Assessment of the activation induced by neutron irradiation in K-DEMO and thermal response under the decay heat

Abstract

The radioactivation of in-vessel components due to the fusion neutrons is an unavoidable trade-off in a tokamak reactor. We investigate the radioactivity level of nuclides and decay heat of conceptual water-cooled ceramic breeder blanket and divertor modules in K-DEMO, and demonstrate that a cooling scheme related to the decay time is important to prevent thermal failure of those components due to decay heat during their maintenance. For K-DEMO with a fusion power of 2.2 GW, the activation levels of blankets and divertors are evaluated regarding a regulatory low level limit in Korea. Total decay heat from radioactivated blankets and divertors reaches 63.4 MW after the full power operation of two years. In an outboard module, immediately after the plasma shutdown, local maximum temperature reaches 1300°C with the temperature difference up to 840 °C inside the module. Conservative natural convection was assumed to validate its integrity to remain within the allowable temperature range of the materials used, when provided that the cool-down time is secured at least a couple of days, the overall temperature of the module is reduced to about 200°C in 10 days. It is worth consideration that a forced convective scheme such an internal passage cooling can be tailored until a critical time corresponding to configurations of each module.