Pressurized water reactor reliable or boiling water, nuclear power plant Advantages and disadvantage

There is no more reliable, there is a difference between the two Boiling water reactor (boiling water reactor) is literally a reactor that uses boiling water to cool nuclear fuel, and its working principle is: cooling water flows from the bottom of the reactor into the core, cools the fuel rods, takes away the heat energy generated by fission, the cooling water temperature rises and gradually vaporizes, and finally forms a mixture of steam and water, which passes through a steam water separator and a steam dryer, and uses the separated steam to drive the steam turbine to generate electricity. The Fukushima nuclear power plant was built in the 70s of the 20th century and is a boiling water reactor.

Pressurized water reactor (pressurized water reactor) is literally a kind of reactor that uses high-pressure water to cool nuclear fuel, and its working principle is: the main pump sends 120 160 atmospheres of primary circuit cooling water into the core, brings the heat energy released by the nuclear fuel out of the core, and then enters the steam generator, and transfers the heat to the secondary circuit water through the heat transfer tube, so that it boils and produces steam; The temperature of the primary circuit cooling water drops, enters the reactor core, and completes the primary circuit water circulation; The high-pressure steam generated by the secondary circuit pushes the steam turbine to generate electricity, and then enters the steam generator through the condenser and preheater to complete the secondary circuit water circulation. A total of 13 nuclear power units have been completed or are under construction in China, with the exception of Qinshan Phase III, which uses CANDU reactor technology, and Shandong Rongcheng, which uses high-temperature gas-cooled reactors, and the rest are pressurized water reactors

The advantage of pressurized water reactor is that it is small in size and large in power, and aircraft carriers and nuclear submarines use this, which is recognized as the safest and most reliable in the world, and now 64% of the world's nuclear power plants are pressurized water. The disadvantage is that the cost is also higher than that of boiling water. Boiling water reactors, which are thermally efficient, simpler, and potentially safer, have the disadvantage of increasing water pressure due to the fact that boiling water increases water pressure, so that the radioactive water can leak out suddenly.

If nothing happens, it's the safest) China's also useful nuclear power plants have pressurized water reactors, which can continue to add fuel when the power of the nuclear power plant is at its maximum, a bit like overclocking the CPU. Fast breeder reactors were long ago discontinued in the United States, the United Kingdom, France and Germany due to safety concerns, although countries such as India, Russia and China still have plans to use them.

Boiling water reactors and pressurized water reactors are both light water reactors, which have the advantages of compact structure, safety and reliability, low construction cost, and strong load following capacity, and their power generation costs are comparable to those of conventional ones.

Thermal power plant competition. Both must use low-enriched uranium fuel and saturated steam turbines.

Boiling water reactor systems are simpler than pressurized water reactors, in particular, eliminating the need for steam generators.

The weak link of this PWR reduces a major source of failure. The recirculation piping of a boiling water reactor is much thinner than the loop piping of a PWR, so the severity of a pipeline rupture accident is much less severe. Some boiling water reactors also replace off-reactor recirculation pumps and jet pumps with in-reactor recirculation pumps, and cancel off-reactor recirculation pipelines, further reducing the probability of accidents.

The treatment of water loss accident in boiling water reactor is simpler than that of pressurized water reactor, because the positive liquid mass of boiling water reactor is always in boiling state, and the accident working condition is similar to normal working conditions, while the pressurized water reactor works normally in the supercooling state, and the volume boiling occurs during the water loss accident, which is quite different from the normal working condition. Secondly, there are two subsystems in the emergency core cooling system of the boiling water reactor that spray water directly from the top of the core, while the emergency water injection of the pressurized water reactor generally has to pass through the loop pipeline to inject cooling water from the bottom of the core.

The flow power of a boiling water reactor has more flexibility than that of a pressurized water reactor.

Boiling water reactors produce steam directly, in addition to the radioactivity of high-temperature steam that is in direct contact with the core.

In addition to the problem, there are gases and volatility when the fuel rods are broken.

The fission products will directly pollute the steam turbine or positive system, so the quality requirements of the fuel rods are higher than those of pressurized water reactors.

Due to the lower burn-up depth (about 28,000 MW·d t) of boiling water reactors (about 28,000 MW·d t) than pressurized water reactors, although the enrichment of fuel is also lower, the natural uranium requirement for the same power generation is greater than that of pressurized water reactors.

In addition to a large number of control rod openings at the bottom of the pressure vessel of the boiling water reactor, there are also neutron detector openings, which increases the possibility of small water loss accidents. The control rod drive mechanism is complex, the reliability requirements are high, and the maintenance is difficult.

The boiling water reactor control rods are introduced from the bottom of the reactor, so the possibility of transient failure to fail to shut down the reactor is greater than that of the PWR.

Failure to emergency shutdown is expected to be transient when the control rod should be inserted into the core in the event of some accident and failed to be inserted due to mechanism failure.

In view of the shortcomings of BWR in terms of technology and safety performance, GE of the United States.

United Japan Hitachi.

The final design of an advanced boiling water reactor developed and designed by Toshiba on the basis of BWR is more advanced, safer, more economical and more simplified than BWR, and has been approved by the U.S. Nuclear Regulatory Commission (NRC). The world's first ABWR, Japan's Kashiwazaki Kariba Unit 6, started construction in 1991 and was officially put into commercial operation in 1996.

Main Differences Between Heavy Water Reactor, Pressurized Water Reactor, and Boiling Water Reactor in a Nuclear Power Plant:

A heavy water reactor is a reactor with heavy water as a moderator, which can directly use natural uranium as nuclear fuel. Heavy water reactors can use light water or heavy water as coolant, and heavy water reactors are divided into two types: pressure vessel type and pressure pipe type.

Pressurized water reactors are nuclear reactors that use pressurized light water (i.e., ordinary water) as a coolant and moderator, and the water does not boil in the reactor.

The working process of the boiling water reactor nuclear power plant is as follows: the coolant (water) flows in from the lower part of the core, and in the process of rising along the core, the heat is obtained from the fuel rods, so that the coolant becomes a mixture of steam and water, and the separated steam is used to drive the steam turbine generator set to generate electricity through the steam water separator and steam dryer.

Heavy water reactor nuclear power plant.

According to its structural type, heavy water reactors can be divided into two types: pressure shell type and pressure pipe type. The pressure shell coolant uses only heavy water, and its internal structural material is less than that of the pressure tube type, but it has good neutron economy and a relatively high net yield for the generation of new fuel plutonium-239. This kind of reactor generally uses natural uranium as fuel, and the structure is similar to that of a pressurized water reactor, but due to the large grid pitch, the pressure shell is much larger than that of a pressurized water reactor of the same power, so the maximum power of a single reactor can only be 300,000 kilowatts.

Pressurized water reactor nuclear power plant.

Pressurized water reactor nuclear power plants use light water as a coolant and moderator. It is mainly composed of nuclear steam ** system (i.e., primary circuit system), steam turbine generator system (i.e., secondary circuit system) and other auxiliary systems. After the coolant absorbs the heat energy released by the fission of nuclear fuel in the core, it transfers the heat to the secondary circuit through the steam generator to generate steam, and then enters the steam turbine to do work to drive the generator to generate electricity.

There are currently about 440 nuclear power units in operation worldwide, of which the vast majority (about 92%) are light water reactors (LWRs), and the rest are heavy water reactors (PHWRs) and advanced gas-cooled reactors (AGRs). Light water reactors are mainly two types: pressurized water reactors (PWRs) and boiling water reactors (BWRs), of which about 75% are pressurized water reactors, and the vast majority of nuclear power plants put into operation and built in China are pressurized water reactors.

Boiling water reactor nuclear power plant.

The boiling water reactor is composed of a pressure vessel and a fuel element in the middle, a cross-shaped control rod and a separator. The separator is located in the upper part of the core, and its function is to separate the steam and water droplets, prevent water from entering the turbine, causing damage to the turbine blades. Boiling water reactors use the same fuel and fuel assemblies as PWRs.

Boiling water acts as both a moderator and a coolant.

A boiling water reactor differs from a pressurized water reactor in that the cooling water is kept at a lower pressure (about 70 atmospheres) and the water passes through the core into about 285 steam and is introduced directly into the turbine. As a result, boiling water reactors have only one circuit, eliminating the need for leak-prone steam generators, making them simple.

Pressurized water reactors utilize light water (plain water H2O) as a coolant and neutron moderator. The cooling system consists of two circulation circuits. The primary circuit is connected to the core and the steam generator in the secondary circuit, and the pressure in the circuit is maintained at about 150 atmospheres, at which the cooling water can be heated to about 343 without boiling.

The cooling water is heated to boiling (about 260 degrees Celsius) in the heat transfer tube of the secondary circuit steam generator, and the water vapor formed (after filtering out the mixed liquid water) is sent to the steam turbine through the secondary circuit to drive the turbine to run. The primary loop water, which releases heat energy in the heat transfer tube, flows back to the core at a temperature of about 290 to complete the primary loop circulation. The secondary circuit water flowing from the steam turbine is condensed into liquid water by the condenser and then returned to the steam generator to complete the secondary circuit circulation.

The reactor core is located inside a pressure vessel and consists of fuel assemblies arranged in a square shape. The fuel is generally sintered uranium dioxide with an enrichment of 2%. Compared with boiling water reactors, PWR cores are smaller in size, and the power density of the core is larger (the core power density of large PWRs can reach 100 kWl), and the power generation efficiency of PWRs is about 33%; However, since the working pressure and temperature in the core are higher than those of boiling water reactors, the requirements for reactor material performance are also higher than those of boiling water reactors.

Boiling water reactors use light water (ordinary water H2O) as a coolant and neutron moderator. The pressure inside the reactor cooling system is maintained at 70 atmospheres. Here, the feed water from the steam turbine enters the pressure vessel and boils at around 280.

The mixture is filtered out of liquid water by a separator and steam dryer above the core and sent directly to the steam turbine. The steam leaving the turbine is condensed into liquid water (feed water) through the condenser and then returned to the reactor to complete a cycle. Because the primary steam in the boiling water reactor goes directly to the steam turbine, the system is called a direct circulation system.

Since the heat transfer rate of the core is directly determined by the circulation rate of the water in the system, large boiling water reactors are equipped with jet pumps outside the core shroud to speed up the circulation.

Compared with pressurized water reactors, boiling water reactors are simpler in structure, and greatly reduce the low working pressure and core temperature of the reactor, thus significantly improving the safety of the reactor and reducing the cost. However, because the circulating system of the boiling water reactor is directly connected to the reactor core and the steam turbine, it can cause radioactive contamination of the steam turbine, causing problems in design and maintenance.

1. The mature heavy water reactor is only the CANDU reactor type, and there are two in the third phase of Qinshan in China, but the operating performance is very average, and its main advantage is that it does not stop piling and refueling, and does not need to enrich uranium, but it is of little significance now. Keep piling and refueling, but it has to be stopped and overhauled like pressurized water reactors.

2. The boiling water reactor has the advantage of missing a loop, but the Fukushima accident almost sentenced it to death, at least in our country, this thing has not been considered much. Its disadvantages, for example, the control rod is inserted upward, unlike the PWR, which has the inherent safety problem of losing power and falling the rod.

3. Pressurized water reactors, except for the third phase of Qinshan in China, other commercial reactors are all there. The technology is mature and the operation experience is rich. In China, M310 and its derivative reactors are the majority.

But the new generation also has AP1000 and the system is a bit too big, and of course the power is also high. AP1000 represents a new concept, and the system used in normal production is not much different from the second-generation reactor, but the safety-related system is passively designed, and I personally believe that AP1000 represents a mainstream development direction.

July 24 22:13 At present, there are only two types of reactors used in submarines: pressurized water reactors and sodium-cooled metal reactors.

The vast majority of submarines in the world use pressurized water reactors because people are more aware of the performance of water and are easy to control. The metal stack has good heat transfer and high efficiency, but the biggest problem is that the corrosion of the system material is difficult to solve and often leaks. So it is used less, only in Russia.

High-temperature gas-cooled reactors are reactors developed from ordinary graphite gas-cooled reactors. The working principle is: graphite is used as a moderator, and gas helium is used as a coolant (this is "gas cooling"), and the temperature of helium is as high as about 800 degrees (this is "high temperature").

The specific process is that when the nuclear fuel in the reactor undergoes a nuclear reaction, neutrons are released, and the neutrons that are too fast are slowed down by graphite collision (because only slow neutrons can react effectively with uranium fuel in this reactor) to maintain the nuclear reaction. A large amount of heat is released during the nuclear reaction, and if the heat is not taken away, the reactor will be burned, so gas (helium) is used to flow through the core, bringing the heat to the heat exchanger, and then the helium is cooled by another coolant, and the cooled helium returns to the core to continue to cool the reactor, forming a closed circulation loop.

This is the simplest principle of a high-temperature gas-cooled reactor. At present, the most used in the world is pressurized water reactors, especially on nuclear submarines, which are basically pressurized water reactors, and there is absolutely no high-temperature gas-cooled reactor on nuclear submarines in various countries (including China), and its volume is too large.

Fusion reactors are even less talkative, the reason for the "spicy cigarette" upstairs has already been elaborated, and will not be repeated.