Ahmed Ismail
What do sticky proteins have to do with safely storing nuclear waste? On the surface, Ahmed Ismail says, they involve considerably different scales of time and size.
A nuclear waste repository “covers tens of square kilometers and its time scale is 10,000 years,” he notes. “Protein interactions take place in nanometers and nanoseconds.”
What ties them together for Ismail, who works for Sandia National Laboratories, are the complex models of molecular-scale interactions that he uses to predict behavior in both regimes.
While a doctoral student and Department of Energy Computational Science Graduate Fellow at the Massachusetts Institute of Technology, Ismail worked on ways to simplify simulations of molecular interactions so they eat less supercomputing time. “This is a widely researched problem, but the applications have not kept up with the theory,” he says.
After his MIT thesis defense — for which the lifelong Red Sox fan prepared while sneaking peeks at Boston’s first World Series win since trading Babe Ruth to the Yankees — Ismail moved to Sandia as a post-doctoral researcher.
At Sandia, Ismail used models to explain why proteins sometimes stick to the non-stick polyethylene oxide (PEO) coatings used to prevent fouling in medical devices. “Proteins like to bond to regular surfaces,” Ismail explains. “Coat with too little PEO and proteins bond to the exposed metal below. Use too much PEO and its molecules will crowd together to form a regular ‘surface’ to which proteins can stick.
“Between those two extremes, water slips between the PEO molecules, creating an irregular surface that proteins ignore. I think of this as the ‘Goldilocks effect,’ because the coating has to be just right to work,” Ismail concludes.
After finishing his post-doc, Ismail joined Sandia’s Carlsbad Programs Group, which supports the world’s only operating nuclear waste repository. DOE’s Waste Isolation Pilot Plant (WIPP) was built to safely hold clothing, test tubes, and other radiation-exposed items for 10,000 years.
WIPP stores sealed waste containers in rooms dug into an underground salt deposit. Over time, pressure from thousands of feet of rock above will buckle the rooms and isolate the containers. The salt rock resists chemical infiltration.
In addition to continuing his PEO work, Ismail tries to imagine how worst-case scenarios might affect the waste. “In 10,000 years, people might forget WIPP is there and drill down to a reservoir of briny water several thousand feet below the repository,” he says. “We want to know what would happen if the brine infiltrated the repository.”
Using models that describe fluid mechanics, geochemistry, and nuclear physics, Ismail studies how radionuclides might react with rock and brine. “If the salt does its job, there’s likely to be very little release to the environment,” he says.
Yet Ismail continues upgrading Carlsbad’s chemical equilibrium model to improve its accuracy, as well as studying sites for the safe storage of more highly radioactive wastes.
Ismail never imagined using his ability to model molecular-scale interactions to understand radioactive containment, but he’s pleased about the added application.
“We’re solving a problem that already exists because we’re storing waste all over the place now,” he says. “Our group is trying to make sure that centralized storage is not a threat to the environment or to other people. I’m comfortable with that.”
