Dose Rate Measurements During the Tritium Campaign at JET and Diagnostic Improvements for the Deuterium-Tritium Experiments

The technological exploitation of the deuterium-tritium campaign at JET is the objective of the EUROfusion work package JET3 and, through the NEXP subproject, it intends to take advantage of the expected significant neutron production to validate the numerical tools used for shutdown dose rate (SDR) assessment and to study the reasons of discrepancies between calculations and measurements. The tritium campaign C40 was held in the first half of 2021 and two active gamma dosimeters based on spherical 1-L air-vented ionization chambers (ICs) were installed in some ex-vessel positions close to the horizontal ports of the tokamak in octants 1 and 2, have been employed to measure the dose rate. Moreover, for the deuterium-tritium campaign C41 (DTE2), a third IC suitable for higher dose rates was installed in octant 1. The present work is dedicated to the analysis of dose rate measurements carried out during the tritium campaign during the inter-pulse periods and the shutdown. Influence quantities and error sources are analyzed in order to calculate the dose rate from the raw signal and experimental uncertainty. Some improvements in the experimental equipment are described as well, as the assessment of the sensitivity of the ICs to the variation of oxygen concentration in the air (to simulate the nitrogen-enriched atmosphere in the JET torus hall during tritium operation) and the upgrade of the acquisition software to interface it with CODAS data store.