CNDA First Wall semi-prototype succeeded in surviving high heat flux test

Sets of plasma-facing finger pairs from CNDA, representative of the ITER Blanket First Wall semi-prototype, performed successfully under high heat flux testing of up to 4.7 MW/m2 for 7500 cycles and 5.9 MW/m2 for 1500 cycles. No unacceptable overheating or temperature jump was observed during the test. The appearance of the First Wall finger pairs also didn’t show any significant alteration. From these test results, the CNDA’s technology for beryllium to copper bonding (i.e. Hot Isostatic Pressure) has been shown to meet the ITER requirements.

CNDA First Wall (FW) semi-prototype is composed of 3 pairs of fingers, whose structure and dimensions are fully representative of those used in the design of the ITER Blanket FW Panel. 3 pairs of fingers were used for the screening test and 2 for the thermal fatigue test.

The high heat flux testing (HHFT) of CNDA’s Enhanced Heat Flux First Wall (FW) finger pairs was successfully completed on August 8, 2016. The results show no unacceptable overheating or temperature jump, which means that CNDA has completed the qualification of the EHF FW, in readiness for the signature of the Procuring Arrangement (PA).

The test was carried out at the Efremov Institute in Russia. According to the ITER technical requirements, the HHFT must be performed on actively cooled mock-ups of semi-prototypes. A screening test was carried out on 3 finger pairs in the beginning. The thermal load on the FW surface was increased from 1 MW/m2 to 4.7 MW/m2 with steps of 1 MW/m2. Each increase in thermal load was made only after the finger pairs had reached temperature equilibrium. No anomaly was observed during the screening test. Thermal fatigue test was then performed on 2 finger pairs over 7500 cycles at 4.7 MW/m2 and 1500 cycles at 5.9 MW/m2, each cycle consisting of 15s heating and 15s cooling. No unacceptable overheating of the two finger pairs was observed during this thermal fatigue test. After the thermal fatigue test, ultrasonic test results did not show any relevant defects on the beryllium to copper bonding, and there was no impact on the function and lifetime of the finger pairs. For the 5.9 MW/m2 test, a couple of hot spots were found but within the bound of acceptability.

The Blanket FW is located inside the Vacuum Vessel of the ITER machine, and will face the 100 million degree plasma when operating. It protects other components from thermal and high-energy particle fluxes. Two different FW Panel designs are being pursued based on the incident heat flux, a Normal Heat Flux (NHF) FW Panel option designed for 2 MW/m2, and an Enhanced Heat Flux (EHF) FW Panel option designed for 4.7 MW/m2. China is procuring EHF FW Panels representing 10% of the 440 ITER FW Panels.

CNDA started its R&D effort on ITER EHF FW Panels in 2004; the work is performed by the Southwestern Institute of Physics (SWIP), and has progressed successfully as illustrated by the following achieved milestones:
- 2011: Manufacture of high-purity beryllium.
- 2013: Manufacture of small EHF FW mock-ups which survived high heat flux testing.
- July 2014: Optimization of mock-ups (including increasing the thickness of the Be tiles from 6 mm to 8 mm), which survived 4.7MW/m2 thermal fatigue test over 16,000 cycles.