HELOKA and KATHELO

The Helium Loop Karlsruhe (HELOKA) is dedicated for testing fusion reactor components under relevant high heat flux using high-pressure (up to 110 bar) and high-temperature (up to 700 °C) helium gas as coolant. 

Technical description

HELOKA facility incorporates three helium loops: HELOKA-HP having operating conditions similar to the helium-cooled breeding blanket; KATHELO operating at similar pressure levels as HELOKA-HP but capable of running at very high temperatures where creep phenomena become relevant; HEMAT operates at low pressure levels but is capable of running for long periods of time at high temperatures using helium mixed (in ppm-range) with water, hydrogen or oxygen.

HELOKA-HP is mainly dedicated for testing breeding blanket mock-ups at an operating pressure from 4 to 9.2 MPa, an operating temperature from 100°C up to 500°C, and flow rates up to 1.3 kg/s. HELOKA-HP has two test sections, each capable of hosting relatively large components (weight up to 3t and volumes up to 0.5m³) that can be tested under vacuum. One of them, HELOKA-HHF is shared with KATHELO and is equipped with an Electron Beam Gun (EBG) having an installed power of 800 kW, device that can apply high heat loads on the surface of the mock-ups. In addition to classical measurement capabilities, the facility has a thermal imaging infrared camera and two pyrometers for non-contact temperature measurements.

KATHELO was built to support the development of a helium-cooled divertor and is operating at pressure levels from 4 to 10 MPa; an operating temperature from 100°C up to 700°C, and flow rates up to 250 g/s.

HEMAT is a low-pressure loop mainly oriented towards material testing at high temperature (up to 650°C) under controlled coolant composition. The loop has a dedicated section for controlling the water content in the coolant providing unique testing environment for investigating corrosion phenomena.

In all the loops, the helium composition can be monitored during operation using a mass spectrometer (GAM 400 made by InProcess Instruments, Inc., Germany) implemented and integrated into the facility control.

Representative Projects

Breeding Blanket Experiments

1.1 First Wall Mock-ups

Two First Wall Mock-ups with different surface materials were tested, one with a 2-3 mm ODS (Oxide Dispersion Strengthened) steel plating joined to EUROFER97 steel by diffusion welding; the other one with Functionally Graded (FG) Tungsten/EUROFER97 coating.

1.1 Breeder Zone Heat Transfer

A mock-up of the Breeder Zone of the EU-DEMO HCPB Blanket was tested in HELOKA (using helium at 300 °C and 80 bar pressure) with different surfaces of the coolant gap to experimentally investigation its heat transfer performance.

 1.3 Safety Experiment (Loss Of Flow Accident)

A prototypical set-up simulating a LOFA (Loss Of Flow Accident) situation in a helium-cooled breeding blanket First Wall (FW) mock-up under typical heat load conditions was tested. The objectives were: (i) reproduce the expected DEMO thermal-hydraulics conditions during normal and off-normal situations to test different thermal-hydraulics issues and coolant flow strategies, and (ii) provide robust data for the design and safety analyses with numerical codes. The FW mock-up was a P92 steel plate with 10 cooling channels.

1.4 Indian Test Blanket Module (TBM) First Wall testing

HELOKA is open for cooperation. In 2017, following a contract with Institute for Plasma Research (IPR in Gujarat, India), a TBM First Wall mock-up was tested [1]. Both normal and accidental operating conditions were investigated.

1.5 Monitoring Coolant Gas Composition at TBM-Like Operating Conditions

During this experiment it was demonstrated the capability of monitoring online the gas composition during a normal (high-pressure) operation of the HELOKA-HP loop. An accuracy of 1 ppmv or lower is reachable. Measurements are reproducible and can be automated. The measurements showed also that the loop filling procedures ensure that the helium stream in HELOKA-HP has a low level of impurities in the range of 0.02 % even after long time operation.

1.6 Corrosion behavior of Eurofer97 steel in contact with Lithium ceramic breeder pebbles

The experiments investigated the impact of the Advanced Ceramic Breeder pebbles in unconstrained contact with EUROFER steel specimens. In a first phase the experiment was run in a HEMAT loop with a Helium coolant containing 0.1% hydrogen. In second campaign, to mimic one of the purge gas compositions foreseen for tritium extraction in DEMO, the experiment was run without hydrogen, but with about 100 Pa (500 ppm based on the volume) water added to the helium flow.

Helium-cooled Divertor Experiments

The proposed concept for a helium-cooled divertor envisages a target made out of toroidaly parallel cooling elements, each individual element having the same length as the target poloidal length and a thickness of 23 mm in toroidal direction. The armor is made out of tungsten slabs of similar shape as the EUROfusion baseline solution (water-cooled, ITER-like, target) that are brazed on the heat sink pipe/vessel. The coolant (helium) is entering the target element trough a distribution manifold installed inside the pipe. The manifold has holes oriented towards the heat-loaded face of the pipe; the jets formed as the helium leaves the manifold though these holes impinging on the inner surface of the pipe. The predictions of the CFD simulations indicate that such a configuration could withstand surface heat loads up to 10MW/m². To validate the results of the simulations as well as certain aspects of the manufacturing process, two mock-ups were tested in HELOKA-HP: (a) DIV-Mockup1 having a straight pipe as distribution manifold installed coaxially with the divertor pipe, helium being distributed over the whole length of the divertor unit; (b) DIV-Mockup2 having a two-chamber manifold, the helium from the first section cooling first half of the mock-up length before entering the second chamber to cool the second half of the mock-up. DIV-Mockup1 received a surface load of 8MW/m² for 1000 load cycles, each loading period being 5min long followed by 100 cycles at 10MW/m². DIV-Mockup2 was tested at 10MW/m² under quasi-stationary conditions.

Representative publications

[1] Ghidersa, B.-E.; Abou Sena, A.; Rieth, M.; Emmerich, T.; Lux, M.; Aktaa, J. Experimental Investigation of EU-DEMO Breeding Blanket First Wall Mock-Ups in Support of the Manufacturing and Material Development Programmes. Energies 2021, 14, 7580. https://doi.org/10.3390/en14227580

[2] Ghidersa, B.-E.; Gonfiotti, B.; Kunze, A.; Di Marcello, V.; Ionescu-Bujor, M.; Jin, X.Z.; Stieglitz, R. Experimental Investigation of a Helium-Cooled Breeding Blanket First Wall under LOFA Conditions and Pre-Test and Post-Test Numerical Analysis. Appl. Sci. 2021, 11, 12010. https://doi.org/10.3390/app112412010

[3] S. Ranjithkumar et al, Performance assessment of the Helium cooled First Wall mock-up in HELOKA facility, 2020, https://doi.org/10.1016/j.fusengdes.2019.111319

[5] M. Zhao, B. Ghidersa, R. Stieglitz, CFD evaluation and optimization of the HEMJ divertor cooling design, Fusion Engineering and Design, Volume 158, 2020, 111669, https://doi.org/10.1016/j.fusengdes.2020.111669

[6] Joon-Soo Lim, Namkyu Lee, B.-E. Ghidersa, Hyung Hee Cho, Enhancement of cooling performance of a helium-cooled divertor through the addition of rib structures on the jet-impingement area, Fusion Engineering and Design, Volume 136, Part A, 2018, 655-660, https://doi.org/10.1016/j.fusengdes.2018.03.048.

[7] Namkyu Lee, Joon-Soo Lim, B-E. Ghidersa, Hyung Hee Cho, Nozzle-to-target distance effect on the cooling performances of a jet-impingement helium-cooled divertor, Fusion Engineering and Design, Volume 136, Part A, 2018, Pages 803-808, https://doi.org/10.1016/j.fusengdes.2018.04.012

[8] R. Krüssmann, B.-E. Ghidersa, Monitoring coolant gas composition at TBM-like operating conditions, Fusion Engineering and Design 166 (2021) 112300, DOI: https://doi.org/10.1016/j.fusengdes.2021.112300