Fukushima Daiichi Nuclear Accident - 26 March status

Fukushima Daiichi Nuclear Accident - 26 March status Barry Brook | 26 March 2011 at 2:13 PM  | URL: http://wp.me/piCIJ-16Z

This post provides an update to the various situation summaries at Fukushima Daiichi. Please switch to using this post for comments on the latest status reports and news to  hand (the old one is now out of date). For general comments on, use the FD Open Thread, and for analysis of the event with respect to future lessons for nuclear power, use this post. Full situation summaries from TEPCO, FEPC and JAIF are given at the bottom of this report.
This is a dramatic before and after photo of the Fukushima Daiichi plant. Click on the image to see more b/a images of the earthquake/tsunami damaged Sendai region (controlled with a swipe tool).

Below is a very brief summary of some key events of the last few days, since the previous status report:
1. There has been concern about salt accumulation in reactor vessels 1-3 (as steam evaporates the injected sea water, the salt is left behind, and if concentrations build to beyond the saturation point, it will begin to deposit and potentially insulate the fuel assemblies). However, NEI now reports the following welcome news:

Fresh water is being injected into the reactor pressure vessel at reactor 3 at Fukushima Daiichi nuclear power plant, Japan's Nuclear and Industrial Safety Agency said.
TEPCO said that radioactive materials discovered at the reactor 3 turbine building possibly came from water from the reactor system, not the spent fuel pool. TEPCO made that statement after collecting samples of contaminated water in the reactor 3 turbine building and conducting a gamma-emitting nuclide analysis of the sample. The reactor pressure and drywell pressure at reactor 3 remained stable on Friday, leading TEPCO to believe that "the reactor pressure vessel is not seriously damaged.
Cooling efforts at Reactor 1 already had switched back to fresh water cooling. Reactor 2 is still being injected with seawater, but is expected to switch to fresh water soon.

The temperature at the bottom head of the reactor pressure vessels are now 149 C (unit 1), 104 C (unit 2) and 111 C (unit 3) -- detailed data in reports below.
2. TEPCO Workers laying cables in the turbine hall of unit 3 stood in ankle-deep stagnant water and their feet were irradiated with beta rays (~180 mSv dose), with shallow burns, after ignoring their dosiometer warnings. They have since been hospitalised. Details in the reports below. 17 personnel have now received doses of >100 mSv, but none >250 mSv -- the dose allowed by authorities in the current situation.
3. Water spraying continues on spent fuel ponds 2, 3 and 4, to ensure the uranium fuel rods remain covered. The temperature in unit 2 pool was recently measured at 52 C (see detailed data below).
4. On radiation: levels around the plant perimeter are relatively low and steadily decreasing. Levels of I-131 in drinking water supplies in Tokyo are now below regulated limits and restrictions have been lifted. The IAEA radiation monitoring data, at a distance of 34 to 62 km from Fukushima Daiichi, showed very low levels. To quote:

On 25th March, the IAEA radiation monitoring team made additional measurements at distances from 34 to 62 km from the Fukushima nuclear power plant. At these locations, the dose rate ranged from 0.73 to 8.8 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.07 to 0.96 Megabecquerel per square metre.

5. World Nuclear News provides a new summary: Fukushima Daiichi two weeks on. To quote:

Investigations are now underway into the unexpectedly high level of contamination in the water, particularly as the basement of the turbine building is not a recognised radiation area. One theory is that there is a leak from the reactor circuit, but pressures in the reactor vessel indicate this must be elsewhere in the loop.
Despite this disappointment, steady progress continues to be made on site. Instrumentation is being recovered at units 1, 2 and 4 and lights are on in the control rooms of units 1 and 3. Power connections have reached all the units and checks are underway before normal systems can be re-energised. The shared pond for used fuel pond has now been reconnected.

Here are some interesting photographs from inside the buildings, taken on 23 March by by the Operational Safety Inspector.
6. Geoff Russell (a regular BNC author on food and climate change issues) has a really good piece, reflecting on many of the issues discussed here over the last few weeks. His original title was: Japanese nukes ... good news in a bleak landscape.
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