University of Sheffield: Dr Corkhill reconstructs nuclear meltdown

University of Sheffield: Dr Corkhill reconstructs nuclear meltdown

 February 11, 2020

Women working at The University of Sheffield in the UK do truly important work that makes an impact on the world around them. For example, Dr Claire Corkhill and her team are reconstructing a nuclear meltdown in Sheffield in a bid to safely deactivate nuclear reactors in Chernobyl, Fukushima and all over the world.

Working to keep environments safe

Dr Corkhill is a Research Fellow in the Department of Material Science and Engineering. She and her team have been working with Ukrainian scientists to understand what’s going on inside Chernobyl's stricken reactor unit 4—and how it can be decommissioned safely. 

“It costs a lot of money to tackle a project of this magnitude and in Ukraine they don’t have quite enough,” Dr Corkhill explains. “The European Bank for Reconstruction and Development (EBRD) are bank-rolling the decommissioning operation, but it’s still down to scientists to understand how to safely remove the melted fuel. They have guys who go into the reactor to assess the status of the fuel, which is corroding badly and creating radioactive dust. It’s someone’s job and they get a high dose of radiation doing it."

Entering the reactor to see the extent of the chaos inside means risking high doses of radiation but, without sending people inside, how do we know what’s happening? This is the problem being faced over 5000 miles away at the Fukushima Daiichi Nuclear power plant. 

Chernobyl disaster site

Holding the key to a solution

In 2011, a 15 metre tsunami breached the protective walls surrounding the Fukushima Daiichi power plant, cutting off the power supply and cooling system for the reactors. In the first 72 hours all three reactor cores largely melted, creating an environment similar to the Chernobyl reactor with the fuel trapped inside the reactor.

“Until we remove the nuclear fuel there will always be a risk of radioactive material from the reactors reaching the environment and impacting upon current and future populations,” explains Dr Corkhill. “The nuclear reactor materials will be radioactive and potentially harmful to people for 100,000 years.” 

To remove the fuel from the reactor we need to fully understand the situation inside. This is particularly difficult at Fukushima because, unlike Chernobyl, nobody has entered the reactor core to see the internal mess of the meltdown. 

Sending people inside the reactor to assess the damage is a no go for the Japanese government, which means it’s difficult to know the mechanical properties of the fuel which is necessary to safely decommission it. However, thanks to the team of Russian researchers who went into Chernobyl in 1991, Dr Corkhill holds a key to unlocking the mystery inside the Fukushima reactor: the melted fuel sample

Chernobyl melted fuel sample

Reconstructing a nuclear meltdown

Dr Corkhill and her team prevent the need for anyone else to enter either destroyed reactor. The team are reconstructing what the fuel inside both the Fukushima and Chernobyl reactors might look like — both physically and chemically — using the melted fuel sample taken from Chernobyl as a reference.  

“What we’ve been doing is trying to recreate what the fuel looks like in Chernobyl in our labs in Sheffield. If we can accurately recreate it then we can use the same process to create a Fukushima fuel simulant, which is essential to help prepare for decommissioning operations and the removal of the fuel,” Dr Corkhill adds

As the fuel is corroding in each reactor it’s producing tonnes of tiny particles of radioactive dust. If it escapes into the air it will contaminate the workers trying to decommission the reactors, and may even enter the local environment. Understanding how the fuel corrodes means Dr Corkhill can estimate how much radioactive dust there might be and how to mitigate the problem. 

As well as an awareness of how the fuel corrodes, the team need to know how hard the debris itself is so engineers can design robots that are capable of cutting it. Without this information the fuel will remain trapped in the reactor core. 

“We’re taking all of the ingredients from the Fukushima reactor and melting them together at temperatures close to those from the real accident,” Dr Corkhill says. When reconstructing the melted nuclear fuel, the team have left out the highly radioactive by-products formed in the fuel during the nuclear fission reaction that generates electricity. This makes it much less radioactive, meaning corrosion and mechanical testing experiments can be performed easily using state-of-the-art equipment at the University of Sheffield.

The end result is a component not too dissimilar from the sample taken from Chernobyl which can be tested by Dr Corkhill and her team. 

The plutonium problem

Sheffield Dr Claire Corkhill

Whilst this might help the Japanese and Russian governments to remove the fuel efficiently and without expelling large amounts of radioactive dust, it doesn’t quite solve a problem presented by the plutonium itself. Plutonium is one of the earth’s most unstable elements and the Fukushima reactors used a mixture of plutonium dioxide and uranium dioxide as fuel.

“When too much plutonium is put together, there's a risk it will ‘go critical’,” explains Dr Corkhill. “Put too much together and you get a huge explosion and massive release of radioactivity."

The Japanese government is concerned that there’s still high amounts of plutonium in the fuel inside the reactors. Understanding the distribution of plutonium inside the reactor is fundamental to safely sorting the fuel as it’s removed from the reactor. To do this, Dr Corkhill has added a non-radioactive alternative to plutonium - with similar chemical properties - into the reconstruction of nuclear fuel debris. 

uranium distribution

Research that could help across the world

Sheffield seems an unlikely place to feature a reconstruction of a nuclear meltdown. However, thanks to the work of Dr Corkhill and her team, the scars left by these nuclear disasters might soon fade.

“The things we’re learning on this project are also useful for decommissioning ‘normal’ reactors around the world," Dr Corkhill concludes.

Read the full article from the University of Sheffield to gain more insight into Dr Corkhill and her team's nuclear meltdown work.

Join Dr Corkhill at the University of Sheffield

At the University of Sheffield, women like Dr Corkhill undertake important research that can make a positive impact on a global scale.

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