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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.
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V. Nizhnik, M. Pickrell SGTS/TND
Then Passive Multiplicity Analysis can be applied for precise U mass analysis
Uranium Metal Production Process
UF4 + 2 Mg Umetal + 2 MgF2
Product: Single U metal piece and burnt matrix material; both of known mass
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.
Conventional Passive Multiplicity Equations
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
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
Plutonium Scrap Multiplicity Counter
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
Rejected by Multiplicity Distribution analysis logic
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
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