Heat is generated in the reactor as a result of nuclear fission. To guarantee optimum cooling of the fuel rods, their cladding tubes must always be covered with a film of water. If they are not completely covered with water in specific areas, this is referred to as “dryout”.
All of Switzerland’s nuclear power plants will cope with an extreme flood of the sort that may occur on average once every 10,000 years, in addition to their ability to cope with other hazards. Even if the external power supply fails at the same time as the flood occurs, the plants can be brought into a safe condition. All the plants are clearly in compliance with the applicable limits.