The TVS-K fuel assembly is the most ambitious project in the modern history of the Russian nuclear fuel industry and of TVEL Fuel Company (part of the Russian State Atomic Energy Corporation Rosatom). The goal of developing fuel for Western- design reactors, set in the beginning of the century, required Russian scientists, designers and engineers to solve a whole range of technology issues.

Although the major technical specifications of pressurised water reactors and Russian design VVER-1000 reactors (consider pressure, temperature, coolant flowrate and velocity) are very close, the final target was far from easy to reach, as the new fuel had to be compatible with the designs already in operation at nuclear power plants abroad. It has taken years of calculations and experimental validations, materials research and study, bench testing of structural components, examination of assembly components in research reactors and technology optimisation, before TVEL was able to enter the market with a new product.

The final TVS-K product is compatible with Western-design reactors, but it is fundamentally different from foreign fuels in terms of fuel assembly design and technology, and it has the best characteristics of VVER-1000 fuel. Thus, TVS-K does not fall short of the traditional PWR fuels; in some regards it even has an edge over them.

The original solutions for the spacer grid and skeleton give the fuel enough rigidity. It also allows for five years of operation while maintaining the original geometry and a higher burnup range (about 70GWd/tU) without compromising safety and reliability.

The special characteristic of TVS-K is the use of two Russian zirconium alloys. These are E110 for the fuel rod cladding and E635 for the fuel assembly skeleton. In our view, the combination of these two materials, with their slightly different properties, is what enables customers to achieve good results in the long-term operation, performance and reliability of the fuel. TVEL is continuing to optimise these alloys, improving their mechanical properties and in-pile behaviour.

A pilot project is taking place in which TVS-K is in operation at Ringhals in Sweden (a plant operated by Vattenfall Group). The practical phase of the project has been running since 2014, when lead fuel assemblies were loaded into the core. As a part of this programme, each year engineers carry out visual inspections, measure oxidation of the fuel assembly components, assess fuel assembly bowing and elongation, and evaluate the current state of single elements after every fuel cycle. So far the operation of the Russian-made fuel, a subject of keen interest of within the global nuclear community, is running within design limits.

In 2019/20 the fuel assemblies are due to be discharged for post- irradiation examination in hot cells and analysis of the actual and design criteria compliance. The results will be presented to the safety authority in Sweden. However, even before the end of pilot operation, Vattenfall Nuclear Fuel and TVEL have signed a commercial contract for supply of TVS-K fuel starting in 2021.

The design of the TVS-K fuel assemblies now in operation at Ringhals was undertaken with a conservative approach and it has the potential for further optimisation. We are grateful to our Swedish partners for their comprehensive feedback and their active role in this project, as it helps us understand the exact components that should be improved or modernised.

After the end of the pilot project, Rosatom, represented by TVEL Fuel Company, will be able to introduce a new competitive product for the global nuclear fuel market, which will enable PWR operators to diversify their fuel supply with the focus on the economically efficient and reliable operation of power plants.  

Alexey Dolgov is Head of Research & Development Department at TVEL Fuel Company