The calculation of light element impurity (α, n) yield curves in a PuO₂ matrix and associated specific yield coefficients: Influence of the reaction cross sections

Journal Article · Sat Oct 22 00:00:00 EDT 2022 · Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment

DOI:https://doi.org/10.1016/j.nima.2022.167630· OSTI ID:1899014

Croft, Stephen ^[1]; McElroy, Jr., Robert D. ^[2]; Favalli, Andrea ^[3]

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1. Lancaster Univ., Bailrigg (United Kingdom)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
3. European Commission, Ispra (Italy). Joint Research Centre; Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Most of the Pu separated from irradiated commercial nuclear fuel is stored as PuO₂. The primary quantitative nondestructive measurement technique used to verify the amount of Pu in storage containers is passive neutron correlation counting. An important physical property of the oxide material is the ratio, α, of the rate of (α, n) neutrons produced inside the item to the rate of neutrons produced by spontaneous fission. This ratio influences the precision of the correlated counting method and affects the interpretation of the data because of how it changes both the primary total neutron production rate and the rate of induced fission events taking place inside the item. In addition to the main O(α, n) contribution, additional contributions come from α-particle interactions with light element impurities that are inevitably present. In this work, we calculate specific (α, n) yield coefficients, expressed in units of neutrons per second per gram of α-emitting nuclide per part per million by mass of the specified impurity element distributed in a pure PuO₂ matrix, for some key α-emitting actinides commonly present in reprocessed Pu (^238–242Pu+²⁴¹Am). These coefficients are directly applicable to nuclear safeguards verification work in which the α ratio is often calculated from the Pu-isotopic composition and chemical information obtained by other means. Further, they also provide a convenient up-to-date reference set against which values generated by other methods can be compared. Results are presented for impurities with atomic number from 3 to 17 inclusive, plus K and Fe. In most cases, these coefficients are not expected to change by more than 5%–10% at any time in the future. However, as new data become available, changes as large as 20% may be needed for some targets (e.g., F). The present yield calculations are limited by the general shortage of quality experimental total (α, n) reaction cross section data, which, together with unexplained variation between determinations, means that an objective and coherent evaluation is not possible. The situation is even less satisfactory for the partial differential cross section needed to calculate neutron spectra.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE; European Commission (EC)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1899014
• Journal Information: Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 1046, Issue A1046; ISSN 0168-9002
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

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46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
(𝛼
n) reactions
Passive neutron correlation counting
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