Basic information about nuclear power
Nuclear power has been produced globally since the 1950s, and in Finland for nearly half a century. The plant options considered in our nuclear energy project are based on this same proven technology. The most significant difference compared to earlier reactors is that the reactors under evaluation are smaller in both size and output, and they also utilise advanced safety solutions based on the latest technology.
Principle of operation of a nuclear power plant
In a nuclear power plant, energy is produced through a controlled nuclear reaction. Fission occurring in the nuclear fuel releases thermal energy, which is either used directly or to generate steam by heating water. The steam is then directed to drive a turbine connected to a generator. The generator converts mechanical energy into electricity.
Different Reactor Types
The roughly five plant options included in our tendering process are based on either pressurised water reactor (PWR) or boiling water reactor (BWR) technology — both of which are currently in use in Finnish nuclear power plants. Both reactor types can be designed either for heat production only, or for combined heat and power generation.
PWRs and BWRs share the same fundamental operating principle but differ in where and how steam is produced. A PWR uses a separate steam circuit, whereas in a BWR the steam is generated directly inside the reactor. Both are safe and widely used nuclear technologies.
Pressurized Water Reactor (PWR)
Operating Principle
In a pressurized water reactor, the reactor core is cooled and the nuclear reaction moderated with water that is kept at very high pressure to prevent it from boiling. This hot water transfers its heat to a separate steam generator, where the secondary‑circuit water turns into steam and is directed to the turbine.
Key Features
- Two separate water circuits (primary and secondary)
- Reactor coolant does not boil
- The steam entering the turbine is non‑radioactive
- The most common reactor type in the world
Boiling Water Reactor (BWR)
Operating Principle
In a boiling water reactor, the water inside the reactor core boils directly. The resulting steam is routed straight to the turbine without a separate steam generator. After the turbine, the steam is cooled back into water and returned to the reactor in a closed-loop system.
Key Features
-
Single water circuit
-
Water boils inside the reactor
-
Steam flows directly to the turbine
-
Structurally simpler than a PWR