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

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  •  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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