UPDATE, 12:30 pm, Friday, Speculation in some media reports that Unit 1 will reach a cold shutdown within a week appears unwarranted; at best it will take about a month to achieve that goal—and that’s if all goes well. Of course, Units 2 and 3 need to reach cold shutdown (and fuel pools, esp. for Units 3 and 4 need to be brought fully under control) before this can move from an “ongoing accident” situation to a clean-up situation. Temperatures in all three units with fuel in the core (Units 1, 2 & 3) remain above the boiling point, meaning water continues to boil off and fuel rods remain exposed.

UPDATE, 12:30 pm, Thursday, Radiation levels in the seabed near Fukushima are reported at 100 to 1,000 times above normal. Japanese officials reportedly are agreeing to help from Britain in measuring radiation in the sea, but continue to bar the Greenpeace ship Rainbow Warrior from coming closer to the site than the 12-mile international water zone. Greenpeace wants to conduct independent radiation monitoring of the water in the area.

UPDATE, 12:30 pm, Friday, Toshiso Kosako, a University of Tokyo professor and radiation expert, resigned as a special nuclear advisor to Japan’s Prime Minister Naoto Kan today, in protest over the government’s handling of the Fukushima crisis. Kosako was appointed as an advisor on March 16. He told a news conference—apparently holding back tears– that ”The prime minister’s office and administrative organizations have made impromptu policy decisions, like playing a whack-a-mole game, ignoring proper procedures.” Kosako specifically pointed to the government’s decision to increase allowable exposures to workers from 100 to 250 MilliSieverts/year (from 10 to 25 rems/year; U.S. allowable level for workers is 5 rems/year) and to the decision to allow schoolchildren in Fukushima Prefecture to be exposed to 20 MilliSieverts/year (2 rems/year; 20 times higher than international standards).

UPDATE, 4 pm, Monday, Japanese activists are alarmed about a government decision to allow children in Fukushima Prefecture to attend schools where radiation readings indicate they could be exposed to 20 MilliSieverts/year (2 rems/year)—20 times the U.S. allowable standard for the public. This decision appears not to be based on risk (and children are more susceptible to radiation than adults), since the government also is relocating people in five villages outside the previous evacuation zone because people in them could be exposed to 20 MilliSieverts/year. Rather, the decision appears to be based on the reality that many schools in Fukushima Prefecture are experiencing high levels of contamination, and the government apparently does not want to require children to go to schools further away, nor further expand the exclusion zone.

UPDATE, Noon, Thursday, As expected, the Japanese government has now turned the 20 kilometer “evacuation” zone into an exclusion zone. People entering the zone can be fined up to $1200 or jailed up to 30 days for entering the zone. Streams of people entered the zone earlier today before the new law went into effect to gather their possessions and check on their homes. The government will now allow a single visit per household, lasting no more than two hours, for people to gather their possessions. People returning from these visits will have to be screened for radiation. It is not clear what will happen to possessions found to be radioactive.

UPDATE, 1:30 pm, Monday, High radiation readings were again measured in seawater near Fukushima over the weekend. Of particular concern were high readings of Iodine-131. With its eight-day half-life, new spikes in Iodine-131 should not be found. This strongly suggests that melting of fuel and new radiation releases continue to occur.

UPDATE, 11:30 am, Thursday, The fuel pool at Unit 4 apparently has experienced an inadvertent criticality at some point in the past month. Tokyo Electric Power (Tepco) has confirmed that some fuel rods in the pool are damaged. A 400 milliliter water sampling from the pool taken Tuesday found elevated levels (as much as 100,000 times above normal) of Iodine-131, Cesium-134 and Cesium-137. As nuclear engineer Arnie Gunderson of Fairewind Associates points out, there should be no Iodine-131 detected at all. All of the fuel from Unit 4 had been removed from the core and placed in the pool well before the March 11 accident. With a half-life of 8 days, the likely way Iodine-131 would be detected in this water would be if there had been a criticality—which given the severe damage to the pool is more than just conjecture. Tepco, however, suggests the readings may be caused by radioactive rubble in the pool or radioactive rainwater coming into the pool.