APES Nuclear Power- 11.3

Physical Characteristics of Uranium (why it is used for nuclear power)

The heaviest naturally occurring element, Can be mined out of the ground, Number 92 on the periodic table, Has a large unstable nucleus (easy to "split")

U.S. Sources of energy

Petroleum- 35%, Natural Gas-34%, Renewable-12%, Coal-10%, Nuclear-9%

1 Nuclear Fuel Cycle

Uranium is mined out of the ground

2 Nuclear Fuel Cycle

Uranium is processed (enriched) to concentrate a specific isotope (U-235) and packed into pellets. A single pellet has the same energy content as 1 ton of coal!

3 Nuclear Fuel Cycle

the pellets get packaged into fuel rods. About 200 fuel rods are packaged together to form a fuel rod assembly

4 Nuclear Fuel Cycle

Fuel rod assemblies are sent to the nuclear power plant. Each fuel rod assembly will last for about 3-7 years before it needs replaced. A typical reactor core will have around 200 fuel rod assemblies being used at once.

5 Nuclear Fuel Cycle

In the reactor core, nuclear fission takes place in the fuel rods causing the fuel rods to get extremely hot

(5) Nuclear Fission

is the splitting of an atom's nucleus. To split Uranium nuclei, a neutron is fired into a nucleus, the nucleus splits, heat is released along with more neutrons. These neutrons hit more atoms causing a chain reaction

6 Nuclear Fuel Cycle

Control rods are used to control the rate of the fission reaction by absorbing/blocking free flying neutrons. They are usually made up of stainless steel filled with boron. For safety reasons, the control rods are usually held in place by an electromagnet, and will fall into place if something goes wrong.

7 Nuclear Fuel Cycle

Heat produced by the fission is moved to steam generators by a fluid called coolant. It is constantly pumped through the core to the steam generator to turn water into steam to spin the turbine. Secondary pumps are used in the condenser to cool the steam back into liquid water to be recycled.

8 Nuclear Fuel Cycle

When most of the uranium atoms in the fuel rods have split, the reaction slows and the material left in the fuel rods is referred to as nuclear waste.

Nuclear Waste

Usually consists of isotopes of uranium, cesium, strontium, and plutonium. These atoms are generally unstable and undergo radioactive decay. This process releases energy in the form of radiation. Nuclear waste is radioactive and remains hazardous for hundreds of years (potentially thousands!) and must be safely stored for that long! Sometimes the waste can be repurposed

Radioactive Decay

The stability of a nucleus is determined by the ratio of protons to neutrons. The forces that bind protons and neutrons together are usually very strong, but some isotopes are less stable than others. As a result, the nucleus of certain isotopes will randomly break apart (decay) in a process known as blank. If the decay causes the nucleus to lose or gain protons, it will become an entirely different element (# protons determines the element)

Decay Chain

the changes that a radioactive atom will undergo until it becomes stable

Alpha Decay

-2 protons and -2 neutrons

Beta Decay

+1 proton, -1 neutron, and -1 electron

Gamma Decay

-1 photon

low level nuclear waste

less hazardous, materials that came into contact with radioactive substances

High level nuclear waste

Spent fuel rods that are hot and radioactive, very hazardous. About 2,000 tons per year is generated in US.

Spent Fuel Pools

spent fuel rods stored underwater in cement/steel lined pools. Cools down the rods and shields from radiation

Dry Cask Storage

after cooling down for a few years, spent fuel rods are moved into dry casks. Stainless steel canisters surrounded by concrete. These are usually located at the reactor

Ionizing Radiation

Nuclear Waste is radioactive and emits this. Radiation that can produce ions when it interacts with matter. As unstable radioactive atoms decay, they emit energy and particles

Alpha Radiation

particle: two protons and two neutrons

Beta Radiation

particle: a single electron

Gamma Radiation

pure energy: gamma rays

Contact with Ionizing Radiation

Immediate cell death. Cell lives, but is unable to reproduce (failed mitosis). Cell increases rate of mitosis (cancer). Cell Death-->Tissue Death-->Organ Failure

Radiation Exposure

A large dosage of radiation in a short period of time with long term exposure. Dental X-ray, chest X-ray, mammogram X-ray, everyday life, and CT scan

Contamination

Even tiny pieces (ash/dust) of radioactive material can emit harmful radiation. These small particles can get on surfaces, and get into the air, water, and soil. These small particles can also be absorbed into the skin, breathed in, or consumed through contaminated food or water. Small radioactive particles can also bioaccumulate and biomagnify up a food chain.

Absorbed Dose

energy deposited per unit mass (joules per kilogram). SI units = Gray. Other units = rad. Conversion 1 gray = 100 rads

Effective Dose

because different body tissues absorb radiation at different rates, effective dose tries to incorporate these differences. It uses absorbed dose in conjunction with tissue weighting factors to better estimate the dose of radiation absorbed in a whole body with the purpose of estimating health/cancer risks. SI units = sievert. Other units = rem. Conversion 1 sievert = 100 rem

Three Mile Island

1979, United States. Small meltdown, quickly contained, no injuries

Chernobyl

1986, Ukraine. Two large explosions blew the top of the reactor. Mass evacuations, radiation burns and sickness, 31 direct deaths, thousands of reported cancer cases, increased rates of cancer, increased rates of genetic mutations in babies.

Fukushima

2011, Japan. Earthquake induced tsunami caused failure of backup cooling generators leading to a meltdown. No direct deaths but radioactive material leaked out (about 1/10 the size of Chernobyl) and many were exposed to it in high doses

Trends in Nuclear Power since 1960

Nuclear power has stalled as other ways of making electricity have become cheaper. Has been increasing!

Current Rates of Supply

If used at current rates and tech, we have about a 200-500 year supply left

Seawater Extraction

Potential to extract uranium from seawater could extend this out to around 60,000 years!

Breeding

However a process called breeding could extend resources for 30,000 of years! Breeding converts uranium into plutonium, a better fuel. Breeder Reactors are used in other countries, but not in the United States. Breeder reactors run hotter and have a higher risk of meltdown associated with them. They are also currently more expensive to operate

Pros

Low environmental impacts (without accidents), emits 1/6 much CO2 as coal, low risk of accidents in modern plants

Cons

very low net energy, yield and high overall cost, produces long-lived harmful radioactive wastes, promotes the spread of nuclear weapons.

Breeder Reactor

Uranium is processed into plutonium and the plutonium is used as the fissile material. As fission happens, the waste produced is also fissile meaning the waste can be used as fuel. Plutonium created could easily be converted to nuclear weapons

Small Modular Reactor

Instead of 1 large reactor with all the fuel rods, many smaller reactors work together. Not enough fuel in each small reactor to meltdown, but collectively have the same power as 1 large reactor THEORETICALLY MELTDOWN PROOF!

Thorium Based Reactor

Thorium fuel is turned into Uranium 233. Cheaper and safer, But much research and development needed. Thorium more abundant and efficient than uranium alone. Less risk of waste being used for nuclear weapons

Fusion Reactor

Forcing two atoms together to form an atom of a new element. Hydrogen must be heated to about 100 million Kelvin and form a plasma for fusion to occur. However, if the heat from the fusion reaction is used to sustain the fusion, then the reaction would produce A LOT of energy with just the continuous addition of small amounts of hydrogen! This energy will have no emissions, no hazardous waste, and will come from the most abundant element in the universe!