Safety Aspects of Nuclear Reactors
- Radioactive substances can be dangerous and some substances have very long half-lives (even billions of years)
- This means that they will be emitting harmful radiation well above background radiation levels for a very long time
- Waste products from nuclear power stations need to be appropriately stored for the remaining time that they are radioactive
- Common methods are water tanks or sealed underground
- This is to prevent damage to people and the environment now and for many years into the future
- Sealing them underground means they are less likely to be dislodged or released due to natural disasters
Nuclear Fuel
- The fuel used in nuclear reactors is called enriched uranium
- This is U-238 enriched with U-235 as U-235 is the isotope that undergoes fission
- The U-238 isotope absorbs fission neutrons which helps to control the rate of fission reactions
- Several measures are in place to reduce the worker’s exposure to radiation
- The fuel rods are handled remotely ie. by machines
- The nuclear reactor is surrounded by a very thick lead or concrete shielding, which ensures radiation does not escape
- In an emergency, the control rods are fully lowered into the reactor core to stop fission reactions by absorbing all the free neutrons in the core, this is known as an emergency shut-down
Nuclear Waste
- There are three main types of nuclear waste:
- Low level
- Intermediate level
- High level
Low-level waste
- This is waste such as clothing, gloves and tools which may be lightly contaminated
- This type of waste will be radioactive for a few years, so it must be encased in concrete and stored a few metres underground until it can be disposed of with regular waste
Intermediate-level waste
- This is everything between daily used items and the fuel rods themselves
- Usually, this is the waste produced when a nuclear power station is decommissioned and taken apart
- This waste will have a longer half-life than the low-level waste, so it must be encased in cement in steel drums and stored securely underground
High-level waste
- This waste comprises the unusable fission products from the fission of uranium-235 or from spent fuel rods
- This is by far the most dangerous type of waste as it will remain radioactive for thousands of years
- As well as being highly radioactive, the spent fuel roads are extremely hot and require additional care when being handled and stored
- How high-level waste is treated:
- The waste is initially placed in cooling ponds of water close to the reactor for a number of years
- Isotopes of plutonium and uranium are harvested to be used again
- Waste is mixed with molten glass and made solid (this is known as vitrification)
- Then it is encased in containers made from steel, lead, or concrete
- This type of waste must be stored very deep underground
Risks & Benefits of Nuclear Power
Benefits
- Nuclear power stations produce no polluting gases
- They are highly reliable for the production of electricity
- They require far less fuel as uranium provides far more energy per kg compared to coal and other fossil fuels
Risks
- The production of radioactive waste is very dangerous and expensive to deal with
- A nuclear meltdown, such as at Chernobyl, could have catastrophic consequences on the environment and to the people living in the surrounding area
