Insight Web Extra October 2009
—Gliding at a glacial three miles per hour along the country lanes of rural Pennsylvania, the two flatbed trucks with their cargo of 500-ton steam generators inch past farms and farmers, most of whom will benefit greatly from their cargo.
While the Amish of Pennsylvania’s Dutch country might not view these 70-foot-long behemoths with anything more than keen curiosity—since, as a community, they do not use electricity—other folks along the 300-mile route may well have had advance word of these “self-propelled modular transporters” coming through and gathered to watch them pass by and ask what the gigantic steel structures were for. In all, about 15,000 people did just that.
Manufactured by AREVA in France, taken by ship across the Atlantic, up the Susquehanna River by barge, and finally loaded onto those trucks for their achingly slow voyage to the Three Mile Island nuclear plant, they represent a $300 million investment by Exelon to replace two steam generators as their older cousins reach the end of their service lives.
TMI’s site vice president, William Noll, made the case simply: “The replacement of the steam generators is part of our plan to operate TMI well into the future.”
The plant, which opened in 1974, just last week received a 20-year license extension from the U.S. Nuclear Regulatory Commission, allowing it to operate until 2034.
But what do steam generators do? The whole point of a power plant is to generate steam in order to turn the turbines that create electricity. In nuclear energy plants, the heat for that steam is provided by atomic fission in the nuclear reactor.
In pressurized water reactors (like TMI), the process is somewhat indirect, with the steam generators acting as heat transfer machines. To do this, two loops of water run past each other in and around a complex series of tubes. The first loop (on the inside of the tubes) is the highly pressurized water heated by atomic fission in the reactor core. The heat from this loop is transferred to the water on the outside of the tubes (the second loop), which turns into steam. It is this steam that runs the turbines.
Pennsylvania generates almost a quarter of its electricity from nuclear energy, which means it is second only behind Illinois in nuclear energy capacity. While some smaller states receive more of their electricity from nuclear generation—needing fewer plants to serve fewer people—nuclear energy remains vitally important to Pennsylvania to help supply its electricity needs.
So whenever large equipment to keep a nuclear power plant in top shape must be delivered, this is how it will be done: in the case of the steam generators, not by trains, planes and automobiles, but via cargo ships, river barges and huge flatbed trucks. And at the end of their slow voyage, they help to ensure that Pennsylvanians can continue to benefit from clean, inexpensive electricity. Photo: A farmer takes a break to watch one of Three Mile Island 1’s two replacement steam generators wend their way through rural Pennsylvania on their long journey from France. [Photo credit: Exelon Corp.] —Read more articles in Nuclear Energy Insight and Insight Web Extra.