TY - JOUR

T1 - Identification of a chemical fingerprint linking the undeclared 2017 release of 106Ru to advanced nuclear fuel reprocessing

AU - Cooke, Michael W.

AU - Botti, Adrian

AU - Zok, Dorian

AU - Steinhauser, Georg

AU - Ungar, Kurt R.

N1 - Funding Information: ACKNOWLEDGMENTS. M.W.C. and K.R.U. thank Dr. Andreas Bollhöfer (Bun-desamt für Strahlenschutz) and Dr. Johan Kastlander (Totalförsvarets for-skninginstitut) for provision of filter samples. D.Z. and G.S. acknowledge financial support from VolkswagenStiftung. Publisher Copyright: © 2020 National Academy of Sciences. All rights reserved. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/6/30

Y1 - 2020/6/30

N2 - The undeclared release and subsequent detection of ruthenium-106 (106Ru) across Europe from late September to early October of 2017 prompted an international effort to ascertain the circumstances of the event. While dispersion modeling, corroborated by ground deposition measurements, has narrowed possible locations of origin, there has been a lack of direct empirical evidence to address the nature of the release. This is due to the absence of radiological and chemical signatures in the sample matrices, considering that such signatures encode the history and circumstances of the radioactive contaminant. In limiting cases such as this, we herein introduce the use of selected chemical transformations to elucidate the chemical nature of a radioactive contaminant as part of a nuclear forensic investigation. Using established ruthenium polypyridyl chemistry, we have shown that a small percentage (1.2 ± 0.4%) of the radioactive 106Ru contaminant exists in a polychlorinated Ru(III) form, partly or entirely as β-106RuCl3, while 20% is both insoluble and chemically inert, consistent with the occurrence of RuO2, the thermodynamic endpoint of the volatile RuO4. Together, these findings present a clear signature for nuclear fuel reprocessing activity, specifically the reductive trapping of the volatile and highly reactive RuO4, as the origin of the release. Considering that the previously established 103Ru:106Ru ratio indicates that the spent fuel was unusually young with respect to typical reprocessing protocol, it is likely that this exothermic trapping process proved to be a tipping point for an already turbulent mixture, leading to an abrupt and uncontrolled release.

AB - The undeclared release and subsequent detection of ruthenium-106 (106Ru) across Europe from late September to early October of 2017 prompted an international effort to ascertain the circumstances of the event. While dispersion modeling, corroborated by ground deposition measurements, has narrowed possible locations of origin, there has been a lack of direct empirical evidence to address the nature of the release. This is due to the absence of radiological and chemical signatures in the sample matrices, considering that such signatures encode the history and circumstances of the radioactive contaminant. In limiting cases such as this, we herein introduce the use of selected chemical transformations to elucidate the chemical nature of a radioactive contaminant as part of a nuclear forensic investigation. Using established ruthenium polypyridyl chemistry, we have shown that a small percentage (1.2 ± 0.4%) of the radioactive 106Ru contaminant exists in a polychlorinated Ru(III) form, partly or entirely as β-106RuCl3, while 20% is both insoluble and chemically inert, consistent with the occurrence of RuO2, the thermodynamic endpoint of the volatile RuO4. Together, these findings present a clear signature for nuclear fuel reprocessing activity, specifically the reductive trapping of the volatile and highly reactive RuO4, as the origin of the release. Considering that the previously established 103Ru:106Ru ratio indicates that the spent fuel was unusually young with respect to typical reprocessing protocol, it is likely that this exothermic trapping process proved to be a tipping point for an already turbulent mixture, leading to an abrupt and uncontrolled release.

KW - Nuclear forensics

KW - Polypyridyl complex

KW - Radiochemistry

KW - Ruthenium

UR - http://www.scopus.com/inward/record.url?scp=85086148431&partnerID=8YFLogxK

U2 - 10.1073/pnas.2001914117

DO - 10.1073/pnas.2001914117

M3 - Article

C2 - 32541038

AN - SCOPUS:85086148431

VL - 117

SP - 14703

EP - 14711

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

SN - 0027-8424

IS - 26

ER -