Fission Waste Disposal

Guest suggests: "...surrouned and infused with moderator materials?"

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Interesting idea. Maybe use cadmium or something like that? Cadmuim is toxic, but maybe surround it with something inert and durable?

-e

or conversely, the welded shapes could be joined to form an empty honeycomb, filled with pure water or other liquid (sodum?) as moderator.

Chris

Uranium and plutonium are chemically very reactive. Wouldn't they still need to be passivated? Else we have the waste leaching into the water. Sodium has its own problems and reacts violently with water/moisture. But I think water as a moderator would be preferable over something else - provided the spent fuel could be passivated, possibly by oxidizing it first. I've seen some of this stuff made into a kind of ceramic, as well.

-e

What role is the moderator meant to serve? The moderator in a reactor slows down the neutrons to increase the possibility of fission occurring.

Storing the waste in metallic form would mean opening the fuel rods and refining the contents into the metallic form, and it would be a mixture of several metals. This would all have to be done in a hot cell environment. It would much simpler to just dispose of the spent assemblies in their current form. Reprocessing for the purpose of reclaiming unused fuel is a different matter but just for the purpose of disposal doesn't seem to make much sense because the fuel is already enclosed in rods that would protect it from water and the atmosphere.

You might be right about the moderator. I understood the moderator was to... well, moderate. Without the moderator, the chain reaction would escalate exponentially, and turn into an explosion or meltdown due to critical mass. Otherwise, if the purpose is to promote fissionable interactions, you might call it an inhibitor or accelerator... so I guess that would be confusing. I will have to look into this.

Regarding the reprocessing of shape, i believe the idea was to encase the original form in a lead or other metal package, forming an ingot.. but you make an excellent point here.

Chris

...you might call it an inhibitor or accelerator...

Right. This should be more descriptive. Graphite is used for both Nuclear and Chemical: It's the only possible container to hold Fluoric Acid (by itself used for etching glass), which would otherwise corrode anything else

The water in an reactor is to cool and is also used as a heat transfer medium (in a BWR, in a PWR the water is changed to steam in the reactor vessel). It does not act as a moderator. The control rods do the modulation. They slow the neutrons down so that there is a much greater Chance that the neutron will hit the nucleus of an atom and knock loose more neutrons that are then slowed by the rods.

The rods are withdrawn to slow reaction.

Baron is used to adsorb neutrons so as to really slow the reaction.

It is a bit more complicated: The water is indeed a moderator, but only there to slow down the stuff so that they have better chance to interact with the next fuel rod.

The moderating rods are ther to be able to controll the system (to be able to stop and start the reactor when we want) as it is quite difficult to change the amount of water between the fuel rods.

In a boiling water reactor the water is in tubes, embeded in the core material, Other tubes contain the control rods. A typical example is the Chernobil reactors. They are easier to make as the pressurized parts are smaller. But they have a problem that the control rods can't be brought back in when the reactor suffers mechanical deformation. As the word says for itself: the water boils in the reactor and gets superheated, those types have the possibility to reach a higher efficacy.

The Pressurized water reactor is a big vessel completly filled with water and the fuel is in rods. The moderator rods are also free in the water, which enables them to be brought in at all moments and as they are typically above the reactor, gravity will help bringing them down. The water dous not boil as this would reduce the amount of water between the rods and thus the rate of moderation, resulting in an unstable process. Which is exactly what we don't want. The heat gets exchanged in the steam generators, making steam of the water of the second cooling system. This separates the irradiated fuid from the rest of the world (this fluid does not leave the reactor house) As the water in the reacor vessel may not boil, the temperature needs to be below the tripple point, reducing the efficacy to a limit of approx 32%. There are many ideas to crank this up, mostly by using other cooling fluids that allow to go higher in temperature and perhaps if possible reduce the pressure (Na is one of those)

From where comes your idea that the water is to cool to act as a moderator? When works need to be done at the level of the reactor content, they fill up the complete reactor bassin with water to moderate the radiation completely to zero. This water is at room temperature or even cooler.

Thank you Gwen. excellent explanations. I have questions though. You said "as it is quite difficult to change the amount of water between the fuel rods." and I am wondering why this is. I can think of a configuration or 2 that might allow the spacings to be changed. The question is... are there other parameters involved, such as geometry, or diameter or shape profile of the fuel rods that need to be considered? As I understand the reaction, it is initiated by having a critical mass of fissile material in proximity. do the rods have to be straight, or can they be curved, or of variable diameter?

just curious.

Chris

...allow the spacings to be changed...

The water is the medium for the exchange of heat. It's not meant to stop or dampen radiation as such.

The whole shabam of moderating radiation (to moderate the "ever rising" water temperature) is a statistical factor of introducing moderator medium/rods (such as graphite) into the basin.

It's an all-in-all populated situation, in which when you lower the moderator rods into the basin, they absorb some of the emitted particles, again, statistically, to lower the reaction dominance as a whole. Statistically. You don't go around chasing individual particle escapees ...

For two to seven it can be done, a spiral groved plate can organise that you can change the distance. But a reactor has much more rods. And it would need a non gravity operated system, bringing more problems in case of trouble (someone needs to turn the plate) A heavy rods fall into the vessel when you want, if you do the design right, they need energy to be kept up and if energy fails they fall.

Form of the rods? I think that you can use everything but in a cylinder you can easely distribute the fission material. The rods are just a way to contain the stuff.

I don't know how the neutrons react with the rod material, does it bounce of if the angle is wrong, or speed to high?

The design of a reactor is quite difficult: you need to adopt the fission material composition to the form and composition of the moderators. Wich interdistance? how many water at which pressure? This is why it is so difficult to swap fuel and start using the weapon grade plutomium, available in nice quantities.

Hi Yuval, Chris and Gwen,

I have bee watching this and thought you might be interested in the CanDU reactor system that is currently under discussion in the blog. Moderators get their name form their function which is it moderate the speed of the neutrons that pass through them. If the neutrons are traveling too fast or too slow the probability of hitting a nucleus in the core is reduced and hence the rate of fission drops. It is the job of the moderator to keep the speed that the neutrons are traveling at within a certain range. In other words the moderator moderates the speed of the neutrons.

The CanDU reactor uses heavy water D₂O as both the primary coolant and moderator. Basically it consists of a collection of cylindrical pressure vessels that contain the core and the D₂O that is under pressure that is used to transfer the heat from the core to the heat exchanger where it generates steam. These small cylindrical pressure vessels are in turn contained within a vessel that is filled with D₂O that is not pressurized. They do have secondary control rods that are used for stabilizing the output of the core but the primary moderator is the D₂O. The problem with using D₂O as a moderator is that it is fairly difficult to change the volume of the D₂O that separates the core elements and therefore it is difficult to vary the amount of moderation. That is why the CanDU reactors use secondary moderators.

D₂O is one of the best moderators available because it has a dramatic affect on the speed of the neutrons while absorbing very few. There are moderators that have a greater affect on the speed of neutrons but they also absorb or block the neutrons and this makes them less suitable as a moderator.

Moderators need to moderate the speed of the neutrons while allowing them to pass through. Things that absorb or block the passage of neutrons are not efficient moderators.

PS Yuval, I see that you can post again, what was causing the system to stop you from posting to threads?

...D₂O is one of the best moderators available because it has a dramatic affect on the speed of the neutrons while absorbing very few...

Is there some elementary "particle-to-particle" physics to explain and describe the phenomenon and effects?

...PS Yuval, I see that you...

I don't know. Probably some technicality. I mostly use clean language. Publically on this site, that is...

...I mostly use clean language. Publically on this site, that is...

"The most popular language programmers use, is profanity" - a quote

"Is there some elementary "particle-to-particle" physics to explain and describe the phenomenon and effects?"

Probably, however nuclear physics was not one of my strong subjects so I have no idea why Deuterium works so well as a moderator.

The explication I once got was that the core of the atom is way bigger than the normal Hydrogen core, this made it bigger for the neutrons.

As Hydrogen has only one electron, which it looses to the oxigen in H₂O the density of the fluid is rather high. The statistical chance that you have a collision is higher than for other molecules, which have a much denser core but as they have more electrons the free space is bigger.

Why the neutrons don't get absorbed?

There is a tritium variant known, very unstable. It only builds up in highly dense neutron reactors.

It could well be that the fast neutrons are way to fast to be captured by the Deuterium core. (Statistics again)

...It could well be that the fast neutrons are way to fast to be captured by the Deuterium core...

This would make sense. I need a "physician", to guide me through it.

I'll see if I can recruit Jorrie or europium through Who's Online

The secondary moderators are the same as those used in most reactors, they are called control rods which don't moderate but they absorb neutrons taking them out of the game.

In the CANDU, if they find that certain parts of the reactor are too active or not active enough, they control it by shuffling the fuel bundles which can be done power on using the same equipment they use for on power refueling.

The purpose of control rods is to absorb neutrons and thereby control the intensity of the nuclear reaction. In addition to the control rods which act as a sort of nuclear volume control, there are generally additional rods which are used to shut down the reactor in an emergency. These rods are generally separate from the control rods and they might be held up out of the reactor by electromagnets, cutting power to the electromagnets, either intenionally or due to a power failure, causes them to fall into the reactor, gravity may be assisted by springs. The idea is to come as close as possible to a fail safe mechanism for shutting down the reactor.

Someone said that withdrawing the rods would slow the reaction. Because the rods are made of neutron absorbers withdrawing them will speed up the reaction.

Now you have control rods and emergency shutdown rods both of which are made of elements that absorb neutrons, not just slow them down. The CANDU reactors have a second emergency shutdown mechanism if the control and emergency shutdown rods fail. They use helium held in tanks under high pressure to force a gadolinium nitrate solution from a storage tank into the moderator, no energy requiring pump is required. Gadolinium "poisons" the moderator by absorbing the neutrons and the nuclear reaction can't continue. According to my contact inside Atomic Energy of Canada Limited, it would take hours if not days to remove the gadolinium from the heavy water using ion change resins before the reactor could be started, pity the poor guy who accidentally triggered the poison system when it wan't required.

Any reactor should be able to burn plutonium in the form MOX, mixed oxide fuels. If the reactor is one that requires the use of enriched uranium fuel, don't enrich the uranium and compensate for the lack of enrichment by the addition of plutonium oxide to the uranium oxide before it is sintered (squeezed into small cylinders, and then heated in a hydrogen atmosphere to form a ceramic pellet somewhat smaller than the original). I assume that the technology for forming the pellets for CANDU systems is probably very close to that for other systems. The pellets are then sealed in metal tubes that are often made of zirconium because it doesn't absorb neutrons. The tubes are then assembled into bundles or fuel assemblies suitable for the particular reactor they are meant for.

Given the relatively long period of time that the fuel remains in the reactor the non-fissile but fertile U238 absorbs neutrons turning into reactor grade plutonium. It is said that as much as one third of the power output of a reactor is produced by the fission of plutonium bred in situ. I wonder why you couldn't substitue some thorium for some of the natural uranium, it too is fertile absorbing a neutron to become fissile U233. I know this can be done in a CANDU but it apparently requires a reactor that is very economical in the way it uses neutrons.

You're right. "Neutron-absorber" might be a better term, as this is what the control rods do. Boron and cadmium are especially good neutron absorbers.

-e

100% pure water is nasty stuff in and by it self! Liquid Sodium? nasty!

How about we turn it into a very fine powder and spread it evenly across the entire globe.

Not evenly spread, perhaps, but Rockwell has done the best job of it so far with their Rocky Flats weapons-plant plutonium fire.

-e

This idea was actually tested to some degree of success, maybe not exactly as mentioned: Chernobyl ! - Remember?

I don't mean spread it as in a disaster, or in a way that would harm people. I may be wrong but its the level of radiation that is a problem. Radioactive sources exist naturally on the earth but are usually of low levels. I wonder if we were to spread out the waste around the globe would the level in any one area be high enough to be a concern.

The problem is dual: natural radioactivity is indeed low and thus rather harmless.

It causes a part of the cancers be have here on earth, statistical data proves that regions with a higher radiation level indeed have more cancers of typical kinds.

The second and more problematic issue is that some of the elements like Pu are direct poison for us. They do not exist here on earth as a natural element, we made it in the reactor and as it is unstable will automatically disappear after some millions of years.

The spreading system is indeed used by the soviets to cope with the contaminated crops, that where needed to feed the people: instead of throwing it away they distributed it over the complete country so that everyone had a small dose. The effect of this will be quite impossible to measure as you don't have a control group anymore. I even think they took into account that regions who did not suffer from the fall out could take more from the contaminated food. Heavily contaminated food was destroyed. They were well organised to minimise the final effect, less to prevent the accident.

Gwen

...I don't mean spread it as in a disaster, or in a way that would harm people...

I know, I know, I was only being sarcastic: "Tested to some degree of success..."

Besides, what was spread worldwide was radioactive Caesium and Tellurium spray, Not Uranium or Plutonium dust.

Ooops!... Being sarcastic again.

In a previous post, I don't remember the author, it was stated that spent fuel was highly enriched and it contained plutonium of the proper isotopic mixture for weapons.

It is taken out of the reactor because it is not sufficiently enriched to provide enough power anymore. The isotopic mixture of plutonium is reactor grade, not weapons grade.

There has been some discussion of what moderator is and why it is called a moderator when in fact it facilitates fission. It is called a moderator because it moderates the speed of the neutrons.

As for the Canadian Nuclear Waste Management Organization, they did a study, prepared a 450 page report that looked at a few options, and gave it to the Minister of Natural Resources. I haven't heard anything else regarding progress in this area. I must send a letter to the Minister and ask.

If intelligent life exists in space it would regard us humans as a virus on the earth and act accordingly . Let's send them our toxics , either they will see it as a distress flare and come to our rescue , or it will get them before they get us. OK , it's a bit of a gamble but we're playing dice already.

The 'Civilized ' world will have to prevent the 'Third-world' burning fossil fuel by giving them nuclear . That's a lot of waste in the hands of too many people .

...regard us humans as a virus on the earth...

As bluntly put in the first "Matrix" movie, near the end, by "Mr. Smith...

It it however, up to us to take good care of this corner of the universe, not up to the aliens. We Should do it for the most selfish reason, our own survival and the future of our descendants,who's permission we didn't have to introduce into the world we leave with our own so-written legacy.

It is up to us. Nobody else. It is not only a responsibility, but also an opportunity, to leave a better world than the one we got, instead of the other way around. It is also a privilege, to become a constructive part of this amazing creation.

Taking good care of our world is a feel-good mission. It is. Just the change of attitude towards it, is a rewarding experience.

You are 100% right Yuval . Sometimes , pessimism gets the better of me . The only ideas I know of at the moment are vitrification and purpose built storage facilities. I shall look out for stats on this subject , since it has such colossal importance to us all. Our ability to do things has increased , but I fear at a greater rate than our ability to live together as a species. Kris.

...Our ability to do things has increased...

I was hoping that such a thread will evoke some out of the box ideas, as wacky as they may be, and that someone of "ours" within the establishment, further roll some of it into it's memos.

I know it may be somewhat naive, but you know, miracles happen, I personally witnessed a few in my time

I often thought, that the fad we know as "Alien Hysteria" is actually a disguised cry for help, something like "Somebody, something, anything, help us here with our mess, be it God, alien civilisation, anybody, please..."

But it's really up to us. This world was entrusted in our hands, so to speak, and it's up to us. No one else is gonna clean our mess. It may be a sad truth, but at least the address is clear and prompt.

As to the what can I do question: Do your humble best. No one is taking notes of your effort but yourself. You're nothing but self-appointed to what you really care about.

That's the natural order of things. You cannot force others to care, and you can't force others to act. You can only be satisfied by you own daily effort with it's little notice of some result. You have a wonder-weapon in this never ending battle: Your thought, your reason, and your tongue.

Speaking wisely, is a very potent influence. Once you inspire someone else is not unlike a little private, landslide victory rewarding both. Give it some real chance and you will be surprised, I'm sure

Hi Yuval,

"I was hoping that such a thread will evoke some out of the box ideas, as wacky as they may be, and that someone of "ours" within the establishment, further roll some of it into it's memos."

That was pretty much the idea behind my An Engineer's Look at the Future of Energy blog. From the response to the discussion on Thorium Fission Reactors it is actually having an affect. So, it's not all wishful thinking, discussions here at CR4 may indeed make a difference in the long run.

Well done and keep up the good work.

P.S. If there is anything that you think warrants discussion on my blog and is not yet on the list, pleas, click on my icon and follow the send masu a message link. Leave me a message with as much detail as you can and I will happily add it to the list.

Thanks masu, so I will.

I guess, given my nature, I will wander from thread to thread, inclined to stay with the long-lasting most.

I gathered you're retired too. So, actually, we have more time on our hand, than the youngsters (It's all relative, of course).

yours, yuval

Very well said Yuval . I'll resist diverting too much from a seriously directed thread , but any cause requires winning peoples minds . I try in my small way to minimize waste in all it's forms , but I think I may be in a minority . An instant gratification culture is not the best launch pad for constructing a life-boat. It may not be impossible , one man initiated the end of the slave trade in Britain .Kris

...I may be in a minority...

Convinced minority is more powerful than a non-caring majority:

If you're a member of a convinced minority you'll take any opportunity presenting itself. If you're a member of the non caring, you're not likely to notice an opportunity as it pops, and furthermore, even if you see an opportunity, you're not likely to care.

The natural order of things. It was built that way.

Ignore the 'not' in my last post , it was a brain spasm ! Even I'm not that Jaded.

Cheers , Kris

It's like the serious magasines, revealing the truth on some popular politicians: those who are interested to read them, would never vote for such a person. those who should better know for who they vote, never read.

People with a clear mind, open for all visions and looking for some reason and truth are rare.

...open for all visions and looking for some reason and truth are rare...

Rare but existing. Ignorance is easy, because it's readily available. To learn you need to make some effort, not just for the understanding of a given context, but also for the comparison of given facts and opinions with the otherwise stated. Then you have to make your own mind.

But once you figured your path out, you implement the results of this knowledge, and that's much more effective than the attempt to figure out. It also has it's gratification for the "right" channeling of your efforts, instead of the frustration of battling up-hill, for something questionable.

this is bull....

Denial is a wonderful thing.

Wouldst thou care to elaborate on that.

This (#159) reminded me of the "So What???" post

#59 reminds me of the joke about someone who describes a town as 'the ass-hole of the world' . A local responds ' so you're just passing through then ?'.

...who describes a town...

In northern Israel, the approaching road to the town called "Afoola" is called "the ruler-road" to signify that it's dead-straight (It's run in a flat valley). So, accordingly, Afoola is often referred to as "the hole at the end of the ruler"

There are some great place names around the world , ther must be a book on them somewhere. Durham (UK) has a Pity-Me which sounds rather sad. There are plenty of '___ Bottom's in the UK . USA has some great ones. Phuket would have caused hilarity to English speakers had it not become known for such a sad reason. Brand-names of food products can cause international hilarity . I recall one of the major auto-makers missing a confusion over a new model name (they do exhaustive research) and it translated as 'small-dick' in Spanish . Whoops.

...Phuket... ? Didn't they protest to change it?

Remember the nice calligraphic way of writing air on a Nike running shoe some years ago.

Nobody at Nike saw that it was the arab word for Allah, ...

Then we have ADIDAS: All Day I Dream About Sex.

At dawn it dawns as sheep?

Seriously now: Why is the camel called the ship of the desert?

"I recall one of the major auto-makers missing a confusion over a new model name (they do exhaustive research) and it translated as 'small-dick' in Spanish . Whoops."

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Another faux pas: The Chevy Nova.

No va = "It doesn't go."

...this is bull....

The guest was correct: lookup "koosh" and you find nonsense.

The correct spelling is "Nubian Kush"

Hey , I mis-spelled Nubian Kush by one letter and nobody talks to me now !

Considering advances in science and engineering over the past century , do notions such as Helium 3 from the moon (and other seemingly far-fetched ideas ) mean that we could address the problem of waste handling by estimating a finite amount of waste to be handled ? A different approach is required for ongoing waste production and a total final amount to be dealt with. To be more explicit , it is almost impossible that in 100 years we would not have an alternative energy source ,or a means of dealing with waste currently produced . The problem then becomes 'what shall we do with x tonnes of waste produced meantime' . The moral choice is recoverable storage , to facilitate later processing. Engineers may come up with a solution , but the decision on what to do will be a political one . Before anyone cites individual action etc , I'd ask how many of us would want to pay a more realistic energy cost today ? Energy being produced on a profit basis , is the biggest barrier to implementing a way forward . None of what I suggest negates the imperative to find a solution , but the estimation of 'x tonnes' could be the most critical guess that is ever made because it will drive cost and political will. Without wishing to divert the discussion Yuval , would anyone out there like to hazard a guess for x ? Even wild off guesses would draw in people from fields other than nuclear (mining,logistics,space etc ) who may be able to make a contribution .

Kris,

What you suggest here, was indeed in relevance to what was bluntly asked on the original post:

"...- Should we get rid of it permanently, or is it likely to have some remote future use or benefit?..."

As to your: "...'what shall we do with x tonnes of waste produced meantime'...":

First, I think anyone can assume safely, that such an estimation as to the total amounts and type of materials, regarded as "present waste", can be made, only the political leaders might consider such estimation to be strategic reluctance, something worth being held confidential. Probably in order to avoid an open international discussion , as held here. I hope I'm wrong, but you make you own mind, as to the chances such info made public.

"...how many of us would want to pay a more realistic energy cost..."

Of all others, maybe this, indirectly, is the most political question, because it deals with collective public behaviour, made into a social and economic habit. Why this question alone may determine the political career of any political, sitting in office, or another, campaigning for office.

"...estimation of 'x tonnes' could be the most critical guess that is ever made because it will drive cost and political will..."

I totally agree, which makes me dread the future, given current political handling of such issues. I fear that what we need is not a new invented solution, but a new type of politicians who care who see their office as a humanitarian commitment and service, instead of a four-year career, a vehicle for personal fame and glory. Sorry.

"...Even wild off guesses would draw in people..."

I too share this hope.

How about a different strategy for communicating scientific information AND consequences to the public at large, without going through politicians. Some international publishing body, using the internet, that attempts to certify the most accurate body of knowledge on scientific subjects such as this, or global warming, etc.

This would be a a formatted type of presentation, where all scientific knowledge could be presented using COMPARISON as the basis for truth instead of semantics and one-sided arguments. Scientific knowledge can be gathered, and presented, simply and accurately, such that any person of sound mind can see the consequences for themselves, and not only discuss issues, but potentially vote on them, on an issue by issue basis.

This approach does not eliminate the need for politicians and government, but it does greatly clarify the decision support information, for both the scientific issues, and for the public support for each option. I have no doubt that there are so many 'vested interests' in energy, that issues, truth, accuracy, and consequences all become extremely clouded in disinformation and confusion. I do not seek to prevent the terrorists from having the knowledge any more than I seek to stop the Beast from having it. I seek truth, accuracy and scientific transparency, and let the public decide what is to be our future.

Chris

There have been many claims regarding the radioactivity and temperature of spent fuel. The following quote is taken from section E.1 of the nuclear FAQ by Dr. Jeremy Whitlock.

"Both the wet and dry forms of interim storage address the two short-term safety requirements of used reactor fuel, cooling and shielding, with relatively simple technology and inexpensive materials. The cooling, by either water or air flow, is required because used fuel contains a small inventory of fission products (created by the fission of less than 2% of the original uranium inventory) that continue to emit energy as they radioactively decay. In fact, immediately upon removal from the reactor core, a used CANDU fuel bundle generates about 10% of the heat that it produced in the core, but this figure drops to about 1% only a day after removal, and less than 0.1% after a year has passed. The average heat generation of a fuel bundle at this point (one year) is about 100 W -- comparable to a household lightbulb.

The radiation accounting for this heating creates a simultaneous need for shielding. About three metres of water are sufficient to absorb the radiation emitted initially by the used fuel, while in the dry-storage phase about a metre of concrete suffices. Unshielded, the radiation dose measured at a distance of 30 cm from a used CANDU fuel bundle, one year following discharge, would be about 50 - 60 Sv/h (5000 - 6000 rem/h) [5], which is lethal after a few minutes' exposure. The radiation level drops to about 1 Sv/h after 50 years, 0.3 Sv/h after 100 years, and less than 0.001 Sv/h (100 mrem/h) after 500 years. At this time the major hazard from the used fuel is no longer one of external exposure; for example, by these estimates, spending an hour about a foot away from a 500-year-old CANDU fuel bundle would result in radiation dose about 1/4 of the average annual background exposure, and thousands of times less than what is known to lead to physical harm".

I thought that perhaps a quotation from someone in the business would help bring some understanding into the group of what the actual condition of spent fuel is. It may not be glowing red hot as some have heard but it is warm and certainly dangerous for many years. It would be nice if we had some sort of economical technology for converting the relativel low temperature differences between fuel that had been out of the reactor for a while and the ambedient temperature into a usefull form of energy. A few thousand fuel bundles radiating 100 watts starts to add up. CANDU fuel bundles at 0.5 metres long are quite small compared to the fuel assemblies from the LWR and PWR reactors used in the US and many other nations.

how about not making anymore of it, and using what we have. you speak of space, but have failed to ask the right questions... 2 important ones for example: why is there hydrogen atoms randomly scattered about the universe? or more importantly, how did they get there? www.members.shaw.ca/mirth/ (check out the orange tab from the homepage)

What a complete deposit of procreating male bovine excrement.

Maybe I'm being a bit harsh with that but the guy that wrote the document you supplied the link for sounds to me like a poet's attempt to explain nuclear physics.