Nuclear Energy

A little review… Radioactive isotopes: Unstable isotopes that undergo radioactive decay: Spontaneous release of material and energy from nucleus. Original element (parent) changes to a new element (daughter) or isotope Types of radiation α= only dangerous if emitted inside body bc can’t penetrate skin β= electrons that can slightly penetrate skin (tritium) γ = most harmful Half life: Average rate of radioactive decay ( amount of time it takes for ½ of the original parent to decay)

Calculating half life If g of carbon-14 decays until only 25.0 g of carbon is left after 11, 460 y, what is the half- life of carbon-14? Given: initial mass of sample = g final mass of sample = 25.0 g total time of decay = y Unknown: number of half-lives = ? half-lives half-life = ? y 11,460 years/ 2 = half life of 5730 years

Thallium-208 has a half-life of min. How long will it take for g to decay to 7.50 g? Given: half-life = min initial mass of sample = g final mass of sample = 7.50 g Unknown: number of half- lives = ? half lives total time of decay = ?

Fraction remaining 7.5 g / 120 g =.0625 or 1/16 SO HOW MANY HALF LIVES WILL IT TAKE? 1/2 * 1/2 = 1/4 * 1/2 = 1/8 *1/2 = 1/16 so that was 4 half lives Time of decay = 4 x 3.053min = minutes

Gold-198 has a half-life of 2.7 days. How much of a 96 g sample of gold-198 will be left after 8.1 days? Given: half-life = 2.7 days total time of decay = 8.1 days initial mass of sample = 96 g Unknown: number of half- lives = ? half-lives final mass of sample = ? g 8.1 days / 2.7 days = 3 half lives 96/2 = 48 / 2 = 24 / 2 = 12 g

Nuclear Fission Fission: nuclear reaction that uses neutrons, which are shot at an atomic nucleus leading to the break down and subsequent energy release. Utilizes energy from radioactive isotopes. Uranium – 235 Chain reaction that can continuously create heat, which can boil water to create heat, which can boil water to create steam … create steam …

The typical Nuclear Fission Reaction

1 Neutron U  236 U  141 Ba + 92 Kr + 3 Neutrons

The 3 neutrons keep the energy going

Nuclear reactor Fuel rods are pellets of uranium in the core Which heats water during reaction Control rods are there to absorb excess neutrons slowing reaction preventing overheating and meltdown.

Fig , p. 372 Small amounts of radioactive gases Uranium fuel input (reactor core) Control rods Containment shell Heat exchanger Steam Turbine Generator Waste heat Electric power Hot coolant Useful energy 25%–30% Hot water output Pump Coolant Pump Moderator Cool water input Waste heat Shielding Pressure vessel Coolant passage Water Condenser Periodic removal and storage of radioactive wastes and spent fuel assemblies Periodic removal and storage of radioactive liquid wastes Water source (river, lake, ocean)

Nuclear power in the US Nuclear power in the US RED = nuclear sites Black = recorded earthquakes in US

Nuclear Waste After three or four years in a reactor, spent fuel rods are removed and stored in a deep pool of water contained in a steel-lined concrete container.

After spent fuel rods are cooled considerably, they are sometimes moved to dry-storage containers made of steel or concrete

Fig , p. 373 Decommissioning of reactor Fuel assemblies Reactor Enrichment of UF 6 Fuel fabrication (conversion of enriched UF 6 to UO 2 and fabrication of fuel assemblies) Temporary storage of spent fuel assemblies underwater or in dry casks Conversion of U 3 O 8 to UF 6 Uranium-235 as UF 6 Plutonium-239 as PuO 2 Spent fuel reprocessing Low-level radiation with long half-life Geologic disposal of moderate & high-level radioactive wastes Open fuel cycle today “Closed” end fuel cycle Triuranium octoxide Uranium hexafloride

Why not more nuclear energy? ● After more than 50 years of development and enormous government subsidies, nuclear power has not lived up to its promise because: ● Multi billion-dollar construction costs. ● Higher operation costs and more malfunctions than expected. ● Poor management. ● Public concerns about safety and stricter government safety regulations. ● Oyster Creek Example Oyster Creek Example Oyster Creek Example

Nuclear Energy  When a nuclear reactor reaches the end of its useful life, its highly radioactive materials must be kept from reaching the environment for thousands of years.  Plutonium, uranium, cesium, tritium  Several reactors in the United States are closing down early

Nuclear Waste  Scientists disagree about the best methods for long-term storage of high-level radioactive waste (uranium and plutonium) ● Bury it deep underground. ● Shoot it into space. ● Bury it in the Antarctic ice sheet. ● Bury it in the deep-ocean floor that is geologically stable. ● Change it into harmless or less harmful isotopes

Chernobyl Nuclear Disaster The world’s worst nuclear power plant accident occurred in 1986 in Ukraine. The world’s worst nuclear power plant accident occurred in 1986 in Ukraine. The disaster was caused by poor reactor design and human error (disconnected control rods and cooling water). The disaster was caused by poor reactor design and human error (disconnected control rods and cooling water). By 2005, 56 people had died from radiation released. By 2005, 56 people had died from radiation released. ● 4,000 more are expected from thyroid cancer and leukemia.

3 Mile Island Disaster March 28, 1979 at 3 mile island nuclear plant in PA a closed cooling water valve led to the overheating of the reactor core and led to partial meltdown. Structure became highly radioactive and unknown amount entered nearby environment No documented evidence of adverse health effects but claims of increased infant mortality and cancers.

Fukushima Nuclear Disaster March 11, 2011 the Great East Japan Earthquake, measuring a 9.0 on the Richter Scale Led to coastline movement of a few meters and a half meter of subsidence. Secondary impact was a giant 15 foot tsunami Led to the malfunction of the nuclear reactor power supply and the cooling station. Largest discharge of nuclear waste into ocean (cesium) Cesium contamination covering 4500 miles 2 and 250 miles around site considered too radioactive for humans and evacuated Increased exposure limits from 1 mSv to 20 mSv to downgrade impact

Future of Nuclear Energy  In 1995, the World Bank said nuclear power is too costly and risky.  In 2006, it was found that several U.S. reactors were leaking radioactive tritium into groundwater. o May increase risk of cancer, but tritium is one of the least dangerous radio nuclides

Fig , p. 376 Trade-Offs Conventional Nuclear Fuel Cycle AdvantagesDisadvantages Large fuel supply Cannot compete economically without huge government subsidies Low environmental impact (without accidents) Low net energy yield High environmental impact (with major accidents) Emits 1/6 as much CO 2 as coal Catastrophic accidents can happen (Chernobyl) Moderate land disruption and water pollution (without accidents) No widely acceptable solution for long-term storage of radioactive wastes and decommissioning worn-out plants Moderate land use Low risk of accidents because of multiple safety systems (except for 15 Chernobyl-type reactors) Subject to terrorist attacks Spreads knowledge and technology for building nuclear weapons

A 1,000 megawatt nuclear plant is refueled once a year, whereas a coal plant requires 80 rail cars a day.