Neutronics analysis of a research reactor using a two-step method with the superhomogenization method

• A systematic error analysis is performed for research reactor neutronics calculations based on the two-step method. • Several influential factors, such as the number of energy groups, the homogenization model, and the S N order, are evaluated. • An improved SPH method is proposed based on the eigenvalue iteration scheme. • The SPH method effectively reduces the calculation errors for research reactors. Research reactors are characterized by significant neutron leakage, tight neutron coupling, and complex core geometries, which make accurate neutronics calculations using the two-step method challenging. This paper analyzes and quantifies the errors introduced by the two-step method for research reactor neutronics calculations. Based on the LVR-15 research reactor, the effects of several key factors, such as the number of energy groups, the homogenization model, and the S N order, are studied in detail by comparing the computed k eff and power with reference values. The numerical results indicate that the factors affecting calculation accuracy, in descending order of impact, are the number of energy groups, the homogenization model, and the S N order. The number of energy groups has the most significant impact on calculation accuracy. Specifically, using too few energy groups, such as 2-group energy structures, leads to significant overestimations of k eff . To further improve accuracy, an improved superhomogenization (SPH) method is proposed. It can stably maintain the k eff error below 500 pcm and reduce power prediction errors from 3.08 ∼ 4.67 % and 1.69 ∼ 2.80 % to 1.40 ∼ 3.49 % and 0.60 ∼ 1.98 % in the control-rod-in and control-rod-out cases, respectively. These findings provide valuable reference guidelines for other researchers aiming to achieve more accurate research reactor neutronics calculations based on the two-step method.