天外飛來巴斯光年

正在練英打，找了一篇英聽題目練習。此為我上聽力課四周來，非情境式日常對話，頭一次聽完無需老師解釋就掌握到重點全部答對的題目，值得紀念一下。（ps.這個大雄英打小遊戲不錯玩。）

NARRATOR: Listen to a professor give a lecture on nuclear power.

Nuclear power currently provides over 17% of the world’s electricity and 7% of global energy. Since the first successful experiment with nuclear fission in 1938, nuclear power has been rapidly researched and developed to become a key power source of the twenty-first century. However, as many developments do, nuclear power has a price; there are many potential risks in its development and use, and thus it has become quite a controversial issue.

The stem of this controversy lies in the problem of storing waste and the possibility of radioactive contamination. Proponents argue that the risks are small and that fear has been the single largest obstacle to the widespread use of nuclear power. They believe that as oil and natural gas production peaks and is unable to meet global demand, nuclear power will be the only realistic large-scale energy source. Additionally, unlike these fossil fuel, nuclear generation does not produce carbon dioxide, sulfur dioxide and other pollutants associated with combustion, and could significantly reduce greenhouse gas emissions.

Environmental groups, on the other hand, point to the problematical history of nuclear power and its continual procession of nuclear accidents from the 1950’s to the present day. Opponents of nuclear power claim that any of the environmental benefits are outweighed by safety compromises and by the risks related to the operation and retirement of nuclear power plants. Nuclear waste is a byproduct of nuclear energy and contains elements such as uranium and plutonium, which are not only radioactive, but toxic as well. These elements emit large amounts of radiation and have long half-lives, thus they are exceedingly difficult to dispose of.

The main objective in managing and disposing of radioactive waste is to protect people and the environment. This means isolating or diluting the waste so that the concentration to the biosphere is harmless. To achieve this the preferred technology to date has been deep and secure burial for the more dangerous wastes. Currently deep mine are used, due to the belief that radioactivity will be unable to migrate through the overlying rocks into the biosphere, thus minimizing contamination.