The problems at the Fukushima Daiichi nuclear power plant continue to be worked on, with no short-term resolution in sight. Here are eight recent notable happenings, compiled from various sources (see list below):

1. Reports indicate that some fuel melted and fell to the lower containment sections of units 1-3, where it dispersed in a fairly uniform residue — but this does not seem to have breached containment in any of the reactor pressure vessels. Re-criticality of this ‘corium’ seems very unlikely, but no details can of course be confirmed until the reactor cores are finally dismantled — which may be years away.

2. Two automated PackBot robots entered units 1 and 3, took photos, and measured temperature, pressure and radioactivity within the buildings. Peak levels were 40-60 mSv/hr.

3. An anti-scattering agent is being sprayed on the ground around the damaged units (about 1,200 square metres in area) to prevent further spread of radionuclides (see photo above).

4. Excess radioactive cooling water continues to be transferred from unit 2’s basement and tunnels to a waste processing facility.

5. Further surveys are being made of the area surrounding the Fukushima evacuation zone and the exclusion area is being policed more strictly. Highest levels were measured at Itate, at about 4 microsieverts per hour (by comparison, the background level is 0.2 — 0.4 uSv/hr).

6. TEPCO have now released a roadmap plan for the restoration of stable conditions at the site, over a 3 — 6 month timetable, leading to a cold shutdown at units 1-3 and various other stability targets. They also released a 27-slide presentation on the timeline of the accident and current situation, that is definitely worth a look through.

7. This is a really useful summary post describing one of the pressing needs facing engineers at Fukushima Daiichi: Day 42: How is a core cooled? In short, heat exchangers are the key…

8. From NEI Nuclear Notes, Russia’s atomic energy chief (Kiriyenko of Rosatom) sees Fukushima as a strong policy incentive for moving more quickly to current- and next-generation reactor designs (I’ll have more to say on this topic in future BNC posts):

Kiriyenko said the impact from the Fukushima plant disaster would not only increase safety concerns but also quicken demand for new reactors to replace the industry’s ageing plants. “There will be a need to build new plants more quickly to more swiftly replace previous-generation plants,” he said. He added that Russia may speed the retirement of its older generation plants in the wake of Japan’s nuclear accident.

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Please use this post to put any new comments about the Fukushima situation (including technical information, situation updates, analysis, questions, reflections, etc.). As such, I consider the earlier FD Philosophical and Technical threads closed — these strands of discussion can now be carried on here, as the pace of comments has died down to a small fraction of that at the height of the crisis.

Here are some other channels I recommend you check on regularly, for up-to-date situation reports on Fukushima Daiichi:

— World Nuclear News (the two latest posts are Changes to evacuation zones and Dust control steps up at Fukushima)

— ANS Nuclear Cafe news and updates (includes links to official reports like JAIF and TEPCO and news feeds from NHK, NY Times, etc.), see also NEI updates

— International Atomic Energy Agency (IAEA) update website (last updated on 21 April, has reactor status and radiation monitoring reports)

— Will Davis at Atomic Power Review blog continues to do an excellent job at providing regular updates and interesting technical analysis on the situation

Note that the Open Threads on BraveNewClimate.com are a general discussion forum; please follow the commenting rules, although the ‘stay on topic’ rule obviously does not apply as strictly here.