Prompt Neutron Decay for Delayed Critical Bare and Natural-Uranium-Reflected Metal Spheres of Plutonium and Highly Enriched Uranium

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Nuclear Technology

DOI:https://doi.org/10.13182/NT11-2· OSTI ID:1038098

Mihalczo, John T ^[1]

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1. ORNL

Prompt neutron decay at delayed criticality was measured by Oak Ridge National Laboratory for uranium-reflected highly enriched uranium (HEU) and Pu metal spheres (FLATTOP), for an unreflected Pu metal (4.5% {sup 240}Pu) sphere (JEZEBEL) at Los Alamos National Laboratory (LANL) and for an unreflected HEU metal sphere at Oak Ridge Critical Experiments Facility. The average prompt neutron decay constants from hundreds of Rossi-{alpha} and randomly pulsed neutron measurements with {sup 252}Cf at delayed criticality are as follows: 3.8458 {+-} 0.0016 x 10{sup 5} s{sup -1}, 2.2139 {+-} 0.0022 x 10{sup 5} s{sup -1}, 6.3126 {+-} 0.0100 x 10{sup 5} s{sup -1}, and 1.1061 {+-} 0.0009 x 10{sup 6} s{sup -1}, respectively. These values agree with previous measurements by LANL for FLATTOP, JEZEBEL, and GODIVA I as follows: 3.82 {+-} 0.02 x 10{sup 5} s{sup -1} for a uranium core; 2.14 {+-} 0.05 x 10{sup 5} s{sup -1} and 2.29 x 10{sup 5} s{sup -1} (uncertainty not reported) for a plutonium core; 6.4 {+-} 0.1 x 10{sup 5} s{sup -1}, and 1.1 {+-} 0.1 x 10{sup 6} s{sup -1}, respectively, but have smaller uncertainties because of the larger number of measurements. For the FLATTOP and JEZEBEL assemblies, the measurements agree with calculations. Traditionally, the calculated decay constants for the bare uranium metal sphere GODIVA I and the Oak Ridge Uranium Metal Sphere were higher than experimental by {approx}10%. Other energy-dependent quantities for the bare uranium sphere agree within 1%.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1038098
• Journal Information: Nuclear Technology, Journal Name: Nuclear Technology Journal Issue: 2 Vol. 175; ISSN 0029-5450; ISSN NUTYBB
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CRITICALITY
DECAY
HIGHLY ENRICHED URANIUM
LANL
NEUTRONS
OR-CEF REACTOR
ORNL
PLUTONIUM
PROMPT NEUTRONS
URANIUM