The German Risk Study: Accident Consequence Model and Results of the Study

The possible accidental releases from nuclear power plants with pressurized water reactors are classified into eight release categories. To assess the damage resulting from these releases, a model for accident consequences (UFOMOD) is set up. In this model, the atmospheric dispersion and ground deposition are evaluated, and the space- and time-dependent activity concentration in the atmosphere and on the ground is calculated. From these concentration values, the potential doses on which the different protective measures and countermeasures depend are first determined. The doses to be expected are then calculated taking into account these protective measures and countermeasures. Based on these doses, the consequences are assessed for the population affected, in terms of somatic early fatalities, somatic late fatalities, and genetic exposure. The consequences are then assessed by running several times through the 8 release categories at 19 sites with a total of 25 reactor units. The calculations for each site are based on 115 different weather sequences of several hours’ duration, assuming that these sequences have the same probability in each of the 36 predetermined wind directions (each of 10 deg). In parallel, the corresponding frequencies of occurrence are determined. From the pairs of values “extent of consequences/frequency of occurrence,” the final results are derived:

1. complementary cumulative frequency distributions for collective fatalities and collective doses
2. expected values of collective fatalities and collective doses as well as distance-dependent expected values of individual fatality
3. contributions of the different exposure pathways to early and late fatalities with respect to the various organs.

As far as possible, confidence intervals of the results are evaluated and the results compared to the American “Reactor Safety Study.”