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Criticality Benchmarks for the Epithermal Test Assembly Experiments

Emily M. Flora, Michael L. Zerkle

Nuclear Science and Engineering / Volume 178 / Number 4 / December 2014 / Pages 539-549

Technical Paper /

The Epithermal Test Assembly (ETA) experiments were performed to test the adequacy of 233U, 235U, and 232Th cross sections in epithermal spectra in support of the Light Water Breeder Reactor (LWBR) Program. The ETA design contained a central heavy water–moderated test region surrounded by a light water–moderated annular driver region. Two series of experiments were performed: ETA-I with 235UO2-ThO2 fuel rods in the test region and ETA-II with 233UO2-ThO2 fuel rods in the test region. The dominant uncertainties in the critical configurations include the test-rod pitch pitch for ETA-I; the test-region fuel-rod fuel density and 233U to (233U + Th) weight ratio for ETA-II; and the driver-region fuel-rod outer diameter, uranium enrichment, and pitch for both ETA experiments. Benchmark model results using MCNP5 are provided for ENDF/B-V, ENDF/B-VI, ENDF/B-VII.0, and ENDF/B-VII.1 cross sections with only the ENDF/B-VII.0 results falling within three standard deviations of the benchmark model keff. The ETA-I and ETA-II benchmark evaluations have been included in the International Handbook of Evaluated Criticality Safety Benchmark Experiments and are replicated in the International Handbook of Evaluated Reactor Physics Benchmark Experiments.

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