news.vice.com – Thirty years ago today, the Number 4 reactor at Chernobyl blew itself to smithereens, resulting in the worst nuclear disaster in history. A radiation cloud drifted over Europe, contaminating food sources that to this day continue to be monitored. Fifty-thousand residents in the nearby city of Pripyat were permanently evacuated. Dozens of people lost their lives.
Yet about 20 years after the disaster, an extensive two-year study led by seven UN agencies and involving the governments of Ukraine, Russia, and Belarus found that the biggest health threat from Chernobyl wasn’t the result of radiation — it was fatalism. People assumed they were going to die early due to radiation exposure, and so failed to take care of themselves as years passed.
Just how many people died in the aftermath of the explosion — including firefighters and rescue workers who succumbed to radiation poisoning shortly after responding to the accident — is somewhat unclear, but the total number is between 50 and 100. Of the 5 million people who lived in the area most affected by radiation and the 600,000 emergency workers who ended up responding in some way, about 5,000 got thyroid cancer. (A terrible consequence, but those cancers typically weren’t fatal.)
The number of long-term cancer deaths that may result is extremely difficult to pin down. One peer-reviewed 2006 paper states: “It is unlikely that the cancer burden from the largest radiological accident to date could be detected by monitoring national cancer statistics. Indeed, results of analyses of time trends in cancer incidence and mortality in Europe do not, at present, indicate any increase in cancer rates — other than of thyroid cancer in the most contaminated regions — that can be clearly attributed to radiation from the Chernobyl accident.”
But there have been estimates. At the high end, a 2006 report commissioned by European Green parties found that there may be as many as 60,000 excess cancer deaths due to the disaster among a population expected to experience several hundred million cancer cases. Detecting that number of excess cancer cases in that population — in other words, spotting an uptick as a result of Chernobyl — would test the limits of epidemiological science because even the highest estimate is, relatively, so small.
On the anniversary of the worst nuclear disaster ever, it may be time to reconsider nuclear power.
* * *
This isn’t a debate about nuclear power versus fossil fuels or renewable energy sources. While that is an important debate, the biggest question raised by Chernobyl is whether humanity should be tampering with fundamental forces of nature and the very building blocks of matter in order to power toasters.
The debate can begin with reactors. If there’s one unbreakable rule governing nuclear reactors, it’s that they must be kept from overheating. Reactors operate by harnessing a nuclear chain reaction, and if you don’t keep that chain reaction under control by, say, cooling it off, then you can end up with what is called a “criticality excursion.” Or, in layman’s terms, a gigantic fuck-up.
At Fukushima, a tidal wave swamped the diesel backup generators needed to cool the reactor, resulting in a meltdown of sorts, though one that fortunately didn’t get bad enough to turn into a full-blown criticality excursion. A related fact: Nobody at Fukushima died from radiation poisoning. Chernobyl, of course, is a different story.
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The specific kind of reactors used at Chernobyl, known as RBMK reactors, say a lot more about the Cold War than they do nuclear power. They were cheap and easy to build, generated a lot of power, and could be quickly configured to manufacture weapons-grade plutonium instead of electricity. In other words, they were everything a Soviet bureaucrat elbow-deep in the Cold War battle to harness the power of the atom could hope for.
That said, the Soviets cut some corners. The RBMK reactors weren’t in a proper containment building to prevent radioactive stuff from getting into the environment if the reactor pressure vessel itself blew up. Meanwhile, the reactor pressure vessel lids were detachable — and therefore less reliable than they could have been — so the Soviets could switch things around if they wanted to make plutonium (i.e., bombs instead of electricity). But even those shortcuts paled in comparison to one very critical detail: The reactor design had a very high “positive void coefficient.”
In very oversimplified terms, that meant the reactor relied on water not just for cooling, but also to slow down a chain reaction. If the flow of water slowed, the water got too hot too quickly and turned to steam. Steam is very bad at absorbing the neutrons involved in a chain reaction, and therefore very bad at slowing a chain reaction. So once the coolant starts to boil, the reactor power spikes. That boils more water, which then slows down the reaction even less, and so on.
“It’s the equivalent, very loosely speaking, of making a car without a gas pedal,” said Mark Mills, senior fellow at the Manhattan Institute and CEO of the Digital Power Group. “When you start the car, the engine is on full-bore all the time. You control the car’s speed with the brake and only the brake. Now, if you get in your car, you can put the brake on with the engine racing and it won’t go anywhere. And if you carefully let off the brake, you can drive the car and it will work. But it’s kind of a risky way to run a car.”
Reactor control simulator at Calvert Cliffs, Maryland. (Photo by Ryan Faith/VICE News)
In the case of the Number 4 reactor at Chernobyl, the operators were running tests to see if and how backup power could have prevented a meltdown. The answer? The power produced by the reactor core spiked to at least 10 times the rated capacity of the reactor. Then, in the seconds following the power surge, just about everything that could go wrong did go wrong. Two explosions destroyed the reactor, ejecting highly radioactive material into the atmosphere — including chunks of burning graphite, which started fires around the reactor.
Originally, the workers at Chernobyl didn’t grasp that the actual core had been breached because their high-precision, low-level radiation detectors had simply maxed out. They had high-dose detectors, but they were buried in the rubble.
What followed was incredible heroism and self-sacrifice on the part of the “liquidators” who fought to get the thing under control: shoveling chunks of fuel back into the reactor and spraying water on the exposed reactor core to keep it cool. For work in the highest radiation areas, soldiers were carried to the roof of the building by helicopter where they shoveled madly for half a minute, give or take, until the helicopter circled back to take them away, since they’d received their maximum dose for the day.
According to the CBC television documentary series Witness, the firefighters who were at the front lines explained what it was like to experience such insane levels of radiation. Their accounts described it “tasting like metal.” They said they felt “a sensation similar to that of pins and needles all over [their] face.”
They died a few days after providing their accounts.
The moral of the Chernobyl story is that we shouldn’t do stupid shit. The question is whether that means, “Don’t do stupid shit like using nuclear power,” or “Don’t do stupid shit when using nuclear power.”
* * *
Contrary to popular belief, Chernobyl didn’t really affect nuclear reactor construction in the US. By 1986, the business of building new nuclear plants had already ground to a standstill because of a complex interaction of cost, fear, and the cost of fear.
Nuclear plants have reasonably manageable maintenance costs, and the fuel cost is, over the life of the plant, very minor indeed. The marginal cost, which is the cost of producing one additional unit of power, for nuclear power is zero or close to it; it’s merely a matter of allowing the chain reaction to run incrementally faster, or changing the way you’re managing heat exchange. A coal or gas plant can increase production only by burning more fuel, while a solar or wind plant can create more electricity only by building more capacity.
Thing is, it takes billions of dollars to build a nuclear power plant — perhaps five times as much as a coal plant and 20 times as much as a natural gas plant. The US government tried to make the financing of nuclear plants less risky by passing a loan guarantee bill in 2005. Other governments, particularly China’s, are following suit, or in the case of the UK, guaranteeing a purchase price for electricity. But it’s still hard to find investors willing to roll the dice on when that massive investment might start producing results (at least in most of the US, where energy prices are set by wholesale markets).
“Let’s say you need money to build a plant that costs $10 billion, but you’re not sure how fast you can recover those costs,” explained Michelle Melton, associate fellow in the Energy and National Security Program at the Center for Strategic and International Studies (CSIS). “There’s absolutely no way an investor is going to give their capital to this project.”
In addition to that overall uncertainty, energy prices have plummeted in recent years. The nuclear energy industry may still be making money on a day-to-day basis, but the real problem is in covering long-term costs and paying back investors.
But back to Chernobyl. Folks in the nuclear industry say the real nuclear energy killer, at least in the United States, was the 1979 accident at Three Mile Island in Pennsylvania. At that reactor, a coolant valve got stuck open and drained a lot of the reactor coolant, resulting in a partial meltdown. Nobody died — one of the reactors is still operating today — but it was a Chernobyl-scale public relations disaster for an industry that could ill afford it.
Nuclear power made perhaps the worst first impressions ever: Hiroshima and Nagasaki. By the 1970s, the US anti-nuclear movement had picked up a lot of steam, leading up to the 1978 release of The China Syndrome, starring Jane Fonda, herself a staunch opponent of nuclear power. In the movie, Fonda, as an intrepid reporter, covers a story at a nuclear plant when an accident occurs. Plying her clever journalistic skills, she uncovers a series of safety cover-ups associated with the reactor.
Twelve days after the acclaimed film premiered, Three Mile Island happened. Despite the fact that the scenario in the movie wasn’t physically possible, and the accident at Three Mile Island didn’t result in a single fatality, the combination was a huge blow to an already-struggling nuclear industry.
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There are, of course, very legitimate safety concerns surrounding nuclear power. Radioactive waste, for instance — both high-level waste like spent fuel rods and low-level waste like tools used in radiologically controlled areas. There’s a lot more low-level waste than high-level waste, but that stuff isn’t impossibly hard to store. The high-level waste is trickier, particularly because some of those isotopes are going to remain radioactive for (in practical terms) ever. Some kinds of advanced reactors can actually burn spent fuel and convert it into energy, and in the US, secured storage installations keep the rods safe, though they’re technically temporary solutions.
The potentially severe effects of nuclear accidents encourage folks to err on the side of caution, but that inclination to add more safety measures can also increase costs. Understandably, no one wants to be the person to say, “It’s safe enough.”
The essential cost of safety, the diminishing returns of each further safety investment, and construction delays over reactor safety all combined with the fundamental economic challenges of nuclear power to keep US nuclear growth more or less comatose for the past several decades.
Yet there are good reasons why people are still interested in nuclear power. Of all the different ways to transmit power, we’ve gotten pretty handy with electricity, whether it’s electric current or stored in a battery. What a power plant does is convert some sort of energy source (fossil fuel, sunlight, uranium, whatever) into electrical power.
This implies two logistical links. One is fuel — how much fuel does a power plant need, how does it get it, and how efficient is the plant at converting that into electricity? The other is transmission — how can we get power to where it needs to go to do its job?
What drives the fuel side of the system is how easy it is to store and transport the fuel that you’re using, and fossil fuels are incredibly effective as a way to store and transport energy. A Tesla Model S has a 1,200-pound battery pack that can store up to 85 kilowatt hours (kWh) of energy, which amounts to the same amount of energy stored in 2.3 to 2.6 gallons of gasoline. And it’s a lot easier (roughly 75 times easier) to store and transport 15 or 16 pounds of gasoline than it is to move or store 1,200 pounds of battery.
The difference between fossil fuels and nuclear fuel is far bigger than the difference between gasoline and batteries: nuclear fuel is about 1.8 million times as energy-dense as gasoline. If you had a way of using Uranium in a car, you’d need only 3.8 milligrams of it — about the mass of a snowflake — to store as much power as you could with 1,200 pounds of battery or 15 pounds of gasoline.
One of the two electricity-generating turbines at the Calvert Cliffs Nuclear Power Plant. This turbine generates enough electricity to power half of Washington, DC. (Photo by Ryan Faith/VICE News)
Thus, nuclear plants generate an immense amount of power with a relatively small amount of fuel, and over the lifetime of the plant, fuel is a very small portion of the total cost. The virtual elimination (or at least dramatic reduction) of fuel needed to keep running also means that nuclear power can be very reliable.
This is not lost on people.
* * *
“Right now there are 43 independent advanced reactor design efforts in North America alone that have collectively raised about $1.6 billion just in private investments, not counting any government investments at all,” said Dr. Leslie Dewan, co-founder and CEO of Transatomic Power, a Boston-based nuclear energy startup.
Four-dozen reactor efforts all trying to figure out basic physics for a measly $1.6 billion would seem like the triumph of hope over experience. However, it might not be all pie-in-the-sky foolishness. If these clever folks can unravel the mysteries of advanced materials — basically, stuff that is good at withstanding the extremely unpleasant conditions created by nuclear chain reactions — it could go a long way toward solving the economic and safety issues of nuclear power.
The goal is called “Advanced Reactors,” or sometimes “Generation IV” reactors. People are still trying to figure out what exactly they mean by this, but the idea of “walk-away safety” is a pretty common feature in all of them. We already know that if there’s one cardinal rule about reactors, it’s that you have to be responsible about keeping the reactor core cooled. However, sometimes relying on humans to be responsible is a bad idea. Thus, the challenge is to design a reactor that either allows you to break the cooling rule, involves a way to shut down before a lack of cooling becomes a problem, or otherwise makes sure that things won’t go straight to hell if a pack of idiots is left in charge of the reactor.
Plants designed to be “walk-away safe” are built so that it requires constant intervention and effort to keep the chain reaction going. If everything goes to hell in a hand-basket — a natural disaster knocks out controls, an operator falls asleep at the controls after binging on donuts — the default for the plant is to, effectively, shut down the chain reaction. This would, in theory, prevent a criticality excursion and meltdown like Chernobyl’s.
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The technologists are (of course) excited and optimistic, while skeptics are (of course) not placing any bets on futuristic designs or whether those new-fangled reactors are actually going to be any cheaper in the long run. Both parties agree that with the current economic situation, it’ll be an easy 10 years before conditions allow for more modern reactors to be deployed.
So while for some, the ultimate lesson of Chernobyl may be that we should run screaming from nuclear power, there may be a more nuanced takeaway — that we should run screaming unless we can idiot- and freak-accident-proof nuclear power. We figured out how to split the atom, so maybe we can figure out how to do that too.
Follow Ryan Faith on Twitter: @Operation_Ryan
1 bình luận về “The Lessons of Chernobyl May Be Different Than We Thought”
Thank Hang for sharing.
Mình gửi vào đây một bài tiếng Việt để tiện tham khảo sau này.
30 năm sau thảm họa Chernobyl, hậu quả vẫn nghiêm trọng
Thứ Ba, 26/4/2016, 11:53 (GMT+7)
Lò phản ứng số 4 tại Chernobyl, Ukraine, vẫn bị bỏ hoang. Ảnh: Reuters
(TBKTSG Online) – Hôm nay 26-4, Ukraine kỷ niệm 30 năm thảm họa Chernobyl – thảm họa hạt nhân nghiêm trọng nhất lịch sử.
Cách đây đúng 30 năm, vào lúc 1 giờ 30 phút ngày 26-4-1986, lò phản ứng số 4 của nhà máy điện nguyên tử Chernobyl tại thị trấn Pripyat, cách thủ đô Kiev (Ukraine) khoảng 100 kilomet về phía bắc, bỗng nhiên phát nổ trong quá trình thử nghiệm an toàn.
Trong suốt 10 ngày, các thanh nhiên liệu hạt nhân tiếp tục cháy, thải ra không khí các phần tử chứa phóng xạ. Theo nhiều chuyên gia, những thành phần này gây ô nhiễm đến 3/4 lãnh thổ châu Âu, nghiêm trọng nhất là tại Ukraine, Belarus và Nga – lúc đó vẫn nằm trong Liên bang Xô-viết.
Hậu quả chưa giải quyết xong
Tổng cộng 116.000 người đã được sơ tán vào năm 1986 trong phạm vi 30 kilomet xung quanh khu vực nhà máy điện nguyên tử Chernobyl, hiện vẫn bị bỏ hoang. Những năm tiếp theo, 230.000 người khác cũng được sơ tán.
Năm 2005, một báo cáo gây tranh cãi của Liên hiệp quốc (LHQ) chỉ nêu có 4.000 người thiệt mạng được xác nhận tại 3 nước bị ảnh hưởng nghiêm trọng nhất. Một năm sau, tổ chức Hòa bình xanh (Greenpeace) thẩm định số người thiệt mạng do thảm họa trên lên đến 100.000 người. Tổng số người thiệt mạng và những ảnh hưởng lâu dài đến sức khỏe vẫn là chủ đề tranh luận quyết liệt.
Sau tai nạn, nhà máy nguyên tử Chernobyl tiếp tục sản xuất điện đến năm 2000, khi lò phản ứng còn hoạt động cuối cùng bị buộc phải ngưng hoạt động do sức ép của phương Tây.
Dù 30 năm đã trôi qua, thị trấn Pripyat giờ không có người sinh sống và cũng không thể có người sinh sống trở lại trong một thời gian dài. Các nhà khoa học ước tính thị trấn nằm gần nhà máy điện hạt nhân Chernobyl này sẽ vẫn trong cảnh không người sinh sống trong ít nhất 3.000-20.000 năm bởi mức độ nhiễm xạ cực cao tại đây. Đây cũng là bằng chứng cho thấy nguy cơ lâu dài của năng lượng hạt nhân.
Hiện, khoảng 5 triệu người Ukraine, Belarus và Nga vẫn sống trong những vùng bị nhiễm xạ với các mức độ khác nhau. Theo báo cáo của Greenpeace, 30 năm sau thảm họa Chernobyl, người dân tại các vùng nhiễm xạ vẫn đang ăn các loại thực phẩm nhiễm xạ. Báo cáo cho biết các mẫu sữa và rau củ tại khu vực này có mức nhiễm xạ cao gấp hàng chục lần tiêu chuẩn. Số người ung thư tại khu vực này cũng tăng lên không ngừng một cách bất thường.
Vẫn còn nghi ngại về năng lượng hạt nhân
Trong vòng 4 năm, khoảng 600.000 người – chủ yếu là quân nhân, cảnh sát, nhân viên cứu hỏa và nhân viên của nhà máy Chernobyl – đã được huy động đến những khu vực bị ảnh hưởng với trang bị bảo hộ thô sơ, thậm chí không có, để dập tắt hỏa hoạn, tiếp theo là xây lớp vỏ bọc lớn bằng bê tông để cách ly lò phản ứng bị nổ và dọn dẹp những khu vực xung quanh.
Lớp vỏ bọc bằng bê tông, được xây vội vã trong 6 tháng, phủ lên toàn bộ lò phản ứng bị nổ, có nguy cơ bị sập và có thể sẽ hất tung vào không khí 200 tấn macma nhiễm xạ cao.
Cộng đồng quốc tế đã cam kết tài trợ cho việc xây dựng lớp vỏ bọc mới, chắc chắn hơn. Một quỹ dành cho mục đích này đã được thành lập và do Ngân hàng tái thiết và phát triển châu Âu (BERD) quản lý. Sau nhiều năm chần chừ, công trình bắt đầu được xây dựng vào năm 2010 để tạo ra khối bọc khổng lồ bằng thép.
Lớp vỏ bọc mới nặng đến 25 tấn, cao 110 mét, có diện tích đủ để phủ kín toàn bộ Nhà thờ Đức Bà Paris. Tổ hợp Novarka, tập hợp 2 tập đoàn Bouygues và Vinci (Pháp), là đơn vị thực hiện lớp vỏ bọc mới với trị giá lên đến 2,1 tỉ euro. Với tuổi thọ tối thiểu 100 năm, lớp vỏ bọc mới này sẽ cho phép các nhà khoa học có thời gian tìm ra biện pháp mới để tháo dỡ, chôn phần còn lại của lò phản ứng gặp sự cố và khử nhiễm khu vực, để một ngày nào đó cỏ lại mọc xanh tại đây.
Câu hỏi đặt ra là ai sẽ là người chi trả việc bảo trì? Theo một nguồn thạo tin, câu hỏi này được đưa ra thảo luận tại hội đồng các nhà tài trợ ngày hôm qua 25-4-2016 tại Kiev.
Ngày hôm nay 26-4, Mỹ cam kết viện trợ 10 triệu đô la Mỹ để hỗ trợ những người bị ảnh hưởng bởi bụi phóng xạ của thảm họa Chernobyl, khi Ukraine kỷ niệm 30 năm vụ tai nạn hạt nhân nghiêm trọng nhất thế giới. Cam kết này bổ sung vào hơn 400 triệu đô la Mỹ mà Mỹ đã cấp cho nỗ lực quốc tế nhằm giúp Ukraine khôi phục địa điểm vụ tai nạn trở thành một nơi an toàn và an ninh về môi trường.