Search

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvären bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition ( 238 Pu, 239 Pu, 240 Pu, 241 Pu, 242 Pu, and 244 Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239 Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244 Pu/ 239 Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 ± 0.31)·10 -5 . In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244 Pu/ 239 Pu ratio of (1.51 ± 0.11)·10 -4 , indicating the possible impact of the first US thermonuclear tests (1952-1958).

In this work we present and evaluate a radiochemical procedure optimised for the analysis of 236 U and 239,240 Pu in seawater samples by Accelerator Mass Spectrometry (AMS). The method is based on Fe(OH) 3 co-precipitation of actinides and uses TEVA® and UTEVA® extraction chromatography resins in a simplified way for the final U and Pu purification. In order to improve the performance of the method, the radiochemical yields are analysed in 1 to 10 L seawater volumes using alpha spectrometry (AS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Robust 80% plutonium recoveries are obtained; however, it is found that Fe(III) concentration in the precipitation solution and sample volume are the two critical and correlated parameters influencing the initial uranium extraction through Fe(OH) 3 co-precipitation. Therefore, we propose an expression that optimises the sample volume and Fe(III) amounts according to both the 236 U and 239,240 Pu concentrations in the samples and the performance parameters of the AMS facility. The method is validated for the current setup of the 1 MV AMS system (CNA, Sevilla, Spain), where He gas is used as a stripper, by analysing a set of intercomparison seawater samples, together with the Laboratory of Ion Beam Physics (ETH, Zürich, Switzerland). [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the potential of combining the conservatively behaving anthropogenic radionuclides 236U and 237Np to gain information on the origin of water masses tagged with liquid effluents from Nuclear Reprocessing Plants. This work includes samples collected from three full-depth water columns in two areas: i) the Arctic Ocean, where Atlantic waters carry the signal of Sellafield (United Kingdom) and La Hague (France) nuclear reprocessing facilities; and ii) the western Mediterranean Sea, directly impacted by Marcoule reprocessing plant (France). This work is complemented by the study of the particle-reactive Pu isotopes as an additional fingerprint of the source region. In the Canada Basin, Atlantic waters showed the highest concentrations and 237Np/236U ratios in agreement with the estimated values for North Atlantic waters entering the Arctic Ocean and tagged with the signal of European Nuclear Reprocessing Plants. These results may reflect the impact of the documented releases for the 1990s. In the Mediterranean Sea, an excess of 236U presumably caused by Marcoule is reflected in the lower 237Np/236U ratios compared to the Global Fallout signal in all the studied samples. On the contrary, the 239,240Pu profiles were mainly governed by the Global Fallout. The impact of Marcoule as a local source is further corroborated when comparing the temporal evolution of these ratios between 2001 and 2013. The lowest 237Np/236U ratios observed in 2001 at the surface reflect a previous local input that is no longer observed in 2013 as it had been homogenized through the whole water column. This work presents the use of 237Np as a new ocean tracer. A more accurate characterization of the main sources is still needed to optimize the use of 236U-237Np as a new tool to understand transient oceanographic processes. Unlabelled Image • 236U, 237Np and 239,240Pu investigated in three full-depth water columns by AMS. • Study of two regions impacted by nuclear reprocessing facilities. • Different 237Np/236U ratios in the Arctic Ocean and the Mediterranean Sea. • 240Pu/239Pu: values close to global fallout in both sampling regions. • 237Np 236U dual tracer is investigated as fingerprint to constrain sources. [ABSTRACT FROM AUTHOR]