Sven Poul Nielsen

Tracking of Airborne Radionuclides from the Damaged Fukushima Dai-Ichi Nuclear Reactors by European Networks

Radioactive emissions into the atmosphere from the damaged reactors of the Fukushima Dai-ichi nuclear power plant (NPP) started on March 12th, 2011. Among the various radionuclides released, iodine-131 ((131)I) and cesium isotopes ((137)Cs and (134)Cs) were transported across the Pacific toward the North American continent and reached Europe despite dispersion and washout along the route of the contaminated air masses. In Europe, the first signs of the releases were detected 7 days later while the first peak of activity level was observed between March 28th and March 30th. Time variations over a 20-day period and spatial variations across more than 150 sampling locations in Europe made it possible to characterize the contaminated air masses. After the Chernobyl accident, only a few measurements of the gaseous (131)I fraction were conducted compared to the number of measurements for the particulate fraction. Several studies had already pointed out the importance of the gaseous (131)I and the large underestimation of the total (131)I airborne activity level, and subsequent calculations of inhalation dose, if neglected. The measurements made across Europe following the releases from the Fukushima NPP reactors have provided a significant amount of new data on the ratio of the gaseous (131)I fraction to total (131)I, both on a spatial scale and its temporal variation. It can be pointed out that during the Fukushima event, the (134)Cs to (137)Cs ratio proved to be different from that observed after the Chernobyl accident. The data set provided in this paper is the most comprehensive survey of the main relevant airborne radionuclides from the Fukushima reactors, measured across Europe. A rough estimate of the total (131)I inventory that has passed over Europe during this period was <1% of the released amount. According to the measurements, airborne activity levels remain of no concern for public health in Europe.

Iodine-129 and Caesium-137 in Chernobyl contaminated soil and their chemical fractionation

Soil samples from areas in Belarus, Russia and Sweden contaminated by the Chernobyl accident were analysed for (129)I by radiochemical neutron activation analysis, as well as for 137Cs by gamma-spectrometry. The atomic ratio of (129)I/137Cs in the upper layer of the examined soil cores ranged from 0.10 to 0.30, with an average of 0.18, and no correlation between (129)I/137Cs ratio and the distance from Chernobyl reactor to sampling location was observed. It seems feasible to use the (129)I/137Cs ratio to reconstruct the deposition pattern of 131I in these areas. The association of (129)I and 137Cs in the Chernobyl soil and Irish Sea sediment was investigated by a sequential extraction method. Similar speciation of (129)I in the Chernobyl soil and Irish Sea sediment was found. Approximately 70% of (129)I is bound to oxides and organic matter, and 10-20% is in the readily available phase, while most of the 137Cs (73%) in Chernobyl soil remains in the extraction residue.

Level and origin of iodine-129 in the Baltic Sea.

Environmental samples, such as seawater, seaweed, lake water, lake sediment and grass collected from the Baltic Sea area were analyzed for 129I and 127I by radiochemical neutron activation analysis. In 2000, the concentration of 129I in the seawater from Borholm and Møen in the Baltic Sea has reached 6.0 x 10(-13) and 16 x 10(-13) g/l, respectively, these are more than two orders of magnitude higher than the global fallout level. The highest value of 270 x 10(-13) g/l being found in the seawater from the Kattegat. By comparison of the level of 129I in the lake water and precipitation in this region, it is estimated that more than 95% of 129I in the Baltic Sea originates from reprocessing emissions, especially from the French nuclear fuel reprocessing plant at La Hague. More than 30% of 129I in the south Baltic and 93% in the Kattegat directly originates from the marine discharges of the European reprocessing plants.

Iodine-129 in human thyroids and seaweed in China.

The concentrations of 129I and the ratios of 129I/127I in normal human thyroids collected in Tianjin, China, and some seaweed samples from the Chinese coast were determined by neutron activation analysis. The mean 129I/127I ratio in these thyroids was found to be 1.13 x 10(-9), which is two orders of magnitude higher than the level of the pre-nuclear era, but one order of magnitude lower than the level in Europe in the post-nuclear era. There is no significant difference between the ratio of 129I/127I in the thyroids for the post-nuclear era from China and other areas, which are considered not to have been directly exposed to 129I emission from a nuclear source, such as Chile, Taiwan and Tokyo. The mean 129I/127I ratio in seaweed from the Chinese coast is 2.35 x 10(-10), approximately two orders of magnitude higher than in seaweed collected in the pre-nuclear age, and similar to that from locations without direct exposure to the emission from nuclear installations, influenced only by global fallout. This indicates that the 129I level in China is within the global fallout background level.

Separation of Sr from Ca, Ba and Ra by means of Ca(OH)2 and Ba(Ra)Cl2 or Ba(Ra)SO4 for the determination of radiostrontium

A simple procedure is developed to separate Sr from a large amount of Ca, which relies on the insolubility of Ca(OH)2 in alkaline solution. Calcium is quantitatively separated from Sr and more than 95% of Sr is recovered from a sample with as much as 50 g of Ca and a Ca/Sr mole ratio of 250. A new procedure for the separation of Sr from Ba and Ra is also investigated, which is based on the difference in solubility of the chlorides of Sr, Ba and Ra in HCl media. In 9.5 mol l −1 HCl or 7.5 mol l −1 HCl–10% acetone media, >97% of Ba and Ra can be removed by Ba(Ra)Cl 2 precipitation, and >94% of Sr was recovered. In the determination of 90 Sr by measuring 90 Y, the separation of Ra and Ba can easily be carried out by precipitation of Ba and Ra as Ba(Ra)SO4, while Y can be quantitatively recovered in the solution. By this method, a further separation of 90 Y from radiostrontium can be completed. The new separation procedure has been successfully used for the determination of 90 Sr in samples with high Ca content, such as 45 l of seawater and 200 l of drinking water. The analytical quality of the results is comparable to that of the traditional method using fuming nitric acid and BaCrO4 precipitation.

Iodine-129 in thyroid and urine in Ukraine and Denmark

Human thyroids collected from Gomel in Belarus, sheep thyroid from Jutland and human urine from Zealand in Denmark were analysed for 129I and 127I concentrations. The ratios of 129I/127I in human thyroid in Gomel are 2.65-11.0 x 10(-9) with an average of 7.21 x 10(-9), which is one order of magnitude higher than those from Asia and South America (10(-10)), but significantly lower than those observed in west Europe (10(-8)). A weak negative correlation (P < 0.05) between 129I/127I ratio in human thyroid and the age of the subjects was observed in Gomel. The average ratio of 129I/127I in sheep thyroids from Jutland of Denmark is 1.81 x 10(-7), which is two orders of magnitude higher than those in south hemisphere, and Asia. It is also significantly higher than those observed in other west European countries before 1984 and that in human thyroid in Gomel. The high thyroid 129I level in Jutland is attributed to the release of reprocessing plants in France and UK. The 129I/127I ratios in human urine in Zealand of Denmark are 0.86-2.86 x 10(-8). The possibility of using urine 129I to evaluate the thyroid exposure to 129I is investigated.

Deposition of 210Pb, 137Cs, 239+240Pu, 238Pu, and 241Am in the Antarctic Peninsula area

210Pb, 137Cs, 239+240Pu, 238Pu, and 241Am were analysed in lichen, moss, grass and soil samples, as well as in lake sediments, from the South Shetland Islands, the Antarctic, in order to evaluate the flux and deposition of these elements. Average inventories of the analysed radionuclides in 1988 were 210Pb (excess): 280±110 Bqm−2 (n = 15),137Cs: 155±95 Bqm−2 (n = 19), 239+240Pu: 4·6±2·6 Bqm−2 (n = 19), 238Pu: 0·95±0·5 Bqm−2 (n = 19) and241Am: 1·6±1·0 Bqmsu−2 (n = 19). From the maximum value of unsupported 210Pb the annual deposition is determined to be 18±5 Bqm−2. The ratios 238Pu/239+240Pu and241Am/239+240Pu of 0·21±0·04 and 0·35±0·08 respectively agree well with expected values in this area. A significant difference in 137Cs/239+240Pu ratios between lichens and moss/grass/soil is observed which may be an effect of submerging and melt water altering radio-nuclide ratios. From one of three lakes studied it is possible to perfom 210Pb dating with reasonably accuracy showing an average annual sediment accumulation in this lake of about 45 gm−2.

Environmental radioactive contamination in Greenland: a 35 years retrospect.

Environmental studies of anthropogenic radionuclides in Greenland over four decades are reported. The studies have comprised the marine as well as the terrestrial environments and emphasis has been laid on measurements of 90Sr and 137Cs. The temporal and the spatial trends of these radionuclides are described. The radiation exposure from consumption of locally produced diets has been calculated from consumption rates and the infinite time integrated levels of 90Sr and 137Cs concentrations in the various food products. Compared with most other Arctic people, the Greenlanders have received relatively low doses from anthropogenic radionuclides. There are several reasons for this, first of all, because of the relatively high consumption of marine products compared with terrestrial products. Secondly, because winter slaughtering of reindeer is less frequent in Greenland than in other Arctic countries and Greenland reindeer consume, in general, less lichen than most other Arctic reinder, and thirdly, because the transfer from deposition to lichen in Greenland seems lower than in other Arctic areas.

The detection of radioactive material from a venting underground nuclear explosion

Abstract In northern Europe, there are many stations in operation for surveillance of airborne particulate radionuclides at low concentration levels. In August 1987, after a leakage from a Soviet underground nuclear weapons test at Novaya Zemlya, at least five countries could detect the event at their national stations. Observed radionuclide concentrations are reported and isotope ratios and meteorological air parcel trajectories are used to characterise the source.

Plutonium in the marine environment at Thule, NW-Greenland after a nuclear weapons accident

Abstract In January 1968, a B52 plane carrying 4 nuclear weapons crashed on the sea ice 12 km from the Thule Air Base, in northwest Greenland. The benthic marine environment in the 180–230 m deep Bylot Sound was then contaminated with 1.4 TBq 239,240 Pu (0.5 kg). The site was revisited in August 1997, 29 years after the accident. Water and brown algae data indicate that plutonium is not transported from the contaminated sediments into the surface waters in significant quantities. Sediment core data only indicate minor translocation of plutonium from the accident to the area outside Bylot Sound. The present data support an earlier quantification of the sedimentation rate as 2–4 mm per year, i.e. 512 cm during the 29 years since the accident. Biological activity has mixed accident plutonium much deeper down, to 2030 cm, and the 512 cm new sediment has been efficiently mixed into the contaminated layer. In addition to the classical bioturbation mixing the upper _~5 cm, the plutonium data indicate the existence of a deeper bioturbation gradually decreasing with depth. Transfer of plutomum to benthic biota is low leading to 12 orders of magnitude lower concentrations in biota than in sediments. Some biota groups show a somewhat higher uptake of americium than of plutonium. Sediment samples with weapons plutonium from the accident show a significant variation in 240 Pu/ 239 Pu atom ratios in the range 0.0270.057. This supports the hypothesis that the Thule plutonium originates from at least two sources of different quality. The radioecological implication of the observed variations is that the use of plutonium isotope ratios in quantitatively determining the influence of different plutonium sources is a very complex affair requiring substantial data sets.