A plant of thousands of tests

A total of thousands of tests are conducted at the Olkiluoto 3 power plant unit before the commercial operation of the unit starts. During the test production phase, all the systems and associated equipment, the joint functionality of the systems and finally the overall operation of the nuclear power plant are tested.

– The commissioning of a nuclear power plant and the associated testing are based on a common procedure that follows a specific sequence. Once a system is ready for service, all the individual equipment associated with it are tested first, followed by testing the operation of the system in different conditions. Next, testing proceeds to system level tests to assess the joint functionality of the different systems. The tests cover several different conditions, from normal operation to abnormal disturbances. The final phase, which is ongoing now, comprises plant-level tests carried out on the plant as a whole. We proceed from small pieces to a larger entity, explains Development Engineer Mika Hassinen.

The purpose of the tests is to verify that the operation of the equipment, the systems and the overall plant complies with plans in all different conditions. That is why the ongoing test production phase also runs over a long period of time, as operation is tested in normal and abnormal conditions as well as in certain accident conditions. In addition to testing the operation of the plant, this way it can be verified that the safety systems all function as planned.

– Of course, tests have already been carried out for a long time before the ongoing commissioning stage. In the turbine island, tests were conducted on individual items of equipment already in 2009, when the commissioning of the first electrical systems started there, Hassinen reminisces.

Modification needs are par for the course

According to Hassinen, it is normal that the tests reveal also issues that need to be adjusted or rectified. In fact, one of the aims of the commissioning stage is to identify any modification needs and to carry out the required repairs in order to ensure the stability of electricity production once the plant is in commercial operation.

– This is something that is often forgotten in public debate. Equipment and systems are tested in the same way in all production and power plants prior to putting them into service and hardly ever are there no problems found in the tests.

Tests of all kinds

The number of tests required at Olkiluoto 3 is even higher than normal because it is a large, complex entity that consists of a magnitude of equipment and systems, including several safety systems. The tests are also designed to cover different types of faults and failures extensively.

– The actual tests vary a lot in nature and duration depending on the object of the test. A test carried out on a single temperature or pressure measurement, for example, can be very straightforward. All that needs to be tested is that correct information is provided from the measurement point to the right receiver.

– Tests on individual pumps then, on the other hand, are much more extensive and time consuming. The pump is operated during the test in different conditions and its operating values and vibrations are measured at various points, describes Mika Hassinen.

The scope of the tests is not limited just to the nuclear power plant. The relationship between the plant and the national grid is also tested together with grid company Fingrid.

– This is an important part of commissioning due to the large size of the production plant. For example, we have conducted large scale loss of power generation tests, such as a reactor trip test, where electricity generation is suddenly lost at OL3. Fingrid has monitored the performance of the grid closely in these tests. We will also carry out a fault tolerance test where Fingrid creates a temporary short-circuit in the grid near the power plant. The fault may not cause the plant to be disconnected from the grid, Hassinen concludes.

Supported by international cooperation

A point that Mika Hassinen also wishes to bring up is that the testing follows an international procedure based on the guidelines of the International Atomic Energy Agency (IAEA).

– The basic concept of proceeding in steps from small pieces to larger entities comes from there. This conformity benefits also us, as similar EPR nuclear power plants of the pressurised water reactor type in Flamanville, France and Taishan, China have been tested using the same concept. Thus, it has been possible to share information and learn from one another.

– Some of the plant supplier representatives conducting the ongoing plant-level tests at OL3, for example, took part in similar commissioning tests in Taishan. They have brought the knowledge gained there to the plant supplier's commissioning organisation in Olkiluoto. Cooperation has in this respect been realised already in the past with us receiving information about plant modification needs identified elsewhere, allowing us to implement changes before the commissioning tests. And any modification needs detected by us have been reported to the other plants.

Mika Hassinen is a veteran in Olkiluoto

Having graduated with MSc in nuclear technology from Lappeenranta University of Technology, Mika Hassinen is one of the nuclear sector professionals who have been part of the OL3 implementation team since the beginning – and actually already a little before that.

– I was recruited for the new nuclear power plant project in 2000, when plans for the new plant were still at a discussion stage. At first my work focused on promoting the project, Hassinen tells.

Once the decision on the construction of the new nuclear power plant was made, Hassinen's work changed. He took part in the preparation of bid invitations and negotiations with plant suppliers. As the project proceeded, Hassinen worked as the Chief Engineer in the Plant Engineering Unit. He even spent six months on loan to Areva.

A few years back he transferred from Engineering to the Operating Unit, because he wanted to be involved in the operational activities of the plant.

– I know this project well, Hassinen sums up, and believes there will be work for him at OL3 also in the future.

– When the commercial operation of the plant starts, we will begin to further develop and improve the process as well as energy efficiency.

Text Ismo Myllylä
Photos Tapani Karjanlahti

Information on electricity production during the test production phase is published on TVO’s website at www.tvo.fi/ol3forecast.

The story was previously published in TVO Group's Uutisia Olkiluodosta news magazine.