What is nuclear waste?

There are two main types of nuclear waste.

Contaminants from nuclear fuels used in a nuclear reactor (direct contaminants)
After the closure of the power plant, some parts of the plant are radioactive, so they are considered as waste and have to be operated (indirect waste).

These two types are dealt with in two ways. However, the most important thing to know first is that nuclear waste is one of the safest stored industrial wastes in the world. Although any other industrial waste is released into the environment from somewhere, nuclear waste cannot be released into the environment for any reason. The direct responsibility lies with the institution and the government of that country. Annual international calculations should also indicate the amount of waste produced in relation to the amount of fuel consumed. There is a separate group of international observers called Safeguard Inspector for things like this.

The most challenging of these is direct waste management. This article tries to explain how to do this.

If you think of nuclear waste as a green glowing liquid, it’s the fault of images and print media. Nuclear waste is a solid substance. The nuclear fuel plant arrives in small cubes (about the eraser piece at the end of a pencil) packed inside a 4 meter high tube made of thin zirconium alloy. It comes out the same way as garbage. Disposal of this nuclear waste through a power plant takes place in two main stages.

Step 1: Wet Storage
Even when removed from the power plant, the radioactive combustible nuclear fuel in these rods (which we do not call polluting right now) generates significant heat. Therefore, these need to be further cooled. Due to this the fuel is stored for a considerable period of time in the large cooling pools (Spent Fuel Pools) inside the power plant. These pools are similar in size to large swimming pools. These fuels usually take 3 to 12 years to cool in the cooling pools.

Step 2 (1): Dry Cask Storage
During this time the heat generation of the waste decreases. So now there is no need to cool these with water. If the fuel is not recycled, these are now transferred to special cylinders made of stainless steel and concrete. These cylinders are designed to be cooled by air convection. Most of the world’s burning fuel is currently stored in an open space near the power plant.

Step 02 (2): Fuel Reprocessing
According to the efficiency of the world’s most widely used power plants, only 5% -8% of the actual energy contained in nuclear fuels is used. More than 90% of the remaining energy is still stored in those burned fuels.

These include non-combustible nuclear fuels; These are uranium-235, an important radioactive substance such as plutonium-239 and amorium-241, which are formed by the reaction of nuclear fuels with neutrons. This cannot be called waste. These are resources.

The rest are various volatile elements formed by the breakdown of uranium fuel. These are commonly referred to as “fission fractions” or FFs. For now, we call these FFs exactly what we call “nuclear waste.” However, some new power plant technologies have the potential to use a significant amount of these as fuel. For the time being, in this article, we will consider these as waste.

Plutonium-239 is a more valuable substance than gold. Because plutonium-239 is not found naturally. That is why plutonium-239 is extremely rare. An essential material for certain research applications and nuclear weapons. Americum is a modern aerospace fuel. This material is now being used to build radio-thermal generators for spacecraft. As a result, many countries reserve this kind of valuable material. Here we call this process fuel reprocessing. Countries like America, Japan, France, Russia and India reprocess fuel in this manner.

During the refurbishment, the fuel rods are first ground and separated from the fuel. It can be separated by a chemical process that separates plutonium-239 and unburned uranium fuels and liquids such as amorphous. These can also be reused as fuel. France, for example, has been recycling burnt fuel from its nuclear power plants for another 24 years.

The rest of the remodeling fractions are in liquid form. Also, this is an extremely radioactive substance. Therefore, it should be considered as a dangerous substance and traded carefully.

Let us now see how one of these highly radioactive materials deals with. There are two main methods used for this.

  1. Safe storage of these by solidification

This is done by mixing it with a glass-like substance and sending it to safe storage by solidification. This is called vitrification. The fifth image shows the appearance of such vitrified waste. The purpose of doing this is to stop it from easily adding to the environment. Glass takes millions of years to decompose. So for a long time this waste will stop being released into the environment because of this. About 200 years later, this waste is no longer radioactive. Then they will have no effect on the environment. So millions of years go by and there is no problem at all.

  1. Actinide Transmutation

This means that most of these FFs contain periodic elements called actinides in the periodic table. These are converted into other unstable elements by particle accelerators or by laser treatment. This is done to reduce the radioactivity time of the FF. Then the time required to vitrify and store these will be reduced. Japan uses this method to some extent.

And the most dangerous thing about this nuclear waste is the intense radioactivity. This is called radiotoxicity. This is why many people are afraid of this. The good news about radiotoxicity is that it can gradually diminish over time. An element that has no other chemical toxins (such as heavy metals) does not lose its toxicity over time. That’s why we have to worry about electronic waste a hundred times as much as we worry about nuclear waste.

A green horizontal line can be seen in the diagram below. This is the radioactivity level of natural uranium. This is very close to our natural environmental radioactivity. Then the purpose of waste management is to bring that waste to this level.

The total radiation toxicity we see now lasts about a million years. But, looking back, it seems that things like plutonium-239 and amorium-241 contribute more to maintaining that toxicity. So it is clear that when they are removed from the mixture, only FF and Curiam are left. Both types of radiation poisoning have a lifespan of less than 500 years. So we can reduce this further by a method like the transmutation mentioned above.

Another thing that many people are worried about now is whether there will be a system like dumping this waste into the sea and whether developed countries will not be able to do so. Incidents like this have been reported as rumors for decades. But now a separate field has developed called nuclear forensics. This way, if that happens, the waste can be traced back to the plant and fuel manufacturer where it was used. It has separate technical teams and databases.

The most important thing about nuclear waste is that it is very small in size. For 60 years in the United States, the total amount of waste used by more than 100 power plants could be as big as a football field. That’s why these things are still stored near power plants in almost every country in the world.

This article does not say that nuclear waste is a safe substance like cheese. Doing these things technically is complicated and expensive. But it is important to know that there are practical ways to manage that material safely, and that they are used and monitored internationally. Even if Sri Lanka ever goes to nuclear power (this is not something that has been decided yet, it will most likely be a decision in the future), all of this will apply to us in the same way.

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