Nuclear reactor safety

Nuclear reactor safety protects people from radiation and prevents the reactor core from overheating. These hazards need attention both while the reactor is operating and after it has been shut down.

Fuel handling and radiation shielding

Nuclear fuel contains fissile material, whose nuclei can split in fission reactions. After use in a reactor, the fuel is highly radioactive because it contains fission products and other radioactive substances. These substances continue to emit radiation after the fuel is removed from the reactor.

Workers can use remote handling equipment to move fuel without being close to it, reducing their radiation exposure. Shielding placed between a radiation source and people absorbs or attenuates the radiation, so less reaches them.

Emergency shutdown and cooling

During operation, fission releases neutrons that can cause further fissions. This is a fission chain reaction. In an emergency shutdown, neutron-absorbing control rods are rapidly inserted into the reactor core. They absorb neutrons, leaving fewer available to cause further fissions, so the chain reaction rapidly decreases.

Stopping the chain reaction does not immediately stop heat production. Radioactive substances in the fuel continue to decay and release decay heat. Cooling must therefore continue after shutdown to remove this heat and prevent the core from overheating.

Radioactive waste management

Nuclear power produces materials that continue to emit radiation after they are no longer useful. Radioactive waste management limits people’s exposure to this radiation and prevents radioactive material from escaping into the surroundings.

Sources of radioactive waste

In a reactor, nuclear fission produces radioactive substances within the fuel. After fuel is removed from the reactor, it is called spent fuel. It remains highly radioactive and must be managed after removal.

Other reactor materials can also become radioactive waste. Radiation can make some materials radioactive; this is called activation. Materials can also become contaminated when radioactive substances get onto or into them.

Waste differs in its activity, which is the rate at which radioactive nuclei decay. It also differs in how long it remains hazardous. Some waste becomes less hazardous relatively quickly, while other waste requires management for much longer.

Handling and storing radioactive waste

Remote handling allows waste to be moved or processed from a distance, reducing workers’ direct exposure to its radiation.

Storage uses containment to reduce the escape of radioactive material and shielding to reduce exposure to the radiation it emits. These have different purposes: containing the material does not by itself guarantee that its radiation is sufficiently shielded.

Radioactive waste continues to decay during storage. Its activity generally falls over time, but some materials remain hazardous for long periods. Decay also produces heat in some waste, including spent fuel, so storage arrangements must allow that heat to be removed. The containment, shielding and heat removal must remain suitable for as long as they are needed.

Risks and benefits of nuclear power

Deciding whether to develop nuclear power means weighing the electricity it can provide against the possible harm it can cause. Both the benefits and the risks matter when making the decision.

Benefits of nuclear power

Nuclear power stations can generate substantial amounts of electricity reliably, providing a steady supply over long periods. During operation, they produce low direct carbon dioxide emissions. This describes emissions from operating the power station, not necessarily emissions from every stage of its construction and fuel supply.

Risks of nuclear power

The risks include exposure to radiation, which can damage living cells. An accident at a nuclear facility could release radioactive material and expose people or the environment to radiation. Nuclear power also produces radioactive waste that must be managed safely, potentially over long timescales.

Assessing nuclear risk

A balanced assessment considers both likelihood and severity: how likely a harmful event is to happen and how serious its consequences would be. An event may be unlikely but still require careful consideration if its consequences could be severe. These risks are considered alongside the benefits of generating electricity.

Safety measures can reduce the likelihood of harm or limit its consequences. However, having safety measures does not mean that all risk has been eliminated.