News Brief, 3/18/11, 10 AM EDT
Spraying of spent fuel pools at Units 3 and 4 is still underway. Visual inspection of Unit 4’s pool showed water in the pool, and so efforts have been temporarily focused upon Unit 3. While efforts at using helicopters to dump water onto the pools had been largely unsuccessful , army firetrucks used in putting out aircraft fires have been employed with some success. The elite Tokyo Hyper Rescue component of the Tokyo fire department has arrived on scene and is conducting missions of roughly two hours in length, during which they spray the pools for 7-8 minutes, wait for steam to dissipate, and spray again.
A cable has been laid from a TEPCO power line 1.5 km from the facility, which will be used to supply power to emergency cooling systems of the reactors at Units 1 and 2.
Backup diesel generators have been connected to cool the spent fuel pools at Units 5 and 6. As of 4 PM JST, temperatures in those pools have reached 65.5 and and 62 degrees Celsius.
Visual inspections have been conducted of both the central spent fuel pool, which contains 60% of the facility’s fuel, and the dry cask storage area. Water levels at the central pool have been described as “secured”, and the dry casks show “no signs of an abnormal situation”. More detailed checks of these areas are planned for the future.
A Japanese government agency has released the results of radiation measurements at dozens of monitoring posts. See the data here: http://www.mext.go.jp/component/a_menu/other/detail/__icsFiles/afieldfile/2011/03/18/1303727_1716.pdf.
These measurements give doses in excess of background radiation, which is why some may appear low. High measurements at reading point 32 are thought to be the result of a controlled containment venting and a simultaneous fire which carried radioactive particles inland. Over the course of the incident, the general trend has been for weather patterns to sweep radioactive particles out to sea.
As a result of these radiation measurements and the ongoing work, the Japanese Nuclear and Industrial Safety Agency upgraded the event to a 5 on the INES scale. This is the same level as the Three Mile Island accident, and two steps below Chernobyl.
Resources: ANS Nuclear Café’; World Nuclear News,; IAEA; Ministry of Education, Culture, Sports, Science and Technology (MEXT).
Note: We earlier reported the temperature of spent fuel pool 6 as 84 degrees C. This was a typographical error. We apologize for the mistake.