MW/m 2 heat flux. Evaluation of W/CuCrZr mockups with larger size at higher heat load conditions will be carried out soon. Since the simplicity, availability and economic of fast brazing technology, it is believed that W/Cu brazing joining could be one of the most promising manufacture technique of divertor modules. 5. References Fig. 5 Surface temperature of monoblock W/CuCrZr mockup among 1000 cycles of 8.4 MW/m2 heat flux [1], X. Liu, J.M. Chen and J.H. Wu et al., Characterization of Chinese Beryllium as the Candidate Armor Material of ITER First Wall 23rd IAEA Fusion Energy Conference, October 2010, Daejeon, Korea. [2], X. Liu, J.M. Chen and Y.Y. Lian et al., Vacuum hot pressed beryllium and TiC dispersion strengthened tungsten alloy developments for ITER and future fusion reactors Proceedings of ICFRM-15.

7 [3], C.C. Ge, Z.J. Zhou, W.P. Shen et al., Status of R&D on fusion materials in institute of nuclear materials in USTB, Fus. Eng. & Des. Vol. 85, issues 7-9, Dec [4], J.P. Song, Y. Yu, Z.G. Zhuang et al., Preparation W-Cu functionally graded material coated with CVD-W for plasma facing components, Proceedings of ICFRM-15. [5], Bruno Riccardi, ITER divertor: requirements, design and EU R&D, Fusion for Energy-Barcelona, June, [6], E. Visca, E. Cacciotti, A. Komarov et al., Manufacturing, testing and post-test examination of ITER divertor vertical W small scale mockups Fus. Eng. & Des. Vol. 86, issues 9-11, Oct, [7], T. Hirai, K. Ezato and P. Majerus, ITER relevant high heat flux testing on plasma facing surfaces Materials Transactions Vol. 46, No. 3 (2005) P