Computational Method Study for Effective Self-Shielding Cross-Section of URR in Fast Reactor Code SARAX

In fast reactors, the neutron flux level in Unresolved Resonance Region（URR） of ²³⁸U is relatively high, and the accuracy of cross-section in corresponding energy regions makes direct influence on the fast reactor spectrum and homogenized cross-section calculation. Aiming at effective self-shielding cross-section calculation in URR of ²³⁸U, this paper improves the spectrum calculation code TULIP in SARAX. TULIP uses background cross-section interpolation in URR, but the accuracy of interpolation significantly affects the final results. Considering that the content ratio of ²³⁸U in fast reactor assemblies is large and the background cross-section of ²³⁸U is small, this paper analyzes the requirements of cross-section interpolation for ²³⁸U in URR, and verifies the effectiveness of improving calculation accuracy with denser background cross-section interpolation points by comparing the reaction rate before and after making denser interpolation points of ²³⁸U. Then, the accuracy of SARAX code at high temperatures is improved.