Equilibrium model for calculation of burnup in a recirculating pebble bed reactor.

Abstract

The general problem of burnup calculations for a pebble bed reactor is discussed An efficient calculational scheme is developed by treating operation at equilibrium with a random distribution of pebbles. Assuming a constant flux level and spectrum, analytical solutions are obtained for time averaged nuclide concentrations. With a specified feed composition average power density, and burnup consistent values of average nuclide concentrations and flux spectrum are derived in an iterative manner, It is shown by physical reasoning and numerical calculation that the assumptions are justified for the large pebble bed reactors based on PuO2 — ThO2 — BeO fuels selected for a reactor feasibility study. The spectrum weighted improved one—group treatment lends itself to efficient coupling of burnup and power plant optimization studies and it may also find application to other reactor systems.