Researchers sent a nuclear waste container on a 14,500-mile odyssey by truck, barge, cargo ship, and train in an effort to understand how well radioactive fuel would stand up to travel.

That’s important to find out. Right now, “the US does not currently operate a large-scale transportation system for [spent nuclear fuel],” according to a report prepared for the Department of Energy in 2016. But one day, the plan is for all the spent nuclear fuel from power plants to go to a central storage repository. And then, “the number of these shipments by road and rail is expected to increase,” according to the Nuclear Regulatory Commission (NRC), the government agency that oversees the nuclear industry.

There have been decades of spent nuclear fuel transportation around the world. “At least 25,400 shipments of [spent nuclear fuel] have been made worldwide, but likely more than 44,400,” the DOE report says. So we know the containers, also known as casks, that the spent nuclear fuel travels in are pretty tough. New container designs go through a series of tests where they’re dropped, lit on fire, and submerged in water before the NRC certifies them for use. None of these containers have leaked in over 40 years of transporting nuclear waste, the NRC says.

“The risk is very low,” says Sylvia Saltzstein, manager of spent nuclear fuel, storage, transportation, and safeguards at Sandia National Laboratories. “I would have no qualms about this driving through my neighborhood.”

But scientists are still learning what actually happens inside those containers — where the spent nuclear fuel is packaged like a radioactive Christmas present. The fuel is made out of hollow metal rods packed with uranium pellets. These rods are bundled together into what’s called a fuel assembly, which is in a basket, inside a canister. That canister is what would get removed from the storage cask at a power plant and put into the transportation container that would go on a truck, train, or barge.

So to find out what happens to the fuel inside all that packaging, scientists at Sandia National Laboratories in Albuquerque, New Mexico, teamed up with the organizations in South Korea and Spain that are tasked with managing their country’s nuclear waste. They didn’t actually send any real, radioactive material on the journey — which took the container from Spain to Colorado and back. Instead, each of the three groups from the US, Spain, and South Korea brought their own faux-nuclear fuel that used lead or molybdenum to stand in for the uranium.

Using sensors like accelerometers and strain gauges, the teams measured how much shaking and rattling the faux-fuel endured during its trip. And the early results are starting to come in. “The fuel has a very smooth ride,” Saltzstein says.

The Verge spoke to Saltzstein about the nuclear triathlon and how nuclear fuel is kind of like Pez candy.

This interview has been edited for clarity and brevity.

What is the Nuclear Triathlon?

The Nuclear Triathlon is a test to understand what shocks and vibrations nuclear fuel would experience during normal conditions of transport. We took surrogate nuclear fuel, so no real nuclear fuel was used or harmed in this experiment. And we drove it by truck through northern Spain, by barge from Spain to Belgium, by ocean liner from Belgium to Baltimore, and then by rail from Baltimore to Pueblo, Colorado, and back again.

We had strain gauges and accelerometers placed on the actual fake fuel that’s inside a basket, that’s inside a canister, that’s inside a transportation cask. All of those were measured — every bit of that — just to see how it shakes, rattles, and rolls. So we’ll be able to say, “Okay, real nuclear fuel can withstand shocks of this magnitude. And during the transportation test, we saw shocks of this magnitude. Do we have an issue or not?” And the same for vibrations. With vibrations, we’re looking at more fatigue failures: if there are little wiggles, millions of little wiggles, is that eventually going to break something?

Is this a journey that spent nuclear fuel makes today?

No. Nuclear fuel really does not make any journeys today. There is no place at this point to put spent nuclear fuel. So it sits next to nuclear power plants all over the country and in every country that has nuclear power. So no, this is not a journey that it would normally take.

The reason we chose this journey is that Spain wanted to also do this test and shared the cost with us. They provided the hardware, and they were interested in truck transport. And then the Koreans also were interested, and they provided funding for the test, and they are going to transport almost all of their fuel by barge. So they wanted to get the barge data. In the US, we were interested in the rail part. We will do a little bit of truck transport to get some of this to the closest rail line and a little bit of barge to get it to the closest rail line. But the majority of our fuel, if we are so lucky, will be transported by rail.

How is spent nuclear fuel stored right now?

Right now, the industry is storing all of these fuel rods in very, very large storage containers. And since we don’t know where this will all be disposed, and we don’t know what kind of rock it may be disposed in, we may need to repackage all of these fuel rods into smaller, lighter disposal packages. And if we have to do that, and I hope we don’t, that’s when it becomes important to know: if it gets opened up after being transported, could you have broken fuel rods?

And the reason why that is important is the fuel is a bunch of pellets inside long tubes. Picture Pez — it’s actually round, but it’s the same idea. There are lots of little pellets inside a tube. There are hundreds of these tubes, and the tubes are long. So if you have to open this up to put it in a smaller container, you don’t want there to be cracks in that tube so that your Pez candy or your fuel can have more exposure to people or the environment.

Are the transportation containers the same as the containers that spent fuel is stored in at the power plant facilities?

When they are sitting next to the nuclear power plant, they have a big concrete container over them to provide shielding from radiation. And the container gets removed from the concrete shielding and then put into an over-pack, like a suitcase around it, and that’s called the transportation cask. And then it would be transported. So that transportation cask can be used numerous times, but the inside container that’s holding everything, that, of course, stays with the fuel.

What are some of the risks that spent fuel could face when it travels?

So, in complete honesty, this is an unbelievably safe method of transporting anything. The transportation casks are designed so robustly that what we’ve done with past experiments here at Sandia, where we have driven locomotives into these casks — we’ve driven trucks into these casks — and they don’t break.

In order to be certified by the Nuclear Regulatory Commission, they have to be dropped from 30 [feet] onto an unyielding target. They have to be fully engulfed in a fire for 30 minutes. They have to be dropped on a pole, like a puncture test. And then they have to be immersed in water. All of those tests have to happen in sequence, in order to get certification by the Nuclear Regulatory Commission, and the cask still cannot leak. So we are very, very confident that there is not an accident in transportation that could cause a big problem.

What we didn’t have information on is what happens to the actual fuel. The fuel maybe sat next to the nuclear power plant for 100 years because we don’t have any place to put it. If we transported it, we know the cask won’t leak. But if we wanted to open it up again at the end when it got to its final destination, would we have any concerns that there would be any cracks in the fuel? What our data will show and what the data is pointing to is that the risk of transport making a tiny crack in a fuel rod is pretty much zero.

After testing your fuel rods for 14,500 miles, what’s the verdict? Will you have nuclear Pez candy spilling around in there?

No. So the verdict, though we’re still analyzing the data, is that we have a huge margin of safety. So PNNL [Pacific Northwest National Laboratory] did an analysis, and they said the largest shock they saw was the equivalent of a wasp hitting a wall. It is very, very, very small. These rods are all contained in an assembly that holds them all together, and they are just not moving. And so even though the truck or the train jiggles quite a bit, the basket and the cask and the canister really hold it all together very well and actually absorb a lot of those little vibrations and bumps and shocks that the rail car experiences. Those energies don’t make it all the way up through the whole system to the fuel. So the fuel has a very smooth ride.

Update August 10th, 11:45AM ET: Updated to clarify how much spent nuclear fuel has been transported worldwide and to correct the unit of measurement for the NRC drop tests.