Abstract:
DEMO (DEMOnstration Power Plant) is intended to be the direct predecessor of commercial Fusion Power Plants. The reference European DEMO is a steady-state device with an output power of 1 GWe. Recognizing the challenges which need to be met for steady-state operation of DEMO, an examination of the consequences of operation of this device in pulse mode is included as part of the European study.
Molten salt energy storage systems are well known and have been used in applications as simple as heating houses. High power applications related to electric energy production for the grid are known from the solar industry. In existing industrial facilities, the sensible heat of a molten salt is always used, but involving a phase transformation (melting) the associated heat of fusion is added to the heat storage capacity of the system.
The power output of the DEMO device during operation is 1 GWe, and with a pulse duration of 4-8 hours and a dwell time of only 5-20 minutes, supply to the grid and re-ignition of the plasma would require several hundred megawatts from the storage system to maintain the power output within acceptable limits.
An intense search for available technologies regarding molten salt energy storage has been carried out, and possible salts and systems to meet the requirements will be presented and directions for further research proposed. Metal hydrides could be the best candidates for such a system for several reasons, like very large heat of fusion and, moreover, an option for combining heat of fusion with heat of chemical reaction, thereby increasing the latent heat based thermal storage capacity. This latter offers controlled recovery of heat and even partial direct conversion of heat to electricity by thermally regenerative electrochemical cells.