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Abstract
Uranium is one of the nuclear materials that is subject to the international nuclear safeguards. The nuclear safeguards system has to be implemented for verification and characterization of nuclear materials. Verification and characterization of nuclear materials necessitate a measurement system capable of measuring all nuclear materials existing in the whole nuclear fuel cycle, or at least all parts of nuclear fuel cycle exit in state. An absolute non-destructive assay technique has been investigated in this work to verify the 235U mass content in different nuclear material samples with different chemical composition. The most intense γ-rays signature at 185.7 keV emitted after α-decay of the 235U nuclei was measured by using Hyper Pure Germanium detector (HPGe- spectrometer). These measurements with combination of mathematical calculation were used for determination of the full energy peak efficiency of the spectrometer. General Monte Carlo transport code (MCNP5) method was applied in this study using the obtained data to estimate the 235U mass content in different nuclear material (NM) samples. This method was applied on standard nuclear material with known of 235U mass content in the standard material. In this study, relative measurements method has also been used a non destructive assay technique to verify the 235U mass content. The technique depends on the calibration curve of the used planer, high purity germanium - γ ray spectrometer. The results of this method showed that the 235U mass content of nuclear material could be verified with an accuracy ranges from -1.85% to 0.24 %.
Due to the relatively low energies and/or low specific activities of γ-rays emitted from uranium isotopes, in some cases, the acquisition of the γ spectrum could be has lengthy procedures. Moreover, due to relatively high density of uranium compounds; the γ-attenuation within the sample can be significant, which requires the estimation of some correction factors that may add a notable contribution to the uncertainty of the experimental results. For such cases, NM assay technique by neutron detection may be preferred. The present study a coincidence neutron detector [Active Well Coincidence Counter (AWCC)] was used in relative method to investigation the possibility of estimtion the 235U mass content in nuclear material samples. The measurements were applied to estimate the 235U mass content in Standard Nuclear Materials (SNM) with different enrichment values.