A previously unknown source of reactor radionuclides in the Baltic Sea, identified by 233, 236, 238U and 127, 129I multi-fingerprinting

Abstract

We present the first application of multi-isotopic fingerprints (i.e., 236U/238U, 233U/236U, 236U/129I and 129I/127I) for the discovery of unrevealed radioactive sources. Our data indicate that, besides the reactor signature from the two European reprocessing plants and global fallout signature, there must be a previously undiscovered additional reactor 236U source in the Baltic Sea. This reactor 236U may come from unreported discharges from nuclear research facilities in Sweden, or it may come from accidental leakage from disposal of spent nuclear fuel on the Baltic seafloor, either reported or unreported. Such leakage would indicate potential problems with the safety of seafloor disposal, and may be accompanied by leakage of other radionuclides. The results demonstrate the high sensitivity of the multi-isotopic tracer systems, especially the newly accessible 233U/236U signature, to distinguish environmental emissions of unrevealed historical or present radioactive releases for nuclear safeguard and emergency preparedness, as well as tracing environmental processes from the releasing sites.

The Potential of 233U/236U as a Water Mass Tracer in the Arctic Ocean

“…Lowest concentrations of 236 U and 233 U may indicate the relative increase of the natural (pre‐anthropogenic) U signal, with estimated, but never measured, values below 10 4 at/kg for both radionuclides (Peppard et al., 1952; Steier et al., 2008). The highest values clearly reflect the presence of anthropogenic U, with 236 U and 233 U concentrations at levels of 10 7 and 10 5 at/kg, respectively (Qiao, Hain, & Steier, 2020; Qiao, Zhang, et al., 2020). 233 U/ 236 U atom ratios show a very large variation, moving from (0.34 ± 0.16) × 10 −2 to values above 10 × 10 −2 .…”