Seminar on radionuclide deposition estimates, results from work in the Nordic countries, possibilities and limitations
13-14 of September 2010, Risø, Denmark
The experience of the deposition from the Chernobyl accident and the atmospheric testing of nuclear weapons is fading into the past, most of the deposition monitoring programmes have stopped or been radically reduced, few are now actively conducting studies in this field. Deposition estimates continue, however, to be important, e.g. for emergency response planning. Estimation of background values is important for assessing potential additional deposition. When a suspected event occurs, there may be no background measurements available and even if they are, they may be too few to be representative for the place or region of concern.
In recent years databases with compilation of nuclear fallout data have become available. Studies on fallout and deposition have been made in some of the Nordic countries, e.g. using precipitation as a basis for deposition estimates. The NKS-B activity DepEstimates has followed up the some of this Nordic work.
At the DepEstimates seminar at Risø results from previous NKS activities (in particular NKS-B ECODOSES) were summarised and description of recent published studies in individual Nordic countries were given by Tone D. Bergan, Mats Isaksson and Jussi Paatero. Sigurður Emil Pálsson presented a study that was carried out within DepEstimates. The study involved a statistical evaluation of the US EML global fallout data set as well as the UK AERE (Harwell) and the Risø data sets. The results showed that in the Northern hemisphere much of the variability in the data can be explained by using only precipitation data along with a general function of time (common for all locations). This simple relationship between precipitation and deposition rates makes it feasible to reconstruct deposition time series, which can be important when time dependent radioecological models are being validated using old data. Such work has e.g. been done within NKS-B PardNor. The model makes it easy to derive approximative fallout maps for radionuclides with a similar behaviour as Sr-90 (such as Cs and Pu). Such maps are important when background estimates are needed. The do not replace sampling at individual spots, they complement sampling. The non-linear behaviour of the model can possibly help to understand depositon better, since the behaviour has the same form as has been suggested for the scavenging coefficient.
The DepEstimate activity is being concluded with a final report giving short summaries of the publications presented at the seminar as well as the study being concluded. At the seminar there was a consensus that study presented should be developed into a scientific paper and participants were invited to become co-authors by contributing to this work. The paper is to be submitted by spring 2011.