Safety Aspects of Nuclear Reactors (AQA A Level Physics)

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

Nuclear Energy in Society

• Nuclear power can scare people if they do not understand it

• It is dangerous if not handled properly, yet it is invisible which can be difficult for some people to comprehend

• However, with increased education on nuclear energy, society can use this knowledge to inform their own decisions and opinions