Nondestructive techniques for the assay of nuclear materials

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Non-destructive techniques for the assay of
nuclear materials

• Techniques developed at the Institute of
  Isotopesof the Hungarian Academy of Sciences

J. Zsigrai, N. C. Tam, L. Lakosi, J.
Bagi Institute of Isotopes, Budapest, Hungary
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Overview

• Novel methods for safeguardsand combating
  illicit trafficking
• Determining the matrix of Uranium samples using
  HRGS
• Gamma-spectrometric Uranium age dating
• Quantitative assay of PuBe neutron sources
• using HRGS
• using neutron counting
• A routine method
• Portable Spent Fuel Attribute Tester using MRGS
• Summary

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Relevant properties of nuclear material
1. Elemental and isotopic composition
235U, 238U, 239Pu
categorization
nuclear process
232U, 236U
2. Total NM content (mass)
3. Matrix
4. Age of the sample
All these properties give indications about the
origin of an unknown NM.
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Determining the matrix of Uranium samples
Based on gamma-spectrometric determination of
U-mass
Measuring the 1MeV gamma-line of 234mPa (daughter
of 238U)

• correcting accurately for self-absorption

• corrected intensity at 1MeV mass of 238U

• mass of 238U enrichment

total U mass

• calibrating the system with a reference U-set

Homogeneous, pellet- or powder-form material
accuracy lt2
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Determining the matrix of Uranium samples
What is the matrix?

• based on the accuracy of the Uranium-mass
  measurement

UO
0,881
2
mU/mtotal
U
0,848
O
3
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Measurement number
Fig. 1. (U-mass)/(Total mass) ratios for
different Uranium compounds
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Uranium age dating using HRGS
Age time since last chemical separation /
enrichment
initially no daughters of U are present in the
sample
First use of a gamma-spectrometric method for
uranium age datingrelevant to safeguards and
combating illicit trafficking.

• Advantages of gamma-spectrometry
• non-destructive
• no special sample preparation needed
• relatively simple equipment

Based on the ratio of the activity of 226Ra
(214Bi) to 234U
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Uranium age dating using HRGS

• Measuring the activity of 214Bi
• By a coaxial Ge detector
• In a low-background iron chamber
• 609keV line of 214Bi
• Relative to 238U (intrinsic efficiency-calibration
  )

• Radon not a real problem
• further studies to improve precision

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Uranium age dating using HRGS

• Measuring the activity of 234U
• By a planar LEGe detector
• Standard methods are not satisfactory
• MGAU, U235
• large systematic errors, especially for smaller
  amounts of NM
• Our method variant of intrinsic
  efficiency-calibration
• Using 121keV of 234U 143keV, 163kev,
  186keV, 205keV of 235U

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Uranium age dating using HRGS
Age

• Age of a HEU (90) sample (inter-comparison
  exercise, 2001)

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Uranium age dating using HRGS
Sensitivity of the present equipment
Detector efficiency at 609keV 0.5

• difficulties with LEU samples

Calculated intensity of the 609keV line of 214Bi
in our 150cm3 coaxialdetector, coming from 10g
of UO2 pellets of various enrichments
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Quantitative Assay of Plutonium-Beryllium Neutron
Sources

• Large number (200) of PuBe neutron sources
  leftfrom industrial applications
• The Pu-content has to be
• accounted for, reported to and inspected by IAEA
• Unreliable data declared neutron
  output undeclared Pu-content

• Determining the Pu content two independent
  methods
• Gamma-spectrometry
• Neutron coincidence counting

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Quantitative Assay of Plutonium-Beryllium Neutron
Sources

• 1. Gamma-spectrometry

0 - 600 keV
0 5 MeV
Gamma-spectra of a PuBe source
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Quantitative Assay of Plutonium-Beryllium Neutron
Sources

• 1. Gamma-spectrometry
• Isotopic composition
• Intrinsic calibration method (MGA code)
• Insensitive to the neutron-induced background
• Total Pu-content
• Evaluating 375keV and 413keV peaks of 239Pu
• absorption correction method
• accuracy 5 in favorable case 15 in
  worst case
• 129keV effective geometry of the source
• Sufficient for safeguards purposes

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Quantitative Assay of Plutonium-Beryllium Neutron
Sources
Results of the gamma-spectrometric measurements
Nominal from the declared neutron yield,
assuming pure 239Pu (basis of present
bookkeeping)
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Quantitative Assay of Plutonium-Beryllium Neutron
Sources

• 2. Neutron coincidence counting
• 14 3He tubes around the source
• home-made electronics, commercial shift register
  JSR11

Moderator

• Coincidence neutrons from
• n-induced fission of Pu
• 9Be(n, 2n)8Be reaction
• spontaneous fissionof Pu (negligible)

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Quantitative Assay of Plutonium-Beryllium Neutron
Sources

• 2. Neutron coincidence counting
• Total Pu-content
• Calibration is required (coincidence
  counts)/(total counts) ? Pu-mass

• Isotopic ratios of 239Pu and 240Pu
• (Total counts) T
• T(R/T,239Pu/Pu,240Pu/Pu)

Fig. Pu-mass as a functionof the ratio of
coincidencecounts (R) to total counts (T)
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Portable Spent Fuel Attribute Tester
In the spent fuel pond of Paks NPP
Cable to MMCA 166
Steel wire

• Detection of unreported irradiation when CVD is
  not usable
• Assistance to IAEA inspectors
• Attributes for SFCs-134, Cs-137,Zr-Nb-95,
  Ce-Pr-144

Container with CdZnTe detector
Modular collimator tubefilled with air
?
Assemblies (spent fuel, Co-containers, absorbers)
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Summary

• Novel methods
• Determining the matrix of Uranium samples using
  HRGS
• Based on high-precision measurement of total
  U-content
• Uranium age dating using HRGS
• The first use of a gamma-spectrometric method
• Quantitative assay of PuBe neutron sources using
• HRGS
• neutron counting
• A standard method
• Portable Spent Fuel Attribute Tester using MRGS
• Hungarian implementation of a widely used concept
• Routinely used at the nuclear power plant Paks