Saturday, April 2, 2011

Japan's nuclear reactor: radioactive leaks

    Reactor leaks: Aerial view
There has been a sharp rise in radioactive iodine in the sea off the Fukushima nuclear power plant, with radioactivity thousands of times higher than the legal limit. The most likely sources of the leaks are Reactors 2 and 3, as detailed here.

Infographic showing the six reactors at fukushima, with reactors 3&4 leaking and the risk levels of the other reactors

It is now believed leaks seeping into the soil, fresh water and the sea are continuous. Radiation has found its way into local produce, milk and tap water as far as Tokyo, 220km (140 miles) to the south.

Theories on main sources of leaked radiation

Reactor 2: Cooling problems damaged the core. It is thought radioactive steam is flowing from the core into the reactor housing and leaking through cracks. Contaminated material may have escaped through the damaged walls of the water-filled suppression chamber beneath the reactor.

Radioactive water in a tunnel underneath the reactor and the turbine (see diagram) is preventing workers from gaining access. This tunnel emerges at the front of the building as a trench - just 55 metres from the sea.

Damaged reactors close-up and diagram showing location of contaminated water

Reactor 3: Uses plutonium in its fuel rod mix - small amounts have been found in soil at the plant indicating this reactor may have suffered a partial meltdown. Sea water is being injected into the spent fuel pool and fresh water is being injected to the damaged core. Highly radioactive water has been detected in reactor.

Reactor 1: Damage to the core from cooling problems. Fresh water is being injected into the core. Highly radioactive water has been detected in reactor.
Decommissioning the plant

The good news is that mains electric power has finally been restored, which brings effective cooling of the fuel rods one step closer.

Once that has been achieved, the next step will be to decomission reactors one to four. This means removing the fuel rods, storing them and then reprocessing them at another plant. Then all non-core buildings will be demolished. Core buildings (which house the reactors) have to remain in tact for at least 40 years because dismantling them would release more radioactive material. Some Japanese nuclear experts are considering whether to cover those core buildings with a special material to stop the spread of radioactive substances.

Reactors 5 and 6 would re-open at some point after consultation with local residents.

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