•Wettability of Eurofer and SS316 by sodium-potassium NaK-78 was studied 50–350°C.•Wettability of the steels is mainly affected by temperature of steel-NaK system.•Wettability of Eurofer by NaK-78 ...can be assured when its temperature is 350°C.•The results aim to achieve optimal filling of the IFMIF HFTM capsules with NaK-78.
Several validation activities were dedicated to the High Flux Test Module (HFTM) of the International Fusion Materials Irradiation Facility (IFMIF) at the Karlsruhe Institute of Technology (KIT) in Germany. The HFTM contains 24 capsules packed densely with Eurofer specimens to facilitate their irradiation in the high flux zone directly behind the IFMIF neutron source. The small gaps among the Eurofer specimens are filled by the sodium potassium eutectic alloy NaK-78 to improve the thermal conduction among the specimens and achieve uniform and predictable temperature distribution. As a result of first trials, the filling process of NaK-78 into the specimens’ capsule had been identified as an issue worth further investigations. Therefore, the wettability of the steels Eurofer and SS 316 by NaK-78 is experimentally investigated to evaluate the applicability of this concept and identify the favorable conditions. In the experiment, the capillary rise of NaK-78 in a two-parallel-plates channel (gap) is investigated versus the following: (i) temperature of both NaK-78 and the parallel plates from 50°C to 350°C, (ii) machining techniques used for the parallel plates, (iii) thickness of the gap between the plates, and (iv) material of the parallel plates including Eurofer and SS 316. The present experimental results will help in defining the working conditions required to achieve an optimal filling of the IFMIF HFTM capsules with NaK-78 and a complete wetting of the capsules’ specimens.
•A reference neutronic model for IFMIF test cell was developed in the EVEDA phase.•The necessary biological shielding thickness was assessed.•The present analysis revealed that all in-cell components ...must be actively cooled.•The higher helium production expected in the test cell liner is critical.
The IFMIF test cell (TC) design has been further developed and optimized in the EVEDA phase, and finally the reference TC design has been proposed. In order to carry out the detailed neutronic analysis for the reference TC design, a very detailed geometrical model for Monte Carlo neutronic calculations has been prepared directly from engineering CAD data by utilizing the McCad conversion software developed at KIT. The geometrical model includes the detailed descriptions of the lithium target system proposed by Japan, all test modules based on the EVEDA phase design, and the 3-dimesional arrangement of the biological shielding. The Monte Carlo code McDeLicious, which is an enhancement to MCNP5, has been utilized in order to adequately simulate the neutron and photon productions from the 6,7Li(d,xn) reactions in the lithium target. The present analysis is focusing on the nuclear heating distribution inside the biological shielding, the nuclear property of the TC liner, and the biological dose distribution around TC during operation. Some countermeasures for reducing the He production in the liner are discussed.
•Rib-roughened channel design for FW cooling was investigated by DES.•Flow and heat transfer characteristics are well resolved by DES.•Correlations for predicting the friction and heat transfer were ...evolved.•Local maxima of heat transfer correlates with peak turbulent levels.•Temperature “hot spots” are located downstream of the rib elements.
Improved cooling channel designs of helium cooled first wall (FW) applications focus on efficient heat transfer enhancement and reduced material temperatures, even for high incident heat flux densities of more than 0.5MW/m2. To this end, thermohydraulics of turbulent flow in a one-sided heated, one-sided rib-roughened channel with squared, round-edged cross section were predicted by Detached Eddy Simulations (DES) at Reynolds numbers ranging from ReDh=1.0E4 to ReDh=1.5E5 and at heat up rates ranging from q+=1.1E−3 to q+=7.48E−4, encompassing the envisaged operation envelope of helium cooled FW cooling channels. The rib-roughened channel wall consists of centrally positioned, transversally oriented rib elements with a rib-pitch-to-rib-height-ratio of p/e=10, a rib-height-to-hydraulic-diameter-ratio of e/Dh=0.0638 and a rib-width-to-channel-width-ratio of l/W=0.6. Mean flow and heat transfer quantities, turbulent fluxes and flow structures were analyzed. Anisotropic, large-scale eddies originated in separated shear layers are shed vertically and laterally to the flow. Maximum heat transfer correlates with regions of maximum span- and crosswise turbulent fluctuations and is located at the rib leading edge. Minimum heat transfer occurs within the region of the counter-rotating vortex behind the rib.
► A very detailed Monte Carlo geometry model of IFMIF target and test cell (TTC) was prepared directly from a CAD model by using the McCad conversion software developed at KIT. ► Nuclear heating, ...displacement damage and gas production rates in the TTC vessel wall were evaluated. ► The result suggests it is very important in the neutronic analysis to consider the detailed configuration of TTC and test modules. ► Substantial improvement in the shielding capability for the top access cell has been demonstrated for the present TTC design.
This work presents neutronic analyses to support the IFMIF target and test cell (TTC) design in the framework of the Broader Approach activities. A very detailed Monte Carlo geometry model of IFMIF TTC based on the modular TTC concept was prepared directly from a CAD model by using the McCad conversion software which has been developed at KIT. The Monte Carlo code McDeLicious, which is an enhancement to MCNP5, was utilized and nuclear heating, displacement damage and gas production rates in the TTC vessel wall were calculated. The calculation result shows that there are two prominent peaks; downstream of the test modules due to the high energy neutron contribution for gas productions and upstream due to neutron back-streaming along the beam ducts. The result suggests it is very important in the neutronic analysis to consider the detailed configuration of TTC and test modules. The dose rate distribution during operation has been assessed for the rooms adjacent to TTC across thick surrounding walls. The necessary thickness for the shielding walls has been examined. The result demonstrates the substantial improvement in the shielding capability for the top access cell with the present TTC design.
•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.
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.
•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.
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, 2mm radius round-edged front- and rear-rib-surface). Turbulent flow and heat transfer for 8MPa pressurized helium-gas with a helium mass flow rate of 0.049kg/s were computed by the Detached-Eddy-Simulation approach. A constant heat flux density of 0.75MW/m2 and 0.08MW/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 7.5kW/m2K and from 7.6 to 8.1kW/m2K 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.
•A gas loop for fusion R&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.
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 0.02–0.38MPa abs., (ii) test section pressure head up to 0.12MPa, (iii) tolerable gas temperature RT – 200°C and (iv) mass flow rate 0.2–12×10−3kg/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.
IFMIF-DONES (International Fusion Material Irradiation Facility- DEMO Oriented NEutron Source) is an accelerator based irradiation facility which is aimed to provide the irradiation data needed for ...the construction of DEMO. The Test Cell (TC) is the central room of IFMIF-DONES enclosing the target and the test module. This work presents the neutronics analyses conducted to provide the relevant nuclear responses for the bio-shield of the TC, including heating, radiation damage and helium production. The results for the TC steel liners covering the inner TC surface have been obtained with an unstructured mesh based interpolation approach. The results show that the softening of the neutron spectrum at the thin layer of the inner wall increases the nuclear heating as well as the helium production in SS316 L. The helium production might be of major concern if re-welding of the liner is required during the lifetime. The impact of a reduced beam footprint size on the TC nuclear responses has been analyzed and found to be insignificant comparing with the normal footprint.
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.
PDF
