COOLING POWER: Japan's 8.9 magnitude earthquake cut power to reactor No. 1 at Fukushima Daiichi nuclear power plant--pictured here in 1975--making it difficult to cool the core.
Image: National Land Image Information (Color Aerial Photographs), Ministry of Land, Infrastructure, Transport and Tourism
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The 8.9 magnitude earthquake in Japan is causing problems for at least one of its fleet of nuclear reactors—and authorities have shut down 10 of the country's 55 units. Tokyo Electric Power confirmed that pressure had been rising inside reactor No. 1 at its Fukushima Daiichi nuclear power plant on the northeast coast, one of the largest nuclear power plants in the world. That means cooling water is not getting to the reactor core, causing a build up of steam inside the containment vessel. The problem, according to Japanese media reports, is a loss of grid electricity to run the pumps that bring in cooling water. The backup diesel generators that are supposed to provide emergency power in that case are out of order, according to the Japan Atomic Industrial Forum, but replacements were being taken to the plant. (Similar diesel generators were providing power to the nation's Rokkasho Reprocessing Plant, which recycles spent nuclear fuel.)
As a precautionary measure, the Japanese government has declared a nuclear emergency and asked people living within three kilometers of the facility to evacuate and people living within 10 kilometers to remain indoors. Tokyo Electric Power, for its part, planned to vent some of the radioactive steam from inside the containment building.
Scientific American spoke with Scott Burnell, public affairs officer at the U.S. Nuclear Regulatory Commission (NRC), the government agency charged with monitoring the safety of the 104 nuclear reactors in the U.S., about what it takes to cool down a reactor.
[An edited transcript of the interview follows.]
How do you typically cool a reactor?
The approach to cooling is very simple: push water past the nuclear core and carry the heat somewhere else. The chain reaction that actually runs the reactor can be shut off in a matter of seconds. What's left over in the core, the radioactive material, will continue to give off heat for a long time. Unless you have a mechanism to remove that, the heat can build up and can eventually damage the radioactive fuel or the reactor.
Pushing water past the core means pumps that are generally run by electricity. What happens when a reactor gets disconnected from the grid?
There are emergency diesel generators. You also have a battery system to keep instruments running, but that can also provide power to safety systems [which prevent a meltdown by cooling the reactor core]. It's all meant to provide defense in depth. First you rely on the grid. If the grid is no longer available, you use diesel generators. If there is an issue with the diesels, you have a battery backup. And the batteries usually last long enough for you to get the diesels going.
How much time is there before a meltdown?
It depends on the plant. It depends on whether it's a boiling-water reactor or a pressurized-water reactor. Basically, [in both] you have the benefit of natural forces such as convection. There is a coolant loop no matter what, so you end up to some degree cooling the core because the heated water rises and colder water gets pulled in. But that's not as effective as a pump bringing in cool water. Just to speak very broadly, you have many hours to restore power to the system to get normal cooling going. It's really not possible to get more specific than "many hours."
But generally, less than 24 hours.
That's fair to say.
What's the worst-case scenario?
The event we are looking to avoid is damaging the core. Once you start damaging the core, you are then releasing radioactive material into the coolant and thereby increasing the chances that something travels outside the reactor.
The reactor that was not cooling properly in Japan, the Fukushima Daiichi No. 1 reactor, was a boiling-water type. How are these different from pressurized-water reactors in terms of cooling?
Particularly useful to boiling-water reactors is a system that is steam driven. It does not require an outside power source. Steam generated by the heat of a cooling down reactor has enough force to run a turbine, which then runs a pump that provides coolant to the core. That sort of system is supposed to withstand an earthquake, and that can run for an extended period. It's a self-limiting condition. That system does use batteries for the controls, but it can also be operated manually. So even in the face of a complete station blackout—you don't have any power at all—there are methods for using the steam-driven pump to continue to keep cooling going.
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24 Comments
Add CommentNRC shut down the three Palos Verdi reactors at Phonix AZ because of reliability of the diesel engines. Each reactor had four diesel engines for each reactor.
Reply | Report Abuse | Link to thisSecondly the emergency control systems must be completely separated from the normal control systems.
In the U.S. all new reactors must have passive shut down systems. That means a large body of water above the reactor core, or in one design a large quanity of ice. Ice has more cooling capacity than water. The United States is fortunate to have an organization like NRC to make sure old reactors are upgraded and safe.Japan may learn a lesson the hard way.
Still nuclear power technology continues to be one of the most reliable, safe and clean technologies in the world. This 9.8 earthquake has been of such a magnitude that nothing could have prevented failure of these units from happening. We should not be mislead by it.
Reply | Report Abuse | Link to thisBefore throwing out nuclear energy have a look a thorium floride reactors. The uranium reactors that we are familiar with are unsafe but they were chosen because they can produce weapons grade fuel and because they require fuel rods it gives the companies that build nuclear reactors a revenue stream. In fact the reactor is the loss leader for companies that make fuel rods. Thorium floride reactors do not create weapons grade material and are much safer.
Reply | Report Abuse | Link to thisAbove article states that "batteries are available to support emergency cooling systems" and it also states that "Emergency cooling systems have to be available for weeks."
Reply | Report Abuse | Link to thisI really wonder what type of batteries are they?
Come on nuclear fans, our lovely earth cannot be your playground. I know that it is very diffucult to quit our current lifestyles, but for the sake of nature we should agree in no time that available energy sources are sun-wind-geothermal only.
I think SA should take action to block any commentor using "html://tinyurl.com/" as a part of their address!!!
Reply | Report Abuse | Link to thisThe junk science anti nuke group is at it again.
Reply | Report Abuse | Link to thisAll the worlds nuclear waste now perfectly contained would fill 1% the volume of the Great Pyramid at Giza which has lasted 5000 years - less than a football field buried 40 feet deep. Not waste. It is fuel enough to power the world for hundreds of years while being destroyed in gen IV reactors like India's new 500 MW first of 5 units. Ironically that is the only way to get rid of it. The tiny amount left is such a low level it can be returned to the mine shaft.
"Japan’s Asahi Shimbum newspaper reported that radiation levels per hour in the area near the front entrance of the No. 1 Fukushima plant reached 0.59 micro Sievert,
Normal exposure rate is 0.23 microsieverts per hour in La Paz, Bolivia. 2 hours in La Paz is like one hour at the front gate this AM of Fukushima.
12 bananas produces about 1 microsievert of radiation
An enormous number of folks have been burned alive in the area by the Greenpeace's preferred transition power source - natural gas. Lots of deadly toll of toxic waste from the areas chemical plants now polluting the soil forever.
The explosion was a hydrogen leak that damaged the outside of the building. It has nothing to do with containment which is well under control.
This accident shows the many layers of nuclear safety work just as well as predicted, just like they did at 3 mile island where the reactor was damaged but nobody injured.
This reactor is a 1950's design slightly upgraded in the 60's. All Gen III+ nukes and all Candu's have passive coolant systems which would have avoided this problem.
The accident puts enormous shame on the Japanese people that the systemic corruption endemic in their culture would have allowed a well known corporate bandit to get away obvious uncorrected maintenance flaws that put the plant and the area in harms way. This sort of graft would result in summary execution in China. It is impossible in the US where the NRC would never allow a nuke on a tidal plain to have backup systems in harms way.
Coal-fired boilers killed tens of thousands before engineering standards made them safer. All technology becomes increasingly safe over time, and nuclear is no different. France gets 83% of their power from nuclear plants, and because of recycling, their waste would fit in a small dorm room. We have to store tons of the stuff, because President Carter elminated the recycling option in the US, as it could be a source of weapons-grade materials. Ironic since we now burn decomissioned weapons material from the former USSR in our own reactors. Pebble reactor designs are melt-down proof, as are other designs. (before you post back, look them up); you can hold their fuel in your hand. We just need to facilitate (simplify & cheapen) permitting new (safe) designs so we can take the older ones offline.
Reply | Report Abuse | Link to this"Still nuclear power technology continues to be one of the most reliable, safe and clean technologies in the world. This 9.8 earthquake has been of such a magnitude that nothing could have prevented failure of these units from happening. We should not be mislead by it. "
Reply | Report Abuse | Link to thisYou realize of course that this is a perfect summation of the argument AGAINST nuclear power. Yes, nuclear reactors are VERY reliable. Yet no amount of human imagination, no quality of systems engineering, no foresight available to human beings will ever make them safe. Nature, malice, and human fallibility can all defeat any design of man.
You cannot rationally discuss the safety of nuclear power without taking into account the gravity of the consequences of an accident. Unlikely they may be, but that only speaks to their frequency. As we have just seen, they WILL happen. When they do the consequences are very dire.
Now, a rational discussion can certainly be had about the relative trade offs of nuclear power vs other techniques for generating power. We may conclude the risks are worth the price, but as DancesWithFascists pointed out, we need to assess those risks/costs in a rather wide context.
"Before throwing out nuclear energy have a look a thorium floride reactors. The uranium reactors that we are familiar with are unsafe but they were chosen because they can produce weapons grade fuel and because they require fuel rods it gives the companies that build nuclear reactors a revenue stream. In fact the reactor is the loss leader for companies that make fuel rods. Thorium floride reactors do not create weapons grade material and are much safer. "
Unfortunately this is simply inaccurate in some respects. Yes, thorium salt reactors have some interesting properties which would make them far less vulnerable to the class of errors which BWR/PWR are, but they have a whole class of unique hazards. Liquid thorium flouride is very hot, and very radioactive. It is soluble in water, and friable. This means if it ever gets out in the environment the consequences would be extreme. Given that a leak would involve a very hot liquid, it would be a real problem. How would you clean it up? Very messy.
Maybe a stupid idea, but why don't they use a secondary steam turbine off the reactor's unwanted heat source to create the energy to drive the cooling pumps instead of generators thereby acting as a governor against the reactor heat?
Reply | Report Abuse | Link to thisIt never ceases to amaze me that amount of gas put out by Tharter. As a shill for gas companies, I suppose we can expect that from him.
Reply | Report Abuse | Link to thisAs we have seen, a worst case accident in a 50's design reactor - the first one in 25 years - caused no damage other than some external bricks and mortar and a few fuel rods in a soon to be commissioned reactor. Sadly the hydrogen gas explosion in the industrial building hurt some individuals but in the grand scheme these were a tiny fraction of the folks hurt by the other gas in the area. The modern reactor with passive cooling is a thousand times is less likely to have the same accident so once these clunkers are gone we can wait 25000 years for another similar no harm incident. Seems like a good deal to me.
His nonsense on dire consequences is a canard.
Given the enormous amount of deaths in the area from Big Green's favorite fuel - natural gas and the forever destruction of land from all the toxic chemical leaks I would think that Tharter's gas should be directed elsewhere.
His pitiful spew on the LFTR is hilarious revealing and utter lack of any sort of knowledge on the subject. He just made it all up.
The LFTR uses primarily Lithium Flouride. The salts do not burn in air or water, and the fluoride salts of the are not soluble in water. The stuff becomes a solid when the reactor cools down even slightly so a hot liquid leak would self seal immediately.
Tharter's spew is as usual just plain horseshit.
I don't know much about the thorium-fluoride reactors, so I can't comment on the second half of tharter's letter, but everything he said in the first part seemed eminently reasonable, sethdayal's childish, vicious, ad hominem attacks notwithstanding. tharter simply pointed out that any rational evaluation of technical risk must balance probabilities and consequences. Is sethdayal actually arguing that a serious nuclear accident is impossible in the U.S.? It must be said that his nasty tone betrays insecurity and suggests maybe he's not really all that sure of himself.
Reply | Report Abuse | Link to thisIt was a 8.9 earthquake. Surely quite a quake, but 9.8 hasn't even been recorded (Valdivia, 9.5, is the record holder) yet. That being said, while I support and encourage further use of nuclear power, the industry must be forthright in telling the public that all engineering projects carry risks, including nuclear power. As proven in Japan, even triple redundant systems can and will fail - all that is needed is a failure mode that is correlated with all three safety systems!
Reply | Report Abuse | Link to thisToo often I hear nuclear engineers bemoaning the supposed ignorant fear of nuclear power in the public. These fears, if uninformed, are justified. Three separate events causing core meltdowns in 32 years is hardly a reassuring track record for the public! Public trust is like respect - it is earned, not bought with patronizing "nuclear energy is safe" TV ads. I can't wait until the youtube nation gets a hold of those ads and starts posting them online.
Rather than belittle the public with ads, therefore, the industry should educate people so they can make an informed decision whether or not to have nuclear power. When accidents happen, as they inevitably will, people will say it was an informed risk they took.
Actually, the fear is rational even for well informed people. At best, the risk of a INES level 7 accident is something like 1 in 10000 during the lifespan of a reactor, which would mean a few percent for the 440 worldwide operating commercial reactors. But many of these reactors are older so they don't meet the same safety standards as new reactors and have a risk of a level 7 accident, which is more like 1 in 1000. Of course nuclear engineers will say, that this is acceptable, because they want to keep their job. But I think it isn't, when considering the effects of a level 7 accident: for the chernobyl accident there were approximately 336,000 people evacuated in an area of something like 10000 km², so the area was not densly populated, if a big city would be in such a zone (which is possible for some nuclear plants), they would have to evacuate millions, which might be impossible in a reasonable timeframe. And also there were millions of people effected outside of the zone, there were areas far aaway from the zone where the radiation was increased significantly.
Reply | Report Abuse | Link to thisAnd CANDU isn't safe eigther, it has some safety advantages to conventional BWS or PWR reactor, but also some disadvantges, i.E. the positive void coefficient, which was one of the reasons for the chernobyl disaster. The void coefficient of CANDU isn't as high as of RBMK, but it still increases the risk of severe accidents compared to designes using a negative void coefficient.
@sethdayal: according to wikipedia lithium fluoride is soluble in water at 2.7 grams per litre at 18°C.
I just seen, thaat this website doesn't display correctly some of the charecters I entered:
Reply | Report Abuse | Link to this10000 km² means 10000 square kilometers.
18°C means 18 degrees Celsius.
My page http://www.firstpr.com.au/jncrisis/ is an attempt to link to sites which are relevant to this crisis, including wind maps, technical sites and discussion forums. Please also see:
Reply | Report Abuse | Link to thishttp://en.wikipedia.org/wiki/Fukushima_I_nuclear_accidents
The MIT report on decay heat: http://mitnse.com/2011/03/16/what-is-decay-heat/ shows that substantial decay heat production will go on for months. It is currently 7 megawatts (unit 1) and 12 megawatts (units 2 & 3). It will be July before these energies are halved.
How will the fuel in these reactors avoid melting and/or being spread into the atmosphere via steam emissions? The desperate measure of pumping in water to evaporatively cool the core has now been abandoned, since all workers have departed the site, due to prohibitively high radiation levels.
- Robin
Seth, go back to school and get your basic science right before you try to 'teach' the public about safe nuclear power. You might want to try a basic physics class in a junior college to start. Specially if you are criticizing other commentator's free and honest opinion. Just so you do not confuse yourself to begin with.
Reply | Report Abuse | Link to thiswhat about china syndrome? X5
Reply | Report Abuse | Link to thisWhy not get all there fire fighting boats and spray it down that way.
Reply | Report Abuse | Link to thisWould it be possible to quickly come up with a very long bucket or attach a wide hose to the existing bucket that the Japanese are using to deliver water to the Fukushimo Nuclear Reactor?
Reply | Report Abuse | Link to thishttp://en.wikipedia.org/wiki/Pebble_reactor#Criticisms_of_the_reactor_design doesn't look as positive as you would have us believe.
Reply | Report Abuse | Link to thiswhy?
Reply | Report Abuse | Link to thisYour comments on tharter are offensive, especially in a allegedly scientific discussion, and the claim that "Big Green" (whoever that is supposed to be) is invested in gas is in contradiction to everything I know about the green movement I'm involved with.
Reply | Report Abuse | Link to thisWould you care to actually use evidence to support 1. the alleged commitment of greens to gas and 2. that tharter is a "shill" for the gas industry?
Then, from the Greenpeace site, we have these two articles that seem to put the lie to your claims:
Liquid Natural Gas: A roadblock to a clean energy future http://bit.ly/dJaagT
While we are glad Penn State will be off coal, it is a SHAME the university did not use this as an opportunity to transition to renewable energy. I was hopeful that Penn State would have the courage to answer the call for 100 percent renewable energy, and be a leader among our country's top colleges and universities. Today, Penn State decided not to lead. http://bit.ly/gK27tf
So, who is blowing gas?
Right now levels are 70+ sieverts (not micro). This causes death in less than an hour. We need to study how to LET a China Syndrome happen as a self encapsulation event. Is it possible to engineer a meltdown? Are there extant supercomputer models?
Reply | Report Abuse | Link to thisThis is not a high tech matter for atomic scientists. It is a matter for plumbers and electricians. As a proper backup in case of grid failure from a variety of threats-natural and man-made,nuclear power plants should be reconfigured to allow the electricity they produce themselves to cool themselves and their spent fuel rods.
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