Dispersion models

Dispersion calculations for Swiss nuclear installations

With the aid of a dispersion calculation, ENSI's emergency organisation (responsible under Article 9 of the Emergency Preparedness Ordinance) can predict the direction in which radioactive substances will move in the atmosphere after being released from a nuclear installation and from what time particular areas will be affected. This allows the population to be alerted in good time and, where necessary, precautionary protective measures to be taken. Dispersion calculations also form the basis for the targeted deployment of measuring instruments and emergency services.

For atmospheric dispersion calculations such as these, ENSI uses the JRODOS system (Java-based Realtime Online Decision Support).

JRODOS: A brief overview

JRODOS was initiated within the framework of international cooperation in the field of radiological emergency preparedness and is developed by the Karlsruhe Institute of Technology (KIT) under EURATOM research programmes.

The programme's development is coordinated by the RODOS Users Group (RUG), an assembly of all registered JRODOS users. Through both its membership of RUG and its service and maintenance contract with KIT, ENSI is able to contribute directly to this development and ensure its own requirements are taken into account.

The modular design of the system makes it possible to define model chains that comprise a sequence of individual modules, each of which handles specific tasks. In total, more than 25 modules are available for dispersion simulations, dose calculations, modelling of the food and feed chain, calculation of the effects of protective measures, and more.

The JRODOS system primarily offers broad simulation coverage and synergies with the National Emergency Operations Centre (NEOC), MeteoSwiss and the competent authorities abroad.

• Weather forecasts

  JRODOS uses three-dimensional weather forecast data provided by MeteoSwiss (including wind, temperature and precipitation) from the ICON-CH1 and ICON-CH2 weather models. ICON-CH1 provides forecasts several times a day with high spatial and temporal resolution. With slightly lower resolution, ICON-CH2 weather data allow a longer forecast horizon of up to five days.

  When using the weather forecasts, the 3D data is downscaled using a wind field model to the resolutions required by the dispersion model, enabling simulations with an even higher spatial resolution than that of the weather models.

  Alongside the wind field, the resolution of the terrain (orology) is also an important variable. The fine-scale topographic landscape of Switzerland, and in particular the Alpine region, places increased demands on modelling, which is why JRODOS uses the best elevation model (DHM25) available from the Swiss Federal Office of Topography, swisstopo.

Operational use of JRODOS

JRODOS is operational for calculations at all Swiss nuclear installation sites:

• Routine calculations with a unit source (1 Bq/s) are automatically performed around the clock at hourly intervals and for three different release heights.
• In the event of an incident and during emergency exercises, incident-specific calculations are available no later than one hour after the ENSI emergency organisation has reached operational readiness.

The main purpose of the routine calculations is to ensure the continuous availability of the JRODOS system and to monitor current dispersion situations (forecasts for the next six hours at all Swiss nuclear installation sites). In addition, routine calculations can be used in the event of an incident to provide an initial assessment.

The main purpose of the incident-specific calculations in the event of an accident at a nuclear installation is to assess the risk to the population in the case of a release of radioactive substances that has already occurred or may occur at a later stage. These calculations form the basis for delineating a potentially affected area and for deciding on any measures that may be required to protect the population.

Example of a dispersion calculation

The video below shows the result of a routine dispersion calculation. It illustrates how a simulated release of radioactive substances would spread in the atmosphere. (Click on the video to start playback.)

• History: why the changes?

  Until 2016, ENSI used the ADPIC programme for dispersion calculations; however, it reached its final stage of development in 2011. ADPIC consistently reflected the state of the art in science and technology and was internationally recognised. In order to continue meeting high quality requirements in the future, ongoing development of the dispersion modelling system is essential.

  For this reason, ENSI launched the RADUK (radiological dispersion calculations in the vicinity of nuclear installations) project in January 2011, with the aim of replacing ADPIC with a more modern system. As a result, the European JRODOS platform has been in operational use at ENSI since 2016.

Originally published on February 21, 2017, last updated on January 20, 2026.

Further information

• MADUK » ENSI