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Nuclear Power

RASTEP - Sweden's nuclear safety tool of choice.

SSM needed a tool of their own to be able to rapidly estimate the source term from a potential severe accident. Here's how we helped.

operations desk

At a glance.

  • Client

    Swedish Radiation Safety Authority (SSM)

  • Asset

    Nuclear power plants

  • Location

    Sweden

Overview

The Swedish Radiation Safety Authority (SSM) is tasked by the Ministry of the Environment and Energy to ensure nuclear safety, radiation protection and nuclear non-proliferation.

SSM needed a tool of their own to be able to rapidly estimate the source term from a potential severe accident at a Swedish nuclear power plant since they cannot rely on enough (or any) information coming from the power plant. They also needed to be able to make an own source term estimation and build up their ownknowledge.

 

How we helped

LR helped SSM by developing RASTEP with plant-specific models. Initially, this began as a research and development project but it is now mature enough to be deployed within the emergency preparedness and response organisation at SSM.

SSM and LR have worked together and the software has undergone significant development. Several of Sweden’s nuclear power plants have been modelled and the final goal for SSM is to dispose of one plant-specific RASTEP model for each operational nuclear power plant unit in Sweden.

At present there are eight such units (Forsmark F1, F2, F3, Oskarshamn O3, and Ringhals R1, R2, R3, R4). RASTEP, along with additional expert judgements, is now the preferred source term estimation tool and is routinely used by the source term group in SA exercises at SSM’s Emergency Preparedness and Response centre.

The source term group surveys and assesses the source terms provided to SSM from the affected nuclear power plant and estimates the source term independently based on available information. This enables the continual renewal of the diagnosis of the overall state of the affected plant and potential changes to this state, including the source term, in the event of radioactive releases. The source term group collaborates closely with the reactor assessment group. The estimated source term is handed over to a group using environmental dispersion codes (e.g. ARGOS) to determine off-site consequences. Finally,SSM provides advice to the rescue team leader at the county administrative board, who decides on the most appropriate protective measures.

As SSM’s emergency centre recently installed a system for electronic transmission of plant process parameters from the Swedish nuclear power plants, a goal for future development is to be able to feed RASTEP automatically with these parameters, to further improve both speed and quality in source term estimation.

RASTEP, along with additional expert judgements, is now the preferred source term estimation tool and is routinely used by the source term group in SA exercises.

The impact

The RASTEP tool is also used frequently by SSM in training exercises to enhance the skills of its users, to improve on overall emergency preparedness and to get a better understanding of the course of events that can lead to radioactive releases. The tool enhances the resolution of the understanding of the course of events since it is not based on pre-defined scenarios such as applied in Safety Analysis Reports.

The RASTEP GUI also makes it simple to produce quick what-if-analyses in conjunction with SA sequences. SSM has recently undertaken a review of Swedish emergency planning zones and distances. As a result, the source term group requested additional RASTEP model functionality to determine if a predicted source term is below, between or above the source terms of two postulated emergency response dimensioning events – one with, and one without functioning radioactive release mitigation systems. This is one example of the flexibility of the RASTEP development process in which specific requests can be met with tailor-made solutions for specific emergency response applications.

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