ABACC's Experience On Using Medium Resolution Gamma-ray Spectrometry Based On Lanthanum Bromide Detectors For Uranium Enrichment Measurements

Verification of the declared uranium enrichment is routinely performed by nuclear safeguards inspectorates during on-site inspections at bulk handling facilities, in particular commercial fuel fabrication, conversion and enrichment plants. Non-destructive assay (NDA) methods have been used for several years for prompt obtention of results whenever their performances are able to fulfill applicable acceptance criteria. For decades the most frequently used methods were based on high- and low-resolution gamma-ray spectroscopy (HRGS or LRGS) using high-purity germanium (HPGe) semiconductor and sodium iodide (NaI) scintillation detectors, respectively. Since 2016, Cerium-doped Lanthanum Bromide (LaBr3(Ce)) scintillation detectors have been tested and approved for regular use during safeguards inspections in Argentinean and Brazilian nuclear facilities conducted by the Brazilian-Argentine Agency for Accounting and Control of Nuclear Materials (ABACC) and the International Atomic Energy Agency (IAEA). This medium-resolution (MRGS) method offers the same usability (detector size and operation at room temperature) and efficiency, but with better stability and energy resolution than low-resolution (LRGS) with NaI detectors. For spectra evaluation and calculation of the uranium enrichment results, the NaIGEM code has been used (A guide for using NaIGEM code, version 1.5 for DOS and Windows, 2001; Nucl. Instr. and Meth. A 458 (2001) 196). The goal of this paper is to present the measurement performance observed by ABACC on actual field applications and comparing it with typical performance values achievable with LRGS. The results indicate that some applications may benefit from the new method, whereas some others have not yet experienced a significant quality improvement.