[en] Highlights: • This paper presents a comprehensive thermo-hydraulic analysis on a kind of V-shaped ribbed-channel. • Heat transfer performance of V-shaped ribbed-channel was compared with smooth, and channel with transversal ribs. • Optimization was done on the rib geometry (rib angle and rib pitch) and channel aspect ratio. • A major mechanism of heat transfer enhancement for the V-ribbed channels is the two large scale circulations induced by the two legs of the V-ribs. - Abstract: Helium gas as a coolant offers several advantages in terms of safety. However the use of standard smooth cooling channel surfaces are limited regarding the cooling of high heat flux components in fusion power reactors. Based on our previous assessments, a round-edged, one-side-ribbed rectangular channel was chosen as the baseline geometry, with the ribbed-side facing the plasma-facing wall. This paper presents the optimization of the V-shaped ribbed channel by means of CFD simulations. Thus the effects of the rib pitch, rib angle and channel height are studied. The main criteria for assessing the results are the heat transfer coefficient which determines the maximum wall temperature and, the friction factor which determines the pumping power. The results are also compared with the standard transversal ribbed channel and smooth channel.

[en] Highlights: • A gas loop for fusion R and D has been built and tested. • Facility requirements and their implementation are given. • The loop's functions and instrumentation are explained. • The loops performance has been characterized. - Abstract: FLEX (Fluid Dynamics Experimental Facility) is a multi-purpose small scale gas loop for research on fluid and thermodynamic investigations, especially heat transfer, flow field measurements and gas purification. Initially it was built for investigation on mini-channel gas-flow to design the HFTM module of IFMIF. Because of its versatility it offers a wide range of further applications, e.g. the research of pressure drops in mockups of breeder units of the helium cooled pebble bed (HCPB) test blanket module for ITER. The main parameters of the loop, which can be operated with inert gases and air are: (i) operation gas pressure 0.02–0.38 MPa abs., (ii) test section pressure head up to 0.12 MPa, (iii) tolerable gas temperature RT – 200 °C and (iv) mass flow rate 0.2–12 × 10⁻³ kg/s for Helium. This paper gives a detailed view of the loop assembly with the components that generate and regulate the mass flow and loop pressure. The measurement instrumentation will be presented as well as a representative mass flow-pressure drop characteristic. Furthermore, the achievable gas purity will be discussed

[en] For fusion material research, minichannel gas flows are designed to cool irradiated material specimens. Since the facility design requires accurate prediction methods for the temperatures in the structure and the specimens, relevant experiments were conducted. This paper reports on the experimental procedures, which are specific to the small scale of the channels, and elucidates results obtained for wall friction, heat transfer and velocity profiles. Comparisons between the experimental data and engineering correlations as well as CFD calculations are presented. These comparisons reveal good accordance of the presented minichannel data with classical engineering correlations, and indicate the fitness of the v2f turbulence model for numerical flow field predictions in the scope of the considered application. (author)

[en] Highlights: • This paper presents a comprehensive thermo-hydraulic analysis of the IFMIF High Flux Test Module. • The turbulence models were validated by in-house experiments. • Multiple fluid domains were employed and simulated with appropriate turbulence (laminar) models individually. • The flow distributions and heat transfer characteristics among various HFTM sub-channels were discussed. -- Abstract: The International Fusion Materials Irradiation Facility (IFMIF) is designated to generate a materials irradiation database for the future fusion reactors. In the High Flux Test Module (HFTM) the test specimens will undergo a severe structural damage caused by neutron fluxes. The HFTM will be with helium gas. This paper presents the comprehensive thermo-hydraulic simulations of the HFTM as a part of the design activities. The turbulence models were assessed by comparing the simulations with in-house annular channel experiments. Since the required coolant flow rates are different for different compartments, multiple fluid domains were employed and simulated with appropriate turbulence (laminar) models individually. The flow distributions and heat transfer characteristics among various HFTM sub-channels will be discussed. Sensitivity study was carried out to assess the impacts of several factors on the simulation results

[en] Highlights: • V-shape rib-arrays are more efficient than comparable smooth channel flows. • Heat transfer is significantly increase for channels structured by V-shaped rib-arrays. • Thermal performance is significant increased by the investigated rib-arrays. • Structured heat transfer surfaces provide an efficient cooling for the First Wall. - Abstract: Rib-roughening the helium-gas cooling channels in the plasma facing components of DEMO (First Wall, limiters or the divertor) enhances heat transfer and reduces structural material temperatures. In the present study the applicability of six different surface-attached rib-arrays and of two different detached rib-arrays was examined for increasing the thermal performance within the helium-gas First Wall cooling concept. The rib-arrays consisted of transversally oriented or upstream directed 60° (with respect to the centerline) V-shaped ribs with different rib cross section (square, trapezoid, 2 mm radius round-edged front- and rear-rib-surface). Turbulent flow and heat transfer for 8 MPa pressurized helium-gas with a helium mass flow rate of 0.049 kg/s were computed by the Detached-Eddy-Simulation approach. A constant heat flux density of 0.75 MW/m² and 0.08 MW/m² was applied at the plasma-facing and breeding-blanket-facing First Wall structural surface respectively. The results showed that structuring the thermally highly loaded cooling channel surface with rib-arrays of 60° V-shaped ribs provides an efficient heat transfer and increases the cooling performance of the First Wall. The corresponding heat transfer coefficient was in the range from 7.1 to 7.5 kW/m² K and from 7.6 to 8.1 kW/m² K for the attached and detached V-shaped ribs respectively. Compared to smooth channel flows, only 14–16% of the pumping power is required to obtain an equivalent heat transfer performance or, from another point of view, the heat transfer coefficient can be increased by 168–172% for a constant pumping power.

[en] Highlights: • Two different single 1:1 irradiation rigs inside a mock-up container are presented. • Pressure drops in the single rig minichannels are measured. • Temperature fields are measured under different heater and flow conditions. • Predictability and reproducibility of the cooling flows can be shown. - Abstract: The hydraulic and thermal testing of two different irradiation rig models A and B, differing in the inlet nozzle design, bottom reflector length and steps inside a mock-up container is part of the HFTM validation activities which support the engineering design of the High Flux Test Module. The pressure drops for all models in the test section are measured for overall mass flow rates of 1–12 g/s and different absolute pressures of 1500 hPa and 2500 hPa at the pressure port at the inlet section. The pressure drops in different sections of the experiment and in the single rig minichannels are also measured with additional pressure ports on the surfaces of the rig models. Predictability and reproducibility of the cooling effects of the main cooling channels in the HFTM irradiation zone can be shown. Rig model B with a backward facing step is for high mass flow rates >∼7.5 g/s (this is the operation regime of the HFTM) superior to rig model A. Uniform perfusion of the multiple parallel minichannels of the irradiation rigs by helium gas is of importance to obtain uniform and predictable temperatures. Temperature fields under different heater and flow conditions have been measured.

[en] Highlights: • Full range of IFMIF HFTM operation temperatures (250–550 C) could be well achieved and well controlled with and without “nuclear” heater power. • The temperature spread measured inside a capsule for the 350 C reference case is fulfilling very well the requirements. • The temperature spread is in the range of  +/−3 K in the lateral direction and +2 K/−8 K in the vertical direction. • No unforeseen thermal hydraulic effects like oscillations, hysteresis etc. could be detected. • To cool down from 350 °C to 50 °C it takes roughly 315 seconds, heating up 135 seconds. - Abstract: During the EVEDA phase of the International Fusion Materials Irradiation Facility (IFMIF), the High Flux Test Module (HFTM) was developed as dedicated irradiation device for Small Scale Testing Technique (SSTT) material specimens in the intensive IFMIF neutron radiation field. The specimens are contained in temperature controlled irradiation rigs. Since one of the requirements for the HFTM is to provide a uniform temperature field for the irradiated specimens, thermal testing was a priority for the performed validation activities. In the HFTM “single-rig” (HFTM-SR) experiments a single rig of 1:1 scale was tested. The heater plates and the specimen region inside the rig were instrumented with thermocouples to monitor heat transfer and specimen temperature spread. In the High Flux Test Module “double compartment” (HFTM-DC) experiments a fully equipped prototype with three heated rigs was tested in the HELOKA-LP helium loop. Special heater cartridges are used to substitute the nuclear heating. These experiments show that the full range of operation temperatures (250–550 °C) required for the IFMIF HFTM could be well achieved and well controlled with and without surrogate nuclear heater power. The temperature spread measured inside a capsule is in the range of +/−3 K in the lateral direction and +2 K/−8 K in the vertical direction for the 350 °C reference case, fulfilling very well the requirements. This compares well to an allowed +/−19 K range according to the requirements. No unforeseen thermal hydraulic effects like oscillations, hysteresis etc. could be detected. To cool down from 350 °C to 50 °C it takes roughly 315 seconds, heating up 135 seconds.

[en] Highlights: • Successful manufacturing of HFTM – shortcomings identified in regard of welding (large deflection). • Brazing and heat treatment of capsule material (P92) to change martensitic microstructure to austenite and carbide. • Important design improvements in “conclusion and improvements”, derived from manufacturing (and operation −>not specified in paper). - Abstract: The High Flux Test Module (HFTM) of the International Fusion Materials Irradiation Facility (IFMIF) is a device to enable irradiation of Small Scale Testing Technique (SSTT) specimens by neutrons up to a structural damage of 50 displacements per atom (dpa) in an irradiation campaign of 1 year. The IFMIF source generates neutrons with a D-T-fusion-relevant energy spectrum and a flux to achieve a damage rate over 20 dpa per full power year (fpy) in a foreseen volume of 0.5 l. Irradiation temperatures are in the range of 250–550 °C. According to the IFMIF conditions and requirements, the IFMIF HFTM has been developed in the IFMIF/Engineering Validation and Engineering Design Activities (EVEDA) phase and a prototype was constructed and tested. The manufacturing process of relevant parts, like attachment adapter and container, is presented – especially with focus on problems in manufacturing accuracy. The capsule manufacturing process with focus on brazing process and finishing of the capsule shape is explained in detail. Optimization potentials derived from the manufacturing process and the experimental experiences are highlighted.

[en] Highlights: • A comparative neutronics assessment of two QT location options provides key information for the IFMIF-DONES TC design. • A parametric study of the neutron streaming effect in the lithium chute has been conducted. • Shutdown dose analysis of DONES test cell shows that the dose rate in the lithium facility room is too high to be hands-on accessed. - Abstract: The quench tank (QT) location in the test cell is an open issue for IFMIF-DONES (International Fusion Material Irradiation Facility- DEMO Oriented NEutron Source) design. Neutronics assessments have been carried out on two QT location options. A parametric study of the neutron streaming in the lithium chute shows a quasi-linear dependence of the neutron flux on the void thickness. For both options, activation calculations at key locations of the QT system indicate that the contact dose rate is higher than the hands-on dose limit over the whole maintenance period. In addition, the shutdown dose rates in the lithium facility room after 1-day shutdown exceed the hands-on dose limit in different levels. Therefore, remote handling is required for the maintenances of the QT in both considered locations.

[en] Helium flows at low pressure (3 bar) are used to cool the specimen capsules and the structure of the neutron irradiated High Flux Test Module (HFTM) of the DEMO-Oriented Neutron Source (DONES). The flow path includes inlet and outlet ducts with large cross sections, but also mini-channels with gap widths less than 1 mm, where a high velocity low Reynolds number flow influences the temperature of the irradiated specimens. The aim of the study was the achievement of thermal requirements to the HFTM. The large span of Reynolds numbers from laminar to fully turbulent is a significant challenge for the simulation of the complete HFTM. Several turbulence models were tested using experimental results obtained in the ITHEX (IFMIF Thermal-Hydraulic Experiment) experimental facility. Reynolds Stress (RSM) and k-ω Shear Stress Transport (SST) models are able to reproduce the heat transfer within the Reynolds number range between 4500 and 10,000. Simulations show that in case of 100% nuclear heating conditions the prescribed temperature of specimen can be achieved by justification of electrical power and variation of helium mass flow rate for each HFTM compartment.