Plutonium Signatures in a Dated Sediment Core as a Tool to Reveal Nuclear Sources in the Baltic Sea

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tva''ren bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, oPu, 241Pu, 242Pu, and 244Pu) 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 239Pu, 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 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 +/- 0.31)center dot 10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 +/- 0.11)center dot 10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958).

Automated summary

The distribution of plutonium in a sediment core from Tva''ren bay in Sweden was analyzed to determine its origin and the history of aquatic release from the Studsvik nuclear facility. The results revealed highly enriched 239Pu, likely from the Swedish nuclear program and the handling of high burn-up nuclear fuel. The analysis of isotopes also suggested the impact of US thermonuclear tests in the 1950s on the sediment.