Glossary for Alternative Energy Resources
- fission:
the breaking up of the nucleus of an atom into usually two smaller nuclei of about equal size. A neutron splitting a nucleus starts a chain reaction in which new free neutrons are generated. Nuclear fuel is considered to have a critical mass (or exceed it) when the concentration of radioactive elements is high enough to sustain a chain reaction (NB: the definition in the text book is incorrect!). Unlike in nuclear bombs, this chain reaction is a controlled reaction in a nuclear reactor. French scientists discovered in 1972 a place in nature where radioactive material actually reached the critical mass repeatedly (6 times about 1 billion years ago). The site was at Oklo in Gabon/Western Africa. To control the chain reaction a nuclear reactor needs a moderator to capture excess neutrons. Water and Graphite can serve as moderator. In a secondary circuit, that is isolated from the primary reactor circuit, water absorbs the thermal energy (e.g. like in a heat exchanger). The produced steam drives turbines.
back to alt. energy
- The 1986 reactor accident at Chernobyl (April 25/26)
Chernobyl had 4 nuclear reactors. During a test run of reactor #4, operators shut down a safety device for cooling when the reactor overheated. Numerous people died instantly in the explosion or soon after (e.g. 30 rescue workers) due to short-term radioactive contamination. Due to high radiation levels in a 35 km radius, 135,000 people had to be evacuated. There were a few 100 victims due to long-term radioactive contamination within a 100 km radius of the reactor. Long-term effects manifested themselves most prominently as thyroid cancer. Cases in children increased by a factor 100 (to one in ten thousand). A steam explosion sent 10% of the radioactive material into the atmosphere causing a fallout over western Europe and Scandinavia. The release of radioactive Cesium (Cs) temporarily compromised agriculture (e.g. pastures and all leafy vegetables were contaminated and cow milk was considered unsafe to drink; venison was recommended not to be eaten for some time; nuts and mushrooms that enrich Cs could not be eaten for years). The reactor that still has 70 tons of reactor fuel is now contained in a containment building. Read more about Chernobyl at wikipedia.org
back to alt. energy
- Hoover Dam
Hoover Dam on the Colorado River was built in the midst of the Depression in less than 5 years. Lake Mead, the resultant reservoir, is the largest manmade lake in the United States. Hoover Dam, which provides hydroelectric power for use in Nevada, Arizona, and California, generates more than 4 billion kilowatt hours a year-enough to serve 1.3 million people. Read more about Hoover Dam at wikipedia.org
For comparison, the Three Gorges Dam in China is scheduled to be finished in 2009. It will
be the largest man-made dam in the world. It will generate 84.7 billion kilowatt hours a year, and will provide 10% of China's energy needs (80% is currently produced by coal).
Dams this large have several problems: 1) the dam will displace 1.9 Mio people after flooding; 2) dams this large emit significant amounts of methane, one of the two most significant greenhouse gases contributing to global warming (5% of conventional power plants in northern reservoirs and 25% in tropical reservoirs); 3) dams this large may induce local seismicity; 4) dams located in a geological environment like Hoover and Three Gorges are fed by tributaries rich in sediments, thereby significantly shorten the lifetime of the dams; read more about Three Gorges Dam at wikipedia.org
back to alt. energy
- renewable energy resources
resources that nature can replace in a short time relative to the human life span
(e.g. solar, wind, hydro-electric).
back to alt. energy
- non-renewable energy resources
resources that take long to replace relative to the human life span
(e.g. fossil fuels, nuclear power).
back to alt. energy