日本核泄漏物即抵美西：三号反应堆用的是钚，后果不容乐观
from: LA Times
美国原子能专家指出，从日本核电站泄露的第一波放射性污染物最快将于18日抵达美国加州等西海岸上空。不过专家认为，辐射物的含量在安全范围以内。
据 3月16日报道，日本大地震和海啸引发核电站泄露事故后，世界各地和美国的检测网络密切监视核污染物的动向。从日本核电站泄露的少量核辐射物正随高空气流 飞跃太平洋飘向北美大陆。美国环保部管理的核辐射检测网络由100个检测站组成，该网络每天24小时不间断地监控全美各地地核辐射情况，此外还有63个联 合国“全面禁止核试验条约组织”管理的监测站在进行同样的工作。
美国专家说，来自日本的第一波核污染物最快将在18日出现在美国西海岸上 空，也有可能晚一周左右抵达。以加州南部的洛杉矶为例，距离日本福岛大约有8,000公里。专家说，2006年朝鲜进行核试验时，大约两周后核辐射物到达 美国西海岸上空。
美国原子能管理委员会专家16日表示，抵达美国夏威夷、阿拉斯加、西海岸的核辐射物不会达到危险水平，不过第一波核污染物 过后，美国上空的核辐射物含量很可能会升高，因为日本核电站核泄漏事故在加剧。该委员会已经要求在日本核电站周边80公里范围内的美国公民迅速撤离。
美 国原子能管理委员会的电脑模拟显示，在福岛第一核电站周围半英里范围内，核辐射水平之高足以致命，即使是80公里处的辐射剂量也超过每人每年正常接收的辐 射量的16倍。不过专家也指出，即使日本核泄漏物在增加，但辐射物在抵达美国上空时已经被大气层冲散，浓度会大幅下降。
报道最后提到，一个 不容乐观的情况是，福岛核电站的第三号反应堆使用的是核燃料钚，这是一种对人类健康极度危险的放射性物质，即使是微小的剂量也会导致严重后果。
--
Small amounts of radiation headed for California, but no health risk seen
http://www.latimes.com/news/science/la-sci-japan-nuclear-usa-20110317,0,1431467.story
Small amounts of radioactive isotopes from the crippled Japanese nuclear power plant are being blown toward North America high in the atmosphere over the Pacific Ocean and will reach California as soon as Friday, according to experts.
A network of sensors in the U.S. and around the world is watching for the first signs of that fallout, though experts said they were confident that the amount of radiation would be well within safe limits.
Operated by the Environmental Protection Agency, the U.S. network known as Radnet is a system of 100 radiation monitors that work 24 hours a day, spread across the country in places such as Anaheim, Bakersfield and Eureka. In addition, a network of 63 sensors is operated by the Comprehensive Test Ban Treaty Organization, an international agency allied with the United Nations.
Atmospheric experts said the material should begin showing up on the West Coast as early as Friday, though it could take up to an additional week for the 5,000-mile trip from Japan to Southern California. Although the organization has told its member countries that the first indication of radiation would hit on Friday, the plume from a North Korean nuclear test in 2006 took about two weeks to travel to North America, U.N. officials said.
The Nuclear Regulatory Commission, which oversees the U.S. nuclear industry, said Wednesday that it did not expect dangerous levels of radioactivity to hit the West Coast, Hawaii, Alaska or U.S. territories in the Pacific. But whatever levels reach the U.S. initially are likely to increase in subsequent days, because radioactive emissions from the damaged Fukushima Daiichi nuclear power plant have grown since the disaster began Friday. The NRC sharply raised its warning to American citizens in Japan, urging them to evacuate an area within 50 miles of the Fukushima complex. Japanese authorities have ordered an evacuation within about 12 miles of the plant.
The NRC released computerized projections showing that within half a mile of the plant, radiation levels were so high that one could receive a fatal dose, and that even 50 miles away one could receive more than 16 times the average annual dose all people are exposed to from natural sources.
Those numbers were sharply higher than ones the NRC released days earlier. But although the Fukushima reactors are leaking more radiation now, experts continued to say that the particles would wash out of the atmosphere before they could reach the U.S.
So far, Tokyo Electric Power Co., which operates the Fukushima facility, and the Japanese government have not released any measurements or estimates of the total amount of radioactivity released by the accident. These numbers would be crucial to better project whether the material could affect other Asian nations, the Pacific islands or even the U.S.
Edwin Lyman, a specialist at the nuclear watchdog group Union of Concerned Scientists, said that although it was true that the more radioactivity released in Japan the more could migrate away from the region, he did not think the U.S. was at serious risk.
"We can never say never," Lyman said. "My judgment is that there will probably be measurable radiation, but except for a few hot spots it is not something we should really worry about."
Lyman said that the NRC's warning Wednesday to Americans in Japan to evacuate 50 miles from the Fukushima reactors was a long-overdue admission that the agency's prior warnings of a 10-mile exclusion zone from U.S. reactors during an emergency was inadequate.
Key federal officials involved in the Radnet monitoring program have so far not disclosed their predictions for U.S. radioactive exposure. The projections are being developed by the National Atmospheric Release Advisory Center operated at the Lawrence Livermore National Laboratory in Northern California. The center, part of the Energy Department, uses sophisticated models on supercomputers to project the movement of radioactive particles and other toxic substances through the atmosphere.
