Thermal-Neutron Spectrum Indexes in D₂O-Moderated Uranium and Uranium-Plutonium Fuel Elements in the Temperature Range from 20 to 200°C

Thermal-neutron spectrum indexes in uranium and uranium-plutonium clustered fuel elements, organic-cooled and D₂O-moderated, were measured in the temperature range from 20 to 200°C, by activation of ²³⁹Pu-²³⁵U and ¹⁷⁶Lu-¹⁶⁴Dy detector pairs. The experimental results were used to test the multigroup transport code HEROIC and associated cross-section libraries.