China's progress on hot helium leak test of ITER shield blocks.

• R&D work on HHLT facility for ITER large vacuum components is successful in China. • A satisfying result (lower than 2.69×10−10 Pa*m3/s) in the 1st HHLT on the shield block full-scale prototype. • H 2 O and H 2 outgassing is the major factor impacting the performance of HHLT facility at different temperatures. • The facilities' performance was improved by at least one order of magnitude after adopting outgassing-removal measures. • HHLT results of 50 shield blocks with the improved facilities are better and stable. China Domestic Agency (DA) will provide ITER with 220 shield blocks (SB) which are important, large, and actively water-cooled components in ITER vacuum vessel, their leakage rate shall not exceed 2.69 × 10 − 10 Pa · m 3 / s in hot helium leak tests (HHLT) at 250±20 °C. The HHLT work started with developing a HHLT facility and manufacturing a SB full-scale prototype (FSP). The result showed the FSP could satisfy ITER's requirement at 235 °C. H 2 outgassing from stainless steel surfaces is the main factor that impacts both the background leakage rate and sensitivity of the testing system in hot testing cases. Hydrogen-removal measures were taken to improve the facility performance, and a new facility was built. A better facility performance came out at 250 °C rather than 235 °C, the background leakage rate decreased by one order of magnitude while the system sensitivity increased by two orders of magnitude. The background is at 10−10 Pa.m3/s and 10−9 Pa.m3/s level at room temperature (RT) and 250 °C, respectively, while the system sensitivity is at 10−12 Pa.m3/s and 10−11 Pa.m3/s level at the two temperatures. With the two facilities, series HHLTs have been carried out on 50 SBs covering two types, with all results complying with ITER requirements. [ABSTRACT FROM AUTHOR]