The following are key points from the latest briefings given today by the Japanese government and nuclear power generator Tokyo Electric Power (Tepco) about the nuclear crisis.

  • Radiation levels at the quake-stricken Fukushima Daiichi complex have varied wildly, with a reading of 11,930 microsieverts at the main gate of the plant at 0000 GMT (8am Malaysian time), up from 596 microsieverts as of 0630 GMT (4.30pm).
  • Elsewhere at the plant, levels reached as high as 400,000 microsieverts an hour (or 400 millisieverts an hour).
  • The government gave no update on the status of a steel container surrounding the core of the plant's No 2 reactor, deemed by observers as most at risk of a meltdown.
  • An explosion on today at the No 2 reactor had caused some damage to its suppression pool, which helps to cool and trap the majority of cesium, iodine, strontium in its water.
  • Later, there was a fire and explosion at the complex's No 4 reactor and this is likely to have contributed to rising radiation levels.
  • The No 4 reactor had been shut down for maintenance ahead of the quake, but a spent-fuel cooling pool associated with that reactor caught fire, causing the explosion.
  • The No 4 reactor's cooling pool, where spent nuclear fuel is stored, may be boiling and the water level may be falling.
  • Radioactivity at the cooling pool is high and Tokyo Electric cannot make checks at the site or determine what has burned.
  • Radiation leakage from complex is likely to spread after a fresh explosion at the plant.
Japan asked local governments to make more frequent radiation checks after explosions at two nuclear reactors, with reports of radiation levels nine times normal briefly detected in Kanagawa near Tokyo.

Below are some facts about the health dangers posed by higher radiation levels.

  • Chief cabinet secretary Yukio Edano said radiation levels near the stricken plant on the northeast coast reached as high as 400 millisieverts (mSv) an hour, thousands of times higher than readings before the blast, but later gave a lower figure. A level of 400 mSV would be 20 times the annual exposure for some nuclear-industry employees and uranium miners.
  • Exposure to 350 mSv was the criterion for relocating people after the Chernobyl accident, according to the World Nuclear Association.
  • People are exposed to natural radiation of about 2 mSv a year.
  • A typical chest X-ray involves exposure of about 0.02 mSv, while a dental one can be 0.01 mSv.
  • Airline crew flying the New York-Tokyo polar route are exposed to 9 mSv a year.
  • Exposure to 100 mSv a year is the lowest level at which any increase in cancer is clearly evident. A cumulative 1,000 mSv would probably cause a fatal cancer many years later in five out of every 100 persons exposed to it.
  • A single 1,000 mSv dose causes radiation sickness such as nausea but not death. A single does of 5,000 mSv would kill about half of those exposed to it within a month.
  • "Very acute radiation, like that which happened in Chernobyl and to the Japanese workers at the nuclear power station, is unlikely for the population," said Lam Ching-wan, a chemical pathologist at the University of Hong Kong.

- Reuters