VTT Technical Research Centre of Finland
Aug 7, 2018
Q: Where are you from?
A: Wade Karlsen grew up in Washington State and received his degree in metallurgy from the University of Washington. Metallurgy is the study of how metals work and how they achieve performance criteria, such as steel. Steel is a general term used to describe materials based on iron, but different combinations of material create various metals with different properties for different uses. For example, carbon mixed with iron produces carbon steel, which is common in construction, and chromium is added for corrosion resistance and added with nickel to create stainless steel. At the molecular level, the main iron lattice, called a crystal lattice, and atoms either sit at the same place that an iron atom is, as chromium does, or between the iron atoms, as carbon does. When materials undergo nuclear radiation, atoms are pushed out of the lattice, changing the mechanical properties of the material itself. After finishing his doctorate degree in Oregon, Wade Karlsen took a job in Finland in 1997 and now studies the effects of neutron radiation on materials at the VTT technical research center of Finland.
Q: What initial conversations led you to connect your degree with the nuclear industry?
A: Wade Karlsen met a professor from Finland at a materials conference in Chicago, who had a career in materials with applications in the nuclear industry. Initial conversations connecting the two centered around non-nuclear topics, such as powder metallurgy. Powder metallurgy is a special process in which a powdered form is created by atomization of melted metal, then is compacted through hot isostatic pressing and consolidated into a solid material. The aim of this process is to take material that is difficult to forge, such as those with a high percentage of alloy material, and put it through hot isostatic pressing in order to give properties similar to forging. The limiting factor in space travel and nuclear reactors is usually material capabilities and performance, which is usually limited by how they can be shaped into something useful. There will always be a need for developing better materials.
Q: Are there other processes that are used to shape or form these materials that were previously difficult to manipulate?
A: Wade Karlsen sees two hot topics in the nuclear industry as it relates to materials, the first being powder metallurgy and the second being 3D printing. In 3D printing, lasers draw on the powdered metal in different layers as materials are fused together. Materials used in 3D printing are determined based on heat and mixtures, which tend to be proprietary to the 3D printing companies. One additive used is phosphorus, which reduces the melting temperature, but can cause embrittlement in the metal. Companies are working to develop better high-powered lasers used for laser welding and 3D printing. After moving to Finland, Wade Karlsen completed some post-doc work at Aalto University with Hannu Hänninen, the professor he met in the U.S. who had previously led a team on materials for nuclear power plants at VTT. Karlsen joined that same team at VTT, went on to lead the group and now leads the Center for Nuclear Safety at VTT. The nuclear materials team focuses on stress corrosion cracking and neutron radiation.
Q: How did you rise through positions of leadership with a language handicap?
A: Wade Karlsen learned Finnish after he moved to the country, mostly through conversation, and was able to rise through positions of leadership due to his natural drive to pursue challenges and his ability to communicate in English had the benefit of influence at the international level. The Center for Nuclear Safety is a green space laboratory, meaning the lab was built on land that was previously forested. The old facilities on campus at Aalto University are undergoing decommissioning. The Center covers two main areas of expertise: support of operating power plants, and radiochemistry and support of final waste repository questions. VTT has been developing technology and completing tests for radiochemistry engineering solutions. Some studies include geological conditions, backfill materials, and capsule materials and how they undergo compression and how different amounts of water affect the properties. Bentonite clay is used as a barrier layer around capsules to protect them from water intrusion. For operating plants, the main mandate of the Center is to act as the “doctors” for the nuclear power plant by verifying materials are functioning properly to prevent failures and safety incidents.
Q: Does the conversation about capture of radionuclides ever come up, as opposed to just fuel degradation?
A: Wade Karlsen’s Center for Nuclear Safety at VTT focuses on the four barriers of a nuclear power plant: fuel pellet, cladding, primary circuit, and reactor containment. The fuel pellet is a ceramic matrix that contains the uranium and fission products. The cladding contains the fission gasses. The primary circuit, which is the main concern of the materials safety group, is where the fuel sits inside the reactor pressure vessel where the water is and includes the piping system that transport steam and water. The reactor containment is the concrete building over the reactor primary circuit. This represents four levels of protection if there were to be a failure in the system. One laboratory at VTT regularly tests the exhaust stacks of the power plants and uses radioactive iodine, due to its short half-life, to capture fission gasses.
Q: At what form does iodine exist at room temperature?
A: The most important activity Karlsen’s Center for Nuclear Safety group performs is testing reactor pressure vessel steel. Iodine exists in liquid form at room temperature. If there was to be an accidental release of a large amount of iodine, it would take a few days to decay. Iodine is a fission gas, so in an accident scenario, it would have to escape the cladding, primary circuit, reactor containment, and exhaust filter to make it outside the plant into the environment. The exhaust filter uses resins, which is a reactive polymer, that absorbs the iodine gas. The iodine can then decay from the resins and be released as normal, non-radioactive iodine. Neutron irradiation causes embrittlement of the reactor vessel over time, which is made out of carbon steel with a stainless steel cladding. Neutrons knock atoms out of place and distort the lattice structure of the steel, which reduces the ductility of the material.
Q: Is your work primarily focused on understanding the behavior of the existing steel alloy used in nuclear plants, or is it more focused on designing new materials that have a better resistance to embrittlement?
A: Wade Karlsen’s work focuses primarily on understanding the behavior of existing steel alloys used in nuclear plants, but also participate in projects that look at effects of different alloying elements to see if materials can be improved. Nuclear plants are reluctant to experiment with new materials since they are so many other variables and some steel alloys have proven effective. Karlsen performs mechanical testing and metalurgraphic examinations to show what properties are present and specimens are tested on a regular basis to determine confidence in the infrastructure. Stress corrosion cracking results as a combination of the materials, loading scenario, and environment that emerges when something happens that was not foreseen, such as a change in the chemical environment that has an accelerating effect, residual stresses in the material, or some fatigue loading that was not accounted for. This cracking cannot be captured in a finite element model, but failure analyses are conducted to identify the areas of cracking. To improve performance, water chemistry might be altered or stress relief may be needed on the surface.