Solving the core cooling problem for safer nuclear energy
Decay heat must be removed from the core of nuclear power stations. An EU-funded project demonstrated a reliable and efficient way of removing decay heat, without the need for external power sources, to enhance the safety of nuclear power plants even under potential (Fukushima-like) severe accident conditions.
© Gesellschaft für Simulatorschulung, 2019
Even when the chain reaction in a nuclear power station stops, the reactor core continues to emit heat. This decay or residual heat must be removed from the nuclear fuel. Under potentially severe accident conditions, existing nuclear power stations rely on external energy sources, or back-up systems such as diesel engines, to transfer the heat to a heat sink, such as a cooling tower or cooling pond, river or sea.
The EU-funded sCO2-HeRo project demonstrated a safer, more reliable and efficient way of removing decay heat, without the need for external power sources. The projects solution can provide a cooling system for the reactor core that will continue to function in the event of an external power cut.
The sCO2-HeRo system has the potential to significantly increase the safety of nuclear power plants, says project coordinator Dieter Brillert from the University of Duisburg-Essen in Germany. It will extend the period of reliable and safe decay-heat removal during a station blackout and will also generate electricity, which is extremely valuable during a long-term blackout.
The projects supercritical CO2 heat removal system is a highly innovative reactor safety concept because it makes use of the decay heat itself to power the heat transfer process.
It is a self-propellant, self-sustaining and self-launching, highly-compact cooling system which exploits the superior heat-transfer properties of supercritical carbon dioxide (sCO2). Acting as a supercritical fluid, sCO2 has advantages over air and steam for closed-loop power generation, by increasing efficiency and power output.
The projects new technology uses decay heat to drive a cooling cycle that transfers heat from the reactor into the ambient air. The cooling cycle is self-starting, and the system could significantly improve the safety of both currently operating and future BWRs (boiling water reactors) and PWRs (pressurised water reactors).
Test loops and model
Project partners built and tested different components of the system. Experiments and tests on these were carried out in the supercritical CO2 test loop SCARLETT at IKE University of Stuttgart and in the test loop SUSEN at Research Centre Å˜e in Czechia.
The testing of the compact heat exchanger, the turbomachine and the sink heat exchanger are finished and validated with simulations to ensure the quality of the individual components, says Brillert.
The full system was assembled in a unique glass model of a PWR at the Simulator Centre of GfS in Essen.
The integration of the components in the glass model has been accomplished as well as the implementation in a full-scope simulator at GfS, which is a 1:1 copy of the control room of the Grundremmingen nuclear power plant, Brillert explains. The simulation tests proved sCO2-HeRo to be a reliable and efficient system for removing heat from a nuclear core without an external power supply.
The next steps will include the construction of a pilot cooling system on a representative scale, and the agreement of national safety authorities and nuclear power plant operators, Brillert explains.
Work is continuing to upscale and refine the technology, and to complete the demonstrations in different types of reactors, in the follow-up project sCO2-4-NPPP. In addition to being applicable to existing reactor types, the system has been designed for integration into future reactor models, including Generation 4 reactors and small modular reactors.
In the long term, Brillert concludes, this innovation supports the renewal of the confidence of the European population in nuclear energy based on the new safety achievements and opens a route to reducing carbon dioxide emissions.