When a market for civilian power emerged, light water had a large head start, and by the time other technologies were ready to enter the market, light water was entrenched. Not only is the LWR used almost exclusively in the USA today, but this type, based largely on technology developed in the USA, is being used for about 80 percent of all the reactors built or under construction in the world today.’’

This happened because everywhere (except in Canada), military issues were the first to be considered In the U.S., in France and the United Kingdom weapons-grade fissionable material was in demand; in the United States naval propulsion was the main application. When these demands had been relieved or were no longer so pressing, civilian power emerged as the main consideration, and the important characteristics of reactors became cost and safety. After a market for civilian nuclear power was established, these concerns remained in the forefront. Very important in the development of nuclear power, though, was the early interest in military applications. The effects which followed from the military’s definition of “best” have been felt ever since.

While perhaps an appropriate decision at the time, it now seems that light water may have been an unfortunate choice.

I see the same thing happening in the drive to GenIV technology in that short-sighted concerns are driving the selection process with little thought to the long term consequences.

There is simply no rush to put GenIV reactors on-line, and doing so without careful evaluation of the consequences of the chosen design will be with us for a very long time.

David LeBlanc told me that “void worth refers to how much reactivity increases if the entire coolant turns to void. It is given in units of dollars or cents (strangely enough) where 1 dollar means you will enter prompt criticality. I think just about any sodium cooled fast reactor will have a positive void coefficient but there are many techniques to try to lower it (and negative doppler coefficient will usually save things). It is all quite complex because a void in the center of the core is much different than a void at the edge. Also things like how much Americium is present has a big effect. ”

David also referred me to this Power Point presentation.
http://www.neutron.kth.se/courses/GenIV/GenIVsafety.pdf

R. N.Hill states, “the void worth is much larger ($4 to $5) in conventional lFR core designs.”

Janne Wallenius states,” Positive void worth of 3–4 dollars acceptable if a prompt negative temperature feedback of -0.5 pcm/K is available (Doppler, axial fuel expansion).

Positive void worth of 7 dollars may not be acceptable with a Doppler feedback of -0.2 pcm/K.”

Several papers on the Information Bridge discus IFR designers efforts to lower void worth which all appear to also lower breeding ratios.

There is a rub. Exactly how high does the breeding ratio have to be before void worth becomes a serious safety problem? Can IFRs safely breed at high enough ratios to overcome their FI handicaps? The papers I have read on the subject seem to suggest that they can’t and that safe IFR breeding ratios may run as low as 1.07 to 1 . If you assert that IFRs can safely breed at higher ratios, where do you find the evidence?

And don’t think I am saying the situation for MSR/LFTR is a done deal ether material wise, only that the suite of problems might not be as large.

First, core geometry is basically a function of the first wall, and there is no question of core components cracking, swelling, and distorting as would be the case with a solid fuel core.

The first wall itself, (assuming a two-fluid design) would need to be neutron transparent, which of course would mean less damage would accumulate, and it would be in relative pressure equilibrium due to the presence of the liquid blanket, thus suffering less tensional stress, a major plus.

Also, the outer wall would be largely shielded by the blanket, which after all is there to absorb neutrons, and this would mean less radiation damage over any given time. In fact the use of ceramics on the outer wall might well be the way to go, where a fair amount of mass would be inexpensive and could draw on existing metal smelting materials.

Your presence and contributions here are fantastic. I am learning heaps from your contributions and others on your web site.

Barry, I want to say again that the lead article here is really helpful. I’ve just seen this video http://atomicinsights.blogspot.com/2010/04/c-span-studentcam-2010-grand-prize.html and thought “wouldn’t it be great if they had known about the relevance of Gen IV, as you’ve laid it out in the lead article, when they made this video”. Perhaps you could send them you article. I expect they are buried in offers of help, but an email from a Professor in Australia might get through.

I see a general move forward in acceptance of nuclear in USA, UK, and Australia. I believe Australia is approaching a ‘tipping point’ on acceptance of nuclear. Once it reaches it, there will be a substantial change of in the level of public support (or acceptance it is necessary) over a fairly short time period.

Transmutation – in this instance an atom changing from one element to another due to neutron radiation

Precipitation – in this instance elements coming out of solution in an alloy

Segregation – the property of these precipitated atoms to clump together with their own kind.

These are concerns because these actions lead to grain-boundary defects that can lead in turn to mechanical failure, due to loss of strength or spontanious cracking.

Some alloys can be treated when this starts to happen by a processes improperly called annealing in the nuclear industry (I say improperly, because they use the term as a catch-all phrase, for several different processes, of which proper annealing is just one) and returned to a serviceable state. Others cannot be short of remelting, and must be scrapped.

There are other considerations like hydrogen and helium sorption that can lead to embitterment.

Again I reiterate: this is not going to stop Gen IV in its tracks – I only bring it up because I don’t believe that there is enough work on going right now on this matter and it is an area that should get more attention.

Look CANDU fuel channels supposedly were proven in the NRX, which was the highest flux neutron source in the world at that time, yet they started to fail prematurely in service after several had been built. They all had to be replaced and this almost killed off the design where it stood. Material issues are not trivial. They can jump up and bite you in the ass when you least expect it.

DV: Please translate meanings in a materials context of “transmutation,” “precipitation,” and “segregation.”

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Four or five years ago, there was great excitement over molybdenum-rhenium alloys for core structural materials until it was found that under certain conditions transmutation was leading to precipitation and segregation that was unacceptable,

On the other hand two composites types are being developed for incore application: carbon fiber carbon composite (CFC), and silicon carbide fibre composite (SiC/SiC.) Irradiation effects studies have been carried out over the past few decades yielding radiation-tolerant CFC’s and a composite of SiC/SiC with no apparent degradation in mechanical properties to very high neutron exposure. So ceramics might come through for us.

The point is that there (IMHO) not enough work being done in this area, because of a dearth of high-flux reactors, and this is not a good thing.

I would really be interested in what the relevant folk in SCGI say in response to DV’s comment about the “materials issue.”

I will put it to them, as I hesitate to debate further on this issue with a materials scientist…

to implement nuclear power in Australia in such a way that it will supply electricity at the lowest possible cost over the long term.

I’ve written this here on more than one occasion and been answered by [crickets] so now I’m going to shout:

YOU GUYS ARE SITTING ON 25% OF THE WORLD’S KNOWN RESERVES OF URANIUM. MANY OF YOUR ASIAN TRADING PARTNERS BUILD REACTORS, BUT HAVE NO DOMESTIC SUPPLIES OF FUEL.

CUT SOME DEALS, FOR PITY’S SAKE

This highlights the enormous commercial risk involved in developing new technology. It points out the problems that commercial firms would have with developing Gen IV designs and taking them through to the stage where they are fully commercial. This supports my argument, that it is going to be a long time until Gen IV is an option for Australia. I hope USA, France, Russia, China, India and Korea will continue RD&D, and Australia should be a part of any cooperative international effort. In the meantime, I believe we need to focus on how we can get nuclear started in Australia. I believe the focus needs to be on implementing nuclear in Australia in a way that will give us least cost electricity over the long term. That should be our primary focus. We need to keep it simple like that. When people ask questions about safety, nuclear waste, proliferation, etc, we can answer those questions, but let’s just get a really simple objective:

to implement nuclear power in Australia in such a way that it will supply electricity at the lowest possible cost over the long term.