Study on the performance of some non-destructive methods to estimate the uranium enrichment in nuclear materials

Abstract

Abstract 235U enrichment determination is one of the most important characteristics for nuclear materials verification. This paper focuses on the investigation of applicability and performance evaluation of two non-destructive methods, viz: the multi-group γ-ray analysis method for uranium (MGAU) and another method based on Monte Carlo simulation code (MCNP). The MGAU is the most widely applied non-destructive γ-ray spectrometry method. Its applicability and performance have been investigated, evaluated and compared with the MCNP method. The investigated samples in our work are U3O8 and UO2. The emitted gamma rays from these samples were measured using a planar high-purity germanium detector (HPGe) of high-resolution. Based on the measured gamma spectra, the MGAU method was used to estimate 235U enrichment of the measured samples through analysis of the net area under the peak of energy 185.7 keV. At the same time, the MCNP method based on the calculated full energy peak efficiency (FEPE) has been suggested to carry out the 235U enrichment calculations. Comparing the obtained results of both MGAU and MCNP with the reference values, it was concluded that the MGAU shows acceptable performance for enrichment measurements, but it gives non-accurate and erroneous results. However, the measurements have been done for a long time, its results of a maximum difference up to 16%; especially for shielded and low 235U amount samples. In addition to that, this method has some limitations and weaknesses coming from its requirements for prior system calibration with standard references having the same geometry as the assayed items. Besides, the dependence of its analysis algorithms on the x-ray region of interfering peaks is dependent on the detector performance as a function of its resolution. On the other side, the performance of MCNP results reveals a good agreement with the enrichments reference values within maximum difference up to 5%.