A multigroup constant library CL50G for fast reactor

The CL50G means CNDC Library of 50 Groups. It includes 52 nuclides and will be used for fast reactor design calculations in China. Its energy structure is the same as those of LIB-IV 50 group Library given by LANL of U.S.A.. In order to test the reliability of the L50G library, the PASC-1 code system was used for calculating 9 homogeneous and 14 heterogeneous critical fast benchmark assemblies with P3S32 and P3S8, respectively. These benchmark assemblies are recommended by CSEWG of the USA. The original calculated results are not good. On the other hand, F28 (ratio of 238U fission rate to 235U fission rate) values are over-predicted strikingly, too. It is found that the elastic scattering cross sections in the high energy region are overestimated. We have further known that the structure material nuclides, for example, iron, chromium and nickel have a complicated resonance structures from 0.3 to 5 MeV, but there are no resonance parameters in the File 2 of the evaluated nuclear data libraries, such as ENDF/B-6, JEF-1, JENDL-3 and CENDL-2. Consequently, self-shielding effects in high energy region for these structure material nuclides can not be calculated using the PASC-1 code system. Therefore the L50G library should be adjusted. In order to avoid the limitation of adjustment, we make the multigroup data adjustment within the range given by the several evaluated microscopic cross sections. The elastic scattering cross sections above 0.82 MeV for iron, chromium and nickel are decreased by 5%. The υ values, fission and capture cross sections for 235U, 238U and 239Pu are modified a little. Compared with others all of calculated results with the CL50G are good. (4 tabs.)