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The supercritical CO2 Heat Removal System

Periodic Reporting for period 2 - sCO2-HeRo (The supercritical CO2 Heat Removal System)

Reporting period: 2017-03-01 to 2018-08-31

The “supercritical CO2 heat removal system”, sCO2-HeRo, safely, reliably and efficiently removes residual heat from nuclear fuel without the requirement of external power sources. This system therefore can be considered as an excellent backup cooling system for the reactor core or the spent fuel storage in the case of a station blackout and loss of ultimate heat sink. sCO2-HeRo is a very innovative reactor safety concept as it improves the safety of currently operating BWRs and PWRs through a self-propellant, self-sustaining and self-launching, highly compact cooling system powered by an integrated Brayton-cycle using supercritical carbon dioxide. This system provides breakthrough options with scientific and practical maturity, The objective of the project is to show the proof of the concept of the sCO2-HeRo system which is defined as the capability of handling different accident scenarios. This capability has been demonstrated by reactor simulation studies at the Gesellschaft für Simulatorschulung GfS, accompanied by simulation studies with the German thermal-hydraulic system code ATHLET. The sCO2-HeRo system objectives are fulfilled and therefore the system can be classified in TRL-3.
The system design of the sCO2-HeRo was performed and the components are specified to integrate the sCO2-HeRo into the glass model loop. This includes the major components as well as minor components like valves, pipes, the control system including the consideration of safety requirement like risk analysis etc. The SUSEN and SCARLET loop are prepared for the component tests to run individual tests for the heat exchangers and the turbo-machine. Within both loops, the component tests have been successfully accomplished and valuable input data has been provided for the design and validation of the numerical simulations which vice versa supports the design. All components are delivered and integrated into glass model. The sCO2-HeRo project had to experience a force majeure event at GfS: on 10th June 2018, at about 4am due to a heavy rain event, a flood caused severe damage to GfS buildings, offices and, unfortunately, to the power supply of the glass model (located at the cellar). Therefore, the tests of sCO2-HeRo cycle cannot be performed as foreseen in the work plan. The new task was to simulate a combined SBO and LUHS scenario using the full scope simulator at GfS for the BWR unit of 3840 MWth (Gundremmingen). The simulator provides a 1:1 copy of the control room of the aforementioned BWR, used for training purposes of reactor personnel. For the purpose of sCO2-HeRo, several operational and transient simulations were successfully performed and demonstrated the capability of the sCO2-HeRo system to handle different accident scenarios.
The status of the project and its objective was presented on conferences and on the “1st and 2nd European supercritical CO2 conference” chaired and organized also by the members of the sCO2-HeRo team. Journalists interviewed the team at the glass model and a TV spot was published on the website. Students and PhD students supported the project with their work and energized the discussion about the nuclear industry.
The sCO2-HeRo project provides a level playing field for top-level scientists to enable their highly innovative ideas to demonstrate the functionality of the advanced self-sustaining safety system by
- designing a compact heat exchanger to transport the decay heat to the supercritical CO2 cycle whose energy is also used for driving the self-propellant cycle,
- designing a turbo-machine set which is self-propellant and self-launching, evaluation of a sink heat exchanger to transport the decay heat from the supercritical CO2 cycle to the alternative ultimate heat sink (ambient air),
- ensuring quality assurance by individual component reviewing and testing the individual components in a supercritical CO2 loop to demonstrate the fulfilment of industrial standards like the KTA and
- finally proofing the concept of sCO2-HeRo regarding safety, reliability and the possibilities for retrofitting by implementing the system into a unique glass model run by the Gesellschaft für Simulatorschulung GfS.
By demonstrating the functionality of the system, it enables the nuclear industry to increase the level of safety for black-outs. In addition the know-how of supercritical CO2 system unleashes some capabilities and options for the energy market e.g. for the concentrated solar power industry and for the environment by using CO2 instead of water which is very rare in the area of the plants for solar power.