Pu In Air Research Articles

Plutonium isotopes in surface air of Prague in 1986–2006

Monitoring of 239,240Pu in surface air of Prague started in 1986 in connection with the Chernobyl accident. Measurable activities of 10–28 μBq m −3 were found from 29 April 1986 to 5 May 1986. In the most of the monitoring periods of 1987–1996, activities of 239,240Pu in air were not measurable. Positive values for 239,240Pu and 238Pu in air could be obtained after installation of an aerosol sampler with higher flow-rate in 1997. Activity concentrations of 239,240Pu and 238Pu in Prague air in the most of quarters of 1997–2006 were in the range 0.53–5.06 and <0.16–1.10 nBq m −3, respectively. Seasonal fluctuations can be found in content of 239,240Pu in air. Activity ratios of 238Pu/ 239,240Pu in air are higher than those in top soil, so it can be supposed that 238Pu is coming to air of Prague also from other sources than resuspension of fallout from atmospheric nuclear tests.

Long-term variation (1986–1998) of post-Chernobyl 90Sr, 137Cs, 238Pu and 239,240Pu concentrations in air, depositions to ground, resuspension factors and resuspension rates in south Germany

Annual mean concentrations in air and annual total (wet plus dry) depositions to ground of 90Sr, 137Cs, 238Pu and 239,240Pu decreased at Neuherberg, south Germany, in the period from July 1986 (i.e. after the end of the initial deposition phase from Chernobyl) to 1998 as follows: 90Sr from 0.77 to 0.05 μBq m −3, and from 0.82 (1988) to 0.28 Bq m −2 year −1; 137Cs from 133 to 2.8 μBq m −3, and from 116 to 3.8 Bq m −2 year −1; 238Pu from 0.95 to 0.063 nBq m −3, and from 1.0 to 0.23 mBq m −2 year −1; 239,240Pu from 8.1 to 0.53 nBq m −3, and from 6.4 to 2.1 mBq m −2 year −1.The values for the non-caesium radionuclides are compared to the few available data from other stations. After an initial phase which is characterised for a given radionuclide by the varying ratio of the Chernobyl-derived inventory to the earlier, weapons fallout-derived inventory, the time courses of concentrations of 137Cs, 90Sr, 238Pu and 239,240Pu in air become more or less parallel (from about 1990), despite the considerable differences in the physico-chemical properties of these elements. By contrast, the time series of radionuclide deposition rates show until about 1994 less similarity among each other and with the respective concentration series in air. From 1994, concentrations in air and depositions to ground become nearly constant, or decrease very slowly. At the end of the observation period, resuspension factors between 1.4×10 −10 m −1 and 1.0×10 −11 m −1 are observed for the various nuclides. The time courses of specific activities (Bq g −1) as well as the time courses of radionuclide ratios show characteristic differences between air and deposition. The data will be useful in predicting the post-accident behaviour of radionuclides a long time after a large-scale contamination event.

Thermal expansion and solubility limits of plutonium-doped lanthanum zirconates

Plutonium-doped and undoped lanthanum zirconates were prepared by solid state reaction. The solubility limit of Pu in La 2Zr 2O 7 was studied by X-ray diffraction, and the solubility limits of Pu in pyrochlore-type phase prepared in air, vacuum and Ar–8%H 2 atmospheres were determined to be 10, 35 and 100 mol%, respectively. The compound with 80 mol% Pu prepared in air and the compounds with 80 and 100 mol% Pu prepared in vacuum showed single fluorite-type phases. Thermal expansion coefficients of (La 1− x Pu x ) 2Zr 2O 7+ y ( x=0, 0.05, 0.10 and 0.80) were also measured by high-temperature X-ray diffraction at temperatures between room temperature and 1273 K in air and He–8%H 2 atmospheres and were found to increase with increasing Pu content. The dependence of the linear thermal expansion coefficients on Pu content is discussed from the point of view of the radii of both tetravalent Pu in air and trivalent Pu in He–8%H 2.

Concentrations of239,240Pu and238Pu in the surface air of Prague in 1993, 1994 and 1995

The activity concentration of239,240Pu and238Pu in the surface air of Prague in the years 1993, 1994 and 1995 have been determined. The content of239,240Pu in air in different monitoring periods of the years studied ranged from <0.5 to 5.5 nBq.m−3. The source of239,240Pu in air is the resuspension of fallout plutonium from the opsoil layer.

Sources for Pu in near surface air.

This paper provides evidence that most of the Pu in the near surface air today is due to resuspension. Vertical and particle size distribution in near surface air over a period of three years were measured. The seasonal variations of Pu in air and the influence of meteorological parameters on these variations are shown. Samples were taken before the Chernobyl accident in an area where only Pu fallout from the atmospheric nuclear tests of the early sixties occurs. The comparison of the behavior of Pu with other trace elements, which were also measured, showed similar behavior of Pu and elements like Ca, Ti and Fe in near surface air. This confirms that most Pu is resuspended because the main source for these elements in air is the soil surface. Resuspension factors and resuspension rate are estimated for all measured elements. A resuspension factor of 0.8 X 10(-8) m-1 and a resuspension rate of 0.09 X 10(-9) s-1 is calculated for Pu.

Oxidation of Plutonium in Moist Air and Argon

The oxidation rate of Pu in air and in argon were compared under both dry and humid conditions at a temperature sufficiently low that changes in oxidation behavior were readily detected. Results indicate that oxidation is anodically controlled. (C.H.)