Speaker
Description
At the European Spallation Source (ESS), maintenance activities on components cooled by the Primary Water Systems—such as the moderator and reflector plug, proton beam window, monolith inner shielding, and monitoring plugs in the Target Station—require complete draining and drying of cooling circuits. This is essential to prevent personnel exposure to activated water during component replacement, leak testing, and handling of components designated as radioactive waste.
The system design addresses the controlled handling of activated water by preventing leaks and spills, maintaining full containment, and enabling water recycling. As an advantage, drained water is collected in dedicated drainage tanks and can be reused. Moreover, during drying operations, potentially contaminated air displaced by the vacuum generation system is routed to the Target Station HVAC off-gas system to ensure safe containment.
Due to the low elevation of components within the monolith vessel, effective draining and drying requires the use of a vacuum pump combined with the injection of air or instrument air to evacuate water in the pipes and components. The process can be performed in three stages, depending on the required level of internal dryness: (1) gravity draining, (2) vacuum-assisted evacuation and air blowing, and (3) active drying. Active drying is implemented using two dedicated programmes: one for drying plugs and another for drying cooling pipes. Under normal maintenance conditions, only plug drying is required. This is achieved using dry instrument air at a vacuum level of approximately 160 mbar. For cases requiring drying of cooling pipes, a pulsed drying sequence with lower pressure and higher airflow can be applied. This approach is more effective at removing standing water pockets.
The drying system is designed for rapid operation and is equipped with dew point measurement instrumentation to monitor and verify drying performance. The effectiveness of the overall design and operational concept is demonstrated through dedicated system tests.