8.1.8 Safety aspects

Enriched Uranium:

• Fuel Composition: Nuclear reactors use enriched uranium as fuel. Enriched uranium contains a higher percentage of U-$235$, which undergoes fission, compared to naturally occurring uranium, which is about 99% U-$238$. In reactor-grade enriched uranium, the percentage of U-$235$ is increased to around 3-5%.
• Role of U-$238$: U-$238$ in the reactor absorbs fission neutrons, which helps control the rate of fission reactions, stabilising the reactor's operation.

Shielding and Safety:

• Concrete Shielding: Nuclear reactors are surrounded by thick concrete shielding, designed to block radiation and protect workers from exposure. This concrete absorbs the radiation emitted from the reactor.
• Long-term Stability: Over time, neutrons can escape the reactor core and enter the shielding material, potentially causing it to become radioactive. Regular monitoring and potential replacement of shielding materials are necessary to maintain safety.
• Emergency Shut-down: In emergencies, control rods are rapidly inserted into the reactor core. These rods absorb excess neutrons, halting fission reactions immediately to prevent overheating. This procedure, known as an emergency shut-down, is crucial for reactor safety.

Types of Nuclear Waste:

1. High-Level Waste (HLW):

• High-level waste includes spent fuel rods, which contain daughter nuclei that are highly radioactive and decay slowly, remaining hazardous for thousands of years. HLW is typically handled remotely to minimise radiation exposure.

2. Low-Level Waste (LLW):

• Low-level waste, such as used tools and gloves, has short-lived radioactivity and can be disposed of near the surface. LLW doesn't require the same stringent containment as HLW, but safe disposal is still essential to prevent environmental contamination.

Storage and Disposal of High-Level Waste:

• Cooling Ponds: Spent fuel rods are initially stored in cooling ponds, which allow heat to dissipate over time. These ponds are often located close to the reactor to minimise the risks associated with transporting radioactive materials.
• Recycling: Usable uranium and plutonium are sometimes extracted from spent fuel for recycling.
• Vitrification and Cask Storage: Remaining waste is often vitrified (encased in glass), sealed in thick steel casks, and stored in deep, geologically stable caverns, chosen to minimise environmental impact. Public consultation is typically part of the site selection process to address any concerns.

Environmental Impact:

• Greenhouse Gas Emissions: Nuclear power stations do not emit greenhouse gases, which makes them an attractive alternative for reducing carbon emissions. Additionally, 1 kg of uranium produces as much energy as 25 tonnes of coal, so nuclear fuel requirements are relatively low.
• Risks and Benefits: Despite the benefits, nuclear power poses risks. High-level radioactive waste and the potential for a nuclear meltdown present serious hazards, requiring stringent safety measures. The decision to use nuclear power is a balance of benefits versus risks. Reducing these risks involves implementing robust safety protocols, managing waste responsibly, and maintaining containment procedures.