Neutron-induced transmutation effects in W and W-alloys in a fusion environment

Abstract

W and W-alloys are among the primary candidate materials for plasma-facing components in the design of fusion reactors, particularly in high-heat-flux regions such as the divertor. Under neutron irradiation W undergoes transmutation to its near-neighbours in the periodic table. Additionally He and H are particles emitted from certain neutron-induced reactions, and this is particularly significant in fusion research since the presence of helium in a material can cause both swelling and a strong increase in brittleness. This paper presents the results of inventory burn-up calculations on pure W and gives quantitative estimates for He production rates in both a fusionreactor environment and under conditions expected in the ITER experimental device. Transmutation reactions in possible alloying elements (Re, Ta, Ti and V), which could be used to reduce the brittleness of pure W, are also considered. Additionally, for comparison, the transmutation of other fusion-relevant materials, including Fe and SiC, are presented.

Surface morphology and deuterium retention in tungsten and tungsten–rhenium alloy exposed to low-energy, high flux D plasma

“…The protons from the D( 3 He, p) 4 He nuclear reaction were counted using a wideangle detector placed at a scattered angle of 135, and the program SIMNRA was used for the deconvolution of the measured proton yields. The D depth distribution was established by a sequence of layers with thicknesses equivalent to the depth resolution of the method ranging from 10 17 W/cm 2 at the surface to 10 19 W/cm 2 at a depth of 7 µm as calculated using the code RESOLNRA [17].…”

“…3). 4 For the sake of convenience, the exposure temperature, T exp , for each sample is indicated in brackets. (Fig.…”

“…Furthermore, irradiation of W with fusion neutrons creates several radioactive isotopes of tungsten and rhenium (Re). There has been a number of studies trying to predict the amount of Re accumulated in W during fusion power plant operation [1][2][3][4]. The most recent forecast by Gilbert and Sublet [4] gives 0.18 at.% of Re for 14 years of ITER operation and 3.8 at.% of Re for 5 years of DEMO operation.…”

Recent progress in research on tungsten materials for nuclear fusion applications in Europe

“…Perhaps the only good news as far as W is concerned is that helium is generated in relatively modest quantities, typically only reaching a few tens of appm over the expected normal lifetime of first wall fusion-reactor components. However, several of the materials under discussion for W-alloys, such as Ti and V, produce an order of magnitude more He compared to W (or Re or Ta), and so the actual ability of W and W-alloys to withstand the effects of the embrittlement mechanisms activated by He must be carefully considered [75].…”

Assessment of DEMO challenges in technology and physics

“…The problems in designing a divertor target element that can take a reasonable heat load in the DEMO environment are large. A recent analysis indicates that, depending on the coolant, a time averaged peak heat flux of 5-10 MW/m 2 must not be exceeded if a life time of about 2 full power years (fpy) is envisaged, which will lead to neutron damage of the order of 5 dpa [9], depending on the thermal power and the material choice. We note that this number is consistent with the expected erosion limits only if the divertor plasma temperature is below 5 eV [10].…”