2.1. Coal-to-Nuclear Path
The implementation of the Coal-to-Nuclear pathway can be a source of savings in terms of the financial outlay for the construction of a nuclear power plant. The level of savings strongly depends on the degree of reuse of the existing coal plant infrastructure. In the case of third generation of reactors, it is not possible to reuse the turbine island due to significant differences in steam parameters. Therefore, savings can be made in terms of reuse of the infrastructure for power output to the transmission grid, car parks, heat extraction facilities, and auxiliary buildings, as well as land and water rights. The potential savings were estimated to be between 11% and 22% on the assumption of a conservative economic analysis. In addition, the decommissioning and demolition (D&D) costs for existing facilities were projected to be between 2% and 4% of the total financial outlay. However, it should be kept in mind that, from the perspective of a potential developer, it may be risky to use operational infrastructure. Nevertheless, any ancillary infrastructure and power derivation should not deviate in their standards from the newly built infrastructure. In [
21], the authors first undertook analyses of the Coal-to-Nuclear pathway later classified in [
18] as the direct pathway. This pathway assumes deep use for nuclear investment of infrastracture of the decommissioning coal-fired power unit, including the turbine island. Due to the requirements of steam turbines operating in coal-fired power plants, only fourth generation of reactors can be used here. Generation IV reactors constitute a large group of designs currently at various stages of development [
22]. Among the IV generation reactors under development, SMR designs—small modular reactors—dominate, which, due to their smaller capacities and modular design, can be produced faster and may have wider applications, such as in district heating and industrial plants. Currently, two HTGR high-temperature reactors in China (HTR-PM) are in commercial operation, with a combined capacity of 500 MWth, driving a 210 MWe turbine [
23]. In view of the maturity of the technology of these reactors and the direction of the transformation of the European market, which assumes a reduction in the number of investments in the coal power segment, the direct pathway should be classified as hypothetical.
The DOE report examined the locations of 157 decommissioned and 237 active coal units for their potential reuse in the construction of a nuclear power plant [
18]. It demonstrated that 40% of the locations of active and 22% of the locations of decommissioned coal-fired power plants are conducive to the construction of high-capacity nuclear reactors. Abdussami et al. [
24] also analysed the potential for C2N in the United States. The coal units were evaluated according to three main groups: (1) socio-economic target; (2) safety target; and (3) proximity target. A key outcome of their work was the identification of several locations conducive to pursuing a C2N pathway and the finding that there is no one-size-fits-all factor that determines the quality of a particular location. Consequently, future evaluations should be based on a multi-faceted assessment. In Poland, the DEsire project [
25] is working on assessing the potential of the Coal-to-Nuclear pathway and developing a roadmap for future investment. Research in the first phase of the project focused on technical and safety assessments [
26] of existing coal-fired power plants and their location. The current focus of work is on the implementation of third generation of reactors, which is motivated by the imminent decommissioning of numerous coal-fired power plants in Poland.
In their article, Chmielewska–Śmietanko et al. [
26] discuss in detail the legal and safety issues of siting an inland nuclear power plant following the Coal-to-Nuclear pathway as part of the DEsire project. The authors highlight that a key aspect of the implementation of a nuclear source investment is the assessment of the potential location of the future power plant. This assessment should be conducted according to three main criteria: (a) the characteristics of the location and surroundings in terms of their impact on the nuclear power plant and potential contribution to the proliferation of radioactive materials; (b) the effects of external hazards of natural and man-made origin; and (c) the population in the vicinity of the location and the identification of factors affecting the implementation of emergency management plans. The authors conducted a comprehensive analysis of 24 locations of existing coal-fired power plants for the construction of third- and fourth-generation reactors, according to their defined criteria. They also defined criteria that excluded a location, such as the risk of flooding, the presence of an airport within a 10 km radius, or mineral extraction within a 30 km radius of an existing coal site. The authors selected four locations for coal-fired power plants in Poland that met the safety criteria for the construction of a nuclear power plant equipped with a Generation III reactor. These locations were: (1) “Dolna Odra” Power Plant; (2) “Połaniec” Power Plant; (3) “Ostrołęka B” Power Plant; (4) “Kozienice” Power Plant. Furthermore, fourth-generation reactors have been proposed for locations where the available cooling water may be insufficient to cool high-capacity units. An important aspect of the DEsire project is the availability of cooling water at the sites of existing coal-fired power plants. The law in Poland also defines the cost of water intake according to the temperature of the discharged water. For temperatures between 26 and 32 °C, the charge is USD 0.17 per 1000 m
3 of water. Above 35 °C, the fee rises to USD 1.08, which has a significant impact on the operating costs of power plants. Qvist et al. [
21] analysed the potential of the C2N concept in Poland. The authors identified 38 coal-fired units with a total electrical capacity of about 10 GWe (units of 200 MW and 360 MW) that are suitable for modernisation using SMR. The authors did not identify the specific SMR technology for which the analyses were conducted. Their conclusion was based on the size of the Polish electricity system, which is dominated by 200 MW coal-fired units. It has been shown that the investment cost can be reduced by up to 35% due to the potential use of the existing turbine section [
27]. This level of cost savings identified by the authors was confirmed in the DOE’s 2022 report [
17]. Haneklaus et al. [
28] also indicated a high potential for C2N in Poland for both high-, small-, and medium-power reactor implementation.
In 2023, Poland had 18.7 GWe of installed capacity from stable coal-based sources, 7.6 GW from lignite-based sources, and 5.14 GWe from gas-based sources. Concurrently, 14.28 GW of capacity was installed in photovoltaic sources and 9.6 GWe in onshore wind. The data indicate that renewable energy sources accounted for 26% of total electricity generation in Poland in 2023 [
1]. This figure is lower than the EU average of 43.6% but higher than that of countries with a similar energy sector. For example, the Czech Republic had a value of 14.9%, while Slovakia had 26.5%. As recently as 2017, the Polish electricity system was still largely based on coal, with 20.1 GWe installed in hard coal and 8.56 GWe in lignite sources. Photovoltaic panels accounted for only 0.23 GWe, while wind power accounted for 5.79 GWe. Renewable energy sources accounted for 11.7% of Poland’s electricity production in 2017. Poland is implementing an energy policy defined until 2040, which is divided into eight main directions [
4]. These include the implementation of nuclear energy, the further development of renewable energy sources, and the optimal use of its own energy resources. According to the plans, the share of coal in electricity generation is to be reduced to below 56% by 2030. It is noteworthy that the document produced in 2021 assumed the development of photovoltaics to a level of 10–16 GWe by 2040, which was already achieved in 2023. This intensive penetration of renewables into the electricity system coincides with the near end of the life of existing coal-fired power plants. The adopted strategy entails the permanent decommissioning of approximately 26.5 GWe of stable coal-fired capacity between 2016 and 2040. Consequently, it is evident that substantial investment in proven and stable sources of electricity is imperative, as evidenced by the outcomes of studies and the electricity system in Poland. Furthermore, Cho et al. [
29] have demonstrated that over-generation of electricity by RES can result in increased costs and reduced environmental benefits. The planned shutdowns of key power plants in Poland, including “Kozienice” Power Plant, “Połaniec” Power Plant, and “Jaworzno” Power Plant, are scheduled to commence in 2030. Consequently, it is evident that there is a pressing need for a significant investment in proven and stable sources of electricity, as evidenced by the findings of various studies and the electricity system in Poland.
In China, coal is the primary energy source [
30], resulting in increased greenhouse gas and particulate emissions and, consequently, a decrease in air quality [
31]. China has committed to achieving total carbon neutrality by 2060 while being the largest emitter of carbon dioxide at 9899.33 Mt in 2020 [
32]. This objective is to be achieved by redefining the structure of the country’s electricity system, in which renewable energy sources, supported by nuclear and biomass power, are to play a dominant role [
33]. Xu et al. [
34] considered the implementation of a Coal-to-Nuclear pathway in China. The authors planned the decarbonisation of China’s power industry using nuclear reactors in three stages: (1) the conversion of coastal power plants with an installed capacity of about 80 GWe, (2) the conversion of inland power plants in the coastal zone with an installed capacity of about 180 GWe, and (3) the conversion of power plants near inland cities with an installed capacity of about 640 GWe. This division is due to the limited experience of Chinese designers with closed-loop nuclear power plant-cooling circuits. It has been estimated that the total potential for implementing the C2N pathway in China is about USD 1200 billion, although the conversion of all existing coal-fired power plants may not be possible due to environmental conditions or local social acceptance. Luo et al. [
35] also discussed the potential of the Coal-to-Nuclear pathway in China. The authors investigated the feasibility of converting a coal-fired power plant to a high-temperature gas-cooled reactor (HTGR). They demonstrated that this type of reactor is more compatible with Chinese coal-fired power plants compared to a PWR. The result of their work is a strategy for applying a steam turbine, steam heaters, and cooling water pumps.
In terms of socio-economic considerations, the C2N concept involves the absorption of existing coal unit personnel, which can form the basis of future employment in a nuclear power plant. A report by the United States Department of Energy [
36], which discusses in detail the extent of similarities between coal and nuclear power plant positions, identifies the occupations of electrical and electronic mechanics or industrial machinery mechanics as being identical between the two units in terms of requirements, using the Standard Occupational Classification System (SOC). Nevertheless, the coincidence of the occupational identification does not imply that workers would be directly redirected to work in the nuclear power plant without prior training and extension of their certificates. At the same time, it was stated that some of the posts in the new unit could not be covered by existing staff, implying the need for external recruitment. These posts included primarily nuclear engineers. The prospect of a Coal-to-Nuclear pathway could lead to increased employment in the local economy. Furthermore, it could provide a favourable alternative to the closure of a coal-fired power plant with no further use of the remaining land. The 2024 E4 Carolinas report identified the economic impact of the nuclear power sector on the southeastern US states [
37]. The region is home to 25 of the 93 operating reactors and 13 of the 55 active nuclear power plants in the United States. Nuclear power provides more than 150,000 jobs and more than USD 13.7 billion in revenue. In 2021, a survey of Polish respondents indicated that 44% believed that the development of nuclear power in Poland was necessary in the event of a shift away from coal power [
38]. Concurrently, only 24% of respondents expressed support for the construction of a nuclear power plant in their vicinity. In 2022, 75% of respondents surveyed indicated their backing for the development of a nuclear power plant in Poland [
39]. The notable increase in support for nuclear energy is largely attributable to the unstable geopolitical situation in the region, which has led to a significant rise in energy prices in Poland due to the disruption of the energy fuel supply chain to EU countries from Russia [
40]. Additionally, there has been a notable increase in public awareness of the country’s energy independence. It can, therefore, be concluded that Poland has the highest public support for nuclear energy among the countries surveyed. In comparison, support in the United Arab Emirates is 63%, 61% in India, 54.3% in Bulgaria, and 53.75% in Belgium [
41].
2.2. Nuclear Power Reactors
The study considered three commercially operating Generation III high-power nuclear reactor technologies: AP1000, APR1400, and EPR1600. These technologies belong to the group of light water-pressurised reactors (PWRs). This is the most popular technology in the world with 307 reactors of this type currently in operation with a total installed capacity of 294.08 GWe [
13]. The second technology, with 47 units and a total capacity of 24.76 GWe, is the Pressurised Heavy Water Reactor (PHWR). The selected reactor technologies are described below.
Advanced Passive PWR–AP1000 [
42]
The AP1000 reactor (Westinghouse Electric Company LLC, Cranberry Township, PA, USA), is a pressurised light water reactor with a rated electrical output of 1200 MWe (gross), developed by the US company Westinghouse based on the earlier AP600 reactor technology. The reactor design ensures the use of a number of passive safety systems to minimise the risk of power loss or human error [
43]. These systems include a Passive Core Cooling System (PXS) to remove residual heat or a Passive Containment Cooling System (PCS) based on natural air circulation and gravity cooling with water from the upper emergency vessels. Yu et al. [
44] analysed the effectiveness of the PCS with respect to the potential location of the AP1000 reactor and, consequently, the different atmospheric conditions under which the safety system operates. The authors showed that the climatic conditions in a region with four distinct seasons significantly reduce the likelihood of a major accident compared to a subtropical region due to lower ambient temperatures and, consequently, better air circulation. Studies have also investigated the robustness of the reactor building to external actions or incidents. Wang et al. [
45] investigated the durability of a reinforced concrete reactor building structure in the event of a direct impact by a civil aircraft. The study was characterised by parallel damage modelling in the concrete and reinforcement areas, as well as extensive sensitivity analysis including both aircraft speed and impact location. Xu et al. [
46] analysed the effect of the water level in the PCS emergency tank on the behaviour of the reactor building structure during an earthquake. It was shown that a decreasing water level in the reservoir reduces the vibration damping of the building structure, which can lead to increased damage in the case of simultaneous PCS and aftershocks.
To date, the AP1000 reactor at the Vogtle nuclear power plant (Unit 3) in the United States has started commercial operation in 2023, with construction of this unit starting in March 2013 [
13]. The Vogtle-4 unit was placed in service on 6 March 2024, with construction beginning in November 2013. There are four AP1000 reactors in operation in China, as Units 1 and 2 of the Sanmen power plant have been in commercial operation since September and November 2018, respectively, and Units 1 and 2 of the Haiyang power plant have been in operation since October 2018 and January 2019, respectively. Based on this experience, the Chinese version of the reactor, CAP1000, has been developed and is currently under construction at Lianjiang and Haiyang power plants. The construction of Units 3 and 4 of the Sanmen power plant, which will be equipped with reactors of this type, is also underway.
Advanced Power Reactor–APR1400 [
47]
The APR1400 reactor (KEPCO/KHNP, Naju, Republic of Korea) is a pressurised light water reactor with a nominal electrical output of 1455 MWe (gross) and a reactor thermal output of 3983 MWt. The reactor was developed in South Korea in 2002 by Korea Electric Power Corporation (KEPCO) and Korea Hydro & Nuclear Power (KHNP). The reactor design is based on the experience gained from the construction and operation of Korea’s first light water-pressurised reactor design, the OPR1000. These reactors have been successfully operated at the Hanbit, Hanul, Shin–Kori, and Shin–Wolsong power plants. The aim of the design work was to develop a reactor with improved safety (achieved through the implementation of passive safety systems) and the ability to compete with other energy sources in terms of construction time and investment costs.
Amuda and Field [
48] presented the concept of a Nuclear Heat Storage and Recovery (NHS&R) system for the APR1400 reactor. The aim of the study was to develop a system that would allow the reactor to operate at a constant thermal output while adapting the steam turbine operation to customer demand [
49]. According to the concept, the heat exchange medium is thermal oil and the actual heat storage is a rock bed characterised by its resistance to high temperatures [
50]. A major advantage of this solution is the easy scalability of the heat storage and the relatively low financial outlay.
APR1400 reactors are successfully operating at the Saeul nuclear power plant in South Korea, with two units having been commercially commissioned to date, in 2016 and 2019, and two more under construction [
13]. One unit of this type has been in operation since 2022 at the Shin–Hanul plant, and the other has been under construction since 2013, with its first synchronisation with the electric grid in December 2023. In the United Arab Emirates, three APR1400 reactors have been commissioned for commercial operation at the Barakah nuclear power plant, with the fourth unit synchronised with the grid in March 2024.
The Evolutionary Power Reactor–EPR1600 [
51]
The EPR1600 (Orano, Paris, France) is a pressurised light water reactor with a nominal electrical power of 1770 MWe (gross). It is the result of a joint design effort between Framatome (Paris, France) and Siemens (Berlin, Germany) based on the experience gained from the construction of about 100 PWR units worldwide. The focus was on the development of multi-level systems to drastically reduce both the probability of a severe accident and its potential impact on the population and the environment. Four-tier redundancy has been applied to key safety systems, including the core cooling system. In the event of a severe accident with core meltdown and reactor vessel rupture, the use of a special safety chamber equipped with protective layers and cooling facilities into which the molten core components would enter was envisaged, as described in detail by Fischer [
52]. Baumann and Terry [
53] describe the design assumptions for the reactor construction and the objectives set, among which the issues of improving the safety of the system and of the personnel operating the nuclear power plant with the EPR1600 reactor were predominant. Among other things, measures were taken to reduce the formation of deposits in the piping due to dead zones, gaps, and bends. These deposits could have been a source of increased radiation.
The first reactor of this type was commissioned for commercial operation at the Taishan power plant in China in 2018, with a construction period of 108 months [
13]. In Europe, construction of the first EPR1600 unit began in 2005 at the Olkiluoto nuclear power plant in Finland, and the unit will be commissioned in 2023. The design life of the EPR-1600 nuclear unit is 60 years with a fuel cycle of 24 months and a unit availability of 92%. The basic parameters of 3rd generation of nuclear reactors are presented in
Table 1.
2.3. Coal-Fired Power Plants
Based on the results of basic evaluation process of all Polish coal-fired power plants [
21], which has been conducted within DEsire project, for an analysis of investments from the specific cooling water condition point of view four Polish coal-fired power plants were chosen:
“Dolna Odra” Power Plant,
“Kozienice” Power Plant,
“Ostrołęka B” Power Plant,
“Połaniec” Power Plant.
“Dolna Odra” Power Plant is a division of PGE Górnictwo i Energetyka Konwencjonalna S.A. and is located in the northwestern part of Poland in the Gryfino, about 25 km from Szczecin. Additionally, the plant is situated approximately 5 km from Poland’s border with Germany, which may potentially pose challenges in the implementation of nuclear power at the site. Power plant consists of four power units (Units 5, 6, 7, and 8) with a total gross capacity of 900 MWe fired by hard coal and biomass. On 31 December, 2020, Units 1 and 2 with a total capacity of 454 MWe will be decommissioned, the former being an emergency source of heat and process steam. In 2022, 1,252,348 tonnes of hard coal and 1517 tonnes of biomass were used at Dolna Odra Power Plant, resulting in total gross electricity generation of 2,732,055 MWh with CO
2 emissions of 922.0 kg/MWh, with total emissions including greenhouse gas emissions (SO
2, NO
x, CO
2, dust) and their equivalent emissions expressed in kg CO
2 amounting to 923.09 kg/MWh [
55]. The Dolna Odra plant has an open cooling system using water from a canal (the so-called Cold Canal) connecting the plant site to the Odra River. According to the data provided by PGE GiEK S.A. (Bełchatów, Poland) in the Environmental Statement, in 2022, the Dolna Odra Power Plant will use 562,389,000 m
3 of water for cooling purposes.
The “Kozienice” Power Plant, operated by ENEA Wytwarzanie, is located in Świerże Górne in Mazovia Province, about 5 km from the town of Kozienice and about 35 km from Radom. It consists of 11 hard coal-fired units with a total installed capacity of 4071 MWe. Units B1-B8 with a capacity of 230 MWe and a total capacity of 1800 MWe are scheduled for decommissioning between 2030 and 2033 [
56]. Units B9 and B10 of the 560 MWe class are scheduled for decommissioning in 2041 and 2042, respectively. The 1112 MWe unit B11 is scheduled for decommissioning in 2048. A preliminary multicriteria analysis recommended only 200 MWe class units with a total capacity of 1800 MWe for repowering using nuclear reactors. The “Kozienice” power plant’s coal requirements are met to 70% by Lubelski Węgiel “Bogdanka”. S.A. (Puchaczów, Poland) deliveries by rail-PKP Cargo is responsible for about 55% of fuel deliveries [
56]. In 2023, “Kozienice” emitted 12,796,315 tonnes of CO
2, a decrease of almost 18% compared to 2022, when 13,945 GWh and 17,118 GWh of electricity were produced. Units B1-B10 emitted 4801.2 tonnes of SO
2, 5325.6 tonnes of NO
x, and 345 tonnes of dust in 2023. As of 2019, ENEA is implementing a planning project to build gas-steam units using the existing infrastructure of the 200 MWe class units. Units B1-B10 have an open cooling system using water from the Vistula River. In addition, the system uses spray cooling towers to ensure that the environmental requirements regarding the temperature of the discharge water are met. Unit B11 has a closed cooling system with a cooling tower. From 2019, ENEA S.A. (Poznan, Poland) will report cooling water intake values for “Kozienice” and “Połaniec” Power Plants jointly. In 2023, 2,490,594,000 m
3 of water from the Vistula River. In 2018, Kozienice Power Plant used 1,486,197,962 m
3 of water [
56].
“Ostrołęka B” Power Plant, owned by Energa Wytwarzanie SA, is located in Ostrołęka, Mazowieckie Province. It consists of three coal- and biomass-fired units with a capacity of 230 MWe. In 2023, “Ostrołęka B” was responsible for supplying 1575 GWh of electricity to the National Electricity System, with a total capacity of 633 MWe from coal-fired sources and 57 MWe from biomass sources [
57]. The equivalent carbon dioxide emissions of Energa Elektrownie Ostrołęka SA (Ostrołęka, Poland) associated with electricity generation in 2023 amount to 1,497,873 tonnes. Units 1–3 use an open cooling system fed by water from the Narew River. In 2023, power plant withdrew 326,758,899 m
3 of water from the Narew River for cooling purposes and 4,345,984 m
3 of water for non-cooling purposes.
The “Połaniec” power station, managed by ENEA Wytwarzanie, is located in the village of Zawada, which lies approximately 3.5 km from Połaniec (Świętokrzyskie Province) and 10 km from Mielec (Podkarpackie Province). The total installed capacity of the power station is 1899 MWe [
56]. The “Połaniec” power station consists of eight energy units-unit B1 with an installed capacity of 200 MWe, which was taken out of ex-operation on 1 January, 2024, Units B2–B6, with a capacity of 242 MWe, Unit B7 with a capacity of 239 Mwe, and Unit B9 with a capacity of 230 MWe, which is fully biomass-fired [
56]. Units B2–B7 are scheduled for decommissioning in 2034 and the last unit, B9, in 2042. In 2023, “Połaniec” Power Plant was responsible for supplying 6628 GWh of electricity to the national power system, a decrease in production of 20.9% compared to 2022. Power plant uses an open cooling system, for which it draws water from the Vistula River. In 2018, ENEA last reported separate cooling water-intake data for “Kozienice” and “Połaniec” power plants, according to which “Połaniec” drew 1,410,373,066 m
3 of water from the river [
56].
2.4. Thermodynamic Model
The thermodynamic model used for the nuclear reactor and steam cycle system is described in detail in [
19]. The model was extended to include the control of the cooling system of the low-pressure condenser parts of the steam turbine. The calculations considered the variable performance of the cooling water pump as a function of the water inlet flow for cooling purposes. The nominal parameters of the nuclear unit were determined using the producer data provided in
Table 1. It was also assumed that the water temperature rise per condenser was 4.65 °C. Operational calculations were conducted with different water temperature increases in order to comply with the legal limits. In addition, the minimum temperature of the condenser cooling water was assumed to be 9.5 °C, since further reduction of the cooling temperature increases the losses in the low-pressure part of the turbine.
Based on Equations (1)–(3), the characteristic condenser parameters were determined:
where
and
are the inlet temperature and steam flow to the condenser, respectively,
is the temperature of the cooling water feeding the condenser,
is the nominal difference between the nominal inlet steam temperature
and
,
is the nominal steam flow, and
is the condensation pressure of the steam equal to the saturation pressure
for temperature
. The heat removed from the condenser
is calculated from the formula:
where
is the flux of the condenser cooling water,
is its temperature rise, and
is its average heat capacity at constant pressure.
The valves on the pipelines were treated as isentalpic throttling elements with the pressure drop factor
, as shown in Equations (5)–(7):
where
and
are the pressure of the medium before and after the throttling valve, respectively,
and
are the enthalpy of the steam before and after the throttling valve, respectively, and
is the temperature of the steam after the throttling valve.
The steam flow in the turbine is determined by the fluxes required to feed the regenerative heat exchangers. For each group of turbine stages, the expansion process from the first group to the last is determined, according to Equations (8)–(12):
where
is the theoretical entropy of the steam after expansion, assuming an isentropic expansion process,
and
are the enthalpy and enthalpy of the steam before expansion,
and
are the theoretical steam temperature and theoretical enthalpy of the steam for pressure
and entropy
, and
and
are the enthalpy and temperature of the steam after expansion, respectively.
The numerical model uses a real gas model, and the functions used to calculate the thermodynamic quantities of the circulating medium comply with the International Association for the Properties of Water and Steam (IAPWS) standard. The model also includes variable steam turbine efficiency values that depend on steam parameters.
Basic indicators for assessing the performance of the nuclear unit were also defined. The gross electrical efficiency
is described using Equation (13):
where
is the gross electrical power of the nuclear unit and
is the thermal power of the nuclear reactor. The net electrical efficiency
is defined as:
where
is the net electrical power of the nuclear unit after considering the coverage of the nuclear power plant’s own needs. The calculation considers the variable power of the cooling water pump, which depends on the water flow directed to the condenser.
The rate of use of available river water for cooling purposes
was determined using the formula:
where
is the flow of water in river.
The hydrological conditions at the indicated power plant sites in Poland were analysed on the basis of measured data from the Institute of Meteorology and Water Management (IMGW) [
58]. The analysis period covered the years 2010 to 2023, with data from different monitoring stations—the temperature values were taken from the station located above the water intake for cooling purposes to avoid the influence of the discharge water on the temperature of the natural water in the river. For each month, the average value for the period under study was determined, along with the maximum and minimum limit values for that period. This allowed for the identification of the most unfavorable hydrological conditions from the perspective of power plants with an open cooling system, defined as instances where the flow of flowing water was lowest or the water temperature was highest during the period under study.
The data on the electricity production of the power plants selected for repowering were obtained from the ENTSO-E Transparency Platform [
1]. These data were obtained for the full year 2023 on a unit-by-unit basis. For each coal-fired power plant, power generation data were presented on a daily and cumulative basis to show the impact of the power plant on the Polish electricity system. The data on the emissivity of individual power plants, cooling water use, and other information on plant operations were obtained from the annual reports of the power plant operators.