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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. Typically SMRs are modular where the individual modules are road truck portable to minimize overall cost.

The acronym CANDU means Canadian Deuterium Uranium and refers to a high efficiency nuclear reactor cooled and moderated by heavy water. CANDU reactors were deployed both in Canada and other countries.

The acronym LWR means Light Water Reactor. Light water reactors have been deployed in many countries. They are relatively low cost but have the disadvantages of low natural uranium fuel efficiency, low TRU production efficiency and requiring enriched uranium fuel.

The acronym FNR means Fast Neutron Reactor which refers to an advanced reactor type that can be made fuel sustainable. If a FNR is rated at less than 300 MWe it is also a SMR. For overall cost minimization FNRs should be designed to be assembled from road truck portable modules.

TRU refers to transuranic atoms. These are atoms with atomic numbers greater than 92 that perform a critical catalyst like function in FNRs. The main source of TRU in Canada is used CANDU reactor fuel.

CANDU REACTORS: CANDU reactors use heavy water for both cooling and neutron moderation. CANDU reactors are twice as efficient as LWRs in terms of electricity produced per unit of natural uranium consumed. CANDU reactors are 4X as efficient as Light Water Reactors in terms of TRU produced per unit of natural uranium consumed.

A Fast Neutron Reactor (FNR) operates using fast neutrons, as distinct from a water moderated reactor that operates using slow neutrons. Starting a FNR requires TRU based core fuel, which in Canada should be obtained by reprocessing used CANDU fuel. Once operating, a properly designed FNR produces TRU atoms faster than it consumes TRU atoms.

With suitable fuel recycling FNRs can produce almost unlimited amounts of sustainable clean energy. FNRs fission high atomic weight isotopes with long half lives into low atomic weight isotopes with short half lives, as required for efficient use of the abundant natural uranium isotope U-238 and for permanent nuclear fuel waste disposal.

There is lack of public appreciation that the electric power produced by wind and solar electricity generation is sustainable but it is intermittent and even with battery backup that power is interruptible whereas the electric power produced by water cooled nuclear reactors is dependable but is not long term sustainable. By contrast, the electric power produced by properly designed FNR is both dependable and sustainable.

Hence these different energy and power supply technologies have different cost structures. Often fossil fuels are used when interruptible clean (non-fossil) power is not avalable. Typically clean energy costs at least twice as much as fossil fuel sourced energy. Typically dependable power costs significantly more than interruptible power. The net effect is that sustainable and dependable clean power is significantly more expensive than fossil fuel sourced power. Politicians who promise low cost power are the primary cause of CO2 driven climate change.

The cost of the energy required to produce and transport each product is embedded in the cost of that product. Hence shifting from fossil fuels to clean energy triggers additional product costs that can only be offset by improved product life and improved energy efficiency.

Both CANDU reactors and FNRs have been built in the past. However, financing of new CANDU reactors is difficult. No one will finance construction of a new CANDU reactor unless there is a reliable source of heavy water for that reactor. Similarly no one will finance construction of a new FNR unless there is a reliable source of TRU based core fuel for that reactor. TRU is primarily obtained by reprocessing used CANDU fuel.

Production of heavy water and FNR core fuel should be done by national governments. These critical materials are required by all subnational parties who plan to engage in production of sustainable nuclear power.

CANDU reactors produce 2 fold more electricity per unit of natural uranium consumed than do LWRs.
CANDU reactors produce 4 fold more TRU per unit of natural uranium consumed than do LWRs.
FNRs with fuel reprocessing produce 100 fold more electricity per unit of natural uranium consumed than do CANDU reactors.

In summary, liquid sodium cooled power FNRs can provide sustainable power for complete displacement of fossil fuels with almost no production of long lived nuclear waste.

During FNR fuel reprocessing the fission products are extracted from the fuel and fissile atoms are moved from blanket fuel rods to core fuel rods.
Over 95% of the extracted fission products decay to safe levels in 300 years. Hence, subject to suitable used fuel component separations, the rate of FNR long lived fuel waste production is about:
100 X 20 = 2000 fold
less than for a CANDU reactor.

The best method of used LWR fuel disposal is to reuse that fuel in a CANDU reactor.

The best method of used CANDU reactor fuel disposal is to reprocess the used CANDU fuel into FNR fuel.

FNRs can then convert 95% of that FNR fuel into short lived fission products.

In summary, liquid sodium cooled power FNRs can safely dispose of spent fuel from LWRs and CANDU reactors.

Fast Neutron Reactors (FNRs) provide the only economic and sustainable means of fully eliminating fossil CO2 emission from global energy production.

However, economic realization of FNR benefits requires national commitments to facilities for: producing heavy water, deploying CANDU reactors, TRU Concentration from used CANDU fuel, pyroprocessing of the TRU concentrates to form new FNR fuel and automated FNR Fuel Bundle fabrication. These shared facilities require a multi-billion dollar capital cost commitment.

The essential nature of FNRs for displacement of fossil fuels was realized by physicists during the 1960s. It took another 30 years to solve the technical issues relating to practical 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 untenable.

Heat is one of the largest public energy usage categories. Economically meeting the heat load with clean 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 economically supply both heat and electricity.

It is physically impossible to completely displace fossil fuels with wind and solar energy. In the circumpolar countries such as Canada and Russia there is insufficient sunlight in the winter and there are extended cold periods with low wind. Very large amounts of efficient energy storage are required to meet human dependable energy requirements during such periods. The only present economical means of efficient large scale energy storage is large hydro-electric reservoirs. However, most of the available large hydro-electric reservoir capacity has already been harnessed. Hence it is economically 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 consume the relatively rare uranium isotope U-235 which resource is rapidly being depleted. Water cooled nuclear reactors also produce unacceptable amounts of nuclear isotopes with long half lives and operate at high internal pressures which make them unsuitable for urban siting.

Thus presently the only safe proven dependable clean power supply technology 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 today there are relatively few workers power FNR operating experience. A power FNR has not been operated in North America since 1994. Relevant reactor theory has disappeared from the North American public education curriculum. Present North American public utility rates are structured to discourage electricity consumption and encourage fossil fuel consumption. Hence the North American public has no pressing financial motivation to adopt FNRs.

In order to address climate change the electricity rate structure must be modified to provide a low cost interruptible electricity rate and a higher cost dependable electricity rate.

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. Large FNRs have been operating in Russia for 30 years and now China is adopting the technology.

What is required today is the political 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 the federal Liberal governmental commitment of about $30 billion taxpayer dollars to expansion of fossil fuel pipeline export 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 that used fuel to harvest the large amount of nuclear energy that the used CANDU fuel contains.

Obstacles to immediate implementation of FNRs are an improper electricity price structure and irrational political resistance to concentration, transportation, storage and reprocessing of used CANDU nuclear fuel. The used fuel components, instead of gradually diminishing in radioactivity as the years pass, would be electrochemically reprocessed and reused about every 30 years. It is contemplated that the initial used CANDU fuel TRU concentration would be done on existing CANDU reactor sites and subsequent FNR fuel pyroprocessing would be at Chalk River, Ontario, which is far from any urban center. A suitable future used fuel storage / reprocessing site might be the old Jersey Emerald mine, which is about 40 km from Trail, BC.

Ideally the fission product interim storage facility should be located close to the fuel rod reprocessing facility. One of the lessons learned from nuclear fuel reprocessing experience in France is that if the used fuel reprocessing and storage facilities are not located close to one another 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 a TRU shortage developing over the coming decades threatens the very existence of the human species. Without sufficient TRU there is no sustainable substitute for fossil fuels.
2) The practical source of TRU in Canada is used CANDU fuel. For now all new water cooled power reactors should be of the CANDU type. These new CANDU reactors should be configured for future fueling with existing used LWR fuel.
3) If we contemplate quadrupling the the world nuclear reactor capacity over the next 40 years using FNRs to achieve sustainability we are committing the entire known mineable natural uranium resource. If we fail to obey the nuclear physics as fossil fuels are exhausted there will be no economic fuel source left but intermittently available renewable energy.
4) The only strategy that can mitigate these problems is conservation of TRU. The present practise of wasting TRU in LWRs or burying spent water moderated reactor fuel containing TRU isotopes is worse than stupid.
5) All the new reactor designs that do not sustainably breed new TRU should be discarded as a waste of critical resources. The regulatory authorities should do all necessary to to accelerate approval and funding of new fuel sustainable reactor designs.
6) From an electricity market perspective all new breeder reactor capacity should have the highest priority for electricity grid access. The existing electricity market mechanisms will just have to be changed to make that happen.
7) The high school core curriculum should have a section that discusses the crucial role of TRU in future energy production and that sufficient TRU will not exist unless breeder reactors are both funded and operated at maximum capacity today irrespective of present natural gas prices.
8) 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 sustainable physical reality. The human species as we now know it will live or die in accordance with the natural physical laws.

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 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 sustainable.

A significant public concern is that FNRs be engineered and operated in a manner that prevents bad actors from 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 military use. This ratio is maintained by irradiating FNR fuel bundles in a first in-first out sequence.

This sequence ensures that each fuel bundle 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 detonation.

Ensuring first-in first-out exchange of FNR fuel bundles requires keeping a public record of the neutron flux exposure history of each FNR fuel bundle. Due to the half life of Na-24 exchanging FNR fuel bundles requires a FNR shutdown of more than a week, so maintaining the required fuel bundle flux exposure records with FNRs 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.
and in the book "Plentiful Energy" by Charles Til and Yoon Chang.

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. The Russians also have an 800 MWe FNR operating since 2015 and are finalizing the design of a 1200 MWe FNR. China is following the Russian lead with two liquid sodium cooled reactors scheduled for completion in 2023. Realistically, as compared to North America, the Russians have at least a 30 year lead in deployment of sodium cooled 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 or to operate with a sustainable fuel cycle.

The practical output power capacity of a fully assembled road truck portable water cooled SMR pressure vessel 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 irradiated fuel disposal problems.

The FNRs described herein do not use reactor pressure vessels. Instead, a FNR has an atmospheric pressure liquid sodium pool. The pool structure is too large for road transport as a single piece so pool sections are prefabricated and later welded together on-site. Almost all the other FNR components are truck portable modules. As compared to a water or gas cooled SMR a 300 MWe FNR provides far superior: working life, fuel efficiency, waste disposal and safety as well as an output temperature of 440 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 region that reasonably projects a future population of 100,000 persons or more a FNR is a much better choice.

Water cooled reactors also have potential void (steam bubble) instability issues that can potentially lead to prompt neutron criticality explosions such as occurred at Chernobyl in 1984. Voids cannot form 10 m deep in a natually circulated liquid sodium pool operating at less than 460 degrees C.

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 bulk non-fossil 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 November 4, 2023

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