How safe is nuclear power?

Disasters and AccidentsPlant OpeningsNatureNuclear PowerYushu Earthquake (2010)Heavy Engineering

Elmer E. Lewis, professor emeritus at Northwestern University and author of two textbooks on nuclear power, took questions about the effort to contain reactors damaged by the earthquake and tsunami in Japan. Lewis' research has focused on the broad problems of dealing with the physics, safety and reliability of nuclear systems.

"The combination of an earthquake of unprecedented intensity followed immediately by a tsunami of historical proportions in Japan has resulted in the most serious nuclear reactor accidents in decades," Lewis said. "Understandably, the uncertainty associated with the further progression of the partial melting of the reactor cores has engendered a great deal of psychological trauma as well as media attention.

"However, it appears that loss of life to the public -- if any -- caused by the radiation releases from these accidents will be minuscule when compared to the thousands of deaths caused by the earthquake and tsunami."

Photos: Scenes of earthquake destruction

Here's the transcript of the chat (moderated by L.A. Times staff writer Ron Lin with help from reader engagement editor Martin Beck):

Martin Beck (@latimesbeck): Welcome! We are ready to go. Ron take it away....

Ron Lin (@ronlin): Thank you for coming to this chat! We'll begin with questions.

Ron Lin: I'll start off: Why is it so difficult to get the reactors under control?

Elmer Lewis:Because of the failure of the emergency cooling systems caused by the earthquake and tsunami. Once they fail, it is much more difficult.

Elmer Lewis: Once high pressure steam has built up, they must have a way to pump water in at high pressure and to relieve the pressure by letting the steam escape. But the steam is radioactive.

Comment From Biff: Okay, if all the containment walls are breached, then what's the worst case scenario?

Elmer Lewis: That is difficult to say. The reactor can melt without the walls being breached. It takes a combination of molten fuel and a leak in the containment [vessel] to have large releases of radioactivity into the atmosphere.

Martin Beck: Note to readers: Thanks for all the good questions. We'll get to as many of them as possible.

Comment From Heather: How bad can this get? Especially for the U.S.?

Elmer Lewis: In the U.S. the effects may not even be detectable and if they are, they will be totally insignificant. The distance from Japan is so great the plume would we too widely dispersed before it arrived here.

Comment From Gary Reyes: What will ultimately come of these reactors? Will they have to be buried in concrete like Chernobil?

Elmer Lewis: It depends on how great the damage is, and that will take many months to tell. They certainly will not be used again. Question is will they be imbedded like Chernobyl or shipped to a waste depository.

Comment From Biff: So then hypothetically, the molten fuel and the leak to containment... what happens then? How much of Japan becomes inhabitable?

Elmer Lewis: Certainly Japan will remain inhabitable. At very worst, I cannot imagine this being as severe as Chernobyl. There the land around the reactor was contaminated so much that it had to be evacuated, more or less permanently, and over a larger area the agricultural products quarantined. And that would be a tiny fraction of the land area of Japan.

Comment From GoneToPlaid: Would you explain to the public exactly how the large volumes of hydrogen gas were produced, which in turn lead to explosions at three of the Fukushima Dai-ichi power plants, and what the consequences of the production of the large volumes of hydrogen gas actually mean in terms of damage to the fuel rods in the reactor cores?

Elmer Lewis: When the zirconium [metal] tubes in which the uranium fuel is located overheat greatly, they react with the water or steam, producing hydrogen as a byproduct. When it comes into contact with air in sufficient concentration, it will burn or explode.

Comment From Ed: Can wind can carry the nuclear radiation up to West of Japan neighboring countries like China and in South Taiwan and Philippines? and if can blow up to there what is the risk of that contamination (what sickness can this people get?

Elmer Lewis: Yes it can but it will be greatly diluted -- hopefully to the point where the concentration is too low to cause any health effects.

Comment From Guest: I think everyone understands that nuclear power isn't safe, but with no real other way to create sustainable power it has become necessary for most countries, my question is can future plants be made to be less of a risk, implementing better equipment, figuring out full proof plans against natural disasters to keep situations like the Fukushima disaster from happening in the future. Japan is a small island considering its huge population, due to the possibility of more earthquakes is it a smart idea to keep on developing a nuclear future for Japan?

Elmer Lewis: Yes, in fact the more recent designs have been made safer than those of the early 1970s. In the Japan situation, the question would be how strong an earthquake and tsunami must you design against. Since we only have a couple hundred years of records, it's impossible to say what the maximum earthquake could be -- say once in a thousand years. Thus a good deal of judgment must be exercised.

Comment From TINA: IS RADIATION CONTAGIOUS...IF FLYING IN AIRPLANE..CLOSED ENVIRONMENT, CAN CONTAMINATED PEOPLE CONTAMINATE OTHER PEOPLE?

Elmer Lewis: In general no, unless you have ingested a great deal of a radioactive substance -- enough to make you sick.

Comment From Guest: What are the concerns of the San Onofre Nuclear plant in Souther California being a resident living witin 10 miles? I hear containment may not be an issue, but what about loss of power etc?

Elmer Lewis: I'm sure that they were designed with much more attention given to the possibilities of tsunamis than here near Chicago. They are also designed to withstand more severe earthquakes than here.

Ron Lin: One question from me: What would need to be done to get this under control?

Elmer Lewis: A number of things. First they must establish a reliable source of water pumped in to keep the uranium under water and a way of venting steam to relieve the pressure. Then they must establish a way of filtering that steam to keep it from taking radioactivity into the atmosphere.

Comment From Karyn: Reactor #3 contains plutonium, which is a whole different ballgame. What will happen if plutonium, which has a half life of 24,000 years and is extremely toxic, is released?

Elmer Lewis: Sorry my connection was lost. I'll try again.

Martin Beck: Welcome back! :-)

Elmer Lewis: Plutonium is not volatile. Like uranium it would stay as part of the molten core in the bottom of the reactor, with exceedingly little -- if any -- being released to the air.

Comment From Baris: Is it possible for the nuclear radiation to pollute the oceans and therefore spread to the entire world?

Comment From Mark: Can the 'so called' China Syndrome occur in Japan? Can a meltdown reach the water table -- which must be shallow here -- and spew huge ammounts of radioactive steam?

Elmer Lewis: It's possible that it will contaminate the ocean in the surrounding area if the very worst happens. But not farther away. The main concern would be if it's concentrated in the fish, and then eaten. But the fish can be examined for this danger.

Comment From tCb: Can you explain what the worst case scenario would be at this point? I feel like every day it keeps changing.

Elmer Lewis: Worst case is that they cannot reestablish cooling and most of the fuel melts.

Ron Lin: Is this what is called a China Syndrome?

Comment From Gisselle: What does the "worst case scenario" mean for neighboring Asian countries?

Ron Lin: Definition of China Syndrome: "The China Syndrome is a term coined by an American physicist in 1971 to describe the hypothetical result of a severe nuclear meltdown in which molten reactor core components penetrate their containment vessel and building and melt through the crust of the Earth (possibly penetrating deeply enough to reach a point on the other side of the world)." LINK

Elmer Lewis: It could be considered the initial stage of a China Syndrome. Conceivably the core structure could collapse, the uranium falls onto the bottom of the pressure vessel and onto the concrete below. Again conceivably it could go into the soil below, but it would not penetrate more deeply than several yards. The main danger would still be the radioactivity released to the atmosphere, not what goes into the ground. It might contaminate drinking water for a small area around the plant.

Comment From JF: Not sure if this is something you can answer - but I've read that the workers at the facility have been exposed to high levels of raditation. What does that feel like for them when it's happening?

Elmer Lewis: You must really be exposed to a lot. The first signs are usually feeling sick in your digestive tract. Unfortunately, by the time there are such symptoms, you already have an elevated risk of cancer long after you have recovered from the radiation sickness.

Ron Lin: Should people in Tokyo begin evacuating?

Elmer Lewis: No, not now. And not likely in the future - but I hate making predictions.

Comment From Megan Garvey, LA Times: At some point will the reactors cool on their own? Is it critical to cool them indefinitely?

Comment From Andrew F: Pardon my ignorance on the matter, but how long can this situation persist being that they have been turned off since the quake? That is, at what point will the reactors begin to self-correct?

Elmer Lewis: The amount of cooling needed will slowly decrease over time until they can finally be cooled by natural processes. But that point is years away.

Comment From Clem: With current Nuclear Plant design what's there to address the possibility of total Power failure, like happened in Fukushima? Is there mechanical mechanism to prevent meltdown?

Elmer Lewis: The primary effort with total power failure is to restore enough power to run emergency equipment. A good deal of attention is needed to doing what-if studies to come up with alternate paths to get power into the plant. In the U.S. the "plant blackout" accident received a good deal of attention about 10 years ago, both in beefing up equipment and training operators to deal with seemingly unpredictable circumstances.

Comment From GoneToPlaid: I agree with Elmer. A partial or full meltdown, breaching the containment vessel, can be contained, just as was done at Chernobyl with the remains of that reactor's core. Elmer, at this point would you say that a greater concern is the fuel rods in the storage pools at #4, #5 and #6 reactors?

Martin Beck: While Dr. Lewis types, here's an interesting comment:

Comment From Morgan: From the beginning of this disaster the Japanese government and the plant operators have been quoted as saying there is little risk of the situation becoming more critical, and yet that's what has been happening with each passing day. It makes it difficult to trust anything they say, as it seems they're not being up front with the public about the present situation. These kinds of events call for complete transparency. This is part of the reason for the rising public distrust over nuclear power.

Elmer Lewis: That's a difficult one to answer, because it has many different aspects. If the spent fuel has been out of the reactor for a few months, the radioactive iodine -- the largest threat -- has almost completely decayed away (Its half life is 8.5 days). However the cesium is still there. The spent fuel requires much less cooling -- which is good -- but it is outside the primary containment -- which is bad.

Hope this helps.

Ron Lin: Some follow-up questions: Why can you not imagine this will be as severe as Chernobyl? And how quickly would officials recognize if massive amounts of radiation is released to the atmosphere? If that happens, what should the public in Japan do?

Elmer Lewis: Chernobyl was a different type of accident only possible with the reactor of Russian design and there was no containment. It was a massive overpower transient that vaporized almost the entire core and injected it directly into the atmosphere. Very different from a meltdown accident.

Massive amounts of radiation in the atmosphere would be recognized immediately. But that is why you evacuate before it becomes possible to insure that no one is close to the plant. Others would stay indoors with windows closed while the plume was over them . That significantly reduces exposure.

Comment From Karyn: You said that plutonium is not volatile, so I assume you mean it won't explode. But, in Chernobyl, the problem was plutonium in the soil. Does it get there through the melting process and what impact will that have on people?

Martin Beck: Note: We're nearing the end of the chat and have time for only a couple more questions.

Elmer Lewis: The main concern would be with isolating the soil so that no one was living on it or using farm products from it. Maybe you would remove some of it to an appropriate waste disposal site. Plutonium, uranium and other heavy elements migrate very slowly through soil (i.e. they would stay put).

Comment From Guest: Is there a reason nuclear power plants cannot be built further away from densely populated areas? it seems logical to build them further from population centers to lessen the impact from Fukushima-like disasters.

Elmer Lewis: Thay are as much as possible. They must have access to cooling water, even under normal conditions, and they shouldn't be many hundreds of miles from where the electricity is used (unless we have a much better grid). In Japan the country has mountains in most places, and a high population density. That's why the plants are concentrated on the coasts. The six at one location is more than you would find in the U.S.

Comment From Karyn: Here's a comment: I feel the "stay inside your home" suggestions at protection are insulting. Homes are not hermetically sealed. I feel so bad for the people who are being told this. They know that is futile.

Comment From Pip: I've been hearing a lot about the Nuclear Power people trying to spin this as not being a 'serious' problem. Most Americans are afraid of something like this happening, especially in California. Yet our elected Representatives still sound gung ho about building more power plants. The 56 Billion supposedly going to GA for building more plants might be better spent on trying to establish solar or wind power. How do you see this playing out in the future?

Elmer Lewis: I think both have major roles to play. But around the world the consensus is that we need nuclear if we are to deal with the shortages of fossil fuels over the long term and to make a serious impact on global warming. China, India and may other countries have large building programs that are unlikely to be terminated because of this accident, which thus far has caused no serious health risks other than the very serious risk to the heroes working in the plants.

Ron Lin: Thank you all for your questions, and I wanted to thank Dr. Lewis for explaining these issues so clearly and concisely. I'll take the last question: What kind of news do you expect to see coming from the facility that would enable us to breathe a sigh of relief?

Elmer Lewis: That the cooling was now adequate to keep the uranium both in the reactors and the spent fuel pits under water.

Ron Lin: What needs to happen for that to happen?

Elmer Lewis: A consistent power supply to pump adequate amounts of water, and to operate the valves (which require much less) and the other control devices.

Ron Lin: Do you have any final words, Dr. Lewis?

Elmer Lewis: Very good questions. You have a very thoughtful and intelligent audience!

Martin Beck: Thanks everybody. For the latest, come back often to latimes.com

Photos: Scenes of earthquake destruction

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