Shutdown dose rate experiment at JET during DTE2

Abstract

The EUROfusion activities on the technological exploitation of deuterium–tritium (DT) operation at JET (started within the work package JET3 and continued under PrIO) were established to maximize the scientific and technological return of DTE2 campaign occurred in the second part of 2021. In particular, the aim of the NEXP sub-project was to take advantage of the expected significant neutron production during DTE2 to validate the numerical tools used for neutron streaming and shutdown dose rate (SDR) calculation for ITER through the comparison between numerical predictions and measurements. In the frame of SDR activity, a dosimetry system to measure the dose rate and based on some ionization chambers (ICs) was installed in the torus hall and upgraded both hardware and software since 2015 by exploiting the previous DD and TT campaigns. Two spherical 1-L air-vented ICs had been installed in some ex-vessel positions close to the horizontal ports of the tokamak in octants 1 and 2 and a third IC, suitable for higher dose rates, was then added in octant 1. As for SDR calculation, numerical tools employed rely on MCNP code for radiation transport and in this regard the MCNP model has been updated to include the last detector installed in octant 1. The present work is dedicated to the analysis of dose rate measurements carried out during DTE2 in the inter-pulse periods and at the shutdown. Influence quantities and error sources are analyzed to calculate the dose rate from raw signal and experimental uncertainty. Some experimental points are chosen and employed for a preliminary comparison with numerical predictions obtained from three-dimensional simulations with Advanced D1S tool. The results are presented and discussed with the major objective to contribute to the optimization of the planned SDR code validation.