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XYLENE POWER LTD.
This web page identifies practical energy sources that have the capacity do work for the benefit of mankind in an environmentally sustainable manner.
As shown elsewhere on this website all energy in the local universe that can do work originates in free electrons and free protons. Aggregation of these free particles in the sun and stars causes overlap of particle energy fields that release kinetic energy. The kinetic energy converts to photons. There are various means of harvesting this photon energy flux to do work.
Over a period of billions of years the solar photon flux contributed to the Earth's chemical energy and the Earth's residual thermal energy.
During this same period aggregation of light elements on the Earth, in part from the solar wind, formed the Earth's potential nuclear fusion energy.
During a prior period stellar nuclear reactions produced the heavy elements that form the Earth's potential nuclear fission energy.
SOURCES OF ENERGY THAT CAN DO WORK:
The sources of energy on Earth that mankind can utilize to do work are: stored chemical energy, present solar energy, nuclear energy, the Earth's residual kinetic energy and the Earth's residual thermal energy. All energy forms available to mankind that can do work are derived from these five energy sources.
1. Stored chemical energy in the form of coal, oil and natural gas that resulted from net absorption of a small fraction of the past solar energy incident on the Earth.
2. Present solar energy incident on the Earth that can produce biofuels, hydroelectric power, solar electric power and wind power.
3. Nuclear energy that can be obtained via fission of heavy elements or via fusion of light elements.
4. Residual kinetic energy from the Earth's rotation and from the Earth-Moon orbit that can be harvested via tidal power.
5. Residual thermal energy, primarily resulting from nuclear decay in the Earth's core, that can be harvested via deep wells drilled in active volcanic areas.
During the last century mankind consumed solid (coal), liquid (petroleum) and gaseous (natural gas) fossil fuel stocks that took many millions of years to accumulate. At present extraction rates fossil fuels will become progressively more uneconomic due to depletion of accessible reserves, increasing costs of extraction and the consequences of increasing the concentration of carbon dioxide in the Earth's atmosphere and oceans.
In practical application fossil fuels are used to heat water to 540 degrees C. The resulting steam expands through a two stage turbo generator and is condensed at 49 degrees C. This temperature range produces good thermal efficiency while staying within the performance range permitted by readily available materials and a natural draft cooling tower heat sink.
In the future fossil fuels will have to be replaced by synthetic fuels that are produced from water and biomass with the aid of electricity and nuclear heat.
SOLAR ENERGY / RENEWABLE ENERGY:
Most of the solar energy that is incident on the Earth consists of electromagnetic photons with wavelengths in the near ultra-violet (.1 um to .4 um), visible (.4 um to .7 um) and near infrared (.7um to 2.8 um) ranges. About 30% of the incident solar photons are reflected back into space. The remaining solar photons are absorbed by various materials such as the ocean surface. A solar photon can cause a change in electron energy state, a chemical reaction, a change in physical phase or a change in temperature. Eventually all the energy carried by the absorbed solar photons is converted into atmospheric temperature heat. A small portion of this heat is directly radiated. However, most of this heat evaporates water that emits infrared radiation into space when it condenses in the cool upper atmosphere.
There are various ways of obtaining work from the processes that convert solar photons into atmospheric temperature heat. Six examples are:
1) Solid Biofuels: Solar photons incident on green plants cause photosynthesis whereby carbon dioxide and water combine to form carbohydrates known as sugars, starch and cellulose plus oxygen gas (O2). The biomatter can be harvested, dried, compacted and directly combusted as a dry fuel. The main difficulty with dried biomass as fuel is transportation and handling problems due to low material density, low energy density and high ash yield. Solid biomatter is generally unsuitable as a transportation fuel.
2) Liquid Fuels: Solar photons incident on green plants cause photosynthesis whereby carbon dioxide and water combine to form carbohydrates known as sugars, starch and cellulose plus oxygen (O2). Various processes involving supply of additional energy and hydrogen can be used to convert carbohydrates into alcohols and oils. Dehydration reactions can remove H2O from alcohols to form oils. Due to density differences and immiscibility oils naturally separate from water. Liquid fuels (alcohols or oils) can be burned in an engine or a combustion turbine to do work. The engine or turbine releases heat into the atmosphere. Note that the dehydration and hydrogenation reactions require externally supplied energy beyond that contained in the biomass feedstock. This extra energy can be obtained either by sacrificing additional biomatter feedstock or by input from another prime energy source such as nuclear reactor or a renewable electricity generator.
3) Hydropower: Solar photons absorbed by lakes and the ocean cause evaporation of water. The resulting water vapor rises and cools at higher altitudes where it condenses emitting part of its energy as infrared photons at the upper atmospheric temperature. The water falls as rain onto high elevation land. This water becomes part of a river that flows downhill to the ocean. Along the way one or more hydro-electric generators can be used to change part of the kinetic energy of the flowing water into electricity. This electricity is transmitted along electricity transmission lines and is converted into heat, chemical, mechanical or radiation energy at the electrical load. The chemical, mechanical and most of the radiation energy ultimately will become atmospheric temperature heat.
4) Wind: During the daytime absorption of incident solar photons by dry ground causes thermal expansion of the adjacent air. Similarly at night the air over dry ground cools. This daily temperature swing of air over dry ground causes back and forth air movement known as wind. Wind is particularly strong near the coast of an ocean or a large lake. The energy contained in this air movement can be harnessed with a wind turbine. The major difficulty is that the wind turbine power output drops to almost zero twice per day. A second difficulty, particularly in Ontario, is that average wind turbine power output is also affected by seasonal issues. Other wind power related difficulties are long distance energy transmission, poor transmission line utilization and expensive balancing energy generation/storage.
5) Solar Thermal Power: During the daytime solar photons are reflected onto a black vacuum insulated tube that contains a pumped heat transport fluid. The hot heat transport fluid is used to form a vapor such as steam which generates electricity via a turbine, After passing through the turbine the vapor is condensed, liberating its heat to the atmosphere. The condensate is pumped back into the vapor generator.
6) Solar Voltaic Power: During the daytime solar photons are absorbed by large area semi-conductor p-n junctions. The solar photons excite electrons over the semiconductor's bandgap causing a voltage between the p and n sections. This voltage causes an electric current in an external circuit that does work.
An advantage shared by all forms of solar/renewable energy is that there is no increase in thermal dissipation in the Earth's atmosphere and hence solar/renewable energy does not contribute to global warming.
Many solar power systems are connected behind customer electricity meters. Such solar power systems reduce electricity energy charges, electricity transmission loss charges and electricity demand charges, which maximizes the financial benefit of the solar power system to the electricity customer. Solar power output also goes through a daily maximum coincident with the daily air conditioning load.
SOLAR VERSUS NUCLEAR:
Solar energy is radiation resulting from nuclear reactions in the sun. At low Earth latitudes, where solar radiation is intense and usually available, solar energy may displace nuclear energy for electricity production. However, at high Earth latitudes, where solar radiation is weak and is frequently unavailable for long periods, nuclear energy will likely become the dominant non-fossil energy source for electricity production.
Nuclear energy is available in two forms, fission and fusion. Nuclear fission power reactors have been deployed for over half a century. Nuclear fusion power reactors are presently at the prototype construction stage.
The origin of nuclear fission energy is stellar end-of-life processes that form heavy atoms such as uranium and thorium. A nuclear fission reaction occurs when a suitable heavy atom absorbs either a neutron or a gamma photon and then breaks into two lighter atoms plus some energetic neutrons. The lighter atoms, known as fission products, are generally radio active and release more energy via a sequence of natural decays. The natural decay products are known as fission daughters and are often radio active.
In a nuclear reactor the energy released by neutron activation product decay, fission reactions, fission product decay and fission daughter decay becomes heat. Most of this heat is used to make steam in a closed system. Steam turbines convert about one third of the heat into electricity. The remainder of the heat is directly or indirectly removed by evaporation of water at close to atmospheric temperature. High altitude condensation of the resulting water vapor emits infrared photons which carry the heat into outer space.
Typically about 10% of the generated electricity is used to power parasitic loads within the power plant, including: superheated water pumps, condensate injection pumps, cooling water pumps, moderater pumps and cooling tower fans.
At the electrical loads most of the delivered electricity becomes atmospheric temperature heat which is also radiated into outer space.
ADVANTAGES OF NUCLEAR FISSION:
The major advantage of nuclear fission based electricity generation is that it is a well understood method of generating bulk electricity without combustion of fossil fuels. The parasitic power requirements are relatively low. Water cooled and moderated nuclear fission power reactors for electricity generation have been successfully deployed for half a century and the related issues are well understood by governments, engineers, equipment suppliers, contractors, major electricity utilities, labor unions and regulatory bodies. Water cooled and moderated nuclear fission technology is well known and is taught at the undergraduate level at numerous educational institutions.
CANDU NUCLEAR REACTORS:
A special category of nuclear fission reactors is CANDU reactors. CANDU heavy water cooled and moderated nuclear reactors have extraordinary fuel flexibility, reliability and safety features. CANDU reactors operate with natural uranium fuel or spent fuel from light water reactors and usually require proximity of heavy water to the fuel for the nuclear reaction to run. If the heavy water is either lost or is replaced by light water the main nuclear reaction stops. In an emergency a CANDU reactor can be flooded with light water which, in addition to providing cooling, forces a nuclear reaction shutdown. That safety advantage has not received adequate public attention.
CANDU reactors, although more expensive to construct than light water reactors, are inherently much safer. Light water reactors and liquid metal cooled reactors both use enriched uranium and/or plutonium fuel. In a nuclear reactor with enriched fuel core melting caused by fission product decay heat can potentially trigger an uncontrolled nuclear reaction whereas in a CANDU reactor with natural uranium fuel core melting cannot trigger an uncontrolled nuclear reaction.
A minor disadvantage of CANDU reactors is that the energy captured by the moderater is discarded, which makes these reactors about 4% less thermally efficient than a light water cooled and moderated reactor having the same electric power output.
An extremely important issue from the Canadian perspective is that CANDU technology provides Canada significant protection from the whims of US politicians, who have a history of not honoring Canadian-US trade agreements. With CANDU technology Canada is not dependent on the USA for nuclear fuel enrichment or for reactor pressure vessel fabrication.
CANFLEX FUEL BUNDLES:
An important innovation by Atomic Energy of Canada Limited (AECL) was the CanFlex Fuel Bundle. The CanFlex Fuel Bundle allows various different types of fuel to be loaded into a standard CANDU nuclear reactor. A CanFlex fuel bundle provides improved cooling water flow and heat exchange and can be configured to use natural uranium, slightly enriched uranium, thorium, plutonium, etc. An obvious application of CanFlex fuel bundles is to use spent fuel and plutonium from light water reactors in CANDU reactors. The Canflex fuel bundle potentially allows major improvements in fuel utilization efficiency and waste reduction while avoiding the greater complexity inherent with liquid metal cooled fast neutron reactors.
CANFLEX reactor fuel bundles can be configured to provide some of the fuel breeding and fuel burn up advantages of fast neutron liquid metal cooled reactors without the difficulties related to liquid metal cooling systems.
In the long term CANFLEX technology provides a practical means of burning up spent nuclear fuel from US light water reactors.
Many of the benefits of CANFLEX fuel bundle technology are currently not being exploited because the government of Canada lacks the moral fiber to stand up to a narrow segment of the population that blindly opposes transport and storage of spent nuclear fuel.
LIQUID METAL COOLED FAST NEUTRON REACTORS:
A liquid metal cooled Fast Neutron Reactor (FNR) has the immense advantage that, with suitable fuel processing and recycling, the radio toxicity decay time of its spent fuel can be reduced to about 400 years as compared to 400,000 years for a water cooled and moderated reactor. The Experimental Breeder Reactor II (EBR II) successfully operated for 30 years with liquid sodium coolant at a maximum temperature of 473 degrees C. When a liquid metal cooled FNR is operating properly there is no doubt that it is more thermally efficient, much more fuel efficient and produces much less high level radioactive waste than a water cooled and moderated nuclear reactor. However, when anything goes amiss in a liquid metal cooled reactor, the practical benefits of water cooling and water moderation become obvious.
1) If water leaks it makes a puddle on the floor that is easily vacuumed up. The water can easily be filtered or distilled for reuse. If radioactive liquid metal leaks it makes a solid metal highly radioactive blob that may be extremely flammable, highly toxic and difficult to safely remove. Liquid metal cooled reactors minimize this problem by use of a secondary coolant loop that typically is non-radioactive sodium.
2) Water cooled reactors usually operate up to 300 degrees C because up to that temperature gasket and O-ring seals can be made with elastomeric materials. In an emergency a small leak in a water system can often be temporarily stopped with a clamp-on elastomeric patch seal. At 473 to 600 degrees C, the target design operating temperature of a liquid metal cooled reactor, realizing maintenance access seals is a much more difficult and realizing emergency clamp-on seals is almost impossible;
3) A small superheated water leak becomes an obvious noisy steam jet. A small liquid metal leak becomes a relatively quiet but potentially lethal jet of hot liquid metal;
4) During a prolonged reactor shutdown the parasitic pumping load of a liquid metal cooled power reactor may be greater than for a water cooled reactor. This issue is very important in the event of an earthquake, tornado or other event that damages the nearby electricity grid;
5) Realizing the full benefits of liquid metal reactors requires fuel reprocessing which introduces process complexity;
6) Liquid metal cooled reactors frequently have coolant drain down and cooling thermal stress related issues that are much more onerous than the corresponding issues in a water cooled reactor;
7) In an emergency a water cooled reactor can be flooded with water from any source. Not so with a liquid metal cooled reactor.
8) Liquid metal cooled fast neutron reactors must be initially fuelled with U-235 enriched uranium and/or plutonium. Light water cooled and moderated reactors require only a small amount of uranium enrichment. CANDU heavy water cooled and moderated reactors can operate with unenriched natural uranium or spent fuel from light water reactors;
9) The fuel bundle design and construction of liquid metal cooled fast neutron reactors is more critical than for water cooled and moderated reactors because the nuclear reaction in a fast neutron reactor is controlled by thermal expansion of the fuel instead of by slow neutrons.
10) The prefered liquid metal coolant sodium is a fire hazard and reacts violently with water.
Hence for practical construction, operating and maintenance reasons electricity utilities have in the past generally have chosen water cooled and moderated nuclear reactors instead of more efficient liquid metal cooled fast neutron nuclear reactors. As a result, water cooled and moderated nuclear power reactors have a long history of operational success. The issues that will likely eventually force abandonment of water cooled reactors in favor of liquid sodium cooled reactors are requirements for safe disposal of high level nuclear waste and for improved fuel utilization.
MOLTEN SALT REACTORS:
Molten salt reactors (MSRs) are fast neutron reactors that use a molten salt as the primary coolant. Molten salt reactors can potentially operate at core temperatures in the range 700 degrees C to 1500 degrees C and hence potentially opens the door to direct use of nuclear energy for high temperature processes such as ammonia production and hydrocarbon fuel reformation. However, molten salt reactors face a legion of practical material problems relating to the confinement tank, the control rods, the primary to secondary heat exchanger and nuclear waste disposal. In a MSR the fuel is dissolved in the salt. The power level of a MSR self regulates via thermal expansion of the molten salt. However, extracting heat from a MSR causes fission products dissolved in the salt to plate onto the relatively cool heat exchange surfaces.
A MSR that uses NaF operates very hot. A MSR that uses either a lithium or a chloride salt to reduce the operating temperature requires at least one expensive isotope separation. At this time the practical economics of MSR technology are questionable.
PROBLEMS ASSOCIATED WITH NUCLEAR FISSION:
Continuing Energy Emission:
The primary problem with nuclear fission energy is that the fission products are radioactive and continue emitting ionizing radiation and heat long after the fission process stops. The thermal output from fission product decay and fission daughter decay shortly after a fission reactor is shutdown is typically about 7% of the reactor's full power thermal output. The parasitic electrical load of the reactor cooling system may be as high as 15% of the reactor's maximum rated electrical output. Inability to adequately remove the fission product decay heat and fission daughter decay heat under adverse circumstances, such as a reactor shutdown in combination with a prolonged loss of grid power, has led to major nuclear reactor meltdown accidents at Chernobyl, Ukraine; Three Mile Island, USA and Fukushima Daiichi, Japan. At Chernobyl and at Fukushima substantial amounts of radioactive dust were released into the surrounding environment. The enormous financial losses related to reactor core meltdown and radioactive contamination of the environment have made the cost of credible third party liability insurance for nuclear fission power plants extremely high.
The issues surrounding long term storage of spent nuclear fuel bundles are yet another aspect of long term fission product and fission daughter decay.
Protection From Terrorist Attack:
The second major problem with nuclear fission power plants is potential attack by terrorists. Protecting nuclear fission power plants and their spent fuel storage bays from potential terrorist attack substantially increases both the plant capital and operating costs and makes distributed nuclear fission electricity generation uneconomic. Furthermore, there is never complete certainty that the anti-terrorist measures will work as anticipated.
Low Ramp Rate:
A third problem specific to water cooled and moderated nuclear fission power plants is known in the electricity industry as low ramp rate. Some of the unstable nuclear fission products and fission daughters have high slow neutron absorption cross sections and are known as reactor poisons. If the operating power level of a fission reactor is suddenly reduced in response to a rapid fall in electricity grid load these reactor poisons may force a complete reactor shutdown lasting about two days while the reactor poisons naturally decay. In the mean time an increase in electricity grid load must be met with other forms of electricity generation. This problem can be circumvented via an engineering trick known as steam turbine bypass, but provision of steam turbine bypass capability increases the plant capital cost and operating with steam turbine bypass functioning wastes both cooling water and nuclear fuel.
Poor Thermal Efficiency:
A fourth problem specific to water cooled and moderated nuclear fission power reactors is poor thermal efficiency. These reactors typically operate at a maximum coolant temperature of 300 degtrees C and are not thermally efficient, are not fuel efficient and are not waste efficient. It is easy to make an academic argument that to substantially improve thermal efficiency, fuel efficiency and waste efficiency water cooled and moderated nuclear power reactors should be replaced by liquid metal cooled fast neutron reactors. However, utility personnel who have to work with major power reactors under real life conditions have a different perspective.
Nuclear fusion is the energy source that powers the stars. Nuclear fusion potentially offers major public safety benefits as compared to nuclear fission.
During the 1950s the world witnessed the development of "hydrogen bombs". The amount of energy released by a "hydrogen bomb" is truly awesome. One typical "hydrogen bomb" releases energy equivalent to about 1000 fission bombs. Just one fission bomb destroyed the city of Hiroshima, Japan, in August 1945.
The primary source of controlled nuclear fusion energy is conversion of deuterium (H-2), lithium-6 (Li-6), and lithium-7 (Li-7) into helium-4 (ordinary helium) via multi-step nuclear processes that involve intermediate production of neutrons, tritium (H-3) and helium-3 (He-3). A fusion reaction releases heat that can be used to produce steam, which can then be used to produce electricity.
The fusion fuels deuterium and lithium are products of solar fusion reactions. Deuterium and lithium are sufficiently common on Earth that for the purpose of fueling nuclear fusion power stations their supply is virtually unlimited. In this respect nuclear fusion energy is "renewable energy" and the use of fusion energy on Earth is limited only by the thermal radiation constraint.
A "hydrogen bomb" uses energy from a fission bomb to trigger a single large scale fusion reaction. A practical nuclear fusion based electricity generation system involves many sequential small scale fusion reactions that use only electicity as the initial energy trigger. Development of this trigger apparatus has been a long, complex and expensive undertaking which is only now approaching fruition. Recent progress has been enabled by advances in materials, electronics and understanding of semi-stable plasma configurations known as spheromaks.
ADVANTAGES OF NUCLEAR FUSION:
Unlike a nuclear fission reactor, when a nuclear fusion reactor is shut down its heat output goes to almost zero.
Unlike fission reactors, fusion reactors do not produce significant long lived radio active waste products.
If a terrorist attacks a nuclear fusion power plant there is relatively little opportunity for causing significant damage outside the plant perimeter. From a public safety perspective the security of nuclear materials inside a nuclear fusion power plant is almost a non-issue. These safety features potentially allow deployment of unstaffed nuclear fusion power plants near smaller communities with potential major cost savings in both skilled labor and long distance electricity transmission.
Fusion power plants are inherently modular. The power output from each module can be rapidly changed to track changes in electricity load. If one module is shut down for service other modules at the same site can continue operating. Hence the overall system reliability is high, the output ramp rate is high and the transmission costs are low making electrical kWhs output from distributed nuclear fusion reactors almost twice as valuable as electrical kWhs output from central nuclear fission reactors.
CHALLENGES OF NUCLEAR FUSION:
The major technical challenges with nuclear fusion as compared to nuclear fission are on-site light isotope separation, fire safety, vacuum systems, plasma confinement, operating temperature, heat transfer, vibration, economics and education. Full understanding of the technical issues related to nuclear fusion is confined to only a tiny segment of the physics and engineering community.
A nuclear fusion power plant inherently needs a liquid lead-lithium alloy cooling system. The lithium will liberate hydrogen gas if it comes into contact with water. In addition the liquid metal cooling circuit will also contain radioactive tritium (H-3), helium-3 (He-3), helium-4 (He-4) and gamma emitting beryllium-7 (Be-7). For safety He-4 isolated heat exchangers should be used to completely isolate the liquid metal cooling circuit from the steam/water circuit, so that a single heat exchanger fault can not cause a fire, tritium release or Be-7 release.
The additional technical complexity of a fusion power plant as compared to a fission power plant makes generation of bulk electricity from fusion appear more expensive than generation of electicity from fission. However, when the full costs of spent fission fuel management, public liability insurance, operating labor and electricity transmission are taken into consideration, the long term economics may favor fusion power.
EARTH'S RESIDUAL KINETIC ENERGY:
Residual kinetic energy of the Earth's rotation in combination with lunar and solar gravity causes ocean tides. At locations with favorable geography tidal energy can be converted into electricity, which at the load becomes atmospheric temperature heat. The major problems with tidal energy generation are: high capital and maintenance costs, intermittant output requiring energy storage, long transmission lines, limited geographic applicability and interference with ocean navigation.
EARTH'S RESIDUAL THERMAL ENERGY:
Residual thermal energy in the Earth's core resulting from decay of radioactive isotopes can be accessed via deep drilled wells in active volcanic areas. To obtain work a pumped flow of water is heated by the hot magma. The resulting superheated water or steam is used to vaporize a working fluid. The working fluid vapor expands through a turbine to generate electricity. Then the working fluid vapor is condensed, releasing heat at atmospheric temperature. The condensed liquid working fluid is recycled. At the electrical load conversion of motive power into heat causes further heat to be dissipated in the atmosphere. Disadvantages of residual thermal energy are: limited geographic applicability, high cost, high thermal dissipation per electrical kWh generated and uncertain working life.
This web page last updated March 16, 2015.
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