ES 115, Test 2 Review (Class 14 and After)

Enriching Uranium

(1) Uranium Gas (UF6) is sent into the centrifuge (2) The centrifuge spins around rapidly, creating centrifugal forces thousands of times greater than the force of gravity (3) Because it's heavier, U-238 tends to migrate toward the edges, while the lighter U-235 tends to stay towards the center (4) Collect the UF6 with more U-235 from the center, which has a slightly higher concentration of U-235 (5) Continue the process of enriching again until the product has high concentration of U-235; then the gas is used for creation of fuel rods -in a "closed fuel cycle", the spent fuel is processed to reclaim its uranium and plutonium fuel content for reuse (this recycling method is used in France, Japan and the U.K.) -"once through" is much simpler than reprocessing, but is a less efficient use of the fuel

Total Operational Reactors Worldwide?

-leads with the U.S. followed by France, China, Japan, Russia, etc. -while France does not have as many plants as the U.S., it has a much smaller population that nuclear represents upwards of 76% of their energy -China's reactors are often behind schedule as well but they expect 2 to come online by the end of 2018 -Turkey is a new player on the nuclear front - it is actually constructing 4 reactors at one site; they are getting assistance from Russia

Fukushima Daiichi (2011)

-3 meltdowns that melted through reactor pressure vessels, chemical explosions, and spent fuel pools being disrupted

CLICKER: What percent chance do you think we have of having an INES-7 scale event within the next 27 years?

-50%

Burner (thermal) vs. Breeder (fast) Reactors

-Burner (Thermal): Neutrons: slow moderator: yes, needed density of fissile nuclei: low operating temp: low bomb physics: not similar design, O&M: easier fuel utilization efficiency: 0.7% to 2% -Breeder (Fast): Neutrons: fast Moderator: no, not needed density of fissile nuclei: high operating temp: high bomb physics: similar design, O&M: more difficult fuel utilization efficiency: 40% to 70%

Building Energy Efficiency Standards

-CA again -requirements for residential and commercial building construction -savings: $2000 per household since 1976 -future: zero-net energy homes

Hyperloop

-Elon Musk -Hyperloop is even more potentially efficient by eliminating (or dramatically reducing) two friction points 1) contact with ground/track and 2) reducing contact with air that usually has to be pushed out of the way to move forward

Shielding

-Fuel Cladding -Purpose: keep radioactivity out of the environment/biosphere -multilayered "defense in depth": fuel cladding, pressure vessel and containment structure *there's shielding around the uranium pellets

Thermodynamic Efficiency

-Nuclear plants usually operate at a temperature around 625K (about 350 degrees Celsius), which means the heat-to-electricity conversion caps out at around 32% or so -roughly stated, a standard 1 GW electricity output for a nuclear plant requires about 3 GW of heat from the reactor

Control Rods

-Purpose: absorbs neutrons, regulates fission, stops fission, used in scheduled shutdown or emergencies -material: Cadmium or boron -will NOT stop decay heat *a reactor scram is an emergency shutdown of the nuclear reactor - caused by the rapid insertion of the control rods to absorb the neutrons and stop the fission

Toshiba and Nuclear Investment?

-Toshiba has struggled to make money in nuclear power since it bought Westinghouse for $5.4 billion in 2006 -chairman, Shigenori Shiga, resigns to take responsibility for Toshiba's $6.3 billion loss

Leaks and Spills at U.S. Commercial Nuclear Power Plants Jan 2017

-Tritium is a radioactive form of hydrogen; it is produced in reactors, have a half-life of 12.3 years and rapidly disperses and dissipates in the environment -71% of current or old nuclear power plant sites have had tritium leaks on-site (as of january 2017, 60% of current or old nuclear power plant sites have detectable levels of tritum on the site); leaks are generally contained within the nuclear power plant site

Breeding

-U-238 is not fissile (cannot sustain a chain reaction); cannot undergo nuclear fission -U-238 is fertile = U-238 sometimes absorbs a fsat neutron, which eventually converts it to Pu-239; in a typical reactor, some U-238 interacts with fast neutrons, resulting in accidental breeding (unintended breeding) of U-238 into Pu-239; U-238 can be intentionally bred to Pu-239 in a breeder reactor -Th-232 can also be fertile (can be bred into U-233) -Pu-239 and U-233 are fissile (can go under nuclear fission)

A Nuclear Reactor Vessel

-a comparable fossil source (e.g. coal furnace) is much larger -this is a very small location to contain 3 GW of heat (remember the thermodynamic efficiency of nuclear means you need 3x to get 1x the amount of electricity out)

Heat Engine

-a device that converts heat into work -very inefficient when they were first developed -many famous physcists and thinkers throughout the decades since the Industrial Revolution all considered ideas about how to improve heat engines -we are running into an upper limit on how efficient we can get heat engines to operate; it is time for another

Heat Pump

-a device that uses work to move thermal energy (heat) from one location to another (usually, transfer thermal energy from outside into your house) -the second law of thermodynamics still applies -but this task can be done with high efficiency -the larger the difference in temperature, the less efficient the heat pump is; the smaller the difference in temperature, the better it works (there is a balance point) -common in European countries

Demand Side Management

-a way that electric utilities can meet future power needs by helping consumers conserve energy and increase energy efficiency -to make more money, sell more electricity -regulates utilities to "decouple" the quantity of sales from profits -allows utilities to charge more money per kWh if they meet efficiency standards (free energy audits, free light bulb and appliance switchouts, other incentives) -CA, mid 1970s

Zero Net Energy Homes

-all new residential buildings to be ZNE or ZNE 'ready' by 2020; commercial buildings by 2030 -defined as an energy efficient building where annual energy consumed is less or equal to energy produced -ZNE relates strictly to production and consumption

Radioactive Types

-alpha radiation: a high energy helium atom; can be stopped with a sheet of paper and can damage tissues if inside the body -beta radiation: can be stopped with a thin sheet of aluminum and can damage tissue if inside the body -gamma radiation: can be stopped with a thick sheet of lead; can cause damage upon any significant degree of external exposure and the most powerful and dangerous form of radioactivity -neutrons: not a part of natural radiation; can be released in the process of fission, and lead to a chain reaction

Clicker! What are the three types of natural radiation, and what is each made out of?

-alpha radiation: hi speed helium atom, can damage tissues if inside the body -beta radiation: hi speed electron, can damage body if inside -gamma radiation: radiant energy (electromagnetic radiation) that is sometimes thousands of times more powerful than x-ray; very dangerous even if exposed outside your body

3 Mile Island (1979)

-among other category 5 incidents -partial meltdown from reactor coolant leak

Cloud Chamber

-as some of the uranium decays, it gives off alpha particles (hi-speed helium atoms) -the cloud created by the alcohol and temperature gradient is highly sensitive to particles that move through it -alpha particles disturb the cloud, leaving trails -you can not actually see the alpha particles, but you can see the trails they leave behind

Uranium Enrichment for a Chain Reaction

-at the natural level of 0.7% U-235, atoms are not close enough together for neutrons to sustain a chain reaction in a standard lightwater reactor -enriched to 4% U-235, there are enough fissile atoms for neutrons from fission (with a moderator) to sustain a chain reaction -enriched to 90% U-235, the release of neutrons from an initial instance of fission can start an uncontrolled chain reaction, resulting in a nuclear explosion

Inactive Energy Types (Potential Energy)

-chemical -mass -nuclear -gravitational -elastic

Kyshtym Disaster

-chemical explosion from a storage tank -kept secret by Soviets for 30 years

Maxwell's Demon

-demon to control hot and cold molecules to make them even -requires information and thus, energy to make the decision/open the door -entropy cannot be destroyed!

First Law of Thermodynamics

-energy can be transferred and transformed, but it cannot be created or destroyed -nuclear energy takes advantage of the mass energy in various atoms and converts them into heat, and then converts some of the heat into work -E=mc^2

Fission Products and Decay Heat

-fission products come in many atomic forms, such as Xenon and Strontium; after fission, these fission products have many excess neutrons in their nuclei, and are highly unstable (and therefore radioactive) -so they themselves undergo decay, emitting beta radiation and often additional gamma radiation as well, changing their atomic structure again (transmutation), usually into other unstable isotopes -each step of decay produces radiation and heat, heating up the fuel rod -the heat from this process is decay heat, and it is very important to take away this heat by pumping a continuous of water over the rods -if this does not happen, there is a risk of a partial or complete meltdown -active cooling needs to be done for a few years but can eventually be moved to dry storage with heat vents

Breeder Reactor

-has a high rate of fertile to fissile conversions as part of its design to yield fissile material, which can be put in a burner, or a nuclear weapon -breeding is a side-effect in burner reactors; while they incorporate accidental breeding into the fuel usage, this type of breeding is much different than in a breeder reactor -Thorium Breeders are common: this is because there is a lot of Thorium available; there is also a lot of U-238 from depleted Uranium stocks, as you have to remove some U-238 to enrich fuel for U-235 levels required by lightwater reactors

Fission Reactor

-has a low rate of fertile to fissile conversions, which are the result of ACCIDENTAL BREEDING

Spent Fuel Rods: Nuclear wastes

-managing nuclear waste is a technical and political challenge; fresh fuel rods are about 96& U-238 and 4% U-235 -nuclear waste from a spent fuel rod is composed as approximately: 1) U-238 = 94% of spent fuel rod = time needed for safety: already safe = the original U-238 in fuel rods; some underwent accidental change 2) U-235 = 1% of spent fuel rod = time needed for safety: already safe = what's left of the original U-235; this is the main target of recycling/reprocessing, after a lot of fission, it no longer exists at a high enough percent in the fuel rod to continue a chain reaction 3) Fission Products = 4% spent of fuel rod = time needed for safety: 500+ years = these are highly dangerous and produce decay heat, but can be safe after a several hundred years 4) Actinides = 1% spent of fuel rod = time needed for safety: 500,000+ years = includes Pu-239 and other heavy elements; comes accidental breeding and other absorption of neutrons that do not lead to fission, not as dangerous but still bad and take a really long time to be safe

Nuclear Fission

-normally, certain heavy atoms resulting in radioactive release -humans can instigate radioactive releases in an atom by shooting slow neutrons at an unstable atom -however, instead of causing the atom to decay, it causes the atom to split into two smaller atoms -this is called nuclear "fission" -the two smaller atoms are called "fission products" -under the right conditions in a reactor, and a properly designed fuel source, humans can create a stable fission process that creates a reliable source of heat -basically: a neutron atom is absorbed by a uranium atom (heavy atom), breaking it into fission products & high-speed neutrons; energy is released over a million times larger than any carbon fuel, to continue the fission reaction, the high-speed neutrons are moderated by water as a coolant

Chernobyl (1986)

-not a lightwater reactor -resulted in a critical incident and chemical explosions, spewing radioactive material into the atmosphere -due to lack of shielding, much of the Soviet Union and Western Europe faced radioactive exposure

Finland's Olkiluoto 3 "Next Generation" Nuclear Plant (1.7 GW Reactor)

-originally planned to enter service in 2010 -still non-operational, hopefully (December) 2018 (postponed to May 2019) -original cost estimate ~$3.5 billion -current cost estimate ~$10.2 billion

Vogtle Nuclear Plant Expansion in Georgia (2 - 1.2 GW Reactors)

-originally planned to enter service in 2016 -still non-operational, hopefully (February 2021) --> actually postponed until November 2021 for 1 unit and November 2022 for the other unit) -original cost estimate ~ $14 billion -current cost estimate ~ $25 billion

Coolant

-purpose: keeps the temperature of the reactor stable, takes heat away for conversion to steam/electricity -must not absorb neutrons -material: water (most common), helium, molten sodium (newer designs)

Active Energy Types

-radiant, heat (thermal), electric or kinetic

Decay and Half-life

-radioactive atoms spontaneously decay, releasing radiation -this is specific to the atom type, including its isotope (number of protons & neutrons) -U-238 is very stable, while U-235 is somewhat unstable -decay occurs at a regular interval, and is not affected by temperature, combination in molecules, compression, etc (this regular decay has a "half-life" for each isotope, the time it takes for there to be half of the original amount -it is generally believed that there is NO CAUSE as to why a particular atom decays; that is, you can't look closer at a given atom to figure out when it will decay (it just does)

Appliance Standards

-refrigerators -furnaces -air conditioners -nationwide impact: CA market is so huge

Lightwater Reactor: Fuel

-several considerations regarding fuel: uranium mining, isotope enrichment, fuel production, fuel cycle, spent fuel rods: waste, and decay heat -Uranium mining and processing has environmental and social impacts, particularly among those that are significantly less represented in the political and social landscape -i.e. Navajo Nation, Uranium Mining's Deadly Legacy Lingers (Navajo land was mined for Uranium needed for weapons)

The Public Insurance Argument that Nuclear is Not Safe Today

-the Public Interest Group Public Citizen expresses concern about the Price-Anderson act -the act limits the financial liability of nuclear facility operators to around $12 billion; beyond that amount, damages are covered by the federal government and indirectly through us, taxpayers -Price-Anderson act understates the potential of a disaster -if going nuclear is so safe, it should be privately insured

Coefficient of Performance

-the amount of heat delivered by the heat pump divided by the amount of work (electricity) you supply to the heat pump

Decay Heat

-the fission products of nuclear fuel rods spontaneously decay like U-235 does BUT they decay at a much faster rate -as these fission products decay, they release radiation, producing heat -as with all radioactive decay of unstable elements, there is no way to stop this from happening; the only thing you can do is take away the heat and wait for the decay peter out, usually by running a continuous flow of water (coolant) over it -if you cannot reliably remove the heat, you run risk of the fuel rods melting down into a radioactive pool of liquid metal that can run out of the reactor *with the decay heat, the heat comes from the decay of fission product (Actinide) itself, not from a Bunsen burner below, or any external heat source -it happens without oxygen in the surrounding environment - that's why nothing, nothing can stay decay heat from building up; the only thing you can do is manage the heat (take the heat away with water)

Moderator: Key Concepts

-the moderator slows down fast neutrons from fission (allows for chain reaction) -most common moderator in the USA: Lightwater (H2O) -other potential moderators: Heavy Water (Canada), Graphite -negative reactor coefficient: keeps rate of fission stable/ prevents runaway chain reaction

Capacity Factor

-the percentage at which a given facility operates at it's nameplate capacity -1 GW at 90% capacity factor is equivalent to 0.9 GW on average over the course of a year -1 GW at 24% capacity factor is equivalent to 0.24 GW on average over the course of a year -nuclear plants have improved their capacity factors over recent years to ~90% -wind plants have capacity factors of ~40% depending on its site -because of the Sun's position in the sky, Solar Plants have a capacity factor of ~27% (even lower for rooftop solar, which cannot track the sun's movement in the sky) -solar and wind electricity output doesn't match nuclear yet because they have lower capacity factors

Efficiencies in Nuclear Energy: Fuel Utilization Efficiency (FUE)

-the percentage of the original natural uranium pulled from the ground that actually undergoes fission -this includes a lot of the U-235, but also any fissile materials that come about from accidental breeding (e.g, Pu-239) -the fuel utilization efficiency of a standard once through cycle in a lightwater reactor is about 0.6% -reprocessing the spent fuel can double the FUE, but processing can be dangerous

Spreng's Triangle

-time, energy, and information are at odds with one another -maximizing one comes at a cost of reducing at least one other, usually both -improving efficiency (reducing environmental harm) will require a better utilization of information

South Carolina Nuclear News

-two half-finished nuclear reactors scrapped as costs balloon -giving up on a project after you have poured billions into it sounds crazy, but sometimes you have to give in to reality and cut your losses -it also sends a signal about your abilities

The Second Law of Thermodynamics

-when energy is converted, entropy is produced

Entropy

-when energy is converted, entropy is produced (disorder/movement/etc) -Entropy is measured in joules/K and has the variable definition of S

Which of the following low-carbon energy sources has the most installed capacity?

-wind

CLICKER: How does the negative reactor coefficient of a nuclear moderator work?

-you need slow neutrons to sustain fission, but neutrons from fission are fast -the moderator slows down the neutrons, but has a property that makes it less effective at doing so when it heats up -this prevents a chain reaction from getting out of hand

Three Major Types of Shielding: Multi-layered "Defense in Depth"

1) Containment Structure: steel reinforced concrete (several inches thick), steel liner (1 in thick), additional concrete (several feet) 2) Pressure Vessel: reactor vessel (8 in thick) 3) Fuel Cladding: fuel assemblies

Debates on the Proliferation Attributes of Thorium

1) Nuclear-energy technologies that involve irradiation of thorium fuels for short periods could be used covertly to accumulate quantities of U-233 by parallel or batch means, perhaps without raising IAEA proliferation flags 2) the infrastructure required to undertake the chemical partitioning of protactinium (step between Th-232 and U-233) could be acquired and established surreptitiously in a small laboratory 3) state proliferators could seek to use thorium to acquire U-233 for weapons production

Major Components of a Lightwater Reactor

Fuel Moderator Control Rods Shielding Coolant

Shielding - includes?

a) fuel rod cladding inside reactor vessel b) reactor vessel itself c) containment structure