Studying the neutron energy spectra at the BFS critical assemblies

A comparative analysis of the calculational and experimental data on investigation of neutron energy spectra in different multiplying media is conducted. Measurements are carried out at the central subassembly of the BFS critical assemblies containing 235U or 239Pu under the conditions approaching those of infinite homogeneous medium. The time-of-flight and proton recoil methods of neutron spectrometry are used. A set of programs providing detail solution of the neutron slowing-down equation for an infinite medium is used for the calculations. The conducted investigation has disclosed that difference between the experimental and calculated spectra in the 1 MeV - 10 keV energy range for all the assemblies arises within the limits of double error of the experiment. Transformation of the calculational and experimental divergences for a hard part of the spectrum for the conditions of a commercial reactor results in the error in determinating a number of displacements per atom for the core structural materials which is equal to +- 30%. When determinating helium accumulation and 232U and 232Pu buildup in a spent fuel this error amounts to +-40-50%. A conclusion is made on the necessity of further analysis of spectrum measuring reliability at the energy above 1 MeV and correctness of joining the parts of spectrum obtained by different methods