Proposals for Disposal of Nuclear Reactor Radioactive Waste

Energy & Power Plants / By Willie Scott / Mechanical Engineering

Introduction to Nuclear Reactors and Radioactive Wastes

Nuclear energy relies on the controlled reactions of enriched uranium UO₂. In a Pressurised Water Reactor, this UO₂ in circular disc form is packed in fuel rods which are bundled together to form the fuel assembly.

The fuel assembly is placed in the core of the reactor where the reactions take place. The speed and the number of reactions that occur are achieved by the use of control rods and a moderator. In the core, uranium atoms are bombarded with free neutrons producing immense heat. This heat is transferred by cooling medium to a heat exchanger where it is used to convert process water to dry high pressure steam.

The steam is then used to drive steam turbine generator units, returning to the heat exchanger via the turbine condenser as in a normal thermal power station operating system.

The radioactive waste produced by this process of raising steam is a direct result of using uranium as a fuel in a nuclear reactor.

There are three categories of waste these being Low Level Waste (LLW), Intermediate Level Waste (ILW), and High Level Waste (HLW). Nuclear power plants are in operation all over the world, each county having its own method of dealing with the different levels of radioactive waste.

Normally LLW can be sent to hazardous landfill sites, but ILW and HLW are stored in various secure containers and mediums whilst a long-term method of storage is established.

Radioactive Wastes Produced by a Nuclear Power Plant

As the Pressurised Water Reactor is the most popular nuclear reactor we shall examine the radioactive wastes produced by this reactor, which fall into three distinct categories.

• Low Level Waste.
• Intermediate Level Waste
• High Level Wastes

Low Level Waste

These wastes include some types of process equipment, protective clothing such as boiler suits and gloves along with rubble from decommissioned buildings. It is not considered as being dangerous to health.

Intermediate Level Waste

This waste is more radioactive than the low level waste and is made up from metal or alloy cladding fitted around fuel rods sludges from various processes, and resins used in coating components.

High Level Waste

These are prevalent in spent fuel and are highly contagious. Fuel rods are replaced periodically and the used ones are highly contagious containing uranium, plutonium along with minor actinides such as curium and neptunium isotopes.

Disposal and Storage of Low and Intermediate Radioactive Waste

• Low Level Waste Disposal (LLW)

Low level radioactive waste can be disposed of by relatively shallow burying in hazardous landfill sites.

Some countries which produce low level waste only permit this type of disposal after the waste has been stored at the nuclear plant for a specified period.

• Intermediate Level Waste Disposal (ILW)

There are two sub-types in this category,

Short Lived Intermediate Level Waste

These types can be treated chemically, incinerated then compacted into manageable bales. The bales are then encases in concrete and either stored in underground concrete lined troughs or held in specially fabricated containers on the surface, being stored for 300 years.

Long Lived Intermediate Level Waste

These are treated similarly to the short lived ILW but due to their higher levels of radiation they have to be handled very carefully to avoid contamination.

Once the waste has been treated, compressed and encapsulated, it is stored underground in concrete or similar lined repositories.

Please read the next sections where we examine the treatment of High Level Wastes, along with their current short term storage measures and long term storage proposals.

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