The extent of the consequences of accidents in NPPs depends strongly on the amount and kind of the released radionuclides and the release conditions. Typically, the amount of a release is specified as a fraction of the existing inventory (source term = inventory * release fraction).

Riskmap consideres severe accidents with the release of a large fraction of the inventory. For this type of accidents, Caesium-137 is selected as the characteristic nuclide for the damage at longer distances. The release fraction of this nuclide was assumed to be 40%. This value is based on a review of existing source term studies (overview in table), which reveal also the uncertainty of this value (variation between 10% and 80%).

The release height is assumed to be 50 - 1000 m, the release duration 1 hour.