糖心视频

Another day, and another “day in the lab” for our technicians – specifically Richard! As I mentioned in my previous blog with Richard, he splits his time 50/50 between the Scanning Electron Microscope labs and the UTGARD (Uranium Thorium beta/Gamma Active Research and Development) laboratory – a large radioactive laboratory within the university. It’s the only facility of its kind in the UK, and is at the very core of research into spent nuclear fuel disposal and recycling, full of fascinating (and expensive) bits of kit dedicated to analysing and making radioactive materials.

After getting all of our PPE on (lab coat, overshoes and, of course, dosimeters), it’s time to head on in! Today, Richard is training up his PhD student Ethan on a piece of kit located in UTGARD called a “spark plasma sinterer” (SPS). The SPS is a bit of kit used when one wishes to quickly turn a powder (in this case, uranium) into a solid pellet. To do this, you add the powder to a graphite die with a punch in each end, and then put it in the machine, which passes an electric current through the die whilst compressing it between the punches, heating the sample via induction to a toasty 1100 C to form a handy pellet of uranium in just fifteen minutes! Just a bit hotter than your standard oven, and a smidge more expensive at ?300,000.

The graphite punch and die – ready for roasting!

This is much faster (and cooler) than using a regular lab furnace – which would bake a pellet such as this in 8-72 hours depending on the size – but it does have the drawback that each sample needs to be prepared and sintered separately, making the regular furnace more useful if you wish to batch cook your uranium. Ethan’s PhD is looking at ways to make nuclear fuels safer for us to use – hence why we’re making pellets of the stuff for him to conduct further experiments with.

First things, first: turning on the SPS! Unsurprisingly, it gets very hot, so has a chiller connected to it to control the temperature. Contamination is also a big issue when working with radioactive materials, so the sample is prepared in a filtered glove box to protect us from any potential spills.

Ethan getting ready to prepare the sample for the SPS. It’s very loud, hence the ear defenders

Inside the chamber are another two graphite blocks, which Ethan has to mount the sample onto. Graphite is used throughout the SPS components due to the fact that it is strong, heat-resistant and conductive, making it the perfect material for this particular piece of kit. The inner granite block will compress the die setup with up to one gigapascal of pressure – enough to make diamonds and rubies if desired! Whilst the SPS is predominantly used to make uranium pellets, it can theoretically be used to make a whole range of materials, including novel alloys, or known alloys such as steel. The lower sintering temperature (that’s the temperature at which powder particles meld together to form one solid piece) of the SPS makes it a lot easier to make difficult high-temperature materials than in a normal furnace – plus with the added bonus that the chamber has a window, so that you can observe your run as you go!

A terrible photo of Ethan loading the sample into the main chamber

With the sample loaded, it’s time to crank up the heat! The SPS is liquid-cooled (by our aforementioned noisy chiller) to ensure that nothing melts as we’re bringing the sample to temperature, and is run under argon, an inert gas, to prevent any unexpected reactions.

To make sure that we’re heating the sample to the right temperature, Ethan and Richard can position an infrared laser thermometer to measure how hot it is getting. The laser is focused on a small hole in the graphite die to get a thermal reading, which is then fed back into a computer, which can adjust the current accordingly.

Peeking through the porthole window, you can see the sample heating up in the SPS!

The pyrometer that the SPS is hooked up to can’t measure temperatures below 300C, so it’s a matter of waiting a few minutes for it to heat the sample up enough for Ethan and Richard to start getting a reading on the computer and track the progress. The computer is programmed with specific instructions as to how much to heat the sample up by, how long for, and how much pressure to apply. Whilst this process is automated, Richard and his students always stick around to keep an eye on the sample to make sure it doesn’t overheat, as the sample will be ruined if this happens.

Ethan keeping a weather eye on the sample.

Whilst uranium has a very high melting point (and is therefore unlikely to melt in the SPS), there is a chance that the pellet could fracture whilst under pressure in the machine. If the pellet breaks, it limits the other types of analysis Richard and Ethan will be able to run on the sample, so fingers crossed that all goes smoothly! Once the sample is heated up to the desired sintering temperature, it sits for 15 minutes before the machine will shut itself off and start the process of cooling down. Sadly I had to run off to another meeting before the cooling process had finished, but Richard showed me one he’d made earlier, in true Blue Peter style:

A small and innocuous uranium pellet, perfect for further study!

?A whole pellet such as this can then be mounted in resin in order to conduct corrosion tests, which will allow Richard and Ethan to see whether different additives have an impact on the rate of corrosion of the sample. Otherwise, the sample may be carted off to the SAFER or XPS labs with Richard to undergo further elemental analysis, feeding into his other role at the University – it’s all cyclical here in the School of Engineering!

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