Too bad Japan didn't use Canadian CANDU reactors

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Canadian CANDU nuclear reactors can't melt down or go critical the way that these GE reactors are doing in Japan.
It's too bad that they were basically forced into using the GE rectors in Japan. Now we will have a new generation of people in Japan that can thank the US for the nuclear "gift" that keeps on giving.
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Sure they can; it's just less likely for that to happen.
--
Tegger

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Home Guy wrote:

That wasn't the problem. It was the back up generators and fuel tanks that were taken out by the tsunami. No back up cooling, not reactor design that is causing the problem.
--
All is as it is.

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Fuddy Dud wrote:

It is the reactor design.
Even when all the control rods are inserted to stop the reaction, the core still operates at 7% heat output - not zero percent. A constantly operating coolant system must be available at all times to maintain this type of reactor in a safe state, even during shut-down. Clearly in an area prone to earth quakes and tsunami's, such a requirement seems to be practically infeasible.
===========Canadian CANDU reactor overview:
The large thermal mass of the moderator provides a significant heat sink that acts as an additional safety feature. If a fuel assembly were to overheat and deform within its fuel channel, the resulting change of geometry permits high heat transfer to the cool moderator, thus preventing the breach of the fuel channel, and the possibility of a meltdown. Furthermore, because of the use of natural uranium as fuel, this reactor cannot sustain a chain reaction if its original fuel channel geometry is altered in any significant manner.
Today there are 29 CANDU reactors in use around the world, and a further 13 "CANDU-derivatives" in use in India (these reactors were developed from the CANDU design after India detonated a nuclear bomb in 1974 and Canada stopped nuclear dealings with India). The countries the reactors are located in are:
* Canada: 17 (+3 refurbishing, +5 decommissioned) * South Korea: 4 * China: 2 * India: 2 (+13 in use, +3 under construction) * Argentina: 1 * Romania: 2 (+3 under construction, currently dormant) * Pakistan: 1
CANDU fuel bundles, each about 50 cm in length and 10 cm in diameter, weight approx. 20 kg (44 lb), generate about 1 GWh of electricity during its time in the reactor.
The Bruce Nuclear Generating Station, the second multi-unit CANDU station, was constructed in stages between 1970 and 1987 by the provincial Crown corporation, Ontario Hydro. It consists of eight units each rated at approximately 800 MWe each, and is currently owned by Ontario Power Generation (OPG) and run by Bruce Power.
The Bruce station is the largest nuclear facility in North America, and second largest in the world (after Kashiwazaki-Kariwa in Japan), comprising eight CANDU nuclear reactors having a total output of 6,232 MW (net) and 7,276 MW (gross) when all units are online. Current output with six of the eight reactors on line is 4,640 MW. Restart of the remaining two units is planned by 2012.
(note: The Kashiwazaki-Kariwa reactor mentioned above is NOT a CANDU-type reactor. It is a Boiling Water varient of a Light Water Reactor, made by General Electric). ========== http://en.wikipedia.org/wiki/Candu
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snip
You forgot this: "The main difference between CANDUs and other water moderated reactors is that CANDUs use heavy water for neutron moderation. The heavy water surrounds the fuel assemblies and primary coolant. The heavy water is unpressurized, and a cooling system is required to keep it from boiling."
The big problem with ALL nukes is cooling. Lose cooling and you get disaster. You see what's going on in Japan? Think there's 6 reactors on one site. And cooling pools for depleted rods. Those also need cooling or you get a disaster. They cool depleted rods for 6-10 years before they can encase them for disposal. And the cooling pools aren't in a containment vessel like the active rods are. That's what's happening in Japan. Even the depleted rods in the cooling pools are melting down and releasing radiation to the atmosphere.
I think nukes are a good energy source, but when it goes wrong, it goes VERY wrong. After this Japan disaster, I only see 2 options for nukes going forward. You need to do both. 1. Radical redesign so cooling loss can't cause disaster. By "disaster" I mean environmental disaster. That's what's scary about nukes. Last I saw 140k people have been evacuated from around the Japan nuke plant. No wonder nukes are subject to NIMBY. If things go bad you can abandon the site, and no harm is done except loss of investment and real estate. This means cooling pools must also be in containment.
2. NEVER have "too much" fissionable material at one site. Go smaller, not bigger. That way when one breaks, there's no way it can be a huge disaster like what might happen in Japan. And they will break. Nobody believes that won't happen. Building more and smaller nuke plants would be more expensive, but that's how it is.
Anyway, that's my cracker barrel view as a newsgroup physicist.
--Vic
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Vic Smith wrote:

That's when it's operating. A Candu core can be shut down without needing a cooling system to remain functioning after shutdown.
This is the key point:
---------- Criticality of CANDU fuel bundles in light water is impossible, avoiding one concern of severe accident analyses that light-water reactors must contend with. Furthermore, since the geometry of the CANDU core is near optimal from a reactivity standpoint, any rearrangement under severe accident conditions ensures shutdown. ---------
http://www.nuclearfaq.ca/cnf_sectionD.htm
http://www.nuclearfaq.ca/cnf_sectionD.htm#q
The CANDU system is a strong example of safety through both engineered redundancy and passive design. The core has numerous triple-redundant detectors that feed to two logically, conceptually and physically separate shutdown systems (shut-off rods and high-pressure poison injection). Each system is capable of shutting down the core within 2 seconds following a LOCA ("Loss-of-Coolant Accident" -- the design-basis accident for CANDU reactors), without credit given to operator intervention.
In addition to engineered safety systems, CANDU reactors have a number of inherent safety features that distinguish it from other reactor designs (e.g. PWRs, BWRs):
* The subdivision of the core into two thermalhydraulic loops (in most CANDU designs), and hundreds of individual pressure tubes within each loop, localizes a LOCA (Loss-of-Coolant Accident) to one small region of the core, and reduces the reactivity effect of a LOCA accordingly. Furthermore, the two core-passes per loop mean that only a quarter of the core would likely suffer a mismatch between heat generation and removal under such conditions (and only the highest-power fuel elements within this one-quarter-core region).
* The large-volume, low-pressure, low-temperature moderator surrounding the pressure tubes acts as a heat sink in large LOCA scenarios, rendering negligible the risk of "fuel meltdown". The moderator, in turn, is surrounded by a thick light-water shield tank (used for biological and thermal shielding) which can also act as a heat sink in severe accident scenarios.
* The moderator also provides a low-pressure environment for the control rods, eliminating the "rod-ejection" scenarios considered in PWR safety analyses. In addition, the location of neutronics measurement devices in the moderator avoids subjecting this equipment to a hot, pressurized environment.
* Heavy-water neutron kinetics is slower by several orders of magnitude than light-water kinetics, reducing the discontinuity between prompt and delayed kinetic behaviour, and making control easier.
* Criticality of CANDU fuel bundles in light water is impossible, avoiding one concern of severe accident analyses that light-water reactors must contend with. Furthermore, since the geometry of the CANDU core is near optimal from a reactivity standpoint, any rearrangement under severe accident conditions ensures shutdown.
* On-power refuelling means that the power distribution reaches an equilibrium within a year of start-up, and remains virtually unchanged for the reactor's operating life. This greatly simplifies the analysis of core behaviour as a result of postulated accidents.
* On-power refuelling also allows defective fuel to be detected and removed from the core, reducing the contamination of the reactor coolant piping and simplifying maintenance.
* The low excess reactivity of the CANDU core leads to relatively low reactivity worth of the control devices, limiting the potential severity of postulated loss-of-regulation accidents.
* The positioning of the steam generators well above the core promotes natural thermosyphoning (i.e. movement due to the coolant's own density differences), which can remove decay heat if shut-down cooling is lost. At the same time, the large amount of small-diameter piping in the feeder network acts as a natural "radiator" under such conditions.
This significant amount of inherent, or "passive", safety in the CANDU system, in conjunction with fast-acting, robustly engineered safety systems and backup safety systems, is the reason why a complex technology like nuclear power can be one of the safest and most reliable energy options available.
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Didn't know about CANDU reactors. But I've read up a bit. I can't argue about heavy water versus light water reactors. But they both use uranium. Saying a CANDU can't melt down when it loses cooling is just wrong. That's what they all say. Let's wait until a CANDU loses cooling, then we'll see. I'll stick with what I said. Good containment of cores and depleted rod cooling pools, and never put too much uranium in one place. Smaller reactors/generating plants, and spread them around. Then when the shit hits the fan it's not a huge disaster. Just a small disaster.
--Vic
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On Tue, 15 Mar 2011 22:46:11 -0700, Smitty Two

Might be a good guess if it really goes to hell in Japan. I hope not. Burning gas, coal and oil kills more people every day than nukes have done in 50 years.
--Vic
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wrote:

Two things: "Burning gas, coal and oil kills more people every day than nukes have done in 50 years." That's until now. We won't know until the stuff has cooled down and the extent of contamination is known.
There are very expensive lessons to be learned from this quake and tsunami. Especially on the West coast. Hopefully the lessons will indeed be studied and acted upon, both the physical threats directly from a tsunami, and the nuclear physics threats from misbehaviors of nuclear plants.
Still, nuclear power seems to me to be a very viable alternative energy source, IF properly executed.
--
Best regards
Han
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Sarcasm noted ...
Punishing I leave to the justice systems. Wait, that involves lawyers. Maybe your god can do it?
By lessons executed I meant (you didn't grok that <grin>?) acted upon the lessons and change whatever needs changing. In ths case, it seems particularly important to make sure that total loss of power doesn't lead to damage of the kinds seen in the Japanese reactors, or make sure the backup power can't be interrupted by earthquakes or tsunamis. The latter probably evokes: Fat chance!
--
Best regards
Han
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wrote:

I, too, hope that some important lessons will be learned here, especially since we have serious earthquake vulnerability on the West Coast. But then I think about what I thought we learned in Vietnam and where we are now and I would say that in 25 years, nearly all lessons learned are forgotten again. )-:
-- Bobby G.
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On Wed, 16 Mar 2011 11:23:08 -0400, "Robert Green"

US wars are always to insure that wealthy Americans can invest abroad safely. The soldiers are there to protect that investment. What was the lesson from Vietnam? To continue to have wars overseas so that the wealthy can make more money, but try to make sure that the outcome is successful. The lesson was not to stop getting involved in foreign wars.
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Sad but true. Vietnam is now supplying us with computer parts for even LESS than Chinese wage slaves can make them. Conquer and turn into a sweat shop. Ironically, we didn't even win in 'Nam!
I had hoped we had learned that a war in which we can't tell friend from foe is a war to avoid. Obviously not. Amazingly in the 80's the various war colleges were full of "lessons learned" from 'Nam but when the old war wagon got rolling and fast promotions started coming, all bets were off.
-- Bobby G.
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bad Japan didn't use Canadian CANDU reactors:

Cumulative off-site toll of Japan earthquake/tsunami nuclear "disaster" as of 3/15/11:
killed: 0 injured: 0 sickened: 0 property damaged due to radiation from plant site: none
--
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Indeed, that is the situation today. We don't know how many of the heroic personnel working on site have been sickened, and how badly. That will not be apparent until later. Moreover, the disaster is still progressing, and if I have to believe others with more knowledge of the half-lives of the fission products, that will be several to many weeks from now. Also, with all those attempts to use seawater for cooling, where has all that gone? I expect that what hasn't become steam, did run back to the ocean, with the radioactive "shit" that dissolved in it or was washed away by it, all into the sea.
--
Best regards
Han
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Smitty Two wrote:

Well, when your local gas-fired plant develops a rupture and explosion of it's fuel source, or when your nearby oil-rig blows up and spews crude oil all over the ocean, or when dozens of miners die in a coal mine digging coal for your local coal-fired electricy plant, or when you divert entire rivers or flood huge areas to create lakes to generate hydro power, it all comes back to the same thing: People want electricity, there are nasty consequences to the ways we generate it, and there are too many people on this planet in the first place.
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and I'm betting that you aren't gonna volunteer to leave.
--
"Even I realized that money was to politicians what the ecalyptus tree is to
koala bears: food, water, shelter and something to crap on."
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On Wed, 16 Mar 2011 09:23:37 -0400, "Stormin Mormon"

Wasn't there just some problem about drilling, I forget, something about the gulf?
But yes, too many people. Be fruitful and multiply. Do not stop when the planet gets full.
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Here's a fact. Unless the Canadians have re-invented the laws of physics, your whole premise and understanding of what's going on is wrong. No nuclear reactor can go from 100% power to zero power instantly or within even a few hours. That has nothing to do with the reactor design, but has everything to do with physics. The fission of uranimum produces radioactive byproducts that in turn decay over time. That decay continues for hours and days after the control rods are inserted. The control rods absorb neutrons and stop the uranium chain reaction, but do nothing to stop the self decay of the other radioactive elements. Every power reactor has to have some means of removing that waste heat or the reactor will start to melt down.
Also, nothing in that cite says anything close to what you claim it does. It comments on one narrow aspect of the design. Show us where it says cooling water is not critical after inserting the control rods.
I'ts also particularly foolish to start claiming some Canadian reactor, which your obvioulsy don't understand, is superior and would have prevented the accident. Wouldn't it be better to first at least find out the full story and sequence of events from an investiation?
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Home Guy wrote:

Well it the generators and generator fuel tanks were underground like in the US they would all be cooling just fine right now with no problems.
--
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