Radiological characterization of ceramic materials considered for the HT-DCLL DEMO reactor.

Abstract

The recent evolution of the Breeding Blanket (BB) Dual Coolant Lithium-Lead (DCLL) concept for the European DEMO from a low temperature (LT) multi-module segment (MMS) approach, limited by the thermal range tolerated by EUROFER, to an advanced high temperature (HT) single-module segment (SMS) architecture, is allowed by the consideration of ceramics and composite materials as main structural material rather than just as thin Flow Channel Inserts (FCI). The amount of the ceramic as main structure instead than as a FCI in the whole reactor could be of several tonnes generating concern regarding the radiological behaviour of such component and the consequent generated waste. For that, a preparatory assessment considering ideal “pure” ceramics has been performed towards a preliminary selection of the structural material, among others, under the criteria of maintenance operations and waste management. To complement such study additional analyses have been carried out considering not only the intendent element but also dopant and impurities which often give rise to significant additional activation. For both the theoretical compositions as well as the industrial ones, with a certain amount of impurities, activation calculations have been performed using the ACAB inventory code. Hence, total beta-gamma activity, specific activity for different nuclides, decay heat and surface gamma dose rate have been analysed with reference to the IAEA and SEAFP-2 standards for waste and handling classifications and to the specific regulations of the near-surface repository El Cabril (Córdoba, Spain). According to El Cabril regulation, pure SiC and TiC would be the best of the options considered since they would be accepted in Level 1 LILW (under detritiation for SiC). This may not be true for industrial compositions with impurities (Level 2), nor according to other standards. Pure zirconia is also a promising option, so further work is ongoing for zirconia and doped zirconia materials.