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

Due to global warming driven by accumulation of carbon dioxide in the Earth's atmosphere and oceans mankind must substitute clean (non-fossil) power for power presently obtained by combustion of fossil fuels. Clean power consists of renewable power plus nuclear power. However, wind and solar generated renewable electricity is only intermittently available. Public electricity systems require dependable power sources.

Both theoretical analysis and practical experience have shown that it is uneconomic for an electricity system to obtain more than about 20% of its total energy from intermittent wind and solar electricity generation. The remaining 80% of the required clean energy must be sourced by hydroelectricity and sustainable nuclear power. Typically the split is 5% hydroelectricity and 75% sustainable nuclear, but this split varies widely by jurisdiction.

The term "sustainable nuclear power" refers to nuclear power cycles that are fuelled by abundant fertile isotopes such as U-238 and Th-232. These two isotopes have sufficient natural abundance that known ore deposits, if efficiently used, can economically meet mankind's energy requirements for millennia. These fuel cycles operate by breeding fertile U-238 into fissile Pu-239 and by breeding fertile Th-232 into fissile U-233.

Nuclear power cycles that rely on fission of U-235 are not sustainable because U-235 lacks the natural abundance necessary to sustainably fully displace fossil fuels.

To quantify the term Sustainable Nuclear Power it is necessary to first calculate the total thermal power presently supplied by combustion of fossil fuels and then project the total thermal power that must be supplied by nuclear power in order to enable leaving fossil fuels in the ground. There is a further important constraint that the sustainable nuclear power is limited by the TRU inventory. This TRU constraint will force a major reduction in the world human population. In large measure this constraint is a direct consequence of use of neutron inefficient Light Water Reactors (LWRs) instead of neutron efficient CANDU reactors. This constraint is also a result of consuming TRU in MOX fuel in Light Water Reactors or disposing of TRU instead of reserving TRU for use as a quasi-catalyst in fuel sustainable Fast Neutron Reactors (FNRs).

During the year 2019 the total world coal production, obtained by summing the productions from the major producers was;
8.13 billion tonnes
= .813 X 10^10 tonnes/year
The corresponding carbon mass that entered the atmosphere in 2019 was about:
0.8 X .813 X 10^10 tonnes / year = .6504 X 10^10 tonnes carbon / year.

The average thermal power liberated by world combustion of coal during 2019 was about:
.813 X 10^10 tonnes coal / year X 32,494 X 10^6 J / tonne coal X 1 year / 8766 hour X 1 hour / 3600 s
= 8.371 X 10^12 watts

The world oil production in 2019 as obtained by summing producers outputs was about 35 billion barrels / year. The corresponding annual carbon output is:
35 X 10^9 barrels /year X .137 tonnes/barrel X .86 tonne carbon / tonne oil
= 0.412 X 10^10 tonne carbon / year
Not all of this carbon immediately goes into the atmosphere because a small fraction of the carbon related to oil production is used to produce asphalt, which may take as much as 50 years to oxidize into CO2.

The thermal power liberated by world combustion of oil is about:
35 billion barrels / year X (5.8 X 10^6 BTU / barrel) X 1055.06 J / BTU X 1 year / 8766 hour x 1 hour / 3600 s
= 6.786 X 10^12 watts

The world natural gas liquids production in 2004 as obtained by summing producers outputs was about 7,393,210 barrels per day. The corresponding annual carbon output is:
7,393,210 barrels / day X 365 days/year X .137 tonnes/barrel X .86 tonne carbon / tonne NG liquid
= .03179 X 10^10 tonne carbon / year
Not all of this carbon goes into the atmosphere because part of the carbon related to NG liquid production is used to produce resins. However, the non-atmospheric carbon amount is likely off set by unreported fossil fuel production, especially unreported coal.

The thermal power liberated by world combustion of natural gas liquids in 2004 is about:
7,393,210 barrels / day X 5.8 X 10^6 BTU / barrel X 1055.06 J / BTU X 1 day / 24 hour x 1 hour / 3600 s
= 0.5236 X 10^12 watts

The world dry natural gas production during 2019, as obtained by summing the producers outputs was:
4100 billion m^3 / year.
The corresponding amount of carbon released to the atmosphere was:
4100 X 10^9 m^3 /year X 1000 lit / m^3 X 1 mole / 22.4 lit X 273/288 X 16 gm / mole X 1 tonne/10^6 gm X .75
= 4.1 X 10^15 lit / year X (1 mole / 22.4 lit) X (273/288) X 16 g / mole X 10^-6 tonne / gm X .75
= 2.082 X 10^9 tonnes carbon / year
=0.2082 X 10^10 tonnes carbon / year
Almost all of this carbon enters the atmosphere.

The average thermal power liberated by world combustion of natural gas in 2019 was:
4100 X 10^9 m^3 / year X 1000 ft^3 / 28.328 m^3 X 1000 BTU / ft^3 X 1055.06 J / BTU X 1 year / 8766 hour X 1 hour / 3600 s
= 4.839 X 10^12 Watts

[8.371 + 6.786 + 0.5236 + 4.839] X 10^12 Wt
= 20.52 X 10^12 Wt
= 20.52 X 10^3 GWt

Accurate measurements of the atmospheric CO2 concentration have been made since 1957. A plot of CO2 concentration versus time shows a "hockey-stick" graph. During any particular year the slope is proportional to the amount of CO2 emitted that year. This slope doubles approximately every 50 years. Thus we can reasonably project that without extensive nuclear power deployment the world fossil fuel thermal power production in 2069 will be about:
2 X 20.52 X 10^12 Wt = 41 X 10^12 Wt.
By 2074 this number will be close to 44 X 10^12 Wt, which is a convenient number for discussion purposes. Of this number, about 25% can be met by the combination of wind, solar and hydro electricity, leaving 75% or 33 X 10^12 Wt that must be met by nuclear energy. If all of that heat is converted into electicity the total available nuclear electric power would be:
33 X 10^12 Wt / 3 = 11 X 10^12 We
= 11,000 GWe

Thus this future projected nuclear load could be met with 33,000 X 1 GWt nuclear reactors (33,000 X 300 MWe SMRs).

The world average fossil fuel thermal power per person in 2019 was about:
20.52 X 10^12 Wt / 7.8 X 10^9 people
= 2.63 kW / person

By comparison in Canada and the USA the average fossil fuel thermal power per person is about 9 kWt and the average electrical power per person is about 1.2 kWe. In the Province of Ontario the average thermal power per person is about 7 kWt per person but the Canadian average is higher, in large part due to energy intensive fossil fuel resource extraction in the province of Alberta.

The world nuclear electric capacity in 2004 was about 372,751 MWe.
Assume an average nuclear power ploant capacity factor of about 0.9.
Then the average nuclear electric power in 2004 was about:
0.9 (372,751 MWe) = 335,476 MWe
= 375.476 GWe

Assume that the average thermal to electricity conversion efficiency is 0.33
Then the total heat emitted by nuclear reactions in 2004 was:
372,751 MWe X 0.9 X 1 MWt / 0.33 MWe
= 1,006,428 MWt
= 1006 GWt

Thus on an average thermal power basis the present installed nuclear capacity is only about 5% of the present fossil fuel thermal capacity.

Total present world thermal power production by combustion of fossil fuels and by nuclear reactors is:
20.52 X 10^12 Wt + 1.006 X 10^12 Wt
= 21.52 X 10^12 Wt

When this power is averaged over the Earth's surface area:
As = 509.55 X 10^12 m^2
the average impact is:
21.52 X 10^12 watts / 509.55 X 10^12 m^2
= 0.0422 watts / m^2

This amount is less than 10% of the present ongoing net heat accumulation due to recently accumulated atmospheric green house gases.

The present average world hydro-electric power production is about 300,000 MWe

The present average world wind power production is about 57,000 MWe

Most renewable energy sources are seasonal. Rivers consistently run much higher in the early spring than in the late summer. In Ontario average wind generation in the summer is about half as much as in the winter. In northern Canada solar energy is almost non-existant in mid winter. Thus, contrary to misleading claims by environmentalists, it is impossible to totally replace fossil fuels with renewable energy without massive seasonal energy storage. The only seasonal energy storage technologies that make any economic sense are hydraulic storage in river valleys between chains of major mountains such as exist in British Columbia and Quebec and synthetic liquid fuels.

A recent agreement between Ontario and Quebec that allows Ontario access to some of the hydraulic energy storage in Quebec is a small step in the right direction, but relying on such an agreement, instead of proceeding with sustainable nuclear power, is foolish procrastination because the the hydraulic energy storage in Quebec is expensive to access and its capacity is insufficient to meet Ontario's requirements. Furthermore, the efficiency of synthetic fuel production is so low that synthetic fuels are uneconomic in many applications.

An issue that many people fail to grasp is that average world hydro electric power production will likely plateau at about 400,000 MWe. Some wind power could in principle be used for production of electrolytic hydrogen. However, the economics of wind generation exclusively for hydrogen production are extremely adverse because none of the power generated earns premium income by dependably assisting in meeting the uncontrolled peak electricity load. Hence, to economically displace fossil fuels, about 75% of the present fossil fuel supplied 20,520 GWt of thermal power must come from nuclear energy. Further energy is required to meet projected load increases for air conditioning, water desalination, synthetic hydrocarbon processing, concrete production and steel production that are not included in the fossil fuel energy total. Displacement of fossil fuels will require at least a:
11,000 GWe /345.4 GWe = 31.85 fold expansion in world wide installed nuclear reactor capacity.
In Ontario the installed nuclear capacity must be increased between 7 fold and 14 fold, depending on the efficiency of heat utilization.

Assume that the average nuclear power plant operates at a thermal efficiency given by:
(electricity output) / (reactor thermal power output) = 0.33

Then displacement of the present fossil fuel consumption requires new nuclear reactors with about:
20,520 GWt (0.33 We / Wt) / (375.400 GWe) = 18.06 times the present world functional nuclear reactor capacity.

Note that this estimate inherently assumes that in both motive power and general heating applications one kWhe can replace 3 kWht. If nuclear reactors are located in urban areas and the waste heat from electricity generation is used for district heating then the related required reactor capacity might drop by as much as a factor of 2.

Perspectives on the closed fuel cycle

A sustainable nuclear fuel cycle can be realized by a fleet of CANDU reactors that, in addition to producing heat, convert natural uranum to TRUs (trans uranium actinides) and feed the TRUs via fuel reprocessing to a fleet of fuel breeding Fast Neutron Reactors (FNRs). In addition to generating more heat the FNRs produce sufficient TRUs from the abundant isotope U-238 for sustainable operation. A sustainable nuclear fuel cycle cannot be realized by reliance on thermal (water cooled) reactors, as is current provincial governmental wishful thinking. A further benefit of a sustainable fuel cycle is that it almost completely destroys TRUs by converting them into thermal energy and fission products with half lives of less than about 30 years.

1) Mine natural uranium which consists of 99.3% U-238 and 0.7% U-235;
2) Form the natural uranium oxide into CANDU fuel;
3) Fission the natural uranium in CANDU reactors to liberate heat. In the used CANDU fuel the U-235 fraction is about 0.2%, the transuranic element (TRU) fraction is about 0.5% of which about 2 / 3 is Pu; the fission product fraction is about 0.9% and the U-238 fraction is about 98.4%. This step havests about 1% of the total energy available from natural uranium.

4) Selectively extract uranium oxide from the used CANDU fuel until the TRU concentration in the residue increases about 10X. This step is key because it makes step (7) economically viable;
5) Interim store the extracted uranium oxide for future use as an input for forming new FNR blanket fuel;
6) Reduce the residue, which is in oxide form, to metallic form;
7) Use a molten salt electrolytic process known as pyroprocessing to selectively remove fission products and uranium metal from the residue;
8) Send the fission products to multi-century interim storage;
9) Use the metallic uranium removed during step # 7 plus recycled Zr to form initial FNR blanket fuel rods;
10) Form the remaining residue, which is a U-TRU metal alloy plus Zr, into Fast Neutron Reactor (FNR) core fuel rods.
11)Steps (1) to (10) above can run as long as there is used CANDU fuel available. The outputs from these steps are: heat, fission products, FNR fuel, surplus depleted U-238 and surplus depleted uranium oxide;
12) Use the newly formed FNR core and blanket fuel rods in fuel breeding FNRs to liberate heat and to further enlarge the fissile TRU inventory. This step fissions about 15% of the TRU mass.

13) Periodically reprocess the FNR fuel rods to reject fission products to interim storage and to move TRU atoms from the blanket fuel rods to the core fuel rods.
14) Replace the TRU atoms removed from the blanket fuel rods with an equal weight of U-238 metal obtained by reducing the uranium oxide extracted during step # (4) above. 15) Build more FNRs to fully utilize the increasing TRU inventory.
16) Repeat steps (12) to (15) every few years and at each repetition fission 15% of the TRU;
17) Steps (12) to (15) above can be repeated as long as there is surplus U-238 from step #(4). When that U-238 is exhausted all energy contained in natural uranium has been harvested.

18) Reprocess the interim stored fission products to recover valuable elements;
19) Periodically check the interim stored fission products to ensure that they are naturally decaying as anticipated. By 300 years (10 maximum half lives) after placement in storage the fission products will be safe and by 600 years (20 maximum half lives) after placement in storage the fission product radioactivity will be below the background level.

The challenge facing the younger human generation today is two fold:
1) Build a sufficient fleets of CANDU reactors and FNRs to thermally fully displace fossil fuels;
2) Build sufficient used nuclear fuel reprocessing facilities to meet the thermal load with FNRs before the minable natural uranium for fuelling the CANDU reactors is exhausted. This natural uranium fuel exhaustion time is projected to be sometime around 2050, depending on further natural uranium ore finds and compliance with climate change goals.

Meeting challenge #1 requires a sufficient commitment of public monies today. Canada has a 60 year history building and operating CANDU reactors both at home and abroad. The USA, Russia and to some extent France together have a 60 year history buillding and operating FNRs.

Meeting challenge number 2 is more difficult because it requires sequential changes in government policy, in building a first-of-a-kind fuel reprocessing facility and in fabrication of a first-of-kind power FNR, all of which must occur prior to large scale fuel reprocessing and FNR deployment. Even if this first-of-a-kind work can be compresed into a 20 year period that leaves at most only about 10 additional years for large scale FNR deployment before the economic natural uranium feeding step #1 is exhausted.

At this time the single most important issue is making the fundamental changes in government policy that would permit preliminary work on used CANDU fuel reprocesing to proceed. The most important changes are to replace the NWMO by a fully funded used nuclear fuel reprocessing company and to fully fund a new FNR development and deployment company in a manner analogous to the funding of AECL during the CANDU reactor development period. Each of these two new organizations would need startup capitalization of the order of $3 billion.

It is impossible to privately fund FNRs without certainty with respect to availability of FNR fuel. It is impossible to privately fund reprocessing of used CANDU fuel to form FNR fuel without an irrevocable government commitment to provide the required used CANDU fuel. There is a fundamental lack of understanding by NRcan and other government departments relating to the interdependence of these matters and the necessary financing.

The present stated NRcan policy is to support provincial SMR choices irrespective of how foolish and unsustainable those choices are. We remind NRcan that during the 1970s Ontario Hydro foolishly built massive amounts of coal fired electricity generation because the decision makers of that time simply did not adequately understand thermal radiation and atmospheric physics. Today the decision makers do not adequately understand fast neutron physics. However, the consequences of making wrong decisions now will be much more dire.

It must be emphasized that any further delay in properly addressing these public policy issues will have catestrophic consequences for young people now living. As many nations similarly default to use of thermal (water moderated) nuclear reactors to fight climate change the price of natural uranium will climb by orders of magnitude. The survivors will be those who have reactor fleets dominated by FNRs which have a net consumption of natural uranium per kWht about 1% of the net consumption of thermal (water moderated) reactors per kWht. A further benefit of proper application of FNRs is near elimination of long lived nuclear fuel waste.

At this time the only sustainable nuclear fuel cycle for which we have proven implementation technology is:
U-238 + n = U-239
U-239 = Np-239 + e
Np-239 = Pu-239 + e
n + Pu-239 = 3 n + fission products
+ 200 MeV

3 n = 2 n (above reactions) + A n (undesired neutron losses) + B n (excess neutrons for extra fissile fuel production)
A + B = 1

Depending on the reactor design detail A and B are each typically in the range 0.2 to 0.6. If B < 0 then the fuel cycle is not fuel sustainable.

There is an important secondary competing nuclear reaction sequence:
Pu-239 + n = Pu-240
Pu-240 + n = fission products + 200 MeV
The operation of this competing reaction in CANDUs and FNRs prevents the TRUs being used to make atom bombs.

Note that the primary fuel is the abundant isotope U-238 and that each Pu-239 fission yields three neutrons, two of which are required to sustain the nuclear reaction and one which is available to meet neutron losses and to increase the fissile atom inventory.

Thought of another way, each Pu atom that fissions emits 200 MeV of heat, enlarges the TRU inventory by 0.2 to 0.3 atoms and supplies sufficient neutrons to balance neutron losses.

Note that both the reactor power and the maximum rate of TRU atom inventory growth are proportional to the TRU atom inventory. Thus any implementation delay has major consequences on the future TRU atom inventory and hence on the future sustainable reactor fleet power capacity.

Each atom of U or TRU fissioned yields about 200 MeV.
One mole of U-238 weighs 238 g and contains 6.023 X 10^23 atoms.
Thus the energy output per gram of U-238 fissioned is:
6.023 X 10^23 atoms X (200 MeV / atom) / 238 g X 1.602 X 10^-19 J / eV X 10^6 eV / MeV
= 8.108 X 10^10 J / g
= 8.108 X 10^10 J / g X (1 Wt-s / J) X (1 kWt /1000 Wt) X (1000 g / kg) X (h /3600 s)
= 2.252 X 10^7 kWht / kg

When initially fuelled with natural uranium the relative uranium isotopic abundances in new CANDU fuel are:
99.2836% U-238; 0.711% U-235, 0.0054% U-234

The components of natural uranium CANDU fuel, after use in a CANDU reactor, become:
___% U-238
___% U-235
____% U-234
____% U-232
0.26% Pu-239
_____% Pu-240
_____% Other transuranics
_____% Fission products including inert gases

In a CANDU reactor typically about 1.0% of the uranium fuel mass fissions, so the actual thermal energy output is about:
2.252 X 10^5 kWht / kg initial natural uranium fuel used.

A typical CANDU reactor contains:
(22 kg natural U / bundle) X 12 bundles / tube X 380 tubes = 100,320 kg natural uranium

Hence, the recoverable energy from this fuel mass via use of a CANDU reactor is:
100,320 kg X 2.252 X 10^5 kWht / kg = 225,920 X 10^5 kWht
22592 GWht

Over 1.1 years the corresponding thermal power is:
22592 GWht / (8766 h/yr X 1.3 yr)
= 1.98 GWt

The corresponding electric power out is about:
1.98 GWt / (3 GWt / GWe) = 0.66 GWe
In fact due to fine tuning the aforementioned parameters modern CANDU reactors typically output about 0.74 GWe

With allowance for 2.0 X load growth due to increasing population and increasing per capita 3rd world energy requirements the installed world nuclear reactor capacity needs to increase by about:
11,000 GWe /(375.400 GWe) = 29.3 fold
over the next 50 years. Viewed another way, the operational world nuclear reactor capacity must double about every 10 years.

A major constraint on the FNR production rate is availability of sufficient fissile TRU to start FNRs. It will be ironic if present attempts to offset fossil fuels with water cooled nuclar reactors and present attempts to prevent nuclear weapon proliferation via restricting use of plutonium as a FNR start fuel lead to extinction of much of mankind due to insufficiency of TRU for starting future FNRs.

At this time there is complete failure of governmental authorities in both Canada and the USA to face this basic nuclear power capacity expansion constraint.

The problem is that the decision makers, including the Canadian federal and provincial governments, are failing to face the issue of how mankind will survive when the available ore bodies of economically recoverable natural uranium ore is exhausted. The most fuel efficient thermal reactor is the CANDU reactor. A CANDU reactor produces 4 grams of TRU plus 2.252 X 10^5 kWht of thermal energy / kg natural uranium consumed.

If the existing fossil fuel load was met by only CANDU reactors the annual consumption of natural uranium would be:
(20,520 GWt X 8766 h / year) / (2.252 X 10^5 kWht / kg natural uranium)
= 798749201 kg natural uranium / year
= 798,749.201 tonne natural uranium / year

The world supply of known and inferred minable uranium is about 8 X 10^6 tonnes at a price less than $260 / kg. Hence, barring a huge uranium price increase there is only enough minable natural uranium to power thermal reactors to meet the present world wide thermal load for about:
(8 x 10^6 tonnes) / ( 798,749.2 tonne / year)
= 10 years.

After the available natural uranium is consumed, unless there is a large fleet of FNRs, there will be a world energy shortage which will have the practical effect of starving to death much of the present world population.

Clearly water moderated reactors are not fuel sustainable.

Another way of viewing this issue is to consider use of fuel breeding fast neutron reactors (FNRs). A FNR requires an initial fissile TRU inventory about 28X as large as the initial fissile inventory of a thermal reactor with the same thermal power rating. However, after initial fuelling, assuming a properly designed fuel cycle, a FNR needs no more TRU beyond the TRU which it produces itself.

Above we found that the natural uranium requirement of initial fuel for a single CANDU reactor is about:
91,200 kg.

Initial fuelling of a single 1000 MWt CANDU reactor requires about 91,200 kg / 2 = 45,600 kg = 45.6 tonnes of natural uranium.
This reactor contains about:
0.007 X 45.6 tones = 0.3192 tonnes of U-235.
Concentrating fissile sufficiently to form FNR start fuel increases the fissile TRU requirement to about:
(0.20 / .007) X 0.3192 tonnes = 9.12 tonnes TRU / 1 GWt FNR.

However, practical 1 GWt FNR designs that feature servicability and safety may require more TRU / reactor. This is an important reactor design issue that needs attention.

Displacing fossil fuels over a 40 year period while maintaining the same standard of living requires at least:
33,000 X 1 GWt CANDU reactors involving: 33,000 X (45.6 tonnes natural uranium per reactor/ fuelling) X 10 fuellings (average)
= 15,345,000 tonnes of natural uranium. This amount is about twice the presently known economic supply

Thus if mankind is to survive it is necessary to start immediately and devote almost the entire minable uranium resource to CANDU deployment and then FNR deployment. Even so the cost of the required uranium may be more than some countries are able to pay. This cost can be partially mitigated by net positive fuel breeding. Even so there will be a substantial period, commencing about 50 years in the future, when energy prices will become very high because the TRU supply via fuel breeding at that time will likely not have caught up with the TRU demand. Those high energy prices will impact the human standard of living everywhere.

One possible mitigating factor might be future use of ~ 1 GeV proton accelerators to produce TRU via neutron spallation. Experiments show that a 1 GeV proton can produce about 30 neutrons by spallation. This process can be compared to TRU production via use of a CANDU reactor. A CANDU reactor produces about 4 g TRU / kg of natural uranium consumed.

We can express the TRU output of a spallation apparatus as [30 TRU atoms / Gev] X [proton accelerator efficiency].

We can express the TRU output of a CANDU reactor as:
[4 g TRU / kg U] X [6.022 X 10^23 TRU atoms / 239 g TRU] X [91,200 kg U / (740 MWe X 1.5 y)] X [1 y / (8766 h X 3600 s / h)]
X {1 MWe / 10^6 We] X [1 We / (J / s)] X [1.602 X 10^-19 J / eV] X [10^9 eV / GeV]
= [(4 X 6.022 X 91,200 X 1.602 X 10^7) / (239 X 740 X 1.5 X 8766 X 3600)] TRU atoms / GeV
= [(4 X 6.022 X 9.1200 X 1.602 X 10^11) / (2.39 X 7.40 X 1.5 X 8.766 X 3.600) X 10^10] TRU atoms / GeV
= [4.2 TRU atoms / GeV]

Thus TRU can potentially be made using a proton accelerator powered by renewable electricity or a FNR, albeit at tremendous cost.

One possible mitigating factor might be future use of hydrogen fusion, not primarily to generate energy but instead to supply highly energetic fast neutrons to increase the rate of breeding of U-238 into TRU. ie In a fusion reactor Li-7 liberates 2 neutrons for every fast neutron that it absorbs. Hence a fusion reactor should use natural Li (Li-6 + Li-7) to breed H-3 and should have enclosure walls that are covered by removeable sections of U-238 in which to breed TRU.

Today the main challenge is getting the public to recognize that today's youth are severely threatened by a future TRU shortage and the only method of mitigating this problem is to immediately adopt fuel sustainable FNRs in which breeding of TRU from U-238 is enhanced as much as possible.

Another possible future energy source is:
Th-232 + n = Th-233
Th-233 = Pa-233 + e
Extract the Pa-233 from the neutron flux to prevent the reaction:
Pa-233 + n = Pa-234
Pa-233 = e + U-233
U-233 + n = fission products + 2.2 n

One of the practical problems with implementtion of this fuel cycle is physical extraction of Pa-233 from the neutron flux as fast as it is formed. Otherwise, before transforming into U-233 the Pa-233 will absorb another neutron to become Pa-234. If Pa-234 forms then there are not enough neutrons to make the process fuel sustainable.

Other problems with this energy production process relate to the materials. In order to perform the Pa-233 extraction the reactor fuel is dissolved in circulated molten salt. Hence the temperature is high. Hence molybdenum fuel tubes are required to localize the U-233 fission from which certain Mo isotopes are extracted. In addition the salts need to be molten chlorides to realize a fast neutron spectrum. To minimize Cl-36 formation Cl-35 must be isotopically removed. Then there must be a substantial molten salt guard band thickness to protect the enclosure walls and heat exchange bundles which contain nickel from neutron embrittlement. This combination of material requirements makes thorium based fuel sustainable molten salt reactors very expensive. There has been some consideration of use of fluoride salts with Be as a moderator, but the Be is expensive and the Li required in the salt mix needs yet another isotope separation.

To put this matter in perspective, if it was possible to adhere to the present OPG/NWMO nuclear waste disposal methodology, which presently contemplates two Deep Geologic Repositories (DGRs), in reality after 60 years 20 DGRs would be required and after 300 years at least 100 DGRs will be required. Clearly the present OPG/NWMO nuclear waste disposal plan is not sustainable. There are certain low atomic weight radio isotopes such as Ca-41, Cl-36, Ni-59 and C-14 where there is no alternative disposal solution other than permanent containment within a DGR. With respect to these long lived low atomic weight isotopes the most important safety measure is to do all necessary to prevent them forming in the first place.

For most of the remaining radio isotopes there are disposal alternatives that potentially cost a lot less in terms of both dollars and environmental pollution than the present plan by OPG and the NWMO and that should be pursued. Most shorter lived radio isotopes only need interim storage for a few centuries rather than permanent storage.

The entire nuclear energy cycle, including both electricity production and nuclear waste disposal, must be made sustainable.

A potential public issue is formation of long lived inert gas radio isotopes. The problem with inert gases is that it is difficult to physically isolate them from the atmosphere for long periods of time. If the entire world is powered by fission nuclear power over time the low level accumulation of long lived inert gas radio isotopes in the atmosphere may become a public issue. In the immediate proximity of used fission fuel concentration plants shorter lived inert gas isotopes such as Kr-85 might cause public concern. The short lived isotopes should be well mixed with the atmosphere before they reach the public. The inert gas isotopes that might become problematic are:
Ar-39269 years
Ar-4233 years
Kr-812.1 X 10^5 years
Kr-8510.7 years

This is where Jerry Cuttler's work on low level radiation exposure is extremely important. The substance of his findings is that small increases in the background radiation level have no negative impact on human health. There have been all kinds of cancer forecasts based on the Linear No Threshold model that predicted increases in human cancers that have not been experimentally observed.

It is of paramount importance that this issue be properly communicated to the public at large.

If we assume that the entire world is nuclear fission powered, at some point in the distant future Kr-81 may raise the background radiation level significantly. Assuming man kind is still around at that point it might become necessary to transition to nuclear fusion to avoid this problem. However, that issue is many centuries in the future.

I presently do not know the production rates of Kr-81 and Kr-85 per unit of fission heat produced. This data likely exists somewhere. The number of each radioactive inert gas isotope atoms formed per kg of TRU fissioned must be determined. The Kr-81 concentration in the atmosphere may become a good indication of the cumulative fission nuclear power production on Earth.

Sustainable Nuclear Fuel Cycles and World Regional Issues

1970 Fast Breeder Reactors

Thermal Breeder Reactors

Long Term Sustainability of Nuclear Fuel

A link list to about 30 files by Jack Devanney addressing climate change, nuclear power regulation and nuclear power sustainability

Any Deep Geologic Repository (DGR) design that is not consistent with long term nuclear power sustainability is not the right design. The DGR concept that is presently contemplated by the NWMO and OPG is not sustainable and hence is not acceptable. Achievement of safe sustainability requires future ongoing storage accessibility. The requirement for ongoing accessibility determines the type of rock in which the DGR should be located and the elevation of the DGR storage vaults with respect to the elevation of the surrounding water table. There must be an adequate provision for future changes in the water table elevation with respect to the DGR elevation. For example, the Niagara escarpment, which is about 100 m high, is only 12,000 years old. Hence as a minimum a DGR vault should be more than 100 m above the present water table.

In Canada the necessary geology for both interim and long term rdio isotope storage is found at Jersey-Emerald in British Columbia.

If dilution of radio isotopes is relied upon as a means of reducing nuclear waste toxicity, and if a DGR open period is 60 years, over 10,000 years the required number of DGRs will increase by a factor of:
(10,000 years / 60 years / DGR) X 45 = 7500 DGRs
causing the average background radiation contribution due to long lived isotopes in DGRs, which may be considered acceptable with two DGRs, to increase by almost four orders of magnitude. Hence dilution of nuclear waste is neither an acceptable nor a sustainable method of reducing nuclear waste pollution. The NWMO/OPG safety case for the proposed Bruce DGR is simply not sustainable.

One of the complexities of the nuclear power industry is the need for multiple reactor types for cost efficient use of uranium. Natural uranium consists of about 99.3% U-238 and about 0.7% U-235. The most efficient way to use both existing power reactors and all the potential energy contained in natural uranium is to use the nuclear fuel in a succession of different reactor types.

The first step is uranium enrichment as is presently done in the USA. That process typically creates low enriched uranium with a U-235 fraction in the range of 3% to 5% and depleted uranium with a U-235 fraction of about 0.3%. The depleted uranium should be stored for future use as FNR (Fast Neutron Reactor) blanket fuel. The enriched uraunium is fissioned in existing LWRs (light water reactors) to make electricity. The used LWR fuel typically contains greater than 1% U-235 plus some Pu and other transuranic elements (TRU).

The second step is to selectively remove uranium oxide from the used LWR fuel. This removed pure uranium oxide contains more than 1.0% U-235 and hence, with minor modification, is usable as CANDU reactor fuel. This pure uranium oxide contains some radioactive U-232, so appropriate biosafety precautions must be followed in new fuel fabrication and handling.

The residue containing Pu, transuranics and fission products from the used LWR fuel is fed to the FNR core start fuel production process.

The pure uranium oxide extracted from the used LWR fuel is used to fuel a heavy water cooled and moderated CANDU nuclear reactor. The CANDU reactor will consume part of the remaining U-235 and will convert a portion of the U-238 into Pu-239 plus other trans-uranium actinides.

Then application of the selective uranium oxide separation process to the used CANDU fuel results in pure uranium oxide plus more residue containing U, TRU and fission products.

The pure uranium oxide is now depleted to about 0.3% U-235 and is set aside for future use as FNR blanket fuel.

The residues containing U, TRU and fission products are fed into the FNR core start fuel production process.

It is then necessary to use an electrolytic process (pyroprocessing) to reduce the concentrated residue to metallic form and to separate the lower atomic weight fission products from the higher atomic weight U, and TRU.

The fission products are placed in 300 year isolated dry storage to allow them to safely naturally decay.

Then the remaining U, TRU metallic fuel with added Zr is used as core start fuel in a liquid sodium cooled fast neutron reactor. This reactor fissions the TRU and converts part of the surrounding U-238 into new TRU.

Periodically the FNR fuel is removed and low atomic weight fission products in the core fuel are extracted and placed in isolated storage for 300 years. The inner ring of blanket fuel bundles is reprocessed to harvest more TRU. The weight of fission products removed from the core fuel is replaced by an equal weight of harvested TRU. The weight of TRU removed from the blanket is replaced by an equal weight of depleted U drawn from storage. Note that this depleted U may contain traces of TRU due to imperfect prior pyroprocessing or TRU concentration.

This fuel recycling methodology improves the energy yield of natural uranium over 100 fold and reduces the future requirement for long term nuclear waste storage by about 1000 fold. However, due to the technical complexities and irrational thinking governments are reluctant to embrace efficient nuclear fuel recycling.

Thorium (Th-232) may also be bred into U-233 for use in CANDU reactors. However, a major problem with the thorium fuel cycle is that thermal neutron fission of U-233 does not provide enough fast neutrons to fully consume the TRU. Sustainable fission of Th-232 relies on some use of ssustainable fission of U-238 to fully consume the TRU. Another problem with the thorium power cycle is that it lends itself to production of concentrated U-233 and hence possible nuclear weapon proliferation.

by Peter Ottensmeyer
The problem, as I see it, is that it’s always a competition for the available neutrons. If you push them towards producing more fission neutrons by increasing the fissile component, you have fewer neutrons left for conversion of fertile to new fissile components. What you gain on the swings you lose on the round-abouts. The first graph (Fig. 33) for the idealized case of “fuel only” (no structural/coolant/moderator absorption) shows calculations for the pairs of U-238/U-235, U-238/Pu-239 and Th-232/U-233 in the thermal range.

The cross-overs maximize both effects, but once one effect falls below 1.0 then either the reactor won’t operate or the conversion ratio is below 1.0. All pairs achieve values greater than 1 simultaneously at low enough fissile concentrations, but not high enough above 1.0 to have working reactors, considering that too many nascent fast neutrons are lost in the thermalization process. That’s why there are no uranium-238 based thermal breeders. The Th-232/U-233 is best in the thermal regime; but are the new-neutron-yields of at best 1.15 high enough at a CR=1 to permit thermalization and a functioning thermal reactor?

A similar calculation at 0.3 MeV (fast spectrum?) (Fig. 37) shows that all fissile/fertile pairs work, with U-238/Pu239 being best.


1. Safe and economical interim storage of the present inventories of spent fuel and other nuclear waste. In this respect recent events at Fukushima Daiichi have clearly demonstrated that the existing inventories of radio toxic materials should be moved to a dry storage location that is high above the local water table;

2. Change in nuclear reactor design from slow neutrons to fast neutrons so that the prime energy source is the plentiful uranium isotope U-238 instead of the much less abundant uranium isotope U-235;

3. Recycling of spent CANDU and other spent water moderated reactor fuel to convert the highly radio toxic long lived trans-uranium actinides into short lived radio isotopes that rapidly decay into non-toxic low energy stable isotopes. This recycling process extracts 99% of the potenial energy from the nuclear fuel instead of only 1% as presently realized with CANDU and other water moderated reactors;

4. Recycling of irradiated nuclear reactor materials such as zirconium to both reduce the cost of new nuclear reactors and to minimize the mass and volume of radio toxic material in storage;

5. Recovery of tritium/helium-3 for sale to third parties to earn income, to reduce the mass and volume of radio toxic material in storage and to provide helium-3 which is required for detecting illicit shipments of fissionable material;

6. Development of safe, economic, accessible and reliable storage for radio isotopes with half lives less than 30 years such that after 300 years the stored material, storage containers and storage space can all be reused;

7. Development of a safe, economical and reliable methodology for concentration, isolation and storage of long lived low atomic weight isotopes such as C-14, Cl-36, Ca-41, Ni-59, Se-79 and Sn-126 that have no present or foreseeable future value. The storage methodology should recognize that dilution is not a solution to pollution and that these isotopes are highly mobile in water. eg Dry storage in double wall stainless steel-porcelain containers;

8. Modification of nuclear reactor designs to minimize future production of long lived low atomic weight isotopes such as Cl-36 and Ca-41 which form water soluble chemical compounds;

9. Modification of nuclear generating station designs to reduce use of concrete by siting the reactors at higher elevations to avoid tsunami and flood risks and by use of liquid sodium primary coolant to avoid the problem of potentially having to contain radio active steam;

10. Use of natural draft cooling towers instead of direct lake water cooling to reduce cooling water requirements, to allow siting reactors at higher elevations with respect to cooling water bodies and to minimize reactor impact on marine species;

11. Change in nuclear reactor design to separate mechanically stressed components from neutron stressed components to extend facility life, to reduce reactor maintenance costs and to reduce formation of neutron activated decommissioning waste.

12. Large scale deployment of helium-3 based neutron detectors to prevent illicit transport of fissionable material.

Unfortunately, the present NWMO and OPG plans for the Bruce DGR fail to address all of the aforementioned issues. The present NWMO and OPG plans are implicitly based on three false assumptions which are fashionable but which have no basis in fact.

1. The first false assumption is that future nuclear reactors will be assembled by skilled tradesmen using the same methodology as was used four decades ago for assembly of CANDU reactors.

2.The second false assumption is that non-accessible burial of unprocessed long lived nuclear waste below the water table is a sustainable activity and that this activity is acceptable to the Canadian population;

3. The third false assumption is that the electricity rate payers are indifferent to:
a) the cost of DGRs,
b) the cost of labor in nuclear reactor construction and
c) the cost of expensive and non-recycled nuclear fuel and nuclear reactor materials.

1. For construction worker safety most of the materials used in nuclear reactor construction need to initially be non-radioactive;

2. When a nuclear reactor reaches the end of its useful working life its radio active components are not recyclable;

3. All radioactive waste material should be permanently consigned to a DGR;

4. The DGRs should be inaccessible after closure and hence should to be located far below the surrounding water table.

5. The rock surrounding a DGR should be soft and inherently unstable to the point of being self sealing as with limestone or salt;

6. The DGRs should rely primarily on the character of the surrounding rock to minimize the rate of diffusion of water soluble material from the DGR into the surrounding environment;

7. Dilution of radio toxic material is considered by NWMO/OPG to be an acceptable solution to pollution.

I suggest that the aforementioned implicit assumptions by NWMO/OPG are all wrong and hence the related conclusions are also all wrong.

1. I have worked on development of advanced microprocessor based equipment control systems and on the design of liquid sodium cooled fast neutron reactors, as described at www.xylenepower.com/FNR%20Design.htm and adjacent Nuclear related web pages. The OPG assumption that the cores of new nuclear reactors will be assembled by skilled tradesmen is not valid because during the last thirty years there have been major advances in robotic assembly technology and because during the same period a sufficient inventory of radioactive material has accumulated to justify automated radioactive material recycling. Canadian robotics were used to assemble the International Space Station. Robotics are now widely used in automotive assembly. By comparison the assembly of a fast neutron reactor is a relatively simple task.

2. With robotic assembly it does not matter if the reactor materials and fuel components are initially radio active. Fast neutron reactor fuel bundles are intended for robotic assembly;

3. Hence neutron irradiated chromium, iron, uranium, plutonium, zirconium, and trans-uranium actinides can all be recycled.

4. Hence the DGRs should remain permanently accessible to permit on-going safety inspections, risk mitigation and material recycling. The DGRs will make extensive use of robotic technology developed by and for the hard rock mining industry;

5. In order to inexpensively exclude water from an accessible DGR the elevation of the DGR storage vaults should be high above the local water table and the DGR should be gravity drained and naturally ventilated;

6. In addition to reliance on the quality of the surrounding rock the nuclear waste stored in the DGR should be further isolated from the environment via long life engineered containers (> 10,000 years) where the contents of each container are uniform. Achieving that objective requires improved waste sorting at the reactor sites using gamma ray spectrometers and may require significant radio chemistry;

7. The DGR should have internal gravity drainage to sumps and should provide ongoing access for remote monitoring, risk mitigation and material recycling. The sump overflows must be gravity drained.

8. Storage vaults for long lived radio isotopes should be about 400 m below grade to provide certain containment of long lived radio isotopes through numerous glaciations;

9. The DGR should be formed in stable high density granite to provide a combination of durability, water exclusion, and safe access for thousands of years;

10. Recycling of spent CANDU fuel involves trans-uranium actinide fission in a fast neutron reactor. As compared to the present CANDU process the spent fuel toxicity lifetime is reduced 1000 fold and the energy per kg available from natural uranium is increased 100 fold;

11. The fast neutron reactor fuel cycle allows for major material, labor and DGR cost savings for the benefit of the electricity rate payer;

12. Recent political polls indicate that at least one third of the Ontario voters are opposed to the projected electricity price increases related to wind generation and its required supporting energy storage and transmission costs and are seeking electricity price mitigation;

13. Contrary to claims by the NWMO there is no evidence that any permanent "receptive community" in Canada is in favor of high level non-accessible nuclear waste burial in that community. The majority of witnesses from the Bruce area before the Joint Review Panel are opposed to the present NWMO/OPG Bruce DGR plans.

14. Any location that is naturally sufficiently dry for safe long term storage of long lived nuclear waste does not have sufficient ground water to support a permanent community.

1. As fossil fuels are phased out part of the energy requirements that fossil fuels presently meet must be met by synthetic hydrocarbon fuels made using nuclear energy;

2. As a result of this increased dependence on nuclear energy the public will become less tolerant of present technical incompetence and wasteful practices at OPG and the NWMO;

3. The public will insist, if only as a cost saving measure, that materials such as iron, chromium, zirconium, and uranium that contribute significantly to the overall cost of nuclear energy, be recycled both to save money and to reduce the radioactive material inventory. Hence for both worker safety and cost reduction nuclear reactor modules will be robot assembled;

4. The informed public will demand fission of trans-uranium actinides to prevent long term pollution of drinking water;

5. In the future mankind will have no practical alternative to liquid metal cooled fast neutron reactors operating with U-238 for fossil fuel displacement, due to depletion of the U-235 resource. Note that the deuterium-tritium-helium-lithium fusion fuel cycle is also a liquid metal cooled fast neutron process.

6. The only known aneutronic energy source is the (H-1) - (B-11) process, but there are serious questions as to whether that process can ever yield enough power gain to be useful as a practical energy source.

7. The relatively high coolant temperature of a liquid metal cooled fast neutron reactor allows efficient heat dissipation via evaporation of water instead of by direct lake or sea water cooling, and thus greatly reduces the impact of nuclear power on marine species.

8. Nuclear reactor designs should be modified to minimize formation of C-14, Ca-41, Cl-36 and Ni-59;

9. With respect to existing CANDU reactors reasonable efforts should be taken to recover tritium/helium-3 to minimize nuclear weapon proliferation.

From a geophysical perspective by far the best nuclear waste storage location in Canada is Jersey Emerald. Jersey Emerald is a 5 million square foot naturally dry depleted Canadian hard rock mine with about 10 km of main access truck tunnels, 12 foot to 60 foot high internal storage vaults and geology that is uniquely suitable for storage of radio isotopes and/or other highly toxic material. The Jersey Emerald workings are 200 m to 600 m below grade but are more than 300 m above the surrounding water table. The lower portions of Jersey Emerald are in extremely dense water tight granite. Jersey Emerald was a critical source of zinc, lead and tungsten during WWII but was closed in 1972 due to low commodity prices. Today Jersey Emerald is likely the most safe and secure facility in North America for nuclear material storage.

In 2013 Jersey Emerald and the surrounding property and mineral rights were available for purchase at a price that was a tiny fraction of the projected cost of the Bruce DGRs.

In August 2013 both the NWMO and OPG failed to even inspect Jersey Emerald when it was available to them, free and clear, complete with 4000 hectares of assembled surrounding property, including both surface and mineral rights, for $67.5 million. For an estimated additional $100 million NWMO/OPG could have acquired an additional 16,000 hectare exclusion zone, giving NWMO/OPG title to everything within an 8 km radius of Jersey Emerald. The failure of both NWMO and OPG to place a $2 million dollar purchase deposit on the Jersey Emerald property prior to December 13, 2013 will likely go down in Canadian history as the worst ever management decision relating to nuclear power. This matter is indicative of the gross incompetence and/or corruption within the executives of both OPG and the NWMO.

Consider a 2 GWt CANDU reactor. It contains 92 tonnes of natural uranium. If we run this reactor for 1.5 years on a single fuel charge it generates 4 g / kg of TRU in the uranium. If we refuel this reactor every 1.5 years and run the reactor for 80 years we have consumed
(80 / 1.5) X 92 = 4907 tonnes of natural uranium. If we concentrate the used fuel 40X we achieve a TRU concentration of:
40 X 4 g / kg = 160 g / kg
which can run a fuel sustainable FNR.

Based on a minable natural uranium supply of 8 X 10^6 tonnes, the number of fuel sustainable FNRs that we can make by following this pattern is:
8 X 10^6 tonnes / (1840 tonnes / FNR)
= 4348 FNRs which can produce 4348 GWt if the thermal capacity of each FNR is 1 GWt.

In order to meet a projected sustained load of 33,000 GWt the thermal capacity of each FNR has to be increased:
33,000 GWt / 4348 GWt = 7.6 X
which is a tall order.

Assume that through rigid population control we can limit the sustained load to 16,500 GWt. Then the required increase in FNR thermal capacity is: 16,500 GWt / 4348 GWt = 3.8
which might be possible. This objective could be reached by building 4 X 4348 = 17,392 CANDUs and running them for only 20 years. Then build 4348 high thermal capacity FNRs.

1) The presently projected sustained fossil fuel thermal load of 33,000 GWt cannot be met by fuel sustainable nuclear power.
2) It is essential to immediately hard cap Earth's human population and implement a one child policy to rapidly reduce Earth's human population;
3) It is essential to find and develop more natural uranium resources;
4) It is essential to operate the FNRs at close to the maximum thermal stress rating of the fuel tubes;
5) It is essential to increase the FNR core zone thickness from 0.3 m to 0.5 m to reduce the thermal stress on FNR fuel tubes. 6) Use surplus high energy neutrons from hydrogen isotope fusion to irradiate U-238 to further increase the TRU inventory;
7) Run the CANDUs out to their reactivity limits to realize a TRU concentration of 6 g / kg instead of 5 g / kg.
8) It is essential to deploy battery electric vehicles to reduce the average thermal load per person in industrialized countries from 10 kWt / person to 5 kWt / person;

If all humans adopt half of the present North American standard of living, without the aforementioned technology improvements, Earth's sustainable human population is limited to about:
4348 GWt / (5 kWt / person) = (4348 / 5) X 10^6 = 869,600,000
Even if all of the aforementioned measures are adopted there is still a substantial sustainable thermal power shortage.

This web page last updated January 8, 2024.

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