#309 Is nuclear waste dangerous?

Is nuclear waste dangerous? It is if it isn’t handled properly.

This was interesting to research. All of the sites I looked at that were run by nuclear organizations said, “no, no, of course not,” while the sites I looked at from other sources said, “possibly.”

When we think about nuclear waste, we think about waste from nuclear power stations. However, this is only part of the nuclear waste that is produced. Nuclear waste also comes from nuclear weapons production, the mining of uranium and thorium, items that have come into contact with radioactive material, and other naturally occurring radioactive material that has been enhanced for industry. All of these things have different levels of danger and are dealt with in different ways. I want to look only at spent nuclear fuel today.

What is spent nuclear fuel? Nuclear power plants work using the principle of fission. Uranium 235 is made into ceramic pellets that are stacked into sealed metal tubes. These are called fuel rods and they are about 3.5 meters long. Approximately 30,000 power rods are loaded into the reactor core. To start the reactor, a neutron source is inserted, such as Plutonium 238. A neutron is released from this and collides with a Uranium 235 atom inside the fuel rods. This makes Uranium 236, which is unstable. The Uranium 236 splits, releasing energy as heat and more neutrons. The extra neutrons hit other Uranium 235 atoms and keep the process going. The released energy heats water that is used to make steam and generate electricity. The fuel in the nuclear fuel rods lasts about 6 years before it is no longer able to produce heat. And this is spent nuclear fuel. There is estimated to be 400,000 tons of spent nuclear fuel in the world at the moment.

The nuclear waste from a nuclear power plant is classified into three categories. Low-level waste, intermediate-level waste, and high-level waste. Low-level waste is the lightly contaminated tools and work clothes. Intermediate-level waste is used filters and components from inside the reactor. High-level waste is the spent nuclear fuel. The high-level waste is only about 4% of all the nuclear waste that comes out of a nuclear power plant, but it has the majority of the radiation in it.

So, is nuclear waste dangerous? The answer is yes and no. If it is handled properly, it isn’t dangerous, but if it is not handled correctly, it is. There are two things that have to be considered. The first is that the fuel is still extremely hot. The fuel rods range from about 900℃ in the center to about 400℃ on the outside of the rod. To cope with this, the spent fuel rods have to be kept underwater so that they don’t overheat. All nuclear power plants have giant pools to store spent nuclear fuel. Water is constantly pumped through the pool, removing the heat. The pools have several different sources of water and don’t have any way that the water can drain away so that, in theory, the fuel rods will never be exposed to the air. If the water leaks out, the fuel rods will be exposed and get hotter, causing a meltdown that releases radiation into the air. The nuclear industry says this will never happen, although it did happen in Fukushima, Japan, in 2011, when the pumps failed. The fuel rods in the storage pools will slowly cool down and they should be safe enough to store in a dry area after about 5 years.

The second thing to be considered is that the fuel is also highly radioactive. The water pool the used waste is stored in also serves to block the radiation. There is 6 meters of water above the spent fuel rods, which is enough to absorb the radiation. This obviously makes the water radioactive, and it needs to be filtered to clean it. The fuel in the rods gradually loses its radioactivity, but that rate varies depending on the type of fuel. Some of the fuel has a half-life of 30 years, but some of the fuel takes longer. It takes about 100,000 years before Uranium is considered safe.

The spent nuclear fuel kept in storage pools is building up year by year. There may not be enough space for it in the near future. Once it has cooled enough, the fuel is moved and stored in dry casks. These are concrete casks with walls almost a meter thick and a steel lining. The spent nuclear rods are sealed in the casks and left. That seems like a temporary problem. Finland thinks it has come up with a more long-term solution. They are building a pit in which to bury the fuel rods. The pit will have lots of tunnels. The idea is that the fuel rods will be encased in copper casks and loaded into a tunnel. A clay called bentonite that absorbs water will be forced around the copper casks. This will stop them corroding. Then the tunnel will be plugged with concrete. And the whole thing will be left there for 100,000 years.

Sorry, but I felt the need for a new paragraph. 100,000 years! They figure the casks will be secure and safe from earthquakes, the shifting of the continental plates, and future humans trying to dig them up. I can’t believe the logic behind that. 100,000 years. How do we tell future humans not to dig them up? Why do we assume humans 100,000 years in the future will be anything like we are now? Humans 100,000 years in the past were very different to us now. I don’t see how that can be a concept. Hopefully, in the next few hundred years, we will work out a way of disposing of the nuclear fuel so it doesn’t have to be buried for 100,000 years.

So, is nuclear waste dangerous? No, so long as its buried deep in the ground for 100,000 years. And this is what I learned today.

Sources

https://www.epa.gov/radtown/radioactive-waste

https://nuclear.duke-energy.com/2020/08/12/solving-the-wonderful-mystery-of-a-nuclear-start-up

https://world-nuclear.org/nuclear-essentials/how-does-a-nuclear-reactor-work.aspx

https://www.energy.gov/ne/articles/nuclear-101-how-does-nuclear-reactor-work

https://www.nrc.gov/reading-rm/basic-ref/students/science-101/what-is-an-spent-fuel.html

https://world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-wastes/radioactive-wastes-myths-and-realities.aspx

https://en.wikipedia.org/wiki/Spent_nuclear_fuel

https://cen.acs.org/environment/pollution/nuclear-waste-pilesscientists-seek-best/98/i12

https://world-nuclear.org/nuclear-essentials/what-is-nuclear-waste-and-what-do-we-do-with-it.aspx

https://www.scientificamerican.com/article/rethinking-nuclear-fuel-recycling/