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

摘要

From time to time nuclear material is detected at a facility that is not obviously connected tothe known nuclear materials or activities of the site. More often than not, the material can betraced to operations that occurred decades earlier, sometimes before safeguards agreementswere 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 paperdescribes the process that starts with the ES data evaluation identifying the presence ofunexpected nuclear material. The data evaluation provides clues on the origin of the materialsuch as the uranium was irradiated several decades earlier, and the probable isotopic ratios ofthe LEU before irradiation. This information helps to focus the subsequent investigation ofthe safeguards records and to identify the source of the detected nuclear material. By using theState’s material transfer records and nuclear material verification data that fit the timeframeand nature of the detected material, the source of the nuclear material is eventually identifiedand confirmed.The case study illustrates the sensitivity of ES and that the detection of unexpected nuclearmaterial can often be resolved using a combination of evaluation methods, historic records,verification data and State declarations.