Too bad Japan didn't use Canadian CANDU reactors

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wrote:

It's good that an earthquake doesn't actually disturb the ground.
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4ax.com:

??? There is no disturbing of the ground if a road splits down the yellow centerline and one half is suddenly 4 feet below the other half??
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Best regards
Han
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wrote in news:f8l4o6h4au5o2b0jaibm2k6sivicpu29hl@

Cut him a break. I don't think English is his first language even though he does remarkably well with it. Given that much of the humor in AHR wouldn't get you a 3AM slot in a comedy club in bum fuck Egypt, it's easy for me to see how people often react poorly to humor or sarcasm.
-- Bobby G.
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On 3/15/2011 6:02 PM, Home Guy wrote:

...
If they can't go critical they wouldn't be of much use... :)
And, they have emergency cooling systems for large and small LOCA just as do LWRs...
<http://canteach.candu.org/library/20040724.pdf
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I think you need to look up the meaning of critical... If it *does* go critical, it becomes a bomb.
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On 3/16/2011 7:05 AM, Doug Miller wrote:

I know the meaning of critical but I'll look it up and explain it for you... :)
For a chain-reacting system, the mean number of fission neutrons produced by a neutron during its life within the system is known as the "multiplication factor" termed "keff" or "k-effective". It follows that keff = 1 if the system is critical; keff < 1 and the system is subcritical; keff > 1 and the system is supercritical.
It does _not_ follow that if the system is supercritical there is a nuclear explosion; it requires going slightly super critical to raise power levels (or to initially startup the reactor in the first place); once the new desired power level is achieved, control rod and/or other poisons (soluble boron in form of boric acid in LWRs) are adjusted to bring keff back to precisely 1 (which is obtained by observing that neutron fluxes are maintained at a constant level by the reactor instrumentation.
chain reaction, fission: A sequence of nuclear fission reactions in which fissions are induced by neutrons emerging from preceding fissions. Depending on whether the number of fissions directly induced by neutrons from one fission is on the average less than, equal to, or greater than unity, the chain reaction is convergent, (subcritical), self-sustaining (critical), or divergent (supercritical).
Note that "supercritical" does _not_ on its own imply the reactor or reaction is out of control; it requires being supercritical for a period to either startup the reactor or to raise the operating power level from, say, 75% to 100% FOP. If the reactor were to remain subcritical its entire lifetime it would never start up and never, therefore, be of any actual practical use.
Nuclear explosions only occur when the value of keff >> 1 and the reaction becomes critical on prompt neutrons alone. That is a physically unrealizable situation in commercial reactors; neither the geometry nor enrichment are adequate.
A pretty good glossary of nuclear terms; not for the totally faint of heart, however, ... :)
<http://docs.google.com/viewer?a=v&q che:fjjM1LufiUwJ:www.osti.gov/bridge/servlets/purl/5609066-o4S1LS/+critical+definition+nuclear+ans&hl=en&gl=us&pid=bl&srcidGEESg0uV0cj6tbQW6eF-x7W6tPhFkW6KXSVOExz2Nx4AQ2r2ET_MuaF_Q4jRjWVMJKgXrVrMwCYvZ2FEZNEJJ2JppYRojEhx2ssmz6vyWrbp4hZSXY6_UDRlBXJJ5momSZE6F86ch5&sig=AHIEtbTGQLNFf-U_xYcrKFLGI4YvlLvbzw>
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Here's a question nobody is asking:
Since the problem always seems to be with outdated reactors; how many outdated reactors are decommissioned every year?
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Molly Brown wrote:

Nobody's asking that question because the question is based on a faulty premis - that the reactors are "outdated".
It's like if I asked you if you still beat your wife (or in your case, maybe your husband).
The basic design of that reactor (and many others made by GE USA in Japan and in the US) requires that it always has a functional cooling system. It doesn't matter if it was old or new - it always needs a functioning cooling system, because the nuclear chain reaction can't be fully stopped in that design.
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So what you're saying is that you would let your wife and two children drive around in a
http://stationwagonforums.com/forums/gallery/files/1/1983_chevrolet_malibu_cl_estate_woody_stationwagon1.jpg
even though it's outdated.
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On 3/15/2011 11:21 PM, Molly Brown wrote: ...

...> even though it's outdated.
Ignore this bozo, Molly; he's totally wrong.
The CANDU reactor also has emergency core cooling systems and requires core cooling after shutdown; see the earlier link I posted that describes the systems.
The issue is that fission reactors of _ALL_ types produce fission products (well, DOH! :) ) which are radioactive and therefore, decay. The process of radioactive decay gives of heat as the decay products are absorbed in the various materials of the reactor and this gives rise to the (amazingly well-named :) ) decay heat which must be removed even after the reactor is shut down.
The fission nuclear reaction has been shut down by "scramming" the reactor and once so, that reaction does (essentially) cease. That is no different in a LWR (BWR or PWR) as it is in the CANDU heavy water design.
(I am, btw, degreed NucE w/ 30+ yrs in commercial nuclear generation with both a reactor vendor and as consultant to power utilities, various US national laboratories, US DOE and commercial clients)
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Well, I am a biochemist of sorts, but I do believe I can reason. Opinions on that vary, but you are not allowed to question my spouse or kids.
Question here is, can you explain how a CANDU reactor gets cooled after a total power loss, and once it is scrammed, fission of the fuel has stopped (mostly), but the fission products still produce prodigious amounts of heat.
TIA! (I'm in favor of nuclear energy, but the problems haven't all been solved, I think.)
--
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Han
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On 3/16/2011 9:49 AM, Han wrote: ...

Very similarly to a LWR (BWR or PWR) in immediate case from power; only real difference is in long-term (after a month or so shutdown so decay heat has significantly decreased from that present shortly after shutdown from steady-state full power operation) they do have sufficient natural circulation (assuming everything has survived the event that got them there, of course).
<http://docs.google.com/viewer?a=v&q che:5o7ZK9axiXgJ:canteach.candu.org/library/19990106.pdf+candu+decay+heat+removal&hl=en&gl=us&pid=bl&srcidGEESjq9Yp9HDPxb5n07aGc2n2q_KBgKHJz0-ws_lsuwk8ci1a0T8H-zUIj0JG4O78uXlkYYpDFcgZj2SovEtvWuAk3LNQOcsNXkPda7sV6ullKXFsROjdwaG0nBtfAHVQVcWTxHcHI&sig=AHIEtbQkvhKArdOSKgdCHCCeBoA_NDTIng>
There are some differences but the really significant ones only come into play over a longer time frame than an initial response to an accident. And, of course, to date no CANDU has been tested to see if the implementation holds for them in practice as well as the theory...
On the last point, there are newer concepts and designs that provide the same kinds of long term self-circulating DHR in LWR designs...they rearrange the primary and secondary piping and some other features.
Unfortunately to address Molly, the reason there are none in the US is the "anti" movement created the business environment nobody wanted to expend the monies required to try to license anything new for nearly 40 years now...thus we're in a crunch worrying about "C footprints" and fossil while the solution is sitting on the sidelines for lack of will and leadership.
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Well, if we want nuclear energy as I think we should, there has to be some rewriting and reflecting for modifications for worst case scenarios. And some re-training of operating personnel.
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Best regards
Han
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It's bigger than that.
60 Minutes did an expose on unfinished nuke plants in the US and some of the reasons the industry fizzled. Sadly, much was due to plain ol' corruption. Containment vessels were not meeting NRC specs cuz unions were skimming on rebar and cement, so inspectors refused to pass them. Some inspectors and their families were threatened. Some passed, some didn't, some inspectors quit rather than endanger their families. Not good mojo. How many substandard plants are out there?
Three Mile and Browns Ferry were far from rare. Rancho Seco, near Sacramento CA where I lived, also got real close to a China Syndrome, though it's not well known outside CA. It was decommission over 20 yrs ago, after only 14 yrs online, before it got outta hand.
http://en.wikipedia.org/wiki/Rancho_Seco_Nuclear_Generating_Station
While I generally approve of what unions stand for, too often they become as bad if not worse than the slimey corporations they claim to protect workers from. My late FIL worked at Diablo Canyon CA, near San Louis Obispo. He was a union electrician that spent most of his time making roach clips out of SS welding rod at $30 hr. Not his fault, jes the way the job was bid. You'll hire this many workers or else.
Too much corruption and money grubbing slimery for nuke power to ever be safe in US, IMO.
nb
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And how well do you know the 60 minutes or the wikipedia folks?
I used to put a lot of credence in 60 Minutes until I happened to see a couple "reports" on subject areas that I am an expert. Bye, bye 60 Minutes' reputation. If they are wrong on the stuff I know about, how can I trust them about the stuff I don't know about?
IMO, they "sold out" long ago.
I've had private conversations with dpb. AHR readers should be happy that we have our own experienced, level headed nuke expert.
Had my engineering career (started in 1975) taken a different turn, I could have be the group's nuke expert. That job at Westinghouse (Hanford, WA) had to do without me.
I've been silent on the whole Japan nuke problem, not my area of expertise.
But I'm glad that dpb takes the time to give us the benefit of his knowledge & experience.
The nuke "non-experts" in AHR should lay off the 60 minutes & wikipedia stuff. Read dpb's posts & learn.
cheers Bob
PS Chernobyl & TMI were way different installations, events & outcomes. Chernobyl was "a nuke in a warehouse" and killed how many? TMI killed how many?
To link these in the same discussion is to show one's lack of knowledge of nukes.
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That comparison was to indicate that design flaws and operator error occurred, just like in the Japanese plant
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Han
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dpb wrote:

When you look at the over-head pictures of the Japanese reactor sites, they really don't look like they were swamped by a tsumai wave.
So I don't understand how or why their coolant circulation systems failed. Seemingly not from mechanical / structural breakage.
On-site diesel electrical generation can be housed in water-tight buildings and can operate for days or weeks - given a competent fuel supply.
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This is all about money. Reactors *could* be built to withstand tsunamis AND earthquakes but no one would be able to afford them. It's only after disasters that business and governments are willing to spend money on additional protections against theoretically rare events.
I think the real problem here was believing the tsunami barriers would work. It turns out they had multiple modes of failure. We do learn an awful lot with each near meltdown. From what I've been reading, designs subsequent to the GE MK1 have incorporated a lot of improvements, much of it learned from failures at TMI and Chernobyl. This accident will probably cause regulators to up the requirements for cooling system survivability, armoring them up perhaps as much as the reactor containment vessels. In all the designs I've seen posted on the net, the cooling systems seem to be a pretty serious Achilles' heel.
As a NucE, what would you say the worst case scenario is in the Japanese crisis? What would it look like compared to Chernobyl?
-- Bobby G.
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I believe Chernobyl is returning to normalcy now after 25 years. How normal, I don't know. I wouldn't want to live there yet. Maybe in another lifetime.
As a total layman, I'd say the bad situation in Japan depends on 2 things: If the cores don't melt down and they don't get exposed. nothing much will happen apart from sick and dead nuclear plant workers - the heroes here (hat off to them).
If one or more cores met down and get exposed, let us hope the wind will blow all the radioactive stuff out over the ocean. You'd have to sample the fish for radioactivity, but that'll be it. I don't think we'll get scary mutant monsters.
--
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Han
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On 3/16/2011 5:04 PM, Robert Green wrote: ...

...
A) Not enough hard data to be able to tell, realistically...
B) Unlikely imo to be nearly as bad owing to the major difference between the reactor design and containment. At Chernobyl, since it was a graphite-pile reactor they manage to actually catch the graphite surrounding the fuel on fire and with no containment building around the reactor at all (other than a metal-covered turbine/reactor building that melted immediately), the whole release was straight to atmosphere.
Here, there is containment around the reactors themselves and afaict at the moment the major problems w/ spent fuel storage pools.
But, I don't have any inside connections to find out what is actually going on in sufficient detail to really be able to judge what the situation is there. That one I do find a little puzzling but I don't know the design of their pools.
So, overall, "I don't know"...whatever it is, they gots their hands full... :(
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