A hot steam leak during baking of ASDEX Upgrade – Consequences and lessons learned

ASDEX Upgrade is a midsize tokamak operated since 1991. A scheduled maintenance and enhancement shut down done about once year. After pump leak search baking procedure started to condition the vacuum vessel for plasma operation. During operation all in-vessel components are water cooled. This cooling system also used with hot at 150 °C. one of these regular periods steam appears in November 2017. The detection has triggered controlled cool scenario. Nevertheless, between appearance identification closing 100 L escaped during from °C 65 into torus. fraction was distributed as over torus condensed coldest parts vessel, preferentially remote ports. In addition, interacts boron containing layers. resulting acid caused additional erosion. paper presents details damages, actions taken remove them well measures avoid future leak.