Heat rejection basins
A massive fill-up
20 Oct 2020
The fill-up operation, which began on Wednesday 14 October is being closely monitored from the temporary control room.
When the ITER Tokamak begins producing burning plasmas and auxiliary systems are operating at full capacity, the amount of heat to be removed from the installation will be in the range of 1100 MW. The extraction and dissipation of such a huge amount of energy requires an oversize heat rejection system that comprises kilometres of piping, dozens of extremely powerful pumps, countless valves and filtres, massive cooling towers, and two water basins (one "hot" and one "cold") equivalent in size to six or seven Olympic pools.
One of the basic requirements for any water basin is to be as leak-tight as possible. Although some loss of water through seepage is inevitable in concrete basins such as ITER's, an "assessment of tightness" was decided prior to turning over the heat rejection system to the ITER commissioning team.
On 14 October, the weeklong operation began. The gate that connects the basins to the nearby Canal de Provence was opened and water rushed in at the rate of 300 cubic metres per hour. Like a crane that needs to be tested at 110 or 120 percent of its nominal lifting capacity, the basins of the heat rejection system were "overfilled" with 27,000 cubic metres of water, or 7,000 m³ more than their operational volume.
The basin walls and floor are thick and sturdy, but the pressure that is exerted by 27,000 tonnes of water is enormous.
Topographic targets installed at several locations on the basin structures are monitoring "settling," which is expected to be in the range of 0.5 centimetres.
A team operation, assessing the leak tightness of the heat rejection system basins involved the ITER Control Division, in charge of instrumentation and control; the Operations Division; the Mechanical Implementation Division; the Field Engineering Installation Division, and Site Coordination.
Once the basins are filled and stabilized, the water level will be closely observed by a set of radars and the measurements compared to "witness tanks" to account for evaporation. If radars register a drop beyond the acceptable leak rate (on the order of a few cubic metres per day due to the porosity of the concrete, the occasional micro-fissures, and seepage through junctions), that would signal a problem.
Five days into the test, all parameters are nominal. Water levels in the basins are rising at the rate of one metre per day; fill-up should be complete by the end of this week.