Greg Zimmerman was heading for his high school parking lot when he learned that an accident had occurred at the Three Mile Island nuclear power plant about 18 kilometres away. His first clue was the school principal barring his exit from the building.

“I thought he was joking,” says Zimmerman, “but he got really mad.”

That teenager is now a physical chemist at Bloomsburg University of Pennsylvania, studying high-temperature conditions in experiments that may help in designing cooling systems for future generations of nuclear reactors. This year as a Canada-U.S. Fulbright visiting chair at Guelph, he is working with a leader in the field: Prof. Peter Tremaine, Chemistry.

Zimmerman studies corrosion reactions in water under high temperature and pressure, key to anyone designing or maintaining steam-generating utilities, including reactors. Tremaine’s lab is one of only a few groups worldwide with technical instruments allowing scientists to precisely measure the properties of reactive chemical species in water under such extreme conditions.

Along with the lab team, Tremaine and Zimmerman are calibrating and refining an experimental device at Guelph used to make those exacting measurements up to 400 C. The only other instrument of its kind is at Oak Ridge National Laboratory in Tennessee.

Last year, Tremaine received new funding to continue studies intended to help in designing nuclear power reactors. So-called fourth-generation reactors expected to be in use by about 2030 will use high- pressure supercritical water up to 600 C, about twice as hot as steam used in conventional facilities.

The Guelph scientist studies water chemistry, including exotic materials to be used in those reactors. Referring to concerns about burning fossil fuels, Tremaine says: “It’s impossible to envision a solution to greenhouse-gas emissions that does not include nuclear energy.”

Zimmerman says nuclear power poses its own challenges, not the least of which is safe and permanent disposal of waste. But he says nuclear generation needs to remain an option among alternatives to fossil fuels. In fact, U.S. President Barack Obama’s latest proposed budget has billions of dollars for the construction of new nuclear power plants. Most of the roughly 400 reactors operating worldwide were built in the 1970s and ’80s.

Zimmerman grew up in Mount Joy in Pennsylvania, about 90 minutes south of the capital, Harrisburg. In March 1979, an accident caused a partial meltdown at the Three Mile Island power reactor nearby.

Barred from leaving school at noon that day, he went to his chemistry class, where his teacher was holding a Geiger counter out the window to check for radiation levels. Nothing was registering, he recalls.

Although no significant radiation was released, the accident caused deep public concern and dramatically slowed construction of new reactors in the United States and Europe, says Zimmerman.

“I felt a deep conviction that reactors must be fail-safe and that scientists have an obligation to ensure they are.”

He had already caught the chemistry bug as a middle-schooler, using an old chemistry set to do experiments and even writing a Grade 8 speech about nuclear waste.

This year he’s on research leave from Bloomsburg University. He’s living in Guelph with his wife, Kathy, and their three sons: Andrew, Joseph and David. Their time here has given them a new look at their northern neighbour.

They’ve tried curling and hockey and have hiked around Guelph, Elora and Niagara Falls. Andrew even sang Canada’s national anthem at a Guelph Hurricanes game with a group from Bishop Macdonell Catholic High School.

“A big part of the Fulbright is getting to know Canada,” says Zimmerman, who’s found Canadians to be generally amenable and approachable — “except driving on the 401.”