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  1. #51
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  2. #52
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    Preliminary experimental results contradict the LNT model

    High radiation doses show a more or less linear dose-response relationship. This is well established from studies of the survivors of the atomic bombings of Japan, among others. Their combined cancer risk increased by about one to two percent, and those exposed to a higher dose had a more or less proportionally higher chance of developing cancer. The data is also compatible with a non-linear curve, it's too noisy to say which curve fits better.

    However, at low doses and low dose rates, the effects of radiation are too small to detect. The lowest dose rate that can currently be linked to increased cancer risk is approximately 100 mSv per year. To deal with this lack of data, the linear dose-response curve established for high doses and high dose rates was simply extrapolated linearly down to zero dose. This is called the Linear No-Threshold hypothesis (LNT), and this model is what radiation protection agencies around the world use in their work.

    The LNT hypothesis postulates that all ionizing radiation regardless of dose or dose rate is harmful, and this has a huge effect on the cost of nuclear power. One example is that if it turns out to be false, then the area around Fukushima should not have been evacuated, or the evacuation zone should at least have been a tiny fraction of the size it is today. Spent nuclear fuel would also have been much less of a problem.

    The LNT hypothesis has long been controversial, there are very good biological reasons to assume that it's wrong. Most biological phenomena do not work this way. To exemplify what a linear no-threshold dose-response curve means, I will use a more familiar agent: Aspirin. Assuming the Aspirin dose-response curve is of the LNT variety, and we give 20 Aspirin to each of 100 persons in a single dose and find that two of them died (a very unethical experiment), then a dose of 2 Aspirin to each of 1000 persons still yields two deaths. Moreover, if we tell the 1000 persons to scrape a tiny bit of their two Aspirin onto their breakfast in such a way that the two pills are consumed evenly over a whole year, the result will still be 2 deaths in the population.

    Aspirin in fact has a hormetic dose-response curve, large studies show that if a population takes 1/2 Aspirin per day, their health improves by a small but detectable amount. On the other hand, some substances show at least some similarities to LNT - there is for example no safe dose of lead.

    Radiation causes cell damage in essentially the same way as a myriad other agents - by breaking random chemical bonds in the cells and their DNA. The oxygen we breathe does the same thing. To deal with this, cells are equipped with extremely efficient repair mechanisms, and if those do not work, the cell will almost always commit suicide. Those that don't may turn into cancer cells. The repair mechanisms are known to be time dependent, and multiple broken bonds at the same time are less likely to be successfully repaired than single breaks happening one or a few at a time. This points towards a non-linear curve.

    There are large studies that hint at a non-linear dose-response curve in real life too - for example, aircrews are exposed to much higher levels of radiation than the rest of the population, the equivalent of more than 1000 extra chest X-rays per year. Yet they have no higher cancer rates. Tens of thousands of people exposed to hard gamma rays from US Navy reactors had lower rates of cancer than their non-nuclear counterparts doing exactly the same kind of work. These results are explained away by referring to what is known as the "Healthy worker effect": For some unknown reason, they must have been healthier than the rest of us to begin with.

    Earlier LNT debunking in the monthly journal "Radiology", from 2009.

    Now there are two experiments underway to test the validity of the LNT hypothesis. Since the effects of very small radiation doses above the normal background are so hard to detect, these experiments instead reduce the background radiation by a large amount. One cuts the background radiation to 1/3 of the natural level, the other removes it almost completely. If this is found to hamper cell growth, then low-dose radiation cannot possibly behave linearly.

    This now seems to be the case. The data is still preliminary, but cell growth is hampered in the low-radiation environment in both experiments.

    Press release from the US Department of Energy.
    Last edited by eledille; 2012-12-12 at 12:33 AM.

  3. #53
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    I think the main conditional remark that "nuclear power" needs to be "done responsibly" and can be beneficial is the crux of my turnoff. IMHO very few contexts barely qualify as responsible - space exploration probably being the only one. One just needs to know how a little of how utilities and governments operate to understand there isn't any accountability towards avoidable catastrophes.

    Fukushima and Chernobyl are disasters deeper than one can glimpse on the news - just the volume of earth and topsoil that will need to be removed in the latter makes it a pharaonic cleanup job. Interestingly enough, some natural species (eg mushrooms) tend to accumulate caesium so they could be ingeniously used as cleanup agents; but even so it is a major undertaking to get anywhere near to baseline.

    (About me for context - 30's, started a major in particle physics in my young days, and am very glad my car won't be powered by nuclear)

    While I used to think that nuclear fission could be a good transitional energy source, now I am convinced that accelerated infrastructure investment in renewables leads to a better and more resilient grid from a technical, ecological and economical perspective. (Even with its high total capital and operational expense) Whether that acceleration is enough to escape carbon, ocean acidification etc thresholds is TBD, as nobody knows where those thresholds really are anyways.)
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    With regards to the above (very nice) post by elefille: There is ample evidence already, more collecting, to completely refute the NLT harm model for ionizing radiation.

    In fact, our cellular systems have evolved under, and in harmony with, continous (background) radiation exposure. It turns out most organisms with DNA actually become unhealthier if background radiation is blocked for long periods of time. This is a bit in analogy to another biologic fact: mammals delivered by C-section and then raised in a completely sterile environment develop disease in their gastrointestinal tract - we are not designed to live in abscense of neither germs nor radiation. And our systems have quite some margin. Earth has been subjected to quite variyng levels of radiation during the evolution of life.
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    EchoDelta:

    If low dose rate radiation like that found in the Fukushima and Chernobyl evacuation zones is found to be harmless, are Fukushima and Chernobyl still disasters? If so, of what magnitude compared to e.g. a plane crash?

    What about reactors that don't need off-site power, backup generators, backup coolant pumps, primary coolant pump, water injectors or even operators for three days at a time, if Fukushima-style radioactive releases are harmless? Such a reactor exists (ESBWR), and that's what the data is might indicate.

    Even if LNT should turn out to be correct after all, one might still ask whether a risk that is too small to detect using the best statistical methods available is worth worrying about when people routinely engage in risky activities like breathing smog, eating meat and driving cars, and the globe is heating up at a disastrous rate.
    Last edited by eledille; 2012-12-12 at 12:28 AM.

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    Quote Originally Posted by eledille View Post
    EchoDelta:

    If low dose rate radiation like that found in the Fukushima and Chernobyl evacuation zones is found to be harmless, are Fukushima and Chernobyl still disasters? If so, of what magnitude compared to e.g. a plane crash?
    * Harmless for humans in 'state of the art for 2012' given the lack of true cohorts and inability to do real experiments seems a bit of a low safety bar to me. As Johan exemplifies, we understand very little about the subtle interplay of environment and the body & mind. I work with- and live with- doctors... they just figured out ~150 ys ago that washing hands and using antiseptics may prevent deaths. My opinion is that we still lack the tools to come to such conclusion.
    * Harm is rarely related to direct exposure other than right during or after an emergency. In the long run you are looking at topsoil and farmland and water systems; each species and physical subsystem has its dynamics for different elements that accumulate or dissipate them. The example I gave above- Caesium being concentrated by mushrooms is a great example - it can be a dangerous contamination vector or a great cleanup tool, depending on your perspective. Very few people will picnic for a while on the plains of fukushima, or carry their pregnancies there, more people will eventually eat drink wear & breathe what grows out of there.
    * I've been following the ESBWR work and the TWR approaches (in my layman opinion the latter seems quite interesting).Maybe too old fashioned, but I spent a summer working in a CANDU which was an interesting experience - everyone in a reactor knows every failsafe, every stable state has threats which have mitigations which in turn have threats etc. I recall the constant feeling that "For the want of a nail..."
    * In addition, the supply chain for uranium is complex & dirty. Development and installation requires highly centralized control and therefore government subsidies and for a policy/monitoring/inspection apparatus.

    Quote Originally Posted by eledille View Post
    Even if LNT should turn out to be correct after all, one might still ask whether a risk that is too small to detect using the best statistical methods available is worth worrying about when people routinely engage in risky activities like breathing smog, eating meat and driving cars, and the globe is heating up at a disastrous rate.
    A big difference with eating meat and drinking coca cola is choice. It is unlikely individuals can choose not to be exposed to radiation from a reactor gone wrong that someone else installed remotely yet too close to your backyard, while they can choose to engage in some of the other risk behaviors. And especially when the approach to measurement of the risk is a matter of policy, politics and debate more than exact science.

    Thinking fairly I have not seen a cradle to cradle analysis of a fission reactor of any kind vis a vis solar panels or wind; relative to kWh generated, and relative to carbon footprint or some other planetary boundary denominator, and prorating all the externalities in R&D and supply chain and disposal and safety. Would love to see a good one one if anyone has pointers. Cheers to all for the engaging discussion.
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    Quote Originally Posted by EchoDelta View Post
    A big difference with eating meat and drinking coca cola is choice. It is unlikely individuals can choose not to be exposed to radiation from a reactor gone wrong that someone else installed remotely yet too close to your backyard, while they can choose to engage in some of the other risk behaviors. And especially when the approach to measurement of the risk is a matter of policy, politics and debate more than exact science.
    People can avoid some of the other risk factors, yes, but certainly not all of them. Coal power kills around 13,000 people per year in the US alone, and I would expect NOX emissions from cars to kill a comparable number. Now, one can of course choose to live in a cabin far away from cars and coal power plants, but that is no real choice.

    Ideally, solar and wind is the way to go, but it is a bit optimistic (to put it nicely) to expect solar and wind to be able to supply 100% of the electricity in the short or intermediate term. As such, nuclear is a very good option, one that should definitely be a part of the grid until such a time as one has the luxury of replacing them with solar and wind.
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  8. #58
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    Quote Originally Posted by EchoDelta View Post
    Cheers to all for the engaging discussion.


    * Harmless for humans in 'state of the art for 2012' given the lack of true cohorts and inability to do real experiments seems a bit of a low safety bar to me. As Johan exemplifies, we understand very little about the subtle interplay of environment and the body & mind. I work with- and live with- doctors... they just figured out ~150 ys ago that washing hands and using antiseptics may prevent deaths. My opinion is that we still lack the tools to come to such conclusion.
    To a certain extent, that's true. In my opinion, it's also misleading.

    There is actually a massive amount of very good science on the effects of ionizing radiation. The fact is that below a certain level, the effects are too small to measure. They may be small, nonexistent or even beneficial, we just don't know which. But they can not be large.

    There is no lack of good cohorts or data. There are many very well controlled and some extremely large studies - but the effects attributable to radiation are simply so much smaller than so many other things that affect cancer rates that no matter how well you control and correct, the effects of radiation cannot be detected much below a one or two percent increase in lifetime cancer risk.

    We do know, however, that the long-term effects from radiation among the survivors of a plutonium bomb detonation directly above a city is on the order of a couple of percent increase in lifetime cancer risk, and that among multiple tens of thousands of navy personnel performing identical work, those exposed to gamma radiation from reactors had lower cancer rates than their unirradiated counterparts. There's a long list of similar results.

    Now we also know that cells are harmed by too little radiation - at least, that's what the preliminary data says.

    * Harm is rarely related to direct exposure other than right during or after an emergency.
    This is not correct. One perfect example is how leaded gasoline was finally banned due to overwhelming scientific evidence of the harmful effects of chronic, low-dose lead exposure. There are many, many other examples.

    In the long run you are looking at topsoil and farmland and water systems; each species and physical subsystem has its dynamics for different elements that accumulate or dissipate them. The example I gave above- Caesium being concentrated by mushrooms is a great example - it can be a dangerous contamination vector or a great cleanup tool, depending on your perspective. Very few people will picnic for a while on the plains of fukushima, or carry their pregnancies there, more people will eventually eat drink wear & breathe what grows out of there.
    Norway received a relatively generous share of the fallout from Chernobyl. We still have to give raindeer and sheep uncontaminated fodder for a while before slaughtering to get the activity count below the legal limits. I personally pick and eat mushrooms and don't worry about it.

    I'm much more worried about the high and rising mercury content of freshwater fish than radiation. We didn't release the mercury either, that comes from European coal fired power plants.

    What really scares me, however, is climate change.

    * In addition, the supply chain for uranium is complex & dirty.
    I'm sorry to say this, but I'm afraid you've been lied to. This is pure propaganda with zero connection to the real world. Compared to coal, the uranium supply chain is almost as innocent as a new-born baby.

    Coal mining digs up and grinds down entire mountains. Such enormous quantities are required that there will be many accidents during mining and transportation and the environmental impact is very large. The ashes contain toxic heavy metals and are hard to dispose of safely. Besides, the stuff contains so much uranium that if burned in a fast reactor, more nuclear energy can be extracted from it than you can get by burning the coal itself. Where does that uranium go? Up the smokestack and into the landfill. This together with the fact that the uranium content of coal power waste is often listed only as "trace amounts" says something about the energy density of uranium - and how dirty coal power really is.

    Some facts:

    Fuel consumption per gigawatt-year (tons):

    Coal
    3500000
    Moderated fission
    160
    Fast fission
    1

    The number for moderated fission is for slightly enriched fuel. 1600 tons of natural uranium is required to produce it, which leaves 1440 tons of depleted uranium. CANDU reactors don't require this enrichment. Fast reactors require higher enrichment in the initial core loading, but they can produce more fissile material than they consume during operation. A new reactor can use the fissile material from a decommisioned reactor, so this is only required for startup, while the total number of reactors is rising.

    Waste production per gigawatt-year (tons):

    Substance Coal Moderated fission Fast fission
    Spent nuclear fuel
    0
    160
    0
    Depleted uranium
    0
    1440
    0
    Fission products
    0
    0
    1
    CO2
    10000000
    0
    0
    Ashes
    350000
    0
    0
    SO2
    35000
    0
    0
    NOx
    25000
    0
    0
    Soot
    1200
    0
    0
    VOC
    550
    0
    0
    Uranium
    1 to 10
    0
    0
    Arsenic
    0.25
    0
    0
    Mercury
    0.19
    0
    0
    Lead
    0.125
    0
    0

    190 kg of mercury is a huge amount. One teaspoonful of mercury in a soluble form will pollute a 5 km2 lake.

    Natural uranium is slightly toxic and weakly radioactive. It is often mined in association with other ores. In Australia, uranium appears together with copper and gold, for example.

    Finally, if we started building IFRs, we would not have to mine any more uranium for the next couple of thousand years. We already have more than enough depleted uranium and spent nuclear fuel in storage. There's a lot of information about the IFR here, or you can read the book "Plentiful Energy".

    A big difference with eating meat and drinking coca cola is choice. It is unlikely individuals can choose not to be exposed to radiation from a reactor gone wrong that someone else installed remotely yet too close to your backyard, while they can choose to engage in some of the other risk behaviors.
    I agree that choice is important. But when it comes to electricity generation, there is no perfect choice.

    When I go fishing for perch or trout with my children, I have to be careful to remind them beforehand that if we get a big fish, we have to put it back, because it's poisonous - it contains too much mercury. We can only eat the little ones nowadays. You should have seen their faces the first time I told them this - incredulity, disappointment, dismay. We don't have any coal plants and I did not invite the European power industry to dump their mercury on Norway.

    We used to have beautiful summers in Oslo, with temperatures between 25 and 30 and sunny weather for weeks on end. The previous six summers have been rain, rain, rain, oh gosh it's not raining today, rain, rain. Climate change? Who knows.

    By the way, I'm not trying to pretend that Norway is an innocent victim or something like that. We export coal from Svalbard and oil from the North Sea and are as guilty as sin too.

    It's entirely unclear whether it's at all possible to replace fossil fuels with undispatchable renewables like wind and solar. We had an interesting argument about that in this thread just a few weeks ago.

    We do know that the environmental risk of nuclear power compared to fossil fuels is very low. The risk of failure compared to undispatchable renewables is also very low.

    And especially when the approach to measurement of the risk is a matter of policy, politics and debate more than exact science.
    Exact science has determined that the risk from even relatively high levels of radiation is too small to detect. That does not mean that it is nonexistent or unknown, it means that it is known to be at worst very small. Science has also determined that pollution from fossil fuels is vastly more damaging to health than that from nuclear fission, and that the risk from CO2 emissions is real and potentially catastrophic. A few degrees of warming might realistically cause massive desertification of the American Midwest and the Russian steppes, for example. This is where most of the world's wheat is grown. We're currently headed towards five degrees or more.

    This is the WHO/UN/IAEA report on the true scale of the Chernobyl accident.

    Thinking fairly I have not seen a cradle to cradle analysis of a fission reactor of any kind vis a vis solar panels or wind; relative to kWh generated, and relative to carbon footprint or some other planetary boundary denominator, and prorating all the externalities in R&D and supply chain and disposal and safety. Would love to see a good one one if anyone has pointers.
    Here is one, brand new. This is a head to head comparison of a combined wind/solar and a nuclear alternative to two Australian coal fired power plants. The report compares the following parameters: Cost, electricity production, greenhouse emission reduction, job creation, area requirements, water consumption, major construction materials consumption, network requirements and reliability.
    Last edited by eledille; 2012-12-26 at 12:57 PM. Reason: grammatical correction

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    Quote Originally Posted by eledille View Post




    To a certain extent, that's true. In my opinion, it's also misleading.
    ...

    Here is one, brand new. This is a head to head comparison of a combined wind/solar and a nuclear alternative to two Australian coal fired power plants. The report compares the following parameters: Cost, electricity production, greenhouse emission reduction, job creation, area requirements, water consumption, major construction materials consumption, network requirements and reliability.
    Thanks for the detailed and constructive post.

    The information about the uranium mining I hadn't seen before and appreciate you sharing it and the links. I generalized from personal closeness to the industry..in Latin America -still anecdotal, but 'innocent as new born baby' is an easy goal when compared to coal extraction.

    Thx again for the data and links.
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