Design procedures for small pebble-bed high temperature reactors

Design procedures for modularized, small-size pebble-bed high temperature reactors have been proposed for the existing fueling schemes, i.e. the multipass, OTTO and peu a peu fueling schemes. The well-established HTR-Module (200 MWth) is taken as the starting point in designing the small-size pebble-bed reactors, and its inherent safety features are conserved in the design procedures by imposing safety related, key design constraints derived from the HTR-Module. The burn-up characteristics of both uranium and thorium fuel cycles with fissile enrichment and heavy metal loading identical with the HTR-Module fuel composition are investigated for the small pebble-bed reactor design. Under the proposed design procedure for multipass and OTTO fueling schemes, small-sized PBRs with fuel burn-up performance competitive to HTR-Module and satisfy the safety constraints can be satisfactorily designed. However, although the proposed design procedure for peu a peu fueling scheme can produce a safe small-size reactor design, the burn-up performance in general is inferior to the HTR-Module design.