EU-STRA-Strålevern

We have studied the quantification of the uncertainties in atmospheric transport of radiological data. This is of large importance in an early phase of the decision making process shortly after an accidental release. Calculations are carried out with the preparedness model SNAP at MET. Assessments are made based on 51 ensembles of the weather forecast and nine emission scenarios for the Fukushima accident. The calculations are compared with ca. 100 surface stations and five other dispersion models to understand the magnitude of the uncertainty, how well it is quantified and how dependent it is on the dispersion model in addition to meteorology and source term. The six different models show consistent uncertainty based on the meteorological ensembles. But, the dispersion models (including SNAP) show a tendency to underestimation when compared to measurements. The properties of the SNAP model is similar to the other models. The SNAP model is also applied to a potential accident in a nuclear vessel ca. 200 km southwest of Stavanger. This study also focuses on the quantification of uncertainties due to meteorology, the emission source and choice of dispersion model. Calculations from SNAP are compared with the Greek preparedness model DIPCOT by employing the same meteorological and emission data. For this case the uncertainties originating from meteorology and the emission are comparable in magnitude. Further, we find uncertainties due to the choice of dispersion model of the same order of magnitude or even higher compared to the uncertainties arising from meteorology and emissions. The results therefore indicate that the uncertainties arising from the formulation of the dispersion model may be as important as uncertainties due to meteorology and emissions.

Work has started on applying the project results to the preparedness routines of DSA, both directly between MET and DSA and through participation in CERAD. This can be of key importance for improving the decision making process and increase the confidence in the dispersion forecast in the future. The research has focused on model evaluations and model inter-comparisons. Good qualitative correspondence with the Fukushima measurements are found for all models participating in the study, still some overall underestimation of the radioactivity is encountered. The project shows that the SNAP model at MET behaves similarly to the other European dispersion models. This gives confidence to the preparedness modelling in Norway. Uncertainties due to meteorology, source term and dispersion model are of similar magnitude. In the future, focus should therefore be given to quantify uncertainties due to the dispersion model itself in addition to those coming from meteorology and source term.

In nuclear emergency management and long-term rehabilitation, dealing with uncertain information on the current situation, or predicted evolution of the situation, is an intrinsic problem for decision making. Uncertain information related to, for instance, incomplete information on the source term and the prevailing weather can result in dose assessments that differ dramatically from reality. Uncertainty is also an intrinsic part of model parameters. In the presence of uncertainty, ineffective decisions are often taken (e.g. too conservative or optimistic predictions, inadequately accounting of non-radiological risks), which may result in more overall harm than good due to secondary causalities as observed following the Chernobyl and Fukushima accidents. Therefore, the reduction of uncertainty, and how to deal with uncertain information, is essential to improve decision making for the protection of the affected population and to minimise disruption of normal living conditions. The Confidence project is comprised of 7 Work Packages (WPs), in which MET is involved in 1 of these: WP1: Model Improvement through Uncertainty Analysis. During 2019 (this application) MET will, according to the agreed work plan of CONFIDENCE, focus on (1) fulfilling the calculations for the Fukushima case, carrying out comparison with observations and thereby estimate uncertainties in dispersion calculations (2) fulfill the calculations of the Western Norway case (a potential accident in a nuclear vessel 200 km of the coastline of Rogaland), estimate the uncertainties in the the dispersion due to the meteorological ensembles for the Western Norway case, and (3) implement and evaluate the use of Radar measurements of precipitation in the dispersion calculations for the western Norway case.