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By Charles Rhodes, P.Eng., Ph.D.

The acronym SMR means Small Modular Reactor, a term which generally refers to nuclear reactors with electricity outputs of less than 300 MWe. The acronym FNR means Fast Neutron Reactor. If a FNR is rated at less than 300 MWe it is also a SMR. Both SMRs and modular FNRs can be designed to be road truck portable.

With appropriate periodic fuel reprocessing a FNR yields about 100 fold more energy per kg of natural uranium than does a CANDU reactor. During FNR fuel reprocessing the fission products are extracted from the fuel. Over 95% of the extracted fission products decay to safe levels in 300 years. Hence on a long lived fuel waste mass per kWh basis the rate of FNR long lived spent fuel waste production is about:
100 X 20 = 2000 fold
less than for a CANDU reactor.

The best method of used CANDU fuel disposal is to reprocess the used CANDU fuel into FNR fuel and then convert this material into short lived fission products in a FNR.

A Fast Neutron Reactor (FNR) operates using fast neutrons, as distinct from a water moderated reactor that operates using slow neutrons.

The nuclear properties of sodium allow design of FNRs that, with suitable fuel recycling, produce almost unlimited amounts of sustainable non-fossil energy. FNRs fission long lived high atomic weight elements into short lived low atomic weight elements, as required for efficient use of the abundant natural uranium isotope U-238 and for nuclear fuel waste disposal. A typical FNR size is 280 MWe, so this FNRs is also a liquid sodium cooled SMR.

Fast Neutron Reactors (FNRs) provide the only economic and sustainable zero CO2 emitting means of fully displacing fossil fuels from global energy production.

The essential nature of FNRs for displacement of fossil fuels was realized by physicists during the 1960s. It took another 30 years to sort out the technical issues relating to realization of reliable FNRs. Since then the fossil fuel industry has viewed FNRs as an existential threat and has used every form of political corruption to delay or prevent large scale FNR deployment. However, the overwhelming advantages of FNR technology for prevention of further climate change make the position of the fossil fuel industry increasingly untenable.

Heat is one of the largest public energy usage categories. Economically meeting the heat load with non-fossil energy requires district heating systems that are fed thermal energy by modular Fast Neutron Reactors (FNRs). These FNRs should be geographically distributed across urban areas to provide mutual support and to economically supply both heat and electricity.

It is physically impossible to completely displace fossil fuels with renewable (wind, solar and hydro-electric) energy. In the circumpolar countries such as Canada and Russia there is insufficient sunlight in the winter and there are extended periods of low wind. Very large amounts of efficient energy storage are required to meet human dependable energy requirements during the the extended low wind and low sun periods. The only economical means of efficient large scale energy storage is large hydro-electric reservoirs. However, most of the potential hydro-electric reservoir capacity has already been harnessed. Hence it is impossible to meet human dependable power and energy requirements from only renewable energy.

Water cooled nuclear reactors are not a sustainable means for meeting future human dependable power requirements. Water cooled nuclear reactors require an on-going consumption of the relatively rare uranium isotope U-235 which resource is rapidly being depleted. Water cooled nuclear reactors also produce unacceptable amounts of long lived nuclear fuel waste and operate at high internal pressures which make them unsuitable for urban siting.

Thus presently the only safe proven dependable power supply technology that does not emit CO2 and that can sustainably meet future human requirements is liquid sodium cooled Fast Neutron Reactors (FNRs).

The scientific issues related to FNRs are well understood. However, due to entrenched governmental corruption by the fossil fuel industry, in North America there is relatively little power FNR operating experience. North American public utility rates are presently structured to discourage electricity consumption and encourage fossil fuel consumption. Hence there is no pressing financial motivation to adopt FNRs.

With appropriate periodic fuel reprocessing a FNR yields about 100 fold more energy per kg of natural uranium than does a heavy water moderated CANDU reactor. During fuel reprocessing the fission products are extracted from the fuel. About 95% of the extracted fission products decay to safe levels in 300 years. Hence on a fuel waste mass per kWh basis the rate of FNR long lived spent fuel waste production is about:
100 X 20 = 2000 fold
less than for a CANDU reactor.

The best method of spent CANDU fuel disposal is to reprocess the spent CANDU fuel into new FNR fuel and then reduce it to short lived fission products in a FNR.

In summary, liquid sodium cooled power FNRs can provide sufficient energy to sustainably displace fossil fuels with almost no production of long lived nuclear waste. FNRs can also safely dispose of spent fuel from CANDU and other water moderated nuclear reactors.

The practical implementation of modular liquid sodium cooled Fast Neutron Reactors (FNRs) is more a political problem than a scientific problem. All the necessary nuclear technology existed in the early 1990s. What is required today is the will to proceed with deployment of FNRs and related fuel recycling in the face of ongoing governmental corruption by the fossil fuel industry. Nowhere is that corruption more obvious than in governmental commitment of many billions of taxpayer dollars to expansion of liquid fossil fuel export pipeline capacity, which expansion is completely contrary to the 2015 Paris agreement on climate change.

Equally disturbing is the continued federal government commitment to burying used CANDU fuel instead of recycling the used fuel to realize the large amount of nuclear energy that the used fuel contains.

Obstacles to immediate implementation of FNRs are an improper electricity price structure and political resistance to transportation, storage and processing of used CANDU nuclear fuel bundles. The spent fuel, instead of gradually diminishing in radioactivity as the years pass, would be chemically/electrolytically reprocessed and reused about every 36 years. It is contemplated that the initial FNR fuel reprocessing site would be at Chalk River, Ontario, which is far from any urban center. Another suitable site might be Trail, BC.

Ideally the fission product interim storage facility should be located close to the fuel rod reprocessing facility. One of the lessons to be learned from nuclear fuel reprocessing experience in France is that if the fuel reprocessing and storage facilities are not properly located highly radioactive materials wind up being transported to and fro all over the country.

1) Presently there is no recognition by either the Canadian or US governments that the Pu-239 shortage threatens the very existence of the human species. Without sufficient Pu-239 there is no sustainable substitute for fossil fuels.
2) Making Pu-239 from U-235 requires consumption of one atom of U-235 for every 1.5 atoms of Pu-239 produced. It takes much more natural uranium to start a FNR than it does to fuel a CANDU reactor of similar thermal output capacity.
3) If we contemplate quadrupling the the world nuclear reactor capacity over the next 40 years using breeder reactors to achieve sustainability we are committing the entire known mineable natural uranium resource. If we fail to do so as fossil fuels are exhausted there will be no economic fuel source left but renewable energy.
4) The only strategy that can mitigate these problems is conservation of Pu-239 and U-235. The present practise of consuming Pu-239 in water moderated reactors or burying spent water moderated reactor fuel containing these isotopes in the ground is worse than stupid.
5) All the new reactor designs that do not net breed new fuel should simply be discarded as a waste of critical resources. The regulatory authorities should do all necessary to to accelerate approval and funding of new breeder reactor designs.
6) From an electricity market perspective all new breeder reactor capacity should have the highest priority for electricity grid access. The existing market mechanisms will just have to be changed to make that happen. The high school core curriculum should have a section that discusses the crucial role of Pu in future energy production and that sufficient Pu will not exist unless breeder reactors are both funded and operated at maximum capacity today irrespective of present natural gas prices.
7) The above observations are dictated by the laws of physics. There are all kinds of claims based on market models that have no foundation in physical reality. The human species as we now know it will live or die in accordance with the natural physical laws.
8) There is a possibility of harvesting natural uranium from the oceans. However, the concentration of uranium in sea water is only about 3 parts per billion so the cost of uranium recovery from the ocean is very high. Possibly there might be some marine life species that naturally concentrates uranium in the ocean which might make harvesting of uranium from the ocean more practical.

A blunt reality that humans must face is that fossil hydrocarbons must remain in the ground. Sustainable production of reliable non-fossil power requires fast neutron power reactors. Fast neutron power reactors initially require about 20% Pu in their core fuel rods for sustained operation. Hence any treaty, legislation or regulation that only permits lower fractions of Pu in nuclear fuel is not compatible.

A significant public concern is that FNRs be engineered and operated in a manner that does not allow bad actors to obtain Pu-239 in a form suitable for making atomic bombs. The important issue is maintaining a sufficient Pu-240 to Pu-239 ratio in the fuel to prevent the plutonium ever being suitable for making fission bombs. This ratio is maintained by doing all necessary to ensure that FNR fuel bundles are irradiated in a first in-first out sequence.

This sequence ensures that in addition to containing Pu-239 each fuel bundle also contains a sufficient fraction of Pu-240 to prevent the contained Pu being used for bomb manufacture. Pu-240 cannot be chemically separated from Pu-239 and is extremely difficult to physically separate from Pu-239. In a bomb assembly Pu-240 causes pre-ignition, which prevents a large scale explosion.

Ensuring first-in first-out exchange of FNR fuel bundles requires keeping a public record of the neutron flux exposure history of the FNR fuel bundles. Due to the half life of Mg-24 exchanging FNR fuel bundles requires a FNR shutdown of more than a week, so maintaining the required fuel bundle flux exposure records is not onerous.

In the USA a 20 MWe fully functional prototype liquid sodium cooled FNR known as the EBR-2 was built and successfully operated from about 1964 to 1994. Under the Bill Clinton administration the USA took a huge step backwards when it cancelled funding of its fast neutron reactor program. The history of a successful prototype FNR in the USA is well summarized by the video:
The Nuclear Option.

In Russia a 600 MWe fully functional prototype liquid sodium cooled FNR known as the BN600 was built and has been successfully operated since about 1984. See 600 MWe LIQUID SODIUM COOLED POWER REACTOR. Today the Russians also have an 800 MWe FNR operating and are working on a 1200 MWe FNR. Realistically, as compared to North America, the Russians have at least a 30 year lead in dsployment of FNR technology. This lead is a direct result of sustained fossil fuel industry corruption of the US and Canadian governments.

The appeal of water or gas cooled SMRs is road truck portability of the water or gas cooled reactor pressure vessel. However, it is physically impossible for a water or gas cooled SMR with a road truck portable pressure vessel to have either a large power rating to or operate with a sustainable fuel cycle.

The practical output power capacity of a road truck portable water cooled SMR is limited to about 50 MWe and the rated output temperature is limited to about 320 degrees C.

Road truck deliverable gas cooled SMRs are more typically rated for 15 MWe. They have huge fuel disposal problems.

FNRs do not use reactor pressure vessels. Instead, a FNR has an atmospheric pressure liquid sodium pool. The pool liner is too large for road transport as a single piece so pool liner sections are welded together on-site. The other FNR components are all truck portable modules. As compared to a water or gas cooled SMR a 280 MWe FNR provides far superior working life, fuel efficiency, waste disposal and safety as well as an output temperature of 490 degrees C.

For a small remote community or a remote mine, where working life, output power, fuel sustainablity, nuclear fuel waste disposal and output temperature are not major concerns, the lower initial cost of a water or gas cooled SMR is appealing. However, for a community that reasonably projects needing multiple SMRs to meet its future peak electricity and/or thermal load a FNR is a much better choice.

Water cooled reactors also have void instability issues that can potentially lead to prompt neutron criticality explosions such as occurred at Chernobyl in 1984.

The public should realize that since about 1980 the fossil fuel industry has spent literally billions of dollars on publicity campaigns and government lobbying aimed at preserving fossil fuel industry energy market share by preventing wider deployment of nuclear energy. In spite of a few highly publicized but relatively minor accidents, nuclear energy has shown itself to be by far the safest and least expensive means of dependable non-fossil bulk energy production.

In the USA there is gradual public realization that US government policy has been politically dominated by fossil fuel industry influence to the detriment of the environment.

December 2, 2019 CBC NEWS VIDEO
New Brunswick, Ontario and Saskatchewan SMR MOU

August 10, 2020
Alberta is to join the MoU signed in December 2019 by New Brunswick, Ontario and Saskatchewan to work together to support the development and deployment of SMRs

For a more complete overview of FNRs students are encouraged to study the web pages titled:

This web page last updated August 17, 2020

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