Cleaning up radioactive waste is a dangerous job for a human. That's why researchers at Manchester are developing robots that could do the job for us.
Five years ago, in 2011, a major earthquake and tsunami devastated the east coast of Japan, leading to explosions and subsequent radiation release at the Fukushima Daiichi Nuclear Power Station. The fuel in three of the reactors is believed to have melted, causing a large amount of contaminated water on site.
This is still to be dealt with today – which isn't too surprising, given that the clean-up of Chernobyl is still underway 30 years after the infamous nuclear accident took place.
Dangers to life
After the accident at Chernobyl, where an extremely high level of radiation was released, workers had to be sent into areas to which you wouldn't want to send a human being. For the safety of others, they entered the plant to survey its condition, extinguish fires and manually operate equipment and machinery – all in an environment that endangered their lives.
The challenge in dismantling the site at Fukushima is the residual radiation level. In the surrounding areas levels have fallen significantly; in some places (still off limits to former residents) radiation levels actually aren't very different from natural background levels in certain other parts of the world. But in the reactor itself a person would receive a lethal dose of radiation almost instantly.
Professor Lennox (left) and Dr Watson (right) holding prototypes of the Avexis ROV. Image by Tracey Gibbs
"At Fukushima, many of the instrumentation systems, such as reactor-water level and reactor pressure, were lost in the incident. This made assessing the integrity of the plant extremely difficult as you couldn't send people to go and look at it," explains Professor Barry Lennox, who, alongside Dr Simon Watson at The University of Manchester, is working to find another way of getting access to such dangerous places: by using robots.
A robotic solution
Professor Lennox and Dr Watson are part of a team working to adapt robots to help clean up Fukushima. They're developing an underwater remote-operated vehicle – the AVEXIS – to help identify highly radioactive nuclear fuel that is believed to be dispersed underwater in the damaged reactor. The robot is already aiding decommissioning efforts at Sellafield, where it will swim around the ponds storing legacy waste to map and monitor the conditions within them.
"Getting the robot to survive the radiation is the primary challenge at Fukushima. A person couldn't survive inside the reactor, nor can certain electronic parts," says Professor Lennox. "The semiconductors in the robot could be damaged, so we need to test how long they last in a radioactive environment."
The Dalton Nuclear Institute's Cumbrian Facility, the University's off-campus, state-of-the-art nuclear research centre, has just the equipment for this. Its Cobalt-60 gamma irradiator allows Professor Lennox and his team to test the stamina of their creations in conditions similar to the Fukushima reactor.
"We've been looking at small electronics, putting them in the irradiator to see how long they'll last," Professor Lennox continues. "It's an extremely high-dose environment inside nuclear reactors, so they don't survive very long."
It's not always easy to recreate real-world situations, though. "Robots aren't quite as adaptable as humans and the world isn't really built for them," Professor Lennox acknowledges. "You might test a robot walking on gravel in the lab, but unless you get the gravel absolutely right, you can't guarantee that it will work in the real environment.
"Likewise, robots can be designed to walk up steps, but the stairs at Fukushima were twisted in the explosion. It's very difficult to design a robot to go up a twisted staircase when you don't know how twisted it is. Even trivial things can be really complicated for robots. They aren't very good at opening doors. Doors confuse them.
"Our robot swims – so we can drop it straight into the water in which the reactor is submerged. The added benefit is that the water shields against radiation, making it much less damaging.
"We need to make the robot very small so it can enter the reactor through a 100 mm port drilled through the thick concrete shell. Once it's in, it needs to be able to see – feeding visuals back to us to navigate – swim, detect radiation levels and its own position, and survive for a ten-hour shift. It also needs to be relatively cheap, as once it's gone in, it isn't coming back out."
Building the bigger picture
The final product will be a group effort, with colleagues at Lancaster University designing a tiny neutron detector and Japanese partners providing an equally tiny sonar system. Once inside, the three elements will come together to build a map. The neutron detector will indicate from where radiation is originating and the sonar system will show the geographical layout.
Putting these together, a picture will emerge showing where the fuel is, allowing decommissioning to move to the next level.
Removing and safely storing the fuel will then significantly reduce radiation levels, which in turn will make the remaining decommissioning process safer and cheaper.
Professor Lennox believes robots have a lot of potential. "They could have been the first responders at Fukushima – checking areas for safety before any humans came near," he notes.
"They have a huge role to play in decommissioning, which now has to be built into any new nuclear plan from the start.
"We're also working on robots that can travel along pipes to check for corrosion inside, so they can contribute enormously to inspection too, keeping running reactors safe."
Energy is one of the University's research beacons. Find out more at www.manchester.ac.uk/beacons.