Article details

30.07.2021 Our Media Coverage

B. Hatala, A. Hanzel and V. Slugeň for Jaderná energie: High-temperature reactors and hydrogen in the light of the world trends

The article deals with new requirements for hydrogen production and the possibilities of efficient, sustainable and reliable hydrogen production.

B. Hatala, A. Hanzel and V. Slugeň for Jaderná energie: High-temperature reactors and hydrogen in the light of the world trends

Hydrogen and the European Commission

The idea of a widespread use of hydrogen in industry, transport, or as a medium for meaningful energy storage can only be welcomed, however in a real technical context. Hydrogen is the most abundant element on the globe. It seems to be very advantageous for energy use, it has a very high calorific value - 141.7 MJ/kg, the highest of all organic compounds, which is 6 times higher than the natural gas. Its big disadvantage is that it does not occur independently in nature and must be produced. At present, hydrogen is mostly produced from natural gas, which is environmentally unacceptable. Such production produces both CO2 and methane. The ecological future of hydrogen can be ensured in a sustainable way only if it is produced:

  • by electrolysis from renewable sources,
  • in nuclear reactors.

The European Green Deal is a plan to ensure the sustainability of the EU economy, which envisages climate neutrality by 2050. According to the European Green Deal, the installation of electrolyzes for the production of renewable hydrogen with a minimum output of 6 GW will be supported in the EU from 2020 to 2024, thus supporting the production of up to one million tonnes of hydrogen per year from renewable sources. Approximately 60 TWh of electricity per year is needed to produce one million tonnes of hydrogen.

Producing such a volume of hydrogen requires a large amount of electricity. For a better idea, both units at Jaslovské Bohunice NPP will produce an average of 7.5 TWh per year. New NPP types (e.g. AP1000) produce approximately 9 TWh of electricity per year. Therefore, if the EU wants to ensure the production of one million tonnes of hydrogen through electricity, it is necessary to build at least 7 new nuclear power plants with an electrical output of 1200 MWe. We only mention the number of nuclear power plants, because a nuclear power plant is a source that can produce energy in a relatively small area compared to photovoltaics and ensures a reliable supply of electricity throughout the year, regardless of the weather. For comparison, Slovenské elektrárne has approximately 1 MW of installed capacity of photovoltaic power plants in Vojany with an area of almost 3 hectares, where the utilization rate is about 12%. It would therefore take more than a million hectares to produce 60TWh of electricity per year by means of photovoltaics.

The European Green Deal has politically stipulated ambitious objectives which are extremely demanding, however there is no analysis of how the objectives stipulated for the next period will be achieved by 2024.

As early as in 1969, the European Joint Research Centre (JRC) in Ispra studied the possibilities of hydrogen production and use, which was followed by a complete research programme. Considering all the laws of physics and chemistry, scientists and engineers, after many analyses, tests and demonstrations, concluded that low efficiency and high economic costs limit the scope for industrial use of hydrogen as an energy carrier.

The case of Germany, where volatile renewable energy sources are largely located, points to significant location-related constraints. The "Energiewende" strategy, which is costly (€25 billion in grants per year for a period of 20 years, equivalent to around €1,000 per family per year), has virtually zero impact in terms of decarbonisation, with wind energy and solar panels producing only 4.3% of the primary energy. The extensive deployment of these technologies results in either excessive or insufficient electricity generation compared to the demand. In case of a shortage, which has been occurring most of the time, Germany, during its gradual decommissioning of nuclear energy, relies on fossil fuels, lignite or hard coal, or imported Russian gas, which explains the low impact of the strategy on decarbonisation. Ideally, in case of overproduction, it would be necessary to provide funds for the massive storage of "green" renewable electricity for its later use. But there are only a few ways to store electricity produced from wind energy and solar panels for a limited period of time: batteries, pumped hydroelectric energy storage, or the use of an embedded energy carrier such as hydrogen.

It therefore makes much more sense to use nuclear energy, the only fully decarbonised primary energy where nuclear power plants are able to massively produce distributable electricity and thus optimize the intermittent deployment of renewables.

In Slovakia, the "National Hydrogen Strategy" was developed and approved by the Government of the Slovak Republic in March 2021 with the subtitle "Prepared for the Future". This document assumes that the production of hydrogen will be ensured by electrolysis in the following quantities. By 2030, an annual consumption of 178 kt is expected and from 400 to 1740 kt of hydrogen per year by 2050.

The electrolysis efficiency is, as stated in various documents, from 60-80%. The additional need for energy for distribution and possible compression reduces the overall efficiency of hydrogen production to 30-40%. If hydrogen is subsequently used for a simple combustion, it will be inefficient. Today's use of hydrogen in fuel cells degrades its energy. Hydrogen is used in fuel cells for only 50% of real work, the other 50% is heat loss.

The National Hydrogen Strategy assumes that hydrogen will be produced from RES. However, resulting from the document, directly or indirectly, RES is not suitable for any separate production of electricity. The problem is that the production of electricity using wind energy or solar panels has an annual maximum utilization (load factor) of only 11-20%. In addition, due to the constant interruption of wind and solar radiation, the necessary electrolysis would also have to work intermittently, and this would bring further problems to the economy.

Hydrogen production in high-temperature nuclear reactors

At present, the public is particularly familiar with the production of hydrogen by means of electrolysers. Electrolysis can produce hydrogen either from water or, more efficiently, from water vapor at high temperatures, which is high temperature electrolysis. As the temperature rises, we need much less electricity to power supply the electrolysers.

Just to remind, the efficiency of electricity production in thermal power plants is about 35%. Subsequently, the electricity produced in this way is used to produce hydrogen in electrolysers from water, where the efficiency of hydrogen production is about 60%. 9 l of water and 60 kWh of electricity are needed to produce 1 kg of hydrogen by electrolysis.

An electric car needs about 20 kWh of electric energy per 100 km and a car using hydrogen needs 1 kg of hydrogen and therefore about 60 kWh of electric energy.

The question is: Is it worth for us to develop hydrogen cars when electricity is a high-quality and an exclusive form of energy? Is it important to develop hydrogen technologies? Does this solution have a logical justification if 1 km in a hydrogen car is three times more expensive than in a car powered by batteries? Or... Can we produce hydrogen in any other way and at the same time efficiently?

Yes, we can.

There are other technologies in the world than producing hydrogen from water. The solution is high-temperature nuclear reactors. Unfortunately, the link between a nuclear reactor and hydrogen production is misunderstood and therefore unacceptable in the European Union, although the results of the JRC's analysis do not provide any scientifically based evidence that nuclear energy is more harmful to human health or the environment than other electricity generation technologies.

The high outlet temperature from the core of the high-temperature reactor makes it possible to efficiently produce hydrogen by means of known high-temperature electrolysis technologies. Another method of hydrogen production is the thermochemical way called hydroiodic acid-sulphur cycle (I-S cycle), which is also used to produce hydrogen with an efficiency of the entire production cycle in the range of 40-50%. Compared to electrolysis, it is more efficient because the heat produced does not need to be converted into electricity with significant losses. The high-temperature reactor enables the combined production of hydrogen and electricity, where the efficiency of the large cycle increases considerably.

The mentioned method of hydrogen production is verified in practice in Japan at the Japan Atomic Energy Agency (JAEA), research institute in Oarai, where the HTTR reactor is operated. The reactor power is 30 MW and it demonstrates an efficient hydrogen production at 850 °C. This temperature is achieved thanks to the use of helium as the primary coolant of the reactor core [4].

A new type of high-temperature reactor HTR-PM was recently put into operation in the Institute of Nuclear and New Energy Technology of Tsinghua University in China, where the cooling medium is also helium, which allows extremely high temperatures to be reached [5].

The construction of the test power plant in China's Shandong Province began in 2012. The project consists of two helium-cooled modular HTR-PM reactors with a heat output of 250 MWt and a turbine with a 210 MWe generator [2].

The core of this reactor is very specific and consists of fuel of spherical shape with TRISO particles. In conventional light water reactors, the fuel is stored in fuel pellets. In this type of reactor, the fuel of spherical shape is 6 cm in diameter and consists of a number of small parts with graphite and silicon cladding. Obviously, China has already mastered the technology of producing this specific type of fuel.

The reactor core has a diameter of 3 m and a height of 11 m, while the reactor vessel has a diameter of 5.7 m and a height of 25 m. Each reactor has 3 three loops. The reactor core is designed with a negative reactivity temperature coefficient, in order to increase safety.

In the EU, a prototype of the ALLEGRO reactor, one of the six types of Generation IV reactors, could be a representative of the high-temperature technology. The ALLEGRO helium-cooled fast reactor represents a unique combination of technologies. It is a fast neutron spectrum reactor that allows the production of high-parameter heat with the possibility of various applications, such as hydrogen production, heat supply for energy demanding chemical technologies, or the production of high-efficiency electricity. The outlet temperature from the reactor core can be up to 850 °C. The ALLEGRO reactor is currently the subject of research and development by a group of countries in France, Slovakia, the Czech Republic, Hungary and Poland. Unlike the Chinese reactor, the question of building this type of reactor in Europe is still open.

The advantage of nuclear technologies is sustainable and reliable production and a very long lifecycle of nuclear reactors. The reactors, currently under construction, have a planned lifecycle of 60 years with the possibility of extension up to almost 80 years.

Even if the European Union wishes for hydrogen technologies, we can seriously state that the technologies for hydrogen production in the EU are far from competitive compared to the rest of the world. Even hydrogen-powered cars are offered mainly by manufacturers outside the EU (Honda FXC Clarity, Toyota Mirai, Hyundai Nexo).


There is no doubt that the demand for hydrogen, which can be used in transport as well as in the heavy chemical industry, will continue to grow around the world.

At present, the industrial hydrogen production is almost entirely based on fossil fuels. The amount of energy required to decompose water for such applications can be provided by direct heat produced in fully decarbonized high-temperature nuclear reactors. The research and demonstration of such reactors is in progress in China, Japan and the United States.

If the European Commission, but also the Government of the Slovak Republic, wants to avoid geopolitical displacement by other regions where such a development is a common practise, it should pay close attention to this topic, but above all it should meaningfully invest in this technology. If there is a real interest in producing hydrogen in the amount stated, this will not be technically possible without nuclear power plants.





[3]        V. Slugeň a kol.: Vysokoteplotné reaktory. (ed. SNUS)    
            ISBN:80-88682-62-2, (2006) 101pp.