Nuclear Waste
One of the most frequently voiced criticisms about nuclear power is “What about the waste?”
I was wondering the same to I decided to have look at it.
Nuclear waste is an emotionally laden topic. But what is the problem?
Nuclear reactors create radioactive isotope. Some of these isotopes have half-lives of more than 20000 years. So it takes a lot of time until this waste has “cooled” off radioactively so much, that it is not hazardous any more.
If we look at the radioactivity over time, it looks like this:
We can see that the so called fission products are not even as radioactive as the natural uranium ore anymore after something like 500 years.
Plutonium on the other hand stays more radioactive than natural uranium for more than 100 000 years.
How is it handled?
The spent nuclear fuel (SNF) is, unlike what you have seen in “The Simpsons”, not a green, liquid oozing out of barrels.
In fact, this is what a container for SNF looks like:
WATCH 👀: Incredible archive footage by @SandiaLabs as researchers test used nuclear fuel transportation containers under the most extreme accident scenarios to confirm their performance.
Learn more: https://t.co/5XTBpxjP7U pic.twitter.com/KshTv09iOA— Office of Nuclear Energy (@GovNuclear) May 26, 2020
They are really rugged. In fact, they are so save that “No one has ever been harmed by commercial nuclear waste. No deaths, no cancers, nothing. Ever.” [CONCA]
But let’s say somebody blew off the lid of one of these casks? Well, the fuel, a solid as I like to remind you, would still be trapped in the fuel rods. There are some radioactive gases inside the fuel rods. So let’s assume that all of the fuel rods also get damaged and all of the gaseous radioactive iodine, krypton and xenon get released. This scenario has been looked at: “the dose at 100 meters from the fuel would be only a one-time 3 mrem (0.03 mSv) dose“. [CONCA]
To give you something to compare this raw number to, “eating a bag of potato chips a day gives you more than 4 mrem/yr“. Radiation is ubiquitous. You are constantly bombarded with cosmic radiation, radiation from the materials around you, radiation even from within your bones. The yearly dose in the US is something like 6 mSv. But there are places around the world, where citizens are exposed to more than 100mSv/y, like in Ramsar. Statisticians are still trying to find out if the effects are either non-existent or mildly positive.
So even if somebody got a device that has even a chance of doing damage to one of these casks, something like an anti-tank gun, short-range missile or even a plane, and even if they got near enough to deploy these devices against such a cask – it would hardly do anything at all.
I think a terrorist would easily find better targets, if they had access to such weapons.
How much waste is there? Where does it get stored?
In the US, there are still ongoing efforts to build the Yucca Mountain deep geological repository. There have been decades of delays already. The idea is to put the waste in a geologically stable “hole in the ground”, an artificial cavern. The debates about this repository are seemingly endless. It’s the same for most countries’ storage facilities, although Finland seems to be heading towards an operational repository.
What’s strange: something similar has already been successfully done, in America nonetheless! It’s called the Waste Isolation Pilot Plant an it has been storing military nuclear waste for some time now in a stable salt formation. So technically, it can be built. The problem is political. [BRAND, p.105] cites Rip Anderson, a Sandia Labs Scientist, as saying: “From a technical point of view, the best place on dry land to store all nuclear waste—wherever it comes from—is at WIPP. We’ve proven that every way you can think of. We have traceability and transparency. Geologically and hydrologically, it’s the safest. There’s room for it, and more panels can be mined out of the salt bed whenever we want. It’s only politics and bureaucracy that stand in the way.“
There is a startup in the nuclear waste space, called DeepIsolation. They leverage an innovation of the oil and gas sector, called horizontal drilling. Their idea is to drill a normal vertical whole and than drill slightly sloping upwards horizontally.
Nuclear waste would be put in canisters and disposed of in these horizontal holes.
This company is still in an early stage, but they seem quite confident that they will be able to offer this permanent, deep geological storage solution on the site of most nuclear power plants. You would not even have to transport the spent nuclear fuel around to a centralized facility. The company already demonstrated that they can retrieve containers from the boreholes, if you need to do so.
So deep geological repositories can be built. There have also been proposal to deposit the SNF in the deep sea. Even if something leaked, the vast quantities of water would dilute the radioactivity quickly to trivial levels.
Until the political will can be mustered, the waste is stored nearer to the surface. To give you an idea, here is Dr. Rita Baranwal, Asst. Secretary for Nuclear Energy in US DOE, standing atop 20 years worth of high-level waste from France and the UK in La Hague:
Yes!! Standing directly over vitrified, remnant high-level rad waste (post- recycling 96% of used fuel), in a room that stores >20 yrs of it. Thanks @OranolaHague, for an informative day on recycling used fuel, & for my best day at @GovNuclear thus far! #itsonlywasteifyouwasteit pic.twitter.com/fKMyFcfwTw
— Dr. Rita Baranwal (@RitaB66) October 23, 2019
In the US, SNF is stored on the reactor site in dry cask storage canister. But there is a proposal to create a centralized interim storage facility in New Mexico. Here is an impression of it by the developers:
In the first phase, 500 canisters with a total of 8680 metric tons of uranium in commercial spent nuclear fuel will be stored. The facility could be extended to 10 000 canisters. Since the first commercial reactors went into operation until now, they have accumulated a total of approximately 80 000 metric tons of SNF. It’s growing at a rate of about 2000 metric tons per year. A back of the envelope calculation shows that this facility could hold the waste of all nuclear reactors in the US since they went into operation in the 1950s and has room for the next 40 years at current levels of waste production.
The storage would take the almost impenetrable canisters and put them in an even more impenetrable storage. It would look like this:
The whole facility would take up 110 acres of New Mexican desert for the storage pads and another 178 acres for auxiliary facilitates.
The energy density of nuclear fuels and the operating principle makes their waste dense as well. It has a really tiny footprint. And interestingly, nuclear power companies are the only business I know of, that pay all of their waste management fees upfront and can account for all of their waste. Contrast that with this picture of a dump for wind turbine blades after their 20 year service life:
What about the terrorists?
So what about nuclear weapons? Couldn’t somebody try to steal it to make a nuclear bomb?
Interestingly, this has been studied. The answer is: not really.
To build nuclear weapons, you need access to as pure as possible fissile materials.
Practically, that means either high purity 235U or 239Pu.
Plutonium from commercial reactors is “tainted” by heavier isotopes, like 240Pu. You need first to extract chemically pure plutonium from SNF, which is not that easy to begin with.
The USA was able to make a device in the 1960s out of SNF from UK Magnox reactors, which were not specifically operated to produce weapons-grade plutonium. By design, the fuel was nevertheless way more suitable for this purpose than the SNF of other designs, like the PWR.
It worked, but badly enough to demonstrate that, if you want to have nuclear weapons, you start a nuclear weapons program. Every state that got to plutonium-driven nuclear weapons choose to build special reactors to breed it. The alternative route was too unreliable and costly. For state actors, mind you.
Fuel in light water reactors has on the order of 3-5% 235U in it, when it enters a reactor. There are maybe 2% left, when it leaves the reactor. The enrichment facilities to get to the 5% are huge, reliant on complex technology and expensive. They need to be large to be able to produce the LEU economically.
That is not necessarily true for getting to >90% enrichment in military settings. There is considerably less economic pressure in military settings. Commercial enrichment facilities are monitored closely.
If you have access to these enrichment facilities and the chemical processing facilities to convert UO2 from SNF to UF6, it would be way more convenient to just buy commercially available natural uranium and start from there for a weapons program. That would be way, way easier, because there are no highly radioactive fission products in the natural uranium.
Plutonium is preferred for nuclear weapons, because you can build smaller devices with it, which are more easily put on a missile. Albeit the trigger mechanism is more sophisticated.
No state has ever gotten nuclear weapons from a commercial nuclear program. There are a lot of states with commercial nuclear programs, but no weapons. And there are two states with weapons, but no commercial reactors, Israel and North Korea.
If state-level funding and national laboratories aren’t able to convert SNF reliably into nuclear weapons, I doubt that terrorist organizations will find the talent and resources to do so.
And that’s assuming they can get their hands on SNF. You have seen these large canisters, right? You understand that these have to be transported by truck? How would stealing the nuclear material work? After the terrorists fought their way into a nuclear facility, which I assume would trigger some kind of alarm with the police and/or military, they get a crane from somewhere and load a canister on a heavy truck and … somehow escape with this slow-moving, easily spottable truck into their clandestinely built reprocessing facility? That doesn’t look credible to me.
Dirty bombs might might be conceivable and sound scary. But luckily, they are actually not really attractive. An unexploded dirty bomb will have a lot of radioactive material in a small place. So it is really dangerous for the terrorist to handle. If it explodes, it disperses the material over a large area. So the radiation per area is not that big. If the bomb doesn’t disperse the radiation, what’s the point anyway? Studies on that conclude that there is not really any danger from these devices other than the initial blast. And frankly, there are softer targets to get radioactive material from than a commercial power plants or disposal sites.
Do we even have to store it?
So it looks like we can easily store the waste for extended periods of time. But the question that is more interesting is: do we even have to? There are multiple technologies that can reduce the amount of waste significantly. Most of them work by extracting the long-lived isotopes from the the fuel.
It has long been known that you can extract Pu from the SNF by the PUREX process, a costly and sometimes dangerous process. The extracted Pu can be used in form of so called mixed oxide, or MOX, fuel in commercial light water reactors.
Recently, it has been discovered that there is a one-step chemical process that extracts uranium, plutonium, neptunium and americium and leaves the fission products behind.
We know since that 1970s that we can recycle 95% of the nuclear fuel by so called pyroprocessing. This process has recently been improved to recycle 97%; which doesn’t sound like a great improvement, but according to one of the scientists involved, “[r]ather than store five percent for hundreds of thousands of years, the remaining three percent needs to be stored at a maximum of about one thousand years.”
Amazingly, there is a whole host of reactor designs that are capable of using the recycled fuel. They contain a mixture of uranium, plutonium and other actinides, which makes them unsuitable for weapons. And there are even some designs, that can use the SNF directly as fertile material and extract dozens of times the energy that has been released during its fist use in a light water reactor.
Even if humanity should decide against using this huge source of energy, there a potential methods to handle the waste. An interesting route is becoming possible by our steadily improving mastery of light. The intensity of laser light has increased exponentially since its conception. We are able to create light more extreme than our solar system has ever seen. One of the people associated with and contributing to this technological advancement is 2018 Nobel laureate Gerard Mourou. He is currently working on utilizing laser to transmute radioactive isotopes. The lasers would be used to accelerate protons and smash them into the nuclei to create new elements by this. This would make the isotopes decay in minutes, rather than thousands of years. Mourou, rather optimistically I think, predicts that a commercial laser for this could be available in 10 to 15 years.
Let’s say it takes 50 years. What does that do to the question of nuclear waste?
Isn’t nuclear waste so bad then after all?
Interestingly, nuclear waste, contrary to popular opinion, is the best waste to have. The reasons are simple, there is only a little of it, it has a high density, can easily be handled and gets less dangerous over time. Other materials, like arsenic or mercury, stay as toxic as they are now for all of eternity.
Strangely, there is hardly any concern about the storage of these materials. I can recommend this entertaining thread on that: