Used nuclear fuel: valuable resource or toxic trash?

All power sources generate waste in some form, but for nuclear power, things are a bit more complicated. While there are a number of different waste forms associated with the operation of a nuclear power plant, the most dangerous and controversial of these is used nuclear fuel. Used fuel is highly radioactive, extremely hot, and remains this way for millennia.

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The United States has the largest fleet of nuclear reactors in the world – 99 to be exact. After over sixty years of commercial and defense nuclear operations, we’ve generated about 80,000 tons of used nuclear fuel. For scale, that’s enough to fill a football field eight yards deep. According to U.S. policy, all of that is waste.

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But, wait a second – at least 95% of used nuclear fuel is recyclable.  From that perspective, isn’t waste at all; rather, it’s a resource. Remember, the uranium that composes nuclear fuel is millions of times more energy dense than all other fuel types...so it’s potentially a very valuable resource.

 

When it comes down to it, whether to recycle or throw away used nuclear fuel is an entirely political decision. Unlike our own country, the United Kingdom, France, Russia, China, and Japan all have policies to recycle or “reprocess” used nuclear fuel. But reprocessing comes with its own share of political complications, as you will see.

 

In this blog, I’d like to examine the different options for dealing with used nuclear fuel, and the complications that arise from pursuing any one of these options. Then you can decide what you think, at least in theory, is the best thing to do.

 

What is used nuclear fuel made of?

 

First thing’s first. What is nuclear fuel made of, anyway?

 

In today’s nuclear reactors, fresh nuclear fuel is made from an element that occurs naturally in Earth’s crust: a metal called uranium. If you don’t know what to picture when I say “nuclear fuel”, think of long, black metallic rods. Harmless enough, right? Actually, natural uranium isn’t very radioactive, and neither is the fuel that goes into a reactor.

 

It’s what happens to the fuel once it goes inside the nuclear reactor that makes it toxic. The fuel undergoes a number of different reactions that change its composition. Over time, a certain portion of the uranium gets converted to other materials.

 

Eventually, the fuel is no longer pure enough to generate electricity efficiently. And after about two years of commercial reactor operation, it’s time to take the used fuel out and replace it with fresh fuel.

 

Here’s a breakdown of what the used fuel looks like at that point:

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• Uranium (94%): ...Well, that’s boring. The vast majority of uranium extracted from used nuclear fuel looks pretty much exactly like the stuff we put inside.  What does that mean? Well, as I mentioned, uranium is not particularly radioactive. It also poses a low proliferation risk – meaning it’s difficult to make weapons out of it. And, obviously, it can be used as nuclear fuel again, greatly reducing the need to mine for more natural uranium.

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• Plutonium (1%): Unlike uranium, plutonium is quite radioactive; although not any more so than the material inside your home smoke detector. Plutonium can be used as fuel in a nuclear reactor by itself, or mixed together with uranium to make mixed oxide or “MOX” fuel. When used by itself, it’s a very efficient fuel for certain types of reactors called “fast reactors" . Additionally, plutonium is one of scant few materials capable of powering the probes that NASA uses for deep space exploration. Most notably, however, certain types of plutonium can be diverted to make nuclear weapons. It is this particular characteristic of plutonium, in addition to economic reasons, that drives U.S. policy on reprocessing of used nuclear fuel. I’ll come back to that in a minute.

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• Other (nasty) materials (5%): The remaining materials are highly radioactive, dangerous to humans, and are not useful for making nuclear fuel – let alone bombs. Regardless of what is done with the uranium and plutonium, this part of the fuel is always going to be waste.

 

Got it? Okay, let’s see what we can do with this stuff.

 

What happens to used nuclear fuel after you take it out of the reactor?

 

Even though a relatively small portion of the spent fuel is highly radioactive, it’s enough to make the entirety of the fuel highly radioactive and very, very hot. So the first thing that happens to the fuel is it gets put in pools of water for five to ten years until it cools down.

 

Sound like a long time? Get used to it. A good rule of thumb is that everything that happens with nuclear power is sloooow.

 

After that, used fuel is put into what are called “dry casks”, or large casks made out of special material to shield the radiation emanating from the fuel. Normally, the casks are located on a pad at the site of the nuclear reactor. There is some debate regarding how long the fuel can safely remain inside of the dry casks, but most people will say around hundred years.

 

The first dry casks were loaded in the United States in 1986. In so far as the integrity of the casks is concerned, the fuel is okay in there for now. After that, a number of different avenues are possible, and that’s where the big policy decisions are made.

 

How can used nuclear fuel be recycled?

 

In a used fuel rod, all of the different materials – uranium, plutonium, and the other stuff – are mixed together. In order to be useful for anything, the useful uranium and/or plutonium must be chemically separated from the other non-useful materials.

 

The most common and widely used process for doing this is called PUREX (Plutonium-Uranium Extraction). PUREX was invented in the United States and widely used in the early years of the nuclear industry, when uranium was considered scarce and plutonium was required to make weapons. But we haven’t used PUREX or reprocessed in the United States for decades.

 

Meanwhile, other countries learned PUREX from us, and improved upon it. Now they know how to do it very, very well.

 

For example, France has been using PUREX without incident since it became national policy in the early 70s. The French currently get 75% of their total electricity from nuclear power, including 20% from recycled nuclear fuel. They regularly ship used fuel across the country in trains to a centralized facility where up to 97% of the used fuel is recycled using the PUREX method.

 

The addition of reprocessing to France’s nuclear fuel cycle only adds 6% to the total lifecycle costs of nuclear power, and drastically reduces the amount of waste they have to deal with to almost nothing.

 

So if reprocessing works so well in France, what’s what’s our big beef with it?

 

Plutonium problems

 

Some people are concerned about the part of PUREX that involves separation of plutonium because certain types of plutonium can be diverted to make nuclear weapons. In fact, the United States has about 34 tons’ worth of nuclear warheads considered excess to current defense needs that are leftover from the early days of using PUREX. Yikes.

 

Before getting too worked up, however, I want to point out that not all plutonium is created equal. There’s an important distinction between “reactor-grade” plutonium – the stuff inside of conventional spent fuel – and “weapons-grade” plutonium – the stuff inside of weapons.

 

Generating weapons-grade plutonium from used nuclear fuel through PUREX requires major deviations from normal commercial reactor operations. For example: the used fuel would need to be removed from the reactor after only a couple of weeks, versus two years, as in an ordinary commercial reactor. No weapons-grade plutonium has ever been made this way from any of the reactor designs used in over 98% of the reactors operating in the world today.

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You can also feel comforted by the fact that weapons-grade material is safeguarded under international law by numerous governing bodies, such as the International Atomic Energy Agency and the U.S. National Nuclear Security Administration.

 

...Fair enough. But this still leaves us wondering – could reactor-grade plutonium ever be turned into weapons-grade plutonium?

 

The answer is that it is extremely difficult, but technically, not impossible.

 

Some countries, like France, separate reactor-grade plutonium, and then almost immediately mix it with uranium and turn it into MOX fuel to be burned in commercial reactors. But other countries – namely Japan – stockpile the reactor-grade plutonium all by itself with no immediate intention to use it.

 

Plutonium by itself isn’t particularly useful in conventional nuclear reactors. Moreover, Japan, of all countries, is not interested in developing a weapon – let alone doing so illegally. Then why, you ask, would they do this?

 

Stockpiles come in different shapes and sizes

 

It turns out that separated plutonium makes really good fuel for a new, improved type of nuclear reactor called a “fast reactor”. There aren’t any commercial fast reactors today, but countries around the world – including our own – have been experimenting with them for decades.

 

The original idea behind fast reactors is that they can be designed to produce more fissile material than they consume. You can see why this might be appealing to Japan, which has no natural resources and is highly dependent on foreign fuel imports . Fast reactors were supposed to provide a virtually infinite supply of energy.

 

But fast reactor development has been slower than anticipated in Japan and elsewhere, leading to a buildup of reactor-grade plutonium above and beyond the existing stockpile of weapons-grade plutonium leftover from the Cold War.

 

Today, between legacy weapons stockpiles and dreams of fast reactors, we have a few countries around the world with exorbitantly large quantities of the stuff.

 

Can you guess who they are?

 

The following list shows the countries with the top six largest plutonium stockpiles:

 

• United Kingdom: 123 tons

• France: 78 tons

• Russia: 52 tons

• United States: 49 tons

• Japan: 47 tons

• Germany: 3 tons

• China: 0.014 tons

 

Note that all the countries on this list, apart from Japan and Germany, are nuclear weapons states. 

 

You probably have come to the conclusion that separating additional plutonium, even if it’s reactor-grade plutonium, isn’t such a good idea. But even if nobody separates any more plutonium from this day forward, we still need a solution to dispose of what we already have.

 

How to get rid of plutonium

 

We have three options:

 

(1) Burn it in a fast reactor.

Over the years, a number of commercial fast reactor designs have been proposed. For example, General Electric’s PRISM reactor is meant to burn plutonium as fuel without breeding additional plutonium, thus eliminating the proliferation risk.

 

(2) Mix the plutonium with uranium to form MOX and burn it in conventional reactors.

Many conventional reactors are capable of burning mixed fuel, and if they aren’t, upgrading them to do so is not that difficult. If fast reactors don’t come online soon, this might be the best option. Note, however, that to make MOX fuel requires the facilities to mix the plutonium and uranium together in the first place. That’s easier said than done. In the United States, we’ve already been struggling unsuccessfully to develop our own MOX production facility for decades.

 

(3) “Dilute and dispose”

The dilute and dispose method is exactly what it sounds like: dilute the plutonium with non-radioactive materials, and dispose of it in a geologic repository. This was the method pushed by the Obama administration. Many argue it is the cheapest and least risky of the three, as it is the only one that doesn’t involve shipping plutonium fuel around the world. But it does require a site for large-scale permanent disposal, and adds to existing tonnage of used nuclear fuel.

 

Phew! Well, I could go on forever about the politics of reprocessing, but let’s save that for another day. Now I want to take a look at what the other option looks like. We’ll see if it’s any less vexing.

 

Used nuclear fuel, in the United States, is nuclear waste

 

Recall that used nuclear fuel, after leaving the reactor, goes first to pools, then to dry casks. You might be wondering – why can’t the fuel remain indefinitely in the dry casks? Well, it stays radioactive for thousands of years, and the casks eventually crack and degrade. Moreover, even once the nuclear power plant itself is decommissioned, the land can’t be reused until the used fuel is moved off-site.

 

In the United States, there are also legal complications. U.S. law states that the used nuclear fuel from commercial reactors must be disposed of in a single, centralized repository deep in the ground; i.e., a “permanent geologic repository”.

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Unbeknownst to most people, the United States actually already has a fully operational geologic repository for defense-related nuclear waste: it’s called the Waste Isolation Pilot Plant, or “WIPP”, located in Carlsbad, New Mexico.

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What we don’t have yet is a geologic repository for the used fuel from commercial nuclear power plants. As a result, utilities throughout the country are suing the U.S. Department of Energy millions of dollars for their failure to provide this solution and their need to pay for continued on-site storage of the used fuel. In case you didn’t realize, that cost ultimately translates to taxpayers.

 

Actually, the U.S. nuclear waste law gets even more specific about where commercial used nuclear fuel should go: a little place called Yucca Mountain, Nevada. If you haven’t heard of Yucca Mountain, do look it up. To say the site has had its fair share of political controversy would be an understatement. Despite being started over thirty years ago, the project hasn’t gotten very far and was in hiatus for the past eight years of the Obama administration.

 

But the controversy surrounding Yucca Mountain is political, not technical. It basically comes down to this: whose decision is it to give the go-ahead for a site? The nation’s? The state’s? The county’s? And what about the Native American tribes? And how about future generations? Oh, and transportation?

 

It’s not that no one wants the waste at  Yucca Mountain, per se; for example, in Nevada’s case, the people of Nye County, where the waste would actually be stored, were all for it, due to the economic opportunities it would bring. For the record, it was the Las Vegans who didn’t like it. Interestingly, a Native American tribe in Nevada called the Goshutes also offered to take the waste, only to be later overruled by the Nevada state government.

 

The real problem here is that there is no good way to decide who qualifies as a stakeholder, and out of all the stakeholders, whose opinion gets to trump all others. That’s especially true in a nation as vast and diverse as ours.

 

And if you’ve been wondering this whole time: is the waste actually dangerous? Well, if it is not properly protected, then yes, extremely – at least for the first few thousand years or so. But according to the experts, technical solutions exist to protect the surrounding population.

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Lots of people tend to get stuck on the issue of transportation of used nuclear fuel. We already know how to do this safely for all kinds of radioactive materials. We don’t transport fuel regularly because of the current political situation, but we’ve done it before, and we know how to do it. Given all the other complex issues at hand, transportation really shouldn’t be the hold up in finding a nuclear waste solution.

 

As for the repository itself, our government spent decades studying how to do this. One conclusion was that a person living directly above the Yucca Mountain repository drinking two liters of the water per day and possessing no knowledge of the waste’s existence would have less of an increased exposure than from working in the U.S. Capitol Building, or from simple background radiation – both of which are far below the levels at which at increased risk of cancer has ever been observed.

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But people don’t trust the government; they would rather come to their own conclusions. And consensus is difficult, if not impossible, to come by.

 

If not here, then where?

 

So that’s what makes geologic repositories hard in a democracy. But we’re not the only ones struggling with this; countries around the world who choose to dispose of their nuclear waste in this manner are having the same problems. Given that, who has successfully built a geologic repository...anyone?

 

Kind of, yes. Finland is the closest. They are constructing theirs and expect it to be operational by 2023. Sweden is next: they are expected to approve the final site this year. Others in Europe are following suit. Switzerland is currently looking at different sites. The French have a law to build one by 2025.

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My guess is that since all of these countries are smaller and in some cases less demographically diverse than ours, it is easier to get everyone on board.

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What should we do?

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Some people get overwhelmed and say we should end the use of nuclear power as soon as possible: you know, shut down all the reactors, end all license extensions, no more fast reactor research, etc.

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But that’s a stick-your-head-in-the-sand kind of non-solution that you’ll discover, upon further inspection, will only exacerbate the problems that exist. So let’s actually think about this. First of all, what are our problems?

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In the United States, we have a great deal of separated weapons-grade plutonium, and a great deal of used nuclear fuel. Both demand solutions in the next few decades or so. Moreover, to accomplish anything and to avoid wasting billions of taxpayer dollars requires commitment to a single policy over the course of decades. That’s not easy for us, in our current political environment.

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In the crudest sense I would say there are two choices: (1) build more reactors to burn the stockpiles and waste that we have, or (2) generate a lot more waste. Either way, in the long term, we need a waste solution; and in the short term, we probably need more reactors. Perhaps we will need to rely on a combination of multiple solution, or perhaps the U.S. government will proceed in a way that makes some people happy, and infuriates others.

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One thing is certain: we do need to move forward – or we’ll just get left behind.