Journal of Nuclear Engineering: Mochovce Unit 3 Delivered Valuable Experience and Know-How for Future Nuclear Projects

When a new nuclear power unit is commissioned in Europe, it is not just an energy-sector event. It is an experience that carries value for the entire industry.

Mochovce Unit 3, a major milestone for Slovak energy, clearly confirms this.

A group of authors from the Institute of Nuclear and Physical Engineering at the Slovak University of Technology, VUJE, and Slovenské elektrárne, Vladimír Slugeň, Gabriel Farkaš, Jana Šimeg Veterníková, Slavomír Bebjak, Peter Andraško and Martin Mráz, systematically captures, organises and transfers unique operational experience gained by Slovak experts for the further development of nuclear energy.

With new nuclear projects advancing only slowly across Europe and the generation of experienced professionals ageing, the paper aims to provide concrete technical and organisational lessons applicable to the commissioning of Mochovce Unit 4, as well as to future nuclear projects anywhere in Europe, including planned small modular reactors, SMRs.

Why the Contribution of Slovak Experts Is Exceptional

The experience gained at Mochovce is particularly valuable because it emerged from a technically demanding and closely monitored project. The peer-reviewed paper shows that the commissioning of a nuclear power unit depends not only on technology, but also on precise process management, team readiness, a rigorous safety culture and effective transfer of know-how.

The commissioning of new nuclear units in Europe is an exceptionally rare event. Over the past 20 years, only three units have entered operation in Western and Central Europe: Olkiluoto Unit 3 in Finland, Flamanville Unit 3 in France, and Mochovce Unit 3 in Slovakia. Each of these projects brought hard-earned lessons related to schedule delays and cost overruns. Systematically compiled findings from this process therefore represent a valuable and difficult-to-replace source of knowledge.

A particular feature of Mochovce Unit 3 is that during the final phase of commissioning, the original reactor designer, OKB Gidropress, was no longer available to assume responsibility for design integrity. The Slovak team had to effectively step into this role itself, which makes this case different from the standard commissioning of reactors elsewhere in the world.

What the Publication Contains

The core of the publication is a systematic set of technical and organisational recommendations collected directly from the physical start-up and power ascension testing of MO3, structured by the authors into three main areas:

People: Preserving the critical knowledge and experience of key personnel ahead of expected workforce turnover associated with MO4 commissioning.

Processes: Reviewing and refining work procedures, ensuring clear accountability, and maintaining consistent communication with the regulator.

Technology: Transferring specific technical solutions, including neutronic characteristics, pressure measurement and secondary-side efficiency.

Read the full publication here: bit.ly/4c9a0SQ

Selected Operational Lessons Learned

• Always use up-to-date, revised documentation with a complete history of changes.
• When dealing with unreliable instrumentation signals during tests, adopt a conservative decision-making approach.
• Do not allow provisional technical solutions, as they increase the risk of failures during power start-up.
• Organise T-48h and T-24h briefings before each first-of-a-kind test.
• Ensure direct participation of the Design Authority in the evaluation of test results.
• Thoroughly document and track non-conformances, including those with long-term implications.
• Communicate openly, proactively and promptly with the Nuclear Regulatory Authority of the Slovak Republic, ÚJD SR.

What These Findings Mean for the Future

The lessons learned from MO3 are directly applicable to the commissioning of Mochovce Unit 4, expected the next. In the broader European context, they are equally relevant to any new nuclear project, from planned Generation III+ units in Central Europe to future SMR deployment. 

The paper also places these technical lessons within a wider energy-policy context, noting that Slovakia, and Europe as a whole, face growing pressure to extend the operating lifetime of existing nuclear units to 60 to 80 years, as intermittent renewable energy sources alone cannot ensure the same level of supply stability and security.

It's precisely outputs like these that carry exceptional value in the nuclear sector.