The Pacific Northwest National Laboratory (PNNL) in Seattle has developed technology to recover elements from spent nuclear fuel from power plants that are typically buried in large underground storage units.
Such fuel retains 95% of its potential to produce electricity and Gregg Lumetta, PNNL chemist and laboratory fellow, says this unsustainable practice is akin to filling a car with 40 litres of petrol, driving just far enough to burn two litres and discarding the rest – over and over again.
‘That is essentially the practice that the US nuclear industry is following,’ Lumetta says. ‘Spent nuclear fuel contains roughly half of the periodic table so, from a chemistry standpoint, there’s a lot going on. And, to reduce proliferation risk, it is best if pure plutonium is not produced at any point in the separation process.’
Researchers at PNNL have developed an innovative capability to rapidly separate, monitor and tightly control specific uranium and plutonium ratios in real time. First, the chemical slurry is fed into a centrifuge processing system, which looks like a giant pillbox with each compartment containing a rotor for mixing. The solution flows from one end of the system to the other, mixing, centrifuging, and adding or subtracting different chemical components along the way.
The breakthrough is being hailed as an important achievement in efficiently controlling the resulting product and safeguarding nuclear material. Lumetta admits that separating spent nuclear fuel is ‘like trying to deconstruct salad dressing with the goal of moving ingredients from vinegar to oil’.
R&D partner and PNLL chemist Amanda Lines adds: ‘Real-time monitoring was pivotal to determining exact chemical elemental ratios. We really focused on the uranium-plutonium percentages and knew exactly what they were at any given point.’ She points out that PNNL’s monitoring capabilities have evolved exponentially over the past 25 years, coinciding with a long history of research into fuel recycling and separation.
‘We can run the same types of separations studies and track the exact composition of uranium fuel components and fission products throughout the recycling processes, similar to what is done at a lab or industrial scale,’ Lines asserts. ‘This technology is cost efficient and enables incredible opportunities to develop and advance recycling approaches.’
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