PREPARATION OF PIN-BY-PIN NUCLEAR LIBRARIES WITH SUPERHOMOGENIZATION METHOD FOR NTRACER AND DORT CORE CALCULATIONS

摘要

This paper presents a study on the behavior of superhomogenization (SPH) factors and on the effect they have on the pin power prediction and on the multiplication factor for the pin-by-pin codes nTRACER and DORT. An SPH module was developed specifically to work with these codes. Improvements in the multiplication factor and in the pin power prediction are experienced for single assembly and consequently for the 3x3 cluster calculations using also the single assemblies cross sections libraries. The largest improvement can be seen for the power of fuel rods with burnable absorbers for which the absorption reaction rates are generally overestimated by using simple flux-volume weighted homogenized cross sections. In addition, sensitivity studies on the SPH factors were performed in terms of fuel temperature, boron concentration, and burnup. The dependences on these variables have been found to be small and they can be approximated by linear or low order polynomials. In conclusion a preliminary study on different approaches for the preparation of the pin-cell cross sections has been evaluated. Since the computation time and memory requirements of the pin-by-pin calculations are considerable, possibility of grouping of similar pin cells together and its impact on calculation time and on pin power prediction accuracy was also studied.