Status, Design and Thermal-Hydraulic Analyses of the Steam Facility for DEMO WCLL Balance of Plant Systems

DEMO is a nuclear fusion power station that has, among others, the objective of demonstrating the possibility to produce several hundred MWs of electrical power from fusion reaction by the middle of this century, increasing the production of carbon-neutral electricity. In particular, the Balance of Plant of DEMO has the key role to demonstrate the feasibility of delivering the power produced within the Tokamak reactor to the grid. The design approach for Water Cooled Lithium Lead (WCLL) Breeding Blanket (BB) Primary Heat Transfer Systems (PHTSs) considers the Nuclear Power Plant experience, adopting components commonly used in nuclear industry. However, their performances could be negatively affected by the discontinuous operation (pulse-dwell-pulse) of the DEMO machine, as well as by low-load operation in dwell time. This makes mandatory a full assessment of the functional feasibility of such components throughout an accurate design and validation. ENEA Experimental Engineering Division at Brasimone R.C. supports the design and qualification of DEMO by realizing STEAM, a water operated facility conceived to investigate the water technologies applied to the DEMO BB and Balance of Plant systems and components. STEAM is mainly composed by a water primary system reproducing the DEMO WCLL BB PHTS thermodynamic conditions (15.5 MPa, 328-295°C) and a secondary two-phase (liquid/steam) water loop reproducing the DEMO power conversion system conditions (6.4 MPa, 238-300°C). The experimental validation aims at reproducing steady-state and transient operation in DEMO-relevant conditions, as well as to perform dedicated tests on a once through steam generator mock-up, representative of the one envisaged for DEMO, aiming at testing its performances during the power phases of the machine. Thermal-hydraulic analyses of STEAM have been performed by RELAP5/Mod3.3 system code. Steady-state qualification results are presented in this paper, along with the characterization of the facility dynamic behavior, realized in order to optimize the system layout and to assess the performances of the main components during the prescribed operating conditions.