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Rod Adams's picture
President and CEO Adams Atomic Engines, Inc.
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Russia Continues Sustained Fast Breeder Reactor Effort

On June 26, 2014, the 60th anniversary of the start of the 5 MWe Obninsk reactor that was the first reactor in the world to routinely supply electricity to a commercial power grid, Russia started up the latest in a series of sodium-cooled fast reactors, the BN-800.

This new nuclear plant is an evolutionary refinement of the successful BN-600 that has been operating in Russia since 1980 and “is said to have the best operating and production record of all Russia’s nuclear power units.”

Here is a quote from a promotional brochure about the project published in 2011 by Atomenergoproekt, the joint stock company that built the power plant.

BN-800 power unit (under design) for Beloyarskaya NPP accommodates all principal concepts and solutions used in its predecessor BN-600, substantiated by over 20 years of its successful operation at high performance (capacity factor 80% at efficiency 42%).

BN-800 Power Unit is designed primarily for the production of heat and energy. The Power Unit as part of the grid operates with constant rated load (basic mode).

However, BN-800 characteristics and physical features dictate its multi-purpose usage. Viz, the reactor is used for:

  • electric and heat power generation
  • plutonium consumption and, if necessary, production
  • processing of long-lived supertransuranics accumulated in the radwastes of reactor of any type
  • production of isotopes.

No other reactor type combines so wide a range of functions.

Equipment of the reactor and its system involved in the handling of fuel assemblies containing isotopes and supertransuranics is designed to perform the above-mentioned functions.

The system builds off some of the successes of fast reactors designed and operated in Russia and the rest of the world and also incorporates features that avoid some of the characteristics that have led to failures in fast reactor programs. In other words, the BN-800 is the result of learning and the progress that can be made with sustained effort in any challenging, but potentially rewarding field of endeavor.

As shown in the below process heat flow diagram, the BN-800 uses a large pool of sodium and three separate heat transfer systems to provide passive safety. This is a concept that is similar to the one that was well-proven in more than 30 years of operation and testing at EBR-II and at previous BN-series reactors.

BN-800 Process Heat Flow Diagram

BN-800 Process Heat Flow Diagram

The BN-series reactors continue to use oxide fuels because they have achieved reasonably good results with that type of fuel and the responsible designers do not see any compelling reason to change. My friends who remain strong advocates of the Integral Fast Reactor have convinced me that a new fast reactor program started today should carefully consider the use of metal alloy fuels because they enable the use of an improved pyroprocessing technique for recycling the used fuel rods. It would be more difficult for a program that has a large investment in the capital equipment and human knowledge required for manufacturing and recycling oxide fuels to make that revolutionary technology choice.

While reading a terrific biography of Leo Szilard titled “Genius in the Shadows”, I found the following quote that illustrates the confused view of nuclear energy that is prevalent among the portion of the American intelligentsia that write books and perform historical research and commentary. It is relevant to this story about incremental progress in fast breeder reactor development.

Szilard’s faith in the peaceful benefits of atomic energy has certainly been rewarded in the development of medical technology, although his hope that nuclear power would help developing countries to prosper has proven impractical. Overstated, too, was Szilard’s faith in his breeder reactor, which has proven to be a dangerous and costly electricity producer in every country that has tried to build one.

My answer to the author of that passage is that virtually every technology ever devised by man would have been considered a costly failure if the inventor gave up after trying to “build one“. As the old schoolyard saying goes, “If at first you don’t succeed, try, try again.”

The post Russia continues sustained fast breeder reactor effort appeared first on Atomic Insights.


Spell checking: Press the CTRL or COMMAND key then click on the underlined misspelled word.
Bas Gresnigt's picture
Bas Gresnigt on Jul 1, 2014

World Nuclear shows a long list of tried and closed Fast Neutron Reactors.*)

Only communist Russia (now 2) and China (1) have operational reactors.
That are also the only big countries in which:
 – cost price; and
 – environmental damage
have a total different meaning…

*) The list is not up-to-date; only regarding the closure of reactors.
E.g. The list indicate that Monju (Japan) still operates while it is in fact closed.
Started in 1994, the plant operated less than 2 years.
Now a commission studies how to decommission it.

Robert Bernal's picture
Robert Bernal on Jul 2, 2014

I really enjoyed reading Charles Till’s book about his work in the development of the IFR. Obviously, it’s not the tech, but the political difficulties which sent the U.S. backwards by the many decades. He also stated the chilling truth about how politics can destroy something good (on bottom of pg 47). The silly president (Clinton) said at his SOTU “We are eliminating programs that are no nonger needed, such as nuclear power research and development”. Hopefully, future presidents won’t be so stupid!

Thanks for keeping us up to date about all these different reactor designs being developed around the world.

Robert Bernal's picture
Robert Bernal on Jul 2, 2014

China and Russia (and any other country that builds a fleet of such meltdown proof reactors) will become the powerhouses of the world. Meanwhile, we’ll be sitting ducks with nothing to power us but a few (by then, broken ???) solar panels and wind turbines.

Nathan Wilson's picture
Nathan Wilson on Jul 2, 2014

Don’t forget India, they also have an active faster breeder program.  Their 500 MWe sodium-cooled prototype at  Kalpakkam is expected to come on-line later this year.

So really, the fate of breeder technology is a reflection of the rest of the nuclear industry.  Those nations which lack adequate fossil fuel capacity like nuclear energy (with the exception of Japan).   Those countries with strong and well supported fossil fuel industries are not very interested in nuclear power (with renewables as a carrot-on-a-stick, held out before a gulible public, they can keep burning fossil fuels indefinitely).

Bas Gresnigt's picture
Bas Gresnigt on Jul 2, 2014

France lacks adequate fossil fuel capacity and left breeder technology after spending endless money and many years to the experimental Phenix reactor and then the demonstration reactor Super-Phenix.

Nowadays, countries with non-friendly neighbours that have nuclear or the capability to develop soon, tend to start with nuclear. It creates nuclear know how which can be used in case a nuclear weapon becomes urgent (e.g. Arabic countries in response to Iran; some tendency in Australia which feels the hidden agression of China as demonstrated in the S-Chinese sea).

Bas Gresnigt's picture
Bas Gresnigt on Jul 2, 2014

The facts show those are no success, even not in Russia despite great dedication:

They built three such reactors (first operational in 1950s, third in 1969).
Then continued with building only one successor, the BN-600 operational in 1980 which successor is now 44years old so near the end of its life; and
Then again continued by building only one successor, the BN-800 (only slightly bigger).

If it was a financial success they would have started to build a fleet after the first decade of experience with the BN-600 (so in the nineties).

So they just don’t want to kill the program, probably also because of the military interest.

Western world
I assume you know the huge financial disasters / tragedies in France, Japan, Germany, …

Do not see any (indication about) improvements, which may change that picture.

Rod Adams's picture
Rod Adams on Jul 2, 2014

@Nathan Wilson

I would put the line of demarkation in a different place. Those nations that have technically compenent, respected advisors who can do math in decision making or decision influencing positions like nuclear energy. Several of them – Sweden, France, Russia, India, South Korea, China, Iran, the UAE, Saudi Arabia and others are keenly interested in building and operating nuclear power plants and taking advantage of their impressive energy output. 

Those nations that are dominated by a love of money rather than a love of humans seem more interested in maximizing profits for their already wealthy members who have learned to prosper in a hydrocarbon-based economy. Those nations tend to have decision makers who think that laws and policies trump math and thermodyamics.

Some of the countries that can do math are not admirable and are also in the nuclear game for the benefits that it can bring to people at the very top, but at least they have not ignored the technical reality that fission is superior to combustion in a number of applications.

Sadly, at least one of the countries that recognizes the value of nuclear energy would prefer if only its friends used the technology, so it has invested time and money supporting movements that discourage nuclear energy by spreading fear, uncertainty and doubt.

Rod Adams, Publisher, Atomic Insights

Robert Bernal's picture
Robert Bernal on Jul 2, 2014

WE need to standarnize the production, maintainence, reprocessing and fission isolation of whatever safest high temp nuclear (or combination of different reactors for different purposes) or the world will have to succumb to inadequate energy supplies (and continued excess CO2).

The only tradegy in France, so far (that I remember) is that people are afraid of a little bit of wastes. The one in Japan is irrevelent (to advanced nuclear) and the costs are also irrevelent, as they do NOT include the externalized costs of fossil fuels (which is still the majority of energy supply no matter how many times solar and wind advocates say it is not). Once the CO2 tax is in place and people realize that a few wind turbines and solar panels will not power all of the world, (and that nuclear can be even safer) they will want nuclear. When they want nuclear, then it will happen.

Bill Hannahan's picture
Bill Hannahan on Jul 2, 2014

I believe that all fast neutron solid fuel reactors should be immediately shut down and defueled, because they have not been proven safe against high reactivity rate super prompt criticality accidents, by fundamental principles of physics. This has been discussed before.

Here is an interesting video of the destruction of the BORAX II reactor by a super prompt critical burst.

Here is an essay providing a FASCINATING inside view of the project. In addition to info on the
BORAX project, it touches on the EBR-1 meltdown, the politicization of nuclear R&D, and the importance of good public relations.

Rod Adams interviewed the author here.

Now imagine running this experiment using a BN-800 core, which is different in many ways.

1… 120 tons of fuel.
2… 20% enrichment vs. 5%
3… Sodium coolant vs. water coolant

In water moderated reactors, neutrons loose speed colliding with hydrogen and oxygen atoms making them more likely to be captured by a uranium atom. In fast neutron reactors the density of fuel atoms is high enough that a fast neutron is likely to be captured and cause a fission before it leaks out of the system.

In a fast neutron reactor, neutron lifetime is about 1000 times shorter than in a thermal reactor, making extremely fast power rise times, and nuclear explosions, possible.

As water is ejected from a thermal core like
BORAX II, the average neutron speed increases, reducing the probability that a neutron will cause a fission, thus reducing the multiplication factor and ramp rate of power, slowing and eventually terminating the pulse.

Sodium is a weak neutron absorber. As sodium is ejected from the core of a solid fuel fast neutron reactor, it makes more neutrons available for fission, accelerating the ramp rate of power, the exact opposite of what is desired.

Supporters of solid fuel fast neutron reactors claim that they can probably contain a very low reactivity rate criticality accident, but they  have  not analyzed a high reactivity rate accident, and they have not proven that a high rate accident is impossible.

I believe that a high reactivity rate criticality accident in a
solid fuel fast neutron reactor could vaporize the entire core and eject it into the atmosphere, creating an accident an order of magnitude or more worse then Chernobyl. This would harm billions of people, not from radiation, from killing nuclear power for another generation or two.

Solid fuel fast neutron reactors are complex machines requiring a great deal of time and money to build and maintain. Their kWhr’s will be expensive even if the uranium cost is negligible.

Simple molten salt reactors can be mass produced at low cost and operated in such a way that the waste stream is only fission products, waste storage time less than 500 years, by recycling plutonium and other actinides until they fission. They use uranium  more efficiently than conventional reactors, making sea water uranium affordable and unlimited for at least a few hundred years.

Why make a Faustian bargain when there is no upside to the bargain?

I support R&D for fast and thermal neutron molten salt breeder reactors because I believe they can be proven safe from high energy criticality accidents from basic principles of physics. Fuel atoms and coolant atoms are mixed on the atomic scale, and I see no way to rapidly eject the coolant atoms and concentrate the fissile atoms.

To prove fast neutron solid fuel reactors are safe, model an accident that envelopes all possible criticality accidents. Start with a core early in startup, very low power, K slightly above 1.0 now crush the core into a pancake in 0.01 seconds, squeezing out all the sodium. If the resulting energy burst is reliably contained I’m satisfied. Feel free to do this with a well designed water moderated reactor or MSR (fast or thermal).

Rod Adams's picture
Rod Adams on Jul 2, 2014

@Job001 Gibson

People are also willing to pay more for energy that is available when and where they need it. No matter how popular it might be to think that the wind and sun are all you need, no human has figured out how to control when the sun shines or the wind blows. Long transmission lines are just as vulnerable to interruption by aggressors as any other kind of fuel delivery system.

If someone owns a nuclear power plant, they are not terribly vulnerable to extortion since they can stockpile several fuel reloads if desired and each reload lasts for 18-24 months.

There are several independent fuel suppliers that are not in any kind of cartel.

Rod Adams's picture
Rod Adams on Jul 2, 2014

@Bill Hannahan

Since you reference Ray Haroldsen’s story about blowing up BORAX, I presume you actually read it. Do you recall the portion where he described in detail the creative engineering he had to invent in order to cause the rod ejection, high reactivity rate to begin in the first place?

There are many protections that prevent such an even from happening in any reactor that can be licensed and built today.

Nathan Wilson's picture
Nathan Wilson on Jul 3, 2014

Certainly since the Three Mile Island accident, safety has been of top importance in every new nuclear reactor design.  So the point of your comment is that you do not believe that fast reactors are designed to that same high safety standard, and/or the engineers and scientists who design them are not competent.

If you have not done so already, I would echo Robert’s suggestion that you read “Plentiful Energy” by Till and Chang (see description by the author here or on Brave New Climate here), which is the story of the IFR fast breeder, designed at Argonne National Labs, told by the program leaders.  I would also suggest you look over the blog of Sherrell Greene, Sustainable Energy Today; he’s the former Director of Nuclear Technology Programs and Director of Research Reactor Development Programs at Oakridge National Labs (to gauge his commitment to public safety).

But regarding your crushed reactor scenario, I would point out that you are also crushing the control rods and scram rods into the pancake, as well as the strongly neutron absorbing breeding blanket.  So it is not obvious to me that the pancake is really more reactive than an intact core.

Furthermore, as is described in “Plentiful Energy”, the IFR’s metal fuel melts and disperses in the coolant (with low energy release) during beyond-design-basis accidents, so I’m skeptical that you can really separate the coolant from the fuel as you have described.

I’m all for molten salt reactor development, but it is too early to tell which breeder will be better (for example, a combination of breeders operated by a few nuclear-supplier-countries and LWRs operated by everyone else could support certain political policies as well).  There should be one safety standard for all reactors, and for all energy technologies.

Bas Gresnigt's picture
Bas Gresnigt on Jul 3, 2014

“People are also willing to pay more for energy that is available when and where they need it…”

So the Germans are prepared to pay more as they do get more when and where they need it!
Thanks to the highly predicable and distributed generation by renewable (wind, solar, hydro, etc).

Reliability increased gradual a factor two when wind+solar became substantial: from ~30min/a out towards ~15min//a now. Thanks to the highly distributed and predictable electricity generation. 
Nuclear US lags far behind with 120min./a out for the av. customer connection, while outages due to specail weather (cold, storms) are not counted. Germany counts all outages incl. those by special bad weather..

In the IT same developments occurred. Distributed generation by many smaller units proved to deliver much higher availability figures, to be much more reliable and cheaper. So in IT the central mainframe is a past era now.
Similar happens in electricity generation now.


Rod Adams's picture
Rod Adams on Jul 3, 2014


Germany’s electricity reliability statistics are interesting but irrelevant in a global sense. Germany is a well developed, relatively densely populated country with an existing grid and neighbors that are quite willing to sell it power when needed or to take its excess production — though the willingness to purchase the excess is becoming saturated.

For example: If your goal is to power a moderately sized city in the American Southeast, you would be daft to believe that wind or solar would be a significant contributor. Geothermal is a non-starter. Hydro works, but there is virtually no available waterway left to dam. (There are many places in the world with similar challenges.)

Rod Adams, Publisher, Atomic Insights

Nathan Wilson's picture
Nathan Wilson on Jul 3, 2014

“… and whatever make the [wind and solar] intermittency issues nearly irrelevant.”

Well no.  There is still no existence proofs that solar and wind can be used affordably on 90%, 80%, or even 60% non-fossil grids (I’m referring to average whole-grid penetration, not the momentary peaks that generate so many headlines, nor the localized offsetting of fossil fuel imports with variable renewable exports).  

There is still no energy storage cheap enough to allow use of solar energy at night or wind on a calm day.  Essentially all grid deployments of advanced batteries have been sub-hour endurance systems designed allow slow-throttling coal plants to co-exist with renewables.

Nations that deploy wind and solar PV instead of nuclear need to learn to like CC&S with their fossil fuel.  Otherwise our CO2 emissions problems will never be solved.

Paul O's picture
Paul O on Jul 3, 2014


” Frankly, it doesn’t matter that no proof exists for affordability  or that storage hasn’t been perfected or that some supplies are intermittent or that controls are tough or that the grid is old or that etc. 

What matters is humans are the most adaptable innovative creative creatures on earth. We can count as fact;they shall survive and adapt even to cartel, monopoly, and utility customer exploitation, or pirates, high tax, or whatever.”

That sounds very much like a Religious Expression of Hope and Faith. (Apologies to Church Goers). You have simply replaced “GOD” with “humans “. The Faith and Hope aspects are practically the same.

*** God at least is supernatural and omnipotent.

Bas Gresnigt's picture
Bas Gresnigt on Jul 3, 2014

The scientists of that densely populated country concluded that it can generate its electrecity using only renewable (mainly wind+solar)!

Stronger they are convinced that such situation without nuclear and fossil, is beneficial for the whole population and have convinced an unprecedented 90% of the population that that is true.

So in Germany renewable generate ~25% of the electricity. Renewable share increases with ~1.5%/a.

Bas Gresnigt's picture
Bas Gresnigt on Jul 5, 2014

German scientists were already convinced in the nineties that renewable can generate all electricity needed!

It was the basis of Germany’s Energiewende decision in 2000.

Until now they proofed to be right!

Rod Adams's picture
Rod Adams on Jul 5, 2014

@Job001 Gibson

Interestingly enough, I founded a company in 1993 called Adams Atomic Engines, Inc. based on a design for a closed cycle gas turbine using a pebble bed reactor, nitrogen as the working fluid and a simple Brayton cycle using compressors and turbines that were designed for the combustion turbine market.

These machines could be made available in a variety of power outputs by choosing the appropriate reactor internal volume, filling it with the appropriate number of pebbles, and choosing compressors and turbines that were already being manufactured, thus avoiding the costs of design and creating whole new supply chains for unique machines run on some kind non standard gas like helium.

It is a well proven and testable fact that pebble bed reactors using TRISO fuel particles can be made so that they can withstand a complete loss of cooling without scram and still maintain all fuel temperatures below the temperature that will damage any of the elements. That statement holds true up to a thermal power level of about 300 MW, so it is not terribly interesting to people who think in terms of reactors with thermal power of 3,000 to 5,000 MW. 

However, since large combustion turbines are generally in the power range of 100-150 MWe, it is a very useful characteristic for someone interested in closed Brayton cycles that are intended to compete against combustion turbines and diesel engines.

Anyway, you can find out more by perusing the documents available at and

Adams Atomic Engines, Inc. by the way, was never successful in raising enough capital to move off of our computers and into actual machinery. Part of the problem was that the TRISO fuel particles that we initially thought had been proven to be good enough were not available anymore. There was, and remains, a very credible fuel manufacturing and testing program that is designed to meet NRC expectations being run by the DOE and the NGNP partnership. That program is scheduled to have licensable fuel ready by 2021 or 2022. We couldn’t wait that long.

Rod Adams, Publisher, Atomic Insights

Bas Gresnigt's picture
Bas Gresnigt on Jul 5, 2014

With the present prices for new nuclear, an overbuild of wind+solar of 100% combined with power-to-gas and some storage increase is still cheaper than new nuclear!

Overbuild is also the direction Germany is going with present scenario studies towards 95%-100% renewable.

Paul O's picture
Paul O on Jul 5, 2014

Your objection has ben answered over and over again. You just ignore the answers and continue to repeat the same mantra.

Why don’t you just admit that you hate Nuclear Power at any cost?

Rod Adams's picture
Rod Adams on Jul 5, 2014

@Job001 Gibson

Let me rephrase – we could not wait that long and maintain any kind of organization. The ideas and the designs still exist and are under careful protection, waiting for the availability of fuel.

I admire Chinese culture and history. I admire their engineering. I do not admire their business practices or their current government. I’m not interested in having the Chinese government as a partner, no matter how much money is involved.

Patience is a virtue.

Leo Klisch's picture
Leo Klisch on Jul 5, 2014

Is the main advantage of gas fueled turbines the ability to ramp up and down resonably efficiently comparded to reactor fueled turbines? If used in subs or large ships,the reactors must have some ability throttle back or do they dump the excess heat from the reactor? If designed for variable output, I would think they could replace NG fueled turbines when a carbon tax makes them to expensive to operate.

Robert Bernal's picture
Robert Bernal on Jul 6, 2014

What’s “power to gas”? The object is to displace fossil fuels altogether.

25% CF for RE requires 4x the overbuild and storage for 3 of that, unless a global grid is built, in which case, less overbuild and less storage would be needed, especially with all the new fancy smart grid hardware. Yes, I believe these are possible at the global level but I believe that it is technically easier (and intrinsically cheaper) to generate more power via high temp nuclear.

Rod Adams's picture
Rod Adams on Jul 6, 2014

@wind smith

Fission is actually more responsive to changes in power demand than combustion. Submarines and aircraft carriers can vary their power level faster than similarly sized oil burners.

The machines I propose would be competitive even without a carbon tax. The complete cost of the manufactured fuel should be less than $2/MMBTU in the early stages of commercial operation, with a lot of room for cost reductions as the manufacturing process is refined and scaled up. (The required fuel is quite different from the traditional light water fuel, so there is a very small installed production base currently limited to Chinese manufacturers. There are pilot scale production facilites in other countries, including the US.)

Rod Adams's picture
Rod Adams on Jul 6, 2014

@Job001 Gibson

I am no Malthusian and I have a great deal of faith in human ingenuity. However, no matter how clever humans are, they still need to follow natural laws of physics, chemistry, meterology, and material science.

The technologies that the “renewable” energy industry promotes are a technological dead end, even if you assume the invention of almost magical materials.

The sun never provides much concentrated power; even if you cover a mini-van sized automobile with 100% efficient solar panels, the instananeous power production at noon on a clear day near the equator would be about 3-4 kilowatts (about 5 hp). That would make a very slow automobile unless you assume a large amount of storage, which always adds considerable weight to the vehicle.

As a long time sailor, I can testify to the fact that trying to collect and use wind power is challenging, fun, and complete unsuited for any application that needs to deliver on a schedule. There is a reason that highly refined clipper ships lost out to primitive, inefficient coal burners in ocean trading more than 150 years ago.

If you understand the potential of nuclear energy and the natural abundance of the fuel – which is an essentially inexhaustible resource – you will have great hope for humanity and our future prosperity.

Malthusian predictions could have come true if the proponents of doom had been able to convince the world that the Haber-Bosch Process should be banned or severely restricted and placed under strict government regulation because it enabled the production of explosives as well as fertilizer.

Bas Gresnigt's picture
Bas Gresnigt on Jul 6, 2014

Your statement: “The technologies that the “renewable” energy industry promotes are a technological dead end, even if you assume the invention of almost magical materials.”

Assume we indeed succeed in making graphene like plates (one molecule thick plates), than the energy a battery of 10kg can store will be enough to drive an electric car 1,000miles…
House owners will install a battery of 50kg and have enough storage to become grid independent (even if solar delivers no electricity during the whole winter).

Solar panels
Assume new materials better than perovskites (cheaper and higher yield e.g. 60%). Than your roof will produce 3times more per m² than the best panels now (so ~600W/m² = ~>600KWh/a), while the investment is only ~$100/m². As panels last >25years the LCOE of your electricity is then <1cnt/KWh.

Assume material that is 10times stronger than present fiber.
That allows for wind turbines with the nacelle at 300m altitude and blades 200m long with a capacity of >50MW. Those will increase the power density of wind turbines (produced MWh/a per m² used) even further above that of nuclear.
While produced electricity by wind will cost <1cnt/KWh in many areas

So these will revolutionize the energy world and make the old fashioned steam-turbine/dynamo combination totally obsolete.

Bas Gresnigt's picture
Bas Gresnigt on Jul 16, 2014

“What’s “power to gas”?”
Conversion of renewable electricitiy into gas. The gas can then be stored. Now 6MW pilot plants run.

“25% CF for RE requires 4x the overbuild and storage for 3 of that..”
German scientists plan much smarter. They plan to use the right combination of different renewable technologies. So the overbuild can be very much smaller.

Bill Hannahan's picture
Bill Hannahan on Jul 22, 2014

Deleted duplicate

Bill Hannahan's picture
Bill Hannahan on Feb 5, 2015

Rod wrote. “There are many protections that prevent such an even from happening in any reactor that can be licensed and built today.”

Rod, here is a summary of reported criticality incidents in the U.S. There have been many more around the world.

Criticality Accidents

If we had a time machine and went back before each accident and described the incident to the people involved as a hypothetical event, I think most would be dismissive, perhaps even annoyed at the suggestion that they or their people would let such a thing happen.

If we interviewed the TMI crew before the accident, they would scoff at the idea that a relief valve could cause a meltdown, pointing out that they have enough emergency pumping capacity to handle a double ended break of the largest pipe on the reactor six times over.

There is a misperception that there is a huge difference between a reactor running at steady power, on delayed neutrons, and a reactor on a very short period on prompt neutrons alone. In reality, there is a very narrow band of multiplication factor separating those two regions (1.000 vs. 1.004), especially in a fast neutron reactor where delayed neutrons are fewer and the consequences of getting into the prompt region are potentially much more severe. Ejecting a massive control rod is not the only way to add a lot of reactivity to a core.

Consider page 18 of this report, Fig 3.3, showing that the Phenix reactor experienced 5 big reactivity and power swings in 1/3 of one second, due to a phenomena that was and is still unknown to the designers.

This graph alone should shake your confidence in solid fuel fast neutron reactors. It is natures way of telling  us we are on risky ground here.

Here is a report describing the work that needs to be done to build a future solid fuel fast neutron reactor. It does not say much about criticality safety, but all the issues discussed impact criticality safety.

Reading between the lines, it is clear that these things are not fully understood today. So why take the chance just to make expensive kWhrs in an expensive complex machine that takes a long time and a lot of money to build?

Bill Hannahan's picture
Bill Hannahan on Jul 22, 2014

In reviewing the links I see that I did not respond  to an interesting comment by EP; I’ll do so here since comments  are closed there.

EP wrote;  ” Hans Bethe analyzed the explosive potential of a fast reactor meltdown and came up with a worst-case figure of 160 kg TNT equivalent.  This is about 670 MJ, or about 200 msec of full-power output of a 3.3 GW(t) reactor.

It would be a real mess inside the containment, but that’s where it would stay.”      

  Three points;

1.  The reactor Bethe evaluated was 53 cm tall and 23 cm in radius, 91 litres. The Superphenix core was about 6,000 liters. Assuming the same energy per liter, the energy yield in Superphenix would be equivalent to 10,000 kg, 10 metric tons of TNT.

In a nuclear bomb core compressed to a few inches in diameter, a few thousandths of an inch diameter change makes a big difference in reactivity, yet a great deal of energy can be released in the short time it takes to disassemble itself. In a large irregular superprompt critical assembly, much larger dimensional changes are required to make the assembly subcritical, and that takes more time, allowing for more energy to be released.

Assuming the energy density in the criticality accident will increase in proportion to the volume of the core, the yield for Superphenix would be 655,000 kg, 655 tons of TNT.

2.   Bethe assumed a slow, gravitationally induced reactivity insertion rate; I am concerned with a high speed, high reactivity rate criticality.

3.  Large fast neutron reactors contain enough fissile material to produce hundreds of critical assemblies, yet proponents only discuss the possibility of a single low velocity criticality accident. What happens if a medium energy criticality creates a high velocity shock wave that crushes the remainder of the core in a few milliseconds?
Bill Hannahan's picture
Bill Hannahan on Feb 5, 2015

Nathan wrote “

“But regarding your crushed reactor scenario, I would point out that you are also crushing the control rods and scram rods into the pancake, as well as the strongly neutron absorbing breeding blanket.  So it is not obvious to me that the pancake is really more reactive than an intact core.”

Right, a thin pancake would not support a chain reaction due to high neutron leakage. But the assembly would have exploded long before it got to the pancake shape.

A high velocity shock wave from above, or from below, or the side would not smoothly reinsert control rods.  But it would rapidly squeeze out the sodium, adding a huge increment of reactivity, driving it deep into the superprompt critical condition.

Nathan wrote “Furthermore, as is described in “Plentiful Energy”, the IFR’s metal fuel melts and disperses in the coolant (with low energy release) during beyond-design-basis accidents, so I’m skeptical that you can really separate the coolant from the fuel as you have described.”

When you say “with low energy release” that is the part that has to be proven for a high reactivity rate accident, not just assumed.

If you build a core with non fissile material and crush it , the coolant will be separated from the fuel rods. If you crush a real core that is critical, K=1, and squeeze the sodium out, you are adding a huge increment of reactivity, and I believe it will explode. It is up to the supporters of fast neutron solid fuel reactors to prove that it will not explode.

Why do they model only slow gravitationally induced accidents, and why are the resulting accidents sometimes predicted to produce prompt fatalities?

Please review NUREG-1368, and then this comment.

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