Fukushima update

The latest release from TEPCO:

Unit 3 (Shut down)

• In order to cool spent fuel pool of Unit 3 we conducted water spray by helicopters of Self-Defense Force at approximately 9:48 am. We are continuously monitoring the spent fuel pool and plan to conduct water spray to other Units.

This appears to be the only "updated" information from TEPCO at the moment - the rest of the press release was identical to prior releases. This is consistent with reported information from yesterday. No reports from TEPCO concerning the spent fuel pool at Unit 4.

From NISA, the Japanese NRC (Note: Trimming to provide only the most recent updates - full report is at the link):

• The electrical cables for receiving electricity from the transmission line of Tohoku Electric Power Co. are planned to be installed (07:30 March 17th)
• The procedures for spraying water into the spent fuel pool of Unit 3 are being checked. (07:00 March 17th)
  
• <Unit 1>
  
  • Seawater is being injected as of 04:00 March 17th.
    
  <Unit 2>
  
  • Seawater is being injected as of 04:00 March 17th.
    
• <Unit 3>
  
  • Seawater was discharged 4 times to Unit 3 by the helicopters of Self-Defence Force. (9:48, 9:52, 9:58 and 10:01 March 17th)
    
  • The riot police arrived at the site for grand discharge. (16:10 March 17th)
    
  • Seawater is being injected to RPV as of 17:30 March 17th
    
• <Unit 4>
  
  • The fire occurred at Unit 4. (5:45 March 15th) TEPCO reported that no fire could be confirmed on the ground.(06:15 March 16th)
    
  • The water injection is suspended as of 17:30 March 17th
    
• <Units 5 and 6>
  
  • Emergency Diesel Generator (1 unit) for Unit 6 is operable and supplying electricity to Units 5 and 6. Water injection to the Spent Fuel Pool through MUWC is progressing. It is scheduled to inject water to RPV after the recovery of external power source.
    

In a welcome development, NEI and NISA also report that technicians are laying electrical lines to connect Unit 2 to offsite power, meaning that cooling pumps could be turned back on, preventing any further fuel damage from overheating and allowing workers to focus on other units.

JAIF reports three operations were attempted to deliver water to the spent fuel pools at Unit 3. One operation involved four "bucket drops" from a helicopter with a lead-lined bottom (and workers in radiation suits). In a second attempt, the National Police agency attempted to spray water from the ground, however the spent fuel pool is at the top of the reactor building, and they were unable to get close enough to do so due to elevated radiation levels. In a third attempt, special pump trucks have been brought in with water cannons (which do not require personnel to leave the truck) and have been reported to have delivered 30 tons of water to the building. Whether this has been effective will be evaluated.

It is unclear at this point what the status of the water levels in the spent fuel cooling pools at Units 3 and 4 are; the latest from JAIF indicates water levels are a current concern for Units 3 and 4.. However, all current reports appear to indicate the focus has been on Unit 3, rather than Unit 4. World Nuclear News reports that Japanese officials have made assurances that some water has been still observed in spent fuel pools during helicopter drops at Unit 4.

NEI also reports that the site boundary readings at the Fukushima Daiichi plant were reading around 2 to 3 millirems per hour. This level is still elevated, but relatively low. Radiation exposure rates at the plant themselves are higher; World Nuclear News has reported them to be around a peak of 400 millisieverts per hour at Unit 3 (inland) and 100 millisieverts per hour at Unit 4 (inland) - this corresponds to a dose rate of around 40 and 10 rem per hour. These are high exposure rates (where acute effects begin to become a concern after prolonged exposures), severely limiting workers' access to peak exposure areas.

Readings from monitoring sites using the SPEEDI tool Alan linked to indicate radiation levels at Ibaraki prefecture (the closest currently operational monitoring site) show levels on the range of 100-200 nGy/hr (about 0.01-0.02 millirad/hr) and are steadily dropping, with no recent peaks appearing in the last 24 hours. These levels are very low and appear to be a good sign.