233U/236U signature allows to distinguish environmental emissions of civil nuclear industry from weapons fallout

Abstract

Isotopic ratios of radioactive releases into the environment are useful signatures for contamination source assessment. Uranium is known to behave conservatively in sea water so that a ratio of uranium trace isotopes may serve as a superior oceanographic tracer. Here we present data on the atomic 233 U/ 236 U ratio analyzed in representative environmental samples finding ratios of (0.1-3.7)Á10 À2 . The ratios detected in compartments of the environment affected by releases of nuclear power production or by weapons fallout differ by one order of magnitude. Significant amounts of 233 U were only released in nuclear weapons fallout, either produced by fast neutron reactions or directly by 233 U-fueled devices. This makes the 233 U/ 236 U ratio a promising new fingerprint for radioactive emissions. Our findings indicate a higher release of 233 U by nuclear weapons tests before the maximum of global fallout in 1963, setting constraints on the design of the nuclear weapons employed.

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

“…E) The Chernobyl accident. Pu from Chernobyl has been found in fallout over central Europe 25 Waters entering the Baltic Sea from the North Sea have 236 U/ 238 U and 233 U/ 236 U atomic ratios set by the balance of reprocessing discharge and global fallout 9,19 . As they distribute in the Baltic and mix with waters from various rivers, these ratios can be altered by addition from local sources of 236 U and 233 U (and minor 238 U in river waters).…”

“…This is several orders of magnitude higher than the 233 U/ 236 U atomic ratio in nuclear reactors, e.g., 1 × 10 -7 -1 × 10 − 6 in LH discharges 11 , which agrees well with reactor model calculations 12 . In the Irish Sea, an average 233 U/ 236 U atomic ratio of (0.12 ± 0.01) × 10 − 2 has been measured 9 , re ecting a dominant reactor signal released from SF. The use of the 233 U/ 236 U atomic ratio helps better distinguishing the origin of 236 U and since being radionuclides of the same element, the 233 U/ 236 U ratio will not be affected during the transport pathway.…”

“…This omnipresent fallout source can make identi cation of unreported sources of reactor 236 U challenging, because of methodological di culties in distinguishing the source of 236 U 9 . In addition, the 236 U/ 238 U ratio does not provide source information because of 238 U of natural origin is ubiquitous.…”

70-year anthropogenic uranium imprints of nuclear activities in Baltic Sea sediments

“…Recently, a 233 U- 236 U paired tracer system was proposed to identify emission sources of 236 U. 8,14,24 This is based on the fact that 233 U (t ½ = 0.16 Myr), another long-lived U isotope, was mostly released from nuclear weapons testing, while almost no 233 U is produced in commercial nuclear power reactors or reprocessing plants. 14 The representative 233 U/ 236 U atomic ratio of global-fallout signal was suggested to be (1.40 ± 0.15) × 10 -2 .…”

“…8,14,24 This is based on the fact that 233 U (t ½ = 0.16 Myr), another long-lived U isotope, was mostly released from nuclear weapons testing, while almost no 233 U is produced in commercial nuclear power reactors or reprocessing plants. 14 The representative 233 U/ 236 U atomic ratio of global-fallout signal was suggested to be (1.40 ± 0.15) × 10 -2 . 14 Discharge data of La Hague and reactor-modeling results indicate that 10 -8 -10 -6 is the representative level of 233 U/ 236 U atomic ratio for the reactor-related releases.…”