International Experience with Fast Reactor Operation & Testing

Below is a highly informative presentation given by Dr John Sackett (Idaho National Laboratory, Retired) at the International Conference on Fast Reactors and Related Fuel Cycles (Paris, 2013). John, with a 34-year career in advanced reactor and fuel-cycle development (including work on the Integral Fast Reactor from 1984-1994), provides a clear summary of historical-international experience with fast reactor programmes and initiatives to recycle used fuel.

This is important information for advocates of ‘Generation IV’ nuclear technologies to understand, because the question of “is it proven to work?” is often asked by the skeptical. Much of this will be familiar to those who have read “Plentiful Energy“, but this is an excellent condensed version of that material. This is also highly relevant in the context of the recently commenced Nuclear Fuel Cycle Royal Commission.

There is a Long History of Fast Reactor Operation
• The first reactor in the world to produce electricity was a fast reactor, the Experimental Breeder Reactor I in December of 1951.
• International experience with fast reactor technology exists in the US, Russia, France, Japan, UK, Germany and India.
• The operating experience with these reactors has been mixed: early problems were associated with fuel cladding, steam generators, fuel handling, and sodium leakage.
• Excellent experience has been gained, however, that demonstrates the robust nature of the technology, the potential for exceedingly safe designs, ease of maintenance, ease of operation and the ability to effectively manage waste from spent fuel.
• It is a mature technology.

EBR-II was a Major Contributor to the Technology
• EBR-I was followed by EBR-II, which was a complete power plant. It was extremely successful, operating for 30 years and advancing the technology in many ways.
• Principal among its contributions were development of metal and oxide fast-reactor fuel, operational-safety tests which demonstrated the self-protecting nature of fast reactors, and fuel-recycle technology that was efficient and secure.
• Perhaps the most important advance in safety was the demonstration of the self -protecting response of sodium-cooled fast reactors in the event of Anticipated Transients without Scram.
• Tests of Loss of Flow without Scram and Loss-of –Heat-Sink without Scram were conducted at EBR-II from full power with no resulting damage to fuel or systems, ushering in worldwide interest in passively safe reactor design.

International Experience Compliments These Examples
• This experience base is fully supported by a combination of small test reactors that explored all aspects of the technology and larger operating reactors that provided power to the electric grid.
• Small experimental reactors were operated in the US (EBR-II), France (Rapsodie), Russia (BOR-60), Japan (JOYO), UK (DFR), Germany (KNK-II), and India (FBTR).
• Power reactors and larger experimental reactors were operated in the US (FERMI1, FFTF), France (Phenix, Superphenix), Russia (BN350, BN600), Japan (Monju). Current operating Fast Reactors are China (CEFR), and Russia (BN600, BOR60)

EBR-II_SiteUS Experience Followed Two Paths
• The US carried forward two separate tracks of technology development, primarily associated with the choice of fuel, metal or oxide.
• The first US commercial fast reactor, Fermi-I utilized metal fuel while the Fast-Flux-Test-Facility (FFTF) and the Clinch River Breeder Reactor (CRBR) utilized oxide fuel.
• Due to perceived low burnup potential for metal fuel, (a problem later solved), the U.S. approach turned to oxide fuel in the late 1960s.
• Russia, France, Germany and Japan all follow technology paths that use oxide fuel.
• It is worthwhile expanding this point because diversion of the technology paths has resulted in very different designs and performance, with the result that EBR-II is somewhat unique in this family of reactors.

Dry Reprocessing of EBR-II Fuel was Demonstrated in the 1960s
• Melt Refining was used to recycle fuel for EBR-II from 1964 through 1969
– More than 700 EBR-II fuel assemblies recycled using melt refining and returned to the reactor in four to six weeks
– ~34,000 fuel pins successfully reprocessed, including remote fabrication by injection casting
– Spent fuel was disassembled, chopped, placed into a Zr2O crucible, and heated to 1400 C
– Chemically reactive fission products reacted with the crucible to form oxides
– Uranium and noble metals remained in the metallic state and stayed with the melt to be returned with the re-cast fuel pins
– The fuel was fabricated remotely by injection casting, the resulting equilibrium fuel composition, called fissium, operated through the life of EBR-II.

Metal Fuel Data Base
• Over 150,000 metal fuel pins irradiated during the 30-year life of EBR-II
• Seven full-sized assemblies (1800 pins) of metal fuel irradiated to high burn-up in FFTF without failure
• Metal fuel attained 20% burn-up without failure
• Fuel compositions
– Uranium-zirconium and uranium-zirconium plutonium over a range of plutonium concentrations, with and without additions of minor actinides
• Peak cladding temperatures to 620ºC
• Maximum in-reactor exposures to 5 years

Safety Testing in EBR-II
• Fuel was extensively tested under off-normal conditions
– Operation with breached cladding (oxide and metal)
– Transient overpower (TOP) events (EBR-II TOPs complimented more severe TOPs in TREAT)
• Inherently safe response of EBR-II was demonstrated after 12 years of extensive testing and analysis
– Loss-of –flow without scram (station blackout)
– Loss-of-heat-sink without scram
• A level one PRA was completed to quantify safety

Fast Reactor Physics has Matured
• The sensitivity of cores to physical changes in core configurations has been seen in a number of “anomalous” reactivity perturbations.
• At EBR-II there was a problem encountered with “flowering” of the core due to problems of the core restraint design.
• The Phenix reactor encountered anomalous reactivity perturbations in four instances, thought to be due to possible “flowering” of the core followed by a rapid return to the original configuration.
• At the FBTR, anomalous reactivity perturbations were also experienced and thought to be associated with changes in core configuration associated with thermal gradients across the core.
• The lesson learned from these events is that proper design of fuel assemblies and core restraint systems is exceedingly important and all phases of operation must be considered.
• The result has been that no or few problems of like nature were experienced in subsequent reactors.

Sodium Leakage
• All operating fast reactors have experienced sodium leaks.
• One of the most famous occurred at the MONJU reactor in 1995 when approximately 640Kg of sodium leaked from the secondary sodium system with a resulting fire.
• A major sodium leak occurred at EBR-II in 1965 when a frozen sodium plug in sodium piping melted during maintenance, releasing approximately 100Kg of secondary sodium.
• As significant as these events were, no injuries resulted nor have any injuries have resulted from leaks at any other operating fast reactors.
• The low pressure of the coolant limits the rate of leakage and improved understanding of designs increasingly prevent and detect leakage.

Steam Generator Failures
• Sodium-steam interaction due to failure of steam generator tubing has also occurred, the most serious at the BN-350 reactor in its early operation. All reactors have experienced steam-sodium leakage with the exception of Superphenix and FBTR.
• In all cases, the failures were traced to poor welds, fabrication or design.
• Much has been learned about prevention, detection and mitigation of the consequences of steam-sodium leakage but perhaps the most important is that such leaks are not catastrophic.
• As with other sodium leaks, no injuries have resulted from failure of steam generators. In addition, physical damage to the plants has been minor.

Reactor Operation is Straightforward
• At EBR-II the reactor was operated with many different core configurations. In all configurations, the reactor was stable in its operation.
• Another aspect is that operating procedures are straightforward, aided by the self-protecting nature of the reactors.
• At EBR-II, extensive tests were conducted that not only included ATWS events associated with loss of flow, but also
– single rod run-out,
– primary pump control malfunctions,
– load following and
– steam system failures
• These tests also demonstrated that EBR-II was tolerant of operators taking an improper control action.
• These characteristics greatly reduced pressure on operators in the event of off-normal events. Rapid operator response was not required.

Fuel Handling Operations are Challenging
• Fuel handling in sodium-coolant is challenging because there is no visual reference for the operations being conducted.
• Perhaps no fast reactor has had more fuel handling operations than EBR-II, >100,000 operations conducted successfully, but three errors occurred, any one of which could have terminated EBR-II operations.
• Similar events have occurred at other fast reactors. The JOYO reactor suffered significant damage when an experimental assembly was not successfully detached from the fuel handling equipment.
• There have been significant efforts to develop under-sodium viewing technology, which certainly has promise.
• In addition, recent advances in visualization technology such as found in aviation (synthetic vision based upon known location and detailed mapping of terrain) has promise.
• The bottom line is that fuel handling systems deserve extraordinary attention in design, maintenance and operation.

Maintenance is Straightforward
• Maintenance of sodium systems has been shown to be straightforward.
• Sodium systems operate at low pressure which significantly reduces the hazards of leakage during maintenance.
• Since sodium is a solid when cooled below 98o C, it is possible to conduct maintenance on sodium systems without draining them. The typical process is to freeze the sodium where the valve is located, cut the valve out of the system and replace it.
• There are also many examples of successful removal, cleaning and repair of primary-sodium system components such as pumps. At EBR-II, each of the two primary pumps was removed twice.
• At EBR-II, it was found that radiation exposure of maintenance personnel was very low, even though there were many maintenance procedures performed on sodium systems and components.
• Access to the reactor building was not restricted during reactor operation because radiation levels were always very low.

Safety Has Been Demonstrated
• The safety record of fast reactors is outstanding.
• Fast reactors benefit from several operating characteristics that enhance safety.
–They operate at near atmospheric pressure.
–The cores are relatively insensitive to spacial power shifts and fission product buildup.
–Sodium is a very effective heat transfer medium, permitting high core power-densities while effectively removing at decay heat.
–Sodium is also non-corrosive to fuel cladding and structural components of the core.
–Passive safety characteristics are easily achieved.
• The technology is robust.

Decommissioning has been demonstrated
• Decommissioning of several sodium-cooled fast reactors has been successfully accomplished.
• The EBR-II reactor was successfully decommissioned after 30 years of operation and both the process and the technology were shown to be effective.
– There was no evidence of corrosion from the sodium coolant following 40 years containing sodium at high temperature.
• Perhaps one of the most impressive decommissioning efforts was that at BN-350 which went through a similar process with the exception that the sodium was highly contaminated with fission products (principally Cs137) following years of operation with fuel with breached cladding.
• As with any reactor system, a key to successful decommissioning is to anticipate the need in the original design. For fast reactors, it is important that provisions for completely draining the sodium be provided, ensuring that there is no opportunity for residual “pools” of sodium be trapped in spaces that will not drain.

U.S. and International Experience in Fast Reactor Operation Has Shown Many Successes
• Fast reactor fuel is reliable and safe, whether metal or oxide. Cladding failure does not lead to progressive fuel failure.
• High burnup of fast reactor fuel is achievable, whether metal or oxide.
• Sodium is not corrosive to stainless steel or components within it.
• Leakage in steam generating systems with resultant sodium-water reactions does not lead to serious safety problems. Such reactions are not catastrophic, as previously believed, and can be detected, contained and isolated.
• Leakage of high-temperature sodium coolant, leading to a sodium fire, is not catastrophic and can be contained, suppressed and extinguished. There have been no injuries form sodium leakage and fire.
• Fast reactors can be self-protecting against Anticipated Transients Without Scram.

Lessons From Fast Reactor Operation
• Passive transition to natural convective core-cooling and passive rejection of decay heat has been demonstrated.
• Reliable control and safety-system response has been demonstrated.
• Low radiation exposures are the norm for operating and plant maintenance personnel.
• Emissions are quite low from sodium cooled fast reactors, in part because sodium reacts chemically with many fission products if fuel cladding is breached.
• Maintenance and repair techniques are well developed and straightforward.

• Several aspects of design and operation have highlighted challenges in fast reactor designs
– Thermal shock to structures is a major design challenge.
– Many problems with handling fuel in sodium systems have occurred.
– Failure of in-sodium components without adequate means for removal and repair has resulted in costly and time-consuming repair.
– Reactivity anomalies have occurred in a number of fast reactors, requiring careful attention to core restraint system design.
– Operational problems have been encountered at the sodium/cover-gas interface, resulting from formation of sodium-oxide deposits and can lead to binding of rotating machinery, control-rod drives and contamination of the sodium coolant.

• Worldwide experience with fast reactors has demonstrated the robustness of the technology and it stands ready for worldwide deployment.
• The lessons learned are many and there is danger that what has been learned will be forgotten given that there is little activity in fast reactor development at the present time.
• For this reason it is essential that knowledge of fast reactor technology be preserved, an activity supported in the U.S. as well as other countries.

By Barry Brook

Barry Brook is an ARC Laureate Fellow and Chair of Environmental Sustainability at the University of Tasmania. He researches global change, ecology and energy.

21 replies on “International Experience with Fast Reactor Operation & Testing”

The United States faces a national security crisis in maintaining its energy capacity, since many old energy generating facilities are scheduled for retirement and no replacement facilities are planned for construction and installation, no plans exist for the modernization of the national energy grid. New nuclear fueled energy facilities are absolutely necessary to the meet the requirements of a modern economy. A fleet of small modular fast neutron reactors must be be proposed and implemented immediately with the eventual nuclear fueled program of 400 to 600 reactors to be installed across the nation.


Many thanks. I had to read parts of this article several times in order to get my head fully around its content.

It has convinced me that I need a copy of Till and Chang’s book “Plentiful Energy”.


I am very interested in IFR but have to admit I haven’t read about it in depth because it is not my primary interest. My primary interest is the economics of nuclear power, irrespective of the type of nuclear power. I am interested in what can be done to remove the impediments that are preventing nuclear power from being cheaper than fossil fuels.

Having provided that background and excuse for not knowing more, I’d like to ask a qurstion about this statement:

Excellent experience has been gained, however, that demonstrates the robust nature of the technology, the potential for exceedingly safe designs, ease of maintenance, ease of operation and the ability to effectively manage waste from spent fuel.

If that is true, why isn’t the Navy using them for powering their submarines and aircraft carriers? Why hasn’t the US navy and other navies been using this technology for the decades?

My suspicion is because it is not economic , and the benefits for the Navy do not outweigh the costs.


Peter Lang – I guess the short answer to your question is that the U.S. Navy would not be primarily driven by economic considerations. Since its core lay in a pool of liquid sodium, I rather doubt that the EBR2 would be welcome in a submarine anyway!

However fast neutron reactors have a very high power density, so they can be designed to be very compact, desirable in an attack submarine. The Soviet Alfa attack class did have a fast neutron reactor, using lead-bismuth as the coolant. It was said to be able to outrun any torpedo aimed at it.

Fast neutron reactors might be attractive for submarines for another reason. They are not limited by the buildup of xenon (which soaks up slow neutrons), so they can be cycled between full power and shut down and full power again. This would allow (the steam condensers of) a submarine to fall silent, at least as silent as the fresh fission products would allow. However the Alfa class was said to be noisy anyway.


Roger Clifton,

I agree the Navy is not primarily concerned about cost. Their requirements are reliability, safety, sustainability, speed, independence from supply ships, etc. But cost is also a factor – lower cost means they can have more boats for the same budget. If the IFR met the requirements at lower cost than LWR or if, when the Navy was reviewing priorities and capability requirements as they do continually, they had believed at any stage in the past 50 years that the IFR might be a better option to meet their requirements than the LWR, then they would have been researching it and expediting its development and demonstration. The fact they haven’t been needs to be taken into consideration in our reality checks – “the Smell Test” I think the host calls it. :)

I certainly believe some Gen IV’s will eventually be the best option for electricity utilities to choose for their next capacity gap. I don’t believe we are anywhere near that stage yet. Therefore, if we want to increase the rate of nuclear roll out my focus is on trying to persuade nuclear advocates to recognise the one key issue that is the real block to nuclear power being accepted – the cost. The rational decisions are made on the basis of what will provide electricity at the least cost for the life of the plant. As soon as nuclear is the cheapest options the scaremongering the anti-nukes use will be easily dealt with. The cost is the block to progress. And that is not a technical problem. It is a regulatory issue. So it can be fixed. We just need to persuade the pro-nukes to change their advocacy methods to focus on what is the key issue and how we need to address it.

I don’t believe IFR’s are cost effective yet or likely to be for decades. I agree we need to keep researching an demonstrating them along with all other promising designs. But most effort need to be focused on removing the impediments that are blocking nuclear power from being cheaper than fossil fuels for electricity generation.


GE Hitachi’s PRISM reactor is in the frame for the disposition of the UK’s plutonium stockpile.

This link gives reason for optimism regarding the low-cost potential to UK taxpayers:

Bearing in mind that the fuel created from the disposition of plutonium will power the reactor for 50 or 60 years, generating 622 MW of emission-free electricity.

Surely it is not beyond the wit of the UK government to agree a subsidised payment to GE Hitachi, per kWh generated over that period of time, to handsomely reward investors for leading the UK into the Gen IV era.

We have the expertise and manufacturing capacity to produce these reactors in their entirety and we have enough of our most precious energy resource to supply all of our energy needs – electricity, heat, liquid fuels, fertilisers – for the next 500 years. Who knows? By then we may have cracked fusion!

We’d need about 1000 of these reactors, grouped at maybe 200 sites, to provide all of our energy – it seems most do-able. Our legacy would be emission-free energy for the foreseeable future, as we burn our ‘nuclear waste’. We’d leave behind minuscule amounts of waste which decays to background radiation levels in only 300 years – easily, cheaply and safely stored.


Thank you. I can’t say I am persuaded.

I’ve been involved in energy projects since the 1960’s, all over the world, including many feasibility studies. I’ve seen many of the claims of enthusiastic researchers and true believers. I can recall the solar power advocates in the 1980s, 1990s and 2000s repeating year after year assertions like: “solar thermal is cheaper than nuclear now, if only the government would give us a bit more money to demonstrate it”.

It takes a long time for new designs to reach maturity and become economically viable. It’s taken 50 years to get to the current generation of reactors. And they are relatively immature in that they are not widely accepted as viable (they are in some places but certainly not in most). The IFR is not even at the “Bleeding edge” stage yet:

I’m just being realistic. If we want to make progress fastest, for all design concepts, by far the most effective thing we can do is to advocate to get the impediments that are making nuclear too costly removed. This can be done. But it takes a change of approach. Advocating for your particular preferred design has not worked in the past, so why should we expect it to work now? It’s a waste of time and effort. Trying to battle the anti-nukes on their chosen ground has been going on for 50 years. It’s clearly not the way forward.


My understanding is that fast reactors are not considered to be economic in the face of the current low cost of miniing and enriching uranium.


The GE-Hitachi PRISM is based on the IFR, and it’s a design that’s ready to be built. Using metal fuel and a closed fuel cycle, which has been demonstrated.

A simple price on carbon would make the economics for nuclear much more attractive. Tax carbon at the source, where fossil fuels are extracted, and let the market decide.

Essential introductory links about sodium-cooled fast reactors in general, and the IFR in particular:
* Interview with Dr. Charles Till – PBS – Frontline
*The Integral Fast Reactor (IFR) project
*Sodium as a Fast Reactor Coolant (PDF)

There’s really no rush to build GenIV nuclear. Modern PWR designs are more standardized (more economical), simpler, safer, and the “spent” fuel can be stored for future burn-up in fast reactors. The first commercial Small Modular Reactors will be PWR designs too. Fast reactor technology will follow. As long as we (humans on planet earth) are replacing coal-fired power stations as quickly as possible, there’s no problem.


As an amateur enthusiast who has read Dr.Till’s book ( at least twice) and as a follower of the LFTR, I don’t know which to throw my support behind.
Would a “contrast and compare” be at all helpful?


This is worth 20 minutes of anybody’s time, to witness the sincerity of belief in the potential for IFRs to power the USA forward:

The rhetorical question posed by those associated with EBR II, in reaction to Dr Sackett’s announcement of closure, needs stamping on the forehead of every member of the USA legislature; watch from 16:19, if you watch nothing else.


Fast reactors are running for power in Russia. Indian PFBR is completed and is in testing and starting phase. The Chinese are close behind. Fast reactors are not priced out of reckoning. They are financially feasible in some locations.
Perhaps the safety could be further improved by replacing the secondary sodium with a cheap and safe salt.


I nuclear is going to be permanent we need breeder reactors. I don’t see any reason to put off building them. The sooner we start the sooner we can get building all the required infrastructure. Sure we should keep the already built nuclear power plants going and maybe build some more PWR-type, but in my opinion we should be building sodium cooled fast breeder reactors now. That should be the number one priority for the industrialized parts of the world.


We know from the book, “Plentiful Energy” that development of the electrofining process was interrupted by the shutdown in 1994. To that extent, the recycling aspect of the “integral fast reactor” has not had the level of proof and testing as the reactor itself.

However you say that “Melt Refining was used to recycle fuel for EBR-II from 1964 through 1969” and go on to say that that recycled fuel was used throughout the life of the reactor. The process of heating fuel in a zirconia crucible seems to be much simpler than electrofining, more credible for remote operation in a municipal power station.

We have heard about the evolution of the isotopic proportions of the fissile content as the fissium goes through many cycles. However I would be interested to hear how the core is managed as the fuel is progressively diluted by zirconium from the crucibles. Also how long the material remains just ductile enough to be extruded as the proportion of non-reacting fission products accumulates.


@ Roger Clifton:
From Dr Tell’s book I gained the impression that everyone on his team were a satisfied about their on -site fuel refining system.
What they lacked, and were not given, was the time and funds to build a commercial scale model and prove the system in an industrial context.


The Navy is not actually involved with cost; it has been accustomed, with little oversight, to soaking up money without much objection from anyone. For primitive reasons, human beings have always been willing to pay more for violence than for peace.

The economics of the fast fuel cycle are occluded by the same factor that allows human beings to engage in the silly and ridiculous practice of allowing coal, oil and gas waste to be dumped indiscriminately into the planetary atmosphere without restriction: External costs of energy are not included.

If consumers had to pay the medical bills of all the people who are injured by air pollution, the coal industry would collapse in a New York second, as would the petroleum industry, and many other industries. If we monetized the destruction of forests, and of land, of distressed supplies of water, if we were compelled to pay to future generations the costs with which have burdened them, I assure everyone that the only solution to any kind of wealth would be very much involved in fast neutron generated energy.

Right now, it is deemed that only internal costs matter. Under these conditions it still seems cheaper to mine uranium, and for that matter coal, gas, and oil, not to mention cadmium and lanthanides for the so called “renewable” energy industry.

In this space I have argued that with the uranium and thorium already mined, we might shut all the world’s mines for beyond a century, and in that century, find more benign ways of obtaining uranium than the primitive ways we have employed thus far. In fact, the path to these ways are already well understood, but not employed, again, because of the failure to include externalities.

In any case, this focus on “what is cheaper” is a little ridiculous.
Cheaper than what? A destroyed atmosphere? A slew of heavy metals lacing the agricultural fields of China and India?

The decision of a few self absorbed generations to consume at the expense of all future generations will eventually become the topic of history, and as recorded in history and judged by history, and as objects of history, we will surely survive in memory in ways that, speaking for myself, can only be sources of shame and regret should we dare to contemplate them honestly.

Have a nice weekend.


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