Investigating the Ghost of Past Activities: An Environmental Sampling Case Study

From time to time nuclear material is detected at a facility that is not obviously connected to the known nuclear materials or activities of the site. More often than not, the material can be traced to operations that occurred decades earlier, sometimes before safeguards agreements were in effect. This paper will present such a case where slightly irradiated, low enriched uranium (LEU) was unexpectedly detected at a facility through environmental sampling (ES). The paper describes the process that starts with the ES data evaluation identifying the presence of unexpected nuclear material. The data evaluation provides clues on the origin of the material such as the uranium was irradiated several decades earlier, and the probable isotopic ratios of the LEU before irradiation. This information helps to focus the subsequent investigation of the safeguards records and to identify the source of the detected nuclear material. By using the State’s material transfer records and nuclear material verification data that fit the timeframe and nature of the detected material, the source of the nuclear material is eventually identified and confirmed. The case study illustrates the sensitivity of ES and that the detection of unexpected nuclear material can often be resolved using a combination of evaluation methods, historic records, verification data and State declarations.