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Nuclear Energy (Fusion Solution? (International Thermonuclear Experimental…
Nuclear Energy
Fusion Solution?
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Depending on age and mass of star, energy may come from proton-proton (H-H) fusion, helium fusion (product would be larger element. If temps high enough, could form something else), or carbon cycle (if temps high enough).
For brief periods near end of luminous lifetime of stars, heavier elements up to iron may fuse, but
since iron at the peak of binding energy curve, fusion of elements more massive than iron would soak up too much energy rather than deliver it - not thermodynamically favourable.
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Proton-Proton
Fuels the sun and other stars which have core temps less than 15 mil Kelvin. Reaction cycle yields about 25MeV of energy.
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Trying to achieve fusion on earth: temp is problem. No material known can contain 6000 deg C - melts.
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Energy has been produced by fusion (by humankind) but has not yet exceeded energy put expended in its production.
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If light nuclei forced together, will fuse w a yield of energy bc mass of the combination is less than sum of the masses of individual nuclei.
If the combined nuclear mass is less than iron at peak of binding energy curve, then nuclear particles will be more tightly bound than they were in the lighter nuclei, and that decrease in mass comes off in the form of energy according to the Einstein relationship.
For potential nuclear energy sources for the Earth, the deuterium-tritium fusion reaction contained by some kind of magnetic confinement seems the most likely path.
Advantages of fusion
A vast, new source of energy.
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Radioactivity of the reactor structure, caused by the neutrons, decays rapidly and can be minimised by careful selection of low-activation materials. Provision for geological time-span disposal is not needed.
Fuels
Deuterium (H isotope): Abundant as can be extracted from all forms of water. If all world’s electricity were to be provided by fusion power stations, deuterium supplies would last for millions of years.
Tritium (isotope): Does not occur naturally, will be manufactured from lithium within machine
Lithium: Lightest material, used as catalyst to produce tritium. Plentiful in earth’s crust. If all world’s electricity were to be provided by fusion, known reserves would last at least 1,000 years.
Biggest challenge is efficiency, heat input.
Once the reaction is established, even though it occurs between deuterium and tritium, the consumables are deuterium and lithium.
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Things to look up
Wexford potential nuclear plant, Consir(?) Point, opposition
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WHO report (Chernobyl ?) - health effects of radioactive waste, physical and psychological issues
Yucca Mountain, Nevada, Nuclear Waste
Germany stopped to focus on renewables, had to return to nuclear - not black and white
Irish gov sent iodine tablets to Irish homes in case of nuclear disaster in UK. I would stay on sites in lung, radioactive I more likely to be flushed thru
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Fission and Fusion
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Mass of nucleus always less than sum of individual masses of protons and neutrons which constitute it. Dif is measure of the nuclear binding energy which holds nucleus together.
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Iron Limit
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Iron-56 is abundant in stellar processes, and with a binding energy per nucleon of 8.8 MeV, it is the third most tightly bound of the nuclides.
average binding energy per nucleon is exceeded only by 58Fe and 62Ni, the nickel isotope being the most tightly bound of the nuclides.
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Uranium -235 Fission
Slow neutron can be captured by U-235 nucleus, rendering it unstable and prone to fission.
Natural uranium contains three isotopes: U-234 (0.006%), U-235 (0.7%), and U-238 (99.3%)
Increasing the concentration of fission producing U-235 isotope in uranium metal fuel was one of the main objectives of the Manhattan project.
Fast neutron will not be captured, must be slowed by moderation (mixed w uranium fuel, ideally low atomic weight and little to no tendency to absorb neutrons - graphite (C) often used) to increase their capture probability in fission reactors.
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Fission Fragments
When undergoes fission, av. of fragment mass is about 118, but v few fragments near that av are found.
Much more probable to break up into unequal fragments, and most probable fragment masses around mass 95 and 137
Most of these highly unstable (radioactive), and some such as cesium-137 and strontium-90 are extremely dangerous when released to the environment.
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Fission Waste
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Due to reactive nature, much more problematic
Radioactive gases too voluminous to store, vented to atmosphere. No evidence of harmful nature, but does not mean is not.
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As of 2008 US has stock-piled 49,000,000kg of spent nuclear fuel, which will cease being radioactive threat after 10,000 years.
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Cold Fusion
March 23, 1989, Stanley Pons and Martin Fleischmann announced their discovery of "cold fusion."
Excitement quickly evaporated amid accusations of fraud and incompetence. When it was over, Pons and Fleischmann were humiliated by the scientific establishment; their reputations ruined, they fled from their laboratory and dropped out of sight.
"Cold fusion" and "hoax" became synonymous in most people's minds, and today, everyone knows that the idea has been discredited.
despite the scandal, laboratories in at least eight countries are still spending millions on cold fusion research.
During the past nine years this work has yielded a huge body of evidence, while remaining virtually unknown - because most academic journals adamantly refuse to publish papers on it.
Story of cold fusion represents a colossal conspiracy of denial. At least, it is one of the strangest untold stories in 20th-century science.
Isotopes
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Bismuth was thought to be last (largest) stable element on the table, but discovered recently that decays very slowly.
More protons to neutrons, less stable
Uranium v unstable, v important for nuclear fuel. 235 92U. Separate 235 from 234 through centrifuging.
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Intro
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Under Merkel, Germany started phasing out nuclear, but not effective bc not producing enough energy.
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Waste Storage
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2014 - At site HLW storage capacity for world’s nuclear generators was 148,000 tonnes (59% full).
Away from site storage capacity 78,000 tonnes (44% full)
Annual production of spent fuel ~ 12,000 tonnes
Reprocessing plants in place in France, Belgium and UK. These western European plants can handle ~1000 tonnes per year.
Types of Nuclear Decay
Alpha rays
If isotope has too many protons – the mutual repulsion experienced between their positive charges is sufficient to break the nuclear binding force and the nucleus ejects a particle
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Beta rays
too many neutrons, one neutron converted to proton (to form new element) by ejection of electron (b-ray).
40K is unstable (19 protons, 21 neutrons), converts to 40Ca+ through the ejection of an electron: 40K = 40Ca+ +e-
Gamma rays
Products of radioactive b and a-decay are often still unstable, irrespective of number of neutrons and protons.
In this case the products are in an excited nuclear state and decay to their ground state through emitting a gamma ray.
This is a high energy form of electromagnetic radiation (more energy than an x-ray), a high energy photon.
Half-life: the time taken for the activity of a given amount of a radioactive substance to decay to half of its initial value
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Waste Disposal - look up
Deep repositories now underway in several countries: Sweden, Germany, and US undertaking this approach.
US - Yucca Mountain, Nevada
to be a deep geological repository storage facility within Yucca Mountain for spent nuclear fuel and other high level radioactive waste adjacent to the Nevada Test Site in Nye County, Nevada, about 80 mi (130 km) northwest of the Las Vegas Valley.
approved in 2002 by the US Congress, but federal funding for the site ended in 2011 under the Obama Administration
project has had many difficulties and was highly contested by the non-local public, the Western Shoshone peoples, and many politicians.The Government Accountability Office stated that the closure was for political, not technical or safety reasons.
leaves US gov and utilities w/o any designated long-term storage site for high lvl radioactive waste stored on-site at various nuclear facilities around the country. Under President Obama the Department of Energy (DOE) was reviewing options other than Yucca Mountain for a high-level waste repository
Under President Trump, the DOE has ceased deep borehole and other non-Yucca Mountain waste disposition research activities.
The DOE was to begin accepting spent fuel at the Yucca Mountain Repository by January 31, 1998 but did not do so because of a series of delays due to legal challenges, concerns over how to transport nuclear waste to the facility, and political pressures resulting in underfunding of the construction.
fter his election, the Nuclear Regulatory Commission told Obama he did not have the ability to abandon the Yucca Mountain project
federal government initially paid utility companies somewhere between $300 and $500 million per year in compensation for failing to comply with the contract it signed to take the spent nuclear fuel by 1998
DOE estimates it has >100 million U.S. gallons of highly radioactive waste & 2,500 m.tons of spent fuel from production of nuclear weapons and research activities in temporary storage
2007, the DOE announced it was seeking to double the size of the Yucca Mountain repository to a capacity of 135,000 metric tons (149,000 short tons), or 300 million pounds
Because of construction delays, a number of nuclear power plants in the United States have resorted to dry cask storage of waste on-site indefinitely in steel and concrete casks
two-thirds majority of Nevadans feel it is unfair for their state to have to store nuclear waste when there are no nuclear power plants in Nevada
October 2007, the DOE issued a draft of the Supplemental Environmental Impact Statement in which it shows that for the first 10,000 years mean public dose would be 0.24 mrem/year and that thereafter to 1,000,000 years the median public dose would be 0.98 mrem/year, both of which are substantially below the proposed EPA limit.
For comparison, a hip x-ray results in a dose around 83 mrem and a CT head or chest scan results in around 1,110 mrem. Annually, in the United States, an individual's doses from background radiation is about 350 mrem, although some places get more than twice that.
International repositories - ideal geology - Russia? Australia? - political opposition. Do not want coming back up from tectonic movements.