Evaluation of Decay Dose Rates for European DEMO Vacuum Vessel Structure

Abstract

Abstract Four types of breeder blanket modules are in consideration for European DEMO pre-conceptual design phase specified by European Fusion Roadmap. In this study two designs (Helium Cooled Pebble Bed (HCPB) and Water-Cooled Lithium Lead (WCLL)) were investigated in terms of their influence on vacuum vessel (VV) nuclear decay dose rates. In both cases, the same vacuum vessel structure is examined. VV model consists of two shells, interspace and thermal shield. The inner shell and outer shell of vacuum vessel are made of Stainless Steel 316L(N)-IG. The interspace layer is made of water for cooling and shielding purposes. Stainless steel constitutes around 60% of all material in vacuum vessel and water makes up the rest. The model of fusion reactor has been developed in the frame of EUROfusion’s Power Plant Physics and Technology (PPPT) programme. This paper presents information about calculation results of the dose rates caused by the neutron irradiation for the vacuum vessel structural elements in DEMO fusion power reactor. In order to perform dose rate calculations, neutron energy spectra are required for different VV segments. Those calculations were performed with MCNP6 code and Joint Evaluated Fission and Fusion (JEFF) 3.2 nuclear data library. Dose rates were calculated with FISPACT-2010 and European Activation File (EAF) 2010 nuclear data library. The dose rates were calculated for European DEMO nuclear fusion reaction after its 20 calendar years lasting operation. Cooling period was considered spanning for up to 1000 years. In addition, radionuclides with contribution of at least 1% to the total value of dose rate were identified. Highest dose rates are attributed to 56Mn radionuclide immediately after the operation until around one day.60Co is the most dominant isotope during intermediate and long cooling periods. Differences in Interspace layer occur due to 16N isotope.