Hydraulic assessment of an upgraded pipework arrangement for the DEMO divertor plasma facing components cooling circuit
Introduction
The European research roadmap, drafted to realize commercially viable fusion power generation, has defined reliable power exhausting as one of the most critical missions. Heat-exhaust systems must be capable of withstanding the large heat and particle fluxes of a fusion power plant, allowing, at the same time, as high performance as possible from the core plasma [1].
The divertor is the key in-vessel component in this context. Being responsible for power exhaust and impurity removal via guided plasma exhaust, the viability of fusion power generation heavily depends indeed on the heat load that can be tolerated by the divertor under normal and off-normal operation [2]. Therefore, particular attention has to be paid to the thermal-hydraulic design of its cooling system, to ensure a uniform and proper cooling, without an unduly high pressure drop.
In the context of the Work Package DIVertor (WPDIV) [3], [4] of the EUROfusion action and in line with previous research activities [5], [6], [7], [8], [9], a research campaign has been carried out by University of Palermo (UNIPA) in cooperation with ENEA to assess the thermal-hydraulic performances of the DEMO divertor Plasma Facing Components (PFCs) cooling circuit.
Attention has been initially focussed on the layout of the PFCs cooling circuit released in early 2019 and consistent to DEMO Baseline 2017 [10], assessing its steady-state thermal-hydraulic performances. These latter shall comply with the requirements on pressure drop ( MPa) and CHF margin (1.4) [11], while providing a uniform flow distribution among PFU channels.
Then, according to the issues arisen from this first thermal-hydraulic assessment, the PFCs cooling circuit layout has been optimized focussing the attention on the inlet manifold branch, thus allowing for a significant pressure drop reduction.
As a consequence, a second optimized PFCs cooling circuit layout has been released in 2019, taking into account both the indications given by thermal-hydraulic calculations and some manufacturing considerations [12]. The thermal-hydraulic performances of this upgraded PFCs cooling circuit have been numerically assessed under nominal steady-state conditions to check if the aforementioned requirements are met.
The research activity has been performed following a numerical technique based on the Finite Volume Method (FVM) and adopting the well-known ANSYS CFX v.19.2 R1 Computational Fluid-Dynamic (CFD) code [13]. The same approach has been already used by authors in similar studies [14] and adopted to evaluate concentrated hydraulic resistances to be used in system codes [15], [16]. Models, assumptions and boundary conditions are reported in the following and thoroughly discussed, alongside the main results obtained.
Section snippets
The 2019 DEMO divertor and PFCs cooling system
In conformity with its 2019 design [11], the DEMO divertor consists of 48 toroidal assemblies (divertor cassettes). Each one includes a Cassette Body (CB), endowed with a Liner and two Reflector Plates (RPs), that supports two PFCs (Fig. 1). These latter are named Inner and Outer Vertical Target (IVT, OVT), and are comprised of actively cooled Plasma Facing Units (PFUs) equipped with Swirl Tape (ST) turbulence promoters.
The cooling scheme adopted for the DEMO divertor, developed by the
PFCs cooling circuit CFD analysis
The thermal-hydraulic performances of the PFCs cooling circuit under the coolant operating conditions of Table 1 [11] have been assessed by running steady-state, isothermal CFD analyses, where the temperature of the fluid inside the PFCs has been supposed to be equal to the average value between inlet and outlet sections, evaluated by means of simple thermodynamic calculations. Moreover, realistic configurations with swirl tape turbulence promoters inside each PFU cooling channel have been
Design optimization
The performed analyses have highlighted the need for a revision of the PFCs layout, mainly intended to reduce both distributed and concentrated hydraulic resistances at the inlet/outlet manifold branches. Therefore, focussing the attention on the inlet manifold branch of the analysed PFCs layout, the thermal-hydraulic behaviour of selected revised configurations has been assessed by running local, steady-state, isothermal CFD analyses.
At first, since both distributed and concentrated hydraulic
Upgraded PFCs cooling circuit CFD analysis
On the basis of the optimization results and of some manufacturing considerations, the Divertor CAD team revised the PFCs cooling circuit layout, introducing similar improvements also for the outlet manifold branching schemes. The mesh parameters selected for the considered PFCs cooling circuit are similar to those reported in Table 2, while the adopted main assumptions, models and boundary conditions are the same of Table 3.
The coolant pressure spatial distribution for the upgraded
Conclusions
Within the framework of the activities promoted by the EUROfusion consortium, University of Palermo in cooperation with ENEA carried out a research campaign to evaluate the thermal-hydraulic performances of DEMO divertor cassette cooling system, posing the attention on the PFCs cooling circuit 2019 configuration.
A theoretical-numerical approach based on the FVM has been followed adopting the well-known ANSYS CFX CFD code.
The PFCs cooling circuit nominal thermal-hydraulic behaviour has been
Authors’ contribution
P.A. Di Maio, R. Burlon, G. Mazzone, A. Quartararo, E. Vallone and J.H. You: conceptualization, methodology, investigation, writing – original draft.
Conflict of interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgments
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratomresearch and training programme 2014–2018 and 2019–2020 under grant agreement no. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
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2023, Fusion Engineering and DesignThermofluid-dynamic assessment of the EU-DEMO divertor single-circuit cooling option
2023, Fusion Engineering and DesignCitation Excerpt :In particular, this latter condition is required to increase the divertor lifetime, affected by neutron irradiation, which causes embrittlement and reduction of strength, and is dependent on the component operating temperature [1,14]. A coolant inlet temperature of 130 °C and an inlet pressure of 70 bar were selected as trade-off values, based on the outcomes of the parametric analysis campaigns, to be compared to 130 °C and 50 bar previously adopted for the PFCs cooling circuit [13], and 180 °C and 35 bar of the CB cooling circuit [12]. It is moreover important to emphasize how the 70 bar inlet coolant pressure choice was dictated solely for further improving the CHF margin of the VTs and, therefore, its actual adoption requires detailed studies to assess the structural integrity of the cassette and of the welds to be performed, and eventually to revise the divertor design.
High-heat-flux performance limit of tungsten monoblock targets: Impact on the armor materials and implications for power exhaust capacity
2022, Nuclear Materials and EnergyCitation Excerpt :The minimum heat flux margin to the critical wall heat flux of nucleate boiling at the pipe wall reached ≥ 40 % (1.4) under stationary heat load of 20 MW/m2. The computational verification of the cooling scheme is found elsewhere [5,18–19]. Hot radial pressing (HRP) was adopted as baseline joining technology [20,21].
Divertor of the European DEMO: Engineering and technologies for power exhaust
2022, Fusion Engineering and DesignCitation Excerpt :The hydraulic parameters of the coolant defined for the targets and the CB (incl. SL and RPs) are listed in Tables 6 and 7, respectively [47,54]. The predicted hydraulic behavior was verified by an experimental test using a full-scale prototype mock-up of the OVT at a water-loop equipped with a diverse diagnostic instrumentation system [55].