The International Fusion Materials Irradiation Facility (IFMIF) is designated to generate a materials irradiation database for the future fusion reactors. The High Flux Test Module (HFTM) is located ...behind the lithium target where a structural damage rate of more than 20dpa/fpy in steel specimen will be achieved in a volume of about 0.5l. This paper concerns the thermo-hydraulic simulations of the HFTM with Ansys-CFX. The simulation domain consists of the whole HFTM with short fluid inlet and outlet sections. The turbulence models were assessed by comparing the simulations with in-house annular channel experiments. The flow distributions and heat transfer characteristics among various HFTM sub-channels are the main focuses of this study.
•Existing first wall designs and expected plasma heat loads are reviewed.•Heat transfer enhancement methods are investigated by CFD.•The results for heat transfer and friction are given, compared and ...explained.•Relations for needed pumping power and gained thermal heat are shown.•A range for the maximum permissible heat loads from the plasma is estimated.
The first wall (FW) of DEMO is a component with high thermal loads. The cooling of the FW has to comply with the material's upper and lower temperature limits and requirements from stress assessment, like low temperature gradients. Also, the cooling has to be integrated into the balance-of-plant, in a sense to deliver exergy to the power cycle and require a limited pumping power for coolant circulation. This paper deals with the basics of FW cooling and proposes optimization approaches. The effectiveness of several heat transfer enhancement techniques is investigated for the use in helium cooled FW designs for DEMO. Among these are wall-mounted ribs, large scale mixing devices and modified hydraulic diameter. Their performance is assessed by computational fluid dynamics (CFD), and heat transfer coefficients and pressure drop are compared. Based on the results, an extrapolation to high heat fluxes is tried to estimate the higher limits of cooling capabilities.
•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).
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 1year. The IFMIF source generates neutrons with a D-T-fusion-relevant energy spectrum and a flux to achieve a damage rate over 20dpa per full power year (fpy) in a foreseen volume of 0.5l. 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.
•Full range of IFMIF HFTM operation temperatures (250–550C) could be well achieved and well controlled with and without “nuclear” heater power.•The temperature spread measured inside a capsule for ...the 350C reference case is fulfilling very well the requirements.•The temperature spread is in the range of +/−3K in the lateral direction and +2 K/−8K 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.
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 +/−3K in the lateral direction and +2K/−8K in the vertical direction for the 350°C reference case, fulfilling very well the requirements. This compares well to an allowed +/−19K 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 315seconds, heating up 135seconds.
•Rib-structuring causes high heat transfer coefficients required for the helium cooled FW.•Semi-detaching the ribs increases the heat transfer and the cooling performance.•V-shaped ribs provide ...higher heat transfer and cooling performance than dimples.
The thermal hydraulics of helium-gas cooled channels for the First Wall of DEMO structured by fully attached and semi-detached upward directed V-shaped ribs and spherical dimples in a staggered array were investigated. Large-Eddy-Simulations with the dynamic Smagorinsky sub-grid scale model were performed. The global and local heat transfer coefficient, pressure drop and cooling performance were analyzed. Compared to smooth channel flows, the global heat transfer coefficient was increased by a factor of 2.6–2.9 and the corresponding pressure drop was increased by a factor of 5.3–5.7 for the V-shaped ribs. Here, the semi-detached ribs provided the highest heat transfer and the best cooling performance. The dimpled structures increased the heat transfer by the factor of 1.1–1.4 without a significant pressure drop rise when compared to smooth channel flows, but regions of local heat transfer deterioration occur over each upstream dimple half.
Overview of the HCPB Research Activities in EUROfusion Hernandez, Francisco A.; Arbeiter, Frederik; Boccaccini, Lorenzo V. ...
IEEE transactions on plasma science,
2018-June, 2018-6-00, Volume:
46, Issue:
6
Journal Article
Peer reviewed
In the framework of the EUROfusion's Power Plant Physics and Technology, the working package breeding blanket (BB) aims at investigating four different BB concepts for an EU demonstration fusion ...reactor (DEMO). One of these concepts is the helium-cooled pebble bed (HCPB) BB, which is based on the use of pebble beds of lithiated ternary compounds and Be or beryllides as tritium breeder and multiplier materials, respectively, EUROFER97 as structural steel and He as coolant. This paper aims at giving an overview of the EU HCPB BB Research and Development (R&D) being developed at KIT, in collaboration with Wigner-RCP, BUTE-INT, and CIEMAT. The paper gives an outline of the HCPB BB design evolution, state-of-the-art basic functionalities, requirements and performances, and the associated R&D activities in the areas of design, functional materials, manufacturing, and testing. In addition, attention is given also to the activities dedicated to the development of heat transfer augmentation techniques for the first wall and the corresponding testing. Due to their nature as design drivers, a brief overview in the R&D of key HCPB interfacing areas is given as well, namely, the tritium extraction and recovery system, the primary heat transfer and power conversion systems, and safety topics, as well as some specific activities regarding the integration of in-vessel systems through the BB. As concluding remarks, an outline of the standing challenges and future R&D plans is summarized.
•Using Electrical Discharge Machining in combination with forming is an option to manufacture a U-shaped First Wall without welding.•Additive Manufacturing (e.g. Selective Laser Melting and Metal ...Powder Application) provides promising options for nuclear fusion applications.•Selective Laser Melting is suitable to manufacture high complex and thin walled segments with internal channel structures.•Metal Powder Application provides cost effective options to build First Wall relevant components.
Different manufacturing routes are investigated at the KIT INR for the realization of First Walls (FW) for nuclear fusion components, such as the ITER Test Blanket Module (TBM) and DEMO Breeding Blankets (BB) for the Helium Cooled Pebble Bed (HCPB) Breeding concept. One conventional manufacturing route mainly basing of Electrical Discharge Machining (EDM) and forming was demonstrated successfully. However, the procurement costs are high. Therefore, options also to apply Additive Manufacturing (AM) as alternative were investigated. This paper compares the HCPB reference concept for FW fabrication to innovative concepts basing on AM.
•We investigated a set of dosimetry reactions for measurement of the neutron fluence in the High-Flux Test Modules of DONES.•Foil stacks irradiated with a neutron source at NPI Rez providing white ...neutron spectrum covering reactions of interest.•All expected induced activities could be determined by gamma spectroscopy utilizing a HPGe detector.•Further work will require to adapt the set of dosimetry reactions to the very high fluences in the HFTM..
The High Flux Test Module (HFTM) carries the specimens to be irradiated with the Early Neutron Source. The knowledge of the total neutron fluence on the specimen will be necessary for analysis. Neutron activation is a widely used method for neutron fluence measurement. We have tested a set of activation materials which seem to be suitable for application in the HFTM considering half-lives of the induced activities, the environmental conditions and the deployment time in the HFTM. Test foils were irradiated for 9.5 h with a cyclotron of NPI Řež in a white neutron field with energies up to 32 MeV. The induced activities were determined 61 days after the irradiation. We present the resulting saturation activities with estimated uncertainties and draw conclusions on the application of the selected activation materials in the HFTM.
For sub-sized fatigue specimens made of EUROFER97 in unconstrained contact to ceramic breeder pebbles, exposed to purge gas conditions for different durations in an oven, a chemical surface attack ...was observed which led to a significant reduction of fatigue lifetime Aktaa et al., 2020. To better reproduce the flow of the purge gas in the breeding zone of a Helium-Cooled Pebble Bed Breeding Blanket, the experiment was now repeated by placing the same kind of samples in the helium loop HELOKA HEMAT, where the gas is permanently circulated in a closed circuit, and its water content is controllable. The composition of the gas was monitored with a mass spectrometer and humidity sensors. The samples were exposed to a mixture of helium and 0.1vol% hydrogen at DEMO relevant operating conditions (550 °C, 1.2 bars abs.) for a duration of 8, 16, 32, and 64 days, respectively. New sample holders were designed which allow direct contact of the samples with the gas mixture. A special procedure for the handling of the test section was implemented to avoid contact of the hygroscopic pebbles with air humidity during the preparation phase and during the extraction of the samples from the test rig.
The present contribution discusses the various considerations on which the test rig design was based, followed by a description of the experimental setup and preliminary results of the testing campaign. These are similar to the results achieved in the oven experiment. In the future, the loop will be used for tests with up to 200 Pa partial pressure of steam in helium; a mixture that is considered relevant for the DEMO purge gas composition.
Recent analysis result in significant impact on the design of the Helium Cooled Pebble Bed (HCPB) Breeding Blanket (BB). Especially the main demanding sub-component of the BB in terms of fabrication, ...the First Wall (FW) is highly affected. As a matter of fact, the relevance of the developments made for the industrial fabrication of the FW used e.g. in the EU HCPB Test Blanket Module (TBM) for ITER is limited: On one hand in terms of the overall dimensions, but also in terms of geometry and cooling channel configuration. Thus, a fabrication strategy for the FW was proposed as an option in 2018 based on Additive Manufacturing (AM) offering a solution to cover the new aspects. The dedicated fabrication routine is based on Cold Spray (CS) in alternation with machining. In terms of manufacturing of non-plasma facing complex shaped thin- or double wall BB structures (e.g. Fuel Pins proposed for the HCPB BB) the use of AM also provides benefits compared to conventional technologies. Therefore, the AM process of Selective Laser Melting (SLM) is also investigated in terms of applicability for BBs. This paper gives an overview about the advances in different AM options applied for nuclear fusion structural low activation steels. Possibilities for spin-offs to other technological fields are discussed and conclusions are drawn reflecting licensing aspects and technological limits.
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