Alternative ENERGY RESOURCES

Nuclear, hydroelectric, wind, geothermal, tidal, solar

NUCLEAR ENERGY

Nuclear energy derived from the properties of the element Uranium. Uranium is a metal

Formation of Uranium deposits (fig 6.5; p. 205-209)

Like many other metals, uranium forms as vein deposits around igneous intrusions.

May be eroded and form “placer” deposits.

May also transferred by groundwater to form “roll deposts” or in reducing black shales; present in phosphate deposits, including those of Florida.

Exploration for uranium

Distribution of Uranium resources

Natural uranium mixture of two isotopes ²³⁸U 99.3%, ²³⁵U 0.7%, (²³⁴U 0.005%). ²³⁵U is important for energy generation.

Energy production from Uranium

235 U is fissionable into Barium and Krypton

235U + n -> 141Ba + 92Kr + 3n + energy

energy is a result of fact that mass of Ba +Kr+3n is less than mass of uranium; matter converted to energy; E=Mc² as predicted by Einstein.

As 3 n produced, they can cause fission of other nearby 235U nuclei - chain reaction.

[also plutonium – ²³⁹Pu is fissile ].

If 235U highly concentrated, and sufficient amount ( critical mass ) , then reaction is uncontrolled - explosion [problem cracked by Manhattan Project }. If controlled, however, just generates heat which can be used for heating gas/water to drive turbines and produce electricity. Controlled reaction first produced at University of Chicago tennis courts in 1930’s

Huge amount of energy produced for small weights of uranium (Fig 6.4)

1gm 235U = 417 tons coal

Nuclear fuel and reactors

Uranium processing

Types of nuclear reactor

Gas-cooled reactors

Water-cooled reactors

Fast breeder reactors

Pebble bed reactors (new design)

Reactor hazards – Three Mile Island, Chernobyl

Nuclear electric power production

Advantages – no CO2, or S emissions - clean

Nuclear waste disposal

US: 103 nuclear power stations produce 2000 metric tones of spent fuel per year; 40,000 tonnes so far. This waste is highly radioactive for nearly 10,000 years. Various schemes for disposal – most involve underground depositories.

• 1970 – bury in salt mines in Kansas. Two years later abandoned because of mixture of political/ technical resistance
• 1982 Nuclear Waste Policy Act investigate sites so that one would be ready by 1998 – included a western and eastern site
• Present US situation revolves around Yucca Mountain.
• 1984 – choice narrowed to Texas, Washington State and Yucca Mt, Nevada. Characterization studies more than $ 1 billion apiece.
• 1987- cost overruns cause Nuclear Wsate Policy amendment Act declares Yucca Mt the winner (“Screw Nevada Bill”)
• 1989 Nevada objects, but funding threatened
• 1990’s Scientific opinion varied and Nuclear Regulatory Commission(NRC) and DOE fight each other. Faulting, young volcanic fields suggest Yucca Mt not that safe.
• 2002 President Bush signs bill to go ahead – Nevada Governor vows to fight.

Hydro-electric power

Very ancient source of energy, but re-vamped for modern age.

Based on dam construction

Geothermal

At present only really feasible in volcanically active areas where geothermal gradient is high. Significant in US (California, Oregon, Washington);

Elsewhere: Iceland, Italy, Mexico, New Zealand

Steam from porous reservoirs with cap rocks turn turbines to generate electricity.

Wind Power

Also ancient source of energy – “windmills” in Holland; water pumps. Useful in areas where constant prevailing winds. US West Coast in particular California (8% state requirements). “Wind Farms” now economically feasible due to improved windmill and generator technology.

Not entirely environmentally friendly. Bird fatalities including endangered California condor.

Tidal

Needs large tidal range – western side of large oceans

For the future

Solar

Ocean Thermal Energy Conversion(OTEC)

Biomass

Nuclear Fusion