Neutron spectrum of the gaseous cavity fuel assembly with an external heavy water moderator in the energy range of O < E < 5eV

Integral neutron spectra have been measured in a spherical gaseous fuel assembly mockup with a heavy water moderator in the 1-5 eV energy range. The technique of stationary neutron source (252Cf) placed in the centre of the cavity filled with BF3 enriched by 10B up to 81.7% is used. Spatial distributions of spectral indexes of 164Dy, 151Eu, 115In, 193Ir and 198Au are tabulated. The measurements have been performed in the BF3 pressure range from 0 to 6 bars which corresponds to the 235U concentrations from 0 to 6.88x1020 atom/cm3 being critical for the assembly. The measured dependences are compared to the calculated ones, carried out using the SI-5 code written in a 15-group P3 approximation. The experimental and calculated indexes for all investigated indicators (except for europium) are close in value