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Experts on Japan nuclear crisis answer questions from Nature readers

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During the morning of April 6, our colleagues at Nature ran a live, online question-and-answer event about the Fukushima Daiichi nuclear crisis. Visitors posted questions for Jim Smith, an environmental physicist from the University of Portsmouth, U.K., and Geoff Brumfiel, Nature’s senior physical sciences correspondent. Brian Owen served as moderator.


Below is an edited excerpt of the hour-long Q&A. Click here for the full transcript, and click here for additional articles from Scientific American about the crisis.

Brian Owens:

To start off, we’ve had a couple of people asking about the safety of traveling 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 travelers?

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.

[Question From ZoeyZoey: ]

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?

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.

[Question From Sonny TrenchSonny Trench: ]
What about contaminated fish that migrate?
Brian Owens:
A good question, I’ve wondered that myself.
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.

[Question From Magdeline LumMagdeline 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 occurred 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.

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 emphasize 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.

[Question From Drew WightDrew 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.

[Question From LizzieLizzie: ]

Is there any great difference in the effect of having ingested radiation (fish, kelp) versus having been externally exposed to it?

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 ionization, potentially leading to DNA damage and cancer – it doesn’t matter where they originate.

[Question From Chinju ParkChinju 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.

[Question From KrisKris: ]

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?

Geoff Brumfiel:

We talked a little about that in a story I wrote earlier this week ( 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.


Actually, I should qualify that: we don’t really know what’s happening in the reactors, but for now it looks stable…

[Question From Adam FAdam 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.

[Question From HowardHoward: ]

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.

Wednesday April 6, 2011 4:37 Jim Smith
[Question From ShelbyShelby: ]

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.

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:


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.

[Question From Claire CailesClaire 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.

[Question From IanIan: ]

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 foreseen.

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.


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Comments 8 Comments

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  1. 1. eco-steve 7:39 pm 04/6/2011

    Will the marine food chain concentrate radioactive elements in the same way as mercury is re-concentrated?
    How much plutonium has escaped, and where has it gone?

    Link to this
  2. 2. pyam 10:58 pm 04/6/2011

    Short answer is no. Iodine-131 has a half-life of 8 days, and it typically takes weeks to get a fish to market, so the isotope shouldn’t be much of a problem for human consumption. Cesium-137 and -134 have half-lives of about 30 years, but animals excrete it during normal metabolic processes over the course of a few months–it doesn’t pile up in tissue like mercury does. Shellfish and bottom feeders in the area could be pretty toxic once the isotopes settle down in the sediment and persist.

    Thanks for commenting.

    Link to this
  3. 3. jtdwyer 12:51 am 04/7/2011

    Without having done any research, I imagine that many of the world’s existing reactors are located near high population areas near seashores. If global warming may produce rising sea levels, the world may need to develop and implement some technical strategy for mitigation of facility inundation effects, especially for existing reactors.

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  4. 4. Ralf123 1:55 am 04/7/2011

    Another issue is that sea defenses have generally not been improved since the reactors were built despite major new seismologic and geologic findings. Just think of the faults found near San Onofre or the Cascadia subduction zone. When many of those reactors were built plate tectonics was not generally accepted yet!

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  5. 5. jtdwyer 7:13 am 04/7/2011

    That is amazing – excellent perspective!

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  6. 6. aglindh 8:31 pm 04/7/2011

    The statements about risks in Japan are woefully incomplete. Young children drink fresh milk, cows concentrate I-131 by factors of thousands. Young children are far more susceptible to I-131 concentrating in their thyroid glands. The first question to ask an "expert" in such case is,"Would you take your young child to Japan and let them drink fresh milk?" I promise you the answer is NO. No sane person would trust the same Japanese bureaucracy whose total incompetence led to this tragedy, to now keep radioactive milk from reaching the markets. Anyone in Japan who is feeding fresh milk to their children should have their head examined.

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  7. 7. Plain-2009 11:53 pm 04/7/2011

    I first put this commentary in the Scientific American article about "a time-lapse map of every nuclear explosion since 1945 by Isao Hashimoto", but I think it is more appropriate to put it here again.
    It is quite interesting that we have no trouble in putting into place the rods of nuclear fuel, and we are having trouble in taking them out in Fikushima Daiichi. ¿Is it necessary to build a special suit, like an astronaut suit, to approach the site and take out the rods in those troubled nuclear plants? If that is the case, let’s do it right away. One thing is quite clear for us, which approximately understand what is going on there. Most of the nuclear plants in operation, if not all, are very primitive. It is going to take some time, for us, to build real efficient and safe nuclear plants. Any way, the foundations are strong and were established by penetrating acute clear minds of people that we shall never forget. I do not have anyone in particular to blame. We are going to make it through and come out stronger with God’s help.
    Additional commentaries: If fuel has melted probably we should find ways to take it out instead of putting concrete over it if we can work fast enough. With respect to damage to health I would say that it is more a psychological risk than a real risk but it is better to be careful and stay away until thing get under control. I am not particularly interested in the effects of radioactivity from a medical point of view,but there are researches working on this area. Obviously the recommendations from medical teams are very important. I would only stress the fact that psychological effects could be very strong and we should be aware of that.

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  8. 8. Plain-2009 3:04 am 04/9/2011

    May be it is not proper to mention at this moment when there is so much pain, especially suffered by the people in the area, in relation to the situation in Fukushima Daiitchi. What about the use of robots, if not possible now, in the future, in case of another nuclear accident (that hopefully never happens)? But on the other hand all alternatives should be considered, if understandably momentarily experts in the field seem to be paralyzed by the fear of further deepening of the problem. We should remain calm, study carefully the alternatives and work fast. It seems to me Japan has the muscle and the wisdom to handle the situation but the world should be ready to give a hand if need arises.

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