At the time of this writing, reactors 4, 5 and 6 are in cold shutdown (sustained temperatures below 100°C). Reactor 4 is defueled. Reactors 1, 2 and 3 are targeted to be in cold shutdown by the end of the year and the nuclear world will be closely monitoring progress towards this goal.
Internationally supported efforts continue to cool the reactor cores and to decontaminate the very large quantities of sea and fresh water used for emergency cooling in the early stages of the accident. Total cleanup will take at least 10 years according to TEPCO and up to 30 years in the opinion of others. TEPCO has announced that reactors 1-4 will be scrapped. The fate of 5 and 6 is uncertain, as is that of Fukushima II. The 20km exclusion zone remains, although a few intrepid souls have returned.
In the wake of the earthquake, tsunami and accident, over half of Japan's 54 reactors are not currently operating, resulting in extreme pressures on the country's electric grid. The debate has been reopened on the future of nuclear power, both within Japan and in the wider world.
Figure 1: Simplified diagram of a boiling water reactor.
Key to diagram: 1. Reactor vessel, 2. Fuel core element, 3. Control rod element, 4. Circulation pumps, 5. Control rod motors, 6. Steam, 7. Inlet water circulation, 8. High-pressure turbine 9. Low-pressure turbine, 10. & 11. Electrical generator, 12. Steam condenser, 13. Cold water for condenser, 14. Pre warmer, 15. Water circulation pump, 16. Condenser cold water pump, 17. Concrete chamber, 18. Connection to electricity grid.