Nuclear Facility Emergency Preparedness RASTEP (RApid Source TErm Prediction)

Fast diagnosis and decision support for emergencies

Applying the RASTEP method to a nuclear or petrochemical plant during an exercise or accident gives you a real-time picture of: Plant status and plausible developments; Concentration and timing of releases (source term). Thanks to the underlying mathematical model, the tool has no minimum information requirement and is also robust to uncertain information. Predicted data can be easily exported to various file formats, such as the IAEA IRIX format. Both plant models and the RASTEP GUI can be customized to support your plant and emergency organization with few technical requirements and low license costs.


The nuclear disaster in Fukushima highlighted the need to improve tools for fast accident diagnosis and forecasting of potential scenarios in situations with scarce information.

By combining best available information from plant PSA/PRA, expert judgements and pre-calculated consequences with observations of an ongoing situation, you are able to follow an efficient and quality-assured process to assess accident progression and predict consequences also in highly challenging situations.

What is RASTEP?

RASTEP is a software tool, developed by Vysus Group in cooperation with the Swedish Radiation Safety Authority (SSM), with the aim of providing state-of-the-art decision support in nuclear emergency situations.

The tool is based on Bayesian Belief Networks (BBNs), representing uncertainty as probabilistic relations among observations, events and variables. The BBN model connects known data and expert judgements with observations of the ongoing situations and maps the outcome to pre-calculated scenarios. Thanks to the inherent properties of BBNs, the tool can always provide a best estimate of the situation at hand, irrespective of available information, relying on data and expert judgements already built into your plant model.

Service Breakdown

RASTEP is in use at the emergency response organizations of the Swedish Radiation Safety Authority (SSM) as well as the Norwegian Radiation and Nuclear Safety Authority (DSA). A set of generic nuclear power plant RASTEP models were also developed, tested and evaluated during the EU Horizon-2020 R&D project FASTNET (Fast Nuclear Emergency Tools). Together, this body of experience makes us ready to model most types of nuclear power plants in the world, enhance your understanding and management of the complex interplay between a nuclear accident and offsite emergency response, improve your exercise programs and provide you with a simple and robust tool, should the worst happen.