Robert Ray/AP/File
Steam escapes from Exelon Corp.'s nuclear plant in Byron, Ill., in this file photo taken last year. A nuclear reactor the plant shut down Monday after losing power.

Q&A: Illinois nuclear plant loses power. What got vented into the air?

A nuclear plant in Illinois shut down one reactor Monday after a transformer failed. The problem is growing for aging nuclear plants. But in this case, the public was never in danger, officials say.  

Nuclear regulators are keeping close tabs on an Illinois nuclear plant after a loss of off-site power to the plant Monday morning.

One of two reactors at the Byron nuclear power plant shut down when a transformer supplying electricity to the plant failed. Backup generators immediately kicked in to supply electricity to the reactor's safety systems, including its cooling system.

Plant workers reportedly saw the transformer, located in the plant's switch yard, release smoke after it failed, but local firefighters found nothing burning when they arrived.

During the shutdown, the plant vented steam containing trace amounts of tritium, a radioactive form of hydrogen. But the release represented no health threat, federal and plant officials told the Associated Press. Candace Humphrey, Ogle County’s emergency management coordinator, added that public safety was never in danger.

How often does a transformer fail US plants?

About six to eight times a year, according to David Lochbaum, a nuclear engineer currently tracking nuclear-safety issues for the Union of Concerned Scientists. Not all result in a loss of off-site power, he says. Some plants can quickly isolate the bad transformer and draw electricity from other sources.

While the number seems small, the number of failures is rising, he adds. In many cases the transformers are as old as the plants themselves and have reached the end of their design lives. While the loss of a transformer can result in an emergency shutdown, as at Byron, the devices are not considered part of an emergency system. So they are not as rigorously inspected as a plant's emergency systems are, Mr. Lochbaum says. The decision on when to replace them is left up to the utility.

Why did the plant let off steam?

To relieve pressure in the plant's cooling system. Byron's reactors are pressurized-water reactors. Water is circulated through the reactor core under high pressure so it can be heated above its boiling point. This superheated water is passed through a steam generator – basically a large heat exchanger that converts water in the secondary cooling system into steam the generators can use.

This system is designed to isolate water that comes into contact with the reactor from the water that is used to produce steam for the turbines.

When a pressurized-water reactor is shut down, this secondary system continues to make steam. But the steam no longer is being run through the turbines and through the cooling towers to be returned as a liquid for another cycle. Steam builds up in the secondary system and must be vented to prevent pipes in this secondary system from bursting.

Where did the tritium come from?

It's a byproduct of the nuclear reactions that take place in the plant's reactors and boron, used in a reactor's coolant to help control the reactor's chain reactions. It found its way into the vented steam at Byron because the piping that carried the reactor water through the steam generator has some small leaks, Lochbaum says.

How dangerous is it?

Tritium loses half its radioactivity in 12.34 years. The form of radioactivity it produces will not penetrate skin, although it can be ingested or absorbed through the skin as a component of water. According to the Nuclear Regulatory Commission, tritium emissions from nuclear power plants “account for less than 0.1% of total background dose” humans are exposed to each year from natural sources. These background sources represent about half of the radiation doses people receive, the NRC notes.

You've read  of  free articles. Subscribe to continue.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to

QR Code to Q&A: Illinois nuclear plant loses power. What got vented into the air?
Read this article in
QR Code to Subscription page
Start your subscription today