Analysis of small modular reactor technologies and socio-economic aspects of their application in the Russian Arctic in the era of digital transformation

. Small modular reactor technologies and social, economic, and technological aspects of their application in the Russian Arctic are considered in the article. An overview of the key factors influencing an implementation of small modular reactor plants in remote regions with a decentralized power grid is presented. The main directions of small modular reactor design activities of the key Russian centers of atomic research and development are given. An overview of current Russian small modular reactor technologies including pressurized water reactors, boiling water reactors, reactors installed on floating nuclear power plants, high-temperature gas-cooled reactors, and liquid metal cooled reactor is conducted. Economic, social, ecological, and digital aspects of applications of small modular reactor in the Russian Arctic are considered. A detailed survey of areas of small modular reactor application including extractive, processing, industrial energy-intensive facilities, and power and heat supply of cities is also given. The importance of digital twins of small modular as an essential element in the development and maintenance of complex engineering products and industrial facilities throughout the entire life cycle is discussed in the article. Conclusions about key advantages and prospects of an application of small modular reactors in the Russian Arctic are made.


Introduction
At present, not only in Russia but all over the world, interest in small modular reactors (SMR) as promising energy sources for remote regions with decentralized power supply is growing rapidly. This is justified by the fact that in difficult Arctic conditions, traditional energy sources are not able to meet the growing demand for heat and electric energy everywhere [1].
The active development of remote areas with the expansion of gold, diamonds, rare metals, coal, iron ore mining, the rise in the production of gas, and the development of the processing industry requires solving energy problems. The cost of transmission of electricity in difficult Arctic natural and climatic conditions and over long distances can be several times higher than the cost of its production. For such power sources, new generation reactors have

Results
Key results of the research are presented in Table 1. The following SMR technologies were overview: Pressurized Water Reactor (PWR), Boiling Water Reactor (BWR), reactors installed on Floating Nuclear Power Plant (FNPP), High-Temperature Gas-cooled Reactors, Liquid metal cooled reactor (LMFR). Potentially these SMR technologies could be applied for providing electricity and heat energy for settlements, ports, enterprises, infrastructure facilities along the Northern Sea Route, extractive, processing, and industrial energy-intensive facilities in Russian Arctic.

Overview of research, development, and engineering centers that design SMR technologies that might be applicable in the Russian Arctic
The experience of the Russian nuclear industry in the development and application of SMR has been more than 65 years. The world's first nuclear power plant, a nuclear icebreaker fleet, the world's only floating thermal power plant -each of these projects is based on Russian small reactor technologies. The key Russian research, development and engineering centers involved in the creation of SMR are JSC "Afrikantov OKBM, JSC "NIKIET", NRC "Kurchatov Institute" and JSC "AKME-engineering" [5].

JSC "Afrikantov OKBM
JSC "Afrikantov OKBM" is a large research and production center of the Russian state corporation "Rosatom" with a full cycle of development, manufacture, and supply of a reliable, safe, and economically effective nuclear reactor for various purposes, equipment, and systems of NPPs and their servicing.
The scientific, engineering, and production capacities of JSC "Afrikantov OKBM" ensure the implementation of the broad range of works on the creation of different types of a nuclear reactor, including the development of design, the implementation of the necessary sophisticated project calculations, R&D work, creation and testing of prototypes, the development of production technology, manufacturing, and installation of equipment at construction site, it`s commissioning, equipment maintenance and decommissioning.

JSC "NIKIET"
JSC "NIKIET" is a multidisciplinary institute engaged in several major nuclear power engineering areas. It is one of Russia's largest nuclear engineering and technology centers. The main areas of activities of the organization include the development of nuclear power reactors for NPPs, nuclear power systems for the Navy, the development of advanced power reactors for the nuclear power of the future, space nuclear power and propulsion systems, new nuclear fuel cycles, neutronic systems of the thermonuclear reactor.

NRC "Kurchatov Institute"
The National Research Centre "Kurchatov Institute" is one of the leading research centers in the world and the largest interdisciplinary laboratory in Russia. A substantial number of Russian nuclear physics facilities have been consolidated in the Kurchatov Institute. The main areas of activities of the organization include the organization of research, development, and engineering works in the field of nuclear power, controlled thermonuclear fusion and plasma processes, the participation in the design, engineering, production, installation, operation, and decommissioning of nuclear and thermonuclear facilities and radioactive waste storage facilities. The NRC "Kurchatov Institute" is engaged in the design of land based SMR ELENA [8].
The key activity of the company is the creation and development of the basic technology of civil reactor plants with a lead-bismuth coolant with a capacity of 100 MW (RU SVBR-100) and its development, as well as the development of standard designs of nuclear power plants (NPP) based on RU SVBR-100, including projects of modular NPPs, nuclear-combined heat, and power plants, desalination power plants, as well as other commercial solutions following market needs [9].

RITM-200 and RITM-200M designed by JSC "Afrikantov OKBM"
RITM-200 is the latest development in III+ or according to some sources, the IV generation SMR water-moderated nuclear reactor developed by JSC "Afrikantov OKBM". Designed for installation on icebreakers and advanced floating nuclear power plants. Six RITM-200 reactors were successfully installed on icebreakers Arktika, Sibir, and Ural. Two reactors of Arktika icebreaker successfully passed all power-up tests during dock-side trials [10].
The RITM-200 reactor facility is designed according to a two-circuit scheme. A distinctive feature of the reactor is 4 steam generators integrated into the core vessel (traditionally steam generators are made in a separate vessel connected to the core vessel by primary coolant pipelines; the integral layout reduces the material consumption and dimensions of the installation, reduces the risk of leaks from the primary reactor circuit, facilitates assembly and disassembly installation). 4 main circulation pumps are located around the reactor vessel.
The reactor will have a capacity of 55 MW of electric power or heat capacity of 175 MW(t) and in the transportable version a shaft power capacity of 30 MW. The reactor requires refueling once in 7-10 years with total design life of 40 years. Uranium enrichment is limited to 20% to meet the criteria of non-proliferation of nuclear weapons international agreements [11].

UNITHERM designed by JSC "NIKIET"
UNITHERM is a small transportable NPP with a capacity of 30 MW(t) and an electrical capacity of 6,6 MW designed using NIKIET's experience in developing marine nuclear propulsion systems. UNITHERM SMR is designed for the generation of heat and electricity, as well as related industries (water desalination, heating of oil strata, liquefaction of natural gas, etc.). The reactor facility was designed to operate for 25 years without reloading nuclear fuel with an installed capacity utilization factor of 0,7. UNITHERM SMR is intended to meet the energy needs of mainly small settlements with a population of 2-3 thousand people. The number of such settlements in the regions of the Far North and East of Russia is quite large. There is the possibility to use UNITHERM SMR to supply power to regional centers and relatively large settlements with a population of 10-15 thousand people [12].

VK-300 designed by JSC "NIKIET"
The VK-50 reactor is the only operating prototype of the VK-300 vessel-type boiling-water reactor in Russia. This SMR is successfully operating in Dimitrovgrad city, Russia. The VK-300 project is focused on the use of technologies created in Russia. The VK-300 unit is designed for the generation of electricity and heat. The turbine unit, operating according to a single-loop scheme with a reactor, is optimized for the conditions of the heating regime. The VK-300 reactor is a vessel-type boiling apparatus with an integral layout: cyclone-type steam separators are located inside the reactor vessel. The VK-300 has a heat output of 750 MW(t) and 250 MW(e) of electricity output. The VK-300 reactor plant uses the following innovative solutions:  Integrated layout with a single-circuit switchgear circuit.  Innovative construction of in-reactor circulation and coolant separation.  The upper location of the drives of the control and protection system.  The principle of the emergency core cooling system -in the event of ruptures, the coolant can be localized, condensed, and returned to the case using passive means without using external sources of water and power supply. VK-300 reactor facility is designed for the effective generation both of heat and electricity for district electricity and heating supply and for seawater desalination, having good safety and economic parameters.

KARAT-45 and KARAT-100 designed by JSC "NIKIET"
KARAT-45 a small tank-type boiling water reactor (BWR) with a nominal capacity of 45 MWe, is a self-contained cogeneration unit to produce electricity, steam, and hot water designed by NIKIET. It is developed as the base facility for the economic and social development of the Arctic region of Russia.
KARAT-100 is a multipurpose BWR of an integral type with an output power of 360 MW (t) and a rated electrical power of 100 MW (e). The design uses engineering approaches that have been tested on prototypes and test facilities. The reactor is designed to produce electricity, heat for district heating, and hot water in cogeneration mode. The design uses natural circulation to remove heat from the core of the primary cooling system in all operating modes. The structural configuration includes passive safety systems to improve safety and reliability.
Both KARAT-45 and KARAT-100 power units have a high load following the capability to cope with daily power variation from 20% to 100%.

RUTA-70 designed by JSC "NIKIET"
RUTA is a nuclear power plant with a low-temperature water-cooled pool-type reactor and an integral layout of the primary circuit equipment. SMR RUTA has no energy conversion system. In the primary cooling circuit, the heat from the core of the reactor is transferred to the primary heat exchanger by forced convection at 100% of power output, and at a power level below 30% of the working capacity, the heat is transferred by natural convection. Forced circulation of the heating medium by using pumps for operation at power levels from 30% to 100% of the nominal power increases the heating medium flow in the primary circuit and increases the temperature in the lower circuit. RUTA-70 can operate continuously without maintenance for about a year.
The RUTA heat supply technology is intended for use in non-electric-deficient municipal district heating systems, which will make it possible to modernize the housing and communal services of Russia and qualitatively improve the life of the country's population. The heat supplied from the RUTA reactor has a lower price than the heat from boiler houses and thermal power plants using fossil fuel. One RUTA-70 unit saves over 50,000 tons of fuel equivalent per year (~ 45 million m3 of natural gas with an export value of about $ 10 million). The environmental effect of the use of this installation is high -if one RUTA reactor replaces gas boiler houses, the reduction of carbon dioxide emissions will amount to 80,000 tons per year.

RUTA-70 designed by JSC "NIKIET"
The ELENA nuclear thermoelectric plant is a direct conversion reactor with water cooling without refueling on site, capable of generating 68 kW (e) of electricity and 3.3 MW (t) thermal power for 25 years without refueling. This is enough to meet the basic energy needs of a small village, the generation method is thermoelectric, which contributes to increased reliability and fire safety (the short-circuit current of the thermoelectric generator exceeds the nominal one by no more than 2 times). The level of output efficiency of about 3% is compensated by the possibility to use the generated heat for heating.
Maintenance activities are not needed for reactor operation. The personnel take part only in assembly or disassembly of the facility, starting its operations and bringing the reactor to the needed power level. The entire operational life of the SMR is limited to one load of fuel into the core of the reactor. During the last twelve years, the SMR "Elena" has been successfully working at the Kurchatov center.

KLT-40S designed by JSC "Afrikantov OKBM"
KLT-40S is a PWR designed for a floating nuclear power plant, delivering 35 MW (e) per module. The design is based on the third generation KLT-40 marine power plant and is an improved version of the reactor that ensures the long-term operation of nuclear icebreakers in more severe conditions than a stationary nuclear power plant. The floating nuclear power plant with the KLT-40S reactor can be manufactured at shipyards and delivered to the site in a fully assembled, tested, and ready-to-operate form. There is no need to develop transport routes, power lines, or preparatory infrastructure required for large NPP, and there is flexibility in choosing a site for a floating nuclear power plant since it can be moored in any coastal area.
In 2009, at the Baltic Shipyard, the slipway assembly of the floating power plant Akademik Lomonosov, project 20870, began. It includes two KLT-40S reactors with a total electrical power of 70 MW and 50 Gcal / h of thermal energy. The overhaul period is 12 years and the assigned service life is 40 years. When creating KLT-40S, the cassette core was modified to address the issue of nonproliferation of nuclear materials and technologiesenough uranium enriched to 20% is sufficient for operation. In 2019 the Akademik Lomonosov started its operations in Pevek and supplied electricity to the grid.
The experience of creating KLT-40S was used in the development of the next generation of shipborne nuclear reactors RITM-200.

ABV-6E designed by JSC "Afrikantov OKBM"
A specific feature of an ABV-type reactor plant is an integral design: the reactor vessel houses not only the core but also the steam generator. This makes it possible to ensure the operation of the reactor at full power with the natural circulation of the coolant, which is significant for economic and safety reasons. The ABV-6E is a reactor that produces 14 MW(t) and 6 MW(e) in cogeneration mode or 9 MW(e) in condensation mode. ABV-6E integral PWR uses the natural circulation of the primary coolant. The ABV-6E design was developed considering the operating experience of PWR reactors and the latest achievements in the field of nuclear power plant safety. The main goal of the project is to create a small shipyard fabricated, multipurpose transportable nuclear power unit for working for about 10 years without refueling on the coast or berthing platform.

VBER-300 designed by JSC "Afrikantov OKBM"
The innovative nature of the VBER-300 reactor plant is to use a ship-type nuclear steam generating unit with pressurized water. VBER-300 belongs to the class of pressurized watercooled reactor, which is the most widely used in the world practice. The design is based on the compact block design of the steam generating unit used on nuclear icebreakers. Considering the operating experience and the existing production and technological base, VBER-300 does not require large-scale research and development work, which is one of the factors in reducing the time and financial costs for project implementation.
VBER-300 can output 917 MW of heat energy. The reactor provides electric power up to 325 MW (e) in the condensing mode, in the cogeneration mode -about 215 MW (e). Heat release is up to 460 Gca/h. The estimated service life of the facility is up to 60 years.

SHELF designed by JSC "NIKIET"
A power unit with the SHELF reactor is designed for use as a source of power supply for facilities located on the sea shelf, including areas of the Arctic coast, as well as areas with practically no energy and transport infrastructure. SHELF is a PWR power for 6,6 MW(e) generation. The power capsule is designed in two versions: containing only all components of a reactor, and a larger capsule which also includes the turbine generator package, an automated and remote-control system, regulation, control, and protection of electrical power generation. SHELF power capsule can be used as both floating and subsea nuclear power units.
The variant of the underwater location of the ASMM power unit assumes the use of surface or underwater objects located on the Arctic shelf as a source of power supply. Electricity is provided to the actual consumer, as well as a complex of surface (coastal or ship) technical means and structures.
The immersion depth of the energy capsule is up to 300 m, the control panels and service systems of the NPP are located on the shore or the ship.
Structurally, the design of SHELF is similar to a marine propulsion nuclear units. The SMR is supplied as a single module, all its components are housed inside a high-strength protective shell. With the capability for long-term unattended automated operation, the SMR and other equipment inside the SHELF module eliminates the need for plant operators inside the power unit and keeps the module unmanned during the automated operation period up to 300 days. During the time of automated operation, the planned maintenance service is conducted once a year for a duration of 15 days.

GT-MHR designed by JSC "Afrikantov OKBM" and project partners
The gas turbine modular helium reactor (GT-MHR) is an international project of design of a graphite-gas reactor assembled in two modules: a high-temperature reactor unit and an energy conversion unit. The first contains the core and the reactor control and protection system, and the second includes a gas turbine with a generator, a recuperator, and refrigerators.
Since the reactor plant can produce high coolant outlet temperatures, the modular helium reactor system can also efficiently produce hydrogen, for example, by high-temperature electrolysis or thermochemical water splitting.
The use of modular helium reactor plants makes the system flexible and allows the use of various energy conversion schemes: with a gas turbine cycle, a steam turbine cycle, and with a high-temperature heat supply circuit to industrial facilities. The gas-cooled modular hightemperature reactor plant has inherent safety features with safe passive removal of decay heat, ensuring a high level of safety even in the event of a complete loss of primary coolant.
The modular design of the helium reactor has proven the modularity of the unit with a wide range of module capacities (from 200 to 600 MW (t)) and a change in NPP power depending on the number of modules. This provides a good variable capacity of the reactor plant for regional energy sources.

MHR-T and MHR-100 designed by JSC "Afrikantov OKBM"
The designs are based on the global experience in the development of experimental HTGR plants. Russia has more than 40 years of experience in the development of HTGR plants of various power from 100 to 1000 MW(e) and for various purposes. The MHR-T production complex makes use of the basic gas turbine modular helium reactor design as the basis for a multi-module plant for hydrogen production. The hydrogen output through the steam methane reforming process or high-temperature solid oxide electrochemical process is performed by coupling the plant with the modular helium power units.
The application of helium SMR makes the system flexible and allows the possibility to use different power unit schemes: steam turbine cycle, gas-turbine cycle, and the circuit supplying high-temperature heat for production purposes. The HTGR unit possesses safety features with passive decay heat removal that provides full safety even in case of the total loss of primary coolant.
The designs are based on world experience in the creation of experimental HTGR installations. Russia has more than 40 years of experience in the design of HTGRs in various capacities (from 100 to 1000 MW) and for various purposes. The MHR-T hydrogen production complex uses the basic design of the GT-MHR reactor plant as the basis for a multi-module hydrogen production plant.
Analysis shows that SMRs with HTGR have good prospects for adding or replacing these regional generations. Based on the study of the development and needs of the electricity market, pre-design work is underway for a commercial MHR100 with a modular helium reactor and multiple power conversion schemes for various power applications.

MHR-T and MHR-100 designed by JSC "Afrikantov OKBM"
BREST-OD-300 is a fast neutron reactor with an equilibrium composition of uraniumplutonium nitride fuel. SMR has a lead coolant and a two-circuit heat conversion circuit operating in a closed nuclear fuel cycle. This technology is developed for practical confirmation of the main technical solutions used in a lead coolant reactor following the concept of natural safety.
Step-by-step justification of the resource characteristics of SMR elements for the creation of industrial nuclear power plants with reactor installations of this type should also be kept in mind. This SMR generates electricity with a capacity of 300 MW (e).

SVBR-100 designed by JSC "AKME-engineering"
The SVBR-100 reactor is a multipurpose small modular fast reactor lead-bismuth (LBE) cooled and one of the main components of an innovative nuclear power system adapted for civil projects, created using a modular power unit with a capacity of 100 MW (e).
An important distinctive feature of the reactor is the integral (monoblock) layout of the primary circuit equipment, in which all the equipment of the primary circuit (the reactor itself, steam generator modules, main circulation pumps, etc.) is placed in a single vessel with a complete absence of pipelines and valves in the primary circuit. SVBR-100 technology belongs to the IV generation.
SVBR-100 can potentially become the world's first commercial medium-power reactor of the fourth generation using a coolant on heavy metals and occupy 10-15% of the emerging world market of small and medium-sized nuclear energy [13].

Economic, social, ecological, and digital aspects of applications of SMR in Russian Arctic
Areas of application of SMR in the Russian Arctic are:  Extractive, processing, and industrial energy-intensive facilities that do not have their own generation of electricity and heat.  Linear and junction power supply substations for railway communication outside the grid generation area.  Situation centers of the Ministry of Emergency Situations  Settlements, cities (up to 50 thousand inhabitants), ports, enterprises, civil and defense infrastructure facilities along the Northern Sea Route, including facilities located or planned to be created on the archipelagos alongside the route. Possible application of SMR is reasonable when electricity and heat power generation with the use of fossil fuel is economically inefficient or technically difficult [14].
The most prospective Arctic areas for application of SMR are:  Economic efficiency is reached in a decentralized energy environment due to a significant reduction of logistic cost of fossil fuel.  Environmental safety is achieved due to a significant reduction in the impact of nuclear power sources on the environment, the absence of emissions and "wastelessness" of the generation process, a significant reduction in greenhouse gas emissions [15];  Stability under a wide range of external influencing factors (both natural-climatic and anthropogenic) is ensured by several design solutions and the possibility of immersed placement of SMRs [16];  Autonomy of operation due to a long-term activity of the nuclear power plant core and the absence of dependence on fuel supply schedules, including maintaining operability in the event of violations in the logistics infrastructure of the region with its complete isolation.  Reduction of SMR construction time due to the module approach.  The ability to increase the capacity by placing additional modules.  The possibility of implementing serial production of SMR.  Reduction of requirements for an SMRs placement site.
One of the key drivers of SMRs development is its economic efficiency considering longterm periods [17]. Preliminary indicators of the economic efficiency of SHELF SMR are stated in the Table 2 (all costs given are without VAT in prices of 2016). Today digital twins are an essential element in the development and maintenance of complex engineering products and industrial facilities throughout the entire life cycle. One of the Russian scientific nuclear centers have started the All-Russian Research Institute for NPPs Operation development of digital twins of SMR with RITM-200N and Shelf-M reactors. The project is carried out with the participation of JSC Afrikantov OKBM, JSC NIKIET, JSC Greenatom.
The digital twin of an SMR will include calculation codes that simulate the physical processes in the SMR (thermohydraulic, neutron-physical, electrical) in various operating modes, modeling tools and models themselves, databases, and service software [18].
The digital twin will perform a wide range of functions at various stages of the SMR life cycle -from design to decommissioning. Including the calculation justification of design solutions and safety, technical and economic optimization of the project, training of personnel of the nuclear power plant, and much more. In other words, on the digital twin it will be possible to work out design solutions before they are embodied in metal, check the compatibility of equipment and control systems, solve safety issues, and train personnel [19].
In the next few years, the development and delivery of digital twins of SMRs along with modules itself may become the industry standard.
As for the ecological aspect, according to the calculation of Rosatom the repayment of decommissioned coal and diesel sources of energy generation with one for example RITM-200 SMR will CO2 emissions for 10 thousand tons per year. SMRs do not generate CO2 emissions or carbon black emission that would help to keep the gentle Arctic environment safe [20].

Conclusion
In remote, hard-to-reach areas of the Russian Arctic, a reasonable alternative to energy sources based on fossil fuel can be small module reactors, fully autonomous, delivered to the place of use in modules, and completely removed after the end of the operation. The use of SMR for electricity and heat supply can be economically efficient and significant from a social and environmental point of view. The development of SMRs is prospective for the development of hard-to-reach territories with severe climatic conditions. The relevance of SMR development is characterized by the Russian power system because the decentralized power supply zone occupies 70% of the country's territory.
The introduction of SMR into regional power systems of the Arctic will reduce regional costs for the purchase of natural gas and fuel oil, increase the systemic reliability of power supply, limit the growth of tariffs for electricity and heat supplied to the population and industrial enterprises, and improve the environmental situation in the location area. The main effect of using nuclear energy sources is large-scale savings of natural gas in the field of district heating and heat supply in large cities [21].
SMR is the future of nuclear industry development. In December of 2020 the state atomic energy corporation Rosatom and the Government of the Republic of Sakha (Yakutia), Russia, have entered into an agreement that establishes the principles of tariff setting for electricity within the framework of the project for the construction of an SMR based on the RITM-200 reactor facility in the settlement of Ust-Kuyga, Ust-Yansky ulus. The projected SMR is distinguished by its compactness and modularity, a shortened construction period and high safety standards, and its service life is at least 60 years. It is expected that its construction will almost halve the cost of electricity in the Ust-Yansky region. In the future, it is possible to establish based on the station the production of environmentally friendly hydrogen for the needs of transport and industry.
Replacement of obsolete coal and diesel sources of generation with energy from nuclear power plants will reduce CO2 emissions in the Ust-Yansk region by 10 thousand tons per year. The construction of the station will provide a stable and clean energy supply for the project for the development of the Kyuchus gold deposit located in the Verkhoyansk region. The social effect of SMR construction will be the creation of up to 800 new jobs. Such projects can serve as a reliable and clean source of heat and electricity both for subsoil users and for residents of remote areas with an isolated power system. According to the plan, the construction of the station will be completed in 2028.