Comparative analysis of WWER-440 spent fuel characteristics, calculated by the NESSEL-NUKO and SCALE4.4 code systems

Spent fuel characteristics such as fission product concentrations and post decay power are very important for spent fuel behavior. They can be determined by applying verified depletion codes with appropriate nuclear data libraries. The paper presents some results, obtained for WWER-440 spent fuel by using two code systems, applied to depletion analysis: NESSEL-NUKO and SCALE-4.4. A brief description of the NESSEL-4 and NUKO codes is given. The calculations of nuclear inventory and post decay power of PWR and BWR spent fuel in the code system are carried out by the control module SAS2H. A comparative analysis is done for nuclide number densities and post decay power at two different final burnup points (30 and 40 Mwd/kgU) and three different cooling time steps - after discharging the fuel, after 1 year and after 6 years of cooling at away from reactor basin. The following nuclides have been chosen for comparison: major (U and Pu) and minor actinides (Np, Am, Cm) and fission products (Kr, Mo, Tc, Xe, Ru, Cs, Pm, Nd, Sm, Eu). The analysis of fission products is needed in order to evaluate the burnup credit. Both computer codes considered could be applied for determination of the WWER-440 time dependent spent fuel characteristics (isotope inventory, post decay power and activity), affecting the spent fuel behavior