Preliminary thermo-mechanical design of the once through steam generator and molten salt intermediate heat exchanger for EU DEMO

The European DEMO is considered to be the nearest-term fusion reactor with the aim to generate several hundred MWs of net electricity, operate with a closed tritium fuel-cycle (achieving the tritium self-sufficiency) and qualify technological solutions for a Fusion Power Plant. Two Breeding Blanket (BB) concepts relying on different cooling and breeding technologies are considered for the baseline design: the Helium Cooled Pebble Bed BB and the Water Cooled Lithium Lead BB. The selection of the BB type is a key factor for the development of the whole DEMO plant design and, in particular, of those systems having the responsibility to remove the plasma generated thermal power and its conversion in mechanical and finally electrical energy, namely: the Primary Heat Transport System (PHTS), the Power Conversion System (PCS) and the Intermediate Heat Transport System (IHTS) - equipped by an Energy Storage System (ESS) - in between PHTS and PCS, which is introduced with the purpose of buffering some energy produced by the pulsed plasma source to allow a continuous production of electricity. This work deals with the preliminary thermo-mechanical design of the once through molten salt/water steam generator exhausting the thermal power during pulse operation and of the helium/molten salt intermediate heat exchanger of the IHTS. The main challenges in the design are given by the implementation of the design rules according to nuclear standards, the cyclic operating load and, for what the main HX is concerned, the novelty of the application as well as the large dimensions of parts. The design criteria and the main design analyses developed to achieve the best simple but robust design are discussed.