Things continue to develop slowly, but I think now to an inevitable conclusion -- barring any sudden turn of events, a cold shutdown (reactor temperature below 100C) should be achieved in units 1 to 3 within the next week (or two?). The other priority is to get the spent fuel ponds can sufficiently covered with water to make them approachable (and ideally to get AC power systems restored to these ponds, as has been the case already for units 5 and 6). The clean up, diagnostics, and ultimate decommissioning of Fukushima Daiichi, of course, will take months and years to complete.
What is the latest news?
First, there is a new estimate of the tsunami damage. According to the NEI:
TEPCO believes the tsunami that inundated the Fukushima Daiichi site was 14 meters high, the network said. The design basis tsunami for the site was 5.7 meters, and the reactors and backup power sources were located 10 to 13 meters above sea level. The company reported that the maximum earthquake for which the Fukushima Daiichi plants were designed was magnitude 8. The quake that struck March 11 was magnitude 9.
Second, the IAEA reports elevated levels of radioactivity in the sea water off the coast of these reactors. That is hardly surprising, given that contaminated cooling water would gradually drain off the site -- and remember, it is very easy with modern instruments to detect radioactivity in even trace amounts. For further details on radiation trends in Japan, read this from WNN. In short, levels are hovering at or just above background levels in most surround prefectures, but are elevated in some parts of Fukushima. However, the World Health Organisation:
... backed the Japanese authorities, saying "These recommendations are in line with those based on accepted public health expertise."
Below is a detailed situation summary of the Fukushima Daiichi site, passed to me by a colleague:
(1) Radioactivity was detected in the sea close to Fukushima-Daiichi. On March 21, TEPCO detected radioactivity in the nearby sea at Fukushima-Daiichi nuclear power station (NPS). TEPCO notified this measurement result to NISA and Fukushima prefecture. TEPCO continues sampling survey at Fukushima-Daiichi NPS, and also at Fukushima-Daini NPS in order to evaluate diffusion from the Fukushima-Daiichi. Though people do not drink seawater directly, TEPCO thinks it important to see how far these radioactivity spread in the sea to assess impact to human body.