5 Biggest Nuclear Reactors

In December of 1942, an experiment that would change the world was taking place at the University of Chicago. After years of research and a month of construction, the world's first nuclear reactor, Chicago Pile-1, was ready for testing. Constructed of a lattice of uranium and graphite blocks stacked 57 layers high, Chicago Pile-1 bore little resemblance to today's nuclear reactors. A three person "suicide squad" was waiting to step in and shut the reactor down in case the reactor's safety features failed. Fortunately, the 50 people in attendance that day were able to share a collective sigh of relief -- as the squad was not needed. The reactor worked without a hitch, and the nuclear era was born.

Today, more than 400 nuclear power plants are located in 30 countries across the globe. Together, these plants produce 15 percent of the world's electricity and 2 percent of the world's total power supply [source: World Nuclear Association]. Nuclear power certainly has its pros and cons, but no one can deny its importance. So now that we know a little about how far nuclear power has come over the past 60 years, we're ready to take a look at the five biggest nuclear reactors on Earth, starting with a couple of reactors that might not be around much longer. 

Today, more than 400 nuclear power plants are located in 30 countries across the globe. See more nuclear power pictures.

  

5: Isar II

Germany has long had an uneasy relationship with nuclear energy. While the country currently depends on nuclear energy for nearly 20 percent of its electricity, concerns about plant safety and nuclear waste storage have resulted in plans to close some of the country's largest reactors. Included on that list are two reactors located in Essenbach, Germany. Together the reactors, known as Isar I and Isar II, generate enough electricity to power more than 1.5 million households each year [source: Nuclear Energy Institute].

 

But Isar II is the reason the reactors are on this list. The reactor, commissioned in 1988, has a net installed electric capacity of 1,400 megawatts [source: E.ON]. According to E.ON, the Germany utility company that runs Isar II, creating that electricity using fossil fuels would add 12 million tons (11 million metric tons) of carbon dioxide to the environment [source: Crowley]. Perhaps that explains why some are rethinking the current plan to decommission Isar I in 2011 and its bigger brother in 2020. Read on to learn about another German reactor that's inspired more than its share of controversy. 

4: Brokdorf

On the banks of the river Elbe, sheep graze lazily on fields of lush green grass, entirely unimpressed with the massive nuclear reactor located only 100 feet (30 meters) away. Brokdorf reactor, which takes its name from the surrounding city, houses more than 110 tons (100 metric tons) of uranium [source: E.ON]. Construction on the plant began in 1981, and by 1986, the plant was operational. One of the world's largest reactors, Brokdorf claimed the title of World Champion of gross annual output in both 1992 and 2005 [source: E.ON]. With an impressive net installed electric capacity of 1,410 megawatts, Brokdorf could easily recapture the title before its scheduled decommissioning in 2018 [source: E.ON].

Brokdorf's electrical capacity makes the reactor the largest in Germany. So perhaps it's fitting that, throughout the 1980s, it was also the site of the country's largest protests against nuclear power. The protests drew tens of thousands of people a day at their peak. The demonstrations often turned violent, with protestors hurling bricks, bottles and even gasoline bombs at riot police, prompting the police to respond with tear gas and mass arrests. Hundreds of injuries resulted, affecting both citizens and riot police alike. Today, the site still draws a few peaceful protestors, but as concerns rise over global warming and increasing energy costs, Germany's attitude toward nuclear power appears to be shifting. Of course, not all countries have had such a contentious relationship with nuclear power. The next reactor on our list is located in a country that gets more of its electricity from nuclear power than any other country on Earth. 

3: Civaux 1 and 2

"No oil, no gas, no coal, no choice." The phrase has become a mantra explaining French support of nuclear power. As instability in the Middle East forced oil prices higher and higher throughout the 1960s, France recognized a need to move away from its fossil-fuel-burning power plants. Today, the country has 59 nuclear reactors responsible for producing 76 percent of France's electricity, and two reactors located in the city of Civaux are among its largest. Fully operational in 1999, Civaux 1 and Civaux 2 cost an estimated $4.1 billion to construct [source: Power-Technology].

While that's a hefty price tag, reactors in other countries can be much more expensive. In fact, power produced by Civaux 1 and Civaux 2 costs about as much as traditionally cheaper electricity generated from coal and natural gas. Turbines in the reactors are more than half a football field in length and weigh nearly 3,000 tons (2,722 metric tons), which helps explain how each of the Civaux reactors produces 1,450 megawatts (net) [source: Power-Technology].

The reactors have some impressive safety features as well, including the ability to shut down in only 2.15 seconds. Even so, Civaux 1 was closed for nearly a year after coolant leaks were discovered. The pipe work was replaced and the reactor was ready to come back online when regulators discovered a problem with harmful bacteria forming in the cooling circuits of similar reactors. To address the problem, engineers added an ultraviolet treatment system capable of killing the bacteria. Now both Civaux 1 and Civaux 2 are up and running, helping France to power not only its own homes and businesses but even export energy to neighboring countries. 

2: Chooz B1 and 2

Like their sister reactors in Civaux, the two reactors known as Chooz B1 and Chooz B2 are part of France's series of technologically advanced N4 reactors. Among the technological innovations are computerized control rooms that provide operators detailed information about the reactors' systems, as well as very efficient steam generators and cooling pumps. Yet even with the advanced technology, Chooz B1 took only 12 years to construct. Even more impressive, the Chooz B reactors have a net installed electric capacity of 1,455 megawatts [source: Davis]. That makes the reactors the most powerful in the world in terms of individual output, capable of generating more than 5 percent of France's nuclear power [sources: Areva].

The advanced technology behind the N4 reactors caused some problems, however; like the reactors in Civaux, Chooz B1 and Chooz B2 had some problems during early operations. They shared the same faulty cooling design as Civaux 1 and 2, for instance, so the reactors were taken offline for a year as their systems were redesigned and replaced. For the time being, though, the kinks seem to be worked out and all four N4 reactors are fully operational.

And if providing a huge portion of France's electricity isn't enough, the Chooz reactors may even provide some perspective on the very nature of matter itself. In July 2009, the construction of a laboratory on the site of the Chooz B reactors was announced. The lab, designed to study the elusive neutrino, could give scientists insight into the very origins of the universe itself.

The next reactors on our list may not solve any scientific mysteries, but in terms of sheer power, they can't be beat. Read on to find out more. 

1: Kashiwazaki-Kariwa

Japan's Kashiwazaki-Kariwa reactors, which were completed in 1997, won't break any records for individual output, but their combined electrical output is uncontested. The power plant, which has seven separate reactors, has a rated capacity of 8,212 megawatts. That's enough capacity to power more than 16 million households each year, providing more than 5 percent of Japan's total electricity [source: Power-Technology].

The Kashiwazaki-Kariwa reactors, like all Japanese reactors, were constructed with extensive safety mechanisms designed to withstand Japan's frequent earthquakes. 

The plant extends deep into the surrounding water where it attaches to the solid ground below, providing a sturdy foundation to withstand shocks. Even so, the reactors were taken offline after a magnitude 6.8 earthquake struck the plant in July of 2007. The earthquake caused extensive damage to the plants, including fires and radiation leaks, though many expected the damage to be much worse. As of today, most of the reactors remain offline as regulators inspect the plants for further damage, though some of the reactors have received approval to resume operation.

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