•We characterize tungsten mono-block components after exposure to ITER relevant heat loads.•We qualify the manufacturing technology, i.e., hot isostatic pressing and hot radial pressing, and repair ...technologies.•We determine the microstructural influences, i.e., rod vs. plate material, on the damage evolution.•Needle like microstructures increase the risk of deep crack formation due to a limited fracture strength.
In order to evaluate the option to start the ITER operation with a full tungsten (W) divertor, high heat flux tests were performed in the electron beam facility FE200, Le Creusot, France. Thereby, in total eight small-scale and three medium-scale monoblock mock-ups produced with different manufacturing technologies and different tungsten grades were exposed to cyclic steady state heat loads. The applied power density ranges from 10 to 20MW/m2 with a maximum of 1000 cycles at each particular loading step. Finally, on a reduced number of tiles, critical heat flux tests in the range of 30MW/m2 were performed.
Besides macroscopic and microscopic images of the loaded surface areas, detailed metallographic analyses were performed in order to characterize the occurring damages, i.e., crack formation, recrystallization, and melting. Thereby, the different joining technologies, i.e., hot radial pressing (HRP) vs. hot isostatic pressing (HIP) of tungsten to the Cu-based cooling tube, were qualified showing a higher stability and reproducibility of the HIP technology also as repair technology. Finally, the material response at the loaded top surface was found to be depending on the material grade, microstructural orientation, and recrystallization state of the material. These damages might be triggered by the application of thermal shock loads during electron beam surface scanning and not by the steady state heat load only. However, the superposition of thermal fatigue loads and thermal shocks as also expected during ELMs in ITER gives a first impression of the possible severe material degradation at the surface during operational scenarios at the divertor strike point.
In order to simulate transient events on beryllium, thermal shock experiments have been carried out in the electron beam facility JUDITH.
Different grades of Chinese and Russian beryllium have been ...loaded in comparison to the ITER reference grade S65C. The pulse length was 5ms, and energy densities covered the range from 1.2 to 5MJ/m2. All tests have been performed at room temperature.
In a second series of tests, the influence ELM-like conditions has been investigated. Multiple shot experiments with up to 10,000cycles on beryllium S65C were carried out at energy densities below the ones for the onset of crack formation in single shot experiments. Most loading parameters were similar to the single shot tests, but in addition the experiments were carried out on hot beryllium surfaces of 250°C.
Post mortem examinations of the samples were carried out by optical microscopy, SEM, metallography and other diagnostic methods.
A present topic of high interest in magnetic fusion is the “gap” between near-term and long-term concepts for high heat flux components (HHFC), and in particular for divertors. This paper focuses on ...this issue with the aim of characterizing the international status of current HHFC design concepts for ITER and describing the different technologies needed in the designs being developed for fusion power plants. Critical material and physics aspects are highlighted while evaluating the current readiness level of long-term concepts, identifying the design and R&D gaps, and discussing ways to bridge them.
Mechanical properties of the austenitic steel 316L (both solution annealed and cold worked) and the low activation martensitic steel Optifer have been investigated by small punch tests. The samples, ...in the form of TEM disks, were irradiated in the target of the spallation source SINQ to displacement doses of up to 11 dpa. Values for yield strength, ductility and fracture energy as evaluated from punch tests are given.
In order to study the influence of fast neutrons on the behaviour of high heat flux components for ITER, miniaturized samples have been neutron irradiated. Neutron fluences were 0.2 dpa in ...carbon/0.15 dpa in tungsten (irradiation campaign PARIDE 3) and 1 dpa in carbon/0.6 dpa in tungsten (irradiation campaign PARIDE 4). Irradiation temperatures were 200 °C approximately for all samples. The irradiated mock-ups as well as un-irradiated reference samples were tested under thermal fatigue conditions by means of a high power electron beam facility. They were loaded up to several thousand cycles and later they were cut and investigated by hot metallography. In addition to these thermal fatigue experiments, the degradation of thermal conductivities for plasma facing materials has been investigated. Samples from CFCs and tungsten alloys have been tested. Thermal diffusivities were measured by a laser flash method, heat capacities by differential scanning calorimetry.
Thermal fatigue experiments on tungsten mock-ups have been carried out by an electron beam facility. Different designs of W monoblock mock-ups as well as a W macrobrush mock-up showed very good ...performance at maximum power densities between 14 and 20 MW/m
2 (absorbed). For two plasma-sprayed tungsten mock-ups, failure limits were reached at 6.5 MW/m
2. But from the test results, it can be concluded that these failure limits could be increased by improvement of the production methods. Vertical displacement event (VDE) simulation experiments followed by a thermal fatigue test were performed on a tungsten macrobrush mock-up. No indication of failure was observed from the macroscopic inspections or from the infrared images. But in the metallographic inspection, some cracks were observed at the interface between the tungsten teeth and the soft copper layer.
Beryllium is one of the most interesting materials to be used in nuclear fusion devices due to its promising properties. However, testing of beryllium components is quite challenging because of its ...toxicity and the required safety procedures.
Within this paper an overview of high heat flux thermal fatigue tests carried out in the electron beam facility JUDITH 2 (Juelich Divertor Test Facility in the Hot Cells) at Forschungszentrum Juelich (FZJ) on actively cooled beryllium mock ups is given. The performance of the mock ups was documented by temperature measurements as well as optical inspections before and after testing. Special attention was paid to the temperature diagnostics during the tests for two different reasons. Firstly, local overheating of the beryllium tiles, which are the proof of bonding failures, is detected by temperature measurements. Secondly, temperature information is exceptionally important to meet the required safety standards because of the toxicity of beryllium. In order to avoid evaporation of beryllium, a temperature limit for an automatic safety shut down of the electron beam facility JUDITH 2 was set to a certain value. Finally examples of the temperature distribution under different loading conditions for the beryllium mock ups are presented within this paper.
The status of RF R&D activities in production and characterization of TGP-56FW beryllium grade is presented. The results of metallographic studies of microstructure and cracks morphology are reported ...for full-scale Be tiles (56×56×10mm) subjected to VDE simulation tests in TSEFEY-M testing facility (VDE-10MJ/m2 during 0.1s, 1 shot) and following low cycle thermal fatigue tests (500 thermal cycles at 1.5MW/m2). First results of plasma disruption tests (E=1.2–5MJ/m2, 5ms), which were obtained during the realization of Thermal Shock/VDE Qualification program of RF beryllium in JUDITH-1 facility, are also discussed.
In order to qualify new beryllium grades for ITER, several Russian and Chinese materials were tested in the electron beam facility JUDITH-1 and compared to the reference material S65C. In a former ...campaign, samples from these materials were loaded in thermal shock experiments with single shots and multiple shots. The present work is an extension of this work to other loading scenarios.
Four actively cooled mock-ups were produced in Russia and in China (two by each party). These mock-ups consisted of a water-cooled CuCrZr body with four tiles from different beryllium grades. Both parties used their own joining techniques, but each of the mock-ups also contained beryllium tiles from the other party, as well as from S65C.
Each tile was loaded by the following scenarios on different surface areas:
* simulation of vertical displacement events (VDEs) at 40 MJ/m
2
, 1 shot, heated area a = 10 × 10 mm
2
, 50-ms ramp-up, 165-ms steady state
* disruption simulation at 3 MJ/m
2
, 1 shot, heated area a = 5 × 5 mm
2
, Δt = 5 ms
* repetitive test with 1000 shots at 80 MW/m
2
(2 MJ/m
2
), a = 10 × 10 mm
2
, Δt = 25 ms. This loading condition is similar to one that was proposed by Sandia National Laboratory for the comparison of different beryllium grades.
Finally, one mock-up by each party underwent a thermal fatigue test with 1000 cycles at 2 MW/m
2
, 15 s heating, and 15 s cooling (heated area: whole sample surface). Heavy melting was observed in the area of the VDE loading, but no detachment of any of the tiles was found. Following the high-heat-flux experiments in the electron beam facility, post-mortem examinations were performed by optical photography and scanning electron microscopy on the surfaces as well as by metallography. From these analyses, no fundamental differences were found for the damage in the different beryllium grades.
In this paper, the authors present the results of investigations into the mechanical characteristics after irradiation of GlidCopAl25/316L(N) and CuCrZr/316L(N)-type joints produced by two joining ...technologies. Specimens of the joints were irradiated in the RBT-6 reactor in the dose range of 10
−3–10
−1 dpa at
Т
irr
=
200
°С and 300
°С. Irradiation at
Т
irr
=
200
°С causes strengthening of the joints specimens (by about 100
MPa at the maximum dose). The uniform elongation drops from 8% in the initial state to 2–3%. But the total elongation remains at a relatively high level of ∼7%. Irradiation at 300
°С does not practically change the ultimate strength of CuCrZr/316L(N) joints, but the total and uniform elongation of the joints decreases monotonously with a dose. But in this case, the level of elongation remains considerably higher than that when irradiated at 200
°С.
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