To explore the development status and safety of nuclear power



A nuclear power equipment industry overview

Nuclear power plant definition and classification

According to the reactor form, nuclear power plants are mainly divided into pressurized water reactor, boiling water reactor, heavy water reactor and fast reactor nuclear power plants, of which pressurized water reactor nuclear power plants are the most widely used, and the future is to develop fast reactor nuclear power plants with higher efficiency and safety.

A nuclear power plant is a facility that converts nuclear energy into electricity through appropriate devices. The third-generation nuclear power plant can be divided into light water reactors, heavy water reactors and fast neutron reactors according to the reactor form, of which light water reactors can be divided into pressurized water reactors and boiling water reactors according to the light water form.

Nuclear power equipment Introduction

The nuclear power equipment is divided into three parts: nuclear island, conventional island and auxiliary system, of which the nuclear island is the core of the entire nuclear power plant, responsible for converting nuclear energy into heat energy, the conventional island uses steam to generate electricity, and the auxiliary system is to ensure the smooth operation of the nuclear power plant.

Nuclear power equipment is divided into nuclear island, conventional island, BOP (other auxiliary equipment). The nuclear island is the core of the entire nuclear power plant, responsible for converting nuclear energy into heat energy, and is the most complex and costly part of the nuclear power plant. Conventional Island uses steam to drive steam turbines to drive engines to generate electricity. Auxiliary system (BOP) mainly includes digital control system, HVAC system, air cooling equipment and loading and unloading machine, which is used to ensure the smooth operation of nuclear power plant.

The core part of the nuclear island is the reactor, which is composed of core fuel, control rods and coolant. The core fission produces neutrons and energy, and the control rods are used to regulate the reactor power. The control rods are mainly composed of boron, which absorbs the neutrons produced in the reactor and regulates the power by adjusting the insertion of the control rods into the core fuel.

To prevent excessive heat in the reaction, light or heavy water is used as a coolant to reduce the temperature inside the reactor. The nuclear island structure of boiling water reactor is different from that of pressurized water reactor and heavy water reactor.

As shown in the figure, the cooling light water in the boiling water reactor nuclear power plant directly forms steam in the pressure vessel, and the pressurizer and evaporator need to be added to the pressurized water reactor and the heavy water reactor to form a second circuit.

Conventional island consists of steam turbine, generator and cooling system. The coolant converts the heat in the reactor into steam and sends it to the conventional island, where the steam drives the turbine to produce mechanical energy, which is transferred to the generator and converted into electrical energy. The steam drives the turbine and is transferred to the condenser where it is liquefied to form a new coolant.

China's nuclear power equipment industry chain

Industrial chain graph

The upstream of the nuclear power equipment industry chain is the raw materials required for production, the midstream is the nuclear island equipment, conventional island equipment and auxiliary equipment three types of nuclear power equipment, and the downstream is the operation of nuclear power plants, and the operation of nuclear power plants is in the monopoly of three state-owned enterprises.

Upstream analysis

The main cost of nuclear fuel comes from uranium, and our country is facing a shortage of uranium ore resources, highly dependent on resource imports, our government is through technology upgrading and overseas acquisition to solve the problem of external dependence is too high.

The core material of the nuclear fuel rod is the fuel pellet, composed of uranium dioxide, which is the main raw material for the heat generated by the fission reaction.

Uranium dioxide is extracted from natural uranium, and uranium ore needs to go through the process of exploration and exploitation, hydrometallurgy, uranium conversion and uranium enrichment, and finally sent to the nuclear fuel processing plant to manufacture nuclear fuel elements. In the nuclear fuel cost structure, natural uranium accounts for the highest proportion, reaching 49%.

Chinese companies engaged in uranium mining and import and export are required to obtain a government license, and only CNNC and CGN are qualified to engage in such business.

Due to the high technical difficulty and national security significance of nuclear fuel element development, nuclear fuel manufacturing in China is monopolized by CNNC North Nuclear Fuel Element Co., Ltd. and CNNC Jianzhong Fuel Element Co., LTD., which are owned by CNNC Group, and nuclear fuel element enterprises have strong bargaining power.

Most of China's uranium resources belong to unconventional uranium, low grade, deep burial, and expensive mining costs, so China's uranium resources production is low, can not meet its own nuclear power development needs, supply and demand imbalance, can only rely on imports. In 2017, the external dependence of uranium resources in China was as high as 85.9%, far exceeding the international warning line of 50%.

Nuclear raw materials subject to the international market will restrict the development of China's nuclear power industry, so China set out to adopt the following methods to solve the problem of excessive dependence on uranium resources.

First, the use of new technology to search for uranium deposits;

Second, establish cooperation projects with countries rich in uranium resources;

Third, investment in overseas uranium mines;

Fourth, vigorously develop the fourth-generation nuclear power technology to reduce the demand for uranium resources.

Nuclear fuel cycle can improve the utilization rate of uranium resources, but our country's spent fuel reprocessing technology is not mature enough, the main solution is still off-reactor storage, and off-reactor storage capacity has tended to saturation, spent fuel processing will become a factor restricting the development of nuclear power in our country.

Nuclear fuel in the reactor by neutron bombardment nuclear reaction, after a certain period of time, nuclear fuel uranium content decreased, can not continue to maintain the nuclear reaction, discharged from the reactor. The discharged fuel is called spent fuel, which contains a large number of radioactive elements and is strongly radioactive, requiring strict handling procedures to ensure safety.

The spent fuel discharged from nuclear power plants contains 95 percent uranium (U-235 and U-238) and 1 percent plutonium, and after reprocessing, U-235 can be converted into fuel. The nuclear fuel cycle can increase the utilization rate of uranium resources by 30%.

However, China's reprocessing technology is not mature enough, and the operation cost is high, processing a ton of spent fuel to generate at least 45 tons of high-level waste, 150 tons of medium radioactive waste, 2,000 tons of low radioactive waste. Until 2021, the main solution for spent fuel is off-reactor storage.

The spent fuel produced by nuclear power plants is related to the plant equipment capacity, and the annual output of spent fuel is about 21 tons per 1 million kilowatts of nuclear power equipment capacity. It is estimated that in 2020, China's spent fuel production has reached 1,071.6 tons, while the spent fuel reprocessing capacity is only 50 tons, which cannot meet the processing demand.

According to China's nuclear power development plan, by 2030, nearly 2,000 tons of spent fuel will be generated every year, and the accumulated spent fuel will be about 24,000 tons, and the storage demand from the reactor will reach 15,000 tons. As of 2021, China has not yet formed reprocessing industrial capacity, and off-reactor storage capacity is also tending to saturation.

Spent fuel disposal will become an important factor restricting the development of nuclear power in China. The construction cost of spent fuel reprocessing plants is high and the construction period is long, with an average construction period of 10 years, so the demand for spent fuel treatment is difficult to meet in the short term.

Midstream analysis

Nuclear power equipment is the most expensive part of nuclear power plant investment and construction, and the degree of nuclear power autonomy mainly depends on the degree of nuclear power equipment autonomy. Among them, nuclear island equipment accounts for the highest proportion in the whole nuclear power equipment because of its technical characteristics.

Nuclear power equipment accounts for the highest cost in the construction of nuclear power plants, its proportion is as high as 50%, because nuclear power equipment is the most critical part of the nuclear power industry chain, and the degree of nuclear power autonomy mainly depends on the degree of nuclear power equipment autonomy.

The nuclear island cost accounted for the highest proportion of nuclear power equipment, reaching 58%, because the nuclear island process is complex, and the safety requirements are extremely high, and the key components in the nuclear island are monopolized by state-owned enterprises due to the high manufacturing process requirements.

After the marketization of nuclear secondary and tertiary equipment was opened in 2015, the price of conventional island and auxiliary system decreased significantly, and the cost ratio also decreased correspondingly.

The components of the nuclear island are fine and diverse, among which the reactor pressure vessel, the main pipeline, the heat exchanger and the steam generator are the three main components of the nuclear island.

The pressure vessel cost accounted for the highest proportion, reaching 23%, because the pressure vessel is the second barrier to prevent the escape of radioactive fission products, bearing an extremely important safety barrier role, so the quality standard of the pressure vessel is very strict, and the manufacturing cost is also high.

Nuclear grade valves are used in the nuclear island, but the cost proportion has gradually decreased, accounting for only 12% in 2019, and the decrease in cost is due to the improvement of the degree of localization of nuclear grade valves, and the price of domestic nuclear grade valves is only 11.5% of that of imported nuclear grade valves, and by 2021, the degree of localization of valves has reached 80%.

The conventional island is mainly composed of pipe system, condenser, steam turbine, generator and steam separation reheater.

Pipeline system and condenser are important equipment to ensure the safe operation of nuclear power plants. The condensing system composed of pipeline, pump and condenser is used to cool the reactor and transport the heat energy in the reactor, and maintain the temperature balance of the reactor, so the technical requirements are higher and the cost is higher.

Pipeline system and condenser are important equipment to ensure the safe operation of nuclear power plants. The condensing system composed of pipeline, pump and condenser is used to cool the reactor and transport the heat energy in the reactor, and maintain the temperature balance of the reactor, so the technical requirements are higher and the cost is higher.

The conventional island is mainly composed of pipe system, condenser, steam turbine, generator and steam separation reheater.

Pipeline system and condenser are important equipment to ensure the safe operation of nuclear power plants. The condensing system composed of pipeline, pump and condenser is used to cool the reactor and transport the heat energy in the reactor, and maintain the temperature balance of the reactor, so the technical requirements are higher and the cost is higher.

Conventional island equipment supply a wide range.

Thermal power, hydropower and other types of power generation principle is similar to nuclear power, are driven by mechanical energy generator conversion into electrical energy, conventional island equipment in addition to nuclear power, but also supply thermal power, hydropower and other types of power generation. Therefore, in addition to some core equipment, the cost of the rest of the equipment is relatively low.

The nuclear island equipment has high technical barriers and fewer market participants, mainly dominated by state-owned enterprises, and private enterprises only participate in the manufacturing of some components, so the gross profit margin of nuclear island equipment is generally high, and the average gross profit margin of core equipment is more than 40%.

Most of the conventional island equipment has no special technical requirements, low technical barriers, more market participants than the nuclear island equipment market, the competition is relatively fierce, so the gross profit rate is low, the average gross profit rate is only 10%

Downstream status

China's nuclear power plants are distributed in the coastal areas, because of the large power demand in the coastal areas and the coastal areas are more conducive to the discharge and treatment of nuclear power plants. However, with the rise of inland economies, nuclear power plants will show a trend of internal relocation.

China's nuclear power plants are distributed in the coastal areas, from the perspective of power demand, the coastal area is more economically developed than the inland area, the power demand is also larger. The greater installed capacity of nuclear power in Guangdong and Zhejiang is related to the high level of local economic development.

From the point of view of site selection, nuclear power plants need a large amount of cooling water, and the cost of seawater as cooling water is much lower than that of using inland fresh water as cooling water. At the same time, the discharge of waste water from nuclear power plants is also an important factor that needs to be considered. Coastal areas can directly use seawater for dilution, while rivers and lakes in inland areas are mostly drinking water sources for residents and are widely used for agricultural irrigation and other purposes. Inland residents are more sensitive to the safety of emissions and have a certain psychological resistance. But as landlocked economies rise and demand for electricity increases, nuclear plants will move inwards.

Market size of China's nuclear power equipment industry

China's nuclear power equipment market scale will expand with the restart of China's nuclear power industry, China's nuclear power equipment market scale is expected to reach 473.2 billion yuan in 2025, the compound growth rate of the next five years is 3.77%.

Market size of nuclear power equipment in China, Forecast 2016-2025

China's installed nuclear power capacity in 2020 has reached 51.027 million kilowatts. By 2025, it is expected that the installed capacity of nuclear power in China will reach 70 million kilowatts and 30 million kilowatts are under construction. Considering the problem of slow payback time in the nuclear power industry, the market size is calculated only by the capacity of completed units.

According to experts, the unit cost of a nuclear power plant is between 11,000 yuan and 18,000 yuan per kilowatt.

China's nuclear power construction is facing the challenge of cost reduction, the cost reduction of nuclear power unit cost is mainly through improving the construction method, and does not involve the reduction of nuclear power equipment price. In the next three years, the proportion of nuclear power equipment in nuclear power investment will increase.

The nuclear island equipment manufacturing process is unchanged in the short term, and it is difficult to produce scale effects, so the price of nuclear island equipment will remain unchanged. The price of conventional island and auxiliary system has been adjusted in the short term after China announced the marketization of nuclear II and III in 2015, and the selling price and gross profit margin have been significantly reduced. In the period from 2018 to 2020, the price has basically remained stable, and the future is expected to have a small decline of about 3%.

The market share of nuclear power equipment can be obtained by calculating the investment in nuclear power plant construction and the proportion of nuclear power equipment in the cost of nuclear power construction.

Safety analysis of nuclear power equipment -- analysis of Chernobyl accident

The main causes of the Chernobyl accident were human error and the design defects of the nuclear power plant itself, and the defects of the Chernobyl nuclear power plant have been completely avoided in the design of the third generation nuclear power plant. The Chernobyl nuclear power plant accident occurred because of human error and the nuclear power plant's own design flaws.

After the power dropped rapidly to 30MWt, a large amount of xenon gas appeared inside the reactor, and xenon gas and water absorbed a large amount of neutrons, making it difficult to increase the reactor power in a short time. In order to reach the power required for the test as soon as possible, the operator shut down the automatic control system and pulled out almost all the control rods. At this time, the reactor core reaches the prompt critical, the power rises rapidly and breaks through the rated power, and the reactor temperature is too high, resulting in a steam explosion. After the explosion, the graphite contacts with the air to produce hydrogen, and a secondary explosion occurs.

There are two flaws in the plant's design.

The front section of the RBMK control rod is made of graphite, and when it is completely removed from the core, it is lowered into the core to provide a small increase in reactor power before normal power reduction.

So the SCram button doesn't shut down the reactor it accelerates the reactor power rise; At the same time Chernobyl used a positive void coefficient, and as the space occupied by steam in the core increased (boiling increased) the fission reaction also accelerated (reactor power increased) after the RBMK reactor accident.

Safety analysis of nuclear power equipment -- analysis of Fukushima nuclear Power Plant accident

The Fukushima nuclear power plant delayed the optimal emergency repair time, resulting in excessive temperatures in the pressure vessel and melting fuel rods. Zirconium wrapped around the fuel rods came into contact with water and produced hydrogen, triggering the explosion.

Immediately after the tsunami in Fukushima, Japan, workers inserted control rods into the core material to shut it down, but the condensing system needed to keep operating because there was still residual heat in the core after the shutdown, and the core fuel would decay and continue to release heat, and the core would take several days to completely cool

However, the external network of the Fukushima nuclear power plant was destroyed, the condensation system lost power supply and could not work, and the nuclear power operation system was in an unbalanced state. Without an engine to drive the pumps to condense the water over and over again, the heat in the pressure vessel will continue to rise, eventually melting the fuel in the core.

The fuel in the core is coated with zirconium. When the fuel gets too hot, the zirconium flows into the water and causes an oxidation reaction to release hydrogen, which accumulates and causes an explosion. Only after the explosion did workers begin pumping seawater into the reactor to cool its core.

In the Fukushima nuclear power plant accident in Japan, earthquake and tsunami are only the fuses, and human factors are the main reasons.

The emergency measures prepared by Tokyo Electric Power after the external network was cut off were not sufficient, and after the battery maintained the condensation system for 8 hours, the generator power was not provided in time, and after the temperature in the reactor was too high, the seawater was not injected into the reactor in time for cost reasons, delaying the ordinary accident to a level 7 nuclear accident.

China has formulated strict management measures for the operation of nuclear power plants, conducted safety training for nuclear power plant personnel, and responded to accidents in a timely manner to avoid major nuclear accidents caused by human factors.