Blog

Only showing posts tagged with 'Chernobyl' Show all blog posts

Researching safe ways to dispose of nuclear waste

Introduction

My name is Robert Worth and I am currently part way through a PhD in Nuclear Engineering with the Nuclear Graphite Research Group at the University of Manchester – how did I get here? Almost by accident. It was during my A Level study in Physics that I first came across the phenomenon of radioactivity, which I thought was a bizarre and exciting process that I had not encountered before, and I needed to know more! This eventually led me to my degree in Mechanical (Nuclear) Engineering at the University of Manchester, which was very enlightening and encompassed many aspects of both mechanical and nuclear engineering. It was during my degree that I stumbled across an email containing upcoming PhD research projects – did I know what a PhD involved? Nope, not really. Did I want to do one? I wasn’t sure. I’m glad I applied, however, as it turned out that this is the sort of work I’d wanted to do all along, I just hadn’t realised it. You are no longer just absorbing information from others – I am also now doing the finding out, and helping answer questions that nobody in the world yet has answers to!

I’ve been very lucky with this PhD project, and have been encouraged to attend many prominent events and conferences around the country, talking with and working alongside some of the most inspiring people and minds in the country. I’ve been fortunate enough to travel further afield too, as far as Lithuania, where we stood on the top of a nuclear reactor core of the same basic design as the famed Chernobyl, and even over to the United States, to visit a research group at Idaho State University and to help on an experiment at a synchrotron particle accelerator in California.

My specific research project is on thermal treatment of irradiated graphite waste. It turns out that there is an awful lot of it (around 96,000 tonnes) in our small country, the UK. So far, there are good ideas about how we might deal with this large volume of radioactive waste, and the Nuclear Decommissioning Authority (NDA) have plans to bury most of it in a future geological disposal facility, a large controlled facility far underground that could house and contain all of our radioactive waste for thousands of years to come. Since a location for this facility is yet to be found, and it is yet to be built, you could argue that a disposal route is not set in stone. Which is where treatment comes in – can we do something else with the graphite waste to reduce the hazard, instead of burying it, which could potentially save money and may leave valuable space in the repository open for other more hazardous wastes? This is a point of controversy amongst the nuclear waste research community! 

In Depth

What is graphite and how is it used?

Graphite is a very stable hexagonal formation of carbon atoms, that can be found naturally but is also artificially manufactured to very high purities, at great expense! This involves many different processes to reach the final product including heating to around 3000oC for a number of days. It is essentially many planes of the material ‘graphene’ all layered up on top of each other, and is found in pencils; the ‘lead’ in your pencil is actually graphite, and it is these layers of carbon atoms sliding relatively easily over each other that allows you to write and draw quite easily.

Graphite is used in many nuclear reactors in the UK in the shape of enormous blocks, which can be over a metre in height, all stacked on top of each other and arranged into a large reactor core. Its purpose is to slow the neutrons in the core down, by acting as a physical barrier for the neutrons to bounce off, a little like billiard balls, so that they will react more easily with the nuclear fuel, producing energy for us to power our homes. 

Why is it radioactive?

Carbon has been selected as a fairly ‘neutron transparent’ material so that neutrons will bounce off and scatter away from the carbon atoms instead of being absorbed. This does not happen every time, however, and on occasion a neutron will be absorbed into the carbon atom, making the nucleus of the atom heavier and larger than it was previously. This can make the atom become unstable, as it can no longer physically sustain itself in a stable state, and so the atom will ‘decay’ by releasing some energy – in this instance, a radioactive carbon-14 atom will spit out an electron from the atom and transmute into nitrogen-14, which is a stable atom. Voila! This is the process of radioactive decay.

What do I actually do?

I spend a lot of time working in a laboratory with radioactive samples, taken from a nuclear reactor, wearing a white lab coat, goggles, layers of gloves, and working with tongs behind special shielding or in a glove box, like Homer Simpson. I also wear a dosimeter to record the amount of radiation I have received from the samples, so that I know I am well below safe levels for working. I then take these samples and place them in a specially designed tube furnace, and very carefully oxidise them using a gas flow of 1% oxygen to try and remove a good fraction of the surface radioactivity as a gas. The radioactive portion of this gas is then trapped and collected in a ‘bubbler system’, where the gas is forced to bubble up through a clever fluid, before it is taken away for analysis to determine how much radioactivity has been successfully removed. I can then use this data to make a reasoned judgment of how I might improve the process, by adjusting the temperature, for instance.

Going Further

More information about the array of Nuclear Engineering research in the School of MACE at the University of Manchester can be found at: http://www.mace.manchester.ac.uk/our-research/research-themes/nuclear-engineering/

A fairly detailed overview of ‘radioactive waste management’ around the world has been produced by the World Nuclear Association, and can be found at: http://world-nuclear.org/info/Nuclear-Fuel-Cycle/Nuclear-Wastes/Radioactive-Waste-Management/

A further insight into the role of the Nuclear Decommissioning Authority in the UK, working on behalf of the government and responsible for overseeing the clean-up of many UK nuclear power sites, can be gleaned from the following website: http://www.nda.gov.uk/what-we-do/