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View Diary: New Nukes: Obama will name Steven Chu his choice for Energy secretary (124 comments)

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  •  Look (1+ / 0-)
    Recommended by:
    LookingUp

    Nobody is denying that graphite will oxidize in certain environments. That's why the engineers take every precaution possible to avoid this situation.

    Nevertheless, even if that does occur, it's not the end of the world.

    By far the biggest risk comes from the decay heat of the radionuclides in the fuel. Oxidation of the graphite is far less worrisome. Actual combustion of the graphite is pretty much impossible.

    I don't know who has been feeding you this stuff, but you're taking it totally out of context. The situation is a bit more complex than you're making out and you're emphasizing the wrong problems.

    Thus, you've concluded, based on the wrong emphasis on the less problematic portions of the design, that the PBMR is somehow flawed because of this, when nothing could be farther from the truth.

    The PBMR has its pros and cons just like any other design. At least try to fairly evaluate them.

    Blessed is the man who, having nothing to say, abstains from giving wordy evidence of the fact.
    -- George Eliot

    by bryfry on Thu Dec 11, 2008 at 01:52:19 PM PST

    [ Parent ]

    •  Oxidation of the graphite is not far less worriso (0+ / 0-)

      Ask anyone who's studied Chernobyl.  Chernobyl would have been smaller than, say, Windscale were it not for the burning graphite.  Decay heat is irrelevant; what is relevant is how effectively decay products are aerosolized, and burning graphite is quite effective at that.  As for "who is feeding me", I read peer-reviewed papers.  You might want to try that some time.  I am not at all convinced given the state of peer-review and the history of modern nuclear reactors that you can justify no containment structure for PBMRs.  You think the engineers at MONJU thought they were going to have a sodium leak?  No!  But nonetheless, they built a containment structure and clad it with thick stainless steel.  It's just due caution when dealing with something that poses as much of a threat as a nuclear reactor.

      The concept of not having a containment structure around a PBMR and treating them as though their fail-proof is such a steaming pipe of hubris.

      •  Interesting stuff... (1+ / 0-)
        Recommended by:
        Plan9

        I think the LFTR is far superior to the PBMR...it really is the only way to go. But...the PBMR will be tested in it's newest incantation in South Africa and China and thousands of hours of data analyzed. The key of course is that with the Helium environment kept at slightly above atmosphere, there is no way for O2 migration to occur that could infect the graphite. The pressure is too low to cause a rupture (a la Chernobyl).

        But I expect these high temperature reactors to be very popular, especially in developing countries with tiny grids. Most African countries have grids under 2,000 MWs. These would be perfect. And they are expandable.

        David

        •  Well, personally (0+ / 0-)

          I prefer not to pick a favorite technology, since I can see the advantages and disadvantages of each design.

          For example, while the "melt plug" passive safety feature of the molten salt reactor (LFTR) it kinda neat, it still means that the fuel has to move during an accident for the safety feature to work. This is a disadvantage, when compared to the PBMR, in which the solid fuel can just sit where it is and there are no problems. The PBMR has the simpler safety feature; thus, there's less opportunity for something to go wrong.

          In terms of concerns over graphite, the LFTR is an epithermal reactor, so guess what provides the neutron moderation: graphite. Unlike the graphite in the PBMR, this graphite is not surrounded by an inert gas.

          By the way, the "helium environment" for a PBMR is far more than just "slightly" above atmosphere. High pressures are needed, or else the helium coolant wouldn't be capable of carrying much heat. The latest slides that I remember looking had the pressure inside the PBMR primary loop at 90 bar -- i.e., roughly 90 times atmospheric pressure.

          So if there's a small leak, the helium will just leak out of the loop, and there will be very little chance for oxygen or water vapor to get into the loop. If there's a large break, the helium will literally blow almost all of the oxygen and water vapor out of the silo and out of the space where the reactor vessel is located. The worries that have been put forward in the comments here of large amounts of oxidation of the graphite pebbles has been vastly overstated.

          Blessed is the man who, having nothing to say, abstains from giving wordy evidence of the fact.
          -- George Eliot

          by bryfry on Fri Dec 12, 2008 at 03:30:51 AM PST

          [ Parent ]

      •  Well, I can see (1+ / 0-)
        Recommended by:
        Plan9

        from your other comment that you are capable of cutting and pasting from technical papers and theses; however, you have yet to convince me that you understand what any of it really means.

        For example, how can you say that "decay heat is irrelevant"?! Decay heat was the key driving factor of not only the Chernobyl accident, but the TMI meltdown as well. The Chernobyl reactor literally blew itself apart in a steam explosion, which is great for shutting down a fission chain reaction. The only thing left to provide the heat that was causing all of the trouble was the decay heat from the radionuclides.

        Bringing the accident under control was not so much the result of the responders "putting out the fire" as the inevitable decrease of decay heat to a sufficiently low level that the core began to cool off. There were chemical fires during the accident as well, but it wasn't the graphite that was burning, in spite of what many very bright, but ill-informed people have said.

        Another thing that you appear to not understand is the effects of irradiation on graphite. Sure, there are changes, but one of the most important changes is that irradiation significantly lowers the thermal conductivity of graphite. Thus, more heat is trapped inside the pebble and this thermal energy has a more difficult time reaching the surface, where by necessity, any kind of ignition would have to occur since that's where any oxygen would be. So if anything, an irradiated pebble is less likely to ignite than a new one, not that there's much of a chance of either.

        As for the papers you cut 'n paste from on silicone carbide, you have failed to understand a key nuclear engineering concept: any fuel will fail if you push it hard enough. This is why, to qualify the stuff to be licensed, researchers have to push it until it fails to understand how and why the failure occurs. Thus, researchers develop models and perform tests. The data resulting from this research are then used by the reactor designers to ensure that the conditions never reach these limits, whether it is by redundant safety systems, or (in the case of the PBMR) by the simple physics of heat transfer.

        These are basic engineering concepts. To apply your standards to other fields, we could never fly in an airplane and nobody would be allowed to drive anything that less rugged than an M1 Abrams tank.

        The decision on whether a containment is necessary should be dependent on the fuel's performance, not on any kind of unsupported dogma. Some of the issues with the fuel have been known for a long time and are not a large concern. For example, some fission products, such as silver and cesium will simply plate out on the surfaces inside the primary loop. The failure of the particles themselves has been well studied and is just part of the fuel qualification process. Some groups are better at producing quality fuel than others, but anyone who hopes to get a license to produce commercial fuel will have to demonstrate that it works well.

        Besides, you are aware that pebble-bed reactors have actually been built and operated, aren't you? Thus, we know quite a bit about them. The Germans, for example, tried an experiment where they turned off the cooling to their reactor, and it heated up and then cooled down, just as expected, without any problems. One of the things that we know from the experience of operating TRISO-fueled reactors is that worker exposure to radiation was far below what is standard for light-water reactors. That TRISO fuel must work pretty well, eh? At least, compared to what we use now.

        Blessed is the man who, having nothing to say, abstains from giving wordy evidence of the fact.
        -- George Eliot

        by bryfry on Fri Dec 12, 2008 at 03:39:23 AM PST

        [ Parent ]

        •  The Chinese all did a full stop/trip (3+ / 0-)
          Recommended by:
          Plan9, bryfry, Mcrab

          on their Pebble Bed HTR in 2004. Thus cut all the power to the reactor and watched what happened. Which was nothing, of course.

          I think Rei's arguement that it is not a 'mature' technology is false. They've run these reactors for years and, as you point out, have a LOT of data. In fact, most of the papers written on the subject are based almost entirely on the AVR experience in Germany. There should be a whole spate of data coming out of China over the next few years.

          The S. African PBMR has no liquid in it, as far as I can see. In fact, even the bearings use magnetic one, not lubricating ones.

          David

          •  Yes, you are correct (2+ / 0-)
            Recommended by:
            Plan9, Mcrab

            There are plenty of data today and there will be plenty more in the future, not only from the Chinese, but also from the Japanese who have their own TRISO-based nuclear program (although not based on pebbles).

            The South African PBMR design is actually a rather conservative design. They have stepped down on the power level from earlier concepts; they use a direct cycle gas-turbine configuration (thus, no leaky steam generators or other heat exchangers). Furthermore, after the experience at Fort St. Vrain, I seriously doubt that anybody would use something other than magnetic bearings for components in the primary circuit.

            Blessed is the man who, having nothing to say, abstains from giving wordy evidence of the fact.
            -- George Eliot

            by bryfry on Fri Dec 12, 2008 at 08:56:46 AM PST

            [ Parent ]

            •  Oh yeah, forgot about Fort St. Vrain (0+ / 0-)

              A lovely experience with HTGRs there too, wasn't it?  Wait, what was that?  Air in the core?  Water in the core?  Stuck control rods?  Fuel failures?  Almost three hundred incidents?

              Hey, but at least HTGRs have a long "history"!   ;)  

              (If I were speaking that line out loud, I would have used air-quotes around the word "history")

          •  The NRC disagrees with you (0+ / 0-)

            about whether it's a mature tech.  Take it up with them.

            FYI, about the South African design, I've seen people who work on HTRs basically making fun of them for that -- overengineering certain parts while not focusing nearly enough on others.

        •  In terms of direct effects, (0+ / 0-)

          decay heat is irrelevant.  It doesn't matter if your core turns to lava (ala Chernobyl) so long as the accident is contained.  

          There were chemical fires during the accident as well, but it wasn't the graphite that was burning, in spite of what many very bright, but ill-informed people have said.

          Apparently you think you know more than the the NEA.  Who do you think you are, trying to rewrite history like this?  I quote:

          The graphite fire

          While the conventional fires at the site posed no special firefighting problems, very high radiation doses were incurred by the firemen, resulting in 31 deaths. However, the graphite moderator fire was a special problem. Very little national or international expertise on fighting graphite fires existed, and there was a very real fear that any attempt to put it out might well result in further dispersion of radionuclides, perhaps by steam production, or it might even provoke a criticality excursion in the nuclear fuel.

          A decision was made to layer the graphite fire with large amounts of different materials, each one designed to combat a different feature of the fire and the radioactive release. The first measures taken to control fire and the radionuclides releases consisted of dumping neutron-absorbing compounds and fire-control material into the crater that resulted from the destruction of the reactor. The total amount of materials dumped on the reactor was about 5 000 t including about 40 t of borons compounds, 2 400 t of lead, 1 800 t of sand and clay, and 600 t of dolomite, as well as sodium phosphate and polymer liquids (Bu93). About 150 t of material were dumped on 27 April, followed by 300 t on 28 April, 750 t on 29 April, 1 500 t on 30 April, 1 900 t on 1 May and 400 t on 2 May. About 1 800 helicopter flights were carried out to dump materials onto the reactor; During the first flights, the helicopter remained stationary over the reactor while dumping materials. As the dose rates received by the helicopter pilots during this procedure were too high, it was decide that the materials should be dumped while the helicopters travelled over the reactor. This procedure caused additional destruction of the standing structures and spread the contamination. Boron carbide was dumped in large quantities from helicopters to act as a neutron absorber and prevent any renewed chain reaction. Dolomite was also added to act as heat sink and a source of carbon dioxide to smother the fire. Lead was included as a radiation absorber, as well as sand and clay which it was hoped would prevent the release of particulates. While it was later discovered that many of these compounds were not actually dropped on the target, they may have acted as thermal insulators and precipitated an increase in the temperature of the damaged core leading to a further release of radionuclides a week later.

          The further sequence of events is still speculative, although elucidated with the observation of residual damage to the reactor (Si94, Si04a, Si94b). It is suggested that the melted core materials settled to the bottom of the core shaft, with the fuel forming a metallic layer below the graphite. The graphite layer had a filtering effect on the release of volatile compounds. But after burning without the filtering effect of an upper graphite layer, the release of volatile fissions products from the fuel may have increased, except for non-volatile fission products and actinides, because of reduced particulate emission. On day 8 after the accident, the corium melted through the lower biological shield and flowed onto the floor. This redistribution of corium would have enhanced the radionuclide releases, and on contact with water corium produced steam, causing an increase of radionuclieds at the last stage of the active period.

          By May 9, the graphite fire had been extinguished, and work began on a massive reinforced concrete slab with a built-in cooling system beneath the reactor. This involved digging a tunnel from underneath Unit 3. About four hundred people worked on this tunnel which was completed in 15 days,allowing the installation of the concrete slab. This slab would not only be of use to cool the core if necessary, it would also act as a barrier to prevent penetration of melted radioactive material into the groundwater. "

          You at least know who the NEA is, right?

          Thus, more heat is trapped inside the pebble and this thermal energy has a more difficult time reaching the surface, where by necessity, any kind of ignition would have to occur since that's where any oxygen would be.

          More heat trapped in the pebble increases the risk of ruptures in the SiC shell.  It is not a good thing.  Furthermore, crosslinking of graphene Sp2 bonds makes it more vulnerable to oxidative attack, not less.

          As for the papers you cut 'n paste from on silicone carbide,

          It's silicon carbide, not silicone.  Silicone is Si-O-Si-O-Si-O... chains.  Furthermore, the papers were about TRISO fuel in general.  I must reiterate that TRISO != SiC.  TRISO is a multilayered fuel, of which SiC is just one layer.  

          you have failed to understand a key nuclear engineering concept: any fuel will fail if you push it hard enough.

          You have failed to follow through with this statement logically: "therefore, any reactor should have a containment structure in case the fuel inadvertently gets pushed too hard."

          whether it is by redundant safety systems, or (in the case of the PBMR) by the simple physics of heat transfer.

          As the papers pointed out over and over and over again, and which you still seem to fail to grasp, failure of PBMR spheres is not only in the case of a general core overheating.  There are several failure modes, and all have been experienced in real-world operating conditions.

          PBMR fans love to talk about how it's passively prevented from overheating, as though this is somehow rare or as though it's the be-all, end-all of nuclear reactors.  They like to point to demonstrations of this.  That's not the problem people are raising with PBMRs.  The problems people are raising are with the lack of a containment structure and problems with the fuel/moderator.

          These are basic engineering concepts. To apply your standards to other fields, we could never fly in an airplane and nobody would be allowed to drive anything that less rugged than an M1 Abrams tank.

          If an airplane or a car could contaminate tens of thousands of square miles and cost billions of dollars in economic damage if it failed, your comparison would be apt.

          The decision on whether a containment is necessary should be dependent on the fuel's performance, not on any kind of unsupported dogma

          Dogma?  In case you haven't read some of my other posts, I'm pro nuclear.  I'm just not for designs without containment structures, and I (and many others) feel that this notion of PBMRs as being inherently safe is nothing but pure hubris.  Thankfully, the NRC seems to have taken this view as well, as they keep remanding PBMR applications.  It's only people like you who are blind to the risks of such a reactor.

          For example, some fission products, such as silver and cesium will simply plate out on the surfaces inside the primary loop.

          Cesium is a highly combustible (even explosive) pyrophorric metal.  Get it slightly wet (even just through atmospheric humidity) and it forms cesium hydroxide, one of the most corrosive bases in existance.   Or did you not know that?

          Once again, I remind you of what happens if there's a leak in the primary: air ingestion at best.

          I notice you only discussed the fate of only two decay products.  Gasseous decay products, for example, increase the internal pressure in the TRISO fuel elements, which means any SiC defects (or degradation) can lead to the fuel element's rupture.  Metals in general can not only pass through the SiC layer, but can bond with it, weakening it (you're forming a M-S junction).  

          Besides, you are aware that pebble-bed reactors have actually been built and operated, aren't you?

          You are aware that pebble-bed reactors have a very small and not very encouraging history, aren't you?  Even in their tiny operational history, they've already had one radiation-*release* accident.

          The Germans, for example, tried an experiment where they turned off the cooling to their reactor, and it heated up and then cooled down, just as expected, without any problems

          The Chinese have done that (rather pointless) demonstration, too.  It was the Germans, by the way, who had the release, so bringing them up doesn't help your case any.

          One of the things that we know from the experience of operating TRISO-fueled reactors is that worker exposure to radiation was far below what is standard for light-water reactors. That TRISO fuel must work pretty well, eh?

          What are you talking about?  There are many different types of TRISO-fueled reactors, and the radiation exposure is going to vary greatly depending on the type.  Which reactor are you talking about -- HTTR?  AVR?  THTR-300?  HTR-10?  If you meant specifically PBMRs, well, that's an obvious one -- they're low power.

          But hey, if you want to talk about standard operating issues, let's talk about how much nuclear waste PBMRs produce, shall we?  Just what we need: a much greater amount of waste to handle.  Yes, same radiation level per unit power, but much larger bulk.  Yippee.

          And FYI: Despite how assertive you are about how foolproof PBMRs are, here's what the NRC has to say:

          "Significant safety research will be required to develop the technical tools, data and expertise need to support an effective and efficient independent NRC safety review of an HTGR application.

          - PRA models and data - Human performance analysis - Advanced Insturmentation and Controls - Thermal-Hydraulic and Systems Analysis - Fuel Performance Analysis including Fuel Fabrication - Materials Performance Analysis - Structural Analysis - Fission Product Transport, Source Term and Consequence Analysis

          There are no HTGR-specific regulatory guides or HTGR-specific standard review plans.  Additionally, the NRC technical staff has limited knowledge and expertise in the design, safety approach and technology of HTGRs.  This will result in additional NRC challenges in conducting an HTGR safety review.  Technical reviewer knowledge and capabilities will need to be developed across a range of technical review areas.

          The PBMR Pty plans to reference in the PBMR design, selected international codes and standards as well as selected US professional society code cases that have not been reviewed and endorsed by the NRC.  NRC review resources will be needed to assess the acceptability of these references.

          Current LWR (e.g., Part 50) requirements either do not apply or do not address significant HTGR design features and use of new technologies.  Deterministic technical and safety requirements will need to be established to address these features and technologies."

          You think this tech is mature and well reviewed?  Inherently safe?  Please.  The NRC sure doesn't think so at this point.

          •  My goodness (2+ / 0-)
            Recommended by:
            Plan9, Mcrab

            So much stuff. I'll try to handle at least most of it.

            Concerning your long quote from the NEA, well, like I said, many people (who frankly don't know any better) have repeated over and over that there was a graphite "fire." The real experts in graphite-moderated reactors usually, but not always, know better.

            After all your own quote says: "Very little national or international expertise on fighting graphite fires existed." That's because not much was generally known about graphite, including whether these are real "fires" or just observations of blackbody radiation from graphite that is heated to very high temperatures by the decay heat (i.e., graphite blocks glowing red).

            More heat trapped in the pebble increases the risk of ruptures in the SiC shell. It is not a good thing.

            Well, yeah, but the essential questions are how much of an increase and how many more ruptures? (The answer to both questions, by the way, is "not much.") Besides, I thought that we were talking about graphite fires. Take your pick. Choose one "disaster scenario" and stick to it, please.

            Geez ... then you have the gall to lecture me on a simple typo (an extra "e" that no spell-checker would catch no less). Grow up.

            I know what TRISO fuel is. What is the essential barrier, eh? It's the silicon carbide.

            You have failed to follow through with this statement logically: "therefore, any reactor should have a containment structure in case the fuel inadvertently gets pushed too hard."

            And you failed to understand my comments. See below about "dogma."

            More nonsense followed. You really go over the top here:

            If an airplane or a car could contaminate tens of thousands of square miles and cost billions of dollars in economic damage if it failed, your comparison would be apt.

            Please consider these questions: How many people died in airplane accidents last year? How many were killed in automobile accidents last year? (About 1.2 million worldwide on average each year according to the WHO.)

            How many people have been killed by graphite moderated reactors, including Chernobyl? Eh?

            I suggest that you drop the silly hyperbole and reconsider your priorities.

            Geez ... I used to think that you used to be somewhat in favor of nuclear power, but you're beginning to sound like an ignorant anti-nuclear nutcase. They typically rely on dogma over reason, and speaking of which ...

            The decision on whether a containment is necessary should be dependent on the fuel's performance, not on any kind of unsupported dogma

            Dogma? In case you haven't read some of my other posts, I'm pro nuclear. I'm just not for designs without containment structures, and I (and many others) feel that this notion of PBMRs as being inherently safe is nothing but pure hubris. Thankfully, the NRC seems to have taken this view as well, as they keep remanding PBMR applications. It's only people like you who are blind to the risks of such a reactor.

            I agree that getting a PBMR licensed in the US would be very difficult, particularly using the old rules for light water reactors, which ... well ... were designed specifically for light water reactors. If we are ever to get past this point, then a new set of rules will be necessary. Fortunately, a new, better set of rules has been developed, but not yet tested. We'll just have to see how it goes.

            Then you descend into trivia. For example:

            You are aware that pebble-bed reactors have a very small and not very encouraging history, aren't you? Even in their tiny operational history, they've already had one radiation-release accident.

            And exactly how much radiation was "released"? From what I recall, a nearby university was quite proud that it had "discovered" this release, since it was so very difficult to detect.

            And what were the consequences of this "release" exactly? How does this "release" compare with the amount released in the TMI accident (which had a containment building, by the way)? Are you steadfastly against pressurized water reactors too?

            Such double standards.

            Then you ask silly questions:

            What are you talking about? There are many different types of TRISO-fueled reactors, and the radiation exposure is going to vary greatly depending on the type. Which reactor are you talking about -- HTTR? AVR? THTR-300? HTR-10? If you meant specifically PBMRs, well, that's an obvious one -- they're low power.

            I can see you obviously were not aware of this. Clearly the amount of worker exposure is measured in terms of energy produced. Duh.

            It is well documented from the German program, and even from the Fort St. Vrain experience, that the exposure levels were well below those of typical light-water reactors per unit of energy produced.

            But hey, if you want to talk about standard operating issues, let's talk about how much nuclear waste PBMRs produce, shall we? Just what we need: a much greater amount of waste to handle. Yes, same radiation level per unit power, but much larger bulk. Yippee.

            Heh ... whatever. All of the "waste" from the entire operating life of a PBMR plant is capable of being stored on site in bins that are part of the design today.

            It depends on what you mean by "waste," by the way. If you mean low-level waste like irradiated graphite, then there is a large volume, but the radiation in this material goes away in a matter of decades. If you're talking about the high level "waste" in the fuel ... well, consider that PBMR's achieve not only a higher thermal efficiency (thanks to the use of high temperatures and a Brayton cycle), but they are also capable of higher burnup than conventional light water reactors. Thus, per kWh of electricity generated, less fuel needs to be used, which means less real high-level waste.

            So where is all of this extra "waste"?

            In fact, if we are talking about disposing of this "waste" in some place like Yucca Mountain, the pebble bed fuel is already ready to go. It is actually easier to dispose of than used light water reactor fuel, because it results in a lower thermal load on the facility, which is the real determinant of how much "waste" can be put down there.

            In a once-through fuel cycle, the pebble bed wins out, no question.

            I fully agree that this technology is not as mature as today's light water reactors. Nobody would deny that. Furthermore, the NRC has almost no experience with this design, and any licensing effort will involve a huge exercise in educating the folks in Rockville.

            However, you are thinking like a bureaucrat or an idiot or both (which is not too uncommon of a combination). Just because something does not meet today's regulatory qualifications does not mean that it will never meet future qualifications.

            I suggest that your pull your head out of your ass and realize that if the engineers who work on the PBMR can demonstrate that it is safe through sound scientific and engineering analysis, then there is nothing that should stop these reactors being deployed. That's how engineering and licensing work.

            If you don't like pebble bed reactors, then fine. You're entitled to your opinion, but stick with credible, relevant facts and reasonable arguments.

            But in case you can't, have you got any other canards to drag out?

            Blessed is the man who, having nothing to say, abstains from giving wordy evidence of the fact.
            -- George Eliot

            by bryfry on Fri Dec 12, 2008 at 10:20:27 AM PST

            [ Parent ]

            •  As far as I'm concerned... (0+ / 0-)

              calling the NEA ill-informed in a discussion about nuclear matters is effectively conceding the debate.

              •  And as far as I'm concerned ... (0+ / 0-)

                I no longer care enough about this to keep going.  Believe what you will.

                It's not as if the pebble bed design is one of my preferred designs anyhow. I think that it's a promising design, but it's just another design of many that are terribly superior to coal or natual gas or oil or solar or wind, etc., etc.

                Blessed is the man who, having nothing to say, abstains from giving wordy evidence of the fact.
                -- George Eliot

                by bryfry on Fri Dec 12, 2008 at 02:11:01 PM PST

                [ Parent ]

              •  NIE is focused entirely on Generation III (0+ / 0-)

                reactors. It's simply not their forte. they represent an industry that runs Generation II reactors and is building Generation III ones. Generation IV is simply way out beyond them right now.

                David

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