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The ITER Collective Thomson scattering (CTS) diagnostic will measure the dynamics of fusion-born alpha particles in the burning ITER plasma by scattering a 1 MW 60 GHz gyrotron beam off fast-ion induced fluctuations in the plasma. The diagnostic will have seven measurement volumes across the ITER cross section and will resolve the alpha particle energies in the range from 300 keV to 3.5 MeV; importantly, the CTS diagnostic is the only diagnostic capable of measuring confined alpha particles for energies below ∼1.7 MeV and will also be sensitive to the other fast-ion populations. The temporal resolution is 100 ms, allowing the capture of dynamics on that timescale, and the typical spatial resolution is 10–50 cm. The development and design of the in-vessel and primary parts of the CTS diagnostic has been completed. This marks the beginning of a new phase of preparation to maximize the scientific benefit of the diagnostic, e.g., by investigating the capability to contribute to the determination of the fuel-ion ratio and the bulk ion temperature as well as integrating data analysis with other fast-ion and bulk-ion diagnostics.

The ITER Collective Thomson Scattering (CTS) system will be the main diagnostic responsible for measuring the velocity distribution function of fusion-born alpha particles in the plasma. As the CTS diagnostic is integrated in the equatorial port plug 12 (drawer 3), with direct apertures to the port interspace where maintenance hands-on operation will be carried out, it is essential to assess the shutdown dose rates (SDDR) in these maintenance areas. In this work, the D1S-UNED3.1.4 Monte-Carlo transport code, based on the implementation of the direct-one-step methodology in MCNP5 v1.60, was used to estimate the dose rate level 12 days (106 s) after shutdown in the port interspace. The results show that the CTS system does not contribute significantly to the SDDR in the area where hands-on maintenance is foreseen with contribution to dose rates less than 1 µSv/h. This is consistent with previous estimates, although with the most recent model of the CTS design there is a slight increase of the SDDR values. This deviation can be attributed to design changes and improved shielding modelling and/or most importantly, to statistical fluctuations of the D1S simulations. From a neutronics point of view, the increase in the SDDR falls within the range of the statistical fluctuations, and the design is still compliant with the radiation safety ALARA principle aiming at minimizing radiation doses, and there is no requirement for further design optimizations.

Abstract. Burnup Credit (BUC) is the concept which consists in taking into account credit for the reduction of nuclear spent fuel reactivity due to its burnup. In the case of PWR-MOx spent fuel, studies pointed out that the contribution of the 15 most absorbing, stable and non-volatile fission products selected to the credit is as important as the one of the actinides. In order to get a "best estimate" value of the k eff , biases of their inventory calculation and individual reactivity worth should be considered in criticality safety studies. This paper enhances the most penalizing bias towards criticality and highlights possible improvements of nuclear data for the 15 FPs of PWRMOx BUC. Concerning the fuel inventory, trends in function of the burnup can be derived from experimental validation of the DARWIN-2.3 package (using the JEFF-3.1.1/SHEM library). Thanks to the BUC oscillation programme of separated FPs in the MINERVE reactor and fully validated scheme PIMS, calculation over experiment ratios can be accurately transposed to tendencies on the FPs integral cross sections.

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