Radionuclides resuspension

Fig. 7-2. Summary of environmental pathways by which terrestrial plants may become contaminated with radionuclides. In the case of an input from atmosphere, or as a result of the process of resuspension , any external radionuclide burden may be reduced by field loss mechanisms conversely, an initially external radionuclide deposit (Rat) may become internalised (i int) following foliar absorption and translocation. Radioactive contaminants of soils may be derived either from atmospheric inputs or from seepage in ground waters. Partitioning of radionuclides in soil—soil water systems controls their availability for root absorption, which normally occurs exclusively from the liquid phase. The chemical speciation of the nuclide in this phase, however, provides a further control on bioavailability which is highly radionuclide specific.

The accident at Chernobyl Nuclear Power Plant and considerable release of radionuclides in particulate fraction renewed interest in hot particles (HPs)—tiny objects of pm dimensions, having density of activity comparable with the one of irradiated nuclear fuel. They pose radiological risk, especially when inhaled with the air after resuspension from the soil. Studies (Osuch et al., 1989 Piasecki et al., 1990), performed on a quite large set of HPs (over 200 species) collected in Autumn 1986, indicated the existence of two, roughly equally populated groups of HPs ... 

The net effect of the above processes is that the bulk of the Cs inventory is transported with water movements with a small fraction being adsorbed to suspended particulate and deposited in bed sediments, whereas a large fraction of the Pu and Am inventory is adsorbed to suspended sediments and deposited in the bed sediments of the eastern Irish Sea. The behaviour of Pu and Am deposited in bed sediments is then determined by the processes of sediment mixing (in which bioturbation is very important), resuspension, and remobilisation of adsorbed radionuclides into the solution phase. 

Radionuclide monitoring, based on the methods developed during the Chernobyl emergency, is being continuously adopted in various areas. Different aspects merit attention, such as, for example, the resuspension of radioactive particles that occurs when fields are ploughed and their impact on forager bees. 

Similarly, the methodologies implemented in state-of-the-art models for predicting the physical processes of radionuclide migration through the aquatic environment are not discussed here. A review of the methodologies, including transport due to water currents, diffusion, settling, and resuspension has recently been published by Monte et al., where the models are briefly described, model parameter values reviewed, and values recommended (Montea et al. 2009). 

Details of the chemical and physical form of the released radionuclides are receiving a great deal of attention. These details need to be known to predict the retention in the reactor coolant system, the revaporization soiuce and the resuspension source. Information needs for the development of accident management strategies are probably less demanding. For many purposes, it can be sufficient to class radionuclides as ... 

This paper defines terms such as resuspension , revaporisation , reentrainment , and revolatilisation and the role of the phenomena described by these terms in the late release of radionuclides from the reactor coolant system and reactor containment. The paper also has a bibliography of research done on this source term. 

During shutdown of a PWR plant and, somewhat less pronounced, also during its startup, a strong increase in the concentrations of corrosion products and the associated radionuclides in the primary coolant is observed, an effect which will be discussed in more detail in Section 4.4.3.3. This process causes a dissemination of the radionuclides over the entire primary circuit and, as a possible consequence, results in increased radiation dose rates in the area surrounding it. For this reason, the origin of these radionuclides is of interest, with their possible source being the resuspension of activated corrosion products previously deposited either inside or... 

Non-volatile radionuclides transported as aerosols out of the containment are partly washed down during steam condensation in the annuli, as was already mentioned above. The temperatures of the sumps here are well below the boiling point, so that a noticeable resuspension of radionuclides by droplet carry-over is not to be assumed. However, a small resuspension of non-volatile radionuclides cannot be ruled out under these conditions, with the mechanism for this being the formation of small droplets by the action of the air flow. As was discussed in Section 6.2.2., experimental studies have yielded a very small carry-over of non-volatiles to the air flow. Due to the differences in the conditions, the results of these investigations cannot be directly applied to the release from sumps in the annuli or in the auxiliary building, but it can be assumed that the experimental values obtained in... 

Options for remediation include removal of surface soil, fixation to prevent mobilization by processes such as wind resuspension, amendment to reduce radionuclide transfer to plants and animals, covering with imcontaminated soils to reduce external radiation dose rates and to reduce uptake into plants and animals. Other potential courses of action include administrative measures to limit the uses of the land, for example, so that it is not used for human habitation, thereby reducing exposures or to exclude access completely. 

Depending on the nature of the release, it may be advisable to set up ground based air samplers after a release has occurred to monitor for the presence of fallout and resuspended radionuclides. The resuspension of radionuclides does not usually give rise to an important pathway of exposure however, it can do so for plutonium or other actinides. 

In unpaved areas, long lived radionuclides gradually penetrate into the soil, which prevents their resuspension in the air. In the long term the sampUng and analysis of airborne radionuclides should therefore be regularly performed mainly in inhabited areas contaminated with plutonium and other actinides. 

Resuspension of deposited radionuclides is generally not taken into account, as it is usually of less importance during the early phases of an emergency (with the possible exception of large scale dispersion of plutonium). The effect of sheltering may be taken into account provided that data are available and that sheltering countermeasures have been effective. The effects of prophylaxis with stable iodine may also be taken into account provided that the exact time of its apphcation is available. 

The set of regularly obtained data on radionuclide concentrations in air can be directly used to assess the annual intake and the associated committed dose. If measurement data are unavailable or insufficient, radionuclide concentrations in air can be roughly estimated from soil deposition rates by using a resuspension model. 

Thus, the resuspension rate A is the fraction removed per second by resuspension process. The use of this quantity with a suitable dispersion and deposition model would enable the movement of a radioactive nuclide from place to place to be predicted. Such an approach is necessary for estimating the radionuclide concentration in air due to resuspension downwind of an area heavily affected by the deposition process. Whether kr or A is used, it is clear that the value of the parameter must be expected to vary with many environmental variables. The most important of these environmental variables will be time after deposition, surface structure, nature of the radioactivity, wind speed, surface moisture and rate of mechanical disturbance of the surface. 

Garland, J.A., Playford, K. (1991). Deposition and resuspension of radiocesium after Chmiobyl. In Proceedings of Seminar on Comparative Assessment of the Environmental Impact of Radionuclides during Three Major Nuclear Accidents Kysthym, Windscale, Chernobyl, Rep. EUR 13574, Luxembourg, 1-5 October 1990, vol. I, pp. 237-253. 

Evaporation or airborne resuspension of radionuclides from the released... 

Garger EK, Hoffman FO, Miller CW. Model testing using Chernobyl data ni. Atmospheric resuspension of radionuclides in Ukranian regions impacted by Chernobyl fallout. Health Phys 1996 70 18-24. 

---