Dose rate analysis for a pre-conceptual design of the high energy beam transport section in the IBTF

Abstract

A pre-conceptual design study to evaluate the Breeding Blanket (BB) performance has been carried out because the BB, producing heat energy and tritium, is a key component for the fusion demonstration reactor. The Integrated Breeding Test Facility (IBTF) is based on an accelerator-driven system using a 40 MeV deuteron beam with a maximum current of 10 mA. Accelerated deuteron reacts with a solid beryllium target to generate neutrons. The total yield of the produced neutrons is estimated to be 6.68E+15 n/sec. The forward direction neutrons irradiate the tritium breeding unit, while the backscattered neutrons through the beam pipes activate the Deuteron Accelerator Unit (DAU) components that require temporary human access maintenance.Therefore, this study did a dose rate analysis for the pre-conceptual design of the High Energy Beam Transport (HEBT) section in the DAU during maintenance. The HEBT section is divided into regions A and B. For the reference HEBT model, the dose rate in only region B satisfies the human access requirement (dose rate ≤ 100 uSv/h) during short-term maintenance (STM) and long-term maintenance (LTM). To reduce the dose rate, the beam pipe material was changed to Al6063, which has a low weight fraction of Mn and Ni compared to SS304. A lead shutter was also used to shield the dose rate from the test cell. As a result, the dose rate in region A is lower than 100 uSv/h during the STM with a cooling time of 1 week. The dose rate in region B satisfies the hands-on maintenance requirement (dose rate ≤ 10 uSv/h). The dose rate in region A is lower than 100 uSv/h except for near the beam pipe during the LTM. The dose rate in region B is lower than 10 uSv/h. The dose rate in the HEBT section is increased as the LTM is repeated. However, the increasing rate of the dose is reduced as the LTM repeats. Neutron transport calculation was performed by SRC-UNED-v3.1.4 with the TENDL2019 cross-section library, and the gamma source was estimated using FISPACT-Ⅱ with the TENDL 2017 cross-section library.