Time Correlation Measurements of 252Cf Source Driven Fission Chains in Bare HEU Metal Assemblies

Conference · Sun Jul 11 00:00:00 EDT 2010

OSTI ID:986418

McConchie, Seth M. ^[1]; Hausladen, Paul ^[1]; Mihalczo, John T. ^[1]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Passive multiplicity measurements of fissile metal assemblies are well established for measuring the multiplication, fissile content, and detection efficiency. In plutonium metal assemblies, most of the neutrons are unambiguously observed from fission chains because of the high spontaneous fission rate. However, uranium metal assemblies have low spontaneous fission rate such that the observed neutrons are a mixture of fission chain neutrons and cosmic-ray spallation neutrons. As a result, the multiplication, fissile content, and detection efficiency are difficult to measure without accurate quantification of the single neutron events unrelated to the fission chains. However, studying fission chains is simplified by knowing when each chain starts, which can be accomplished using a time-tagged active source such as a ²⁵²Cf ionization chamber or a deuterium-tritium (D-T) neutron generator with an alpha detector. This paper presents time correlation measurements that have been performed with up to five 18 kg highly enriched uranium (HEU) storage castings and a ²⁵²Cf ionization chamber placed near the center of each assembly. The measurements included liquid scintillators with pulse shape discrimination operating on the timescale of fission chains and ³He proportional counters whose traditional use in multiplicity counting is well understood within a point-kinetics framework. Neutron time correlation distributions have been measured to characterize each assembly and are compared with the equivalent distributions collected passively.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 986418
• Resource Relation: Conference: INMM 2010, Baltimore, MD (United States), 11-16 Jul 2010
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
CASTINGS
DETECTION
EFFICIENCY
FISSION
HIGHLY ENRICHED URANIUM
IONIZATION CHAMBERS
LIQUID SCINTILLATORS
MIXTURES
MULTIPLICITY
NEUTRON GENERATORS
NEUTRONS
PLUTONIUM
PROPORTIONAL COUNTERS
SPALLATION
SPONTANEOUS FISSION
STORAGE
URANIUM
Nuclear Criticality Safety Program (NCSP)
Time Correlation Measurements
Highly Enriched Uranium (HEU) Storage Castings
252-Cf Ionization Chamber
3-He