CHARACTERIZATION OF (U,La)O_2 FUEL FROM THE STANDPOINT OF POWER REACTOR APPLICATIONS

摘要

Lanthanum doped UO_2 was investigated for possibleuse in pressurized heavy water reactors (PHWR). It wasargued in the past that the (U,La)O_2 fuel system hasadvantages in retarding fission gas diffusion, stabilizingthe fluorite structure under oxidizing conditions, andenhancing the thermal conductivity. Consequently,Lanthanum- doped UO_2 fuel pellets were fabricated atCanadian Nuclear Laboratories (CNL) with differentconcentrations of La, ranging from 0.09 mol% up to 4.3mol% La in UO_2 to establish the effect of lanthanum onthe grain size and density. Decreases in grain size anddensity were observed with increased lanthanumconcentrations. Above 800°C, there is no difference inmeasured thermal diffusivity between doped and undopedfuel samples. Based on the reactor physics modelling, theeffect of lanthanum on fuel burnup for CANadianDeuterium Uranium (CANDU) fuel bundles was alsoestablished. It has been demonstrated that utilization ofLa in UO_2, even at relatively very low concentrations <0.5 mol% of La in fresh fuel, requires slight enrichment ofthe fuel. The necessary level of enrichment does notexceed 1.0% of 235U for doping with less than 1 mol% La.This required enrichment is less than what has beenproposed in the past for other advanced nuclear fuel forPHWR applications, such as LVRF (Low Void ReactivityFuel) and ACR (Advanced CANDU Reactor fuel).However, the use of slight enriched uranium (SEU)requires additional licenses for fuel fabrication at theindustrial scale (e.g., Cameco, BWXT, etc.) and forreactor operation in Canada.