OL3 EPR project reaches hot functional test stage

18.12.2017

The hot functional testing stage has started in the Olkiluoto 3 EPR project. These tests are part of commissioning and take several months. After successful completion of the hot functional tests, it will be possible to obtain an operating licence for OL3 and continue the project towards nuclear commissioning.

At the hot functional test stage, the systems of the OL3 plant unit are tested as a whole, but without the fuel. The temperature and pressure values of the water in the primary circuit* are gradually raised to the levels that will prevail during actual production operation.

This is the first plant-level test where the nuclear island and the turbine island are operated together as a whole. Several different tests at different pressure levels will be carried out during this stage. The water temperature is raised utilising the thermal energy produced by the reactor coolant pumps.

* The primary circuit refers to the circulation of water between the reactor pressure vessel and the steam generator. The temperature of the water is increased to 328 Celsius degrees in the reactor pressure vessel, and the water is then led in the reactor coolant piping to the steam generators, where heat is transferred to the secondary circuit and further as steam to the turbine. The water returns from the steam generators back to the reactor. A high pressure is maintained in the primary circuit to prevent the boiling of the water.

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