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Non-destructive techniques for the assay of nuclear materials

Non-destructive techniques for the assay of nuclear materials. Techniques developed at the Institute of Isotopes of the Hungarian Academy of Sciences. J. Zsigrai , N. C. Tam, L. Lakosi, J. Bagi Institute of Isotopes, Budapest, Hungary. Overview.

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Non-destructive techniques for the assay of nuclear materials

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  1. 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

  2. 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

  3. 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.

  4. 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 <2%

  5. 1.0 0.9 0.8 0.7 0,5613 U- acetate 0.6 U-nitrate 0,474 0.5 0.4 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 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 8 Measurement number Fig. 1. (U-mass)/(Total mass) ratios for different Uranium compounds

  6. 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-spectrometricmethod 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

  7. 234U 230Th 226Ra 222Rd 218Po 214Pb 214Bi 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

  8. 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

  9. Uranium age dating using HRGS “Age” • Age of a HEU (~90%) sample (inter-comparison exercise, 2001)

  10. 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

  11. 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 outputundeclared Pu-content • Determining the Pu content: two independent methods • Gamma-spectrometry • Neutron coincidence counting

  12. Quantitative Assay of Plutonium-Beryllium Neutron Sources 1. Gamma-spectrometry 0 - 600 keV 0 – 5 MeV Gamma-spectra of a PuBe source

  13. 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

  14. 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)

  15. Neutron detectors (3He tubes) PuBe sampleholder 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)

  16. 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)

  17. 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 SF:Cs-134, Cs-137,Zr-Nb-95, Ce-Pr-144 Container with CdZnTe detector Modular collimator tubefilled with air ? Assemblies (spent fuel, Co-containers, absorbers)

  18. 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

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