Active Planet: Japan's nuclear reactor's fluctuating radiation levels

The Fukushima reactor plant is suffering substantial changes in radiation levels as measured at the plant's gate. Within the past eight hours, the rates varied by 20% and then surged to levels that resulted in plant crews being ordered to evacuate.

As at 12:52 pm local time today, a major earthquake (magnitude:6) off the north-east coast led to widespread shakes over a large area: tidal changes resulted but no tsunami threat resulted. However, as far away as Narita the shaking was recorded as more than magnitude:4 but no damage is reported.

However, before that quake, the Fukushima plant's Reactor 3 has begun to smoke and fears of a fire in a storage facility at Reactor 4 for expired fuel rods. However, the smoke has subsequently been classified as steam or vapour and that the increase at 10am local time this morning - when the discharge was identified - has rose significantly. But it was a short term surge; a 60% fall was recorded within twenty minutes. Staff which had been withdrawn were instructed that it was safe to return.

The plant has six reactors and four them have identifiable problems. Ironically, efforts to keep the plant cool are hampered by a lack of electricity.

Temperatures have increased in the plant: it is now double the normal level. Reactor 4 suffered a fire and an explosion was heard. There is a substantial hole in the external wall of the building and part of the roof has collapsed. However, although there is opinion that the explosion resulted from a build-up of hydrogen, the exact reason has not been identified.

But a similar explosion on Reactor 3 has resulted in the building being severely damaged.

Reactors 5 and 6 have failed: these, and Reactor 4 were non-operational at the time of the 'quake, offline for routine maintenance.

But, as the temperature rises, the water surrounding the spent fuel may have evaporated, say the authorities. If that has happened, if the rods reach a temperature of 1200 degrees C, they may begin to melt. If that happens, Japan is facing a Chernobyl-scale disaster.

Efforts to pump in sea water to keep the rods cool are frustrated: batteries designed to keep pumps working have expired; helicopter drops have been ruled out because it is regarded as too dangerous for fly-over.

But radiation levels are so high that workers cannot get close to the storage pools: although the 250 milisevers (half the international limit) has been set after a doubling of the usual limits applicable at the plant, it remains too dangerous for them to try to run pipes from fire trucks.

The number of dead and missing now exceeds 11,000. Tokyo is seeing large numbers of people evacuating the city which is only 250 km from the reactor. In cities nearer the site, petrol stations are reporting queues of 3 hours. This is making it difficult for people to leave the area, including those physically devastated areas. Aftershocks are frequent, some as high as six-plus : Japan uses a different scale to the rest of the world - it ranges from zero to seven. More than 44,000 people are in temporary shelters in the north-eastern region.

Travellers are anxious to leave but cannot get fuel to travel to the airport, local reports say. Although international airlines are currently flying into Tokyo as scheduled, several are allowing free cancellation, re-routing or rescheduling of flights both into and out of the district.

There are conflicting reports about an evacuation zone around the reactor: some reports say that the authorities have ordered a 20 km exclusion zone while others say that there is no evacuation order.

The weather in the region is deteriorating: heavy rain is being replaced in some areas by snow.

With precipitation come additional fears of radioactive rain. Those in shelters are being advised to stay inside and others are being warned not to go out unless it is essential. Shops have run out of fresh food across large areas and many shops are closed, leading to additional pressure on those that remain open.