Managing Radioactive Waste: Modern Solutions and Innovations
Modern Solutions for Radioactive Waste
Nuclear energy has been one of the few advances we have made to lower our carbon footprint. Nuclear is the world's second largest source of low-carbon power (26% of the total in 2020). Even though nuclear energy is one of the most efficient ways of producing energy, it has been well opposed by many due to the many issues it brings with it, one of them being radioactive waste.
Inside nuclear power plants, nuclear reactors and their equipment contain and control the chain reactions, most commonly fueled by uranium-235, to produce heat through fission. The heat warms the reactor’s cooling agent, typically water, to produce steam. The steam is then channeled to spin turbines, activating an electric generator to create low-carbon electricity.
During this process, the power plants produce radioactive waste with varying levels of radioactivity which have to be disposed off properly to prevent any mishaps.
This includes its collection and sorting; reducing its volume and changing its chemical and physical composition, such as concentrating liquid waste; and finally, its conditioning so it is immobilized and packaged before storage and disposal.
Most low-level radioactive waste (LLW) is typically sent to land-based disposal immediately following its packaging for long-term management.
Radioactive waste is firstly treated and conditioned so that it becomes suitable for handling during storage and the final disposal. Its main aim is to reduce the hazardous nature and minimize the volume of waste that has to be processed.
Incineration is a very common technique applied for waste which can be used to reduce volume. It is widely used when handling other kinds of waste, but for radioactive waste, it is mostly used to treat low-level radioactive waste. The waste is incinerated in a special kiln at temperatures above 1000C. The resulting products after incineration are then subjected to conditioning such as cementation or bituminization so that they can be disposed of.
Cementation is a very common technique in which the waste is immobilized using containers where the processed radioactive waste is placed along with a specially formulated grouting mix. After a while, the two mix and set forming a big block of concrete waste.
HLW or high level radioactive waste is generally conditioned using a process called vitrification. HLW which is mostly liquid is dried down to a granular powder which is then mixed with some molten glass and then poured into stainless steel canisters. These containers are then ready for storage and disposal.
For used fuel designated as high-level radioactive waste (HLW), the first step is storage to allow decay of radioactivity and heat, making handling much safer. Storage of used fuel may be in ponds or dry casks, either at reactor sites or centrally. Beyond storage, many options have been investigated which seek to provide publicly acceptable, safe, and environmentally sound solutions to the final management of radioactive waste. The most widely favored solution is deep geological disposal.
The Swedish proposed KBS-3 disposal concept uses a copper container with a steel insert to contain the spent fuel. After placement in the repository about 500 meters deep in the bedrock, the container would be surrounded by a bentonite clay buffer to provide a very high level of containment of the radioactivity in the spent fuel over a very long time period.
Another solution is using various methods of storage for the radioactive waste such as using storage ponds, storage casks, and other multi purpose canisters. Metal containers incorporated with neutron absorbers are used to store the racked fuel assemblies. These are then submerged into deep water pools with depths of 7-12m to allow the water to fully cover these assemblies.
There are many other ways for the storage and transport of the radioactive waste or spent fuel cells from these nuclear power sites. They mostly include storing the fuel in a Multi-purpose canisters which the fuel assemblies along with inert gases. After being welded with a secure stainless steel lid, they can be used for storage and transport.
Credits: Paarth Agarwal- Tech Tuesday, COEP BLOGS
References:
https://www.iaea.org/newscenter/news/what-is-nuclear-energy-the-science-of-nuclear-power
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