Search

Mineral-insulated (MI) cables and Low-Temperature Co-fired Ceramic (LTCC) magnetic pick-up coils are intended to be installed in various position in ITER. The severe ITER nuclear radiation field is expected to lead to induced currents that could perturb diagnostic measurements. In order to assess this problem and to find mitigation strategies models were developed for the calculation of neutron-and gamma-induced currents in MI cables and in LTCC coils. The models are based on calculations with the MCNPX code, combined with a dedicated model for the drift of electrons stopped in the insulator. The gamma induced currents can be easily calculated with a single coupled photon-electron MCNPX calculation. The prompt neutron induced currents requires only a single coupled neutron-photon-electron MCNPX run. The various delayed neutron contributions require a careful analysis of all possibly relevant neutron-induced reaction paths and a combination of different types of MCNPX calculations. The models were applied for a specific twin-core copper MI cable, for one quad-core copper cable and for silver conductor LTCC coils (one with silver ground plates in order to reduce the currents and one without such silver ground plates). Calculations were performed for irradiation conditions (neutron and gamma spectra and fluxes) in relevant positions in ITER and in the Y3 irradiation channel of the BR1 reactor at SCK•CEN, in which an irradiation test of these four test devices was carried out afterwards. We will present the basic elements of the models and show the results of all relevant partial currents (gamma and neutron induced, prompt and various delayed currents) in BR1-Y3 conditions. Experimental data will be shown and analysed in terms of the respective contributions. The tests were performed at reactor powers of 350 kW and 1 MW, leading to thermal neutron fluxes of 1E11 n/cm2s and 3E11 n/cm2s, respectively. The corresponding total radiation induced currents are ranging from 1 to 7 nA only, putting a challenge on the acquisition system and on the data analysis. The detailed experimental results will be compared with the corresponding values predicted by the model. The overall agreement between the experimental data and the model predictions is fairly good, with very consistent data for the main delayed current components, while the lower amplitude delayed currents and some of the prompt contributions show some minor discrepancies.

ITER will be the first fusion device able to maintain fusion for long periods of time and therefore suitable to test integrated technologies, materials, and physics regimes necessary for the commercial production of fusion-based electricity. Therefore, ITER provides a harsh radiation environment that represents an important challenge for diagnostic systems located in various regions inside the tokamak, in particular the first wall, divertor areas, and ports, but as well ex-vessel areas, where radiation levels are also significantly high for some electronic components. The radiation induced effects in functional materials have been identified and studied in the past in the fusion and fission community. These effects comprise nuclear heating, changes in physical and mechanical properties due to transmutation and displacement damage, radiation induced conductivity (RIC) or radiation induced electrical degradation (RIED) effects on insulators, radiation induced absorption (RIA) for optical materials, radio luminescence observed in fibers and windows, etc. This paper summarizes the current status of the functional material selection for ITER diagnostic systems and the expected radiation conditions in the areas where they are located. Additional testing will be required for some materials and assemblies, such as bolometers and magnetic coils. Special attention is paid to the tests required for qualification of safety important components, such as diagnostic window assemblies and vacuum feedthroughs. Finally, as one of the best ways to reduce the impact of radiation in materials is to develop a proper shielding strategy, some of the shielding options envisaged for ITER are presented and discussed in this paper. [ABSTRACT FROM AUTHOR]