Deterministic Neutronics Calculation Method of Small Lead-cooled Reactor Based on Venus-Ⅱ Criticality Experimental Facility and Its Verification

Small reactors with complexity and flexibility are now the focus of research in many countries. Small lead-cooled reactor (SLR) is an important direction for the future development of small reactors. Compared with the traditional fast reactor, the core neutron energy spectrum of SLR brings challenges to the traditional deterministic neutronics analysis methods, which are more complex and the core geometry is special. Monte Carlo methods based on continuous energy and fine geometry modeling have unique advantages, but it has the disadvantage of high memory usage and high computational resource expenditure. Deterministic neutronics calculations are characterized by high computational accuracy, stability, and efficiency, and have been the core algorithms of nuclear reactor design software for the past decades. Deterministic methods are limited by the two-step homogenization process as well as the multi-group cross-section approximation, which generally require specific algorithmic models for the physical characteristics of the core. This paper established a new deterministic neutronics calculation method and computational model for the characteristics and challenges of the complex neutron spectrum and complex geometry of the solid lead-cooled reactor. The works were based on the full spectrum nuclear reactor analysis code SARAX. The few-group cross-section calculation established the corresponding cross-section generation methods for different energy intervals, in which the ultrafine group method, hyperfine method, and improved Bondarenko method were used in the high-energy, intermediate-energy, and indistinguishable resonance energy, respectively. The discrete ordinate method based on triangular mesh was used for 3D core calculations to meet the requirements of complex geometric modeling. The calculations of the Venus-Ⅱ were carried out by using the nuclear reactor analysis code SARAX, and compared with different homogenized cross-sections, core critical state, and special control rod cross-section generation models. Then it was verified and validated using the criticality experimental data of Venus-Ⅱ. The results show that the SARAX code system can generate high-precision homogenized cross-sections in the criticality analysis of the solid lead-cooled reactor with a complex neutron spectrum and complex geometry. Under the pin-by-pin model, the error of the k_eff is less than 300 pcm compared to the experimental values, and the control rod value relative error is within 5% with the proposed control rod cross-section generation model. By using the equivalent homogenization model, the computation time can be reduced from 450 hours to 13 hours while guaranteeing the same computational accuracy, which significantly improves the computational efficiency of the Venus-Ⅱand small reactors.