E. Holm

Origin and isotopic ratios of plutonium in the Barents and Greenland Seas

Abstract Isotopic ratios 238 Pu/ 239 + 240 Pu and 241 Pu/ 239 + 240 Pu vary depending on the source of the Pu. The values for samples contaminated from distinct sources can be compared with those affected only by global fallout. The present study reports isotopic ratios determined radiochemically in samples collected in the Barents and Greenland Seas during the Swedish Arctic Expedition “YMER 80”. Long-range transport and transfer factors of plutonium from European nuclear fuel reprocessing facilities into the Arctic Ocean were evaluated. About 80% of the plutonium released in dissolved form from such facilities is removed by sedimentation processes before reaching the Barents and Greenland Seas.

Radiochemical measurements of99Tc: Sources and environmental levels

A method of99Tc determination has been developed based on sample decomposition followed by purification from interfering elements by hydroxide and oxide precipitations. Technetium is extracted by TBP and electrodeposited onto stainless steel discs from sodium hydroxide solution.99Tcm is used as yield monitor. The method has been applied to study releases from different sources and contents in different samples of atmospheric, terrestrial and marine origin. Results show enhanced99Tc/137Cs activity ratios for samples collected in recent years which are only expected to be contaminated from fallout from nuclear tests. Integrated fallout measurements did not reflect these enhanced ratios.

Studies of transuranics in an arctic marine environment

Since the accidental loss of four nuclear weapons by a B-52 at Thule Airbase, Greenland in 1968, the marine environment at Thule has showed enhanced levels of Pu and Am. Most of the activity is confined to the benthic environment within a distance of 50 km from the crash site of the B-52. Samplings of sediments, benthos, seaplants, fish, and water have been carried out in 1968, 1970, 1974, 1979, and in 1984. The study presented herein intends to answer the following questions: What is the mean residence time of these transuranics in the benthic communities? Do Pu and Am behave differently in the environment?

Plutonium and americium in arctic waters, the North Sea and Scottish and Irish coastal zones

Plutonium and americium have been measured in surface waters of the Greenland and Barents Seas and in the northern North Sea from 1980 through 1984. Measurements in water and biota, Fucus, Mytilus and Patella, were carried out in North-English and Scottish waters in 1982 and Fucus samples were collected from the Irish coast in 1983. Fallout is found to dominate as a source of 239+240Pu north of latitude 65°N, while for 238Pu a substantial fraction originates from European nuclear fuel reprocessing facilities. The 238Pu/239+240Pu isotope ratio provides clear evidence of the transport of effluent plutonium from the latter to Spitsbergen waters. Fallout plutonium in Arctic waters has a residence time of the order of several years, while for Pu from Sellafield we estimate mean residence times of 11–15 months in Scottish waters and, tentatively, 1·5-3 y during transport from the North Channel (north of the Irish Sea) to Spitsbergen. 241Am found in Arctic waters probably originates from the decay of fallout 241Pu and, like Pu, tentatively has a residence time of the order of several years. Americium from Sellafield has an estimated mean residence time of 4–6 months in Scottish waters.

Time Trend of 99Tc in Seaweed from Greenland Waters

In the past few years the development of a suitable analytical method [1] for determining 99Tc in low-level concentrations has intensified the study of this radionuclide in the environment [2–4].

Determination of227Ac in environmental samples by ion-exchange and alpha spectrometry

A new method of227Ac determination is based on total sample decomposition, followed by preconcentration as oxalate and hydroxides, and purification from thorium isotopes and rare earths on ion-exchange columns with nitric acid. The actinium is electroplated on stainless-steel discs with near 100% yield from a water/propanol medium and measured by alpha spectrometry.225Ac is used as a yield monitor. An immediate first count gives overall tracer recovery (typically around 80%). A second count two months later gives a sensitive measure of227Ac through its decay products at 5.5–6.1 MeV. Analysis of reference samples gave satisfactory results.

Determination of237Np in large volume samples of sea water by a radiochemical procedure

A radiochemical procedure followed by alpha spectrometry has been developed for the determination of237Np present at low activity concentrations in seawater. The analytical procedure is based on concentration of actinides from 1800 1 sea water samples by hydroxide precipitations. Neptunium is isolated by ion exchange, fluoride precipitation and extraction with TTA (thenoyltrifluoroacetone). As a radiochemical yield determinant239Np or235Np is used. Neptunium is electroplated onto stainless steel discs before alpha-spectrometry for about 10 days. The procedure allows for sequential separation of plutonium, americium, technetium and radiocaesium together with neptunium. The radiochemical yield for neptunium is only 20–50%, but the procedure has been applied with success on several samples contaminated with237Np at fallout or close to fallout levels.

Technetium-99 in the Baltic Sea

Technetium is released to the biosphere from nuclear facilities, from nuclear detonation tests and by the use of 99Tcm in nuclear medicine.

Technetium-99 in Algae from Temperate and Arctic Waters of the North Atlantic

Different species of algae were used as bioindicators for 99Tc in the marine environment, close to the release sources [1–3]. It was then shown that different species of brown algae were the most suitable.

Comparative study of plutonium and Americium bioaccumulation from two marine sediments contaminated in the natural environment

Plutonium and americium sediment-animal transfer was studied under controlled laboratory conditions by exposure of the benthic polychaete Nereis diversicolor (O.F. Muller) to marine sediments contaminated by a nuclear bomb accident (near Thule, Greenland) and nuclear weapons testing (Enewetak Atoll). In both sediment regimes, the bioavailability of plutonium and 214Am was low, with specific activity in the tissues < 1% (dry wt) that in the sediments. Over the first three months, a slight preference in transfer of plutonium over 241Am occurred and 241Am uptake from the Thule sediment was enhanced compared to that from lagoon sediments of Enewetak Atoll. Autoradiography studies indicated the presence of hot particles of plutonium in the sediments. The results highlight the importance of purging animals of their gut contents in order to obtain accurate estimates of transuranic transfer from ingested sediments into tissue. It is further suggested that enhanced transuranic uptake by some benthic species could arise from ingestion of high activity particles and organic-rich detritus present in the sediments.