Creation of a Simplified Benchmark Model for the Neptunium Sphere Experiment

Conference · Sun Apr 25 04:00:00 EDT 2004

OSTI ID:977429

Mosteller, Russell D. ^[1]; Loaiza, David J. ^[1]; Sanchez, Rene G. ^[1]

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1. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Although neptunium is produced in significant amounts by nuclear power reactors, its critical mass is not well known. In addition, sizeable uncertainties exist for its cross sections. As an important step toward resolution of these issues, a critical experiment was conducted in 2002 at the Los Alamos Critical Experiments Facility. In the experiment, a 6-kg sphere of ²³⁷Np was surrounded by nested hemispherical shells of highly enriched uranium. The shells were required in order to reach a critical condition. Subsequently, a detailed model of the experiment was developed. This model faithfully reproduces the components of the experiment, but it is geometrically complex. Furthermore, the isotopics analysis upon which that model is based omits nearly 1 % of the mass of the sphere. A simplified benchmark model has been constructed that retains all of the neutronically important aspects of the detailed model and substantially reduces the computer resources required for the calculation. The reactivity impact, of each of the simplifications is quantified, including the effect of the missing mass. A complete set of specifications for the benchmark is included in the full paper. Both the detailed and simplified benchmark models underpredict k_eff by more than 1% Δk. This discrepancy supports the suspicion that better cross sections are needed for ²³⁷Np.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 977429
• Report Number(s): LA-UR--04-0525; LA-UR--04-525
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
29 ENERGY PLANNING, POLICY, AND ECONOMY
BENCHMARKS
Benchmarks
COMPUTERS
CRITICAL MASS
CROSS SECTIONS
Criticality
FUEL CYCLE
HIGHLY ENRICHED URANIUM
MCNP
MISSING MASS
NEPTUNIUM
NUCLEAR POWER
Neptunium
Nuclear Criticality Safety Program (NCSP)
PHYSICS
RESOLUTION
SPECIFICATIONS