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Hot functional tests completed successfully at OL3


Commissioning of the Olkiluoto 3 plant unit is proceeding. The hot functional tests were carried out with success and preparations have already been started for the next milestone, i.e., loading of fuel.

- This was an extremely important phase of the commissioning process, with the nuclear island and the turbine island operating for the first time together as an entity. The hot functional tests proceeded well and provided us with valuable experience and capabilities for nuclear commissioning, says Jouni Silvennoinen, TVO's OL3 Project Director.

The hot functional tests, which took a little over five months, were designed for the verification of the safety and operability of the plant without fuel. The start-up procedure from cold state to hot functional state was carried out in both the nuclear island and the turbine island according to the Operating Manual of the plant. Overall, more than two hundred different tests were carried out at different pressure and temperature levels during the hot functional testing.

At the final phase of the extensive test programme, the turbine was driven with steam for the first time. The operating speed of the turbine is 1,500 rpm, and it was reached in the tests. The turbine generator is quite a massive piece of equipment; the shaft is 68 metres long and the weight of the rotating mass is 1,500 tons. The energy required for this test was produced using the thermal energy of the main circulation pumps.

The preparatory phase for the loading of the fuel starts immediately upon completion of the hot functional tests and will continue for several months. Fuel loading will mark the start of the final stage of the project – nuclear commissioning.

Interview requests:
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The primary circuit refers to the circulation of water between the reactor pressure vessel and the steam generators. The temperature of the water is increased to 328 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 sufficiently high pressure is maintained in the primary circuit to prevent the boiling of the water.