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2021 ANS Winter Meeting and Technology Expo
November 30–December 3, 2021
Washington, DC|Washington Hilton
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Nuclear Science and Engineering
Fusion Science and Technology
ORNL researchers employ extraction probe for rapid safeguards analysis
International nuclear safeguards verification relies on a precise count of isotope particles collected on swipes during International Atomic Energy Agency inspections of nuclear facilities and isolated through a series of lengthy chemical separations that can take about 30 days to complete. On October 15, Oak Ridge National Laboratory—a member of the IAEA’s Network of Analytical Laboratories (NWAL)—announced that analytical chemists at the site have developed a faster way to measure isotopic ratios of uranium and plutonium collected on swipes, which could help IAEA analysts detect the presence of undeclared nuclear activities or material.
Tony H. Shin, Michael Y. Hua, Matthew J. Marcath, David L. Chichester, Imre Pázsit, Angela Di Fulvio, Shaun D. Clarke, Sara A. Pozzi
Nuclear Science and Engineering | Volume 188 | Number 3 | December 2017 | Pages 246-269
Technical Paper | dx.doi.org/10.1080/00295639.2017.1354591
Articles are hosted by Taylor and Francis Online.
Neutron multiplicity counting (NMC) techniques are widely used for nuclear materials accountability and international safeguards applications to quantitatively evaluate characteristic properties pertaining to fissile material. Mathematical models for NMC moments have been previously derived for systems that use capture-based detectors; however, these models are not applicable when scatter-based detectors are used because of “neutron cross talk.” Neutron cross talk occurs when a single neutron scatters and deposits energy above threshold into multiple detectors causing spurious increase in multiplicity counts; this, in turn, has caused fissile mass to be overestimated when not treated. In this paper, we propose new mathematical models derived from point kinetics to correct for neutron cross-talk effects up to any arbitrary order N, where N denotes the maximum number of counts a single neutron can cause. The new models were used to estimate the fissile mass of plutonium metal and oxide samples with effective 240Pu mass ranging from 2.5 to 250 g. The adequacy of the models was confirmed using simulations of a conceptual scatter-based neutron multiplicity counter (e.g., organic scintillators) using MCNPX v2.7e with the PoliMi fission event generating extension. The fissile mass estimates with no correction for neutron cross-talk events yielded an average relative deviation from the true 240Pueff mass of 55.94% and 84.56% for metal and oxide samples, respectively. When neutron cross-talk events of order N = 2 are included in the model, the fissile mass estimates yielded an average relative deviation of 11.89% for metal and 13.21% for oxide samples. Accounting for neutron cross-talk events of order N = 3 resulted in fissile mass estimates with an average relative deviation of 9.58% and 10.51% for metal and oxide samples, respectively. These mass estimates were compared to a reference case (i.e., no neutron cross-talk effects) that yielded an average relative deviation of 6.81% and 4.77% for metal and oxide samples, respectively. The discrepancy between the estimates from the proposed model and the reference case is attributed to the assumed value of N, which sets a finite upper bound on the order of cross-talk events the model treats (i.e., the model for N = 3 assumes that a neutron will never cause more than three counts).