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

The object of this web page is to convey to non-scientific persons the vital role of Trans-Uranics (TRU) and Fast Neutron Reactors (FNRs) in the future of mankind.

Today nuclear energy is mainly obtained via fission of the rare uranium isotope U-235. However, the economic supply of that isotope is limited and reasonable projections indicate that, due to resource depletion, U-235 will become very expensive during the coming decades. However, vast amounts of clean, dependable and sustainable energy are potentially available from the abundant uranium isotope U-238. Large reserves of U-238 exist in natural ore bodies, in used nuclear reactor fuel and in tailings from uranium U-235 enrichment plants. However, TRU and FNRs are needed to access the energy contained in U-238.

Trans-Uranics (TRU) are atoms with atomic numbers (number of protons per atom) greater than 92, the number of protons in a uranium atom. The TRU elements are: Neptunium, Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, etc. TRU does not naturally occur on Earth today because all the TRU atom isotopes have half lives that are much shorter than the age of planet Earth. The only way that TRU atoms occur on Earth today is via synthesis using either a particle accelerator or a nuclear reactor. For this reason TRU elements are sometimes referred to as man made elements.

Mankind needs Fast Neutron Reactors (FNRs) to provide dependable and sustainable nuclear power to displace fossil fuels. In a fuel sustainable FNR TRU acts as a transmution quasi-catalyst that enables use of U-238 for production of dependable and sustainable nuclear power. The power output of a FNR is proportional to the size of the FNR's TRU inventory. Due to the large U-238 resource the potential cumulative energy output from FNRs has almost no practical upper limit.

An important aspect of TRU in sodium cooled FNRs is the relatively large linear Thermal Coefficient of Expansion (TCE) of TRU. This TCE has an important role in passive FNR fuel temperature control.

Today one of the main problems with exploitation of FNRs as a nearly unlimited source of energy is lack of public awareness. The TRU necessary to access this energy is routinely being wasted by parties who lack a basic understanding of fast neutron nuclear physics. In both Canada and the USA there is ill conceived regulation and legislation, favoring the fossil fuel industry, that prevents utilization of this enormous source of sustainable and dependable clean energy.

The most common TRU isotope is Pu-239, which if isolated can potentially be used to make implosion type nuclear bombs. However, from the perspective of FNRs the TRU elements and their isotopes act as a group. Keeping the TRU elements and their isotopes together as a group prevents their use in atomic bombs and aids in their disposal.

TRU has a physical parameter which is important in the design of inherently safe fast neutron reactors. TRU is more than 50% plutonium (Pu). Solid metallic plutonium has a relatively high linear coefficient of thermal expansion of about 50 ppm / deg C as compared to about 10 ppm / deg C for most other metals. Plutonium further thermally expands when it commences a phase transition at about 602 degrees C. Even if the core fuel alloy of a fast neutron reactor (FNR) is only 20% Pu the linear coefficient of thermal expansion for the FNR core fuel is still at least twice that of most other metals. This feature enables the reactivity versus temperature curve of a FNR with TRU based core fuel to have a certain negative slope. This negative slope makes a FNR inherently safe by stopping the nuclear reaction if the FNR core fuel gets too hot. It is a mistake to assume that a FNR which operates safely with TRU based core fuel will be equally safe if the TRU is replaced by enriched U-235.

Since the dawn of nuclear electric power the fossil fuel industry has viewed the prospect of dependable and sustainable nuclear power as an existential threat and has falsely convinced both the public and governments that:
a) TRU is a proliferation danger;
b) TRU is an unsolvable pollution problem;
c) TRU should be buried in deep geological repositories;
d) TRU / U-238 reactors should not be permitted to displace fossil fuels;
e) Small amounts of ionizing radiation are dangerous.

However, the reality is that:
a) TRU can be made unsuitable for use in nuclear weapons;
b) TRU can readily be disposed of using Fast Neutron Reactors (FNRs);
c) That mankind needs a large TRU inventory to enable FNRs to sustainably displace fossil fuels;
d) That small amounts of ionizing radiation are health beneficial.

The water cooled nuclear power reactors that are in wide use today are not fuel sustainable. Further, due to now obvious climate change, many countries now have new water cooled nuclear reactors either planned or under construction. A problem today is ensuring future economic supply of sufficient fuel for all these new water cooled nuclear reactors. These reactors are fuelled in part by the rare uranium isotope U-235 for which there is only a limited resource that will likely be depleted within a few decades.

Fortunately there is an alternative nuclear fuel cycle that is sustainable.

As early as the 1960s the concept of using fuel breeding Fast Neutron Reactors (FNRs) to produce sustainable nuclear power was well known. During the 1980s and early 1990s such FNRs became an experimental reality in several countries. Some power FNRs have operated for over 30 years. The concept is to fission the Pu-239 in TRU with fast neutrons and to use the resulting excess fast fission neutrons to both fission other TRU atoms and to breed abundant fertile U-238 into more TRU. The original concept was to periodically extract plutonium from the U-238 using a chemical process known as PUREX, which process was originally developed for making Pu-239 based nuclear bombs.

There were several practical implementation problems with the original concept.
a) There was public fear about use of plutonium and nuclear weapon proliferation;
b) As long as natural uranium is cheap and readily available the FNR process is too complex and too expensive as compared to simple fission of U-235;
c) The PUREX process works only on plutonium and produces difficult to manage waste streams;
d) The robotics necessary to automate the FNR fuel reprocessing and fabrication did not exist at the time;
e) Originally climate change was not perceived by the funding governments as a pressing issue;
f) People with the necessary competence in fast neutron physics were in short supply.

Due to unsubstantiated and irrational public fear about nuclear and radiation matters, for the three decades 1990 to 2020 there was little world wide new nuclear power reactor deployment and there were only about 400 major power reactors operating. If those would be the only continuing drain on the U-235 resource there would not be a U-235 availability problem this century. However, about 2020 voters and politicians in many countries were finally convinced that CO2 emissions from combustion of fossil fuels are a serious problem and that nuclear power reactors provide dependable clean power without CO2 emission.

Today most major countries have plans to build additional nuclear power reactor capacity to mitigate climate change. Within two decades the operating nuclear power reactor capacity is expected to double and that capacity will probably double again during the subsequent two decades. In short, by 2060 the economic U-235 natural resource on planet Earth will likely be seriously depleted.

At that time, unless other dependable clean energy supply technologies have been fully developed and deployed, planet Earth will likely revert to use of fossil fuels and soon thereafter the consequent rise in lower atmospheric temperature will cause a mass extinction of large land animals.

Used fuel from present Light Water Reactors (LWRs) contains fission products, TRU, U-235 and U-238. This used LWR fuel can be converted into CANDU reactor fuel.

Used fuel from CANDU reactors contains fission products, more TRU and U-238. The TRU can be concentrated and the fission products, which have relatively short half lives, can be extracted. The concentrated TRU acts as a quasi-catalyst which enables ongoing transmution of U-238 into Fast Neutron Reactor (FNR) fuel for millennia. However, while the cumulative energy output from a FNR is only limited by the supply of abundant U-238, the sustained FNR power output is limited by the FNR's TRU inventory.

To understand FNRs and efficient TRU production we must return to the 1960s.

After WWII Canada developed a nuclear power reactor technology known as CANDU (CANadian Deuterium Uranium). This technology uses heavy water for both cooling and neutron moderation. Heavy water is similar to ordinary light water except that the hydrogen atoms are replaced by deuterium atoms. Instead of the single proton nucleus of hydrogen a deuterium atom nucleus has both a proton and a neutron. Ordinary water contains a small fraction of heavy water. Heavy water can be separated from ordinary water by suitable cascade contact, distillation and electrolysis processes. However, these processes are expensive. Hence, in CANDU nuclear power plants (NPPs) extraordinary measures are taken to prevent heavy water leakage and to recover any heavy water that does leak.

A CANDU reactor provides three important benefits.
a) It can be fueled by either natural uranium or used LWR fuel. LWRs rely on fuel enrichment which is inefficient and expensive and if selected would make Canada dependent on foreign fuel enrichment plants. Right now Russia, which is politically unreliable, dominates the enriched nuclear fuel market.

b) CANDU reactors maximize the TRU production at about 4 grams / kg of natural uranium as compared to about 1 gram / kg for Light Water Reactors (LWRs).

c) CANDU reactors produce tritium, which is needed for future nuclear fusion, which in principle could be used to increase the rate of TRU production.

When formed the TRU atoms are widely dispersed in used reactor fuel. However, via fuel recycling the TRU can be redistributed to make both FNR core fuel and FNR blanket fuel.

The tritium is embedded in the heavy water but can be selectively extracted.

We now move forward to about 2010. Questions were being asked about whether nuclear power could be used to prevent further climate change. However, it soon became obvious that within a few decades a shortage of U-235 would prevent ongoing use of water cooled power reactor technology for long term climate change mitigation.

Circa 2010 Peter Ottensmeyer (or one of his students) came up with an insightful idea that would potentially change everything.

The PUREX concept was to selectively extract plutonium from everything else in used nuclear reactor fuel, because that is the proven process used to make a nuclear bomb. However, for making FNR fuel the objective should instead be to selectively remove most of the uranium oxide from used CANDU reactor fuel and then to selectively extract fission products from the residue using a high temperature molten salt electrolytic process known as pyroprocessing.

The trick to making this new process economic is to first concentrate the TRU by selectively removing uranium oxide using a simple physical process involving aqueous crystal manipulation. That process can be done automatically in bulk using a microprocessor controlled recrystallization cascade.

In the resulting FNR power reactor technology the TRU is self replicating. Thus, with this new technology the door is open for powering future generations for millennia using FNRs, where the fuel is the abundant uranium isotope U-238 and there are almost no long lived nuclear waste products.

Peter Ottensmeyer has provided the following graph showing U-235 depletion, Fission Product (FP) formation and TRU production in CANDU reactor fuel as a function of fuel dwell time in the reactor. Note that after 1.5 years (18 months), which is the working life of CANDU fuel, the TRU concentration plateaus at about 0.4%.

However, while the energy available from a FNR is proportional to the available amount of the abundant isotope U-238 the FNR power output is limited by the FNR's TRU inventory. In a suitably designed FNR this TRU inventory will gradually grow over time.

The CANDU reactors that Canada presently has produce about 4X as much TRU per unit of natural uranium used as do the Light Water Reactors (LWRs) presently used in the USA and many other countries. This issue has four important implications.
1) All new thermal neutron power reactors should be CANDU rather than LWR. This is a major political issue, especially in the USA;
2) The US nuclear regulatory environment must change because presently CANDU reactors cannot be licensed in the USA;
3) As the price of natural uranium rises the new CANDU reactors should be fueled with used LWR fuel. The TRU so formed will further increase the TRU inventory;
4) When parties with LWRs recognize the consequences of their lack of TRU, they may have predatory designs on parties that do have TRU.

During the early 1960s Atomic Energy of Canada Limited (AECL) Studied the design of an Intense Neutron Generator (ING). The ING apparatus consisted of a high energy high current proton accelerator with a lead target. The proton beam impacting the lead target was to create a large neutron flux by a process known as neutron spallation. However, during the 1960s U-235 was sufficiently plentiful that it was less expensive to produce a large neutron flux using a CANDU reactor. Hence in 1965 the ING Project was cancelled. However, in the future when U-235 is much more expensive the ING project can be revived. If the lead target is surrounded by neutron absorbing U-238 it will breed TRU without any use of U-235. This process is projected to emit enough heat, which converted into electricity, will power the required proton accelerator. Hence a ING can potentially act as a TRU source which is almost independent from the rest of the energy system.

Another potential source of a large neutron flux is fusion of deuterium and tritium. That fusion reaction yields 13.6 MeV neutrons. If these high energy neutrons are absorbed by a neutron multiplier material such as Li-7, the result is a large flux of lower energy neutrons. That neutron flux can be absorbed by U-238 to make TRU. Hence using fusion of hydrogen iotopes to make TRU may be a more profitable way to harness fusion than using fusion simply to make heat and hence electric power.

Largely due to use of heavy water, CANDU reactors are more expensive to build and maintain than LWRs. If the world proceeds today with new LWR construction to mitigate climate change the economic benefit period will be short and after that, due to poor natural uranium utilization and a severe TRU shortage, there will not be sufficient dependable and sustainable power to support even a reduced world population. People will revert to use of fossil fuels and there will be a consequent global extinction of large animals.

If instead the world proceeds today with CANDU reactor construction the capital and operating costs are larger than for LWRs but the benefits are that the grace period until U-235 is depleted is twice as long and when that grace period is over there should be sufficient TRU to produce enough sustainable nuclear power to support a reduced world population.

However, getting people today to make a rational decision to spend more money now on nuclear technology to benefit their children and future descendants is not easy.

There are related industrial funding challenges which include TRU concentration, converting TRU concentrates into FNR fuel and subsequent recycling of the FNR fuel. These processes involve working with highly radioactive substances that must be fully automated. Getting these automated processes working smoothly on a large scale together with a prototype power FNR will probably cost about $5 billion.

In Canada the Trudeau government is presently committing $30 billion to an oil pipeline expansion but has refused to spend even one dollar on TRU recovery. The federal government regards nuclear power as a provincial responsibility and the provincial governments, in order to comply with near term federal government CO2 emission reduction requirements, want to follow the fastest and least expensive route to near term CO2 emission reduction, which is LWRs.

The reality of today's ill considered government decisions is that the remaining economic U-235 resource will be rapidly depleted and when that resource is depleted, due to lack of TRU, the dependable power requirements of mankind will far exceed the dependable power supply capacity. At times of low renewable power production: during the winter circumpolar populations will freeze in the dark and during the summer equatorial populations will die of heat stroke. In many countries shortages of fresh water for summer agricultural irrigation are already a major problem. As the rising atmospheric temperature reduces summer river flow, renewable electricity generation is reduced and huge amounts of additional energy will be required for water desalination.

Unfortunately, at every turn there is irrational and uninformed opposition to sensible nuclear and climate change mitigation policy.

Building wind turbines may temporarily satisfy uneducated voters, but CANDU reactors, fast neutron reactors and their TRU based fuel systems are what is required to provide sustainable and dependable clean power.

A commercial issue that must be immediately addressed is TRU concentration. However, even its large scale demonstration requires a few million dollars that the Canadian government prefers to spend subsidizing fossil fuel production.

1) Natural uranium is 0.7 % U-235, 99.3 % U-238.
2) The energy available from the U-238 content of natural uranium in a Fast Neutron Reactor (FNR) is potentially about 100X the energy that can be obtained by fissioning the U-235 content of natural uranium in a CANDU reactor;
3) A CANDU reactor produces about 2X as much energy and 4X as much TRU per kg of natural uranium as does a Light Water Reactor (LWR);
4) The projected relative scarcity of natural uranium indicates that we should choose CANDU reactors in preference to LWRs;
5) As the cost of natural uranium rises CANDU reactors can be fueled with used LWR fuel instead of natural uranium, which should also increase the TRU inventory.
6) The sustainable power available from a FNR fuelled with U-238 is proportional to the FNR's TRU inventory.
7) Failure to maximize TRU production today will constrain future sustainable and dependable power production.
8) The TRU supply can be increased by reviving the old AECL ING project.

These facts need to be clearly presented to the public.

This web page last updated February 22, 2024

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