B&W Spectral Shift Control Reactor Lattice Experiments: Evaluation of Core I and Core VIII

This paper summarizes the evaluation for core I and core VIII of the Babcock & Wilcox Spectral Shift Control Reactor critical experiment program. The Spectral Shift Control Reactor concept, moderated and cooled by a variable mixture of heavy and light water, envisaged changing of the thermal neutron spectrum during the operation to encourage breeding and to sustain the core criticality. Core I contained 484 fuel rods with 4% UO₂ fuel in light water while core VIII contained 2188 fuel rods with 93% enriched UO₂-ThO₂ fuel in a moderator mixture of heavy and light water. For core I, the criticality experiment and measurements of the thermal disadvantage factor were evaluated. For core VIII, only the criticality experiment was evaluated. For both cores, experimental uncertainties were determined confirming the good level of accuracy achieved by the experimentalists. Based on the experimental configurations, benchmarks were proposed, and their biases were determined.