Size matters to speed nuclear waste cleanup


Cleaning up the radioactive waste left over from nuclear weapons production has been a daunting, time-consuming and expensive process.

Now, researchers at Pacific Northwest National Laboratory (PNNL) have designed and demonstrated a simple particle separation technology that can reduce the time and money needed for cleanup. Application on an industrial scale is described in Chemical Engineering & Processing: Process Intensification.

Additionally, the technology may have many industrial uses, including in food processing, advanced manufacturing, aerosol science, supercritical fluids, oil and gas, and environmental waste treatment.

Researchers at Pacific Northwest National Laboratory have developed patent-pending technology — applicable in a variety of industries — to separate particles of different sizes. In this video, Michael Minette and Nathan Phillips demonstrate how the separator works when treating sludge through a three-inch pipe in a high-rise lab. (Video: Pacific Northwest National Laboratory)

If the particle matches

Cleanup of nuclear waste is complicated. For radioactive and chemical waste, such as that stored in underground tanks at the Hanford site, it can be beneficial to the treatment process to separate solid and liquid raw waste by particle size.

In PNNL tests of simulated waste – in this case, buckets of granular oxides mixed with water in a slurry – the newly developed separation technology quickly and successfully separated larger particles from smaller ones at different scales. with several different solid-liquid mixtures.

The bench-scale demonstration maintained 94% flow for seven hours without downtime due to clogging. Additionally, the tests ran at a flow rate of 90 gallons per minute through a three-inch hose, which is an optimal flow rate for industrial operations.

“This flow rate of 90 gallons per minute was the number needed for potential industry applications, and faster flow rates are achievable,” said Leonard Pease, lead inventor and chemical engineer at PNNL. In most research settings, Pease said, you can design the concept and maybe do one or two lab tests in a year. But PNNL had the right facilities and the right people to bring the project to scale quickly.

PNNL researchers have invented an ingenious but simple solution to sort particles of different sizes from suspended substances such as radiological vessel waste or fracturing fluids. Using a 3D-printed filter, this “mesofluidic separations” process will accelerate the removal of large particles to at least 90 gallons per minute, allowing for industrial-scale processing. This patent pending filter design is exceptionally cost effective. It can operate for much longer periods of time than conventional dead-end filters and cross-flow filters before the inevitable clogging – and it requires much lower operating pressures than conventional filters. Full-scale mesofluidic separation filter testing was performed at the PNNL Multiphase Transport Evaluation Loop facility in early 2019. Andrea Starr | Pacific Northwest National Laboratory

Pachinko of particles

The cleverly designed divider system looks like a series of hollow hockey pucks filled with rows of individual posts. Each row of descending posts is slightly offset from the row above. The team dubbed it “pachinko” because of its resemblance to the popular game used at carnivals and game shows.

With fluid flow moving at speeds of up to 90 gallons per minute, the poles create unique flow fields that cause larger particles to move in the desired direction. The researchers created “express lanes” in the system to remove larger particles. The new post arrangement is a major improvement for turbulent flows.

In a large-scale system, multiple sets of pucks with different post designs will guide the particles down their own express lane, separating relatively large pieces (about 1 centimeter or the size of a lemongrass candy) down to 20 microns. (about the size of a white blood cell). By stacking pucks one behind the other, “you get economies of scale without adding more expensive infrastructure,” Pease said. The splitter works in both horizontal and vertical mode, including downward and upward flow, Pease added.

Brainstorm bumps

Inspired by bump arrays used in the medical field, Pease and colleagues Michael Minette and Carolyn Burns knew that large particles could be separated from process streams at very low flow rates, but the process had not yet been demonstrated at high flow rates.

A small, slow current – called laminar flow – is calm, steady and predictable. As the flow becomes larger and faster – called turbulent flow – it begins to swirl.

They thought they would have to stick with laminar flow to keep the particles in the right paths. In 3-inch steel pipe – common for nuclear waste management operations – this would limit flow to less than five gallons per minute, which is not ideal. Operating in turbulent conditions was the only way to achieve the desired operational flow rates.

So the team members designed their initial device to work in a vertical pipe. They expected an arduous design process to overcome turbulent flow issues. They were wrong.

“Conventional wisdom said the system would only work on steady laminar flow, but we’ve proven it works on turbulent flow as well,” Minette said.

Success under turbulent flow conditions led the team to the concept of flow tracking dynamics, Minette said. “We realized that most of the larger particles weren’t bouncing off the poles, but were being carried along by flow currents created by the poles.”

Carolyn Burns, along with her colleague Nathan Phillips, led the testing of the mesofluidic splitter device at various scales. Burns is shown here in front of the engineering-scale setup in a high-rise lab. (Photo by Andrea Starr | Pacific Northwest National Laboratory)

In this design, the posts create flow streams that direct large particles down the express lane so they can be removed, which greatly reduces pin erosion and extends the life of the fixtures, Burns said. , a chemical engineer who stepped up experiments in the lab. .

“I was amazed that the pins didn’t break or erode – they held up to flux and harsh materials,” Burns said. “This experimental proof was a major advance in the functionality of the system.”

The particle separator is available for licensing or collaboration opportunities, said Sara Hunt, chief marketing officer of PNNL.

The separator was initially funded by the PNNL laboratory-led research and development program. The PNNL team includes Leonard Pease, Carolyn Burns, Nathan Phillips, Jason Serkowski and Michael Minette, as well as former PNNL colleagues Xiao-Ying Yu and Tim Veldman.

Article courtesy of the Department of Energy’s Pacific Northwest National Laboratory.



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