Neutronic analysis of the PB-AHTR integral design

The Pebble Bed Advanced High Temperature Reactor (PB-AHTR) neutronic characteristics are analyzed for multiple combinations of graphite-to-heavy metal atomic ratio (C/HM) in the range from 200 to 600 and fuel kernel diameters in the range of from 200 to 1,000 μm. It was found that the attainable burnup is close to 130 GWd/tHM when fuelled with 10% enriched uranium; it is similar to that of a helium-cooled pebble-bed reactor and of prismatic fuel very high temperature reactors cooled by either flibe or helium. The peak-burnup uranium loading and the energy generated per pebble of the PB-AHTR are nearly 2.5 times those of a helium-cooled PBMR. The PB-AHTR fuel temperature reactivity feedback is negative over all the design space studied while to maintain the coolant temperature reactivity coefficient negative the C/HM must be < ∼400. The PB-AHTR can also be designed to burn TRU from LWRs; its transmutation performance is similar to that of the DB-MHR. (authors)