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DEPENDABLE POWER:
Most of the value of an electricity grid lies in its capacity to supply clean, sustainable and dependable power whenever required by consumers. The main electricity generation sources that are clean, sustainable and dependable are large hydroelectric dams and fast neutron nuclear power plants.
Large hydroelectric dams can only be built in places that have both suitable geography and suitable politics. For example, damming the upper Niagara River would enable energy storage between Lake Erie and Lake Ontario, but there are so many conflicting political parties and jurisdictions involved that obtaining project consent is considered impossible.
Wind and solar energy are clean and may seem desirable due to their superficial simplicity and sustainability but they lack thermal capacity and they have common mode failures which makes them not dependable. Net wind and solar electricity generation varies widely both daily and seasonally. The amount of energy storage and related energy transmission required to make wind and solar electricity generation dependable is usually cost prohibitive.
Wind and solar electricity generation also do not provide the moment of inertia needed for electricity grid stability.
As a result unconstrained wind and solar electricity generation can provide at most 20% of the annual clean energy required by an electricity grid. The remaining 80% of the annual clean energy required by an electricity grid must come from dependable hydroelectric and nuclear power sources.
This limit on the maximum fraction of clean energy that can be supplied by unconstrained wind and solar electricity generation arises from practical electricity grid: load following, energy storage, transmission and stability constraints.
Nuclear electricity generation usually relies on the existence of a nearby large heat sink. Hence most nuclear power plants are located in the proximity of a dependable source of water such as a major river, lake or ocean.
A fission type nuclear power plant operates by splitting large fissionable fuel nuclei into smaller fission product nuclei. The difference in rest mass between a fissionable nucleus and its fission product nuclei becomes thermal energy which is absorbed by the nuclear reactor coolant. This thermal energy is used to make high pressure steam which is fed to a turbogenerator to produce electricity. The rate of electricity production is usually controlled by controlling the rate of nuclear heat production. The turbogenerator discharges low pressure steam into a condenser which transfers the steam's latent heat to an external heat sink.
A fission type nuclear fuel cycle is considered sustainable if the available surplus fission neutrons also convert abundant fertile fuel nuclei into new fissionable fuel nuclei at a rate sufficient to sustain the power production process.
Only dependable power sources can be used to black start a 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 large scale supply of dependable clean electricity.
The electric power output from a fleet of nuclear power stations is much more 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 combined wind and solar generator capacity factor of about 30%;
b) Fast neutron reactors can be made suitable for load following;
c) The failure modes of nuclear generators are statistically independent whereas renewable generators have solar exposure related common mode failures;
d) The cost of sufficient transmission and energy storage to make seasonally variable wind and solar electricity generation dependable is prohibitive.
A summary of world nuclear power reactors is A Review on the Development of Nuclear Powwer Reactors
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 almost all the wind generators in a fleet stop producing electricity during low wind periods. Redundant generation and transmission sufficient to compensate for the large scale local fluctuations in wind generation is prohibitively expensive.
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 major problem in circumstances where electrically powered compressors are used 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 combustion turbines, it is impossible to use combustion turbines to immediately black start the electricity grid.
The issue of potential failure of electrically powered natural gas pipeline compressors is of national importance in the USA because much of US natural gas is sourced in Texas.
Due to absence of sufficient energy storage and 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 at the generator 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 circumpolar urban markets it is usually more economic to provide dependable district heat from urban sited nuclear reactors than to provide an equal amount of dependable electric heat from any form of remote clean electricity generation. The thermal electricity generation apparatus used with nuclear reactors rejects large amounts of low grade heat that can, in combination with in-building water source heat pumps, be used 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 of long lived nuclear waste atoms. The nuclear process must emit enough free neutrons to sustain conversion of abundant fertile isotopes into fissionable isotopes.
Here is a link to a textbook on Nuclear Reactor Physics
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:
Important advantages of advanced fast neutron reactors include protection of the reactor structure from neutron damage and conversion of almost all long lived heavy isotopes into fission products that have short half lives.
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 unsustainable use of the limited supplies of the fissile isotopes U-235 and Pu-239 in thermal neutron power reactors is of enormous concern. As fossil fuels are phased out the amount of available dependable power will be limited by the available fissile isotope supplies. It will likely take at least a century to quadruple the fissile isotope inventory via fuel breeding. Reference: Long Term Sustainability of Nuclear Fuel
A major problem today is that existing electricity markets reward nuclear reactor owners for low cost per kW output without adequately rewarding either maintenance of the fissile isotope supply or elimination of long lived nuclear waste. The existing water moderated nuclear power reactor technology is not fuel sustainable, is rapidly depleting the natural fissile isotope resource and produces large amounts of long lived nuclear waste.
LIQUID SODIUM COOLED REACTORS:
Another concern is squandering of limited public resources on development of new thermal neutron reactor types that are not fissile isotope sustainable and do not address disposal of long lived nuclear waste. It is imperative to apply the limited public resouces to deployment of liquid sodium cooled Fast Neutron Reactors (FNRs), because only that reactor type provides a proven sustainable nuclear fuel cycle that can fully displace fossil fuels and that recycles 99.9% of the solid nuclear waste.
Major benefits of liquid sodium cooled FNRs are:
1) They are conceptually simple;
2) Low pressure operation permitting urban siting with no public exclusion zone;
3) Operation in a temperature range compatible with readily available sealing gaskets, chrome steel and stainless steel components;
4) There are no FNR life limiting chemical corrosion issues;
5) 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;
6) The sodium cooled FNR fuel cycle is 100X more efficient in use of natural uranium than is the existing water cooled reactor fuel cycle;
7) The sodium cooled FNR fuel cycle with fuel reprocessing can be operated to reduce long lived nuclear waste production more than 1000 fold as compared to existing water moderated reactors.
8) Sodium cooled FNRs can be designed to totally avoid production of decommissioning waste;
9) The FNR use of sealed fuel tubes with plenums for inert gas storage permits the fuel reprocessing to be carried out at a shared remote facility instead of at each reactor site;
10) Sodium internal to fuel tubes improves heat transport and together with small silica balls causes safe fuel disassembly in a prompt neutron critical condition;
11) Sodium internal and external to fuel tubes prevents fuel tube corrosion by chemical capture of the corrosive fission product elements;
12) Metallic blanket fuel rods which slide inside the fuel tubes enable simple scanning and mechanical sorting of irradiated blanket fuel rods and simple electrolytic and/or chemical fuel reprocessing.
13) The dominant fissile core fuel component should be Pu-239 instead of U-235 to ensure a decrease in reactor reactivity with increasing fuel temperature.
A major issue in the design of liquid sodium cooled reactors is ensuring that the primary sodium never contacts air or water and that any secondary NaK combustion is inconsequential. To achieve this objective each liquid sodium cooled reactor has multiple independent secondary heat transport circuits. Each secondary NaK circuit is isolated from its companion steam generator by an atmospheric pressure nitrate salt loop. The NaK is pressurized sufficiently to prevent either primary sodium or nitrate salt from entering the isolated NaK circuit on a heat exchange tube failure.
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 selectively remove protactinium. This selective protactinium removal is enabled by dissolving thorium in a molten salt coolant that can be continuously circulated for chemical processing and/or heat removal.
The molten salt reactors can be further divided into:
a) Chloride salt cooled fast neutron reactors with fuel tubes which maintain the core fuel geometry;
b) Fluoride salt cooled thermal neutron reactors that use a rigid moderator (graphite) to maintain the core fuel geometry and hence can operate without fuel tubes.
The practical molten salt cooled reactor fuel enclosure alloys that can withstand the required high operating temperatures all contain a substantial fraction of nickel. However, in a neutron flux over time all nickel alloys become brittle due to accumulation of He atoms at metal grain boundaries as a result of Ni-60 being an alpha emitter. To avoid this problem it is necessary to design the reactor so that the enclosure is protected from the neutron flux. That design requires localization of the neutron flux near the center of the reactor fuel enclosure.
Fuel sustainable chloride salt cooled fast neutron reactors localize the neutron flux near the center of the enclosure by use of fuel tubes. However, there are unresolved developmental issues related to the required fuel tube material and to on-line protactinium extraction from the fuel salt in these fuel tubes. The most suitable fuel tube material is believed to be Mo depleted in Mo-95 which is both extremely difficult to obtain and extremely difficult to fabricate.
Fuel sustainable fluoride salt cooled thermal neutron reactors localize the neutron flux near the center of the enclosure by use of a rigid moderator. The experimentally demonstrated moderator material is graphite, but after about four years of operation graphite swells too much and must be replaced. The problem with hydrogen based moderator compounds is that they spontaneously decompose at the required operating temperatures. Use of Be as a moderator is prohibitively expensive for bulk power generation.
A second problem with fluoride salt cooled reactors is that the fuel salt is in continuous rapid motion. That motion quickly moves the recently made fission products which supply the delayed neutrons out of the moderator established reactor core zone. That issue leads to power control instability at high liquid fuel flow rates.
Thus while molten salt reactors superficially seem simple they have multiple unresolved practical implementation problems.
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 problems that could limit 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 reactor years (17,000 running hours) of molten fluoride salt cooled laboratory size reactor operating experience in North America and there is zero operating experience with chloride salt cooled reactors. There remain challenging unresolved moderator and fuel tube 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 Canada and the USA is 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, India and South Korea are now dominating the world nuclear power industry and in North America US companies are doing limited new reactor demonstrations 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 Terrapower (Natrium Reactor) and ARC Nuclear both claim to be working on development of sodium cooled power 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 a fusion reactor must be used to sustain the fusion reaction. Hence fusion based electricity generation requires more than twice as much capital equipment per net kWh produced as does fission based electricity generation.
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, large ongoing plasma energy loses via energetic neutron emission and cumulative fast neutron damage to the reaction chamber inner wall. 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 electromagnet materials.
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 completely and sustainably displacing fossil fuels during the coming few decades while avoiding production of significant amounts of long lived nuclear waste. At a future date, after development of suitable molybdenum isotope fuel tubes, this technology will likely be supplemented by breeding Th-232 into U-233 in molten chloride salt reactors.
It is the intent of this author to eventually produce web pages addressing all of the above mentioned topics.
This web page last updated March 4, 2023.
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