Updated 16/03/2011 09:30 GMT
There has been an astonishing warning from TEPCO that “The possibility of re-criticality is not zero.” This can only mean that they have put so much fuel in the storage pool that it could start a nuclear reaction outside the reactor. This would not explode, but could cause the fuel rods to release radioactive particles outside of containment. This would spread radiation throughout the area.
— Original article —
There is a lot of misinformation and fear being spread about the nuclear reactors at Fukushima. I would like to present the correct information here.
- All the explosions have been of hydrogen, and outside the reactor. The visible damage is the metal outer shed. It is unknown but thought unlikely that the reactors themselves have been breached. Talk of a “nuclear explosion” by the press is highly misleading.
- Most of the radioactive particles in the steam vented from the reactors have very short half lives and will decay to nothing after a few seconds. A tiny amount of more harmful materials may have been released.
- The highest level of radiation recorded near a reactor, 400 millisieverts-per-hour, is less than half that required to cause nausea and vomiting and less than an eighth of a possibly lethal dose, (3.5 sieverts) and that was right next to the reactor. At the site entrance it was only 8 millisieverts.
- The largest release of radiation so far and the main risk of more has come from spent fuel rods in the storage pond next to reactor 4. These have caught fire twice in the last 24 hours. Fuel must be kept in cooling storage ponds for several years after being removed from the reactor. Al Jazeera has more information.
- Spent fuel rods in storage ponds will not meltdown, but radioactive particles may be released if they are not kept under water, and especially if they catch fire.
- There is a danger of more highly radioactive particles leaking from fuel if any reactor containments are breached. So far none have been since explosions have been outside the containment.
- If any reactor cores do reach a state of meltdown, that means that the fuel will become a molten pool of metal on the floor of the reactor. The containment is designed to keep this in and prevent a leak. It will eventually cool down and be removed.
- All of the reactors at Fukushima Dai-ni are in a state of cold shutdown.
- Reactors 4,5 and 6 at Fukushima Daiichi were already shut down for inspection at the time of the earthquake.
- A hoax is circulating which informs people that radiation has spread to other parts of Asia. This is not yet the case. More info at the BBC.
The situation is serious, radiation has been leaked, and that is not good, however the people have been evacuated and issued with iodine tablets (Potassium iodide prevents radioactive iodine from lodging in the thyroid) and the radioactive particles should decay and dissipate quickly. The worst thing that could happen now is a breach of the containment, in which case the area could become irradiated and uninhabitable. This is unlikely to happen.
Disclaimer: I have not had time to provide references for any of this. I suggest that you read reliable sources on the subject, such as the IAEA and NOT a news agency. (Especially not Fox.)
For up to date information, please see the International Atomic Engergy Agency. The IAEA website is at www.iaea.org however it is under heavy load so they are publishing all information on Facebook at www.facebook.com/iaeaorg
You can also view press releases from the Tokyo Electric Power Company (TEPC) at www.tepco.co.jp/en/press/corp-com/release/index-e.html however their website is also under heavy load and may not respond.
Note: The reactors at Fukushima are 40 years old and of very poor design compared to modern ones. New reactors can shutdown and cool themselves without power or human intervention. Germany and the USA were about to replace 40 year old reactors with modern designs but have suspended this in reaction to events in Japan. This means that 40 year old designs will be kept in operation.