Lifetime performance of HCPB power plant in-vessel components using HERCULES

The PPCS plant models explore a range of physics and technology assumptions spanning from near-term, ITER-like assumptions to very advanced scenarios. They were named A to D following an order of increasing extrapolation from current expertise, and differ substantially in plasma parameters, electrical output, blanket and divertor technology. Plant model B (PMB) employs a helium-cooled, pebble bed (HCPB) blanket concept. The structural material is the reduced activation EUROFER grade steel. Creep, both thermal and irradiation, is the primary limiting mechanism for in-vessel component lifetime, with the bulk of cumulative damage due to power-on period. Lifetime improvement is possible if the time-to-failure at the full power-on stress level can be extended, which can be achieved through geometrical shape optimization. The helium-cooled concept is prone to fatigue limited lifetime, unless the plasma control is such that it limits the overpower transients and at the same time keeps their number to a minimum. Also, at higher temperatures, the structure becomes more susceptible to fatigue and even a small number of large duration events is capable of reducing lifetime significantly. Redesign of the in-vessel build could rely on a slimmer tritium generating blanket (∝40 cm) instead of ∝ 50cm, with first wall acting as a ''shielding'' blanket of ∝ 10cm thick. The concept relies on extending the first wall and breeding blanket lifetime significantly, by limiting creep and fatigue, without losing the breeding capability of TBR>1. HERCULES was used for a neutronics analysis and the extraction of engineering parameters. A comparison with previous creep-fatigue analyses of helium cooled blankets and first walls, show that this new concept is capable of doubling the lifetime, with adequate TBR∝1.16 (original TBR∝1.36). The concept needs further refinement and optimization, but it is promising to deliver not only engineering parameters but also economic performance. (orig.)