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      CommentAuthormaryyugo
    • CommentTimeMar 16th 2011 edited
     
    Good idea. But how do you throttle up and down the reactor's thermal output? And what if that fails and remains at full throttle? (sorry, don't know about those)
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    The reactivity is thermally controlled. Good wikipedia page;

    http://en.wikipedia.org/wiki/Pebble_bed_reactor
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    I don't like them, mainly because of them generating shedloads of intermediate level waste.
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      CommentAuthormaryyugo
    • CommentTimeMar 16th 2011
     
    Thanks for the link. Interesting article. Superficial read suggests many problems with the tech that were discovered when the German AVR was decommissioned.
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      CommentAuthorAngus
    • CommentTimeMar 16th 2011
     
    Posted By: joshsI wouldn't consider a CANDU really passively safe.


    Can you explain? The reactor itself is at ambient pressure - only the fluid transfer pipes are pressurised. Loss of pressure means loss of the moderator. Fuel is unenriched U.

    Not my area, but I'm curious as to what available designs would be safer.
    • CommentAuthorjoshs
    • CommentTimeMar 17th 2011
     
    They still require active cooling, and they still have to mechanically move control rods.
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      CommentAuthorAngus
    • CommentTimeMar 17th 2011 edited
     
    Posted By: joshsThey still require active cooling, and they still have to mechanically move control rods.


    Surely any reactor that drives a steam turbine is being actively cooled. Is there another way of extracting thermal energy other than by cooling the reactor? I take your point about the control rods but dumping the D2O working fluid automatically shuts off the fission in this type, I think. Sort of a control rod override.
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      CommentAuthorsaner
    • CommentTimeMar 17th 2011
     
    • CommentAuthorenginerd
    • CommentTimeMar 17th 2011
     
    My issue with the whole debate is that we rarely see the alternatives compared. Instead, we list the downsides of whichever source of energy we are investigating. Nuclear power facilities make a small amount of nasty waste. Coal fired plants make a large amount of fairly benign waste. Coal mining has many envromental problems and has certainly killed more people than the whole train of of nuclear power (mining, building, operating, catastrophes) combined. This is an unfair comparison because coal has been with us for a long time and nuclear power not so long, but still, there are fair comparisons that can be made.

    Which is cheapest per kw-hr, which causes more deaths per kw-hr, which harms more owls, which presents more risks to humans, for which do we have more fuel available to be mined? How do those compare to natural gas?

    It's always about trade-offs and cost/benefit choices.
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      CommentAuthormaryyugo
    • CommentTimeMar 17th 2011
     
    mmm... coal mining kills mainly people involved in mining (I suppose you can argue about acid rain and air pollution). But nuclear power plants, as we are learning, have immense inherent risks which can lay waste to hundreds of square miles, kill thousands of uninvolved people, and even endanger whole populations thousands of miles away.

    It seems that now, the situation at F1 is that the affected spent fuel pool can't be seen or approached. There is no certain way to move water towards it. That's almost inconceivable. I don't want to accuse anyone -- the tsunami was an extreme event -- but still, placing something like that pool in harm's way without any tested and simulated plan for rescuing it under almost any eventuality seems negligent almost to a Chernobyl level if in a different way. Sticking that thing between the reactor and a thin fragile roof on a delicate building really doesn't make much sense. At this point, the building is mainly in the way. And radioactivity makes it difficult and dangerous to remove. What an f'n mess. Coal won't create that sort of situation. Not that I like coal either.
    • CommentAuthorjoshs
    • CommentTimeMar 17th 2011
     
    Posted By: enginerdMy issue with the whole debate is that we rarely see the alternatives compared. Instead, we list the downsides of whichever source of energy we are investigating. Nuclear power facilities make a small amount of nasty waste. Coal fired plants make a large amount of fairly benign waste.
    Coal also spews radionuclides and heavy metals directly into the atmosphere. Coal is dirty nasty business.
    Coal mining has many envromental problems and has certainly killed more people than the whole train of of nuclear power (mining, building, operating, catastrophes) combined. This is an unfair comparison because coal has been with us for a long time and nuclear power not so long, but still, there are fair comparisons that can be made.

    Which is cheapest per kw-hr, which causes more deaths per kw-hr, which harms more owls, which presents more risks to humans, for which do we have more fuel available to be mined? How do those compare to natural gas?

    It's always about trade-offs and cost/benefit choices.
    Do you want to start a real discussion on various power options, what they mean, and how we should approach any particular one?
    • CommentAuthorjoshs
    • CommentTimeMar 17th 2011
     
    Posted By: maryyugommm... coal mining kills mainly people involved in mining (I suppose you can argue about acid rain and air pollution). But nuclear power plants, as we are learning, have immense inherent risks which can lay waste to hundreds of square miles, kill thousands of uninvolved people, and even endanger whole populations thousands of miles away.

    It seems that now, the situation at F1 is that the affected spent fuel pool can't be seen or approached. There is no certain way to move water towards it. That's almost inconceivable. I don't want to accuse anyone -- the tsunami was an extreme event -- but still, placing something like that pool in harm's way without any tested and simulated plan for rescuing it under almost any eventuality seems negligent almost to a Chernobyl level if in a different way. Sticking that thing between the reactor and a thin fragile roof on a delicate building really doesn't make much sense. At this point, the building is mainly in the way. And radioactivity makes it difficult and dangerous to remove. What an f'n mess. Coal won't create that sort of situation. Not that I like coal either.
    Coal poisons entire populations, slowly, steadily, and very effectively. There are things we can do to mitigate those effects, but we have to be willing to spend money to do so. Largely as a population, the USA has resisted. When it comes to nuclear power the risks are different. Nukes are for the most part very clean until something goes wrong in a big way. Then we have a mess characteristic of any big civil engineering disaster.

    In California, dam failures have killed thousands. Misjudgments with water distribution and drainage created a huge toxic mess in the famed central valley that produces most of the USA's fruits and vegetables. No one has stopped building dams, or locating populations that would be devastated by a failure. California fruits and vegetables remain a staple in the USA and abroad. what this tells us is that we have an odd quirk of often mishandling risks. Call me an optimist, but that is something I think is within our power to greatly improve.

    This week we are experiencing a tragedy with very old designs that were near retirement and were subjected to very high stress. I think the intelligent thing to do is take stock of the situation, and learn what we can from it. What I think would be a terrible mistake would be to knee-jerk label anything nuclear as bad ju-ju.
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      CommentAuthorAngus
    • CommentTimeMar 17th 2011 edited
     
    It has been pointed out many times that in normal operation the radioactive emissions from a coal fired plant exceed those from a nuclear plant.

    That's radioactivity alone - the chemical emissions from a coal plant of course far exceed anything from a nuclear plant.
    • CommentAuthorjoshs
    • CommentTimeMar 17th 2011 edited
     
    Not only do the radioactive emissions from a coal fired plant exceed a nuke, they vastly exceed a nuke. Coal is dirty, dirty, business.

    ETA: A handy table-

    A 1GW coal plant puts out 8.8 billion KWh / year. So in rough numbers, just multiply the the numbers below by 9 for each coal fired plant.


    Radionuclide............................mCi/billion KWh

    Rn-220......................................1.1 x 10^2 = 110

    Rn-222......................................2.0 x 10^2 = 220

    U-238........................................1.5 x 10^0 = 1.5

    U-234........................................1.5 x 10^0 = 1.5

    Ra-226......................................1.2 x 10^0 = 1.2

    Po-218......................................3.8 x 10^0 = 3.8

    Pb-214......................................3.8 x 10^0 = 3.8

    Po-214.....................................3.8 x 10^0 = 3.8

    Pb-210.....................................3.8 x 10^0 = 3.8

    Po-210.....................................3.8 x 10^0 = 3.8

    Po-216.....................................2.4 x 10^0 = 2.4

    Pb-212.....................................2.4 x 10^0 = 2.4

    K-40........................................5.3 x 10^0 = 5.3
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      CommentAuthormrflora
    • CommentTimeMar 17th 2011
     
    Traveling Wave Reactor, advocated by Bill Gates.

    Regards,
    M.R.F.
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      CommentAuthormaryyugo
    • CommentTimeMar 17th 2011 edited
     
    Angus, I don't understand your point. Few people have problems with the *normal* operation of nuclear power plants and most who do are nuts. The problem I have is that once they turn to shit, in theory, they can kill thousands and injure hundreds of thousands and they can make hundreds of square miles uninhabitable for centuries. I realize that's a doomsday scenario. But those ponds. Why are they not in very solid (say ten foot thick) containments? Damn the cost-- consider the consequences we may soon see. What if a melted reactor core did encounter a water table? What the fuck then? Coal, evil and devious though it is, won't do that. And while we're at it we can clean that up to. Edit: two... uh... TOO.
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      CommentAuthorAngus
    • CommentTimeMar 17th 2011
     
    Coal plants injure and pollute on the same scale, though less intensely, and they do it continuously. So run them long enough and they can do an arbitrary amount of damage. I agree that nuclear plants are extremely dangerous in the sense that the cost of a low probability error can be very high. This is the tail of the distribution and is always hard to deal with. But in a country that is apparently happy to contain many thousands of fission and fusion devices specifically intended to cause damage, it would seem possible to co-exist as well with fission devices intended to produce power. It may well be true that the military safeguards are better than the civilian ones imposed on power companies. All the more reason to make power generation the subject of equivalent safeguards. If you can pay for it with bombs, you can pay for it with reactors.
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      CommentAuthorTrim
    • CommentTimeMar 17th 2011
     
    Posted By: mrfloraTraveling Wave Reactor, advocated by Bill Gates.

    Regards,
    M.R.F.


    U238 into Plutonium 239 ??????
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      CommentAuthorTrim
    • CommentTimeMar 17th 2011
     
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      CommentAuthoralsetalokin
    • CommentTimeMar 17th 2011 edited
     
    interesting.
    Depleted uranium is widely available as a feedstock. Stockpiles in the United States currently contain approximately 700,000 metric tons of depleted uranium, which is produced as a waste byproduct of the enrichment process.[12] TerraPower has estimated that these stockpiles represent an energy resource equivalent to $100 trillion worth of electricity.[11] Company scientists have also estimated that wide deployment of TWRs could enable projected global stockpiles of depleted uranium to sustain 80% of the world’s population at U.S. per capita energy usages for over a millennium.


    Projected global stockpiles of DU? Who is depleting all that uranium, and why?


    ETA: Molten sodium as coolant... won't that be fun....