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Discussion in 'Home Power and Microgeneration' started by Gordon, Sep 8, 2006.

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  1. Gordon

    Gordon Guest

    A Hydrogen-Oxygen mixture: That's water.
    Sounds to me like they were electolysing water into hydrogen
    and oxygen, but not separating it. That would be a rather
    potent mix to put into a IC engine.
    My worry over this is that the PVC pipe is not a suitable
    material for a pressure vessel.
     
  2. I run an Industrial Controls company. A while back I got a call to
    come quote a new control. The "company" turned out to be two old boys,
    (by that I mean 65+) that were making "Auto Fuel" in their garage.
    What they had was a vessel made of 8" PVC pipe, about a foot-and-a
    half long capped on one end, a multi- electrode inside with both
    positive and negative plates. The top was capped and fitted with an
    outlet and a pressure gage 0-100 psi.

    They had found/bought/built some kind of little box that would do
    something..supply dc or pulses or whatever...and it was connected to
    the electrodes. They wouldn't tell me what it did for reasons which I
    will explain later. Anyway, one unit was working while I was there.
    They had 55 psi in the pipe, I assume an H and O mix since they were
    using water and an electrolyte and electricity. They wanted to scale
    up the operation.

    Having a Hydrogen-Oxygen mixture in a pipe without rupture plates or
    pressure reliefs set off alarm bells in my noggin, and I politely
    declined the job and left. I did drive smartly getting away from
    there. This is why I didn't get the "secrets". <g> They did have a
    small engine there that they said would run from their "fuel" but I
    just wanted to get the F out of Dodge.

    I'm for alternatives to oil and stuff, but Methinks these two old men
    are gonna buy it. Wouldn't that setup make a decent bomb? Or is it me
    that is off base?
     
  3. Look back a few posts at 'Anyone seen this before?'.
    Pete.
     
  4. Tom Peel

    Tom Peel Guest

    watching the news.

    T.
     
  5. Me too. I'm a long way from a chemist but I do know that
    electricity+water+electrolyte = Hydrogen on one electrode and Oxygen
    on the other: both electrodes were in the same container (stacked like
    the plates in an electronic air cleaner) and the pressure gage read 55
    psi at the top. As I said, it set off enough alarm bells that I left.
     
  6. daestrom

    daestrom Guest

    Well, I doubt *those* guys have taken the time to work it out, but BWR nuc
    plants have a system that carries a mixture of O2 & H2. The radiation in
    the reactor will disassociate a small percentage of the water into 2H2 and
    O2, and this gas mixture finds its way to the condenser where it is removed
    by steam-jet air ejectors.

    As long as the mixture is mixed with steam, it is below the flammable
    percentages. But the mixture is then passed through an 'after condenser'
    where the steam is condensed out and you're left with a stoichometric
    mixture of 2H2 and O2 at between 14 and 20 psia. Normally this mix is
    passed over a catalytic bed to recombine it, but problems are inevitable.
    So, all the piping and components are designed to contain an explosion (and
    just about every plant has had an 'ignition' of this mix with little or no
    damage, some have had multiple 'ignitions').

    The piping is kept narrow bore (maximize surface to volume 6" typical), and
    is made from Schedule 80 steel. Bottom line is, some containers can be
    designed to contain such an explosion, but I'm sure these guys haven't got
    one. PVC surely won't do.

    daestrom
     
  7. governments

    governments Guest

    Nope, you need a spark plug in the top of it to make it a decent bomb. : )
    --
    Mike
    Some say we must tax corporations more. What they do not understand is
    that corporations do not pay taxes. One of our governments conditions
    for a companies existence is they collect the taxes from their
    customers and pass them to the government.
    Mike Swift
     
  8. daestrom

    daestrom Guest

    Try again. Typical numbers for a BWR off-gas flow is 20 cfm air and 160 cfm
    O2/2H2. The jets carry quite a lot more than what the off-gas meter reads.
    The off-gas flow meter is *after* the recombiner so it doesn't sense the
    O2/2H2. GE (the sole manufacturer of BWR's in this country) has a couple of
    nice documents that discuss it at length.

    As far as 'approach flammability', you are also wrong there. From the after
    condenser to the steam-dilution jet it is almost perfect O2/2H2 mix. The
    dilution jet is just that, used to dilute the mixture back below the point
    of flammability before going further. But that section of pipe before it is
    most *definitely* an explosive mix. Got some pretty pictures that show the
    heat damage from a 'fire' that ran constantly for several hours one time.

    Recommended actions for an off-gas H2 fire in a BWR is to throttle down the
    suction of the jets to reduce the inflow of H2/O2 to the after-condenser.
    Have to watch condenser vacumn though, and reduce power as needed.

    The charcoal beds typically isolate at >2% H2 at recombiner outlet, and flow
    shifts to the "30-minute holdup pipe" (which *is* rated for H2 explosion in
    BWR-2/3/4/5/6 designs).
    If by 'trace' you mean at rates of >160 cfm, then yes, you have it exactly.
    Most 'ignitions' have occurred upstream of the dilution jet. The piping in
    the section from after-condenser to the recombiner is designed for H2
    explosion. The charcoal beds are not. Charcoal beds are *not* supposed to
    be in service when the recombiner is out of service. H2 accumulation in the
    beds is not supposed to happen, that's why there is an H2 monitor before
    them. What did you folks do, run with the H2 analyzer off-line, or ignore
    the alarm??
    Then why do you put out 'bad information' about the H2 content in BWR. Go
    talk to your chem techs and find out where you screwed up. I can get you
    the data from a couple of plants for the current month if you really need
    it.
    Did Brown's Ferry 1 even *have* recombiners? Adding recombiners and
    charcoal bed was a backfit to most BWR. FitzPatrick, NMP1 and Oyster Creek
    didn't install them until '79. NMP2 had them as original equipment.

    Maybe your memory is fading, but H2/O2 is *not* just a 'trace' component in
    BWR off-gas.

    daestrom
     
  9. daestrom

    daestrom Guest

    Well, he's right we got off-topic. Today at work I did some further
    research. GE has a Subject Information Letter (known as a 'SIL') number 150
    on the subject. They reviewed h2 explosions/ignitions at several plants and
    note, "Ignitions have occured in several parts of the off-gas system.
    Except for a few cases where the explosion damaged filters or charcoal beds,
    no appreciable damage has occured" According to them, radiolysis of water
    in an operating reactor generates between 0.04 and 0.065 SCFM / MWth. So
    for a typical 2500 MWth plant, that's about 125 SCFM H2 when at full power.
    For Neon's Brown's Ferry plant, units 2 & 3 are listed as 1100 MWe, so that
    would be about 3300 MWth. That would generate H2 on the order of 165 SCFM.
    Quite a bit more than a 'trace'.

    daestrom
     
  10. Eeyore

    Eeyore Guest

    Such measures are only used in the USA.

    Any chance of using something that makes sense to the rest of us ?

    Graham
     
  11. AJH

    AJH Guest

    You spoiled an interesting post with this unnecessary ad hominem
    comment John, why not just accept he's argumentative and a contributor
    to the forum.

    Andrew Heggie
     
  12. daestrom

    daestrom Guest

    165 SCFM of H2 is a mass flow rate of about 0.856 lbm/minute. That is a
    mass flow rate of 388.7 grams/minute for you metric folks

    daestrom
     
  13. daestrom

    daestrom Guest

    No, like I said before the volume of air flow from air in-leakage to the
    condenser is only on the order of 20 SCFM. The radiolysis of water produces
    H2 at rates in the range of 100 to 180 SCFM. Last time I looked, 165 SCFM
    is not a 'trace compared to' 20 SCFM. If you have access to some of GE's
    NEDO documents, I'll look up the number of a good one about off-gas systems
    for you. Sounds like you could use some refresher training.

    If you think the volume of air removed from the condenser makes 165 SCFM
    look like "a trace", then you have no clue about condensers.
    Not in BWR's. The water chemistry in BWR's consists of making the
    feed-water as pure as possible. Heck, chemistry gets 'excited' when the
    iron content of feed-water rises to 5 ppb (parts per *BILLION). This can
    happen if your condenser tubes are made of certain alloys, as warm summer
    temperatures raise the rate iron comes off the tube bundles with the
    condensate.

    In BWR's the reactor chemistry is maintained as close to pure water as
    practical. But because of the concentrating affects of *boiling* water,
    even tiny traces in feed-water will accumulate. So the BWR design includes
    a Reactor Water Clean-Up system that circulates reactor water through a
    filter/demineralizer bed. The resin is simple H-OH so the water coming out
    is neutral (pH 7).

    Some BWR's inject a small amount of H2 into the feed-water to raise the
    overall concentration of H2 in the reactor. This is done to 'scavenge'
    oxygen, reducing the overall O2 concentration in the water. But it has
    little affect on the total H2 that leaves the reactor vessel and travels to
    the condenser. It increases recombination, but at the expense of more H2 in
    reactor water.
    Nonsense. You obviously don't understand what the charcoal beds in the
    off-gas system are used for. The activated charcoal provides a long 'hold
    up' time for the two principle radioactive gasses discharged from the SJAE,
    Xenon and Krypton. NOT for collecting/controlling H2. These noble gasses
    are 'adsorbed' (not absorbed) by the large number of adsorption sites in
    'activated' charcoal. (believe it or not, most plant's charcoal is made from
    coconut shells) Because these trace gasses are adsorbed and later released
    from the charcoal, the charcoal is not 'used up', but can be used
    indefinitely. Our current load in the off-gas beds has been in service
    since '92. But the purpose is so that the gasses are 'held up' in passing
    through the beds for a long time. With typical air flow rates, the Xe is
    held up for an average of >100 hours and the Krypton for > 70 hours. This
    time is long enough for a substantial part of the radioactive gasses to
    decay.

    But the charcoal adsorption sites are sensitive to water vapor. If the
    incoming air has a relative humidity of just 20%, the water vapor will
    preferentially adsorb to most of the sites, dislocating the noble gasses.
    You end up with a 'burp' of radioactive gasses going out the stack and no
    more 'holdup' of the noble gasses (been there, done that). To protect the
    beds, the air is passed through a dryer system first. Some plants use a
    'refrigeration dryer' system, where the air is cooled with mechanical
    refrigeration down to about -20F. This removes the moisture as frost. The
    darn things have to automatically switch-over to the standby unit every few
    hours so the first unit can go through a defrost cycle. Other plants use a
    dessicant dryer system, where the air is passed over a dessicant. Of
    course, the dessicant 'fills up' with moisture and the system switches air
    flow to another dessicant bed while the first one is regenerated (dried out)
    by passing heated air through it. But the dessicant dryers are much
    smaller, simpler and more reliable. BWR-2's and some early BWR-3's use the
    refrigeration dryer system, -4's and above generally all have dessicant
    systems.

    The whole point is, with the charcoal beds in service, the radioactive
    discharge rate of the plant out the stack is *much* lower than when they are
    out of service. Simply because the Xe and Krypton discharge is delayed long
    enough for substantial decay.

    The dryers and charcoal are both *downstream* from the H2 recombiners. The
    recombiner is *upstream* of the dryers so that the flow rate through the
    dryer and charcoal beds is reduced from ~200 SCFM to 20 SCFM by removing the
    H2 O2 from the flow stream. Only the 'air' from condenser in-leakage
    remains (and trace fission product gasses).
    You can't 'flare off' the H2 and still contain the radioactive gasses. So
    you'd have to 'flare' after the charcoal beds, and because you'd have much
    higher flow rates through the charcoal (air + H2 +O2), the beds would need
    to be much larger. The H2 would interfere with the adsorption of Xe and Kr,
    reducing the effectiveness of the charcoal. And because you must remove all
    the moisture that you can from the flow stream *before* the charcoal beds,
    you'd have a very flammable mixture. Dumb idea.
    Guys, don't pay attention to this, he's either talking about a one-of-a-kind
    system that no other BWR in the world uses, or he's forgotten more than he
    remembers.
    The H2 recombiner is where the platinum is, not the charcoal beds. The
    recombiner is *upstream* of the charcoal beds. The recombiner removes the
    H2/O2 *before* the dryer, and the dryer is *before* the charcoal beds.
    Not all plants use refrigeration drying. Most -4's and up use dessicant
    dryers and don't bother cooling the flow stream at all. The cooling is
    primarily to remove moisture, which ruins the charcoal bed's ability to
    adsorb Xe and Krypton gasses. For example, NineMile Point Unit 1, Vermont
    Yankee and Oyster Creek (BWR-2's) use refrigeration dryers. FitzPatrick,
    GrandGulf, RiverBend and NineMile Point Unit 2 (-4, -6, -5(??) -5
    respectively) use dessicant dryers.
    Which is probably why all the follow-on Off-Gas systems were completely
    redesigned. The recombiner is 'continuous duty', runs between 700F and
    1000F. The recombiner is *before* the charcoal beds so the beds don't 'load
    up' with a lot of H2. Recombiner temperature is mostly controlled by the
    flow of 'dilution steam' that is injected just as the flow enters the
    recombiner. The 'dilution jet' also provides motive force to create flow.
    After-condenser outlet is right about atmospheric (14.78 psia), the dilution
    jet discharge is about 40 psia. This pressure is what overcomes the
    frictional losses through the recombiner, recombiner condenser, dryer
    (either dessicant or mechanical), and the charcoal beds and vent to the
    stack.

    Ignitions are commonly caused by not having dilution steam cut-in to the
    recombiner inlet flow, or a problem with certain metal 'fines' containing
    silver that get blown/flushed out of the recombiner into sections of piping
    where they don't belong. Then when H2 contacts them, the flame propogates
    inside the pipe back to the after-condenser where the SJAE steam is being
    removed from the mixture, creating a flammable ratio. If SJAE's are left in
    service, the 'fire' will continue right there in the after-condenser outlet
    for as long as you let it. Temporarily shutting SJAE suctions can stop the
    flow and put out the fire, but they must be reopened before vacuum is lost.

    Most plants also have a system to bypass the recombiner and charcoal beds
    during startup. The after-condenser is routed to a 'drip pot' and then a
    2400' long pipe known as the "30 minute holdup" pipe. Then a mechanical
    vacuum pump that draws a slight vacuum on the far end of the 2400' pipe.
    From there, a HEPA filter and the stack. But when this flow path is used,
    the stack release rates are much higher (the Xe & Kr haven't decayed).

    And then even a third system that uses mechanical vacuum pumps (nicknamed
    'hoggers') that are used to initially draw a vacuum from atmospheric down to
    about 25" Hg or so. Then the SJAE's are placed in service through the
    30-minute hold up pipe. Once the turbine is on-line and there is enough H2
    in the offgas to sustain the recombiner, it's placed in service followed by
    the charcoal beds.
    You either have a bad memory, or Brown's Ferry 1 has a one-of-a-kind system,
    unlike any other plant. All the BWR's I've been to, the recombiner is
    easily accessable. But due to the short-lived radioactive gasses, it's a
    high-radiation area while operating. But the recombiner is quite accessible
    when shutdown.

    The charcoal beds, which adsorb the radioactive gasses *do* get pretty 'hot'
    radioactively speaking. But they are located in the base of the stack.
    Nevertheless, chemistry techs sample them once a month, so it isn't *that*
    bad, just don't 'linger'.

    You may be confusing them with the charcoal beds used in the Standby Gas
    Treatment system. *That* system is located in a separate building and is
    used for controlling the release of radioactive gasses from the primary
    containment (drywell). After a major accident, there may be a large amount
    of radioactive gasses in the containment. If it becomes necessary to vent
    the containment (see BWROG EOP guidelines for when this may be necessary),
    these charcoal beds filter and adsorb a lot of the noble gasses. Under
    *those* conditions, they can be quite 'hot' and may not be approachable
    (they are behind a shield wall). They can adsorb so much radioactive gas
    that provisions are made to cool the bed after use in an accident to remove
    decay heat (not to be confused with reactor decay heat).

    Some plants also have recombiners for H2 control of the containment
    atmosphere after a major accident, but not all (Mark II containments do,
    Mark I containments don't). H2 can be produced from zirc-water reaction (if
    the cladding overheats, the zirconium reacts with the superheated steam
    producing a lot of heat and H2), or fuel material coming in contact with
    concrete in the containment. These recombiners are safety-related and dual
    trains of them are installed.
    Yeah, sounds like they completely re-designed the flow path and system after
    you're screwed up system. In BWR-2 thru -6's it goes from after-condenser,
    to dilution jet, to recombiner, recombiner-condenser, to dryer, to charcoal
    beds, to stack. Only place with flammable H2 is between after-condenser and
    recombiner. Flow through the dryer is only about 20 scfm, same as the beds.
    The beds are not that 'hot'. With a lot slower flow rate through the
    charcoal beds, hold up times are quite good. No H2 reaches the beds.
    Dilution jet adds a lot of steam (~15 klbm/hr) to the flow to carry heat out
    of the recombiner (still, it runs about 800F). Dilution steam, with the
    recombiner heat, condenser in-leakage air and reformed H2O are all passed to
    the recombiner condenser where the H2O is condensed and the mixture cooled.
    From there, the air flows at about 70F to the dessicant dryer (or a
    refrigeration dryer) depending on the recombiner-condenser's cooling water
    temperature.
    Which Browns Ferry Unit you talking about? Unit's 2&3 are very 'generic'
    BWR 5's, I've worked on several BWR 5 units. None of their off-gas systems
    are as you've described. Unit 1 has been shut-down ever since the 'candle
    incident' (or was it the ATWS incident?)
    Ah, now the ad-hominem attack. Admits his memory is a bit fuzzy, that he's
    only had one encounter with offgas system, that he's not an expert, but that
    doesn't stop him from attacking others. Do the letters 'SRO' mean anything
    to you? As in Senior Reactor Operator? We 'eat' engineers like you for
    lunch and spit you back out. Been to any nuc plants besides your
    one-of-a-kind with a totally screwed up offgas system?

    Try a little research before you start putting out disinformation based on a
    fading memory of one time when you were involved with an offgas system....

    GE SIL-150
    NUREG/CR-0727
    NUREG-0442
    The above documents are 'non-public' or 'proprietary', so they are not
    available on the Web. But they are probably in any BWR's reference library.
    Including yours, if you really work at one.

    IE Bulletin 78-03
    http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1978/bl78003.html
    This discusses an explosion at Millstone I that occured in the base of the
    stack. Normally no H2 gets that far. But this explosion resulted in injury
    and damage. They had another explosion earlier that same day, confined to
    the offgas system but "Damage was relatively minor". Note that as of the
    date of this bulletin (February '78) there were "...approximately 25 known
    hydrogen gas explosions that have occurred within the offgas systems of
    operating BWRs." That was in 1978.

    IN 86-43
    http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1986/in86043.html
    This discusses that using silver zeolite in sampling the offgas system can
    be hazardous as the silver will act as a catalyst and can spontaneously
    ignite the H2 in the sample stream, which in-turn can propogate back into
    the offgas system. Wouldn't be a problem if H2 was just a 'trace' in the
    flow stream now, would it?

    NUREG-0800, NRC's "Standard Review Plan", Chapter 11.3 "Gaseous Waste
    Management Systems"
    http://adamswebsearch2.nrc.gov/idmw...062:&LogonId=6be469c35b500f52efb12c758b4ef023
    (don't know if this link will work, but search ADAMS on the NRC site to find
    it.) Section II. B. 6 (specific criteria to meet the relevant requirements
    of the commission), states in part, "...For a system designed to withstand
    the effects of a hydrogen explosion, the design pressure for the system
    should be approximately 20 times the absolute operating pressure (including
    the intermediate stage condenser for BWR offgas systems." Notice they
    explicitly mention the offgas system. Further down on the same page..."For
    BWR systems with steam dilution upstream of the recombiners, analysis for
    hydrogen...should be downstream of the recombiners and upstream of the delay
    portions of the system." That is, the dilution jet, then recombiners, then
    charcoal beds. Get it??

    Generic Tech Specs for a BWR-4...
    http://adamswebsearch.nrc.gov/scrip...urnPage]=results_list.html&CQ_CUR_DOCUMENT=39
    Subsection B 3.7.6 (about 3/4 of the way down), describes the off-gas system
    in general terms and the various LCO's and SR's needed. In the BASES
    section, "This system uses a catalytic recombiner to recombine
    radiolytically dissociated hydrogen and oxygen. The gaseous mixture is
    cooled by the offgas condenser; the water and condensibles are stripped out
    by the offgas condesner and moisture separator." Sounds a lot more like
    *my* description than yours.

    Even the next generation "ESBWR Design Control Document"
    http://adamswebsearch.nrc.gov/scrip...urnPage]=results_list.html&CQ_CUR_DOCUMENT=89
    Section 11.3.2 (about 1/2 down the document) the first 'Major process
    function" listed: "recombination of radiolytic hydrogen and oxygen into
    water to reduce the gas volume to be treated and the explosion potential in
    downstream process components;" followed by, "dyanamic adsorption of krypton
    and zenon isotopes on charcoal at the approximate temperature shown in
    Table..." Under 'Releases', "The significant gaseous wastes discharged *to*
    [emphasis added] the OGS [offgas system] are radiolytic hydrogen and oxygen,
    power cycle injected gasses [such as H2 for chemistry control] and air
    in-leakage, and radioactive isotopes of krypton, xenon, iodine, nitrogen,
    and oxygen.

    Want some more? Go to http://www.nrc.gov/reading-rm/adams.html and search
    away. Or go talk to the system engineer for offgas (you admit it isn't
    you). Or look at the operator training program's system design lesson plan.
    Talk to someone from another BWR plant. Ask GE if your pocket book is deep
    enough.

    As to using a 'nym, I value my privacy. But I've been using the same 'nym
    for several years now. If you do some searches you'll find that I live in
    central NY near Lake Ontario. I drive by two BWR's (Nine Mile Point Unit 1
    and Unit 2) to get to work at the third BWR (James A FizPatrick). Look 'em
    up.

    daestrom

    P.S. Sorry to the rest of you folks for the long-winded post. But this guy
    accused me of being a "low level tech, if he's even involved with nuclear
    power at all." Toured my first 'atomic plant' when I was six years old (Big
    Rock Point, also a BWR), been in the nuclear field for 32 years and this
    'yahoo engineer' thinks he knows everything about nuclear plants because he
    was 'involved' with an off-the-wall offgas system 30 years ago. I think the
    boy has been fairly well 'spanked'. Maybe he'll do some research before
    responding and wasting our time again.
     
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