This presentation will explain why the burnup, initial enrichment, and cooling time of a used fuel assembly – collectively called the BIC set of variables – characterize it to first order for the purposes of nuclear-materials safeguards and burnup credit. From an analysis by basic nuclear engineering, it will be shown that the physical properties and the isotopic content of a used fuel assembly are basically three-dimensional vector spaces. Based on extensive referencing of the NDA literature, it will then be shown that the BIC variables are independent variables with respect to the physical properties and the isotopes. Therefore, the knowledge of all three BIC variables is a necessary condition for the accurate characterization of a used low- or high-enriched uranium (LEU or HEU) fuel assembly. Logically, then, it is necessary to make at least three independent NDA measurements to achieve a unique solution (characterization) if a reliance on information provided by the reactor operator is to be avoided. By this fact, the common question, ‘‘What is the accuracy of a particular NDA technique?’’ is revealed to be a poorly posed one with regard to used fuel assemblies. The result of this analysis is a better paradigm for interpreting and improving the NDA practice of both the safeguards community and the burnup-credit community.
Reference: This talk will be based substantially on my published paper: A. M. Bolind, “The use of the BIC set in the characterization of used nuclear fuel assemblies by nondestructive assay,” Annals of Nuclear Energy, Vol. 66 (2014), pp. 31-50.
Alan Bolind earned his Ph.D. degree in Nuclear Engineering, from the University of Illinois at Urbana-Champaign. He then held two successive post-doc appointments in Japan, at Ibaraki University and at the Japan Atomic Energy Agency (JAEA). His research at JAEA was on the science behind NDA techniques for characterizing used nuclear fuel assemblies for safeguards purposes. Since May 2014, he has been working as an Assistant Project Scientist in the Nuclear Engineering department at the University of California, Berkeley. His current main work is on the high-temperature corrosion of materials by liquid metals.
