Many components of ITER Neutral Beam (NB) will be subjected to significant heat loads, and therefore require active water cooling during their operation. The cooling network that is an integral part of exposed structural elements will be manufactured using the deep-hole drilling (DHD) technique.
In a maintenance scenario, these components will be removed and transported to a maintenance facility. ITER requires that in such a scenario there is no liquid water left anywhere inside the internal cooling circuitry as it may contain tritium. Although most of the components will be drained by gravity, the NB duct liner cooling panels will require fast blow-out using nitrogen gas. Such purging procedure shall remove most of the water and leave all passages clear. At the end, dry heated nitrogen gas will be circulated through the same coolant circuits to evaporate the remaining water.

The main problem with the force blow-out arises in circuits with parallel flow paths. In such arrangements, it is possible that the adequate pressure required for purging cannot be sustained for all parts of the cooling circuit. This is especially problematic for vertical arrangements will a large hydrostatic head and poorly balanced coolant networks.

A number of analysis projects had been conducted for the ITER NB duct liner, fast shutter and exit scraper to balance their cooling network and to demonstrate success of the blow-out sequence using the available nitrogen pressure supply. The required two-phase flow transient simulations were performed using WAHA [2] or RELAP5 Mod 3.3 code.