1 / 10

Passive Neutron Assay of Uranium Mass Measurements in Scraps and Wastes

Passive Neutron Assay of Uranium Mass Measurements in Scraps and Wastes. V. Nizhnik, M. Pickrell SGTS/TND. Conventional Passive Multiplicity. Passive multiplicity is based on a theoretical hierarchy called the Point Model So named, because it is a zero dimensional.

freira
Download Presentation

Passive Neutron Assay of Uranium Mass Measurements in Scraps and Wastes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Passive Neutron Assay of Uranium Mass Measurements in Scraps and Wastes V. Nizhnik, M. Pickrell SGTS/TND

  2. Conventional Passive Multiplicity • Passive multiplicity is based on a theoretical hierarchy called the Point Model • So named, because it is a zero dimensional. • Therefore, spontaneous fission, multiplication, and alpha-n production are UNIFORM across the sample. • Therefore, the sample nuclear material is evenly distributed in a homogenous matrix.

  3. The Modification Necessary to Measure Uranium Wastes • What happens when the material is not uniform and evenly distributed? • The conventional method develops a bias error. • This work developed a modification of the Point Model / Passive Multiplicity equations to analyze non-uniform, inhomogeneous samples. • Applied to uranium wastes with metal ingots mixed with diffuse oxide powder.

  4. Passive Multiplicity (PM) Assumptions Kill this slide • Homogeneous distribution of nuclear material through an item matrix material • The same chemical form of Uranium material in the item, i.e. uniform (a,n)-neutron production rate in the item volume • Uniform physical property of uranium material (mostly concerns material density) • If item properties are in compliance with listed statement: • all the neutrons are equal in the term of multiplication • Alpha parameter is the same for any point of item material Then Passive Multiplicity Analysis can be applied for precise U mass analysis

  5. Wastes: “Close Look” Example Uranium Metal Production Process Ideal Case UF4 + 2 Mg  Umetal + 2 MgF2 Product: Single U metal piece and burnt matrix material; both of known mass In reality UF4 + 2 Mg  X·Uchunks + Y·UF4 + Z·MgF2 + W·Mg Product: Number of U metal chunks, un-burnt UF4 in un-burnt Mg+MgF2 matrix. Their mas ratios are unknown. • Impact on Neutron Multiplicity: • Non-homogeneous distribution of U material • Multi-component chemical composition • Unknown mass ratio for uranium material components • Non-uniform (a,n)-neutron production rate • Spatial dependent neutron multiplication

  6. Passive Multiplicity Conventional Passive Multiplicity Equations Long Crocs Modified Passive Multiplicity Assumptions and known parameters: Assign: x –U metal fraction in total U mass in item Then: (1-x) – fraction of UF4 in total U mass in item U metal chunks are pure: no (a,n)-neutrons production (a = 0) Dispersed un-burnt UF4 material in Mg+MgF2 matrix is non-multiplying media due to low density (M = 1) Alpha value for UF4 is known, based on U isotopic information

  7. Modified Passive Multiplicity UF4 term U metal term M – multiplication in the metal chunks x – U metal fraction in total U mass in item mU – total U mass in measured item • Corrects for non-uniform distribution of multi-component Uranium material • Determines total Uranium mass in measured item • Determines U mass in metal and UF4 form • Determines neutron Multiplication in metal phase (gives information on average metal chunks size)

  8. Example of U Waste Measurements • Counter: • Efficiency 55%: allows fast acquisition of neutron multiplicity data with good statistics • Size of the measurement cavity: d=20cm, h=42cm • Items: • 34 Uranium waste items with various Gross Weight (up-to 30kg) • Packed in Poly bags to fit in the measurement cavity • Target total uncertainty: • Not more than 2.3% for 1 Sigma confidential interval Plutonium Scrap Multiplicity Counter

  9. Rejection of Cosmic Rays Bursts Cosmic rays prompt neutron “bursts” when interacting with High-Z (Uranium) material nuclei; they produce high multiplicities of detected neutron and affect counting rates. Cycle-by-Cycle Multiplicity Distribution Rejected by RSD based rejection logic Good Cycle Bad Cycle Good Cycle Rejected by Multiplicity Distribution analysis logic

  10. Analysis with Modified PM Theoretical bias of Conventional vs Modified PM for NU U metal average multiplication: M=1.05 UF4 Alpha value a=3.85 Conventional vs Modified Method Results Measurement of a batch of uranium waste items (individual item U mass and Total U mass) Relative content of UF4(1-x) Bias of Total U mass in the measured batch Theoretical Bias The bias is higher in case of analysis of enriched Uranium since values of Multiplication in metal phase and Alpha in UF4 phase are higher then for natural Uranium

More Related