This is a recent discussion and eye opener for those who wish to know more about which reactors are competing with LFTR. It is also a basic crash course on why the LFTR is better than a Sodium-cooled Fast Breeder reactor.
Energy from Thorium is the voice of Kirk Sorensen
Energy from Thorium:
I strongly disagree with the content of this letter. The sodium-cooled, fast-spectrum breeder reactor is a bridge to nowhere. It has derailed thorium reactor efforts before and if allowed to continue it will do so again. It will be more expensive than current nuclear reactors which are already too expensive. I am d…isappointed that so many people that I consider good friends signed this letter.
Independence Day Letter to President Obama – Re: Nuclear Energy Summit | The Energy Collective
Joel Riddle: Hmm, they probably should have left out any specific technology in their letter. I agree with what I saw as the main idea – that America HAS to make a commitment to nuclear energy as a whole.
Energy from Thorium: But the direction they propose–the sodium fast-breeder–has been tried and has failed economically over and over and over again. There are legitimate safety concerns with the design, and its overall goal (reducing the cost of the fuel) is already a small cost in nuclear operation anyway.
Jack Gamble: Given the amount of $ we send up smoke stacks and out tail pipes, I don’t see how any reactor, be it LFTR or FBR would be considered too expensive. Why not do both?
Given the state of all things energy, I don’t think one nuclear technology will derail another even though it did occur in the past when the two technologies were in their infancies
I think the far more likely problem would be antinuclear activists and dirt burners derail all nuclear work as a whole. In-fighting between Uranium and Throium proponents hurts both IMO and can only help the wrong people.
Joel Riddle: I would definitely say that thermal spectrum thorium reactors would deserve some “air-time” at this summit, and I dare say many of the signatories would agree with that sentiment. If America doesn’t develop a LFTR first, I would imagine that India will.
Robert Margolis: I consider the letter as the impetus for furthewr discussion rather than a final plan. Upon getting nuclear going again in the US, there will be opportunities to investigate thorium. Lightbridge is already doing a lot work on the thorium cycle.
Adam Freidin: I think a nuclear summit would be nice, it’s not a forgone conclusion that it would result in a sodium breeder.
Let’s have the summit. Then we can discuss the pros of LFTR and the cons of fast-spectrum breeders.
@Robert: I thought lightbridge was going the route of solid-fuel thorium cycle, which has worse spent-fuel and reprocessing issues than uranium? EFT raised some serious concerns in this regard about lightbridge that haven’t gone away.
Jim Stevens: Kirk: What are your thoughts on Hyperion and the small reactors mentioned in this letter?
Energy from Thorium: The war between fast-spectrum and thermal-spectrum is a war between plutonium and thorium. It’s really just about that simple. Although I understand that most people don’t know what that means and don’t care, we should care, and here’s why. If we take the fast-spectrum, plutonium route, we drastically limit the potential expansion of nuclear power in a future world. The difficulty of taking this approach will sop up all available funds just like it did in the 50s through the 70s. There won’t be any room for thorium in this scenario, no matter how well-intentioned people are at the outset.
It is very much like the war between DC electricity and AC electricity a hundred years ago. Most people at the time had only a vague idea what electricity was or how it worked. Among those who knew, there was a sense that DC was more straightforward and easier to understand, and indeed it was. AC was more complicated. But AC had a profound advantage that was worth fighting for. It was extremely versatile and could be transformed easily and inexpensively in ways that DC simply couldn’t. If DC had won the “war of the currents” then most of the country wouldn’t be electrified today. Only in big cities with power generation close to the consumer would electricity be available.
By extension, there is a “war of the spectra” and though it may seem esoteric it is not. Thorium and the thermal-spectrum and the salt-reactor technology is versatile and adaptable. Plutonium and the fast-spectrum and solid fuel is rigid, expensive, and difficult. If the plutonium fast-breeder again becomes the dominant reactor in future planning, it is a win for fossil fuels as surely as solar and wind power. Because we won’t build 1000s of those reactors. They are simply too dangerous. We will build a handful and spend billions trying to get them to behave properly. It will be much like the fusion effort.
Thorium, the thermal-spectrum, and liquid-fuel are the “AC electricity” of the nuclear industry. They’re different, poorly understood even by nuclear engineers, but versatile and capable of taking us to the widespread nuclear-powered energy economy of the future.
Joel Riddle: Disclaimer: I am “merely” an ME, not an NE. Kirk, it seems that the bottom line of what you are saying is that the advantages of a LFTR versus all fast-spectrum reactors need to be articulated in a form that could be easily understood, even by non-technical types.
If the LFTR is going to happen in America, it will most certainly require some level of government support, even if it received immense private sector support (maybe through the Gates Foundation or Intellectual Ventures? Assuming they could simultaneously back the TWR and LFTR).
So, the message needs to be clear and easily understandable, and it needs to be heard by the right people.
How would you rank “competing technologies” in terms of their distraction from thorium/LFTR deployment (SMRs, the IFR/sPrism, the TWR, or any other reactor designs)?
Energy from Thorium: Joel, I’m an ME too, and almost an ME and NE.Yes, this is a story that needs to be told and told clearly.
Energy from Thorium: ME = mechanical engineer
Robert Steinhaus: Pushing Liquid metal-cooled, fast-spectrum technology in the letter to President Obama just represents one more large opportunity loss for Thorium Fuel Cycle and holds off for another miserable decade the commercialization of Thorium Fuel Cycle in LFTR and the development of the safe and cost effective technology that America and the developing world needs to live in energy abundance and peace.
Lars Jorgensen: I think we need to look to find synergies with other approaches to jointly support funding of key aspects of the R&D we need for LFTR.
Specifically, Dr. Peterson’s AHTR has the heat exchanger, salt pumps, in common. It may also have the He purge and tritium isolation in common. There may be other choices for him but I think he likes LFTR long term so he may be willing to tilt his selections to make them common with ours.
IFR extraction of TRU’s has some commonality with our central repository processing especially in extracting the Am, and Cm components. I doubt we will have any influence with this group but we can still use their results.
One could create a recycling flow to process LWR wastes that looks an awful lot like the flow we want for LFTR (of coarse with some extra steps to convert the solid fuel to liquid fluoride salts). The first stage could extract the gases and noble metals and uranium. The second stage would separate the TRUs from the salt seeking fission products. This could be a way to do the R&D we need for the chemical processing portion of LFTR without engaging in a battle royal with IFR etc.
We still need funding for a prototype reactor itself that we will have to win on our own but by getting some of the R&D completed jointly with others we can reduce the funding required to get the reactor running.
Energy from Thorium: Lars, if we lived in a logical world I would totally agree with you. Unfortunately, the list of supporters of fast-breeders is long and worldwide. This is mostly because of the billions that have already been expended in the pursuit of plutonium breeders and the past experience many of these people have with this technology. There is no such huge expense or experience with thorium reactors, thus our list of advocates in the nuclear industry is far smaller. But we have the right answer. Thorium reactors can operate in a thermal-spectrum that is vastly safer than the fast spectrum. Only thermal-spectrum reactors can operate in their most-reactive configuration, and that is a huge safety feature.
Lars Jorgensen: So it really comes down to a political call on how do we get sufficient funding to make LFTR a reality. I’m not particularly worried (within limits) about how much funding solar,wind, or uranium reactors get so long as we get sufficient funding.
Daniel Riggs Fielder: The safety issues are paramount, feasibility aside. One mishap is all it would take to sink nuclear power for yet another 20 years. The fast breeder reactor is more of a threat to thorium than wind and solar ever will be.
Robert Margolis: Fast reactors have good safety features as well. Not sure attacks on fast reactor safety will help the overall cause. Please remember that Vogtle 3/4 and other reactors in COL stage are neither fast reactors or thorium. If the renaissance is not started with these light water reactors we’ll all be waiting a long time or be working in Asia. 
Robert Steinhaus: The US cannot currently build LWRs that it pioneered at the dawn of the nuclear age in commercial sizes without help from foreign industrial nations. Large forgings like Reactor containment vessels on the order of ~600 tons are beyond the industrial infrastructure that currently exists in USA. The queue to obtain heavy commercial forgings from … Japan Steel is substantial and will limit the rate at which the US nuclear renaissance can happen. Japan Steel currently can build a total of about 4 LWR reactor vessels per year in their facility for all domestic and international customers. Areva Newport News hopes to make heavy forgings eventually but it is not clear at this time whether the facility will be able to make modern commercial forgings (~600 ton) for current NRC certified commercial reactors. LFTR does not require heavy forgings to be safe (everything in the primary loop operates at near atmospheric pressure). LFTR could be built in America today without foreign industrial help given current US industrial infrastructure. Manufacture of LFTRs in the USA could be practically scaled to permit LFTRs to replace the electricity produced from all US coal fired power plants in less than a decade.
http://www.bloomberg.com/
Energy from Thorium: Robert, I would disagree that fast reactors have good safety features. By design, they eliminate many of the physical mechanisms that contribute to a negative temperature coefficient of reactivity. This is troublesome, as are the contrary “desirements” between controllability and breeding ratio. One wants a softer spectrum and the other wants a harder spectrum.
Then again, fast reactors may have significant economic advantages when it comes to the nuclear battery approach, and it doesn’t look like we need the government to help with that, as Toshiba/Westinghouse, TerraPower, and Hyperion seem to be doing it on their own.
Energy from Thorium: Carl, read WASH-1222 and Weinberg’s own memoirs. The fast-breeder killed thorium.
Barry W. Brook: I think it is dead wrong to call it a ‘war’ between Pu and Th, and this is among my deepest seats of disagreement with Kirk (although we agree on most things). I want to see both the FBR and the MSR succeed, and we should be encouraging both. Denigrating one as a ‘dangerous’ competitor of the other is totally fraught with risk.
Robert Margolis: EBR-2 (the basis for IFR) had a strong negative temperature coefficient and the liquid metal coolant is harder to boil off than water in a light water plant. As one who had worked at a thorium fueled reactor (Ft St Vrain used thorium as fertile fuel due to the epithermal neutron spectrum), I certainly believe in thorium’s potential. However, FBRs are as safe or safer than light water reactors. To call them unsafe may throw ammunition to those against the AP-1000, EPR, and other designs that are the current leaders in the renaissance.
I see the effort as getting the first movers (i.e., light water reactors) built, then focus on the Gen-IV technologies.
Energy from Thorium: The EBR-2 had a negative temperature coefficient because the core was so small. Larger cores had positive temperature coefficients.
Barry, I am open to having my mind changed on LMFBR safety, but I have yet to see the analysis that would let me sleep well at night if an LMFBR was sited anywhere near me. The basic mechanism of sodium reactivity leading to an intrusion of moderator (water) leading to supercriticality is far too troubling for my taste.
The letters to congress and the president have made no mention of LFTR. It appears the course being advocated is to fund R&D for fast reactors and to be silent on LFTR. We have safety and cost doubts about fast reactors. Fast reactors have had the opportunity to build several prototype machines thus far. I want to see a 20x growth in … See Morenuclear power but that requires 20x more safety than current LWRs and a cost lower than coal. Are you making those kind of claims for fast reactors?
I agree that it would be better for us to argue for funding both and see where things stand after some R&D has been spent. Are you game to argue for equal funding for LFTR and IFR? As things now stand it looks like IFR is arguing for all the funding.
Where did hear that large core Breeders are positive? I thought that the reactivity control was through the fuel and … See Morecladding expansion. Assuming that a larger reactor uses the same size fuel rods, just more of them I don’t see how that would change the coefficient.
I think that the IFR is just fine safety wise. My biggest concern is that it requires 20% enriched Uranium. That just doesn’t sit well with me. 20% > is in the weapons usable range. Being able to run off with a fuel rod and make a bomb out of it without processing is a horrible risk. (400kg is a tough but not unmanageable amount of material to steal)
I … See Moretried to engage Yoon Chang on a discussion about thorium. He refused to believe it could breed, and he refused to look at the data about the corrosion resistance of the container materials. He wouldn’t read the technical references I sent him. I emerged from the encounter very unimpressed with the technical open-mindedness of the IFR advocacy group out of GE and Argonne.
If there is one thing that is certain about sodium-cooled fast reactors, it is precisely that they are *controversial* !!
Antinukes who might be prepared to accept a new generation of LWRs will scream their heads off at the prospect of serial FBR construction – that is 100% guaranteed !
Of course their opposition is baseless, to a large extent, but its the politics that rules.
To that extent, the biggest advantage of thermal spectrum molten salt reactors is simply that they don’t carry the old stigma associated with FBRs.
Beyond that, there are of course several significant technical advantages of thermal spectrum MSRs over FBRs.
But IMO, it is probably more productive to play on this controversy issue with FBRs, if we want MSRs to win out.
In this respect, it would be helpful to emphasize MSR designs that accentuate the differences relative to FBRs – not just the neutron spectrum, but also fissile enrichment level well below that used in FBRs.
Those brilliant letter signatories really need to re-think their argument & position, IMO.
I don’t understand how the IFR would develop … See Moresuch a large isotopically pure fissile inventory. Shouldn’t we get a mix of Pu239, 240, and so on? And in a moving-reflector design like the 4S, isn’t the inventory mostly U-238, with the Pu burning or transmuting as it goes?
If sodium is your concern, what’s wrong with lead-cooled designs such as those used on Russian subs for many years?
FWIW, the BN-600 (a sodium pool design like the IFR) apparently achieved a 75% capacity factor over a period of 15 years, with the best core configuration achieving
http://www.energyfromthori um.com/forum/viewtopic.php ?f=5&t=136
#2, the Pu quality is superb in a fast spectrum because Pu-240 doesn’t form NEARLY so often as it does in the thermal spectrum, and because Pu-240 can fission directly in the fast spectrum. So most of your Pu is 239 and it can be chemically isolated from the rest of the reactor to provide very high quality material.
#3, lead is very corrosive. Sodium is not corrosive, just extremely reactive. By contrast, halide salts are not reactive at all, but can be corrosive if placed in the wrong container materials.
#4 How many BN-600s do we see out there? Not many. FBR programs in the US, Japan, and France have all run aground in the last 30 years. Not for a lack of money expended.
“Sodium Void Coefficient
“Sodium coolant in the reactor expands as the reactor heats up or the number of sodium atoms decreases. This results in a decrease in the number of neutrons absorbed. While this is small in power reactors, changes resulting from other considerations are important.… See More
“One of the primary safety considerations in the design of a fast-breeder system is that loss of part or all of the sodium will not result in a net positive increase in reactivity. Such a condition might result from a rupture in the sodium system, blockage of flow in coolant channels causing sodium vapor formation, or the introduction of a significant amount of entrained gas. Regardless of the cause, the effect is to produce a general hardening of the neutron spectrum because of the reduction of the number of scattering collisions in the void region due to the removal of coolant nuclei. Also, with the removal of the sodium the log energy decrement (xi) is reduced, contributing to the harder flux. Figure 10.8 shows how eta increases with energy, indicating that there will be more neutrons released per fission at higher average energies. It can be noted that the increase for 233U is less than that for 235U or 239Pu. This effect tends to produce a negative reactivity change in fissile material. On the other hand, when fertile material is present, the harder spectrum causes more fissions and consequently a positive reactivity change.
“Leakage (L^2*B^2) is increased because sigmaS is decreased by removal of the sodium atoms from the voided volume. Thus, the transport mean free path is increased by the reduced scattering cross section. Leakage is related to neutron current flow, which is, in turn, proportional to the flux gradient. A volume near the center of the core is much less affected since (partial phi/partial ybar = 0) while the slope increases toward the outer boundaries, increasing leakage from peripheral volumes.
“In small cores B^2 is large and the leakage overrides the positive reactivity effect of the hardened spectrum. In large power reactors this may not happen because B^2 is too small to allow the change in L^2 to have sufficient effect to override the positive effect of the harder spectrum. A local void at the center of a core tends to produce a positive contribution to reactivity due to the small neutron current flow at this location, but near the outer boundary of the core the effect would be negative. Overall, then, the result in large reactors is to produce a positive coefficient of reactivity.
“Positive void coefficients are of concern because the void might cause autocatalytic propagation through the whole core and a resulting loss of coolant flow accident could be even worse.”
“Construction is well advanced on Beloyarsk-4 which is the first BN-800 … It has improved features including fuel flexibility – U+Pu nitride, MOX, or metal, and with breeding ratio up to 1.3 … operating cost is expected to be only 15% more than VVER.
Regarding Pb-cooled designs, they say:
“Russia built 7 Alfa-class submarines, each powered by a compact 155 MWt Pb-Bi cooled reactor, and 70 reactor-years operational experience was acquired with these.”
Reactivity Changes in Fast Reactors
Small changes in reactivity can be introduced into a fast reactor in much the same fashion as into a thermal reactor. These allow power increases with long periods. The fast fission in 232Th or 238U causes the fraction of delayed neutrons to be slightly larger in a fast core than a thermal core. Table 10.6 shows delayed neutron fraction for various fissile and fertile species. Since the fraction of delayed neutrons from 232Th and 238U is so much greater than that from thermal reactor fuels, a smaller reactivity change will give the same period (see Fig. 10.5).
Image
The prompt neutron lifetime is the order of 10e-7 s for a fast reactor compared to 10e-3 s for a thermal core. This results in even a faster rate of increase in flux and power for a prompt critical excursion, making prompt criticality all the less desirable.
Some of the reactivity changes discussed earlier in this chapter do not occur in fast reactors. Since there are no thermal neutrons, changes in temperature alone do not change the neutron spectrum. The 135Xe and 149Sm cross sections are fairly small for fast neutron energies, so their effect can be neglected.
Three significant factors affecting reactivity changes of fast reactors are:
(1) The Doppler effect
(2) The sodium void coefficient
(3) Fuel rod expansion
Doppler Effect
During a prompt critical power excursion in a fast reactor it is important to have an inherent mechanism for the rapid insertion of negative reactivity. There is no time for a mechanical scram system to operate. The Doppler effect may provide significant negative reactivity. As the temperature increases in the material through which neutrons are diffusing, there tends to be a broadening of any resonance peaks. This is because the velocities of the target atoms can add to or subtract from the neutron velocity near the resonance region, broadening the resonance peak but keeping the area under the curve constant.
The net reactivity temperature coefficient depends to a large extent on opposite Doppler broadening of resonance peaks in the fissile and fertile fuel. Increasing temperature results in increased absorption in the fissile material (positive coefficient) and decreased absorption in the fertile material (negative coefficient). Therefore, there must be a limit to the ratio of fissile to fertile material in order to maintain a negative coefficient of reactivity in the fuel.
The important resonances involving the Doppler effect in fast reactors in the range of 0.5 to 20 keV are on the lower tail of a fast-reactor spectrum. The softer the spectrum, the more neutrons there are in this low energy region and the larger the Doppler effect. A metal-fueled reactor has the hardest spectrum, followed by carbide fuels and then oxide fuels.
In a small metal-fueled reactor the Doppler effect is not significant, but in reactors using a lot of sodium a significant number of neutrons reach the 0.5 to 20 keV range. This results in the negative temperature coefficient arising from the Doppler effect. Furthermore, it requires extremely accurate data to determine the lower energy neutron flux and the reactivity changes. The addition of BeO to large fast reactors has been studied in some detail (Reference 8). The purpose of the BeO is to degrade the energy spectrum and thus enhance the negative Doppler coefficient.
Table 10.7 shows two cores, where case B has added 8.3 volume percent BeO to soften the spectrum. Note that the mean neutron energy is 0.23 MeV for the hard spectrum of case A and 0.10 MeV for the soft spectrum of case B. The Doppler coefficient is twice as big for case B. Also, delta-k for sodium loss from core and blanket is -0.0051 compared to a positive value of 0.0070 for the hard spectrum. Figure 10.7 shows the dynamic response to the addition of $1.50 reactivity in 10 ms to the two cores. For case A fuel failure would occur probably followed by boiling and expulsion of sodium from the core before the scram could act at 400 ms. The fuel in case B will survive this reactivity insertion, the major difference being in the values of the Doppler coefficients. Note the magnitude and short duration of the power pulse in both cases.
The introduction of BeO into a reactor may prove difficult, practically, because the potential power generation of the reactor will be reduced due to the lower fuel volume.
The Doppler coefficient can cause a reverse effect in a cold sodium accident when the sodium temperature drops. This could occur with a large power reduction, not accompanied by a reduction in flow rate, or if a slug of cool sodium is pumped into a hot core unintentionally.
The Doppler coefficient is linked to the sodium void coefficient because of the hardening of the flux due to a void. This can reduce the Doppler coefficient by as much as a factor of 2.
The use of ceramic fuels with their softer spectrum than metallic fuels does penalize the breeding gain and the doubling time in a fast reactor. However, the long burnup times make ceramic fuels desirable. Lower breeding gain along with the Doppler effect must share the economic penalty.
Fuel Rod Expansion
Lateral expansion of long fuel pins with temperature increase leads to a reduction in fuel density. This results in a leakage of neutrons and a decrease in reactivity. In reactors fueled with pellets it may be difficult to calculate this reactivity because in accident conditions fuel meltdown could lead to an increase in reactivity.
In fast reactors control by means of neutron absorbing control rods may not be satisfactory because of their low rod section. However, in the Enrico Fermi fast breeder reactor, control rods using 10B were used. The Fermi reactor used two rods for control and eight rods for shutting down. In other fast reactors, such as Dounray in England and EBR-II, fuel assemblies are moved in to increase reactivity and out to decrease reactivity. A third means of control is by moving the reflector in or out of the reactor in a manner similar to the fuel movement.
Xe-135 has two major differences from Sm-149. The first is that it is radioactive. It goes away if you leave it for awhile. It has a half-life of about nine hours. Sm-149 doesn’t go away. It is not radioactive. It is stable.
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