How the Wrong Kitty Litter Caused a Nuclear Leak

Sam Westreich, PhD

Crazy but true — in some cases, the right brand matters that much.
“Hah! That sign can’t stop me, ’cause I can’t read!” Cats, probably.Photo byPhoto by Kilian Karger on UnsplashonUnsplash

If you saw a story about “leaked radioactive material,” you’d probably think of misplaced nuclear weapons, or a nuclear power plant experiencing a dangerous meltdown, or maybe even some tale of war, spies, and sabotage.

You probably don’t think about kitty litter. You know, the grainy stuff that you pour into a litter box, so that a pet can poop and pee in there.

But in 2014, someone made the wrong decision about kitty litter, and it caused a chain of events that led to an explosion of nuclear waste, and a very angry New Mexico Secretary of the Environment.

And it all happened because someone decided to go organic.

Nuclear waste is the reactor’s leftovers

Most of the nuclear waste that’s stored in the world falls into one of three categories, depending on its radiation level:

  1. Low-level waste: this is mainly from hospitals and industry, and can usually be incinerated without any special procedures needed.
  2. Intermediate-level waste: this level requires some shielding, and it’s usually stuff like resins, chemical sludges, and metal fuel cladding, as well as contaminated materials from reactor decommissioning. It’s usually sealed in concrete for disposal.
  3. High-level waste: the spent fuel from a nuclear reactor and the byproducts from producing nuclear weapons during the Cold War; this is the stuff produced in the reactor core. It’s stored initially in ponds, but is then transferred to “dry cask storage”, where it’s placed in steel canisters, that are then surrounded with concrete.

It’s this third category, the high-level waste, that is the real serious stuff.

We’d ideally want to move the high-level waste to a permanent storage facility — and this would be something really secure, like a bunker dug deep underground, in an area that is confirmed through geologic surveys to be stable. We wouldn’t want any earthquakes or ground shifts to lead to this material accidentally being released.

Right now, however, the only disposal location for permanent holding of this waste is WIPP, the Waste Isolation Pilot Plant in New Mexico. WIPP has rooms mined in an underground salt bed layer over 2000 feet from the surface.

And it’s here that, in February 2014, a 55-gallon drum of waste material burst open.

Pack your nuclear waste in kitty litter

One of the goals when dealing with nuclear waste is to keep it as stable as possible. Liquids aren’t that stable; they slosh around, they can seep out through tiny holes, and they can corrode surfaces that they touch. It’s better to store your nuclear waste as a solid.

There are a number of techniques to do this, including vitrification, where the nuclear waste is mixed with molten glass to trap it in the solid glass once it cools.

An easier, more cost-effective method, however, is to use kitty litter. Most traditional kitty litter is made of pulverized clay, which in turn is made of silica (the same stuff in those “do not eat” packets in your new clothes) and sodium bentonite, a material that absorbs water and swells to hold it trapped in its structure.

Clay is pretty non-reactive. It won’t burn, melt, or break down into dangerous compounds. This makes it pretty safe to add to nuclear waste — it absorbs the liquid, trapping it as a solid, and won’t have any negative reactions with the waste material.

But when contractors at the Los Alamos National Laboratory (LANL) were packing up these drums of radioactive waste, they decided to use organic cat litter instead of the traditional stuff.

Organic cat litter is usually made of biodegradable products, such as paper pulp, wood chips, corn husks, or other “waste” material that is really cheap and would otherwise be discarded. Cats like it because it’s lightweight and they can easily bury their waste in it, and it doesn’t require mining or extraction, unlike clay.

But organic kitty litter has two big downsides:

  • It has carbon in it, which can burn.
  • It can react and create hydrogen gas — which is explosive.

Can you see what happened?

The nuclear waste combined with the organic kitty litter (which in this case, was discarded wheat chaff) and caused runaway heat-producing reactions. Eventually, the drum ruptured and caught fire.

What was the outcome?

Fortunately, the outcome was fairly minor — at least compared to how bad things potentially could have turned out.

On one hand, this was an expensive mistake. Estimates for the full clean up are north of half a billion dollars.

Why so high? Well, that’s actually linked with the silver lining; estimates are that somewhere between 500 and 700 drums were produced by LANL with this incorrect mixture of organic kitty litter added. But only one of them has reacted and ruptured.

Why did just that drum rupture? Researchers aren’t sure, but it likely has to do with the specific reactions that occurred between the radioactive waste and the wheat refuse. Perhaps certain compounds formed in that particular drum that were more volatile than others, leading to the spontaneous eruption.

The other drums that were filled mistakenly with the organic cat litter aren’t currently being replaced, but they are being monitored by the Department of Energy and are being reinforced.

Takeaway: keep organics out of your nuclear waste!

These days, when we talk about nuclear power plants, we have to think about the waste products. Current power plants produce solid waste products that are easily stored in secure facilities, but we also have lots of leftover liquid sludge, a scary remainder from producing nuclear weapons in the Cold War.

We are working to secure these, and part of that process involves adding sorbents, such as clay, to absorb and stabilize the liquids. This process works great with inorganic materials, and kitty litter happens to be a great bulk option for sorbents.

But we need to be careful not to add potentially reactive organic materials — such as organic kitty litter! This slip-up in 2014 showed that, while it won’t always lead to disaster, it has the potential to do so, and it’s an expensive mistake to make!


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A microbiome scientist working at a tech startup in Silicon Valley, Sam Westreich provides insights into science and technology, exploring the strangest areas of biology, science, and biotechnology.

Mountain View, CA

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