Study on the neutronic effects of annular metallic fuel irradiation swelling in a fast reactor core

The metallic fuel is a fast reactor fuel with good application prospects. Due to the anisotropic irradiation swelling of the metallic fuel slug, the spatial distribution of fissile materials in the core is changed, and the reactor neutronics performance is affected by the changes of neutron energy spectrum and neutron leakage rate of the core. In this paper, the Monte Carlo code RMC is used to establish the calculation model of a lead bismuth eutectic cooled fast reactor (LFR) with annular slug metallic fuel. The neutronics calculation of the core under different fuel swelling and different fuel burnup conditions is carried out. The quantitative calculation of the influence of three factors on k eff , including radial swelling, axial swelling and fuel temperature rise, was performed. The influence of irradiation swelling on the neutronics parameters of the core and its change with fuel burnup are analyzed. The results show that the radial irradiation swelling of the core introduces positive reactivity, while the axial swelling and the rise of the fuel temperature caused by the fuel swelling introduce negative reactivity. There is a linear relationship between the axial elongation of the core and the introduced reactivity. For every 1 % axial elongation of the UZr and UPuZr fuel slug, the introduced reactivity is about −100 pcm. Considering the irradiation swelling of the fuel, the absolute values of the fuel axial expansion reactivity coefficient and fuel temperature reactivity coefficient increases by 35 % and 16 % respectively, and the core reactivity decreases by about 300 pcm ∼ 500 pcm. Combined with the irradiation swelling approximate model of annular metallic fuel, an approximate evaluation model of reactor reactivity caused by irradiation swelling under different burnup was obtained. • Neutronic Effects of Annular Metallic Fuel Irradiation Swelling in a LFR Core. • Quantitative results of fuel irradiation swelling on reactor reactivity and reactivity coefficient were obtained. • Every 1 % axial elongation of the UZr/UPuZr fuel slug companies with about −100 pcm reactivity. • Proposed an approximate evaluation model of reactor reactivity caused by metallic fuel irradiation swellingin a LFR.