Thursday, February 28, 2013

Restoring U-M’s most extreme windows

Kevin Mayra wipes down the last pane in the window. Photo: Joseph Xu, Michigan Engineering.

Cleaning three-foot-thick windows, composed of 6-inch-thick panes that weigh up to 740 pounds each, was never going to be an easy task. But by undertaking it, Alex Flick, an engineer in the department of nuclear engineering and radiological sciences (NERS), could get the university’s second hot cell up and running again.

The hot cell will help the Radiation Materials Science group, led by Gary Was, professor of NERS, to gain insights on the aging of components that have spent decades in nuclear power reactors. Most of the reactors in the US are approaching or surpassing 40 years of service, and many are set to operate for another 20 years. With no new reactor construction since 1977, US reliance on fossil fuels will have to rise steeply if these reactors shut down before new ones can take their places. To keep them running safely and efficiently, nuclear engineers need be smart about making repairs – and that means figuring out what components will break and when.


A difference you can see. Photos: Alex Flick.

Three-ton radiation-proof windows might not spring to mind when you think of Corning glassware, but back in 1958, the company provided the University of Michigan with six of them. Infused with lead to help absorb high-energy particles and rays of light, they offer yellowed views inside a concrete bunker, allowing researchers to stand outside and safely manipulate radioactive materials with robotic arms.
Phil Simpson peers into the hot cell and uses robotic arms to manipulate a radioactive sample inside. Photo: Joseph Xu, Michigan Engineering.

By the mid-1990s, all three windows in the north cell were fogging over. With the Ford Nuclear Reactor shut down in 2003, the demand for the hot cells dropped - researchers no longer needed them for handling fuel. The remaining cell sufficed for preparing experiments in Was’s Irradiated Material Testing Laboratory.

The irradiated materials team uses the hot cells when they handle metal samples that have been exposed to radiation in test reactors, which has made the samples radioactive. The team sets these samples into chambers that subject them to the extreme temperatures and pressures of nuclear reactors while applying mechanical stress, encouraging the formation and growth of cracks. By studying how materials break following radiation damage, the team can draw conclusions about how long they will last in power reactors.

Since the pressurized water chambers block most of the radiation from the sample, the team can wheel them into the laboratory next door and leave them for months, with some experiments running for upwards of half a year. However, they would like to run tests with samples that have received much higher radiation doses, simulating longer periods inside a power reactor. These samples are so radioactive that the experiment would need to stay in the hot cell.

Flick and Mayra slide a pane of glass out of the window with industrial-strength suction cups. Photo: Joseph Xu, Michigan Engineering.
“In order for us to test the more radioactive samples, and for other people to use the hot cells, we need the second cell to be active. So the problem of solving the glass issue fell to us,” said Was.

Flick asked hot cell specialists for a quote on repairing the windows, and the company wanted almost a quarter of a million dollars. It wouldn’t be easy to raise that much cash, so the team considered alternatives. That’s when Phil Simpson, a hot cell operator and U-M retiree, discovered a 50-year-old instruction manual detailing how to pull the windows apart. Flick thought it looked doable.

“We said, ‘Well, let’s give it a shot,’” said Was.

To tackle the foggy windows, Flick and Simpson enlisted Kevin Mayra, a member of the Memorial Phoenix Laboratory building staff, and NERS graduate students Justin Hesterberg and Jeff Katalenich. They disassembled the first window, moving the panes one at a time with a hydraulic lift. At an estimated cost of $100,000 per pane of glass, Flick has been very meticulous about protecting them from chips and other breakages. “I don’t know if there’s a facility in the US to make such a piece of glass right now,” he said.

Flick arranges the sling around a monster pane of glass. Photo: Joseph Xu, Michigan Engineering.

The team rested the first five panes on specially constructed wooden racks while the last pane out went directly onto the table where they would try to clean it. This was the moment of truth for the project.

Without oil between the glass, each pane creates a reflection, as Flick demonstrates. Photo: Joseph Xu, Michigan Engineering.
The panes were covered in oil that bends light to the same degree as glass does. At its best, the oil fills in the gaps between the panes of glass, creating a seamless view. Without it, reflections appear in the window where the light hits the layers of air.

The team hoped that the oil was also the cause of the fog, having degraded as oxygen crept in through a loose seal. If the glass was still cloudy after the surface was clean, it meant that the window had been filled with the wrong type of oil, and that oil had etched the glass. In that case, they might have to hire a specialist after all.

“First, we tried the cleaning solutions recommended in the old manual, but they didn’t work particularly well,” said Flick. Then they tried rubbing fresh oil over the grubby glass.

“They were able to just literally wipe them clean,” said Was. And with the window reinstalled, he added, “The vision is perfect. It’s beautiful.”

Beautiful. Photo: Joseph Xu, Michigan Engineering.

As of last week, Flick’s team has de-fogged all three windows. Between labor and materials, such as fresh oil and custom gaskets to seal the windows, the project was a bargain at about $16,000. The hot cell is expected to be ready for use in a couple more months.

See more window cleaning action on Flickr.

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