Nuclear, chemical, and physical characterization of nuclear materials

Management of Radioactive Waste from HTGR Reactors including Spent TRISO Fuel—State of the Art

In light of the increasing demand for energy sources in the world and the need to meet climate goals set by countries, there is growing global interest in high temperature gas cooled reactors (HTGRs), especially as they are known to be inherently safe nuclear reactors. The safety of HTGRs results, among other, from the nature of the nuclear fuel used in them in the form of coated TRISO particles (tri-structural-isotropic) and the reduction of the total amount of radioactive waste generated. This paper reviews numerous methods used to ensure the sustainable, feasible management and long-term storage of HTGR nuclear waste for the protection of the environment and society. The types of waste generated in the HTGR cycle are presented as well as the methods of their characterization, which are important for long-time storage and final disposal. Two leading nuclear fuel cycle strategies, the once-through cycle (direct disposal or open cycle) and the twice-through cycle (recycling or partially closed cycle), are discussed also in relation to TRISO spent fuel. A short review of the possibilities of treatment of TRISO spent nuclear fuel from HTGR reactors is made.

Identification of uranium signatures relevant for nuclear safeguards and forensics

The paper describes the applicability of different characteristics (signatures) in nuclear safeguards and forensics for assessment of uranium material provenance in terms of production process. The study follows a uranium ore concentrate production from an ore to a U₃O₈ product. It turned out that rare-earth elemental pattern, radiochronometry (age of ore body and material production date), sulphur and organic impurities are useful to find out the origin or history of the material, while certain trace-elements and isotopics of Pb or Sr were found to be inconclusive. The results will be important to understand the signatures in nuclear safeguards and forensics.

Nuclear forensic analysis of a non-traditional actinide sample

Nuclear forensic publications, performance tests, and research and development efforts typically target the bulk global inventory of intentionally safeguarded materials, such as plutonium (Pu) and uranium (U). Other materials, such as neptunium (Np), pose a nuclear security risk as well. Trafficking leading to recovery of an interdicted Np sample is a realistic concern especially for materials originating in countries that reprocesses fuel. Using complementary forensic methods, potential signatures for an unknown Np oxide sample were investigated. Measurement results were assessed against published Np processes to present hypotheses as to the original intended use, method of production, and origin for this Np oxide.

Validation of reference materials for uranium radiochronometry in the frame of nuclear forensic investigations

The results of a joint effort by expert nuclear forensic laboratories in the area of age dating of uranium, i.e. the elapsed time since the last chemical purification of the material are presented and discussed. Completely separated uranium materials of known production date were distributed among the laboratories, and the samples were dated according to routine laboratory procedures by the measurement of the (230)Th/(234)U ratio. The measurement results were in good agreement with the known production date showing that the concept for preparing uranium age dating reference material based on complete separation is valid. Detailed knowledge of the laboratory procedures used for uranium age dating allows the identification of possible improvements in the current protocols and the development of improved practice in the future. The availability of age dating reference materials as well as the evolvement of the age dating best-practice protocol will increase the relevance and applicability of age dating as part of the tool-kit available for nuclear forensic investigations.