An innovative pool with a passive heat removal system

Heat removal systems are of primary importance in several industrial processes. Some of them are aimed at guarantee plant safety; these systems are equipped with a heat sink. As heat sink, a water pool or atmospheric air may be selected. The first solution takes advantage of high heat transfer coefficient with water but it requires active systems to maintain a constant water level in the pool during the operating phase; the second solution takes benefit from the unlimited heat removal capacity by air with time, but it requires a larger heat exchanger to compensate the lower heat transfer coefficient with air and is more critical in the first phase of intervention. In nuclear power plants during a nuclear reactor shutdown, as well as in some chemical plants to control runaway reactions, it is possible to use an innovative heat sink that joins the advantages of the two previous solutions. This solution is based on a special heat exchanger submerged in a water pool designed so that when heat removal is requested, active systems are not required to maintain the water level; due to the special design, when the pool is empty, atmospheric air becomes the only heat sink. The special heat exchanger design, proposed and described in the paper, allows to have not an over-sized heat exchanger and to have a system able to operate for unlimited period without external interventions. In the paper, a heat removal transient concerning the innovative heat exchanger is compared with the transient phases of alternative solutions. This innovative system provides an economic advantage, due to the smaller heat exchanger, as well as enhanced safety features, due to the passive characteristics of the system and the unlimited operating period without active actions.