Enrichment Determination of Uranium in Shielded Configurations

Conference · Thu Nov 17 00:00:00 EST 2011

OSTI ID:1021995

Crye, Jason Michael ^[1]; Hall, Howard L. ^[1]; McConchie, Seth M. ^[1]; Mihalczo, John T. ^[1]; Pena, Kirsten E. ^[1]

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

The determination of the enrichment of uranium is required in many safeguards and security applications. Typical methods of determining the enrichment rely on detecting the 186 keV gamma ray emitted by ²³⁵U. In some applications, the uranium is surrounded by external shields, and removal of the shields is undesirable. In these situations, methods relying on the detection of the 186 keV gamma fail because the gamma ray is shielded easily. Oak Ridge National Laboratory (ORNL) has previously measured the enrichment of shielded uranium metal using active neutron interrogation. The method consists of measuring the time distribution of fast neutrons from induced fissions with large plastic scintillator detectors. To determine the enrichment, the measurements are compared to a calibration surface that is created from Monte Carlo simulations where the enrichment in the models is varied. In previous measurements, the geometry was always known. ORNL is extending this method to situations where the geometry and materials present are not known in advance. In the new method, the interrogating neutrons are both time and directionally tagged, and an array of small plastic scintillators measures the uncollided interrogating neutrons. Therefore, the attenuation through the item along many different paths is known. By applying image reconstruction techniques, an image of the item is created which shows the position-dependent attenuation. The image permits estimating the geometry and materials present, and these estimates are used as input for the Monte Carlo simulations. As before, simulations predict the time distribution of induced fission neutrons for different enrichments. Matching the measured time distribution to the closest prediction from the simulations provides an estimate of the enrichment. This presentation discusses the method and provides results from recent simulations that show the importance of knowing the geometry and materials from the imaging system.

• 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: 1021995
• Resource Relation: Conference: INMM 52nd Annual Meeting, Desert Palm, CA (United States), 17-21 Nov 2011
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ATTENUATION
CALIBRATION
DETECTION
DISTRIBUTION
ENRICHMENT
ENRICHED URANIUM
FAST NEUTRONS
FISSION NEUTRONS
FORECASTING
GAMMA DETECTION
GEOMETRY
IMAGES
MATERIALS
MEETINGS
METALS
NEUTRONS
ORNL
PLASTIC SCINTILLATORS
SAFEGUARDS
SECURITY
SHIELDS
SURFACES
URANIUM
URANIUM 228
URANIUM 235
USES
Nuclear Criticality Safety Program (NCSP)
Uranium (U)
Enrichment Determination
Method
Results
Simulations
Imaging System