《1 Engineering research fronts》

1 Engineering research fronts

《1.1 Trends in Top 12 engineering research fronts》

1.1 Trends in Top 12 engineering research fronts

The Top 12 engineering research fronts as assessed by the Energy and Mining Engineering Group are shown in Table 1.1.1. These fronts involve the fields of energy and electrical science, technology, and engineering; nuclear science, technology, and engineering; geology resources science, technology, and engineering; and mining science, technology, and engineering. Among these 12 research fronts, “regulation and control of theories and methods in power systems using a high proportion of renewable energy”, “low-cost direct air carbon capture (DAC)”, and “design of key materials for high-efficiency proton exchange membrane (PEM) hydrogen production reactor” represent energy and electrical science, technology, and engineering research fronts; “research on inherent safety of nuclear fuel, characteristics of reactor safety mechanism, and multidisciplinary strong coupling mechanism”, “mechanism and coupling experiments of digital reactor with multi-physical field and multi-space-time scale”, and “physical and experimental verification of China Fusion Engineering Test Reactor (CFETR)” represent nuclear science, technology, and engineering research fronts; “key technologies and challenges for natural gas hydrate exploitation”, “research on climate change based on the Earth System Model (ESM)”, and “efficient breaking mechanism of hard rock by high temperature and compression” represent geology resources science, technology, and engineering research fronts; and “multi-information perception and early warning of hidden danger of mine disasters”, “fundamental theory for the efficient exploitation of shale oil”, and “rock burst mechanism and early warning methodology” represent research fronts of mining science, technology, and engineering.

The annual publication status of the core papers related to each frontier from 2015 to 2020 is shown in Table 1.1.2.

《Table 1.1.1》

Table 1.1.1 Top 12 engineering research fronts in energy and mining engineering

《Table 1.1.2》

Table 1.1.2 Annual number of core papers published for the Top 12 engineering research fronts in energy and mining engineering

(1)    Regulation and control of theories and methods in power systems using a high proportion of renewable energy

High-proportion renewable energy power systems mainly refer to new power systems using renewable energy that accounts for more than 30% of total power generation. Renewable energy such as wind power and photovoltaics power will replace fossil energy for power supply, significantly changing the characteristics of power systems. The power system changes ① from the deterministic system to the strongly random system, where a deterministic system dominated by thermal power units and regular power loads shifts to a random system with strong uncontrollability in both power generation and load demands. Traditional control and operation methods cannot meet the developmental requirements of power systems. Existing research focuses on the modeling and impact assessment of uncertainty factors, decision-making under uncertainty, and stability evaluation in an uncertain environment. The spatio-temporal and seasonal power and electricity balance problems need to be solved urgently; ② from the electromechanical system to the power electronics dominated system. The basic characteristics of power systems evolve from the electromechanical transient process dominated by rotating electric machines to the electromagnetic transient process with power electronics, thereby, changing the stability mechanism. Existing research focuses on the dynamic behavior characteristics of power electronics devices and basic theories of new stability problems. In the future, it will be necessary to accurately describe the operational stability boundary of the high- proportion renewable energy power system; and ③ from a single power system to an integrated energy system. The existing power system will be interconnected with heating power pipelines, natural gas pipelines, and transportation networks to form a complex energy system. Existing research focuses on the coupling and interaction modeling of power systems and other energy networks. In the future, it will be necessary to conduct in-depth research of the integrated cross-energy systems.

(2)  Research on inherent safety of nuclear fuel, characteristics of reactor safety mechanism, and multidisciplinary strong coupling mechanism

Inherently safe nuclear reactors are an important aspect of reactor design research. The water-cooled reactor possesses inherent safety characteristics, which indicates natural shutdown in case of water loss. Fully Ceramic Microencapsulated (FCM) fuel has potentially inherent safety characteristics owing to its multiple encapsulated structure of fission products, high mechanical stability, and excellent thermal conductivity compared to other fuel forms. The composite silicon carbide cladding has high-temperature mechanics and strong oxidation resistance. The combination of these two approaches, in addition to features based on advanced core and structural design can conduct the residual heat of the core to the final heat sink through thermal radiation and structural heat conduction, without relying on external safety facilities under the hypothetical most serious accident conditions (loss of cooling), to ensure that the core does not melt and the reactor structure remains intact. This eliminates the risk of large-scale radioactive material release, fundamentally eliminating serious accidents, and achieving inherent safety in preventing off-site emergencies. At the same time, the high-temperature tolerance of the fuel allows the core to directly generate superheated steam for direct circulation, thereby, simplifying the system and improving the thermoelectric conversion efficiency, which enhances the economy of the power system. The research involves many scientific issues and key technologies such as the inherent safety mechanism characteristics of small superheated direct cycle water-cooled reactors based on FCM fuel, multidisciplinary strong coupling core design technology for complex behavior in the reactor, FCM fuel design, and manufacturing coupling mechanisms, all of which are difficult to implement.

(3)  Key technologies and challenges for natural gas hydrate exploitation

Natural gas hydrate is an ice-like solid crystal composed of natural gas and water molecules. Natural gas is mainly composed of methane, commonly known as combustible ice that can be ignited in the air. The basic idea of natural gas hydrate recovery is to decompose the hydrate into water and natural gas underground to extract the gas. The biggest difference between the hydrate reservoir and the conventional natural gas reservoir is that there is no sealing or diagenesis; thus, the conventional natural gas exploitation method cannot be easily applied to hydrated natural gas exploitation. The large-scale development of natural gas hydrate mainly relies on four key technologies: natural gas hydrate reservoir reconstruction and protection technology, natural gas hydrate reservoir drilling and completion technology and equipment, bottom hole gas-water rapid separation technology and equipment, and technologies and processes for improving the mining energy efficiency of natural gas hydrates.

To date, more than 100 wells have been drilled globally for natural gas hydrate research and exploration, mainly concentrated in North America and the Asia-Pacific region. With the gradual acceleration of global energy transition, natural gas hydrate has significant resource potential as a large-scale and efficient type of new clean energy, attracting increasing attention globally. At present, there are many problems associated with the exploitation of natural gas hydrates. First, there are technical challenges of effectiveness and safety; second, there are challenges of reducing costs and improving production efficiency; third, the exploitation of natural gas hydrates produces environmental problems; and finally, geological disasters also pose a challenge. These problems currently restrict the large-scale and effective development of natural gas hydrates and are also research directions for key technologies for natural gas hydrate development in the future.

(4)  Multi-information perception and early warning of hidden danger of mine disasters

With the increase in mining depth and intensity of coal resources, the risk of dynamic disasters such as rock bursts, coal and gas outbursts, fires, and water inrush increases significantly. Due to unclear understanding of the formation process and evolution mechanism of dynamic disasters under the coupling multiphase conditions and multi-physical fields, the backward technology of disaster precursor information collection, sensing, transmission, and mining identification and the lack of disaster risk identification and early warning module, the early identification of dynamic disaster risk is still subjective, blind, and uncertain.

To meet the major needs of coal mine typical dynamic disaster prevention and control, it is urgent to research identification, monitoring, and early warning mechanisms and key technologies of typical coal mine dynamic disaster risks; study the dynamic mechanism of coal mine rockburst instability and multi field coupling disaster mechanism; the disaster mechanism of coal and gas outburst and breeding mechanism of compound dynamic disaster; study the breeding and evolution law of coal spontaneous combustion disaster under high temperature environment; research the space-time breeding and evolution law of water inrush disaster, develop an intelligent identification and early warning theory and technology of multi parameter precursor information of typical coal mine dynamic disaster; study new sensing and multi network fusion transmission methods and technical equipment of precursor information of typical coal mine dynamic disasters; develop multi information mining and analysis technology of typical coal mine dynamic disasters based on data fusion; form an early warning method of typical coal mine dynamic disasters based on big data and cloud technology; provide support for the early warning and prevention and control of potential mine disasters; and ensure the efficient mining of deep coal resources.

(5)  Low-cost direct air carbon capture (DAC)

Direct air carbon capture (DAC) refers to the extraction of CO₂ from the atmosphere by absorption or adsorption. Absorption/ adsorption-based DAC and subsequent sequestration or utilization provide effective negative emission pathways to remove CO₂ from the air, reduce the negative shadow of fossil fuel utilization, and establish a closed carbon cycle. DAC technology was originally used for air pre-purification in air separation units and trace CO₂ removal in confined spaces such as submarines and spacecrafts. At present, DAC has become a research hotspot due to the threat of global climate change. Early DAC systems used alkali or alkaline earth metal hydroxide absorbers to extract CO₂ by causticizing or substituting causticizing processes. Such absorption processes require high-quality heat sources (~ 900 °C) for regeneration, thus limiting the application scenarios and increasing operating costs. In contrast, large-scale deployment of DAC by adsorption is technically and economically feasible and is expected to capture 1% of global annual CO₂ emissions in the near future. The energy consumption of the DAC system based on the adsorbent reached 0.113−0.145 MJ/mol CO₂. If the system is applied to a DAC on a large scale, the capture cost will be reduced to USD 60−190 /t CO₂. The DAC is still in its early stages of deployment. The development of low-cost adsorbents with large adsorption capacities, fast kinetics, and low decay rates is critical for reducing the operating and maintenance costs of the DAC process. In addition, in the development of DAC technology, attention should be paid to the pressure drop in the adsorber system. New gas-solid contactors with structured adsorbents can effectively reduce the power consumption of fans, and steam purge at negative pressure can reduce the regeneration temperature of the DAC, making it possible to couple renewable energy or regenerate industrial waste heat.

(6)  Design of key materials for high-efficiency proton exchange membrane (PEM) hydrogen production reactor

Water electrolysis based on proton exchange membrane (PEM) has many advantages, including a compact structure, low ohmic loss, high current density, and high hydrogen purity. However, high voltage and strong oxidizing environments pose much higher requirements for the durability of key materials of water electrolysis stacks based on PEM. PEM-based water electrolysis cell stacks are mainly composed of membrane electron assemblies (MEAs), gas diffusion layers (GDLs), bipolar plates, collector plates, and endplates. The MEA is composed of anode and cathode catalytic layers on both sides of the PEM. The durability of PEMs and electrocatalysts for hydrogen evolution and oxygen evolution has always required and urgent and efficient action/solution. In addition, the cost of PEM water electrolysis cannot be ignored. Both the anode and cathode GDLs of PEM water electrolysis are made of titanium, as it is difficult for the carbon fiber to meet the corrosion resistance requirement. As the anode bipolar plates, collector plates, and endplates should be more resistant to corrosion, they are also mainly made of titanium; however, the cathode can be made from graphite, stainless steel, and other metal materials that will require special treatment. The formation of a passive film on the surface of titanium materials increases the ohmic loss; thus, pretreatment is required, such as platinum plating. In addition, it is also difficult, time- consuming, and expensive to process titanium materials.

(7)   Mechanism and coupling experiments of digital reactor with multi-physical field and multi-space-time scale

With the development of information technology, numerical algorithms, and the improvement in supercomputing capabilities, the design, development, and operation of reactors are becoming digitalized and intelligentized. Digital reactors have adopted model-based systems engineering methods, large amounts of test data, and high-precision calculation software. On the one hand, digitalization and intelligent algorithms can promote the rapid iterative optimization of the forward design of the reactor; on the other hand, multi-professional high-precision software can be used to verify and predict the behavior characteristics of the reactor to support design verification and operation, so as to save research and development cost, shorten research and development cycle, and improve reactor performance. The successful research and development of digital reactors must solve the following key problems: neutron transport, working fluid flow and heat transfer, fuel material behavior evolution and other professional mechanism problems, accurate and stable solutions of coupling problems across multiple time and space scales in multiphysics, support for universal use mechanism tests and precise measurements required for advanced model research, large amounts of reactor operation and test data, comprehensive integration of multi-source heterogeneous data and software in various disciplines, multi-objective comprehensive optimization algorithms, and efficient parallel algorithms. Currently, digital reactors are mainly used in pressurized water reactors. In the future, they will continue to be expanded to other types of reactors to improve reactor research and development, design, operation, and maintenance capabilities.

(8)   Physical and experimental verification of China Fusion Engineering Test Reactor (CFETR)

The China Fusion Engineering Test Reactor (CFETR) is the next tokamak fusion device planned in the magnetic confinement fusion development roadmap of China, whose operation will be divided into two phases: In the first phase, 200 MW fusion power and tritium self-sustained steady-state operation will be realized; in the second stage, 1 000 MW fusion power will be achieved, and the fusion power output will be demonstrated. CFETR will focus on solving the physical and technical engineering problems between international thermonuclear fusion experimental reactor program (ITER) and Fusion Demonstration Reactor (DEMO), including the realization of steady-state operation of deuterium-tritium fusion, the proliferation and cyclic self-sustainment of kilogram- level tritium, and the development of material technology that can withstand high thermal load and strong neutron irradiation for a long time, to lay a solid foundation for China to independently build fusion power stations by 2050. In recent years, the overall design team of the national magnetic confinement fusion reactor has conducted a detailed physical engineering design of the CFETR and established a world- class research and development platform.

The physical design and integrated engineering design of CFETR (large radius is 7.2 m, small radius is 2.2 m) are currently in progress. In terms of physical design, the overall design team of the national magnetic confinement fusion reactor is conducting research on the corresponding operation schemes of the steady-state and hybrid operating modes of CFETR based on the 1.5-dimensional integrated simulation program under the OMFIT framework, comparing it with the 0-dimensional program. OMFIT uses more advanced and accurate physical models to perform detailed integrated simulations for the device, which can predict the performance of the fusion reactor and optimize the auxiliary heating systems and diverter components more accurately. In terms of engineering design, the detailed design of superconducting magnets and cryogenics, vacuum chambers and internal components of the device (cladding, diverter, etc.), cladding and tritium plants, and remote operation and maintenance systems have been performed. The “Integrated Research Facility for the Key System of Fusion Reactor” project, a major scientific and technological infrastructure in the 13th Five Year Plan of Hefei Comprehensive National Science Center, is under construction, and the CFETR integrated engineering design research project (2017−2021) is progressing smoothly. This research and its progress, projects, and implementation will lay a solid foundation for developing fusion energy in China.

(9)  Research on climate change based on the Earth System Model (ESM)

The Earth system is composed of the atmosphere, hydrosphere, cryosphere, biosphere, lithosphere, mantle, core, solar-terrestrial space, and human activities. Using a holistic view of the Earth system, climate change research based on Earth System Model (ESM) studies the impact of the Earth’s spheres, subsystems, endogenous and exogenous interactions, and the evolution of human activities on climate change and feedback mechanisms; from the Earth evolution perspective, it studies the critical thresholds and triggers for climate change and evaluates the impact of climate change on the evolution of life. The ESM uses the idea of the Anthropocene to establish the status and role of human activities in global changes, quantitatively studying the cascading effects of human activities such as carbon dioxide, methane, and other greenhouse gas emissions on the Earth system, especially the magnitude, rate, and driving mechanism of changes in key global climate and environmental parameters on time scales from ten to 100 years. Furthermore, the ESM quantitatively predicts the catastrophic consequences that human activities may bring to the Earth’s climate and environment, clarifies the human carrying capacity, and critical threshold of the Earth system establishes an early warning mechanism to respond to sudden extreme climate events, and proposes overall scientific solutions.

(10)    Efficient breaking mechanism of hard rock by high temperature and compression

The Earth’s crust contains a large amount of precious mineral resources. Decades of continuous large-scale mining has led to the depletion of shallow mineral resources in China. The development of mineral resources in the future will be at a greater depth (1 000–2 000 m). Deep mining of deeply buried metals will become the norm. On one hand, high ground stress increases the probability of engineering disasters in a deep mining environment, significantly inhibiting the large- scale production of mines. A high subsurface temperature will also reduce labor productivity, induce industrial accidents, and influence the performance of equipment. On the other hand, under the condition of deep high stress, tremendous energy is stored in subsurface hard rocks. Once an appropriate method of inducing fractures is found, catastrophic damage to the rocks can be damaged under controlled conditions. This safe and efficient mining of deeply buried minerals can be conducted under these circumstances.

To date, cutting-edge studies on mining include in situ mechanical behavior of deeply buried mines, long-term stability of deeply buried surrounding rock, stress field and disaster dynamics, multi-field and multiphase seepage under strong disturbance and long-term potentiation, stress and energy fields of deeply buried mines, simulation and visualization, high-stress induction and energy control, rock deformation monitoring, and early warning systems. Non-blasting mining will become the main method for high-temperature and high-stress breaking of hard rocks in the future; it is expected to realize high-stress induced mechanized continuous mining, making deep mining more efficient, intelligent, green, and safe.

(11)  Fundamental theory for the efficient exploitation of shale oil

Shale oil generally refers to oil trapped in source rocks, such as shale. Shale oil resources are abundant in continental basins in China and have been preliminarily estimated to have a technically recoverable resource of 7.4−37.2 billion tons. Shale oil is a key strategic replacement resource for oil and gas accumulation and has great significance in alleviating the outer dependency on oil and gas and ensuring national energy security. There are significant differences in geological conditions between the continental shale oil in China and marine shale oil in North America, including unclear enrichment characteristics and uncertain “sweet-spot” distribution. The exploitation of shale oil in China also faces challenges from an engineering perspective with complicated exploration and development conditions, including a harsh engineering environment and poor resource endowment. Consequently, given these differences, adept shale oil and gas exploitation technology in North America is not applicable to China. In summary, the “sweet-spot” of shale oil and gas exploitation technology in China is still at an early stage, and it is urgent to explore the related theory and technology suitable for the exploration and development of continental shale in China. The main research areas include continental shale oil occurrence mechanism and quality evaluation index system, shale oil reservoir geophysical prediction technology, key ultra-long horizontal well drilling technology, horizontal well “one trip drilling” technology, anti-collapse drilling fluid technology for shale formation, multi-scale complex fracture network fracturing technology in the whole-well section of shale oil reservoirs, shale oil geology-fracturing integrated technology, and shale oil well factory multi-layer system 3D development technology. Breaking through the basic theory and technology of efficient exploitation of shale oil, realizing large-scale shale oil production and accumulation, and triggering the shale oil revolution in China will provide a solid guarantee for China’s energy security.

(12)  Rock burst mechanism and early warning methodology

Rock bursts are a power destabilization disaster caused by the rapid release of accumulated elastic energy from the hard and brittle surrounding rock in a high-stress state under the action of engineering excavation or other load disturbances, resulting in rock exfoliation, fragmentation, and ejection. Rock bursts have the characteristics of suddenness and danger, threatening the safety of construction personnel, machinery, and other equipment. Its main research directions include rock explosion mechanisms, classification, breeding processes, and prediction and control measures. Technical findings show that it is difficult to accurately identify the calm period of microseismic sequences, and it is necessary to find more short-term precursor information. The range of predicted rock burst locations is generally larger than the actual occurrence range, unfavorable for effective rock burst prevention and control. Thus, it is necessary to explore the micro-seismic prediction of high explosive risk areas in conjunction with other physical techniques to achieve more accurate predictions and improve the efficiency of rock explosion prevention and control. As the manual processing of microseismic monitoring data is certain to have human errors and low work efficiency, it is necessary to further study intelligent methods for automatic, efficient, and accurate processing and analysis of microseismic data and the rapid prediction and forecasting of rock bursts.

《1.2 Interpretations for four key engineering research fronts》

1.2 Interpretations for four key engineering research fronts

1.2.1 Regulation and control of theories and methods in power systems using a high proportion of renewable energy

As the largest energy producer and consumer in the world, China’s resource endowment determines that the energy structure of China is based on fossil energy. To achieve carbon peak and neutralization goals in 2030 and 2060, respectively, and promote the transformation of the energy system, it is necessary to build a “clean, low-carbon, safe, and efficient” energy system in which a new generation of electric power systems with a high proportion of new energy is an important link.

Compared with existing power systems, the high proportion of renewable energy will result in strong uncertainty in the power system. The power side has gradually evolved to be dominated by new energy sources such as wind power and photovoltaic power generation, which have a strong uncertainty and uncontrollability in both time and space. On the load side, high electrification leads to a diversified load structure. The active features of the electricity utilization are prominent, and the unpredictability of the load increases. Therefore, the “boundary conditions” of the future power system will be more diversified. To achieve power balance and sufficient capacity of the power system, relevant research needs to change from deterministic to probabilistic thinking to ensure the safety of the entire system.

The grid connection, transmission, and consumption of a high proportion of new energy rely on power electronics devices, leading to a significant trend in power electronization in the power system. It is difficult to apply the basic theory of traditional power systems based on AC technology. The low inertia, weak immunity, and multi-time scale response characteristics of power electronics devices make the time constant of the power system smaller, the frequency domain wider, and the safety domain more complicated. In the case of disturbance, the electromechanical transient and electromagnetic oscillations of the system interact significantly. To ensure the stable and optimized operation of the future power system, it is necessary to redefine its stability zone, system short-circuit rate, and other indicators.

In addition, to give full play to the flexibility of the energy system, in the future, barriers in different energy fields such as electricity, heating, gas, and transportation will be broken, realizing the interconnection of different energy networks, and energy supply and demand balance on a larger scale. Current research in this direction mainly focuses on a small area; as it matures, it is necessary to further consider the impact of factors such as scale effects or network transmission restrictions on its cost and performance.

In the engineering research front of “regulation and control of theories and methods in power systems using a high proportion of renewable energy”, the top three countries in terms of the number of core papers published (Table 1.2.1) are the USA, China, and the UK, all of which have been cited more than 23 times. Among the Top 10 countries with the most published papers, the USA and China have more cooperation, followed by Iran and Portugal (Figure 1.2.1). The institutions that produce a large number of core papers include Tsinghua University, University of Lisbon, and Imperial College London (Table 1.2.2). Among these 10 institutions, University of Lisbon has more cooperation with the University of Beira Interior and University of Porto (Figure 1.2.2). In the amount of citing core papers, the top three countries are China, the USA, and the UK (Table 1.2.3). The main output institutions of citing core papers are the North China Electric Power University, Tsinghua University, and Aalborg University (Table 1.2.4).

1.2.2 Research on inherent safety of nuclear fuel, characteristics of reactor safety mechanism, and multidisciplinary strong coupling mechanism

Small-scale water-cooled reactors are currently the mainstream of small-scale reactor research and development because of their better technical foundation; its main development direction is high system simplification and module integration. However, the current small-scale reactor technology has not broken through the scope of the current pressurized water

《Table 1.2.1》

Table 1.2.1 Countries with the greatest output of core papers on “regulation and control of theories and methods in power systems using  a high proportion of renewable energy”

《Table 1.2.2》

Table 1.2.2 Institutions with the greatest output of core papers on “regulation and control of theories and methods in power systems using a high proportion of renewable energy”

《Table 1.2.3》

Table 1.2.3 Countries with the greatest output of citing papers on “regulation and control of theories and methods in power systems using a high proportion of renewable energy”

《Table 1.2.4》

Table 1.2.4 Institutions with the greatest output of citing papers on “regulation and control of theories and methods in power systems  using a high proportion of renewable energy”

《Figure 1.2.1》

Figure 1.2.1 Collaboration network among major countries in the engineering research front of “regulation and control of theories and

《Figure 1.2.2》

Figure 1.2.2 Collaboration network among major institutions in the engineering research front of “regulation and control of theories and methods in power systems using a high proportion of renewable energy”

reactor in terms of design concepts and safety mechanisms and cannot fundamentally achieve inherent safety. Special safety facilities are still required to alleviate serious accidents. At present, the FCM fuel at home and abroad is mainly focused on replacing existing light water reactor fuel assemblies, and there is no systematic and innovative research on reactor design technology and safety mechanisms. Without breakthroughs in mechanism innovation, inherent safety cannot be realized.

Based on the innovative FCM fuel and advanced core design, superheated steam is generated in the reactor to achieve the ultimate simplification of the system and improve the thermoelectric conversion efficiency. In the event of an accident, the reactor can be shut down automatically, and the residual core heat can be automatically removed by radiation heat exchange to eliminate the risk of large-scale radioactive release and fundamentally achieve inherent safety. This topic can significantly improve small-scale, inherently safe reactor technology research and development capabilities and independent innovation in China.

After the Fukushima incident, the nuclear industry has paid more attention to accident-tolerant fuels. FCM fuel has potential inherent properties owing to its fission product multiple encapsulation structure, high mechanical stability, and excellent thermal conductivity compared to other fuel forms. Safety features are one of the important fuel forms that meet the design requirements of small reactors. The Oak Ridge National Laboratory (ORNL) of the USA conducted an experimental study on the oxidation performance of FCM fuel in a high-temperature water vapor environment, demonstrating its strong corrosion resistance. The Korea Atomic Energy Research Institute (KAERI) and ORNL have jointly conducted research on the use of FCM fuel to replace the current fuel assembly of light water reactors. The preliminary results of this research indicated that FCM fuel has a sufficient safety margin for loss-of-flow accidents and loss-of-water accidents. Domestically, Nuclear Power Institute of China has performed design evaluation for small modular-integrated pressurized water reactors (SM- IPWRs) using the FCM fuel and completed the conceptual design of the FCM fuel assembly, neutronic performance evaluation, thermal performance analysis, and radiation- thermal-mechanical coupling performance. Numerical research and other studies have been conducted on the concept of an ultra-safe smart microreactor. Xi’an Jiaotong University conducted a neutronics design study on a SM- IPWR using the FCM fuel. Results showed that the SM-IPWR concept meets the design standards. Furthermore, Harbin Engineering University launched an innovative conceptual design based on FCM fuel.

The design of a new type of reactor that can achieve inherent safety based on innovative fuels is an important direction for the current reactor design.

According to Table 1.2.5, the countries with the highest output of core papers in this direction are the USA, China, Germany, and South Korea, with the USA accounting for 34.11%, China accounting for 11.46%, Germany accounting for 8.85%, and South Korea accounting for 8.59%. Figure 1.2.3 indicates that China, Germany, and South Korea have relatively close cooperation with the USA.

Table 1.2.6 and Figure 1.2.4 show that the institutions with the largest number of core papers in this research direction are the Idaho National Laboratory, the ORNL, and Los Alamos National Laboratory.

1.2.3 Key technologies and challenges for natural gas hydrate exploitation

The basic idea of natural gas hydrate exploitation is to decompose it into water and natural gas underground and extract the gas. Owing to the high energy density of natural gas hydrate, 1 m3 of natural gas hydrate will ideally release 164 m3 of natural gas. The biggest difference between a hydrate reservoir and conventional gas reservoir is that there is no capping rock or diagenesis, leading to the fact that the conventional natural gas production method is not suitable for hydrated natural gas production. The exploitation of natural gas hydrate, worldwide, is still in the experimental and exploratory stages. Its resource environment is very complex, and the exploitation process may cause environmental and safety problems. Therefore, we should be very cautious about the large-scale commercial exploitation of natural gas hydrates worldwide. At present, research in this field is still in the stage of mechanism discussion, exploiting technology demonstration, and small-scale experimental production. The safe and efficient utilization of natural gas hydrate resources depends on innovations and breakthroughs in engineering technology theory.

There is an urgent need to focus on the four key technologies

《Table 1.2.5》

Table 1.2.5 Countries with the greatest output of core papers on “research on inherent safety of nuclear fuel, characteristics of reactor safety mechanism, and multidisciplinary strong coupling mechanism”

《Table 1.2.6》

Table 1.2.6 Institutions with the greatest output of core papers on “research on inherent safety of nuclear fuel, characteristics of reactor safety mechanism, and multidisciplinary strong coupling mechanism”

《Table 1.2.7》

Table 1.2.7 Countries with the greatest output of citing papers on “research on inherent safety of nuclear fuel, characteristics of reactor safety mechanism, and multidisciplinary strong coupling mechanism”

《Table 1.2.8》

Table 1.2.8 Institutions with the greatest output of citing papers on “research on inherent safety of nuclear fuel, characteristics of reactor safety mechanism, and multidisciplinary strong coupling mechanism”

《Figure 1.2.3》

Figure 1.2.3 Collaboration network among major countries in the engineering research front of “research on inherent safety of nuclear fuel, characteristics of reactor safety mechanism, and multidisciplinary strong coupling mechanism”

《Figure 1.2.4》

Figure 1.2.4 Collaboration network among major institutions in the engineering research front of “research on inherent safety of nuclear fuel, characteristics of reactor safety mechanism, and multidisciplinary strong coupling mechanism”

for a long time in the future, including natural gas hydrate reservoir reconstruction and protection technology, natural gas hydrate reservoir drilling and completion technology and equipment, well bottom gas and water rapid separation technology and equipment, and technology and processes to improve the energy efficiency of hydrate exploitation. With the progress of theory and engineering technology, the exploitation cost of natural gas hydrate will continue to decrease, causing this large-scale clean energy to be eventually used throughout society.

At present, a large number of key papers in this field have been published by countries such as China, Singapore, and India. The number of key papers in China accounts for 65.66%, with a citation frequency of more than 1 500 times (Table 1.2.9). The three scientific research institutions that published the largest number of core papers were from China, which are Chinese Academy of Sciences, Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, and China University of Petroleum, accounting for 38.38% (Table 1.2.10). The countries that focus on cooperation in this field include India and Singapore (Figure 1.2.5). The institutions with the most cooperation are Chinese Academy of Sciences and Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development (Figure 1.2.6). The main output countries citing core papers include China, the USA, and India, with a proportion of core paper citations close to 70% (Table 1.2.11). The main output institutions of citing core papers include Chinese Academy of Sciences,

《Table 1.2.9》

Table 1.2.9 Countries with the greatest output of core papers on “key technologies and challenges for natural gas hydrate exploitation”

《Table 1.2.10》

Table 1.2.10 Institutions with the greatest output of core papers on “key technologies and challenges for natural gas hydrate exploitation”

Dalian University of Technology, and China University of Petroleum (Table 1.2.12).

1.2.4 Multi-information perception and early warning of hidden danger of mine disasters

With the great demand for coal production, the gradual reduction of shallow coal resources, and the continuous increase in mining depth and intensity, the risk of dynamic disasters such as rock bursts, coal and gas outbursts, fires, and water inrush increases, significantly restricting the safe and efficient production of coal mines and posing a severe threat to miners’ safety. The formation process and evolution mechanism of typical dynamic disasters under the condition of multiphase and multi-field coupling are still unclear, and the disaster precursor information collection, sensing, transmission technology, and mining identification technology are still backward, resulting in a lack of disaster risk identification and early warning modules and making early warning of disaster risk difficult. To meet the major needs of coal mine power disaster prevention and control, it is urgent to research the accurate identification, monitoring, and early warning mechanisms and key technologies of coal mine power disaster risk.

The main research in this field includes three aspects: The first is research on the disaster mechanism of typical disasters, including the research on the dynamic mechanism of coal mine rock burst instability and multi-field coupling disaster mechanism, the disaster mechanism of coal and gas outburst, the breeding law of coal spontaneous combustion disaster under a high-temperature environment, and the space-time

《Table 1.2.11》

Table 1.2.11 Countries with the greatest output of citing papers on “key technologies and challenges for natural gas hydrate exploitation”

《Table 1.2.12》

Table 1.2.12 Institutions with the greatest output of citing papers on “key technologies and challenges for natural gas hydrate exploitation”

《Figure 1.2.5》

Figure 1.2.5 Collaboration network among major countries in the engineering research front of “key technologies and challenges for natu- ral gas hydrate exploitation”

《Figure 1.2.6》

Figure 1.2.6 Collaboration network among major institutions in the engineering research front of “key technologies and challenges for natural gas hydrate exploitation”

breeding and evolution law of water inrush disasters. The second is the research on information perception technology, which, with the help of the key technologies and equipment of the mine, the Internet of Things, and human-machine- environment state, multiple information reflecting the temporal and spatial state characteristics and internal key information of various external and internal disasters can be perceived and obtained in real-time. As such, scientific, reasonable, and effective multi-information perception and early warning analysis methods have been proposed, and the theory and technology of intelligent identification and early warning of multi-parameter precursor information of typical dynamic disasters in coal mines has been developed. The last part is the research on multivariate data processing methods. Based on multivariate heterogeneous big data, the multivariate and massive information is integrated to inversely deduce the temporal and spatial evolution law of mine disasters by utilizing data mining, artificial intelligence, cloud computing, and other means to realize the quantitative and accurate identification of precursor characteristics throughout the process of single major disasters, coupling disasters, and derivative/secondary disaster evolution dynamic risk capture and automatic early warning to reduce major risks and hidden dangers, providing support to improve the accuracy and soundness of mine disaster supervision.

Among the major coal-producing countries in the world, China faces the most serious security threat caused by deep mining and has invested more in research and development. Regarding the engineering research front of “multi-information perception and early warning of hidden danger of mine disasters”, China and the USA have the largest number of core papers, accounting for 69.86%, while the UK and Italy have the highest number of citations per paper (Table 1.2.13). The institutions with the highest output of core papers are China University of Mining and Technology, University of Science and Technology Beijing, and Xi’an University of Science and Technology (Table 1.2.14). China, the USA, and Australia have more cooperation (Figure 1.2.7). In the institutions with a large output of papers, China University of Mining and Technology have the closest cooperation (Figure 1.2.8) with University of Science and Technology Beijing. The main output countries of citing core papers are China and the USA, accounting for more than 60% of the total publication. The citation year was concentrated in 2019 (Table 1.2.15). The main output institutions of citing core papers are China University of Mining and Technology, Chinese Academy of Sciences, and Shandong University of Science and Technology, accounting for 49.62% (Table 1.2.16).

《2 Engineering development fronts》

2 Engineering development fronts

《2.1 Trends in Top 12 engineering development fronts》

2.1 Trends in Top 12 engineering development fronts

The Top 12 engineering development fronts assessed by the

《Table 1.2.13》

Table 1.2.13 Countries with the greatest output of core papers on “multi-information perception and early warning of hidden danger of mine disasters”