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.

by "environment clean generations"

 

Safer Nuclear Reactors For The Future?

Areva's Taishan 1 EPR Facility Under Construction in China.

At this time last week, the Nuclear Renaissance was in full swing. Plans were moving forward to use the $36 billion in loan guarantees for new reactors in President Obama's 2012 budget. 

China was approving reactor stations at a steady pace, and nations across Europe were considering new nuclear sites of their own. Seven days later, the push toward more and better nuclear power has come to a full stop, as the crisis at Japan’s crippled Fukushima Daiichi power station threatens to unravel into the worst nuclear disaster in history.

 

But amid a strong, worldwide nuclear backlash, it's important to remember that the next generation of nuclear reactors are designed to prevent exactly what went wrong at the 40-year-old Fukushima Daiichi plant. Which is good, because according to the experts, a future weaned from fossil fuels will include nuclear power whether we like it or not. Here's what that future may look like. 

In the days since the 9.0-magnitude quake and resulting tsunami heaped human tragedy and potential atomic disaster on Japan, things have gone from bad to worse at Fukushima Daiichi, sparking a flood of conjecture about the future of nuclear energy worldwide. Switzerland quickly suspended the approval process for three new plants, Germany's Chancellor announced that country would undertake a "measured" exit from nuclear power, and even China--the vanguard of the global nuclear energy charge--showed apprehension, freezing all new approvals for new nuclear power plants.

It’s too early to begin tallying the lessons learned in Japan, but technically speaking most of what’s gone wrong with Fukushima Daiichi's 1970s-era reactors has already been learned and accounted for in the latest nuclear power plant technology. 

Keeping a nuclear plant safe means keeping it cool in any circumstances, including those in which man-made or natural disaster knocks out the usual cooling methods. This highlights the importance of safety features built into so-called Generation III-plus nuclear plant models, the latest feasible plant designs. These redundant and passive safety systems work without the help of an operator, or even electricity, during times of duress, be it man-made or natural.

Generation III-plus includes a handful of high-tech plant designs, many of which still await regulatory approval. Others, like France-based Areva’s Evolutionary Power Reactor (EPR) and Westinghouse’s AP1000 (both are pressurized water reactors) are already under construction, and they are designed to withstand exactly the crisis the 40-year-old Japanese reactors are failing to deal with, whether operators are around to trigger emergency countermeasures or not.

“The new reactors really have a lot of features that were not available thirty, forty years ago,” says Michael Podowski, a visiting professor in MIT’s department of nuclear engineering and an expert on nuclear plant safety systems. “These new advanced reactors will employ more passive safety systems that will make them safe without any external intervention.”

Areva is currently building four EPR reactors, two in China and two in Europe. The design includes four independent redundant cooling systems, two of which are engineered to survive an airplane crash.

Westinghouse’s AP1000 packs a battery of passive systems that use natural air flow, gravity, and other natural phenomena to remove pumps and valves from the equation; if the plant begins to overheat these measures will automatically cool the core for up to three days with no external intervention whatsoever.

 by "environment clean generations"

Onkalo - The Largest Underground Nuclear Waste Repository

Ceremonies will be held around the world on Tuesday to mark the 25th anniversary of the Chernobyl disaster but, in truth, Chernobyl is one event we're in no danger of forgetting. For one thing, the earthquake in Japan has given the world a second Level Seven incident on the International Nuclear Event Scale, refreshing public fears with almost cosmic timing. For another, the legacy of Chernobyl will be remembered for much, much longer than anyone would wish. According to estimates, this area of northern Ukraine will be uninhabitable for decades, if not centuries.

We like to think of our architectural treasures as milestones of human progress. The Egyptian pyramids, say, or the Eiffel Tower. Perhaps we imagine a Planet of the Apes-like scenario where our ruined monuments will stand as testament to our civilisation long after we're gone. But what will most probably outlive anything else we have ever built will be our nuclear legacy. Whatever its pros and cons as an energy source, one thing that's non-negotiable about nuclear power is the construction it necessitates. Less than a century after we first split the atom, we're now coming to appreciate the vast technological, engineering, financial and political resources nuclear technology demands. In terms of scale, complexity and longevity, much of this stuff makes Dubai's Burj Khalifa look like a sandcastle.

It is too early to know what will be done about Fukushima. A 20km exclusion zone has been imposed and radiation levels will not be brought down to safe levels for at least another six months. Even at Chernobyl, the 1986 accident is by no means dealt with. Immediately afterwards, the Soviets hastily cobbled together the most effective structure they could to contain further radioactive contamination. Unromantically named the Object Shelter, it was a concrete and steel sarcophagus resting on the remains of the ruined reactor. Owing to the high levels of radioactivity, it had been impossible to bolt or weld the Object Shelter together, so within a decade it was on the verge of collapse. 

Given that 95% of reactor four's nuclear materials are still inside, another nuclear disaster remains a possibility. Hence the current longer-term plan, called the New Safe Confinement. This €1.6bn (£1.4bn) project calls for the erection of an arch-shaped hangar, bigger than a football pitch and high enough to fit the Statue of Liberty inside. Because of the radiation levels, it must be built 500 metres away then slid over the top of the reactor and the Object Shelter. At 32,000 tonnes, it is just about the heaviest object ever moved.

"In some ways, this is how the engineers of the pyramids must have felt," says Eric Schmieman, chief technical adviser on the New Safe Confinement. "The steel structure has a design life of 100 years, so there are very rigorous requirements to demonstrate all the materials will last that long. The Eiffel Tower has been around that long but it's been protected from corrosion by painting. You can't repaint this because of the radiation."

The structure of the New Safe Confinement is carbon steel, protected by inner and outer layers of stainless steel cladding. Its purpose is not to shield radioactive emissions but to prevent the release of radioactive dust and other materials, and to keep out rainwater, which could carry contaminants into the water table. 

Work is currently proceeding on the foundations, and the arch will be assembled and slid into place by 2015. Then huge, remote-controlled cranes inside will dismantle the Object Shelter and begin retrieving the hazardous materials inside.

The structure will be visible from space, a hulking shell of steel in the midst of a landscape of industrial devastation. By the time it reaches the end of its 100-year life span, it is hoped that all the radioactive material will have been removed, but then comes the problem of where to put it. At the beginning of the nuclear era, the emphasis was very much on the power stations, including Basil Spence's heroic 1950s design for Trawsfynydd, in Snowdonia. But very little consideration was given to what came after. Those early power stations became obsolete: Trawsfynydd was decommissioned in 1991. What's more, the industry has so far generated nearly 300,000 tonnes of high-level nuclear waste, and counting. To be safe, it must be isolated from all living organisms for at least 100,000 years.

Current opinion is that the best thing to do with nuclear waste is put it underground in what is known as a "deep geological repository". At present, there are no such repositories in operation anywhere. In Britain, all the nuclear waste produced since the 1940s is stored above ground in Sellafield. Preliminary moves have been made towards finding a site in Cumbria but there's a powerful local resistance to such schemes, and no long-term solution is expected before 2040. In the US, a site was earmarked decades ago at Nevada's Yucca Mountain, 100 miles from Las Vegas, but the Obama administration finally abandoned the scheme last year.

Some countries are further ahead, though. Sweden's nuclear operation presents itself as a model for the rest of the world, and shows how much effort a fully joined-up operation requires. 

After cooling on site for a year, spent fuel from Sweden's three coastal nuclear sites is transported in purpose-built casks, on a specially designed ship, to a central interim storage facility. There, robotic arms transfer the fuel into storage cassettes underwater. These cassettes are then sent to another storage pool 25 metres beneath the facility to cool for at least another 30 years. Then the waste is moved to another plant to seal in copper canisters before it arrives at its final resting place in the geological repository.

Sweden has numerous other nuclear facilities, including the Äspö hard rock laboratory, an underground research laboratory open to visitors. Bizarrely, Äspö's surface buildings could be mistaken for a traditional farmstead: a collection of buildings in red and white timber. 

The folksy tweeness only points up how alien the rest of the nuclear landscape is. This is the heaviest of heavy industries, and it is often the least visible: a hidden parallel realm of anonymous industrial facilities, restricted zones, clinical chambers and subterranean vaults

.

Sweden has identified a site for its deep geological repository, in Forsmark, but the Finns have been building theirs since 2004. Situated on the northwest coast, a few miles from its Olkiluoto nuclear power stations, it consists of a 5km-long tunnel spiralling 400m down to the bedrock, where a honeycomb of storage vaults fans out. Named Onkalo, whose literal translation is "cavity", it was the subject of a documentary last year, Into Eternity. Retitled Nuclear Eternity and broadcast on More4 tomorrow, the film fully appreciates the Kubrickian visual aspects of the nuclear landscape and the staggering challenges the project presents to our notions of permanence, history – even time itself.  

Onkalo will be ready to take waste in 2020, and then will be finally sealed in 2120, after which it will not be opened for 100,000 years. By that time, Finland will probably have been through another ice age. Little trace of our current civilisation will remain. The prospect of designing anything to last even 200 years is unlikely for most architects; the Egyptian pyramids are "only" about 5,000 years old.

Plan like an Egyptian 

This longevity poses Onkalo's custodians, and others in their position, with another unprecedented design issue: what sign should you put on the door? As one expert says in Into Eternity, the message is simple: "This is not an important place; it is a place of danger. Stay away from the site. Do not disturb the site." But how to communicate with people so far in the future? Put up a sign in a language they don't understand and they are sure to open it just to see what's inside. Ancient Egyptians on the pyramid planning committee probably grappled with the same issues.

One of the Finns suggests using an image of Munch's The Scream; another suggests a series of monoliths with pictographs and an underground library explaining the tunnel; another wonders if it is better not to tell anyone Onkalo is there at all. When a team pondered the same issue in the US in the 1990s, they came up with proposals for environments that communicated threat and hostility. They imagined landscapes of giant, spiky, black thorns or menacing, jagged earthworks, or vast concrete blocks creating narrow streets that lead nowhere.

If architecture is about designing spaces for human habitation, this is practically its opposite. These subterranean cities are places no human will ever inhabit or see, places designed to repel life and light. They are a mirror image to our towering achievements above ground and, like the pyramids, they are both monument and tomb. Every nuclear nation is compelled to build them, at great effort and expense, and to continue building them until we find a better way to deal with nuclear waste or a better alternative to nuclear power. Until then, we must live with the thought that in some unimaginable future aeons hence, this could be all that remains to prove our species was ever here.