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Since 1987, the Department of Nuclear Safety Research, Risø National Laboratory has developed procedures for analysis of low-level amounts of radioactivity in large samples of 200 liters seawater, 10 gram sediment, soil and other environmental materials.These analytical procedures provide high chemical yields, good resolution and excellent decontamination factors for large environmental samples analysed by alpha spectrometry and mass spectrometry (ICPMS). The procedures have been checked throughpractical analysis work and are used in Norway, the Netherlands, Germany, Spain, France and Denmark., A procedure for the determination of plutonium in seawater is described. The plutonium is pre-concentrated by scavenging with Fe(OH)2 and Fe(OH)3 .This purifies for Ca2+, Mg2+ and amphoteric elements. The method is based on a new procedure in which the principle of controlled valence is applied. The redox system SO32- / NO2- was used (1) first to reduce to Pu3+ and afterwards to oxidize to Pu4+. The Pu3+ is separated from U and 210 Po by solvent extraction with TIOA – 6-10 M HCl. Followed by anion exchange of Pu4+ in 8 M HNO3. The decontamination factors of the procedure are >1.7 ⋅ 106 for U and >6.3 ⋅ 104 for Th. The chemical yield is 70-85%.

Selected activities of the Environmental Science and Technology Department during 1990 are presented. The research in the department is predominantly experimental, and the research topics emphasized are introduced and reviewed in eight chapters: 1. Introduction, 2. The Atmospheric Environment, 3. Plant Genetics and Biology, 4. Nutrient Efficiency in Plant Production, 5. Chemistry of the Geosphere, 6. Ecology and Mineral Cycling, 7. Other Activities, 8. Large Facilities. The department's contribution to national and international collaborative research programmes is presented together with information about large facilities managed and used by the department as well as activities within education and training. Lists of scientific and technical staff members, visiting scientists, Ph.D. students, publications, lectures and poster presentations are included in the report.

Since the middle of the 1970s, discharges of radiocaesium to the Irish Sea from the British Nuclear Fuels Ltd. Sellafield (formerly Windscale) installation in Cumbria have increased the concentrations of 137Cs and 134Cs in the northern North Atlantic. The authors report that radiocaesium from Sellafield is now detectable in the East Greenland polar current. The transit time from Sellafield is estimated at 6-8 yr. The concentrations in the polar current are approximately one thousandth of those found in the North Channel by the outlet from the Irish Sea

A long-term study (1962-1976) of the Pb content of food has been performed using samples of Danish food substances collected annually at the Riso National Laboratory. Samples so far investigated are: 150 samples of dried milk from 7 factories; 500 samples of Danish cereals (spring and winter wheat, Triticum vulgare, and barley) from 10 of the state experimental farms; and 70 samples of total diet collected in 8 areas covering all of Denmark. Pb concn. in the ash of dried milk varied from 13 to

The environmental contamination resulting from the B-52 accident in 1968 at Thule was studied by scientific expeditions in 1968, 1970 and 1974. The contamination was mainly confined to the marine environment, where plutonium was preferentially located in the sediments and the benthic fauna. Plutonium concentrations down through the sediment layers decayed exponentially with a half-depth of 1-2 cm. The horizontal distribution of the plutonium may be described by an exponential expression: mCi 239,240Pn km-2 = 460e-0.28R or by a power function: mCl 239,240Pu km-2 = 370 R-1.2, where R is the distance in km from the point of impact. The inventory of 239,240Pu in the marine environment from the accident was estimated at 25-30 Ci. The amount of 238Pu was about 0.5 Ci. The bottom animals, such as worms and molluscs, showed a horizontal distribution of radioactivity similar to that of the sediments. From 1968 to 1970 the 239,240Pu concentrations in the biota decreased by an order of magnitude, since 1970 the decrease has been less evident. In 1970 and 1974 there were no indications of increased plutonium concentrations in surface seawater or in sea plants or zooplankton. Higher animals such as fish, seabirds and marine mammals have shown no tendency to increasing plutonium levels since the accident. (C)1977Health Physics Society

Shed deciduous teeth were collected in 1962-1965 from 25 schools in Denmark, the Faroes and Greenland. Approx. 10,000 teeth from children born in the period 1950-1958 are included in the present investigation, which compiles 215 90Sr analyses. The 90Sr level in deciduous teeth crowns increased by a factor of four from 1953 to 1958. Faroese teeth contained nearly 4 times as much 90Sr as teeth from Denmark and Greenland. Incisors contained approx. three fourths of the level found in second molars. The 90Sr diet levels measured in 1962-1966 in Denmark, the Faroes and Greenland showed a similar variation between locations as the 90Sr in deciduous teeth from children born in 1950-1958 in the same areas. The 90Sr mean level in shed deciduous teeth is considered as an estimate of the 90Sr content in the tooth donors bone when he was 1 year old. (C)1968Health Physics Society

The lithium-drifted germanium detector enables determination of europium-155 on a routine basis in environmental samples contaminated with debris from nuclear weapons. From measurements of europium-155, cesium-144, and strontium-90 in air filters collected between 1961 and 1966, the yield of europium-155 from weapons was estimated at 1400 atoms per 10$^{6}$ fissions, which is close to the yield of europium-155 from fast fission of uranium-238.

Of the five first Chinese nuclear test explosions, No. 3 and No. 5 detonated on May 9, 1966, and December 28, 1966, respectively, have been the most powerful. According to the U.S. Atomic Energy Commission1 both explosions were in the lower end of the intermediate range, that is, they corresponded to a few hundred kilotons of TNT.