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.

UPDATE, 12:30 pm, Tuesday, As predicted, the Japanese government has officially upgraded the status of the Fukushima accident to Level 7. In doing so, however, the government appears to be downplaying the actual radiation releases, with several media reports this morning quoting government officials as saying releases have been about 10% of those from Chernobyl.

UPDATE, 3:00 pm, Monday, One full month after the earthquake, tsunami and onset of the Fukushima nuclear disaster, the Japanese government is preparing for evacuation of five more villages about 25 miles or so northwest of Fukushima Daiichi, including Iitate and Namie, which we have noted numerous times below have been experiencing high radiation levels for a month now. Five other villages are being considered for evacuation. However, the planned evacuations are not immediate and may take weeks to happen.

UPDATE, 6:00 pm, Friday, Activists in Japan are putting out an urgent appeal to stop schools in contaminated zones from opening. In Japan, schools are scheduled to open for the year over the next two weeks. Radiation levels in many areas outside the evacuation zone remain high. For example, measurements taken April 5 in Iitate Village (40 km northwest of Fukushima Daiichi) range from 9.5 to 18.2 MicroSievert/hour, or nearly 1-2 millirems/hour. Allowable annual exposure level in the U.S. is 100 millirems/year, meaning people exposed to this level of radiation could receive their annual dose in 50 to 100 hours. But it’s even worse in the town of Namie, also northwest of the site: levels there were measured April 5 at 18.8 to 23 MicroSievert/hour. Children are more susceptible to radiation exposure than adults.

UPDATE, 3:15 pm, Thursday, Today’s earthquake (which we have seen variously reported as between 7.1 and 7.9 in magnitude) has knocked out power in some sections of northeast Japan. The single-unit Higashidori Boiling Water Reactor and the Rokkasho reprocessing plant have lost offsite power and are running on emergency diesel generators. Offsite power may also have been lost to the three unit Onagawa nuclear complex, although there is a report that power remains for the reactors themselves, but not for the fuel pools and that those are relying upon emergency diesel generators.

UPDATE, 12:30 pm, Thursday, A 7.1 earthquake struck northeast Japan about an hour ago (11:30 pm Japan time); workers were temporarily evacuated from the Fukushima Daiichi nuclear site. There are no immediate reports of additional damage at the site.