Perspectives on the future of nuclear energy in Slovakia

Abstract

The Slovak electric power generation market is small compared to that of other European countries. Anyhow, quite a unique mix of energy sources, a small number of inhabitants, and a well-developed nuclear industry make the story of Slovakia interesting and worth knowing. The status of new builds and decommissioning activities is given with the following brief presentation of the Slovak University of Technology in Bratislava with a focus on the Institute of Nuclear and Physical Engineering. The last part of the contribution is devoted to the new platform for education in nuclear being established in Central Europe. European Nuclear Experimental Educational platform aiming to simplify access to research reactors and specialized laboratories for students and researchers is introduced and discussed.

1 Introduction

To achieve the climate goals stipulated in the Paris Agreement [1], nuclear power seems to be one of the primary alternatives to renewables for reducing carbon emissions in the electric sector [2]. The necessity to reduce carbon emissions is emphasized by the high-level nature of the Paris Agreement, which is a legally binding international treaty on climate change adopted by 196 Parties at COP 21 in Paris, on 12 December 2015 and entered into force on 4 November 2016. The Slovak electric power generation market is small compared to that of other European countries. Anyhow, quite a unique mix of energy sources, a small number of inhabitants, and a well-developed nuclear industry make the story of Slovakia and former Czechoslovakia interesting and worth knowing.

The era of the nuclear power industry in Czechoslovakia started in 1958 with the construction of the first experimental A1 nuclear power plant. As can be found in archives [3] (see Fig. 1a), Czechoslovakia during that era had one of the highest energy demand per capita in the world with the growth of that demand relatively high compared to other nations. This energy demand growth was determined by rapid development of heavy industry. The emphasis was given to energy-intensive production (designated by the Council for Mutual Economic Assistance), such as metallurgy, heavy machinery, and coal mining. Due to the limited availability of other primary sources, the nuclear option seemed to be the most attractive [4]. The A1 reactor (see Fig. 1b) is situated on the Jaslovske Bohunice site. The construction of the A1 power plant finished in 1972. It had one heavy water type experimental reactor, the KS-150 designed in Czechoslovakia, which used non-enriched uranium as a fuel and was cooled by gaseous CO2. This seemed ideal to the Czechoslovakian government because it would have allowed the use of domestic uranium deposits together with its own heavy water, thus freeing the country from dependency on foreign source material. However, the whole project suffered from, continuous problems, which resulted in two serious operational events. The first accident occurred in 1976, a fresh fuel assembly was ejected right after its loading into the reactor channel, and the cooling gas partially leaked. Two workers lost their lives during the event. A second INES 4 accident occurred during the refueling on February 22, 1977. The cladding of the technological reactor channel has failed in its core and the moderator penetrated the cooling circuits. The cladding and steam generator tube corrosion under water-saturated by carbon dioxide occurred and resulted in the contamination of the primary and secondary circuit as well as the reactor hall [5]. After the second major accident considering the economical and safety aspects, a decision was made to shut down the reactor down. Although the whole project had to be closed, it provided valuable experience for use in future planning and development of the nuclear fleet.

Fig. 1

Energy growth and historical picture of A1 NPP

Based on the knowledge gained in the A1 project, the complex nuclear power program was formulated by incorporating Soviet-designed light-water reactors. In 1978 the first light water reactor was built in west Slovakia. This was the VVER 440/V230 reactor, modified by Czechoslovaks, based on their own research and elements obtained from western models [7]. The next unit of the same type was finalized in 1980. By 1983, the Czechoslovakian economic planners admitted the need to increase the energy potential by building nuclear power plants [8]. As can be seen from Fig. 2, the stated goal yielded to almost continuous construction of new units (U) temporarily interrupted in the politically unstable 90 s, when the Soviet Union dissolved, and Czechoslovakia split into the two independent countries Czechia and Slovakia (1993). Most constructions were VVER 440/V213 types, except the Temelin NPP (ETE), which comprised 2 units of VVER 1000/V320. As the current last unit in a row, on the 31st of January 2023, unit 3 of the Mochovce nuclear power plant was connected to the grid for the first time. These unique continuous building effort (remarkably two units at the same location were connected to the grid in 1986) and tight cooperation ensured the preservation of knowledge and skills of nuclear, nuclearized, and nuclear-aware personnel in both countries.

Fig. 2

Preservation of nuclear skills–construction year and name of the NPP

The nuclear industry is Czechoslovakia was not limited to nuclear power plants only. The whole industry with ancillary services was developed, and even the relevant share of the components of the nuclear plant itself was manufactured in engineering factories using Soviet licenses and technical cooperation (e.g. pressure vessels at Škoda Plzeň, pumps in Prague, turbines at Chomutov, and ancillary nuclear systems at Tlmače) [7]. However, lots of manufacturing abilities were already lost due to the transition to the market economy and associated political changes.

2 Current status

The following sections are devoted to providing overview on the current energy mix, actual decommissioning activities, and new nuclear projects being implemented or prepared in Slovakia.

2.1 Energy mix of Slovakia

Slovakia generates electricity in nuclear power stations, hydro-power stations, natural gas, and coal-fired power stations as well as from renewable energy sources. In 2021, Slovakia generated 30,093 GWh of electricity, while the total consumption amounted to 30,867 GWh. Thus, after years, the electricity demand was almost covered by production. As shown in Fig. 3a, the balance between supply and demand was mainly achieved thanks to the decreasing electricity demand noticeable in the last 5 years and the increase of production in the last 2 years [9]. Slovakia is heavily dependent on Russian oil and natural gas, so the goal of becoming a net exporter of electricity is a matter of national energy security. Nuclear fuel is also imported from TVEL, but can easily be stored in stockpiles, allowing time to diversify supplies. For a better understanding of the electricity structure in Slovakia, the load-curve coverage on the day of the yearly peak in 2021 is shown in Fig. 3b.

Fig. 3

Yearly and yearly peak electricity production and consumption in Slovakia, 2021 [9]

To give the reader an overview of the regional context, the following section is devoted to the description of the structure of electricity sources in Central European countries valid in 2021. As can be seen in Fig. 4a, hydropower is traditionally an important sector of the Austrian energy system, where almost 61 $\%$ of the national electricity generation comes from hydropower, making this share the largest compared to other Central European countries. In Slovakia, this share is smaller, but still quite impressive in comparison with other countries reaching 15.30 $\%$ of the total electricity production. The total amount of hydropower potential in Slovakia is estimated at the level of 6 700 GWh per annum, where 70.6$\%$ of total potential is already in use and where 29.4$\%$ remains unexploited [10].

Fossil fuels play an important role in electricity production in Central Europe (shown in Fig. 4b). Poland has the largest reserves of coal in the European Union and thus naturally more than 72$\%$ of electricity production comes from coal. In the Czech Republic, both lignite and hard coal accounted for a combined 40.3$\%$ of total electricity generation. In other Central European countries, the share of fossil power is below 40$\%$. From a long-term perspective, the production of electricity in fossil power plants in the Slovak Republic is gradually declining and the importance of nuclear energy and energy from renewable sources is growing. This can be demonstrated by the plans of the Slovenske elektrarne and Slovak government to close the largest thermal plant - Novaky till December 2023 due to its economic, social, climate, health, and environmental impact. Units no. 3 and 4 (2 × 110 MWe) of ENO B were already shut down as of the 31st of December 2015.

Fig. 4

Share of electricity from hydropower and fossil fuel in EU (2021) [11]

Summarizing the share of renewable energy sources, except hydropower, (see Fig. 5a), the highest share of net electricity generation is in Austria with 30.7$\%$. The second place belongs to Hungary where 19.2$\%$ of energy comes from renewables (solar as a leading source). In Slovakia, the share of renewables reached just 7.9$\%$.

Figure 5b shows that the highest contributions of nuclear power can be found in Slovakia (52$\%$) and Hungary (46$\%$). Totally 6 reactors in the Czech Republic supply about 36$\%$ of overall electricity. In contrast, there is no nuclear power in Poland and as it is well known, no nuclear power is in Austria. It should be noted that in Slovakia, Mochovce unit 3 is already in the energy start-up process and unit 4 is scheduled to follow about 1 or 2 years after unit 3. Both will be able to provide about 13$\%$ of Slovakia’s electricity needs when operating at full capacity, thus potentially reaching 78$\%$ of nuclear shares in the electricity grid.

In Slovakia, radioactive waste and spent fuel are managed by the governmental-owned JAVYS company. Spent fuel is stored for a few years in reactor pools at the NPP sites before being transported to an interim spent fuel storage facility in Bohunice. Slovakia also manages spent fuel generated from the past operation of three nuclear power reactors as well as radioactive waste from current decommissioning at the Bohunice site. Very-low-level radioactive waste and low-level radioactive waste are being disposed of at a near-surface disposal facility (national radioactive waste repository) at Mochovce. Slovakia plans to develop a geological disposal facility for spent fuel and radioactive waste not suitable for disposal at the near-surface disposal facility.

Fig. 5

Share of electricity from renewables and nuclear in EU (2021) [11]

When limited to the countries of Central Europe, Fig. 6a shows that the southern countries (Austria and Hungary) are net importers of electricity, the consumption and supply are almost balanced in Slovakia and Poland; and Czech Republic is a net exporter of electricity to neighboring countries. A high deficit in the south of Europe covered by resources from the north as well as high volumes of electricity production from renewable energy sources results in high electricity flows that endanger the electrification transmission system of the Slovak Republic. To reduce the imports of electricity and despite the war in Ukraine, Hungary has issued a permit allowing the construction of two new nuclear reactors (VVER 1200) by the Russian state-owned company Rosatom [12]. Hungarian officials expect the two new units to be operational by 2030. The electricity price for households in Slovakia was competitive in the region at the beginning of the crisis in Ukraine (Fig. 6b). The prices for the year 2023 has been decided by the Economy Ministry thanks to the so-called “institute of crisis regulation.” In Slovakia, a large part of households is heated by burning gas, the prices of which have increased by approximately 15$\%$, electricity prices have not changed. Without government intervention, electricity prices would increase by 380$\%$, gas by 225$\%$, and heating by 80$\%$. The biggest Slovak electricity producer, the Slovenske elektrarne a.s., agreed to supply cheap electricity in exchange for the government’s pledge to non-tax electricity suppliers any further in the coming years [13].

Fig. 6

Electrity balance and electricity price for households

Even though a broad spectrum of technologies is used to generate electricity, all have some impact on the environment. Fossil fuel power plants release air pollution, which is already a major health hazard to millions of people. They are the primary producers of carbon dioxide and moreover, coal contains dilute radioactive material which is then released into the environment. Nuclear power plants generate and accumulate radioactive waste and renewable energy facilities can affect wildlife (fish and birds), involve hazardous wastes, or require cooling water. The two most widely cited estimates attribute around 7 million deaths per year, due to air pollution [16]. With the significant contribution of nuclear and hydropower sources in electricity production in Slovakia, the mortality caused by air pollution (see Fig. 7a) is one of the lowest in the central European region.

Fig. 7

Air pollution caused mortality and greenhouse emissions

The necessity to reduce carbon emissions is scientifically evident, where the energy sector is one of the biggest contributors in all developed countries. Figure 7b clearly shows that the smallest share of greenhouse gas emissions per capita can be seen in Slovakia and Austria, again thanks to the extensive use of renewables and nuclear energy sources. Poland, which is the largest producer of greenhouse gases, is intensively looking for an opportunity to implement nuclear energy technologies.

Based on the data presented, the Slovak Republic already has a low-carbon mix of electricity sources; the share of carbon-free electricity production in 2021 was almost 80$\%$. With the higher utilization of nuclear in close future, this number will become even higher.

2.2 Decommissioning of NPPs

Slovakia is one of the most experienced European countries in terms of decommissioning of nuclear power plants. This is mostly due to the nuclear power plant A1. The life cycle of the nuclear power plant A1 is shown in Fig. 8.

At the time of the decision to definitively shut the A1 reactor down, there was no sufficient experience in safely handling the process of decommissioning. In Czechoslovakia, there was no legislation establishing the framework for the decommissioning of nuclear facilities, nor the technical conditions for the implementation of such activities. Thus, the phase called “shutdown after accident” took almost 20 years and the real planning of decommissioning started only in 1995 [19]. The work until 1994 was focused on eliminating the consequences of the operational events. The continuous process of decommissioning, which is divided into five phases, began in 1999, after receiving the permission from the Nuclear Regulatorily Authority of Slovakia.

Fig. 8

Life cycle nuclear power plant A1 [20]

The activities carried out in Phase I were related to unloading the fuel and transporting outside Slovakia (back to the Russian Federation [21]), solving the problem of long-term storage, processing the liquid radioactive waste (RAW) in external facilities from contaminated waters and technological equipment of the main production unit. In Phase II the activities were related to the selection and treatment of contaminated soil and concrete, monitoring and remediation of underground waters, processing the historical RAW and decommissioning of technological equipment. The original decommissioning plan aimed on reaching the so called “green field”. This later turned out to be unrealistic, especially from an economic and a technical point of view, and the definition of the goal was changed to the decommissioning of nuclear power plants to a “brown field”. Therefore, Phases III & IV are carried out jointly. Here the activities are focused on the continuation of the decommissioning of the long-term storage for spent nuclear fuel, the processing of sludge from the long-term storage, and liquid RAW from the external tanks their repository. Phases III & IV also include the decommissioning of technological parts closely connected to each other, such as steam generators and their accessories, turbo-compressors, or sectional fittings. The subject of the Phase V will be the nuclear reactor itself and the related equipment in the reactor shaft, the short-term storage of spent nuclear fuel (SF), the pool storage for SF and the equipment located in the reactor hall, which were built and used for the decommissioning process itself. Currently the decommissioning of NPP A1 is in Phase III & IV and the activities are relatively on time. Phase V will be finalized by 2033 and the area will be available for industrial applications. The costs of decommissioning for nuclear power plant A1 are covered by the contribution, which is collected by the operators of transmission and distribution systems and is used to pay the so-called “historical debt”. This contribution is collected from end users of electricity, is part of the price for delivered electricity and serves not only to cover the costs related to the final part of the A1 nuclear power plant, but also to cover the costs of the activities of the final part of the decommissioning of NPP V1. Funds for the decommissioning are currently provided by the National Nuclear Fund to the JAVYS company, which annually submits applications for the provision of funds from is the holder of a permit for the decommissioning of this power plant. The total amount of funds delivered between 1995–2018 were 682.7 M € and the estimated amount of funds for the next period is 578.4 M € [22].

The story of the V1 NPP began in 1966, when it was decided to build a second power plant in Jaslovske Bohunice. Initially the A1 NPP plant was considered, such as the one that was already under construction. In the end, Czechoslovakia accepted an offer from the former Soviet Union, to build a power plant with a V230 type VVER pressurized water reactor, with a capacity of 440 MW. The life cycle of NPP V1 is shown in Fig. 9. The construction of both units started on the 24th of April 1972, the first unit reached criticality on the 27th of November 1978 and the second unit on the 15th of March 1980. This power plant became the first industrial type nuclear power plant in Czechoslovakia, with fully mastered and serially produced equipment. During its lifetime, the nuclear safety of the NPP was steadily increased, with more than 1300 implemented technology improvements, a small reconstruction in 1992 – 1993 and a large continuous reconstruction between 1996 – 2000. Nevertheless, as part of the negotiations for the entry of Slovakia into the EU, in 1999 the Government of Slovakia undertook a decision, to definitively shut down both units of the V1 nuclear power plant. Following this decision, the first unit was shut down in 2006 and the second unit in 2008.

Fig. 9

Life cycle nuclear power plant V1 [23]

The decommissioning of NPP V1 has been taking place since 2011, after finalizing the operation phase (also called phase 0 of decommissioning) and obtaining a decommissioning permit for two stages, with a completion date of 2027 [23]. The shutdown of both reactors was followed by activities including cooling and removal of SF, preparation of the NPP for disassembly and demolition, as well as the preparation of the necessary analyzes and relevant license documentation required for issuing the decommissioning permit. The immediate decommissioning option (IDO) was chosen by a multicriteria analysis. The main feature of this option is the immediate and smooth dismantling of the equipment in the shortest possible time after the end of the operation, followed by the demolition of the buildings down to the bottom of the construction pit and the preparation of the site for further industrial use called “brown field”.

In Phase I, which started in 2011, the historical RAW produced from the operation was processed, the systems enabling disconnection from the existing infrastructure were modified, auxiliary systems were dismantled and RAW from dismantling was processed. Also, the documentation for Phase II was prepared. Phase II started with the dismantling of the reactor cooling circuit and the main components of the primary circuit, followed by the dismantling of auxiliary systems of the primary circuit. Currently, the dismantling and demolition of buildings are carried out and the dismantled material is handled, documented, and will be safely released into the environment. The next activities include the disposal of RAW and its storage in the Republic Repository in Mochovce. The last step will be the remediation of the area, monitoring, and release of the site from the surveillance of the Nuclear Regulatory Authority of Slovakia [24]. The costs of the decommissioning of the V1 nuclear power plant are covered by funds collected for decommissioning purposes during the operation period between 1995–2008, which, however, do not cover the total need, and therefore partial financing is required from levies intended to cover the historical debt, similarly to the case of coverage costs for decommissioning the A1 nuclear power plant. A major part of the costs for the decommissioning of the V1 nuclear power plant is covered by EU resources through the Bohunice International Decommissioning Support Fund (BIDSF) as a mitigation of the financial impact of premature decommissioning of this power plant. The estimated total budget of BIDSF is 620 M € [25]. The decommissioning of this power plant is carried out in the form of partial projects, while funds from EU sources are drawn in the form of grant agreements for the implementation of individual decommissioning tasks. By the end of 2020, 18 grant agreements for the financing of V1 NPP decommissioning projects were concluded with the European Bank for Reconstruction and Development, and from the resources of the BIDSF funds the total amount of 471.51 M € was used [26]. Partial costs are also covered by the National Nuclear Fund, which represents approximately 15 M € per year. The total expected amount of costs for the actual decommissioning of the V1 nuclear power plant without costs related to the spent nuclear fuel are 1.239 billion €. Costs for the handling of spent nuclear fuel are gradually paid to the holder of the decommissioning permit, the JAVYS company [27].

2.3 Nuclear new build projects

After the commissioning of unit 2 of NPP Mochovce in 1999, the construction of the last two units (3 and 4) was put on hold. For almost 10 years, the Slovak nuclear development program was waiting for a new project, fortunately, in 2008 the program was re-launch by an official restart of the works on unit 3 and unit 4 of NPP Mochovce and Government resolution on the new NPP in the Jaslovske Bohunice locality. Initialization of the new nuclear unit deployment was related to the final shutdown of NPP V1 in Jaslovske Bohunice, although the preparatory works began in the early 2000 s. This decision to continue the development of the nuclear program was implemented in all strategic documents of the Slovak Government, such as the National Energy Policy of SR or the Strategy of Energy Security of SR. The story of NPP Mochovce 3 &4 construction was challenging but will result in positive outcomes. The project was restarted in 2008 when the construction part was finalized to 70 $\%$, and the machine and technology part was prepared to about 30 $\%$. The original plan was to reach the first criticality in 2011, which proved to be too ambitious. The story of NPP Mochovce 3 &4 construction involves several start-up delays, budget increases, political changes in Slovakia and Italy (a significant share of Slovenske Elektrarne is own by the Italian ENEL company), and owner transformations, which made the construction one of the most expensive NPPs per energy generated. An initially estimated budget of around 1.5 billion € has reached a value of 5.4 billion € and is probably not the final number. Although the finalization of the construction lasted more than 15 years, it has allowed implementation of new technologies, design improvements and transformed the NPP, originally designed in the 80 s, into a modern and unique facility. The increased output power of each unit from the designed 440 MWe to 471 MWe will partially compensate the construction costs from the beginning of the commercial operation. Moreover, the severe-accident management system, the best I &C digital technologies, the improved seismic resistance, and the enhanced fire protection systems will provide safe and secure operation for the next decades and fulfill the desired post-Fukushima requirements. As for March 2023, unit 3 is in an energetic start-up phase (has reached 55$\%$ of nominal power), meaning that the unit is already producing electric power, and within 2023 will start the commercial operation at full power. The construction of unit 4 is approaching 90 $\%$ of completion and the start-up phase is planned for 2024. In parallel to the construction of NPP Mochovce 3 &4 the Slovak nuclear development program incorporates a completely new NPP at the existing site of Jaslovske Bohunice, known as Bohunice 5. One to two additional pressurized water reactors with a total electrical output of 2400 MWe are planned, however the specific technology has not yet been chosen. One 1700 MWe unit or two 1200 MWe units are considered. JESS (Jadrova energeticka spolocnost Slovenska, a.s.) was established as a joint venture of JAVYS a.s. and ČEZ a.s. in 2009 for the purpose of establishing this new nuclear facility. The environmental impact assessment process (EIA) was successfully completed in 2016. Implementation of new legislation changes of the Atomic law, valid since 2021, allowed to start the process of obtaining a permit for the location of a new NPP without the knowledge of the specific project design by applying the so-called envelope approach with defined boundary conditions of the placed NPP. Based on the new legislation, JESS applied for the issuance of a permit for the deployment of the new NPP. According to the EIA Scoping Report, six reactor types are taken into consideration for this project: AP1000, EU-APWR, MIR1200, EPR, ATMEA1 and APR1400.

2.4 Public acceptance

To continue in the new nuclear project, the public acceptance is crucial. Public opinion on nuclear energy related topics is based largely on impressions, as few feel very well-informed about the topic. Ironically, public opinion can significantly influence strategic political decisions, which can naturally yield to not programmatic decisions jeopardizing the further development of the nuclear industry. The valuable source of data in Slovakia is the public opinion survey done for Nuclear regulatory Authority by the FOCUS agency in 2019 [28]. The opinion poll was done on a representative sample of 1026 Slovak citizens aged over 18 years. The most important conclusions found in the report are as follows. The most trusted entity providing information on nuclear energy and nuclear safety is the National Regulatory Authority (60$\%$ of respondents), followed by international organizations dealing with nuclear technology (38$\%$), nuclear plant operators (32$\%$), and scientists (19$\%$). The Slovak public is of the opinion that the Slovak nuclear power plants are safe. Overall, almost three-quarters of the population (73$\%$) are in favor of this view, with 20$\%$ of respondents believing that nuclear power plants in Slovakia are “definitely safe”| and 53$\%$ of respondents believing that they are “rather safe”. Three-quarters of the Slovak population (76$\%$) believe that Slovak laws effectively ensure the nuclear safety of Slovakia. In overall these results can be judged as support for further utilization and development of nuclear power in Slovakia.

3 Education and training

The finalization of decommissioning activities, safe operation of current power plants and the future of new NPP projects strongly depends on the available workforce, its skills, and the overall level of nuclear education. Therefore, the following sections are devoted to a short description of the most relevant academic institution active in E &T activities related to the nuclear engineering. The later part introduces the new legal entity established with aim to improve the quality of hands-on education in nuclear in central European region, called ENEEP. The Slovak higher education system currently includes, 20 public universities, 3 state universities, and 10 private universities, however the education in nuclear power engineering is conducted only at the Slovak University of Technology in Bratislava.

3.1 Institute of nuclear and physical engineering

The Slovak University of Technology in Bratislava (STU) is a modern educational and research institution, and it is ranked as the best university in chemical technologies, computer, and technical sciences in Slovakia. It continues the legacy of the 250-year-old Mining Academy in Banská Štiavnica, where the foundations of vocational and practical learning were established. STU offers education in technical fields and involves students in research in natural sciences, computer sciences, construction, architecture, materials technologies, chemistry, and food technologies. At the international level, STU has closed hundreds of collaboration agreements with foreign universities, faculties, and research institutes. Every year almost 500 students are sent abroad on internships, study visits, or participate in student exchange programs. Over the last decade, research teams from STU have been involved in approximately 500 research projects funded by international grants and have established hundreds of research contracts commissioned by businesses. Currently, the teams of STU scientists and engineers are involved in more than 100 international research projects, among which 44 projects are funded by Horizon H2020 and 11 projects are funded by Horizon Europe. The Institute of Nuclear and Physical Engineering (INPE) is one of the 10 institutes working as a part of the Faculty of Electrical Engineering and Information Technology (FEI) of STU. It is responsible for university education in nuclear and physical engineering. INPE is active in various fields of nuclear research and development. There are currently 16 laboratories devoted to nuclear physics operated at INPE. The most important are Laboratory of Reactor Physics, Laboratory of Material Science, Laboratory of Detector development, Laboratory of Mossbauer spectrometry and Laboratory of Supercomputer Applications. INPE is the only academic institution in Slovakia providing education in nuclear power engineering. The numbers of graduates in nuclear engineering topics are shown in Fig. 10.

Fig. 10

Number of graduates in nuclear engineering in Slovakia and Chechia [29, 30]

In the graph, Level I and II represent the number of B.Sc. and M.Sc. graduates, and level III is the number of Ph.D. graduates. Comparing Slovakia to Chechia the numbers are relatively low, however, given the size of the nuclear industry in Slovakia and the very high employment rate of graduates in the nuclear sector the number is almost satisfactory for the actual needs.

In addition to the standard education process, INPE has a wealth of experience in various vocational training and lifelong education activities. The first postgraduate courses “Operation of Nuclear Power Plants” were annually organized from 1965 until 1987. Since 1997, the new revised double semester postgraduate program “Safety aspects of the operation of nuclear facilities” has been conducted. The lifelong learning program is organized for employees working in the nuclear industry in Slovakia and in the Czech Republic. The program creates preconditions to obtain and broaden professional skills and specialized knowledge of safety systems, accidents, and failures, reliability, legislation, management of severe accidents, human factors, the safety of technological and electrical parts of NPPs, chemical and material aspects, RAW disposal and spent nuclear fuel issues, operation of nuclear power plants, radiation protection and environmental aspects. Lectures are provided by well-recognized university staff as well as by experts from the industry. The first semester consists of two 90 h long weekly camps. To support the theoretical lectures, a technical tour of selected nuclear facilities in Switzerland is organized. Normally, visited laboratories include the research center NAGRA - Grimsel Test Site and Mont Terri Underground Rock Laboratory, nuclear power plants Beznau and Leibstadt, ZWILAG - Würenlingen (Interim Storage of SF and RAW Processing) and ENSI Brugg (Swiss Nuclear Regulatory Authority). The second semester is organized in the form of two five-day camps of 45 and 46 h, respectively. The final exams of the first and second semesters are usually held on the tenth day after the end of the lectures. The program is completed by the final defense of the final thesis in front of a committee of lecturers. Successful graduates of the postgraduate lifelong learning program are awarded a certificate, proving their increased qualification. In total, the lifelong learning program of Safety aspects of the operation of nuclear facilities performed in 16 courses has been successfully completed by 307 employees of the nuclear industry. During the years, which were influenced by the COVID-19 pandemic, the postgraduate and lifelong education activities were conducted in a hybrid form, where the lectures were provided both in-person and online. The online tools developed for those activities have been used since then for international education activities through projects and initiatives in which STU is actively involved, such as ENEEP.

3.2 European nuclear experimental educational platform

An essential element in the implementation and safe operation of nuclear facilities is a knowledgeable and skilled workforce. Nuclear skills however cannot be built without experimental hands-on education & training (E &T). Hands-on education requires research reactors (RRs) of various types and designs and laboratories, where basic nuclear principles can be demonstrated in an interactive way. As of March 2023, 222 research reactors are in operation worldwide, among which 31 are in the European union (no RR in Slovakia). Since the operating costs of these infrastructures are quite high, a significant operation time is allocated for commercial activities, such as isotope production for medical applications, or silicon doping, thus the time available for E &T is always limited. Therefore, there must be always a compromise between the commercial activities and the available time for E &T activities, which requires international cooperation and optimization of the available infrastructure on EU level.

To cope with these challenges and to help countries such as Slovakia, the European Nuclear Experimental Educational Platform (ENEEP) is being established. It started as an international project supported by the EU’s H2020 program [31], and currently continues its legacy as an open civil association. It is being established with four establishing members, Slovak University of Technology in Bratislava (leader, Slovakia), Budapest University of Technology and Economics (Hungary), Jozef Stefan Institute (Slovenia) and Czech Technical University in Prague (Czechia), with 3 new members willing to join after the establishment, namely Technical University Vienna (Austria), University of Pavia (Italy) and Penn State University (PA, USA). The mission of ENEEP is to fulfill the needs of its users to significantly improve their E &T and hands-on activities in the nuclear curricula, particularly in the field of nuclear safety and radiation protection. The timeline of ENEEP is shown in Fig. 11. The activities started in 2019 with joining 5 central European partners and started implementing the ENEEP projects, collecting and unifying their experience and synchronizing their activities. As a result, more than 50 standard E &T experiments were defined, and 7 demonstration courses were carried out in 2022. The demonstration activities were designed as both group and individual activities for master and Ph.D. students as well as young professionals. From more than 100 applications 39 fellows were selected from 14 countries. The knowledge of the participants was measured before and after the E &T activities, and the feedback was collected to further improve the quality of the education process. We managed to improve the knowledge of each fellow and received a satisfaction rate of more than 80

Fig. 11

Timeline of activities in the ENEEP association [32]

Currently, after the end of the H2020 project, the ENEEP association follows all activities and establishes regular Summer and Winter schools. The portfolio of E&T activities is shown in Fig. 12. The expertise of ENEEP partners makes it possible to cover a variety of E&T fields, each partner can provide a baseline of nuclear E&T skills with some specifics, which cannot be achieved elsewhere. This leads to both complementarity and substitutability and maintains the flexibility of the academic environment.

The ENEEP course puzzle shown in Fig. 12b consists of four important pieces, Preparation, Execution, Evaluation, and Improvement. In the preparation of courses, custom education materials are created and distributed in advance, online tutoring is provided, and the knowledge of fellows is measured before the training. In the execution phase, the fellows are actively involved in education through assignments and teamwork activities. In the Evaluation phases, the progress of participants is measured through post-tests, the assignment, and teamwork results are defended, and feedback is obtained from the fellows. The most important Improvements then are the new knowledge and experience of fellows and the feedback towards the organizers to further improve the quality of the E &T process.

The ENEEP association is expanding inside and outside the EU, looking for new partners to be part of the platform as well as end-users, who could benefit from the standard or tailored E &T activities. For more information follow our website www.eneep.org, where information about the new courses as well as possibilities for partial or full support for participants could be found.

Fig. 12

Portfolio of the ENEEP E &T activities

4 Challenges

The two principal challenges faced by Slovak nuclear industry are the need for nuclear fuel supply diversification and the rise of the renewables share in the electricity grid.

4.1 Nuclear fuel diversification

Due to the conflict in Ukraine, several European countries, which rely on nuclear fuel supply from Russia, accelerate communication with alternative vendors to diversify their nuclear fuel supply. Czechia has already signed a contract with Framatome and Westinghouse for their VVER 1000 Temelin NPP [33] and currently expands its cooperation with Westinghouse to supply fuel to NPP Dukovany [34]. Moreover, Finland and Bulgaria signed partnership agreements with Westinghouse to develop, license, and deliver nuclear fuel for their NPPs [35]. Slovakia also communicates with western companies such as Framatome and Westinghouse. A Joint Declaration has been signed between the Department of Commerce of the USA and the Ministry of Economics of SR to foster cooperation in the diversification of nuclear fuel supplies for VVER nuclear reactors, with special attention to the issue of licensing of fuel supplied by alternative providers [36]. Slovak NPPs have a valid contract with TVEL company till 2026, which offers enough time to overcome all issues connected to the licensing of the new fuel. The question remains whether this forced diversification of the fuel suppliers will at least keep the fuel price at the current level and ensure the reliable operation by which VVER technology is characterized.

To manage these issues, the diversification process is supported also by EC through funding schemes. The first funding initiative was issued in 2016, where the commission supported several EU companies, including VUJE, by 2 mil. €. grant to investigate possibilities and requirements of new nuclear fuel licensing. In 2022, the EC opened a special call in the Horizon Europe grant scheme to force activities towards a coordinated approach to the licensing of alternative fuel for VVER reactors, maintaining the highest nuclear safety standards for the deployment of alternative fuel for VVER reactors in the EU Member States and Ukraine. The two consortia led by Westinghouse and Framatome participated in this call.

4.2 Renewables in electricity grids

As shown the baseload electricity generation in Slovakia is provided by hydro, fossil fuels, and nuclear. Currently, the strong movement towards renewable energy imposes higher requirements on nuclear reactors including significantly variable power demands. Contrary, new devices such as electric vehicles could back-export electricity to the grid, and thus may reduce the dependency of variations in demand on the weather. Anyhow, these variable power demands might influence the capacity factor of reactors and thus negatively impact their economy. The missing link in the energy system could be the symbiotic cooperation of small and medium nuclear reactors (SMRs) [37] with various energy storage systems. This cooperation has the potential to allow the operation of the reactor at a constant power level by storing cheaper off-peak electricity, which can then be sold at a higher price in the event of high demand.

The IAEA usually defines small and medium-sized or modular reactors as reactors producing up to 300 MW(e) (small-sized or small modular) and reactors producing 300–700 MWe (medium-sized). The reactors currently operated and constructed in Slovakia (VVER 440) might be thus already judged as medium-sized reactors. A new generation of SMRs would benefit from flexible power generation options, a wide range of applications, enhanced safety resulting from inherent passive safety features, reduced upfront capital investment, and possibilities for cogeneration and non-electrical applications. The higher awaited share of nuclear energy in the grid with a significant portion of renewables will enlarge the need for load-following operation for baseload energy sources and will open the possibility of storing off-peak electricity in energy storage systems.

Worldwide and in Slovakia as well, NPPs face difficulties adapting to the shifting electricity grid dynamics due to regulatory constraints and limited experience ramping electricity production and operating flexibly. The Slovak VVER units have limited capacity to adjust the electric output. These limitations are mainly given by the performance of nuclear fuel and associated turbogenerators. There is no limit to the number of power changes in the core below 5$\%$ of rated power (RP). Within the 5$\%$ and 10$\%$ RP there are no limits for changes slower than 3$\%$ RP per minute, but limitations of approx. 2500 cycles are given for the faster changes [38]. For bigger RP changes, the allowed numbers are decreasing dramatically. In modernized designs of VVER 440, there are 2 turbines per reactor with approx. 250 MWe with an allowed change of 3$\%$ of rated power per minute. The current version of European Utilities Requirements expects that an NPP must at least be capable of daily load cycling operation between 50$\%$ and 100$\%$ of its rated power, with a rate of change of electric output from 3–5$\%$ of rated power per minute [39]. The request for load-following operation of NPPs naturally opens questions about the economics, safety (limited by the fuel performance), and impact on the aging of equipment due to load following. The fuel performance needs to be studied and the new generation of fuel needs to be developed with the support of new simulation tools and experimental data [40]. According to the literature [41], no significant impact is estimated with the aging of equipment components. It is understandable that load-following decreases the utilization factor and thus negatively impacts the overall economy.

As can be seen, the load-following operation of NPPs is economically and technically difficult, and more viable is to store the excess or off-peak electricity using energy storage technologies. The significant use of these technologies has the potential to improve the economics of NPPs and might provide cost-effective grid services such as backup power, frequency regulation, and fast response reserves. As shown in previous paragraphs, an increase in the share of nuclear energy and renewables in Slovakia in the future will set workable conditions for incorporating energy storage options into the grid. However, the coupling of a large energy storage system to a nuclear reactor brings several challenges to guaranteeing the safety of the combined system. It can be assumed that thermal large energy storage will improve safety due to the additional thermal inertia coupled to the reactor, no temperature transient on the side of the core, and the capability to absorb decay heat if needed. Some of the energy storage systems may provide emergency backup power useful for cooling, starting after the grid black-out or other purposes. One can imagine concerns about the reliability and integrity of such systems, fires in the case of battery energy storage systems, chemical interaction of sodium in sodium-sulfur batteries, floodings caused by failures of hot and cold-water storage systems, molten salts frozen and blocking heat exchange from the reactor, hydrogen explosions and other. Finally, the regulatory challenges posed by the coupling of a large energy storage system to a nuclear reactor are significant, where the whole methodology of safety assessment including new simulation codes supported by experimental work needs to be developed. Based on these findings a proper internationally accepted licensing framework needs to be established and adopted by the national regulators.

5 Conclusion

Electricity is a necessity that people cannot live without in the modern day. For Slovakia, access to electricity brought about a sea change to the quality of life and development of the industry. The successful story of Slovakia stands on the shoulders of the Czechoslovak nuclear power program started by A1 NPP and followed by continuous builds of VVER light-water reactors. The valuable experience in operation, construction, and decommissioning was accumulated in the country over the years. The wise strategic decisions and continuous public support for the nuclear industry yielded a low-carbon mix of electricity sources in Slovakia. It should be admitted, that despite the nuclear power is the strategic electric source for Slovakia, there exists continuous political discussion about the future and the tax conditions of the nuclear industry which brings investor distrust and effectively prevents the capital-intensive build of new possible sources. Public opinion is mainly driven by emotions, thus great efforts need to be invested by the regulator, international community, and scientists to carefully educate and inform decision-makers about the advantages and disadvantages of nuclear power. It was already proven, that communication errors not considering the inaccurate perception of risk related to nuclear and safety-related incidents lead to a gradual phasing out of nuclear energy in several EU Member States.

Younger generations’ interest in nuclear studies is gradually decreasing in Slovakia. In the meantime, the first generation of senior nuclear experts started to retire, with a resulting gap between incoming and outgoing flows of experts. This may pose a risk of a shortage of qualified professionals and an increased risk of loss of valuable knowledge for the nuclear community. As a response to the situation, the European Nuclear Experimental Educational Platform is being established as an open civil association. The platform aims to simplify access to research reactors and specialized laboratories for students and researchers and thus significantly improve the quality and attractiveness of delivered hands-on education in nuclear engineering.

The strong movement toward renewable energy and the construction of new NPPs in Slovakia brings challenges to the effective and economical operation of baseload power sources. On the other hand, these challenges may be judged as possibilities for new technologies. Undoubtedly energy storage systems are of great interest to the scientific and industrial community and their possible interaction with nuclear reactors seems to be mutually beneficial. This viable cooperation may even help to decarbonize the electric sector and thus achieve the set climate goals. There is a variety of potential large energy storage systems with different levels of maturity that could be considered for the application. A big advantage for the future is that in terms of power level, the nuclear units located in Slovakia can be logically replaced by the new generation of small modular reactors without compromising the already deployed standalone energy storage systems.

The conflict in Ukraine motivated Slovakia to actively investigate the possibilities of the diversification of nuclear fuel supplies. However, the qualification of the fuel from a new vendor is a quite complicated task both from the technical and legislative aspects. To achieve the high standards of quality and safety associated with the fulfillment of this task, international cooperation and much higher national expenditures on research and development of nuclear engineering are necessary.

Finally, from many aspects, nuclear energy seems to be a relevant and sustainable option for Slovakia. In addition to contributing to the reduction of greenhouse gas emissions, nuclear energy can stimulate and support further economic development after the successful diversification of nuclear fuel suppliers. However, decision-makers should understand, that the nuclear option is not a short-term commitment, it is a strategic decision, thus more systematic support should be given to R &D projects and education in nuclear-related sciences.