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- 50 questions and answers about nuclear energy and our nuclear power plants
- Building nuclear power stations
Building nuclear power stations
What kinds of reactors are used in Belgian nuclear power stations?
The four reactors at Doel and the three at Tihange are all 'pressurised water reactors' (PWR), which are among the safest in the world.
The design of nuclear power stations is based mainly on rules and practices applied in the United States that have been adapted to the Belgian context. For each Belgian nuclear power station, the requirements for construction and operation are set out in a safety report, the operating permit and the environmental permit.
In PWRs, pressurised water carries away the heat given off by a nuclear fission reaction from the reactors. This happens in the primary circuit. The water heated under high pressure is then channelled to a steam generator, where it is pumped through thousands of small tubes.
On the other side of these tubes, the water in the secondary circuit vaporises into steam. The primary circuit is completely separate from the secondary circuit. This prevents any radioactive particles from ending up in the secondary circuit. The steam from the secondary circuit drives a turbine and the generator connected to it. The generator generates electricity. The steam that leaves the turbine is channelled into a condenser to be cooled using water from the tertiary circuit. The steam cools and condenses into water, which is re-channelled to the steam generators. The condenser uses cooling water from the river Scheldt. The cooling water used in the condenser is drawn from the Scheldt and heated slightly by the water from the secondary circuit. For this reason, it is cooled in the cooling towers before being sent back to the condenser or released into the Scheldt at a temperature which does not exceed the maximum values defined in the environmental legislation. Compared with a conventional power station that burns fossil fuels, it is therefore mainly the way heat is generated to produce steam that is different in a nuclear power station.
How is the environment protected?
Three successive barriers isolate the highly radioactive fission products from the environment. The three successive barriers are:
- A hermetically sealed metal containment structure contains and protects the fuel pellets that contain uranium oxide.
- The reactor vessel has a 20cm-thick steel wall.
- The reactor building is a double bunkered building with a reinforced concrete housing. The innermost enclosure prevents radioactivity from being released outside the reactor building. It can withstand strong internal pressure. The second enclosure protects the facility from external impact.