Replacement strategy of the EU-DEMO and CFETR breeding blanket pipes

Both EU-DEMO and CFETR need a workable replacement scheme for their tritium breeding blanket (BB). The radioactive environment dictates that all associated operations must be carried out through remotely controlled tools. Accessing and extracting the large BB segments requires their feeding pipes to be removed first from the upper vessel port and later re-installed. In the current design, each of the 80 BB segments is connected with four feeding pipes, two for cooling and two for tritium extraction. Thus, in the process of BB maintenance operation, 320 pipes must be cut, removed and rewelded. The developed concept for this task is presented here. It aims at reducing the associated plant downtime, thereby increasing the overall plant availability. Features underpinning this integrated BB pipe service concept are: (i) parallel pipe service operations, (ii) pipes in each upper port are grouped in a pipe forest and handled as a single component, (iii) the configuration of the individual pipes is standardized such that cutting and joining locations are aligned and with good accessibility from the top, (iv) the number of pipe sizes is limited to two, reducing the number of required tool sets, and (v) the same pipe configuration is adopted in each of the 16 upper ports. The paper will present design solutions and the progress on the manufacturing of prototypes developed for the challenging cutting and welding tasks from both within and outside, as well as the leak detection methodology and pipe stub handling. Prototypes will be used to perform design validation and verification on dedicated test benches currently being implemented in close collaboration between European laboratories and the Comprehensive Research fAcility for Fusion Technology (CRAFT) at ASIPP in China.