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European Consortium for the Development of Fusion Energy (EUROfusion) project


KIT experts aim to continue the Power conversion studies (1994) for a modular concept of a Helium Primary Heat Transfer System (PHTS), combined to a Power Conversion System (PCS) with the integration of a thermal energy storage device for a pulsing DEMO fusion power plant (see Figure 1).

This activity in our group is performed as part of the EUROfusion PPPT (Power Plant Physics & Technology) work program focused on Balance of Plant. 


Figure 1. Simplified Fusion Power Plant (FPP) schematics


The task of Balance of Plant is to use heat from different sources such as Breeding Blanket (BB), Divertor (DIV), and Vacuum vessel (VV) for power conversion to enhance the efficiency of the DEMO reactor and to provide solutions for future FPPs.

KIT’s contribution started with a review of the DEMO concept to define essential interfaces and requirements for BOP. BOP is responsible for transferring exhaust energy into usable and valuable electrical energy, the next step in fusion development after ITER. Compared to other energy conversion systems, the internal energy need of a fusion reactor is very high, so that energy harvesting becomes indispensable. Because of that, KIT asked different internal power consumers to provide the excess heat on usable temperature levels, e.g. the cooling of gyrotrons, etc. As a typical cross-cutting subsystem, BoP has multiple interfaces to other subsystems as shown in Figure 2. Here the relationships are also visible; solid lines indicate exchange of mass and/or energy, dashed lines indicate logic or electric interfaces.


Figure 2. Interaction of BOP with other DEMO sub-systems


Balance of plant (BoP) is subdivided into the power conversion chain (PCC) composed of the primary heat transfer system (PHTS), an intermediate heat and storage system (IHTS) with an thermal energy storage system (ESS) to cope with dwell times (due to DEMO pulsed operation), and the power conversion system (PCS) itself (see Figure 3).



Figure 3. Balance of plant (BoP) schematics


As part of the overall design of DEMO KIT develops a plant model based on the industrial code EBSILON© (STEAG) to get a fast information of the consequences of design modifications. The design takes into account safety requirements, as well as design limitations due to the availability of large components such as heat exchangers and pumps. The current design developed together with CEA (France) comprises of 3 in-board (IB) loops and 6 out-board (OB) loops. Starting with the 6 OB and 3 IB loops the energy of the plasma is transferred by helium via an Intermediate Heat Exchanger (IHX) to the solar salt, which transport it out of the tokamak building to the IHTS storage building, which is actually an industrial 2-tanks design. The steam generator (SG) boils and superheats the feed water and delivers it to the steam turbine (ST). The steam turbine design follows state of the art concept, but is not finally optimized. Taking into account a pulse time of 2h and a dwell time of 0.5 h, DEMO can operate permanently under 80% power and/or allowing flexible power operation without interfering with plasma operation. Due to the live steam extraction at high pressure and low pressure turbine stages, the efficiency of the PCS is increased, also during dwell time reducing the burden to the energy storage system.

In summary, all presently developed mechanisms of fossil fired plants to cope with fluctuating grid demands are available, plus the heat stored in the ESS. Using all these techniques, a future FPP is perfectly suited to replace fossil fired power plants also for grid stabilization.


Education and training


In this framework KIT offers bachelor and master thesis on different topics such as component design and optimization, simulation and safety analyses.



[1]  W. Hering, E. Bubelis, “Final Report on Deliverable PHTS and BOP Safety Requirements Document (PBSD)”, EUROfusion, KIT report No. INR-2/16, FUSION 484 (2016)
[2] W. Hering, E. Bubelis, “PHTS and BOP Safety Requirements Document (PBSD)”, EUROfusion (2015)
[3] E. Bubelis, W. Hering, “Conceptual designs of PHTS, ESS and PCS components for DEMO BoP with Helium cooled BB and water cooled BB concepts“, EUROfusion, KIT report No. INR-4/16, FUSION 485 (2016)
W. Hering, E. Bubelis, “Final Report on Deliverable PHTS and BOP Safety Requirements Document  (PBSD)”, EUROfusion (2016)