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

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 x 10(-10) Pa . m(3)/s in hot helium leak tests (HHLT) at 250 +/- 20 degrees 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 degrees 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 degrees C rather than 235 degrees 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.m(3)/s and 10(-9) Pa.m(3)/s level at room temperature (RT) and 250 degrees C, respectively, while the system sensitivity is at 10(-12) Pa.m(3)/s and 10(-11) Pa.m(3)/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.