IAEA Nuclear Material Round Robin: Summary of Results and Recommendations for Safeguards Laboratories

The International Atomic Energy Agency (IAEA) is responsible for independently verifying the nuclear material inventories in bulk handling facilities in States under safeguards. Part of the verification process includes the collection of representative nuclear material samples and the measurement of the key fissile isotopes in those samples at the IAEA Nuclear Material Laboratory (NML). The NML carries out almost all of the nuclear material sample analysis for the Department of Safeguards. Although the construction of a new NML building was completed in 2013, Member States also recommended that the Department of Safeguards enlarges its Network of Analytical Laboratories (NWAL) for nuclear material sample analysis in order to strengthen the quality assurance of the NML results and to provide a reliable backup to the NML should an unexpected shutdown occur. In 2013 the NML conducted a nuclear material ‘round robin’ among laboratories nominated for the nuclear materials NWAL qualification, as well as for laboratories that routinely process and measure such materials. Several sample types were selected for the round robin with the goal of assessing measurement precision and accuracy, and to judge against the 2010 version of the International Target Values reference. Measurement precision was assessed using U mixtures and Pu mixtures made from in-house standards. The mixtures were made to different atom ratios of U-235/U-238 and Pu-240/Pu-239 in order to represent analogues to typical inspection sample compositions. All thirteen participating laboratories utilized thermal ionization mass spectrometry for the determination of isotopic ratios. To more easily facilitate the shipment of the samples and to address specific sample preparation needs, the laboratories received either nanogram quantities of material pre-loaded on tungsten or rhenium filaments, or microgram quantities of dried U or Pu nitrates in TeflonTM containers. The accuracy of measurements was assessed using several different uranium certified reference materials and one plutonium certified reference material. Full results of the round robin test were presented and discussed with the participants during a Technical Meeting held in Vienna, Austria, 26-28 June 2013. A summary of the round robin results, lessons learned and recommendations are presented in this paper.