W. Kühnlein

Brittle destruction of carbon-based materials in transient heat load tests

Abstract To investigate the phenomenon of brittle destruction (BD), isotropic fine-grain graphites and carbon fiber composites (CFCs) with and without silicon doping have been exposed to intense transient thermal loads in the electron beam test facility JUDITH. For different pulse durations (1 to 5, 100, 5000 ms) the deposited energy density has been increased stepwise to determine the threshold for the BD process. Particle emission was diagnosed using time-resolved measurements of the absorbed current and by digital photography. A clear correlation of the absorbed current and the onset of the particle emission processes has been established.

Reference testing of actively cooled mock-ups for the neutron-irradiation experiments PARIDE 3 and 4

A neutron irradiation campaign has been performed with new designs of high heat flux components. In parallel to this irradiation, reference tests have been carried out with un-irradiated samples of the same type. This paper reports on the testing of un-irradiated divertor mock-ups from tungsten and CFC attached to water-cooled heat sinks from CuCrZr.

Mechanical properties of pure tantalum after 800 MeV proton irradiation

Abstract Specimens prepared from a spent tantalum target of the pulsed spallation source ISIS, irradiated with 800 MeV proton to a maximum fluence of 1.7×10 25 p m −2 at temperatures lower than 200 °C, were investigated by micro-hardness, three-point bending and tensile tests at room temperature (RT) and at 250 °C. All three types of mechanical measurements consistently showed irradiation hardening. Furthermore, the tensile tests showed that the increase in yield strength is accompanied by a reduction of the strain-to-necking at both test temperatures. For instance, at RT, the strain-to-necking was reduced by irradiation from initially 30% to about 10%. This drop in ductility occurred at doses below 0.6 dpa, whereas afterwards the strain-to-necking remained constant up to the maximum dose of about 11 dpa. The results of tests at 250 °C were similar to those at RT. SEM investigation revealed typical ductile fracture surfaces even for the highest doses. Optical micrography after bending tests showed no cracks even after bending of a 2 mm thick specimen end to end, indicating that pure Ta retained very high ductility after proton irradiation.

Light emission from carbon-based materials under ITER relevant thermal shock loads

Light emission from carbon-based materials (fine grain graphite, CFC and silicon doped CFC) was observed during ITER relevant thermal shock loads by means of in situ optical diagnostics. The light emission which corresponds to particle release clearly indicated different particle release processes in the three materials. The differences were also found in the initiation temperatures of particle release and the surface morphology of the loaded areas. These results are related to the thermal stress in bulk materials. In addition to particle release, vapor cloud formation caused by thermal shock loads were observed as CII lines and lines from the C2 Swan system. No Si lines but lines from SiC2 molecules (Merrill–Sanford bands) were observed in Si doped CFC. This indicates that atomic silicon is not released under ITER relevant thermal shock loads.

Testing of actively cooled high heat flux mock-ups

Abstract Several un-irradiated CFC monoblock mock-ups have been loaded in thermal fatigue tests up to 1000 cycles at power densities 2 . No indication of failure was observed for these loading conditions. Two of the mock-ups were inspected by ultra-sonic methods before thermal cycling. It could be proved that the voids found in the post-mortem metallography existed before and had no effect on the integrity of the mock-up. For the first time, neutron-irradiated CFC monoblock mock-ups have been tested in the electron beam facility JUDITH. These mock-ups had been irradiated before in the High Flux Reactor at Petten up to 0.3 dpa at 320°C and 770°C. All samples showed a significant increase of surface temperature, due to the irradiation induced decrease in thermal conductivity of the CFC materials.

THE NEW ELECTRON BEAM FACILITY FOR MATERIALS TESTING IN HOT CELLS - DESIGN AND PRELIMINARY EXPERIENCE

Testing of materials which have been subjected to neutron irradiation will be carried out for the fusion reactor research programme at the KFA. An electron beam test apparatus Ju elich Di vertor T est Equipment in H ot Cells (JUDITH) has been installed in the Hot Cells of the Institute for Materials in Energy Systems, complementing the test equipment available in Japan, USA, France and RF [1–3]. Gamma ray emitting specimens are to be tested under thermal shock, thermal cycling and long-term loading conditions.

Behaviour of carbon and beryllium under thermomechanical loads

An extensive test program has been set up to evaluate the performance of beryllium, carbon materials and tungsten as plasma facing materials for the divetor in thermonuclear fusion devices. Experiments described in this paper represent pre-irradiation testing being part of a comprehensive study on neutron damage of several plasma facing materials and components. Thermal shock tests were carried out with several grades of beryllium, carbons and tungsten, at heat loads up to 5.3 MJ/m2. In these experiments CFC materials and tungsten show less erosion than the beryllium grades. Best erosion behaviour of the beryllium grades is observed for S 65-C and for TGP-56. Steady state heating tests with actively cooled Be/Cu samples and CFC/ metal samples, respectively were performed at loadings up to 5.8 MW/m2. The main objective of these tests was the pre-selection of components to be included in a neutron irradiation program and to determine the heat removal efficiency before neutron irradiation. All samples investigated in steady state heating tests (Be/Cu and CFC modules) did not show any indications of failure, and are thus qualified to be used in the forthcoming neutron irradiation program. CFC modules however, show a strong variation of surface temperature due to the deviations in thermal conductivity of the CFC materials.