Application of the virtual density theory in fast reactor analysis based on the neutron transport calculation

The geometry distortion introduces one of the most important reactivity feedbacks in the fast reactor. To evaluate the reactivity caused by the geometry distortion, this paper presents a new approach applied in the steady-state fast reactor code SARAX. This approach is based on the discrete ordinates nodal method, first-order perturbation approximation and virtual density theory. In this way, the virtual material density is changed instead of changing the geometry in modeling the distortion. Compared with other methods to get geometry distortion reactivity, this method has better geometric adaptability and better efficiency in the multi-case evaluation. A series of verification are carried on, including the uniform expansion, the non-uniform expansion and the local geometry distortion. The results show that the virtual density method has good accuracy and efficiency in evaluating the geometry distortion reactivity.