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DEPENDABLE POWER:
Most of the value of a clean electricity grid lies in its capacity to sustainably supply dependable and CO2 emission free power when required by consumers. The main sources of clean and dependable electricity are large hydroelectric dams and nuclear power plants.
A fission type nuclear power plant operates by splitting large fissionable fuel nuclei into smaller fission product nuclei. The difference in rest mass between the fissionable nuclei and the fission product nuclei becomes thermal energy which is absorbed by the coolant of the nuclear reactor. This thermal energy is used to produce high pressure steam which is fed to a turbogenerator to produce electricity. The rate of electricity production is controlled by controlling the rate of nuclear heat production. The turbo-generator discharges low pressure steam which is condensed by latent heat rejection into a large body of water, a cooling tower or a district heating system.
A fission type nuclear fuel cycle is considered sustainable if the fission process also converts abundant fertile fuel nuclei into new fissionable fuel nuclei at a rate sufficient to sustain the fission process.
Renewable energy may seem desirable due to its apparent simplicity but it lacks thermal capacity and due to output variability it is not dependable. Wind and solar electricity generation vary both daily and seasonally. Those variations are not statistically independent. As a result unconstrained wind and solar electricity generation can provide at most 20% to 30% of the required clean energy. The remaining 70% to 80% of the required clean energy must come from dependable hydroelectric and nuclear power sources.
The limit on the maximum fraction of clean energy that can be supplied by unconstrained wind and solar electricity generation arises from practical electricity grid energy storage, transmission and stability constraints.
Only dependable power sources can be used to black start the public electricity grid.
With the exception of a few jurisdictions such as British Columbia, Quebec, Washington State and Norway which have both plentiful hydroelectric power and the geography required for seasonal hydraulic energy storage, most jurisdictions must rely on nuclear electricity generation for supply of large scale dependable clean electricity.
The electric power output from a fleet of nuclear power stations is much more economic and dependable than the electric power output from a fleet of wind and solar generators of similar plate capacity because:
a) Nuclear generators have a capacity factor of over 90% as compared to an average wind and solar generator capacity factor of about 30%;
and
b) The failure modes of nuclear generators are statistically independent whereas renewable generators have common mode failures;
and
c) The cost of sufficient transmission and energy storage to make seasonally variable wind and solar electricity generation dependable is prohibitive.
Random shutdown of one nuclear generator in a fleet of nuclear generators does not diminish the electric power output of the remaining nuclear generators whereas all the solar panels in a fleet stop producing electricity at night and all the wind generators in a fleet stop producing electricity during low wind periods.
Natural gas fuelled generators, in addition to emitting CO2, have a common mode failure related to the natural gas pipeline pressure. This issue is a big problem in markets where electrically powered compressors are required to maintain natural gas pipeline pressure. A loss of natural gas pressure due to high home heating loads during a cold snap can cause an electricity generation failure which, due to lack of gas compression, causes a cascade failure of both the electricity and natural gas systems such as almost occurred in Texas in Februaty 2021. Then, absent liquid fuel backup for the combustion turbines, it is impossible to use the combustion turbines to black start the electricity grid.
Due to absence of voltage source power inverters at existing distributed wind and solar generators it is also impossible to black start the public electricity grid using wind and solar electricity generation.
Thus practical electricity grids require a substantial fraction of coal, oil, hydroelectric or nuclear generation to provide resiliency, which is ability to black start and operate for a significant period using only fuel available on site. In jurisdictions which lack hydroelectric capacity closure of coal and oil fueled electricity generation triggers an immediate requirement for nuclear power plant capacity to provide electricity generation resiliency.
HEAT:
A large fraction of present fossil fuel energy consumption is for production of comfort heat. In urban markets it is usually more economic to provide dependable district heat from an urban sited nuclear reactor than to provide an equal amount of dependable electric heat from any form of remote clean electricity generation. The thermal electricity generation used with nuclear reactors rejects large amonts of low grade heat that is suitable for urban district heating.
NUCLEAR POWER SOURCES:
There are two methods of producing nuclear energy, fission of high atomic weight elements and fusion of low atomic weight elements. Both methods are explored in this web site section.
However, from a practical economic public power perspective nuclear energy released via fission of unstable heavy isotopes, that are bred from abundant more stable fertile heavy isotopes, is the only dependable, sustainable and economic source of clean power that can fully displace fossil fuels. Much of the nuclear energy must come from fast neutron induced fission to dispose of long lived nuclear waste and to sustain conversion of fertile isotopes into fissionable isotopes.
A 2013 overview of the various nuclear reactor technologies is contained in the text New Technologies Associated to the Construction of Nuclear Power Plants.
Public misconceptions about nuclear power are concisely addressed in a PragerU Video.
The status of civilian nuclear power in 2019 is summarized in Ensuring the Future of Nuclear Power.
The design of conventional light water cooled nuclear power reactors is summarized in the:
Nuclear Engineering Handbook
ADVANCED FISSION REACTOR DEVELOPMENT OVERVIEW:
A technical overview of current nuclear power issues is presented in the text: A Nuclear Green New Deal by Darryl Siemer. This text provides the perspective of a retired senior Idaho National Laboratory scientist on the future of nuclear power.
A March 2021 report titled: "Advanced" Isn't Always Better by Edwin Lyman raises a number of issues which must be addressed by the various advanced reactor technologies. An important responding document is a Letter from Dr. Alex Cannara.
NUCLEAR FUEL SUSTAINABILITY:
Advances in Fast Neutron Reactor (FNR) technology have rendered obsolete past concerns about nuclear reactor safety and nuclear waste disposal. However, the present wasteful use of the limited supplies of the fissile isotopes U-235 and Pu-239 in unsustainable nuclear fuel cycles is of enormous concern. As fossil fuels are phased out the amount of available dependable power will be constrained by the available fissile isotope supplies. It will likely take at least a century to quadruple the fissile isotope inventory via fuel breeding.
A major problem today is that existing electricity markets reward nuclear reactor owners for low cost per kW output without adequately taking into consideration either long term fissile isotope supply sustainability or nuclear waste disposal. The existing water cooled nuclear reactor technology is not fuel sustainable and is rapidly depleting the natural fissile isotope resource.
LIQUID SODIUM COOLED REACTORS:
Another concern is squandering of limited public resources on development of new nuclear reactor types that are not fissile isotope sustainable and/or do not address nuclear waste disposal. It is imperative to apply the limited public resouces to deployment of liquid sodium cooled Fast Neutron Reactors (FNRs), because only that reactor type presently provides a sustainable nuclear fuel cycle that can fully displace fossil fuels and that recycles 99.9% of the solid fuel waste.
Ten major benefits of liquid sodium cooled FNRs are:
1) They are conceptually simple;
2) Sodium cooled FNRs operate in a temperature range compatible with readily available sealing gaskets, chrome steel and stainless steel components;
3) There are no FNR life limiting chemical corrosion issues;
4) Sodium is chemically compatible with the other base metals (Fe, Ni, Cr, U, Pu, Zr, Mo) that are used for economic FNR and heat exchange bundle fabrication;
5) The sodium cooled FNR fuel cycle is 100X more efficient in use of natural uranium than is the existing water cooled reactor fuel cycle;
6) The sodium cooled FNR fuel cycle can be operated to reduce long lived nuclear waste production more than 1000 fold as compared to existing water moderated reactors.
7) Sodium cooled FNRs can be designed to totally avoid production of decommissioning waste;
8) The FNR use of sealed fuel tubes with plenums for inert gas storage permits almost all of the fuel reprocessing to be carried out at a shared remote facility instead of at each reactor site.
9) Sodium internal to fuel tubes improves heat transport.
10) Sodium internal and external to fuel tubes prevents fuel tube corrosion by chemical capture of the corrosive elements.
11) Metallic fuel rods inside the fuel tubes enable simple mechanical sorting of irradiated fuel and simple electrolytic and/or chemical fuel reprocessing.
A major issue with liquid sodium cooled reactors is ensuring that the primary sodium never contacts air or water and that any secondary sodium combustion is inconsequential. To achieve this objective each liquid sodium cooled reactor has multiple independent secondary heat transport systems. Each secondary sodium circuit is isolated from its companion steam generator by an atmospheric pressure nitrate salt loop. The secondary sodium is pressurized sufficiently to prevent either primary sodium or nitrate salt from entering the secondary sodium circuit.
MOLTEN SALT COOLED REACTORS:
Another class of potentially fuel sustainable nuclear reactors is molten salt cooled reactors fuelled by thorium, which is naturally at least 3X more abundant than is uranium. Thorium fuelled reactors operating with a sustainable fuel cycle require continuous chemical processing of their blanket fuel to continuously selectively remove protactinium. The selective protactinium removal is enabled by dissolving thorium in a molten salt coolant that can be continuously circulated for both chemical processing and heat removal.
The molten salt reactors can be further divided into chloride salt cooled fast neutron reactors with fuel tubes which maintain the core fuel geometry and fluoride salt cooled thermal neutron reactors that use a rigid moderator to maintain the core fuel geometry and hence can operate without fuel tubes.
Molten salt reactors superficially seem simple but they have numerous practical implementation problems related to their higher temperature of operation, complex corrosion issues, moderator degradation and the sophisticated chemical fuel processing that must be implemented at each reactor site. The fluoride salt cooled thermal neutron reactors also have a safe power limit related to the required minimum flowing liquid fuel residency time inside the moderator assembly.
ADVANCED REACTOR DEPLOYMENT:
As of 2020 there are over 100 reactor-years of liquid sodium cooled nuclear power reactor operating experience in several countries. The Russians have had a large size liquid sodium cooled power reactor program for many years. Their top of the line unit with a five year operating history is the BN-800.The Chinese with Russian assistance have two liquid sodium cooled power reactors under construction with scheduled completion in 2023. There are no scientific or engineering constraints to immediate large scale deployment of liquid sodium cooled reactors operating with sustainable fuel cycles to meet the challenge of climate change.
By comparison there are only about 2 years (17,000 running hours) of fluoride salt cooled laboratory size reactor operating experience in North America and there is no operating experience with chloride salt cooled reactors. There remain many unresolved material and chemistry issues with molten salt cooled reactors. The Chinese have had a large team of engineers working on molten salt reactor issues for over a decade. In spite of best intentions there is almost no possibility that molten salt cooled reactors operating with a sustainable fuel cycle can be scaled up and deployed sufficiently quickly to significantly impact climate change during the next few decades.
A major problem with reactor development in the USA is US governmental corruption by the fossil fuel industry. The US Democratic party is unwilling to face the reality that in 1994, at a time when the USA led the world in liquid sodium cooled fast neutron reactor technology, then Democratic president Bill Clinton cancelled the entire multi-billion dollar program in favor of cheaper fossil fuels. The US Republican party has long been dominated by fossil fuel interests. Both parties have embraced a rigid nuclear regulatory regime that is focused on obsolete light water cooled reactors. The result is that China, Russia and India are now dominating the world nuclear power industry and in North America US companies are doing limited new reactor demonstration in Canada due to Canada's more flexible nuclear regulatory regime. Unlike the new Chinese and Russian sodium cooled power reactors, no existing US power reactor technology is capable of sustained displacement of fossil fuels. However, the US companies Natrium and ARC Nuclear both claim to be working on development of sodium cooled reactors.
FUSION:
Other than via renewable energy, fusion based electricity generation is difficult and expensive to realize on Earth. For fundamental thermodynamic efficiency reasons, as long as low cost fission fuels are available, the cost per kWhe of Earth based fusion energy production will always remain much higher than the cost per kWhe of Earth based fission energy production. The fundamental difficulty is that over half of the electricity generated by fusion reactor technologies must be used to sustain the fusion reaction.
A possible avenue of future nuclear fusion fuel cost mitigation is mining He-3 from the surface of the moon. In theory it is possible to breed H-3 and hence He-3 in fusion reactors but sustaining the required controlled fusion reactions on Earth is extremely difficult. The problems include a low plasma density, a small fusion reaction cross section and large ongoing plasma energy loses via energetic neutron emission. The fusion reactor size required for a self sustaining fusion chain reaction with a reasonable net electric power output is believed to be too large for economic construction with present superconducting electromagnets.
FOCUS OF THIS WEB SITE:
This web site section primarily focuses on liquid sodium cooled Fast Neutron Reactors (FNRs) fueled by U-238 bred into Pu-239/Pu-240 because this technology in combination with renewable energy generation provides the only viable way of sustainably and completely displacing fossil fuels during the next few decades while avoiding production of long lived nuclear waste. At some future date this technology will likely be supplemented by breeding Th-232 into U-233.
It is the intent of this author to eventually produce web pages addressing all of the above mentioned topics.
This web page last updated October 21, 2021.
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