Isotopic composition of Uranium in soil and ground water samples collected around 30 km Chernobyl Exclusion Zone

Abstract

Abstract. Precise and accurate measurement of uranium isotope ratio is essential in environmental monitoring of any contamination in nuclear safeguards. 234 U, 235 U and 238 U are naturally occurring alphaemitting long-lived radionuclides, which are taken up daily at low levels with food and drinking. IUPAC has established natural isotopic composition of 235 U/ 238 U to be 0.00725. Therefore, isotope ratio measurements are important to provide information on the origin of uranium. The isotope ratios of uranium, 234 U/ 238 U, 235 U/ 238 U and 236 U/ 238 U were measured using a VG Sector 54 thermal ionization mass spectrometer (TIMS) as well as high resolution inductively coupled plasma mass spectrometry (ICP-MS) in soil samples as well as in some water samples collected in the exclusion zone of Chernobyl nuclear power plant. The isotopic composition of Chernobyl soil samples showed significant deviation from the natural uranium and presence of 236 U is quite noticeable. The 234 U/ 238 U activity ratio varies in the range 1.06 to 2.1 and 1.42 to 5.75 for soil and water samples, respectively. Enrichment of 235 U was also noticeable for soil as well as ground water samples.

Isotopic evidence of natural uranium and spent fuel uranium releases into the environment

“…1,2 Accidental releases involving nuclear fuels have been studied using isotopes measured in soils and plants after the criticality accident in Tokai-mura [3][4][5] or the Chernobyl explosion. 6,7 The consequences of the routine release from nuclear facilities (namely uranium-enrichment and nuclear fuel fabrication plants) have also been investigated in the air and in the surrounding plants with uranium isotopes. [8][9][10] The main difficulty when quantifying uranium released into the environment arises from the precision needed to detect a small amount of enriched or depleted 235 U above the background.…”

“…However, the determination of 236 U concentration in an environmental matrix using Sector Field-ICPMS or Multi-Collector-ICPMS has recently allowed this difficulty to be overcome. 6,[11][12][13] Indeed this isotope is formed as a result of neutron capture during irradiation in nuclear reactors. Low 236 U/ 238 U ratios are expected from earth surface samples ( 236 U/ 238 U in order of 10 À14 ), whereas spent nuclear fuel exhibits high 236 U/ 238 U ratios reaching 10 À2 depending on the reactor type and burn-up history.…”

Elemental and Isotopic Mass Spectrometry

“…In the same way, determination of tomatoes (berries, "passata," tinned tomatoes, sauce, double and triple concentrate) geographical origin is made by virtue of different 87 Sr/ 86 Sr ratios and δ‰ values [315]. Therefore, isotope ratio measurements are important to provide information on the origin of uranium [318]. Furthermore, differentiation of cattle's beef geographical origin, located in 12 different European regions within France, Germany, Greece, Ireland, Italy, Spain, and the UK has been managed by strontium isotope ratio 87 Sr/ 86 Sr variations [317].…”