More than just electricity
Numerous European countries are examining or planning the use of Small Modular Reactors (SMRs) as part of their future energy supply, partly with substantial government support. In some cases, the focus is not solely on electricity generation: SMRs are also to be used to provide district heating or so-called process heat for industrial applications; hydrogen production is also one of the goals. In this way, SMRs could become part of so-called hybrid energy networks in the future in which different energy sources, storages and conversion processes are combined.
With regard to safety, this raises the question of whether and, if so, how such a hybrid network and the SMR connected to it could influence each other. Finding answers to this question was the aim of the TANDEM research project funded by the European Commission, in which GRS participated alongside numerous research organisations from abroad.
Modelling a hybrid network with SMR
Within TANDEM, a hybrid network was modelled using MODELICA software. This software can be used to simulate physical systems such as power generation plants, turbines, valves, generators and heat exchangers as well as their control systems. Experts at GRS used the ATHLET thermohydraulic code developed in-house at GRS to model a generic SMR. Among other things, this special software allows the simulation of repercussions, such as sudden load shedding after a power grid failure, on the behaviour of a reactor. In order to be able to simulate the mutual influences of the hybrid network and the SMR, both systems were then coupled with each other.
As part of the subsequent analyses, sudden changes in heat and electricity demand were simulated, such as those that could occur in the event of a short-term, unplanned outage of a large consumer. These so-called load changes were assumed to a degree that would be equivalent to abnormal operation or even an incident.
New application for analysis tool
For the researchers at GRS, another point of particular interest in the TANDEM work was the extent to which GRS's own simulation code is suitable for analysing such a scenario, which has not yet been done in this form.
Sara Beck, Head of the Safety Research Division, adds:
„An essential aspect of our research is to continuously adapt our analysis tools, such as ATHLET, to technological innovations – this applies above all to the development of new reactor types such as SMRs, but also to changing operating conditions. This is the only way we can make reliable statements about the safety of installations in our European neighbourhood in the long run, and that is what makes international projects such as TANDEM so valuable to us.“
Sara Beck,Head of the Safety Research division
TANDEM results
The work carried out in the TANDEM project has shown that SMRs can, in principle, be suitable for controlling the assumed events as part of a hybrid energy network. For example, a sudden drop in heat demand led to the SMR's power control system establishing a new steady state and thus a safe condition by means of a controlled reduction in core power. However, it was also shown that, depending on the design of a real SMR, it may be necessary to limit the power of the reactor core using plant-specific control systems in order to avoid situations that would otherwise lead to reactor scam. Another important finding for future analyses is that the coupled system of ATHLET and MODELICA can be used to perform safety analyses even with complex control systems and in hybrid energy systems.
Detailed documentation of the results of TANDEM can be found on the project website.