What is nuclear power
Nuclear power generation involves nuclear fission of uranium in a nuclear reactor and the use of steam generated by the heat associated with the fission reaction. The nuclear reactor and uranium fuel are respectively analogous to the boiler and oil or coal fuel in thermal power generation.
The security of energy supply is a critical issue for many countries, hence nuclear energy is used to service a large portion of the electricity demand in those countries. Nuclear power generation is characterized by good availability of uranium as fuel, the capability to supply electricity stably for a long period, and the capability to recycle fuel. Nuclear power, therefore, is an indispensable power generation method in the developed nations. Another significant advantage of nuclear power is that it does not emit carbon dioxide (CO2) during power generation.
Because uranium, used as fuel for nuclear power generation, is a radioactive material, multilayered safety measures are taken based on the "defense in depth" concept, so that radioactivity will not be released in the event of an accident.
Nuclear power generation involves nuclear fission of uranium in a nuclear reactor and the use of steam generated by the heat associated with the fission reaction. The nuclear reactor and uranium fuel are respectively analogous to the boiler and oil or coal fuel in thermal power generation.
The security of energy supply is a critical issue for many countries, hence nuclear energy is used to service a large portion of the electricity demand in those countries. Nuclear power generation is characterized by good availability of uranium as fuel, the capability to supply electricity stably for a long period, and the capability to recycle fuel. Nuclear power, therefore, is an indispensable power generation method in the developed nations. Another significant advantage of nuclear power is that it does not emit carbon dioxide (CO2) during power generation.
Because uranium, used as fuel for nuclear power generation, is a radioactive material, multilayered safety measures are taken based on the "defense in depth" concept, so that radioactivity will not be released in the event of an accident.
Mechanism of Nuclear Power Generation
In nuclear power plants, uranium fuel undergoes nuclear fission and generates an enormous amount of heat. The heat makes high-temperature and high-pressure steam that rotates turbines to generate electricity.
Light Water Reactor (LWR)
LWRs use light water (normal water) as coolant and moderator. Coolant removes heat produced during nuclear fission from a reactor core. Moderator reduces the speed of neutrons produced in nuclear fission to facilitate further fission reaction and sustain a chain reaction.
There are two types of LWRs - a boiling water reactor (BWR) and a pressurized water reactor (PWR). Each type is adopted in almost equal numbers in Japan.
Boiling Water Reactor (BWR)
The same water loop serves as a steam source for turbines.
In nuclear power plants, uranium fuel undergoes nuclear fission and generates an enormous amount of heat. The heat makes high-temperature and high-pressure steam that rotates turbines to generate electricity.
Light Water Reactor (LWR)
LWRs use light water (normal water) as coolant and moderator. Coolant removes heat produced during nuclear fission from a reactor core. Moderator reduces the speed of neutrons produced in nuclear fission to facilitate further fission reaction and sustain a chain reaction.
There are two types of LWRs - a boiling water reactor (BWR) and a pressurized water reactor (PWR). Each type is adopted in almost equal numbers in Japan.
Boiling Water Reactor (BWR)
The same water loop serves as a steam source for turbines.
- A reactor pressure vessel is made of steel and fuel assemblies are installed inside.
- A control rod controls the power of a nuclear reactor. By inserting control rods, excessive fission is prevented.
- A reactor containment vessel, made of steel, accommodates a reactor pressure vessel.
Pressurized Water Reactor (PWR)
The primary water loop transmits heat through the tube walls to the surrounding water of the secondary cooling system to generate steam and rotate turbines.
The primary water loop transmits heat through the tube walls to the surrounding water of the secondary cooling system to generate steam and rotate turbines.
Safety Measures at Nuclear Power Plants
Nuclear power plants in Japan have multiple safety measures, which are designed on the assumption that they must ensure the safety of the neighboring communities so that there will be no adverse impacts on their health.
Nuclear power plants are designed to prevent abnormal incidents from occurring. Even if abnormal incidents do occur, nuclear plants are also designed to prevent the potential spreading of abnormal incidents and leakage of radioactive materials around plants, which may cause adverse impacts on the surrounding environment.
Many power plants utilize redundant safety measures to keep residential communities around them safe at all times. Measures to be put into action in order to ensure safety during unusual events can be summarized in the following three points:
1. To shut down operating reactors
2. To cool down reactors so as to remove heat from nuclear fuel
3. To contain radioactive materials
High-level Radioactive Waste (HLW)
Management Reprocessing spent nuclear fuel recovers 95%-97% of reusable uranium and plutonium, and separates out the remaining 3%-5% of high-level radioactive waste.
This means reprocessing of spent fuel can greatly reduce the amount of HLW.
HLW is mixed with melted glass and poured into durable stainless canisters (this is termed vitrified) at the reprocessing plant and then stored at HLW storage facilities for 30-50 years to allow cooling.
Final Disposal of (HLW)
After the temporary storage for 30-50 years, HLW will be laid and disposed of in a stable geological formation at a depth of more than 300 meters so as not to pose a threat to either human beings or the natural environment. The disposal adopts a multiple barrier system. Overpacks and their surrounding butter clay work as artificial barriers and stratums work as natural barriers to prevent radioactive materials from leaking.
Low-level Radioactive Waste
Low-level radioactive wastes from nuclear power plants are mainly work clothes, gloves and paper used for operation and maintenance of the plants, and enriched liquid waste.
They are incinerated or compressed to reduce their volume or solidified with cement and asphalt and then packed in metal drums.
These metal drums are safely shipped and laid underground in the Low-level Radioactive Waste Storage Center in Rokkasho village, Aomori prefecture. They will be monitored until they have no adverse impact on the environment.
Nuclear power plants in Japan have multiple safety measures, which are designed on the assumption that they must ensure the safety of the neighboring communities so that there will be no adverse impacts on their health.
Nuclear power plants are designed to prevent abnormal incidents from occurring. Even if abnormal incidents do occur, nuclear plants are also designed to prevent the potential spreading of abnormal incidents and leakage of radioactive materials around plants, which may cause adverse impacts on the surrounding environment.
Many power plants utilize redundant safety measures to keep residential communities around them safe at all times. Measures to be put into action in order to ensure safety during unusual events can be summarized in the following three points:
1. To shut down operating reactors
2. To cool down reactors so as to remove heat from nuclear fuel
3. To contain radioactive materials
High-level Radioactive Waste (HLW)
Management Reprocessing spent nuclear fuel recovers 95%-97% of reusable uranium and plutonium, and separates out the remaining 3%-5% of high-level radioactive waste.
This means reprocessing of spent fuel can greatly reduce the amount of HLW.
HLW is mixed with melted glass and poured into durable stainless canisters (this is termed vitrified) at the reprocessing plant and then stored at HLW storage facilities for 30-50 years to allow cooling.
Final Disposal of (HLW)
After the temporary storage for 30-50 years, HLW will be laid and disposed of in a stable geological formation at a depth of more than 300 meters so as not to pose a threat to either human beings or the natural environment. The disposal adopts a multiple barrier system. Overpacks and their surrounding butter clay work as artificial barriers and stratums work as natural barriers to prevent radioactive materials from leaking.
Low-level Radioactive Waste
Low-level radioactive wastes from nuclear power plants are mainly work clothes, gloves and paper used for operation and maintenance of the plants, and enriched liquid waste.
They are incinerated or compressed to reduce their volume or solidified with cement and asphalt and then packed in metal drums.
These metal drums are safely shipped and laid underground in the Low-level Radioactive Waste Storage Center in Rokkasho village, Aomori prefecture. They will be monitored until they have no adverse impact on the environment.