Nuclear power plants require a great deal from paint
The paints used in nuclear power plants are high-class, special products. Their quality is verified through heavy testing programmes.
In Finland, the YVL Guide and the STUK-YTO-TR 210 Report, issued by the Radiation and Nuclear Safety Authority (STUK), specify the requirements for paints and coatings used in nuclear power plants. In addition, the plant orderer and plant supplier set their own requirements.
Teknos as a paint supplier for Olkiluoto plants
Teknos has long-standing know-how in special industrial coatings for nuclear power plants.
"We started out in this sector in the 1970s, as a paint supplier for the Loviisa 1 nuclear power plant. This was followed by paint deliveries to Loviisa 2 and the present Olkiluoto plants (OL1 and OL2). In 2010, in addition to paints for OL3, we delivered a special polyurethane coating for the ground-supported floors of OL1’s turbine hall. We have delivered paints and coatings for all nuclear power plants in Sweden and for some plants in Russia. The biggest nuclear power plant project is now Olkiluoto 3, currently under construction", states Research and Development Director Kurt Blomqvist.
There are over 400,000 m² of concrete surface at OL3. Five Eiffel towers could be built using the iron in OL3’s structures. The number of paint work contractors is ten.
A nuclear power plant’s steel and concrete surfaces are painted almost entirely with two-component epoxy coatings. In addition, some polyurethane and zinc silicate paints are used for elastic floor coatings and outside surfaces.
The suitability of paints and coatings can be demonstrated in many ways, based on a variety of testing methods. Coatings for the containment building’s inner structures are subject to the most demanding requirements. Besides their normal protective qualities, these paints are expected to have good radiation resistance, durability in a simulated accident situation, and to be capable of easy decontamination.
When used in nuclear power plants, paints must also provide chemical resistance, sufficient adhesion, wear resistance, as well as fire resistance in the case of floor coatings. Chemical resistance is tested using sulphuric acid, hydrochloric acid, nitric acid, alkali, ethanol and acetone, in other words, with the chemicals used in a power plant’s various processes.
R&D Chemist Ari Vaha reviews DBA test samples at VTT Technical Research Centre of Finland.
A simulated accident situation test, known as a DBA test (Design Basin Accident), is especially heavy. In this test, painted test samples are stressed in an autoclave for a week, at a high temperature and steam pressure. In addition, test samples are exposed to shock cooling. At the end of the test, the coating must still adhere well to the surface.
"This test is extremely demanding for coatings, especially thick floor coatings. It was quite a challenge for us. However, through intensive research and development work, we found a solution in our special products particularly developed for this purpose", R&D Chemist Tero Ojala reports.
Many pipes and brackets are painted multiple times prior to installation. After installation and inspection, the welded joints are touch-up painted.
R&D work is a process lasting several years
The DBA test, as well as radiation resistance, decontaminability and fire resistance tests, are performed at VTT Technical Research Centre of Finland. Teknos performs the chemical resistance, wear resistance and adhesion tests in accordance with the STUK-YTO-TR 210 Report.
"These tests are no picnic either – some chemical tests can even take half a year", Blomqvist elaborates.
As a process, R&D on special paints for nuclear power plants stretches over several years, comment Teknos’ R&D Director Kurt Blomqvist (left) and R&D Chemist Tero Ojala.
"The development and testing of these special paints and coatings takes several years altogether. This process has involved a dozen people. Besides me, R&D Chemist Ari Vaha and Sales Manager Mikko Nihtilä belonged to the core group handling technical issues. An important part of R&D work was also carried out by laboratory staff. Other employees were involved in producing test bases, painting, measuring film thicknesses, testing, documenting the test results, preparing quality certificates, ensuring product tracking, and everything else required for this kind of elaborate R&D process".
"Besides the OL3 reactor building, Teknos is also supplying paints for the main steam turbine plant. These paints have passed the full set of demanding tests", says Tero Ojala.
When a paint product is approved by a nuclear power plant, this is a sign that the paint is extra high-grade and technically advanced.
Strong special know-how
A nuclear power plant is an extra-heavy test location for paint products.
"When a paint product is approved by a nuclear power plant, this is a sign that the paint is extra high-grade and technically advanced. At Teknos, we have invested strongly in producing such paints, both financially and in terms of hours worked. We can proudly declare that our own products have taken us to the leading edge in this area. In Finland and elsewhere, we are keenly following the start-up of new nuclear power plant projects. We will be ready when the expected renaissance of nuclear power begins in earnest", Blomqvist envisions.
The article was written by Juhani Ikonen, the Head of Information Department TVO, Teollisuuden Voima Oy. Photographs by Hannu Huovila, TVO Image Gallery and Teknos.
TVO, Teollisuuden Voima Oyj is an unlisted public company, founded in 1969 to produce electricity for its shareholders at cost price. Further information: www.tvo.fi