Joint neutron measurements on the flat-top HEU critical assembly machine - 14388

Conference · Tue Sep 15 04:00:00 EDT 2015

OSTI ID:23100858

Hutchinson, J.; Smith-Nelson, M.; Hayes, D.; Sanchez, R.; Cutler, T.; Sood, A.; Richard, B.; Bahran, R. ^[1]; Chapelle, A.; Casoli, P. ^[2]; Richard, Benoit ^[1]; Robinson, R. ^[3]

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1. Los Alamos National Laboratory, MS B228, P.O. Box 1663, Los Alamos, NM, 87545 (United States)
2. Commissariat a l'Energie Atomique et aux Energies Alternatives - CEA Valduc (France)
3. Alabama A and M University (United States)

Flat-Top is a critical assembly with a spherical core (either ∼17 kg of HEU or ∼6 kg of δ-phase Pu) surrounded by a spherical 1000 kg natural uranium reflector. In 2013, joint LANL and CEA measurements were conducted to measure Flat-Top configurations with the HEU core using He-3 detector systems. Similar experiments were previously documented in which the Caliban and Godiva critical assemblies were measured. The core and reflector of Flat-Top have a glory hole in which nuclear material or non-nuclear material may be placed. Five configurations were measured and included subcritical configurations at various reactivity states as well as a configuration at delayed critical. The various reactivity states were achieved by varying the placement of the safety blocks and control rods (composed of natural uranium). A description of the assembly and the specific configurations measured will be presented. The subcritical and delayed critical measurements were analyzed using the Hage-Cifarelli formalism of the Feynman Variance-to-Mean method. This analysis can be used to calculate the multiplication of each configuration, from which the multiplication factor and reactivity are determined. These results are compared to the reactivity states based upon control rod worth curves and MCNP simulations. For this work, a new MCNP model was made to accurately represent the measured configurations. The ICSBEP handbook contains a benchmark of Flat-Top but all models are very simple and do not have the required fidelity to accurately represent the measured configurations. This work also examines the number of neutrons emitted per fission for this assembly (which has a significant contribution of induced fissions in U-238 due to the large natural uranium reflector). (authors)

• Research Organization: American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
• OSTI ID: 23100858
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
42 ENGINEERING
CONTROL ELEMENTS
CONTROL ROD WORTHS
FISSION
MULTIPLICATION FACTORS
NATURAL URANIUM
NOISE
REACTIVITY
SIMULATION
SPHERICAL CONFIGURATION
URANIUM 238
ZERO POWER REACTORS