Analysis of a Set of Critical Homogeneous U-H₂O Spheres

A group of 11 aqueous critical experiments fueled by ²³³U and ²³⁵U and performed by Gwin and Magnuson have been analyzed to serve as integral tests of nuclear data important in reactor design. Measured eignvalues were corrected for various effects including the presence of the aluminum container, departures from sphericity, delayed-neutron importance, and room return. Eigenvalues were calculated in simplified P-3 approximation using 60 energy groups, and determinations were made of the eigenvalue uncertainties (±0.1%) associated with this treatment. Within the eigenvalue uncertainties (±0.25%) resulting from fuel inventories, it was concluded that fissile nuclide and H(n,γ) cross sections were adequate to match calculations and experiments but that there was evidence of erroneous nuclear data important in determining neutron leakage. In particular, a substantially harder ²³³U fission neutron spectrum seems to be indicated.