Sunday, September 17, 2006

What is the function of dams, and what are the reservations against them?

By Juergen Giesecke, Energie-Fakten

Mankind already manages water flows since 4 millennia, to provide for the necessities of life. The practice of storing large water quantities using dams started with ancient Mediterranean cultures, and has been continuously developed  until modern times. The world has about 46,000 dams that are higher than 15 meters (earthfill and masonry). There were 6 billion people on this planet in 2002 - a number  increasing with 80 million each year, and 20% of them suffer from water scarcity. And about a third lacks basic sanitary facilities.

Well over 70% of large dams around the world are used for the irrigation of agricultural land to secure food supply. Further important functions are the supply of drinking water for citizens,  process water for industry and commerce, and cooling water for thermal power stations. A further function is flow control for flood protection and electricity generation from hydropower, the most effective use of this constantly regenerating energy.

By holding water in reservoirs and releasing it as the need arises, dams modify the existing natural conditions of life for animals and plants, as well as the habitat of  local population, primarily through the relocation of people who must leave the area where they settled, live and cultivate land. Roads change, and religious and cultural sites are disturbed for the future reservoir. Accumulation of nutritient-rich sediments not only leads to silting of the reservoir, but it also deprives the river downstream of natural sedimentation and manuring, and it  disturbs its seasonal flow where areas are intermittently flooded and drained. In addition, depending on the characteristics of subsoil and soil layers, groundwater levels may change. Changes in the micro-climate near artificial large reservoirs can be significant in tropical climates, through increased water evaporation, and the slack water near dams facilitates development of life-threatening diseases. Also, we cannot ignore security risks, resulting from the storage of large water quantities, and possible collapse of the barrage construction. 

Dams have, depending on type and provisions, demonstrated lifetimes of well over 100 years. They provide a large contribution to the basic necessities of life for the resident population and they have become an essential part of the human imprint on the cultivated landscape. But they require careful precautions and provisions to minimize ecological damages, impact on landscape aesthetics, influence on the habitat of people, animals and plants, and to keep risks small.

For this purpose, over the last 3 decades and on a global scale,  professional societies have developed  comprehensive instructions, manuals, regulations and training/education programmes.

Interdisciplinary cooperation of specialists from engineering, natural sciences, economics and humanities have now become as self-evident for large dam projects, especially those with considerable use of hydro power, as have public relations and awareness raising with the broad population.

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When can we expect nuclear fusion?

By Joachim Grawe 

In partnership with Energie-Fakten

Nuclear fusion offers a great hope for mankind's future energy supply. It imitates in a technical process the physical phenomena occurring in the sun and all other stars, where hydrogen nuclei are combined ('fused') into helium nuclei, releasing giant quantities of energy according to Einstein's formula E=mc2.

On earth, it is impossible to achieve the enormous pressure of 100 billion bar inside the sun. Therefore, fusion of the lighter nuclei of 2 isotopes (i.e. atoms with a different number of neutrons in the nucleus) of hydrogen is being pursued: i.e. deuterium (with a nucleus of 1 proton, as in 'normal' hydrogen and 1 neutron) and tritium (1 proton + 2 neutrons). Deuterium is abundantly available in oceans at a concentration of 140 g/tonne. Tritium can be produced from the common metal lithium.

To initiate ('ignite') the fusion process, the D-T mixture needs to be converted into a plasma - i.e. a state whereby nuclei are separated from the electrons that normally surround them. The plasma needs to be heated to at least 100 million degrees, under extreme compression, and kept for a prolonged period while containing its heat inside. At all times, contact of the plasma with its container - a round tube called 'torus' - needs to be avoided. This is achieved through very strong magnets.

Containment of the plasma has been achieved already in 1951. The European test facility JET in Culham (UK) could achieve in 1997 to generate 16 MW of heat for a short while, consuming twice as much power to conduct the experiment. A larger reactor will be constructed from 2007 in Cadarache (France), through world-wide cooperation. This reactor will for the first time produce an energy surplus. It will be used for 10 years to build experience. If the results are positive, construction of the first demonstration reactor 'DEMO' will start. The energy return of this reactor should be a factor 4.

From 2060, nuclear fusion could provide a sizeable contribution to energy supply. It represents the next stage of development for nuclear technology, after the 'backup solution' nuclear fission. Fission is expected to contribute from 2020 with so-called Generation-IV reactors, which offer better reactor safety.

This contribution was originally published in the German languageon september 7, 2006 by Energie-Fakten.