The BN-800 Fast Reactor – a Milestone on a Long Road

Guest post by Russian commenter Syndroma who was trained in IT and now works in his family business. The BN-800 was commissioned this week.

The Past 

The Russian fast neutron reactor program was started in the early days of the nuclear age. Scientists back then realised that thermal neutron reactors are no more than a stopgap solution. Yes, they’re simple, but ugly from the scientific point of view. They’re inefficient, burning no more than 1% of natural uranium, and they leave a lot of highly radioactive long-term waste, which can’t be dealt with meaningfully without fast reactors. Scientists, being a bit idealistic, couldn’t believe someone would want to deal with thermal reactors in the long term.
The first attempt at fast neutron reactor with non-zero power was called BR-2 (‘B’ for fast, ‘R’ for reactor). Its power was just 100 kW, it was fueled by metallic plutonium and cooled by mercury. Just a few months after the start of operations in 1955, mercury revealed itself as a terrible coolant for a reactor. It was highly corrosive, damaging fuel cladding and pipes. Mercury leaks were a common occurence, dealt with casually. After a year of operations the experiment was declared a failure. The rector was dismantled, the mercury was decontaminated and sold for civilian use. The same building and infrastructure were used for BR-5 reactor, which was commisioned in 1959. It was a different project with power output of 5 MW, later upgraded to 10 MW, fueled by plutonium oxide and cooled by sodium. [1]

Figure 1: The evolution of sodium-cooled fast neutron reactors in Russia. [2]

BR-5/10 was operational until 2002 and proved to be a great success, providing the first operational experience and a lot of scientific data on behaviour of fuels and materials in fast neutron field. Still, it was limited in its geometry and power, so a bigger sibling BOR-60 (‘O’ for experimental) was commissioned in 1969. BOR-60 is still working to this day, being used for materials research by Russian and international teams. It is expected to be replaced around 2020 by MBIR (multipurpose fast research reactor), which is under construction right now.

The success of research reactors paved the way for the first commercial fast neutron project – BN-350 (‘B’ for fast, ‘N’ for sodium). It was built in Kazakhstan near a uranium mine, its power output was 350 MW shared between electricity generation, district heating and desalination. The first years of BN-350 operations were extremely troublesome. [3] Nobody could predict the issues caused by scaling up. The core of BN-350 contained 300 times more sodium than BR-5. Sodium was leaking from unexpected places. Sodium was freezing in unexpected places. But the worst problems were related to steam generators. Sodium is lighter than water, so it doesn’t leak into water, water leaks into sodium and reacts violently. The steam generators were prone to small leaks which were hard to detect promptly, contaminating entire loop with products of the reaction. The problem was so severe that the reactor was shut down and all heat exchanging pipes in the steam generators completely replaced.

After so much trouble with BN-350, BN-600 project had to prove that large-scale sodium reactors could be operated safely and reliably. It was accepted that leaks are inevitable, the focus was placed on detection and mitigation. Steam generators were partitioned into small sections which could be cut off and repaired. Early leak detection systems and fire suppression methods were implemented. There were at least 27 leaks with up to a tonne of sodium spilling into the air, none of them causing any significant downtime. [1] But there was a price to pay – BN-600 required a lot more piping than any other commercial reactor, severely damaging its economics. Still, 36 years after commissioning it remains the most successful fast neutron reactor in the world, and its operational lifetime is likely to be extended.

The Reactor

BN-800 reactors were supposed to be the first serially built fast neutron reactors. Their construction started in late 80s, 125 km away from the place where the modern BN-800 was built. But first Chernobyl, then the collapse of the USSR interfered with the plans. Construction was halted, leaving giant holes in the ground. By the 2000s, when the new Russia was ready to return to construction, BN-800 design was considered outdated. There were new, exciting possibilities. A significant number of scientists thought that sodium is a waste of time and the future belongs to lead. They proposed a revolutionary, lead-cooled fast neutron reactor BREST-300. They’re still committed to building it, sometime next decade. Other scientists were reluctant to build just a bigger version of BN-600, they wanted to build a revolutionary BN-1200 with completely different layout. But the cooler heads noted, that Russia has not built a fast neutron reactor in a generation, and given past experiences anything revolutionary tends to fail spectacularly. They proposed to build an updated conservative design just to prove that Russia still has the capability and talent to do so.

Figure 2: BN-800 scheme

Nobody saw it coming, but the US played a major positive role in the fate of BN-800. Russia and the US reached an agreement to destroy excess amounts of plutonium to make the world a safer place. The US has choosen to burn it in conventional reactors, Russia has choosen to use it as a fuel for fast reactors. BN-600 was not suitable for the task because by 2018, when the destruction of plutonium had to be started, it’d be nearing its end of design lifetime. And the only other project which had a chance to be implemented before 2018 was BN-800. The downside of the agreement for Russia was restriction to use breeding blanket around the core and restriction on reprocessing of the spent fuel. BN-800 was forbidden from operating as a Pu breeder, only as a Pu burner. The restrictions were irritating, and that was one of the reasons why Russia recently withdrew from the agreement.

The BN-800 project was dusted off, updated to modern standards and materials, its nominal electric power output was increased to 880 MW. Its construction started in 2006.

Figure 3: BN-800 reactor under construction

A 25 years long break took a heavy toll on the nuclear industry. Some things had to be re-learned. Some things had gone for good. For example, the producer of pure sodium for BN-600 has long disassembled the equipment due to lack of customers. Sodium is bought once for the entire lifetime of a reactor. The producer agreed to restore the production line only if guaranteed orders, the company wasn’t interested in a one-time job. Luckily, the French, who had a respectable sodium reactor program of themselves, kept their production. French sodium was transported 4 thousand km, reheated and pumped into the BN-800.

BN-800 went critical in June 2014, was connected to the grid in December 2015 and was commissioned this week.

The Fuel

Although the design of BN-800 was choosen to be very similiar to BN-600, it was decided early on that the fuel composition should be radically different. BN-600 runs on highly enriched uranium, BN-800 should have been run on plutonium MOX fuel. There are two kinds of plutonium: weapons-grade, which is relatively easy to handle, and reactor-grade, which is more radioactive. Russia committed to destroy excessive amounts of weapons-grade Pu, but also it has a significant stockpile of reactor-grade Pu from reprocessing of spent nuclear fuel. If the fuel assembly line was designed to handle only weapons-grade Pu, than it’d be useless for a closed nuclear fuel cycle. So, it was decided that the fuel plant should be built with all the necessary protection (and it was – inside a mountain). But then the planners stumbled upon a minor issue with a long-reaching consequence.

There were several institutions in Russia which worked on MOX fuel fabrication. And over the course of decades two competing technologies were developed. One is classical: mix plutonium and uranium powders, make pellets out of it and pack the pellets inside a tube. The other one is innovative: mixed powder is vibro-packed directly inside a tube, skipping the pellets stage. Vibro-packed MOX process claimed some important technological advantages related to utilising of defective tubes and reprocessing of spent fuel. The advantages were attractive enough for the technology to be chosen as the basic for BN-800. It turned out to be a polarizing issue, with holy wars breaking out between the opposing camps at meetings and conferences.

But reality reigns supreme. In time it had become obvious that vibro-packed MOX technology has issues at scaling up. It’d be ready a decade after the BN-800 launch. It was unacceptable. Worse, much time had been lost, and the pellet technology would not be ready either. There was no other choice than to load BN-800 mostly with the same old highly enriched uranium. ‘Mostly’ because small-scale MOX fuel lines of both kinds were capable of producing around 20% of the required fuel. And the resulting reactor core of HEU, pellet MOX and vibro-packed MOX was called “hybrid core”.

Obviously Pu and U are different elements and are expected to behave differently. Placed in the same core, they produce slightly different amounts of energy. But the coolant flows at the same speed in the reactor. To prevent thermal irregularities, small plugs were placed at the base of some assemblies to decrease the flow through them. Time was short, the modification looked simple, no proper testing was conducted. And when the fuel was loaded into the BN-800, and its giant coolant pumps started pumping liquid sodium through the core, the plugs started vibrating and unscrewing themselves. To make matters worse, when an assembly is extracted from the reactor it has to be washed out from the sodium leftovers with an interesting liquid, which makes it impossible to get it inside the reactor again. The only way to safely work with an unwashed assembly is to place it inside an inert gas atmosphere. And the closest workshop with such an atmosphere happened to be at the BN-600. Years of operational experience came to the rescue once again. [4]

The mishap cost the program about a year of delay. The assemblies were modified, reloaded, and the reactor went online with the hybrid core in December 2015. About the same time the pellet MOX fuel plant went online too. It is expected that BN-800 will be fully loaded with MOX fuel by 2019. Vibro-packed MOX fuel is not abandoned either, it will be used in research reactors.

Figure 4: BN-800 fuel load. 1 – low Pu content, 2 – medium Pu content, 3 – high Pu content, 4 – breeding blanket, 5 – steel shield, 6 – boron shield, 11 – spent fuel. [5]

Is everyone happy? Nope. The designers of BN reactors wanted neither pellet MOX nor vibro-packed MOX. The key characteristics of a fast neutron reactor directly depend on the density of the fuel. The denser it is, the more neutrons it captures, the higher reactor’s breeding ratio becomes. Research of a dense fuel is a major program of the Russian nuclear industry. So-called SNUP fuel (mixed nitride uranium-plutonium) is in transition from lab experiments to limited loads at BN-600. It’s perfomance and safety is thoroughly evaluated, and it is expected that the proposed BN-1200 will be loaded with the SNUP, eventually.

The Future

Although BN reactors have many advantages, they’re more costly than VVER (PWR) reactors. They require much more metal for construction: a bigger reactor vessel (but not pressurized) with intermediate pumps and heat exchangers, and a complicated steam generators. The main goal of BN-1200 project is to lower the cost of the unit to be competitive with conventional reactors. To achieve that goal, all systems need to be reviewed and optimized. But one system is of particular interest: the steam generators. BN-600 SGs consist of 72 sections, BN-800 SGs consist of 60 sections. BN-1200 proposes to return to integrated SGs with only 8 sections. It’s a risk, but things changed a lot since BN-350 times. Modern materials, simulation algorithms and testing capabilities could allow for much more reliable steam generators.

Figure 5: BN-800 and BN-1200 steam generators (one loop). BN-800 has 3 loops, BN-1200 has 4 loops. [6]

Another proposal is to change the layout of the reactor building, reducing pipeline length up to 1.8 times. If BN-800 sodium pipes look like a squid monster, BN-1200 proposes a more radially symmetrical approach.

Figure 6: BN-800 and BN-1200 sodium pipes.

The construction of BN-1200 is expected to start after 2019. The road to sustainable nuclear energy is long, but it’s definitely worth the effort. One just needs to see things in perspective.

Figure 7: BN-800

References (all in Russian)


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23 Responses to The BN-800 Fast Reactor – a Milestone on a Long Road

  1. Alex says:

    Thanks. Very interesting. How come Rosatom can come up with great designs that are economic, when most of Russian industry is a disaster. This is despite being state owned with political appointees.

    Anyone know whether the PRISM design solved the heat exchanger problem?

  2. ducdorleans says:

    good article, thanks …

    a tribute to the human mind, how it should and can (and has to) work since we have been chased from the Garden of Eden …

  3. Euan Mearns says:

    Syndroma, many thanks for an interesting and informative article. Scotland used to be a world leader in breeder technology but our 250 MWe machine got taken off line in 1994

    Which other countries have breeder technology and how does this compare with the stage of development in Russia?

    • Syndroma says:

      I’m confident that the fast neutron reactor technology is essential for our civilization, and the more countries work on it the better. I feel sad every time some government decides to shutdown a FBR, because often it means that the entire program will be abandoned. I read at your link that the load factor of the Dounreay reactor was 26.9%. That’s typical for the first large scale project, and I’m sure the next one, built with lessons learned in mind, would be much better. But the line was severed and the hard-earned experience is withering away. The Japanese are mulling closure of Monju, and I’m afraid that spells doom for the FBR program there.

      I must admit I have a low opinion of paper reactors. Of course they’re much better than the real ones, they do not corrode, do not leak, and are cheaper. I’m pretty sure the first real reactor of any of the novel designs (including Russian lead-cooled BREST-300) will be a financial disaster, maybe a technological one too. And one should be ready for that, one needs a resolve to continue the program and commit oneself to building the next version. Only this way will lead to a working design which can become mainstream. And given the nature of nuclear energy and timescales for testing of new ideas, the commitment should be multi-generational. This is what we should look for, not a specific technology but a commitment. I can see it in China. They lack a lot of technologies, but I’m pretty sure they’ll have their own home-grown large-scale FBR this century.

      • ducdorleans says:

        “I can see it in China. They lack a lot of technologies, but I’m pretty sure they’ll have their own home-grown large-scale FBR this century.” …

        surely ! … and much faster than “this century” …

        but …

        in the mean time …

        we (i.e. the Old Western World) will have millions of wind turbines and gazillions of solar panels …

        and who will beat us to that ?


      • jfon says:

        Syndroma, do you know how the Indian fast reactor programme is going?

        • Syndroma says:

          Unofficially there was a sense that Russian BN-800 is in a race with Indian PFBR (500MW). A good, friendly competition. PFBR construction started in 2004 and was expected to be complete by 2010. When the plugs mishap happened at BN-800, the Russians were like “all is lost, Indians will be the first”. But now BN-800 is commissioned while PFBR has not reached first criticality yet. It’d be interesting to read what went wrong there.

    • ducdorleans says:

      the USA, at the Argonne laboratory, had a FBR (called IFR, integral fast reactor) that – I think, but I’m no specialist, – was ready to be deployed …the story can be read on the internet … but somehow, for some reason, the Bill Clinton administration thought it useless ! … and stopped it ..

      (and I’ve also no idea whether it can be relived … some of the scientists involved must be pensioners already …)

      • Peter Lang says:

        Read the IFR Facts and Discussion Series here:

      • Alex says:

        The PRISM reactor is a follow on proposal to the IFR. As Syndroma might point out, it’s a paper reactor, but is closely modelled on the IFR.

        Interesting discussion of paper reactor. Of course, paper reactors no longer exist. They are now built in CAD/CAM models and everything can be simulated and tested before anything is built. Will that over come the issues that Syndroma has and Admiral Rickover had?

        Perhaps it’s too early to tell. Was Flamenville built from a CAD model? The EDF project managers at Hinkley claim they have already built Hinkley C in CAD models – coupled with real life experience at Flamanville, this should help construction. Normally after doing everything in a CAD model, we’d like to print a SLA model, but generally, digital design and mock up really does help with every day object. Whether it will with nuclear, remains to be seen.

  4. brianrlcatt says:

    Really interesting,. And a clear answer to US promoters of paper reactors when their government is strongly avoiding them in favour of easy money renewables, for lobbyists payola, that can’t deliver the energy they will need on any realistic science measure.. So they wlil have to make a panic switch to nuclear that works as the wind, water and solar powered lights go out as parasitic renewables capable fossil host declines. So that’s a shitload of ready to generate PWRs. Same in UK.

    As for FBR deployment, You have to break some eggs to make an omelette. No different in nuclear engineering, and needs sustaining across generations if developed countries are to stay that way, as stated above – that’s real science that politicians with their small time time in office, belief in their own BS and general lack of technical understanding don’t get, it’s too hard for most, anyway.

    I also feel vindicated for pointing out why we shouldn’t be planning to go direct to FBRs from Thermal PWR’s, even more so Thorium salt designs, we have to do it step by step within a mix. The Russians seem pretty brave, but they have not gone Thorium’s way. Also seems to me no one has run an FBR for 60 years to gain the essential materials technology insight that brings, and reduction in “unexpected leaks”. Keeping such an extreme environment reliably contained inside something for 60 years won’t be easy.

    BTW, Japan went from mediaeval agarian to proto British Empire status strong enough to challenge the USA and British Empire, manufacturing all it needed, in about 80 years, thanks to Thoma Blake Glover and native ability. China will make the moves required to replace coal then gas with nuclear, it is making them now. Russia will be close or ahead, it’s not dominated by a self serving doom industry and regressive climate change for profit industry, using the fearful, and wholly regressive in a modern society, precautionary principle, that would stop evolution if it could. etc.

    The end is only nigh if you STOP advancing. The sky will fall, when the sun runs out of hydrogen we are all toast. Better use what we have while it’s there to create the sustainable intense nuclear energy supply we eed to ensure a sustainable future after the fossil has gone, the cliamte changes and the sea levels go up and down, at least until the end of the human presence on Earth when we are all recycled back into the space we came from

  5. Peter Lang says:


    Very interesting and very well written. Thank you. I totally agree that FBR’s have to be the future. there is no other energy sources that will be able to supply the worlds ever increasing demand for energy for (nearly) ever.

  6. Jan Steinman says:

    Time was short, the modification looked simple, no proper testing was conducted.

    This reminds me of another LMFBR, Fermi I, in Monroe, Michigan — the world’s first (and probably still only) breeder developed and implemented by private industry.

    Well, someone was worried that, in the event of a melt-down, a critical mass of plutonium could form at the bottom of the reactor vessel, causing a catastrophic “fizzle yield” that would be nowhere near the power of a proper atom bomb, but which would spread plutonium all over Detroit.

    So, as Syndroma said, “Time was short, the modification looked simple, no proper testing was conducted.” A flat zirconium cone was fashioned and fastened to the bottom of the reactor core, to keep molten plutonium from forming a critical mass.

    And how ironic was it that, during its first full-power test, that undocumented zirconium cone flew off and plugged coolant circulation, causing a severe melt-down? The cure for a possible consequence of a melt-down instead causes one!

    Of course, “No one was injured” and “the public was never in any danger” and “no radiation was released.” Tell that to the family of Phil Harrigan, an engineer at the plant. I played with his son in a garage band, and in the summer of `66, Phil took me on a tour of the plant, showing me the ham radio station he had set up there. (I was on the way to getting my ticket, which I still hold: N7JDB.)

    Then in October, all hell broke loose. They were working around the clock, eventually neglecting personal dosimeters. They couldn’t think with the constant radiation alarms blaring… so they disconnected them. What is true is that “no release of radiation was ever measured,” which is sort of the same as not releasing any, right?

    Phil described cutting holes in pipes and fashioning long articulated arms to put mirrors into the core. They found an obstruction, but what could it be? The plans they were working from, struggling to bring the plant under control, didn’t even show the zirconium cone.

    The following year, strange things happened on our farm, five miles from Fermi I. We had kittens born with extra heads. We had “jelly goats” born at full term, that never developed bones. At least half the animals born that year died or were deformed.

    Ten years later, I heard Phil Harrigan died of leukemia, in his early 50s.

    There probably wasn’t an autopsy, and if there had been, there would have been no little red flags inside Phil’s lifeless body, saying “Fermi I did this!” Others who worked at the plant in late 1966 have also died prematurely. But, “the public was never in any danger.”

    My Mom has had bladder cancer twice (treated successfully), and my sister had a non-malignant thyroid tumor (associated with I-131) removed, but (knock wood) so far, the rest of us seem none the worse for wear.

    If we’re going to do nukes, we gotta get it right. Because culpability is so easy to hide. Or, I should say, culpability is often impossible to trace.

    (I’m not checking the “Notify me of new comments” box, because my last experience with commenting here attracted so much vitriol from nuke fan-boys. So, post away. I’m ignoring you. I’m not absolutely against nukes, but we must foster an ethic of “zero tolerance” and “fail safe.” But I fear that when timelines stretch out and budgets get exceeded, someone will always start cutting corners.)

    • Syndroma says:

      Did Phil Harrigan ever regret that he worked there?

    • Peter Lang says:

      Nothing is fail safe. The indisputable facts are that nuclear is the safest way to generate electricity. Any other technology causes more fatalities per TWh of electricity supplied. This is well known and has been for over three decades. If you weren’t aware of that, please do objective research before posting.

      You might also consider the fastest way to improve safety is to encourage development, and deployment. If progress had not been stalled by the anti-nuke protest movement in the late 1960’s and since, nuclear power might now cost around 10% of what it does and be orders of magnitude safer. For comparison consider the aviation industry. In the US, from 1960 to 2013, passenger-miles increased by a factor of 19 while fatalities per passenger mile decreased by a factor of 1051. that’s a learning rate for passenger safety of 85%. Similar could have been the case with nuclear if not for the anti-nuke protest movement.

      There! Ignore that and continue posting ignorant, scare-mongering comments all over the web!

    • Euan Mearns says:

      @ Jan

      The main cause of the partial meltdown was due to a temperature increase caused by a blockage in one of the lower support plate orifices that allowed the flow of liquid sodium into the reactor. The blockage caused an insufficient amount of coolant to enter the fuel assembly; this was not noticed by the operators until the core temperature alarms sounded. Several fuel rod subassemblies reached high temperatures of around 700 °F (370 °C) (with an expected range near 580 °F, 304 °C), causing them to melt.[3]

      Following an extended shutdown that involved fuel replacement, repairs to vessel, and cleanup, Fermi 1 restarted in July 1970 and reached full power. Due of lack of funds and aging equipment it was finally shut down permanently on November 27, 1972, and was officially decommissioned December 31, 1975 under the definition of the Atomic Energy Commission. Later, the Nuclear Energy Commission replaced the AEC and under their new definitions, Fermi was re-designated as being in SAFSTOR due to some remaining radioactivity at the site. On May 16, 1996, decommissioning was restarted. However, by November 2011 with very little activity remaining, a decision was made to halt further work. It is currently in SAFSTOR.[3]

      In Wiki it says that the reactor was repaired and re-entered service which to me does not seem compatible with an accident on the scale you claim.

      • robertok06 says:

        “In Wiki it says that the reactor was repaired and re-entered service which to me does not seem compatible with an accident on the scale you claim.”

        Jelly goats with no bones! That’s the best.
        How more troll can this guy be?

    • jfon says:

      Proponents of sodium-cooled reactors claim that, in the event of fuel rods being breached, radioactive iodine will bind to the sodium, rather than being boiled off as in an overheating water- cooled reactor. ( Molten salts and lead also supposedly greatly reduce the vapour pressure of volatile fission products like cesium 137 and iodine 131).
      Do you have any evidence for contamination around the Fermi I reactor, or of increases in cancer rates in the area ? We can all tell cancer stories, but science needs numbers.

  7. Peter Lang says:

    We had kittens born with extra heads. We had “jelly goats” born at full term, that never developed bones. At least half the animals born that year died or were deformed.

    Absolute nonsense, unless you were feeding them poison. Provide authoritative sources for your assertions (not from well known anti-nuke protesters like Helen Caldicott and her ilk) or you have zero credibility.

  8. Peter Mott says:

    Very interesting. It does seem that scaling these reactors up brings a lot of problems. Why not have lots of little ones rather than one big one?

    • Syndroma says:

      In a sense, it was the chosen solution for BN-600 and BN-800. Instead of a few big steam generators there are lots of little ones. It comes with a heavy price tag.

  9. RDG says:

    The bankrupt fools over at EDF crying over their complexity trap called the EPR must be really envious of the BN-600/800/1200/1800/2400/ sinkhole…Syndroma and Hirsch should join forces and write a book entitled ‘Reality is not an Option’, foreword by ‘Geniuses at CERN’.

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