Reading the Information Inherent to Uranium Materials

Abstract

Uranium materials hold more information than normally exploited for safeguards evaluation purposes. The information inherent to the material arises from the isotopic, physical or chemical properties of the sample. Retrieving such additional information is of growing importance in nuclear safeguards, and of fundamental importance to nuclear forensics and environmental sciences. For example, the measurements of minor isotope abundance ratios of uranium in micrometer sized particles collected at nuclear facilities may be used to (1) substantiate equipment or plant design modifications, (2) indicate information about irradiation history, or (3) evaluate mixing, and decay scenarios. Furthermore the isotopic information inherent to uranium materials is also of relevance in geochemistry and earth sciences. Uranium series dating is one such tool that can be applied in such different fields as climate change, seismic hazard, archaeology, and volcanology. The chemical impurities in uranium samples may be native to the ore or process-inherited. In nuclear forensics, the chemical impurities may provide a wealth of information on the provenance of the material and the process it was subjected to. Reliable measurements of trace element concentrations and minor isotope ratios in uranium and the interpretation of the data are the basis for exploiting this source of information. With regard to the minor abundance ratios of uranium and impurities in uranium materials, there is a continuing effort invested by safeguards authorities , manufacturers, research institutes and analytical laboratories in improved measurement techniques, procedures, quality control and reference materials. These two specific topics, measurement of minor isotopes and chemical impurities in uranium materials, were addressed in two dedicated workshops organised by the ESARDA Working Group on Standards and Techniques for Destructive Analysis (WG DA) together with the IAEA. Participants in these workshops included representatives from the main European and international nuclear safeguards organisations and nuclear measurement laboratories, as well as fuel manufacturers and experts from geochemistry and environmental sciences institutes. This paper provides a synthesis of the workshop recommendations on protocols for sample collection, sample preparation, analytical methods, data evaluation techniques, quality control and reference materials for measurements of minor isotopes and impurities in uranium samples. Performance recommendations are also proposed, complementing the current set of International Target Values for Measurement Uncertainties of Nuclear Material for Safeguards.