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Nuclear software

RASTEP (RApid Source TErm Prediction)

Fast diagnosis and decision-making in case of a nuclear emergency.

Stylised cooling towers


The nuclear disaster in Fukushima asserted the need to improve tools for fast accident diagnosis and forecasting of potential scenarios. This would enhance the application of level 5 defense in depth principles, adopted to mitigate the consequences of radioactive material release through appropriate off-site emergency response.

RASTEP supports nuclear emergency preparedness organizations by providing an independent view of the accident progression and predicting the possible off-site consequences to the public and environment.

What is RASTEP?

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

RASTEP is a single, dynamic tool capable of modelling causes and effects in complex cases with lots of free variables, missing or incomplete information and where the level of uncertainty is high. The tool is based on Bayesian Belief Networks (BBNs), representing uncertainty as probabilistic relations among observations, events and variables.

It takes prior beliefs at the outset and, as information on the progression of an event becomes available, modifies and updates these beliefs. To deliver diagnoses and predictions, the tool maps Deterministic Safety Analyses (DSA) to the observed state of the plant using results from Probabilistic Safety Analyses (PSA). The tool can thereby always provide a best estimate of radioactive releases – the radiological source term – for the situation at hand.

RASTEP in action

The RASTEP user answers a series of questions on specific parameters of the affected plant. In an emergency situation, the plant operator would follow Severe Accident Management Guidelines (SAMGs), and the questions posed to a RASTEP user by the tool's interface reflect the structure of the SAMGs. This aligns the RASTEP user's ambitions to diagnose the state of the plant and potential consequences with the plant operator's efforts to manage the situation. The answers are fed into a pre-loaded model of the plant, mapping the interconnections between all significant systems. As circumstances develop, new or updated information on specific system parameters are entered by the user, creating a continuously updated diagnosis, including the radiological source term. Today, RASTEP is in use at the emergency response center of SSM together with plant specific models for the nuclear power plants currently in operation in Sweden. RASTEP has also been selected to be used within the FASTNET (FAST Nuclear Emergency Tools) project funded by the European Commission, with LR developing generic RASTEP plant models for PWR, BWR, VVER440-213, CANDU 6 and spent fuel pools.

The graphical interface

The user-friendly interface shows the most probable plant states. Clarity is facilitated by the way questions are presented to the RASTEP user. The resulting presentation has been developed to deliver a clear risk picture. Different panels provide real-time information on system status, predictions of source terms and visualization of radiological releases over time, with one section set aside for dialogue with the user. Data for off-site radiation dose assessment and atmospheric dispersion calculations can be easily exported.

RASTEP screenshot

What are the benefits?

RASTEP gives you a real-time picture of:

  • Plant status and plausible developments;
  • Release paths of radioactive isotopes; 
  • Time of radioactive releases; 
  • Concentration of the isotopes (source term).


The outcome is shown in an easily digestible format to facilitate usage in a highly challenging situation.

Why choose LR?

lWe are uniquely placed to support your nuclear facility. Along with our marine industry heritage, we draw on decades of experience in energy. We have helped to shape and grow the nuclear sector from its very beginning, through supporting client projects as well as research and technology advancement.

For RASTEP support & information

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