MEASUREMENTS OF NEUTRON FLUX SPECTRA IN THE THERMAL REACTOR

neutron flux spectra in the core and the reflector of the thermal reactor are measured by multiple foil method. There are 26 kinds of foil detectors selected for the measurements. neutron energy-range from 10~(-4) eV to 20MeV is divided into 640 groups. In consideration of neutron capture and scatter of foil itself. neutron self-shielding factors for 14 kinds of thermal and intermediate foils are calculated by single neutron energy approach in each group. energy-dependent activation cross sections of each detector are selected under the requirement of good accuracy and consistency between foils. results of computed flux spectra and their errors are given, The macroscopic spectral values, i.e. thermal neutron fluxes, neutron temperatures, values of Fermi-spectrum, Fermispectrnm deviations and integral fast neutron fluxes are given at two measured positions too. reaction-rates, the uncertainties of cross sections and initial flux spectrum used in the iteration VS. the sentivity of flux spectrum are tested. In the cases of a rather large change of initial flux spectrum the roughly consistent results are obtained. Rather reasonable distributions of flux spectra are also obtained in two energy ranges, one is 0.01 eV, where cross sections of the foils are almost 1/ν, and the other is about 10～500keV, where all foils are insensitive.