Brian Owens: Hello, and welcome to our Q&A session on the Fukushima nuclear accident in Japan. We have Jim Smith, an environmental physicist from the University of Portsmouth and Geoff Brumfiel, Nature’s senior physical sciences correspondent with us to answer your questions.
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Brian Owens: To start off, we’ve had a couple of people asking about the safety of travelling to the region, including someone whose daughter is studying in Japan, and someone on their way to Korea. Jim, could you tell us a bit about the risks from radiation to travellers?
Jim Smith: I guessed this would come up, so here's one I prepared earlier:
There is no significant risk for travel to countries outside Japan – you’re likely to get a much higher radiation dose from cosmic rays on the flight over than you would from the radiation. Even in Japan, the risks of radiation are very very low. This is because (1) contaminated products are being kept out of the food supply (2) apart from in the area within, say 40-50km there isn’t a big risk from deposited radioactivity. (3) the radioactive iodine which is causing all the concern at the moment is decaying away. All of it will be gone within a few weeks. I’d be more worried about the disruption to services and anxiety caused by the earthquake, tsunami and nuclear accident.
Brian Owens: Thanks Jim. Hope that help reassure nervous travellers. And one for Geoff. Peggy asks on the blog: Is there any practical typhoon and earthquake proof solution for storing the contaminated water needed to cool the fuel? What are the chances that leaks of highly contaminated water will worsen to the point that they will be unable to keep the fuel cool?
geoff.brumfiel:
So these are two million-dollar questions. Unfortunately, I'm not sure anyone can provide a very good answer at the moment. In the short-term, engineers at the plant are planning on using existing storage tanks to store highly radioactive water. To make room, they're dumping several thousand tons of slightly irradiated water into the Pacific. These containers are obviously somewhat earthquake and typhoon proof in the sense that they've just survived the biggest quake and tsunami in recent memory. But I don't think that necessarily makes them a good long-term solution.
geoff.brumfiel: In terms of your second question: it's hard to predict the chances of leaks worsening, in part because we don't know how extensive the damage inside the plant actually is. TEPCO has recently sealed the worst leak (around unit 2), but they admit there may be others to deal with. Still, I think it's worth noting that for the past ten days or so, conditions inside the reactors seem to have been fairly stable.
[Comment From Zoey]
1. Although there are high levels of Cesium 137 and Iodine 131 in the water around Japan many people believe that it is not cause for concern because of the ocean’s ability to vastly dilute what is put in it. Do you believe other countries should be concerned or do you agree that the ocean can fix it?
Brian Owens: Jim, could you say somthing about that?
Jim Smith: Yes, there is enormous dilution of radioactivity in the marine system. By the time any contamination got across the ocean to other countries (if any did), the concentrations would be tiny and wouldn’t present any risk. The concern for the marine system is mainly in the local area to Fukushima.
geoff.brumfiel: I would add that a French team has done some modelling for the IAEA on this. It doesn't necessarily answer the question, but it gives a sense of how the material is dispersed:
http://sirocco.omp.obs-mip.fr/outils/Sy ... iJapan.htm
[Comment From Sonny Trench]
What about contaminated fish that migrate?
Brian Owens: A good question, I've wondered that myself.
Brian Owens: Jim, any thoughts on fish that might leave the area?
Jim Smith: That's a good question. Not sure what the fish species are in the region and how far they might migrate. If they were in the contaminated region for a long time (it takes time for radioactivity to get up the aquatic food chain into fish) they might get contaminated. During migration they would lose some of that as they expel it as well (I-131 would all go by decay) but some Cs-137 could remain. Guess they'll have to monitor migratory species if there are any.
Brian Owens: While we wait for Jim's answer, here's another question for Geoff
[Comment From Magdeline Lum]
How long do you expect the Fukushima situation to continue to be in play? The mainstream media has played it out like a disaster movie and now seemed to be lost as to what to do now that there isn't a foreseeable conclusion.
geoff.brumfiel: To be fair to the media Magdeline, I think everyone's at a loss right now. The situation at the reactors is unpredictable and the next steps are far from clear. What we can say is this: the situation at Fukushima is going to be with us for years. First, the reactors will need to be brought under control, but then they'll need to be cleaned up, and that is going to be very difficult...
geoff.brumfiel: I was looking at the British Windscale accident earlier today, which occured in 1957. Cleanup is still underway. Three Mile Island took 14 years. I'm not sure where Fukushima fits, but it's going to be over a decade. Probably many decades.
[Comment From Senkei Umehara]
What is the major source of information for you guys outside Japan? I'm in Tokyo and know foreign press is invited to conferences, but concern how frequently they get updated.
Jim Smith: Re: migratory fish again. There was a similar concern after Chernobyl about migratory birds. As I remember, radioactivity was measured in migratory birds in countries far from Chernobyl, though as far as I know this didn't cause problems for the food chain.
Jim Smith: Brian - think you missed off the first part of my answer about migratory fish.
geoff.brumfiel: In answer to Senkei: Actually the Japanese agencies have done a pretty good job of translating material into English. And in the past few days Chief Cabinet secretary Yukio Edano's press conferences have also been webcast with translation. So there's lots of primary source information out there. How reliable it all is is another question entirely...
Brian Owens: We’ve also had several questions here and on the blog about the safety of food and milk in Japan. Jim, could you give us your thoughts on that?
Jim Smith: As I said in my answer about travel above - I don’t think there will be significant risks from ingesting contaminated food/milk/water in Japan. Levels in water are now very low, and the Japanese authorities are working hard to keep contaminated products out of the food supply chain. That will be a difficult job given the that they are also dealing with an earthquake and tsunami. I couldn’t say for sure that some “contaminated” products won’t slip through the net, but I would emphasise that the risks from consuming some products above limits are still very low. The limits are set so that products can be consumed at that level for a long time. So if somebody were to inadvertently eat products above the level, it doesn’t mean that they would get an unsafe dose.
[Comment From Drew Wight]
Moving forward, how can nuclear power facilities (particularly in earthquake prone areas) be designed differently to withstand seismic activity?
geoff.brumfiel:
Many of the newer designs are supposed to be "passively safe" meaning that, even if the control room is completely destroyed or incapacitated, the reactor will cool itself down on its own.
I think a much more difficult question is how to make existing reactors safer. In the case of Fukushima Dai-Ichi, the position of the diesel backup generators relative to the coast was clearly a problem. I imagine regulators world wide will be looking at the number and state of various back up systems to see if they can be improved.
[Comment From Lizzie]
Is there any great difference in the effect of having ingested radiation (fish, kelp) versus having been externally exposed to it?
Brian Owens: Jim, your thoughts?
Jim Smith: The main difference is that it stays in your body for some time. This is taken account of in the risk models. For example Cs-137 is excreted from the body over a period of months, I-131 much faster. Some people also think there is a bigger risk because the radioactivity is inside you. I don't agree. The distinction between “internal”and “external” emitters is a bit false. An X-ray or external gamma ray causes the production of high speed electrons in the body in the same way as internal emitters do. It’s the high speed electrons which cause ionisation, potentially leading to DNA damage and cancer - it doesn't matter where they originate.
[Comment From Chinju Park]
If it takes over decades, does it mean that the spreading of radioactive materials continue during that time?
geoff.brumfiel: Jim may have some thoughts on this too, but no, I don't think we need to be worried about the continuous spreading of radiation. For one thing, the fuel will continue to cool down in the coming years, and will be far less dangerous than it is now. For another, engineers should be able to come up with some measures to reduce the spread of any radiation that does escape. I've already seen that TEPCO is spraying resin on the site to keep radioactive dust down, for example.
That doesn't mean that there couldn't be a significant release further down the road, but overall, I expect that the radiation will decline at the site.
Jim, anything to add?
Jim Smith: Radioactive Cs-137 is held in soil for decades (the amount halves every 30 years). It doesn't spread too far - tiny amounts are spread by the wind and water. As the reactors are now (hopefully) much more stable, the problem for the land system is the radioactivity that is already out there in the soil.
[Comment From Kris]
The fuel rods in Unit 1 has been reported to have exposed up to 70% and they are trying to dilute the hydrogen concentration by incubating Nitrogen. This means that the cooling of unit 1 has been failing... possibly by build up of salt (no water circulation). In your opinion(s) what would be the worst case scenario for this?
Brian Owens: Jim and Geoff both might have ideas about this.
geoff.brumfiel: We talked a little about that in a story I wrote earlier this week (
http://www.nature.com/news/2011/110405/ ... 1.211.html). Basically if cooling has failed, then there's a chance that the core has melted partially or entirely through the reactor and ended up in the concrete drywell below. That would mean a longer, costlier and more dangerous cleanup.
Another danger is that there is some transient power-producing fission inside the reactor, or that the reactor could inadvertently restart. That could be a real problem (obviously) both in terms of radiation release and managing the accident.
But the evidence that this has happened is slim for now. As I said earlier up, things appear stable.
geoff.brumfiel: Actually, I should qualify that: we don't really know what's happening in the reactors, but for now it looks stable...
Jim Smith: I'll leave that one to Geoff...
[Comment From Yuri]
Could you explain the similarities and differences between Fukushima and Chernobyl in regard to the spread pattern and the speed of radioactive substances to the surrounding soil and ocean?
Brian Owens: Jim, you wrote a book about Chernobyl, any thoughts on how these two compare?
Jim Smith: Chernobyl didn't significantly affect marine systems - there was radioactivity in the Baltic and Black seas (both a long way away) but concentrations were much lower. At Fukushima, the marine system is obviously a greater concern. There are similarities between the depositions from Fukushima and Chernobyl. We're concerned mainly about the same radionuclides - iodine and caesium. Though, at Chernobyl the explosion and major breach of primary containment spread "hot particles" within about a 10 km area. So the near zone of Chernobyl was contaminated with plutonium, strontium and other radionuclides which are much less volatile than Caesium and Iodine
[Comment From Brendan]
Are there any plans to move radioactive material from Fukushima at this time to a long term storage facility (are there reasonable options)? Or will the material have to just sit there in perpetuity?
geoff.brumfiel: This is a really good question Brendan. I haven't heard of any plans as of yet, but it seems to me that they may want to think about moving the material at some stage, as it's obviously in a risky location. Realistically, it will probably be years before they can do anything. They've got to wait for the fuel to cool.
[Comment From Adam F]
At Chernobyl they encased the reactor in a concrete tomb. What are the advantages and disadvantages of this sort of technique. Would it do more harm than good at Fukushima?
geoff.brumfiel: I was speaking to somebody about this the other day. The risk of a big concrete tomb is that it would have to be there for decades, even a century. Given the seismic and other environmental risks in the region, I think it would be extremely difficult to go down the sarcophagus route. Jim may have other thoughts.
Jim Smith: That makes sense to me, though it makes it more difficult to decommission when that starts.
[Comment From Howard]
Is the neutron beam that has been reported a sign of fission on the site? What is the best and worst case situation concerning that release of neutrons?
geoff.brumfiel: Ah yes, the mysterious "neutron beam". First of all, it's almost certainly a translation problem: they more likely mean a neutron "burst". Second, most of the physicists I've spoken to have disregarded the reports of neutron beams near the site. There are (roughly) three reasons:
1. Neutrons are extremely difficult to detect, so it would be a tough measurement.
2. The readings are fairly low, and could be caused by noise from the much higher levels of gamma radiation on the site.
3. It just doesn't make sense. The readings are far from the buildings. It's hard to understand why neutrons would be making it out of the containment vessel, even if they are being released.
That said, there's definitely neutron activity in these reactors as a result of other fission products in the fuel and it's certainly dangerous.
Jim Smith: If there was fission going on, you would also see some evidence in very short-lived fission products appearing in air and water monitoring data - I haven't seen any clear evidence of this yet, though I haven't seen much air monitoring data at the site.
[Comment From Aya Diab]
Jim, In your view, how will this accident affect the nuclear renaissance?
Jim Smith: Good question. I think it's too early to discuss this question, and was surprised that some politicians have started to do so whilst we're still in the middle of an accidental situation. I'm going to give you my immediate reaction, though. I'm an environmental scientist and (believe it or not) after 20 years of studying Chernobyl and even with Fukushima going on, I'm still pro-nuclear. I think we need nuclear as well as renewables to provide an electricity supply which is low in CO2 emissions and as a security of supply of raw material (uranium and plutonium) for the coming decades at least.
[Comment From Stuart McIntosh]
In addition to Drew Wight's question, do you think that countries susceptible to earthquakes and tsunamis should adopt other methods of obtaining energy?
Brian Owens: A follow-up to the nuclear renaissance question.
Jim Smith: That's also a good question, but one which I would leave until we're past the immediate accidental stage and we can start to learn the lessons from Fukushima. As Geoff pointed out, though, modern reactor designs are much better...
geoff.brumfiel: All nuclear reactors are built with certain risks in mind, and its worth pointing out that the nuclear reactors at Fukushima were faced with a disaster far worse than they were designed to withstand and (more-or-less) have survived in one piece.
That being said, I think this is a question that regulators and the public in many countries will have to answer in coming years. Indeed, we're already seeing a lively debate in countries like Germany.
[Comment From Shelby]
Most of the radiation readings around the 19km zone have been made in a somewhat less than scientific manner, often driving around from point to point, not including critical details such as wind direction at the time of reading. Can we trust these readings to be accurate when large swings from high readings to low readings could be attributed to things like wind direction or the large areas between reading sites? It would seem we only have a vague idea at best of the actual dumping of radioactive particles over this vast area.
Brian Owens: There has been a lot of debate over the quality of data available, Jim, Geoff, any thoughts?
geoff.brumfiel: I'll let Jim go first, then add a comment...
Jim Smith: In the early stages (i.e. when the contaminated material is in the air) the readings will be very dependent on things like wind direction, and will vary a lot. But once the radioactivity is deposited on the ground, the wind direction won't affect the readings. Soil moisture will, and I notice that the readings say whether it is raining or not, but it doesn't make too much difference. Generally I'm happy with the data, but sometimes it's been difficult to interpret because, as you say, there needs to be more accompanying information on methods etc. This may be a problem of translation - maybe the Japanese version is more complete.
geoff.brumfiel: The US Department of Energy has done some surveying with aircraft that provide a pretty good picture of where the radiation has spread:
http://blog.energy.gov/content/situation-japan/
Beyond that, I'd add that, to be fair, this is a really tough situation. It's easy to second-guess the Japanese, and indeed it's worthwhile to do so in many cases. But we shouldn't forget that, especially in the immediate aftermath of the tsunami, instrumentation was limited, as was access to the region.
Brian Owens: We're almost out of time, so just a couple more questions I think. First, one for Jim:
Jim Smith: I'd agree with Geoff on that - I wouldn't criticise the Japanese given what they have to deal with.
[Comment From Claire Cailes]
How does any increase in cancer risk from exposure to Fukushima radioactive contamination compare to other cancer risks such as smoking?
Jim Smith: Certainly much lower. As an example, the radiation dose to the Chernobyl clean up workers was about 100 mSv on average. That translates to about a 0.5-1 % additional risk of fatal cancer in later life. Continual smokers have about a 50% chance of dying from a smoking related illness.
[Comment From Chris Pook]
There is lots of data out there, and the Japanese are making absolutley everything available, but the big gap is the interpretation and trend line, and most importantly how this translates into regulatory decisons, e,g on food stuffs. Any thoughts on the best parameters for making these decisions?
Brian Owens: Jim, what information do policymakers need to make these important decisions?
geoff.brumfiel: The one thing I'd say is that I've noticed a real problem in how the press has reported on the crisis: they tend to give peak values. Especially because the danger from radiation depends on exposure over time, I don't think these numbers are always very helpful. Indeed, a low, but steady reading can be more dangerous than a brief peak.
geoff.brumfiel: Beyond that, it's probably a better question for Jim to answer...
Jim Smith: Yes, there are guideline limits for radioactivity in the event of a nuclear accident. So there are limits which are being used by Japan to check their foodstuffs against. But these are difficult to interpret, as Geoff says, which makes them open to misinterpretation by the media.
One important trend that is emerging from the data, though, is that the external radiation dose rates in the contaminated areas are falling rapidly in this early stage because short lived isotopes - Te-132 and I-131 are decaying.
Brian Owens: One final question, then we'll have to go.
[Comment From Ian]
Is there an international watchdog that inspects nuclear power stations or are such inspections left to national regulatory control? Clearly there seems to have been a lack or insight into risks that perhaps could have been forseen.
Brian Owens: Geoff and Jim, your thoughts on international coordination?
geoff.brumfiel:
The International Atomic Energy Agency has some authority to inspect civilian nuclear reactors, but mainly it's just to ensure that they are not being used for nuclear weapons development or other covert purposes. I imagine that some people will ask whether their authority should be expanded in the aftermath of this accident.
Jim Smith: Just what I was going to say...
geoff.brumfiel: Ultimately, however, safety is likely to remain squarely in the hand of domestic regulators, for better or worse.
times here.... and yes, each time, some one did shout "concrete aaya.. concrete aaya" and some one corrected that the pumps are modified to shoot water,,, 
.... And, to put it mildly, no one was talking about 'surface burns' ... (we are not likely to see surface burns.. or even feel something.. if we get 10-20 Sv radiation on feet.) 