Who hasn’t marveled at the sight of a droplet gliding across a hot surface, somehow surviving well past its logical lifetime? Interestingly, MIT’s Jacopo Buongiorno and Lin-Wen Hu say curbing that mundane phenomenon could lead to big benefits in terms of producing electricity.
Buongiorno is an assistant professor of nuclear engineering and Hu is associate director of the MIT nuclear reactor lab. The two want to deploy what are known as nanofluids as circulating coolants in nuclear plants. If it works, the gains could be startling. “You can think about taking a 1,000-megawatt plant,” says Buongiorno, “and turning it into a 1,400-megawatt plant.”
Nanofluids are liquids that harbor nanoparticles. And the reason these near-infinitesimal objects may be able to boost a nuclear plant’s output relates to those gliding droplets.
The droplets survive, notes Buongiorno, because “there’s a vapor film that forms between the droplet and the surface. That allows the droplet to dance around for a while before it boils away.”
What works for a droplet doesn’t for a nuclear plant, though. One key to the efficiency of such plants is how well heat is transmitted to the coolant as it works its way up through the vertical pipes bearing the high-temperature nuclear fuel.
If the coolant simply boils, that’s fine. But if a vapor film forms between the liquid and the piping wall adjoining the radioactive materials, notes Hu, “the ability of the system to transfer heat to the coolant goes down dramatically.”
The scientists want to reduce the chance such films will form by using nanofluids. The fluids’ nanoparticles may be any of a range of materials, from aluminum oxide to — yes — diamond dust. But what’s striking about the approach is that it takes a truly minuscule supply of particles.
“We get dramatic enhancements of the critical heat flux with the nanoparticles at concentrations of .001 percent,” notes Buongiorno. “It’s almost magical.”
No one quite understands how particles at such concentrations can do what they do. In fact, Buongiorno and Hu are exploring that point.
The first nuclear-plant applications of nanofluids may not be as day-to-day coolants but rather as replacements for the emergency coolants every plant must have. That in itself would save meaningful sums. The use of nanofluids as circulating coolants, meanwhile, must await further studies of issues like whether they might damage a plant’s piping.
“Preliminary results from experiments at MIT’s research reactor have been promising,” notes Hu, “but we need additional in-core testing to determine how these specialized nanofluid particles will react under the harsh radiation environment of a working power plant.”
Assuming those studies pan out, though, the potential’s great. “There are more than 400 nuclear plants worldwide,” says Buongiorno, “and in principle, most of them could be retrofitted to handle nanofluids.”