Safety Aspects of Nuclear Reactors (AQA A Level Physics): Revision Note

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

Nuclear Energy in Society

• Compared to other fields in physics, the history of nuclear energy is much more recent and controversial

• Naturally, once scientists began to understand the nucleus, they wondered how to harness its power

• The earliest developments in nuclear energy were as follows:

  • 1939: Nuclear fission discovered by scientists Hahn, Meitner and Strassman

  • 1942: First chain reaction achieved by a team led by Enrico Fermi

  • 1945: First (and last) atomic bombs dropped at Hiroshima and Nagasaki

  • 1951: First nuclear fission reactor to generate electricity

• Following the rise of nuclear energy and nuclear weapons, the world entered the 'Nuclear Age'

• This age continues to have a major impact on science, as well as politics and ethics

  • Today, a significant proportion of the world’s electricity is generated by nuclear fission reactors

  • The future promises a 'clean energy' revolution with the development of the nuclear fusion reactor

  • The threat of nuclear weapons highlights the importance of international cooperation and peace

• As a result, people in society tend to have mixed feelings about nuclear power, with some viewing it positively, while others are fearful of it

• With increased education on nuclear energy, people in society can use this knowledge to inform their own decisions and opinions

Risks & Benefits of Nuclear Power

Benefits

• Nuclear power stations produce very little pollution

  • During operation, nuclear power plants do not produce carbon dioxide or sulphur dioxide

  • The amount of greenhouse gas emissions over the entire life cycle of a nuclear power station is significantly lower than coal or gas power stations

  • Nuclear power combats global warming, improves air quality, and prevents acid rain (due to sulphur dioxide) by reducing reliance on fossil fuels

  • As a result, nuclear power is a far more sustainable and 'clean' source of energy compared to fossil fuels

• Nuclear fuel is a highly reliable source for the production of electricity

  • Nuclear power stations provide a continuous energy output, unlike some renewable sources such as wind or solar

  • Many (but not all) nuclear power stations can adjust their output quickly to meet higher demand

• Nuclear fuel has the highest energy density of any fuel

  • The energy density of uranium-235 is over a million times greater than that of coal and other fossil fuels

  • This means it produces much more energy per kg of fuel, making it a highly efficient energy source

• Nuclear reactors produce some useful by-products

  • For example, medical isotopes such as molybdenum-99, which is used in the production of technetium-99m

Risks

• Nuclear fuels are non-renewable energy resources

• The production of radioactive waste is very dangerous and expensive to deal with, with long-lasting effects (see Nuclear Waste above)

• Commissioning (starting up) and decommissioning (shutting down) a nuclear power station is expensive and time-consuming

• A nuclear meltdown, such as at Chernobyl, could have catastrophic consequences on the environment and on the people living in the surrounding area