Studying nuclear engineering in Moscow and Bulgaria (0:55)
0:55-7:02 (Kostadin describes his journey into nuclear engineering.)

Q. How did you get involved in the nuclear space?
A. Kostadin Ivanov is originally from Bulgaria. After high school, Kostadin recognized that he was skilled in physics and math. At that time, Bulgaria was beginning to build their first nuclear power plant: Kozloduy. Kostadin decided to study nuclear engineering, and attended a university in Moscow, where he received both a bachelors and master’s of engineering. Because the government of Bulgaria financed his studies, Kostadin was required to work at Kozloduy for three years after finishing his education. He began as an operator and then became chief engineer of one of the units. He then moved to the core design division. After, Kostadin applied for a PhD to study reactor physics at the Bulgaria Academy of Sciences. During this time, he worked at the Institute of Nuclear Energy, which is part of the Bulgaria Academy of Sciences. Kostadin stayed at the Institute after completing his PhD as a research scientist. He then applied for a Fulbright fellowship for optimizing core design and reducing the fluence on the reactor vessel, which is the damage caused over time from neutrons.

VVER designs (7:03)
7:03-15:45 (Kostadin discusses the VVER projects that he worked on when a PhD student and research scientist in Bulgaria.)

Q. Why don’t they put a sacrificial material in front of the vessel?
A. They did, but Kostadin performed calculations of how the neutron damage impacts the welds and the overall lifetime of the pressure vessel. The weld is affected more severely than other parts of the vessel due to the filler material used in the weld. The neutrons leave physical marks in the metal of the weld.

Kostadin worked on two major simultaneous projects after finishing his PhD. One project involved analyzing the new VVER-1000 reactors, which were more complex than the VVER-440. The 440 design was different from the US pressurized water reactors (PWRs) because the 440 had shroud, which changes calculation methods from the PWRs. The shroud absorbs neutrons and is similar to boiling water reactors where the assemblies are physically separated. The 1000 design adopted an open configuration, creating a more powerful reactor.

In most cases Russian reactor designs follow US designs, but in some cases Russia has introduced their own designs. For example, one of the new VVER-1000 designs changed to an 18 month cycle, which is similar to some of the US designs. These changes make the VVER more competitive. Some reactors in Finland have combined Western control instrumentation with the Russian VVER core design. There is also a trend to move to digital controls. However, the requirements for redundancy complicate the adoption of digital technology.

The BN-800 fast reactor (15:46)
15:46-19:33 (Kostadin explains his involvement with the BN-800 fast reactor project. He also discusses the BN-800’s configuration.)

Q. What does the configuration of the BN-800 look like?
A. In addition to the VVER project, Kostadin worked on the fast reactors. At the time, the Obninsk nuclear power plant near Moscow had the largest fast reactor center. The Bulgarian team was responsible for the optimization of core design, specifically looking at axle blankets. BN-800 is a fast reactor in Siberia that is currently in operation and produces 800 megawatts.

It is a hexagonal geometry with ceramic pellets on the inside. It has a sodium core reactor. It has both radial and axle blankets. The blankets contribute to reflecting neutrons but their main function is to produce plutonium from uranium-238. The blankets are assemblies of mostly uranium-238 which are breeding and are placed in rings. The rings are then reprocessed.

Penn State’s nuclear research projects (19:34)
19:34-24:44 (Kostadin describes the work he did at Penn State.)

Q. What kind of projects did you work on at Penn State?
A. After this project, Kostadin was working on a project with the International Atomic Energy Agency on fuel management. One of the people working on the project was Dr. Sam Levine from Penn State. Kostadin wrote Levine’s name on his Fulbright application as the person he wanted to work with. After 6 months, Kostadin was informed that he was one of ten people chosen to receive the Fulbright fellowship and would be working at Penn State. In 1993, Kostadin came to the US to work with Dr. Levine.

The project’s focus was developing optimization methods for VVER under Dr. Levine’s guidance. Kostadin also became involved with other projects in the department. At the time, the department was one of the strongest for nuclear research in the world, having strong connections with plants such as Three Mile Island and a total of 8 reactors in the state. Westinghouse and the Nuclear Regulation Committee (NRC) were also closely connected to Penn State. Kostadin worked with Westinghouse on a project involving the AP600 reactor.

Kostadin returned to Bulgaria after the fellowship, but immediately secured another fellowship with the International Atomic Energy Agency in Germany looking at the safety of VVER reactors. After eight months, Penn State reached out to Kostadin and asked him to return as a postdoctoral scholar. He eventually became a fixed research professor and resigned from the Institute in Bulgaria to stay in the US.

Deciding to stay in the US (24:45)
24:45-39:43 (Kostadin explains why he chose to stay in the US rather than work in Bulgaria.)

Q. What made you want to stay?
A. Kostadin saw a larger opportunity to develop professionally while staying in the US. Bulgaria was going through some rough political and social changes during this time. These changes did not encourage the scientific community in Bulgaria to flourish, and many members of the Institute left to work in western countries. The fall of the Soviet Union and the transition to an independent Bulgaria was peaceful, but the prior communist party was still powerful and guided decisions. Economic power and industrial growth became more important than science and education.

Kostadin stayed in the US and became an assistant professor. He then became an associate professor with tenure track in reactor design and safety analysis. After seven years, Kostadin became a distinguished professor. He focuses on using experimental data to validate computational tools. Kostadin began with reactor physics, but moved towards researching coupling with other physics to understand safety and design. He focuses primarily on the reactor core rather than the entire system.

Developing benchmarks (29:44)
29:44-42:00 (Kostadin explains his involvement in developing benchmarks. He also states the importance of developing high fidelity simulations to help industry address challenges.)

Q. How are benchmarks used to design reactors?
A. In addition to their connection with the NRC and the US industry, Penn State was also involved in international projects. Kostadin worked with the Nuclear Energy Agency OECD to develop the moot physics benchmark. The moot physics benchmarks were designed to test the moot physics tools and how they predict initial steady state and transient evolution. These benchmarks were developed using real reactors, starting with Three Mile Island. Many organizations from about 20 countries participated in the development and the NRC eventually adopted the benchmarks.

The main steam line and large break loca have different benchmarks. The moot physics is lost in large break loca. The main steam line break has a high probability to happen and has coupling effects. The main steam line break happens in one of the steam generators when the barrier between the primary and secondary loops is compromised. This causes overcooling in one part of the core, creating power gradients. Pressurized water reactors have two potentially dangerous situations involving mixing: temperature and boron mixing. Boron mixing causes a power spike. Kostadin’s computational models predict these accidents and the core response. Most of the feedback interactions happen within the core. Reactor physics, fuel, neutron behavior, temperature and coolant interact and Kostadin simulates these interactions and benchmarks.

It is challenging to model accidents because there are many parameters, especially on the local level. This means the team must approximate, introducing errors to calculations. They are moving towards high fidelity tools, though, that model everything on a higher resolution to see direct responses. Kostadin is now a chair in the working party of reactor systems with the nuclear science committee at the Nuclear Energy Agency. He is involved in several expert groups: uncertainty analysis in modeling and moot physics validation. He now works on creating more sophisticated benchmarks. They use the Consortium of Advanced Simulation for Light Water Reactors (CASL) to validate the new high fidelity systems and create new international benchmarks. Understanding what is happening on the pin level versus the assembly level avoids approximations and reduces error. With better predictions, the margin is known and can increase operational flexibility. Crud, or the build up on the outside of fuel pins, is also better understood with high fidelity modeling. These simulations helps address industry challenges.

Working with the government to secure the future of nuclear (42:01)
42:01-46:06 (Kostadin outlines the challenges that the industry faces and how working with the government can help secure the future of the industry in the US.)

Q. Where do you think the industry will go in the future?
A. Kostadin believes that the industry has challenges. The safety issues of Fukushima have been addressed and Kastadin believes there are technical solutions to other challenges that the industry faces. We now need to find political solutions to challenges. Cost and time are the major challenges that must be overcome to be competitive with other energy sources. However, Kostadin sees a positive outlook for nuclear in the US because of the new advanced reactor developments and the support of the government. North Carolina State University has formed an alliance with the state government to work with the nuclear sector and the Carolinas have extended the life of the existing plants. Kostadin believes the nuclear industry must be proactive to ensure its future.