An Overview of Small Nuclear Power Plants for Clean Energy Production: Comparative Analysis of Distributed Generation Technologies and Future Perspectives

Abstract

There is a steady trend in the world to increase the share of distributed generation. The volume of self-generated energy commissioning is constantly growing, with projected increases in growth rates in the future. At the same time, demands for efficiency and environmental safety in new power plants are constantly increasing. In this regard, one of the promising areas for the development of distributed energy is the transition to small nuclear power plants (SNPPs). As in the case of wind and solar power plants, SNPP operations are not accompanied by emissions of toxic substances or greenhouse gases into the atmosphere. In addition, SNPPs consume a much smaller volume and mass of fuel compared to conventional small-capacity fossil fuel power plants. This paper describes the characteristics of the main types of distributed generation. The key technical and economic characteristics of existing and prospective small-capacity nuclear fuel facilities are systematized. The results of a comparative analysis of the cost of electricity produced by SNPPs and competing power plants are also presented. In addition, a number of promising regions of the Russian Federation for the introduction of SNPPS have been identified, and a review of the methods of energy storage for SNPPS, which are necessary when working in an isolated power system, has been carried out.

1. Introduction

1.1. Relevance of Distributed Energy

The world’s energy consumption has been rising over the past 50 years due to population growth and the increasing industrialization of countries in the third tier. The emerging trend has predetermined a number of serious environmental consequences, among them global warming. With a high probability, a rising concentration of CO₂ in the atmosphere is the main reason for the observed process [1].

One of the important ways to reduce carbon dioxide emissions is through the decarbonization of the energy industry, including small energy sources used as distributed energy facilities [2,3]. In Russia, the active development of the Arctic and the Northern Sea Route predetermines the importance of power supply to remote regions. At the same time, small and medium-capacity power sources with minimal emissions of harmful substances should become a key component of future isolated power systems [4].

Distributed energy facilities are characterized by their location close to consumers of energy products. These power plants are not connected to the grid but supply power directly to consumers. They are widely used for the power supply of isolated or remote facilities, for which connection to the unified power system is not justified from an economic point of view. Consumers can be both residential buildings and commercial/industrial enterprises.

The main advantage of distributed generation compared to centralized production of energy products is the absence of the need to build and maintain long-distance transmission lines. Additionally, there is less dependence on the power grid and centralized sources of power supply and more flexibility for decarbonization.

The disadvantages of distributed power generation are due to the need to maintain the mode of operation of distributed generation in accordance with the requirements of one consumer, which requires the use of energy storage systems and reserve capacity. In addition, a change in the nature of consumer load leads to the need to change the methods of load forecasting and pricing in integrated power systems since new distributed generation capacities are not visible and are not monitored by operators. Therefore, there is a growing risk of power system unbalance and an increase in load curve irregularity if incentives to increase the maneuverability of distributed generation facilities are not properly calculated.

1.2. State of the Art of Distributed Energy

Power plants related to distributed generation can be classified according to the type of primary energy: fossil fuel, nuclear or renewable energy, or waste heat. Combustion-based plants, depending on the type of fossil fuel, can be divided into those using natural gas, coal, peat, wood, oil, diesel, gasoline, etc. The most common fuels for 1–100 MW plants are natural gas, diesel and coal, as they have a significant heat value, are low-cost and are available in large quantities. In the case of natural gas or diesel, electricity can be generated using open cycles such as the Brayton, Otto and Diesel cycles. They can be implemented in gas turbine plants (GTPs), gas piston plants (GPPs) and diesel generator power (DGP) complexes. When using any organic fuel, a closed energy cycle implemented in steam turbine power plants (STPs) can be used. Closed power cycles on water or organic coolants can also be used to generate electricity from industrial waste heat [5].

When using renewable energy sources, the type of power plant chosen depends on the specific type of primary energy. It is possible to use photovoltaic cells for the direct conversion of photon energy into electrical energy or use solar radiation to heat the coolant. In the second case, the heated coolant can be directly used to generate electricity in a closed or open cycle or transfer heat to another cycle. In the case of using wind energy, it is possible to use vertical or horizontal wind generators that use the mechanical energy of the wind to rotate the generator rotor and produce electricity. In the megawatt class, horizontal-axis wind turbines are the most common. To reduce the cost of electricity, it is possible to increase the unit output of the windmill, which is achieved by increasing the disc area by increasing the span of the blades. It is also possible to use the faster wind, which is observed at high altitudes, in the coastal zone and over water. Large offshore wind turbines achieve the greatest power where the wind speed is highest. In addition, it is possible to use the energy of rivers, geothermal waters, tides and sea currents; however, the availability of these types of primary energy significantly depends on the location of the generation facility, which makes them non-versatile and unsuitable for distributed energy [6].

Separately, fuel cells (FCs) are specified, which can directly produce electrical energy and heat as a by-product. The most common are low-temperature fuel cells (alkaline and with proton membranes) that use hydrogen or methanol as fuel. They have high efficiency (efficiency at the level of 50–70%). At the same time, their cost is high. In addition, most fuel cells are characterized by low power, and the fuel for their operation is expensive. Due to the listed shortcomings, fuel cells are not widely used for distributed generation.

An alternative way to produce electricity is through small-capacity nuclear power plants (SNPPs). The use of SNPPs makes it possible to have an energy source that is almost independent of external conditions. At the same time, during their operation, harmful combustion products are not released into the atmosphere.

In addition to electricity generation, distributed generation facilities can be used to produce heat, hydrogen, and other useful products. The greatest economic effect is usually achieved with cogeneration (co-production of heat and electricity) or trigeneration (co-production of heat, electricity and hydrogen) in steam turbine plants burning fossil fuels or using nuclear, geothermal, or solar energy. A rational solution is the useful utilization of heat from flue gases in fossil fuel open-cycle power plants for the combined generation of electricity and heat. Moreover, solutions based on the use of solar radiation or electric heaters (when using wind turbines or photovoltaic solar panels) to produce heat for subsequent supply to heating systems have found application [7].

The main consumers of distributed energy are large and medium-sized industrial enterprises that seek to reduce the price of consumed electricity (Figure 1). Furthermore, power and heat supplies to settlements are possible. At the same time, both thermal power plants using fossil fuels or biofuels and power plants using renewable energy sources can function as distributed energy facilities.

According to [8], the rate of introduction of new distributed generation capacities in the world will be higher than that of centralized power plants (Figure 2). First of all, this is due to an increase in the efficiency of small-capacity electricity generation technologies and a constant decrease in specific capital costs. This effect is especially noticeable for wind and solar power plants [9].

In Russia, small-capacity power plants are also being introduced for distributed generation (Figure 3) [10]. This is primarily due to high electricity tariffs for enterprises and the lower cost of own generation based on gas pistons, diesel generators and gas turbine plants.

At the moment, most of the installed capacity of distributed energy in Russia is represented by thermal power plants (Figure 4). Wind and solar power plants are mainly located in southwestern Russia, which is characterized by maximum insolation, wind speed, and population density. Small-capacity solar power plants are also available in the south of the Krasnoyarsk Territory, where the insolation is quite high. There is also a floating nuclear power plant (FNPP) at Akademik Lomonosov in Russia, in the city of Pevek, with two nuclear reactors (KLT-40S) and an installed capacity of 70 MW. In addition, three of the four EGP-6 power units of the Bilibino NPP with an installed capacity of 36 MW are still in operation. In other words, there are currently two SNPPs operating in Russia.

1.3. Prospects for the Development of Distributed Energy in Russia

In Russia, as well as throughout the world, the development of distributed energy can be ensured primarily through the growth of tariffs for centralized electricity and heat supply. At the same time, it should be noted that in the balance of the integrated power system of the Russian Federation, there are many generating facilities older than 35 years whose share of installed capacity exceeds 55% [11]. In addition, many existing CHPPs are redundant for local power systems, and the wear of centralized heating systems in the country is on average 50–60% [12]. Therefore, for a number of regions of Russia, the development of distributed energy is also relevant in order to replace existing exhausted boiler houses and large CHPPs with small cogeneration plants (Figure 5a). At the same time, power plants with a capacity of more than 100 MW can become widespread, since large industrial enterprises wishing to have their own power generation facilities are most interested in the introduction of distributed generation (Figure 5b).

One of the most promising areas is the development of distributed energy for power supply to remote areas where it is necessary to meet the energy needs of large enterprises or residential settlements. In this case, the power system under consideration is isolated or has little connection with the integrated power system of the country, which determines the importance of the ability to regulate the load and ensure the reliability of the power supply. Due to the remoteness of a number of regions, the price of fuel is significantly higher than in most power systems. In addition, its delivery may also be a problem, which requires the creation of reserves.

2. Distributed Energy Technologies

2.1. Small Thermal and Renewable Power Plants

At the moment, thermal power plants are the most common among distributed generation facilities. Small-capacity power plants (up to 50 MW) use piston internal combustion engines fueled by natural gas or liquid fuels. This is due to the unit output limitation of the most efficient four-stroke engines at 20 MW. At the same time, the efficiency of piston engines grows from 37.8 to 48% (Figure 6) [13,14,15], with diminishing returns as the unit output grows from 1 to 20 MW.

Micro-GTUs from Capstone, Bladon Jets, Kawasaki and Ansaldo have a similar capacity level. However, their efficiency and service life are lower than those of internal combustion engines, and the capital cost is higher, which is the reason for their little use.

For power plant capacities of more than 50 MW, it is possible to use gas turbine and combined-cycle plants, which are mainly manufactured by GE, Siemens and Mitsubishi. In addition, it is possible to use steam turbine power units burning coal, natural gas and other fuels.

Wind power plants (WPPs) have similar installed capacities and can scale up to hundreds of megawatts by increasing the number of installations. Currently, Vestas, Goldwind, and GE [12] account for about 40% of the total wind turbine market. The main way to reduce the cost of electricity from WPPs is to increase the unit output of the plant, which is achieved by increasing the sweep area and hence the length of the blade and the diameter of the rotor (Figure 7) [16,17,18,19,20]. The unit output of a wind turbine also differs significantly depending on the area of use (onshore and offshore). Onshore installations have a lower capacity, which averages 2.5–3 MW and can reach 7 MW, while coastal installations have an average capacity of 3.6 MW and can reach 18 MW [21]. Higher capacity with similar rotor diameter dimensions is primarily associated with higher wind speed over the sea surface and a corresponding increase in IEC Wind Class to I [22].

For solar power plants, the most important indicators are efficiency and unit cost. There are two main types of solar power plants: those based on a thermodynamic cycle, in which the radiation energy is concentrated on a thermal energy storage device to increase the temperature of the working fluid, and those based on direct conversion, in which photon energy is converted into electrical energy using semiconductor materials. At the moment, photovoltaic solar panels are the cheapest and most common [23]. There are solar cells based on silicon, perovskite, selenide, copper, indium, gallium, cadmium, telluride, their organic compounds and other materials. From a technology point of view, solar cells are single-crystal, in the form of a thin film, multi-crystal, multi-junction and others. In 2021, more than 95% of all new PV panels were silicon-based, of which 85% were made from single crystals [24]. The average efficiency of the most common single-crystal silicon panels is 20–22%. At the same time, the laboratory samples of cells can reach higher efficiency: silicon single-crystal without a concentrator—26.1%; multi-crystal without a concentrator—24.4%; in the form of a thin film—23.35%; using perovskite—32.5%. The most efficient are multi-junction PVs, which allow the use of solar radiation in a wider frequency range and achieve an efficiency above 40%; for example, four-junction cell 4-J,665x made by Fraunhofer Institute for Solar Energy Systems in Germany has reached 47.6% [25].

When conducting a comparative analysis of the technical and economic characteristics of the most common distributed energy facilities, it is advisable to choose the completed installations, the operation of which does not imply the provision of special conditions. Such installations include piston internal combustion engines, gas turbine plants, steam turbine plants, onshore wind power plants and solar power plants using single-crystal silicon cells.

2.2. Small Nuclear Power Plants

The use of SNPPs is especially important for the power supply in remote regions. The main advantages of SNPPs compared to fossil fuel plants are the absence of harmful emissions and the small volumes of fuel consumed, which must be delivered to the site and stored. Moreover, compared to renewable energy sources, SNPPs can have a constant and controlled source of electrical and thermal energy that is almost independent of external conditions, which is important when operating in an isolated power system with a small number of generating units.

Depending on the technology, small-capacity reactors are subdivided into water-cooled land-based and sea-based reactors, high-temperature gas-cooled reactors, and fast-neutron liquid-metal reactors using molten salts. At the moment, SNPP projects already exist and are being developed around the world. In China, the 210 MW HTR-PM reached its full capacity in 2022, and work began on the construction of the 125 MW ACP100 reactor. In Argentina, the 25 MW CAREM reactor is under construction. In the USA, NuScale is going to build six reactors with a capacity of 50 MW each, and the British company Rolls-Royce SMR plans to build plants for the production of equipment for SNPPs. Russia has already built a floating nuclear thermal power plant with a capacity of 70 MW with two KLT-40S reactors and nuclear icebreakers with 53 MW RITM-200 reactors. Moreover, it is planned to create ABV-6, Shelf-M and SVBR-100 reactors with capacities of 6–9, 10 and 100 MW. The distribution of existing and most developed SNPP reactor designs in comparison with alternative power generation technologies depending on power is given in

Table 1. Nuclear power plants and competing power plants.

	Electric/Thermal Power, MW
	up to 25/100 MW	25–50/100–200 MW	50–100/200–400 MW	100–200/400–800 MW	200–300/800–1200 MW
	Model of a nuclear power plant reactor
Thermal neutrons	HTTR, HTR-10, ABV-6, SHELF-M	KLTS-40S, CAREM, RITM-200	NuScale, RITM-200M, ACPR50S	HTR-PM, ACP100, SMR-160, SMART, DHR400, mPower	VBER-300, VK300, CAP200, Westinghouse SMR, BWRX-300
Fast neutrons	LFR-TL-X, 4S		KP-FHR	SVBR100, IMSR	LFTR, BREST-OD-300
	Competing power plants
	STP, GTP, DGP, GPP, SPP, WPP	STP, GTP, DGP, GPP, SPP, WPP	STP, GTP	STP, GTP	STP, GTP

[26]. Most of the installations are based on thermal neutron reactors, which use a water coolant and operate under pressure.

To develop the far north of Russia, independent small-capacity power supply sources with minimal emissions of harmful substances are needed [27], so SNPPs are one of the promising ways to develop the sea route and explore the Arctic [28].

Table 2. Main characteristics of Russian small-size nuclear reactors.

Reactor Model	Shelf-M	ABV-6	KLT-40S	RITM-200	SVBR-100
Power, MW	6.6	8	35	53	100
Efficiency, %	23.2	21.1	23.3	32.1	35.7
Cost, million USD	51.4	61.7	232.5	314.2	400.0
Service life, years	60	40	40	40	60
Mass of fuel composition, t	-	1.9	2.1	4.3	10.4
Uranium load, t	-	1.4	1.5	3.2	9.2
Average uranium enrichment with the 235U isotope, %	19.7	16.5	17.4	17.5	16.5
Time between core refueling, years	8	10–12	4	10–12	4
Burnup, %	-	61.9	55.3	56.6	22.0

shows the characteristics of Russia’s most developed projects or small-size nuclear reactors already in operation [26,29,30]. The presented models cover a wide range of electrical and thermal capacities. A distinctive feature of SNPPs is a higher degree of fuel enrichment compared to standard NPPs, which are limited to 20% due to IAEA requirements, and a lower burn-up fraction.

The results of a comparison of the main technical and economic characteristics of most of the known distributed power generation installations are presented in

Table 3. Parameters of different electricity generation technologies.

Technology	Products	Unit Capacity, MW	Efficiency, %	Construction Time, Months	Lifetime, Years	Capital Cost, USD/kWe	Minimal Power, %	Capacity Factor, %	CO2 Emissions, g/kWh
ICE gas	electricity, heat	0.005–20	38–48	2–5	20–30	450–1450	40–50	70–85	450–530
ICE diesel	electricity, heat	0.005–3	38–47						530–620
Gas turbine	electricity, heat	0.02–100	20–39	1–6	10–15	300–1000	30–40		510–1000
STU gas	electricity, heat	0.2–100	20–40	12–24	15–25	850–1450	40–50		500–1000
STU coal	electricity, heat		20–38				50–60		1200–2280
Wind	electricity	0.01–18	20–40	2–6	20–25	1000–1450	not regulated	15–25	-
Solar	electricity	250–400 W	15–22	4–6	25–35	550–1150		10–20	-
SMR	electricity, heat	6.6–100	20–35	36–60	30–80	2150–7850	85–90	85–95	-

[12,31,32]. For small-capacity plants, capacity strongly affects the unit cost of plants (this is characteristic primarily for plants where the number of equipment units is almost independent of the installed capacity of the power unit), which leads to a wide range of changes in capital costs. At low capacities, the cheapest are piston internal combustion engines. For higher installed capacities, gas turbine plants have the lowest capital cost, followed by internal combustion engines and solar power plants. This is followed by steam turbine plants and wind power plants. The cost of NPP installed capacity is the highest and several times higher than the cost of alternative technologies; however, NPP service life is also much longer, which reduces the share of capital costs in the cost of electricity. It is also worth noting that plants with the same installed capacity will produce different amounts of electricity per year due to the need for repairs, changes in external weather conditions and other factors, which are reflected in the capacity factor and will significantly affect the cost of electricity.

Internal combustion engines have the highest efficiency at low capacities, followed by gas turbine and steam turbine plants with similar efficiency. This is followed by wind, nuclear and solar power plants. Since renewable power plants do not consume fuel but use only available energy sources, the efficiency parameter is irrelevant to them. Therefore, in the case of RES, the efficiency and potential of renewable sources are reflected in the CF (capacity factor), and the cost of electricity produced is most affected by the unit capital cost of the plant.

Carbon dioxide emissions from power generation depend primarily on the type of fossil fuel used and, secondarily, on the efficiency of the plant. The most environmentally friendly fossil fuel is natural gas, followed by diesel and coal, which lead to significantly more harmful emissions. Therefore, the lowest carbon dioxide emissions are achieved when using an internal combustion engine running on natural gas, followed by an internal combustion engine running on diesel, STP and GTP on natural gas and STP on coal.

Thus, the review made it possible to conclude that the main characteristics of distributed generation plants, including energy efficiency and cost, differ significantly. Therefore, the feasibility of introducing a specific electricity generation technology will largely depend on specific scenario conditions, first of all, the cost of fuel. To identify the influence of the mentioned factor on the economic attractiveness of various distributed generation plants, a technical and economic analysis was carried out.

3. Feasibility Study

Several types of power plants were selected for the technical and economic analysis. Among the fossil fuel plants, internal combustion engines, gas turbines and steam turbines were considered. Wind and solar power plants were chosen as power plants using renewable energy sources since their construction does not require the presence of rivers, bays or unique infrastructure facilities, and they can be easily scaled to meet specific consumer needs. Separately, SNPPs operating on the basis of traditional thermodynamic cycles, for which nuclear fuel serves as an energy source, were considered.

All of the technologies presented were compared based on the levelized cost of electricity (LCOE) they produce, calculated according to Equation (1). This indicator was chosen as a criterion since it allows comparing the economic efficiency of the use of various energy units under the condition that their operation is in an isolated power system.

$$\mathrm{LCOE}=\frac{I+{\sum }_{t=0}^n\frac{O\&M+F}{{(1+r)}^t}}{{\sum }_{t=0}^n\frac{E}{{(1+r)}^t}}$$

(1)

where I—is capital investment in the generation technology, O&M—operation and maintenance cost per year, F—cost of fuel per year, E—electricity generated per year, r—discount rate, n—lifetime.

3.1. Overall Comparison

To roughly assess the different technologies of LCOE, an average value of efficiency, capacity factor, capital cost and lifetime was used (

Table 4. LCOE calculation input parameters.

Technology	Efficiency, %	Capacity Factor, %	Capital Cost, USD/kWe	Lifetime, Years
ICE	41	70–85	950	25
Gas turbine	30		650	12.5
STU gas	30		1150	20
STU coal	29		1150	20
Wind PP	30	15–25	1225	22.5
Solar PP	19	10–20	850	30
NPP	28	85–95	5000	55

). The O&M cost was assumed to be 5% of the capital cost for all technologies considered. The discount rate was assumed to be 10%.

The price of natural uranium in the long term is about 80 USD/kg [33]. Since the most common small-capacity thermal neutron reactors use fuel with a ²³⁵U fraction of 16–18% [29], it is necessary to enrich natural uranium in 33–38 stages [34], with each stage costing approximately 100 USD [35]. Adding up the cost of natural uranium and enrichment stages, we obtain the price of enriched uranium at a level of 3400–3900 USD/kg. Multiplying the decomposition heat of 1 kg of ²³⁵U, equal to 24 GWh, by the degree of uranium enrichment (17%) and the degree of burnup (50–60%), we obtain the amount of heat that will be released by 1 kg of nuclear fuel during the operating cycle (2000–2400 MWh/kg). Dividing the cost of one kilogram of enriched nuclear fuel by the heat released during the operating cycle of a nuclear reactor, we obtain a cost for SNPPs equal to 1.4–1.9 USD/MWh. Taking into account the delivery to remote regions, the cost of thermal energy from uranium was accepted in a wide range (2–10 USD/MWh), since the degree of enrichment, burnup and the cost of natural uranium can vary significantly depending on the specific technology and market conditions.

The results of the LCOE calculation for various power generation technologies depending on the CF and the cost of fuel are given in Figure 8. It can be seen that the cost of a kilowatt of energy depends significantly on the type and cost of fuel. In this case, the heat of nuclear fuel is the cheapest. It is followed by the heat of coal, natural gas and diesel fuel. On the other hand, a significant difference in fuel costs is compensated by differences in capital costs and CF for the technologies under consideration. Thus, SNPPs are the most capital-intensive, as evidenced by the significant levelized cost of electricity even at zero fuel cost compared to fossil fuel installations. However, due to the low cost of thermal energy released during the decay of uranium 235 compared with the cost of heat released during the combustion of fossil fuels, the levelized cost of electricity for gas turbine plants, internal combustion engines, STPs and nuclear power plants turns out to be similar.

Figure 9 shows the ranges of the levelized cost of electricity for the considered range of the cost of heating fuels, taking into account differences in the CF. According to the results of the calculations, it can be seen that the most expensive sources of electricity are internal combustion engines and gas turbine plants running on diesel fuel. In turn, the cheapest electricity is produced by coal-fired power plants (it should be noted that this calculation did not take into account the costs of introducing flue gas cleaning systems, which make a significant contribution to the cost of electricity). Next are the natural gas, solar, wind and nuclear power plants. Given the intersection of the cost ranges of rationed electricity for the technologies under consideration, the choice of option should take into account the specific conditions at the site of the proposed construction of the power facility. As a result of the calculations, we can conclude that the demand for SNPPs is highest in situations where the cost of fossil fuels is high and the energy potential of RES is low.

3.2. Comparison of SMR and Alternative Technologies

To assess the economic effect of the use of SNPPs, it is necessary, first of all, to estimate capital costs. The most relevant and reliable information on this issue became available after the creation of the first Russian floating nuclear power station, Akademik Lomonosov, which uses two KLT-40S reactors with a capacity of 35 MW each, with the unit cost of the main floating power unit of the station being approximately 6400 USD₂₀₂₂/kWe [36]. Therefore, for SNPPs with a capacity of 5 to 100 MW, the unit cost was taken in the range of 7850–4000 USD/kWe. The initial data for calculating the parameters of generation of various capacities are given in

Table 5. Characteristics of the chosen distributed energy generation technologies.

Reactor Model	Shelf-M	ABV-6	KLT-40S	RITM-200	SVBR-100	K-100	Jenbacher J 920	SGT-800	SPP	WPP
Power, MW	6.6	8	35	53	100	108.8	10.4	57	5	54
Efficiency, %	23.2	21.1	23.3	32.1	35.7	34	48	40	-	-
Price, million USD	51.4	61.7	232.5	314.2	400.0	96.4	4.7	17.5	4.0	81.7
Service life, years	60	40	40	40	60	25	25	15	30	25
CF, %	85–95					70–85			10–20	15–25

[26,37,38,39].

A comparison of different technologies depending on the power level is given in Figure 10. Since solar and wind power plants have comparable unit capital costs and there are no fuel costs for them, the cost of electricity produced is approximately at the same level (unchanged).

For an installed capacity of less than 25 MW, the most profitable option is the use of solar power generation. However, it should be borne in mind that when working in a closed power system, the uninterrupted operation of renewable energy sources requires the installation of energy storage systems, which will increase the final cost of electricity. The dependences obtained indicate that the LCOE for the SNPP based on the Shelf-M and ABV-6 reactors is equal to the LCOE for the internal combustion engine in the range of natural gas prices from 65 USD/MWh to 87 USD/MWh. The same tendency will be observed when using diesel fuel.

The use of a gas turbine plant has proven to be more expensive than the use of wind power plants. However, for the power range of 25–50 MW, the cost of electricity from SNPP turns out to be comparable to that of wind power plants and gas turbine plants: at a fuel heat price over 40 USD/MWh for the RITM-200 and over 50 USD/MWh for the KLT-40s.

In the power range of 50–100 MW, SNPPs turn out to be comparable to STPs at fuel costs of 20 USD/MWh and 30 USD/MWh for SVBR-100 and RITM-200. Compared to GTP, the SVBR-100 is competitive at a fuel cost of 30 USD/MWh. Thus, SNPPs with an installed capacity of 30 MW or more may be a more promising energy supply option at high prices for fossil fuels and low potential for renewable resources.

It should be noted that not only natural uranium but also thorium can be used as fuel [40]. Thorium in nature is three times more abundant than uranium, but thorium fuel has not yet been put into commercial operation and has not passed market testing. This is because there are several problems in the front and back of the thorium fuel cycles:

• Irradiated ThO₂ and ThO₂-based spent fuel are poorly soluble in HNO₃ due to the inertness of ThO₂.
• High-gamma radiation is associated with short-lived ²³²U daughter products, which are always associated with ²³³U and require processing and recovery of fuel.
• Protactinium generated in the thorium fuel cycle also causes some problems that need to be addressed accordingly.
• High-gamma radiation associated with short-lived ²³²U daughter products that are always associated with ²³³U requires remote processing and remanufacturing of fuel.
• Protactinium generated in the thorium fuel cycle also causes some problems that need to be properly addressed.

Due to these factors, thorium-fueled cycles will not be considered [41].

When comparing installations of different capacities with each other (Figure 11), it can be seen that at low costs of fossil fuels, the lowest cost of electricity is achieved when using a gas turbine engine. With the cost of fossil fuels over 10 USD/MWh, a gas piston engine allows for a lower levelized cost. The most expensive in terms of electricity production is the use of a steam turbine power plant.

If the cost of fossil fuels is over 30 USD/MWh, the use of SPP or SVBR-100 may be more economical (depending on external conditions). The use of RITM-200 becomes more economically feasible compared to fossil fuel installations at a fuel cost of 50 USD/MWh, KLT-40C from 55 USD/MWh, Shelf-M and ABV-6 from 65 USD/MWh. The levelized cost of electricity from RITM-200 and KLT-40S is in the WPP range, and RITM-200 and SVBR-100 are in the SPP range.

The results of studies of the influence of fuel cost, CF, capital costs and the discount rate on the change in the levelized cost of electricity for various power plants are given in Figure 12. The initial data for calculating the sensitivity of LCOE to changes in the listed characteristics are given in

Table 6. LCOE sensitivity calculation input parameters.

Discount Rate, %	10
SNPP/STP/WPP/SPP CF, %	90//8020/15
	9.2
Price of heat from uranium, USD/MWh	2

.

As can be seen, LCOE for SNPPs has the lowest sensitivity to changes in fuel costs compared to alternative technologies. The fuel cost has the greatest impact on the LCOE for GTP, and then on the LCOE for GPP and STP, due to differences in efficiency levels and capital costs for these units.

The discount rate has the least effect on the levelized cost of electricity produced by GTPs, which is associated with short service life and moderate capital costs. The discount rate has a moderate effect on the levelized cost of electricity for SNPPs, SPPs and WPPs, which is due to the absence of fuel costs (when the cost of electricity is determined primarily by capital costs) in the case of RES and significant capital costs and a long service life in the case of SNPPs.

For similar reasons, capital costs and CF have a significant effect on the levelized cost of electricity produced by SNPPs and RES. The moderate influence of these parameters on the LCOE is typical for a steam turbine power plant. Moreover, capital costs, CFs and fuel prices have about the same effect, which is associated with higher capital costs and lower efficiency compared to other fossil fuel power plants.

Thus, with a significant increase in the cost of fossil fuels, the cost of electricity produced by STPs, GTPs and GPPs will grow much more than when using SNPPs, which is important for remote regions with difficult fuel supplies. The LCOE for RES is highly dependent on the CF and is largely determined by weather conditions. The volatility and difficulty of predicting the latter predetermine the maximum requirements for the volume of energy storage systems. SNPPs, whose capacity can be regulated, do not have this problem. This means that they require a smaller volume of storage systems.

3.3. Perspectives on SMR Use in Russia

SNPPs are characterized by a small share of fuel costs in the structure of the cost of electricity. At the same time, they have a significant unit cost of installed capacity, which is the main obstacle to large-scale applications. Therefore, an urgent task is to reduce specific capital investments by reducing the dimensions of the reactor, heat exchange equipment and turbomachines, which can be achieved, among other things, by switching to new coolants [42,43].

At the same time, these installations may be of particular demand to solve the problem of power supply to large industrial enterprises in remote or isolated regions where the cost of delivering hydrocarbon fuel is high and renewable energy resources are insufficient. In addition to electricity and heat, SNPPs can also produce carbon-neutral hydrogen, which can be used to reduce the carbon footprint of industrial processes such as iron ore recovery, ammonia production, and others. Thus, SNPPs represent the least location-dependent way to produce electricity and heat without carbon dioxide emissions.

Based on the analysis of the strategy for the development of the Arctic zone [44], the cost of fuel [45] and the availability of renewable energy sources in Russia [46], the regions with the most favorable conditions for the use of SNPPs were selected (Figure 13). First of all, this is the north of the Krasnoyarsk Territory, the Republic of Sakha, Chukotka and the Khabarovsk Territory, as well as the Magadan Region and the Kamchatka Territory.

4. Conclusions

• Despite the widespread use of fossil fuel power plants in Russia among distributed generation facilities, the development of a direction related to the creation of small-capacity nuclear power plants is relevant, especially for remote regions of the north and the Arctic.
• Electricity produced by SNPPs is more expensive than natural gas and coal thermal power plants, wind and solar power plants, but cheaper than the diesel option due to its high cost. According to the results of calculations of the levelized cost of electricity, it was found that the use of SNPPs can be profitable when renewable energy potential is low and fossil fuel prices are high. Thus, in the range of installed capacity up to 25 MW, SNPPs Shelf-M and ABV-6 allow for cheaper electricity compared to internal combustion engines at a fossil fuel cost of more than 65–87 USD/MWh. In turn, in the range of installed capacity of 25–50 MW, SNPPs RITM-200 and KLT-40S make it possible to obtain cheaper electricity when compared with gas turbine plants, at a cost of fossil fuels of 40–60 and 50–70 USD/MWh, respectively. In the range of installed capacity of 50–100 MW, RITM-200 and SVBR-100 make it possible to obtain cheaper electricity at a fossil fuel cost of 20–30 and 30–45 USD/MWh, respectively, compared to steam turbine power plants.
• A study was carried out on the effect of fuel cost, capital cost, CF and discount rate on the levelized cost of electricity.
• Based on the calculation of the levelized cost of electricity, the cost of fuel, and the availability of renewable energy resources in the regions, a map of promising SNPP locations was compiled. The most promising regions for the use of SNPPs were the north of the Krasnoyarsk Territory, the Republic of Sakha, Chukotka and Khabarovsk Territory, as well as the Magadan Region and Kamchatka Territory.