An interruption of electrical power on 18 March has knocked out the cooling systems of the Fukushima spent fuel pools and part of the wastewater treatment systems. It has not affected the cooling water injection systems into units 1-3, the PCV gas control systems or one of the unit 2 spent fuel pool cooling systems. Some systems were recovered on 19 March, including a unit 1 spent fuel pool cooling system and the wastewater treatment system. TEPCO estimates that it would take days for the spent fuel pools to heat up to a significant temperature (65°C). The shortest duration is unit 4, which would take more than four days. Investigations of the cause of the shutdowns, and their restoration, are under way.
Engineers have completed their investigation of the eight unit 2 vent pipes that lead to the torus, and has found no water leakage or evidence of major water leakage. Most of the invesgations were carried out in early March. This would appear to suggest that at least the lower parts of the unit 2 reactor structure are more intact than previously thought. It does beg the question of how exactly radioactive contamination has leaked out of the reactor and into the turbine building.
Workers have closed the unit 2 blowout panel. Unlike units 1, 3 and 4, the upper structure of unit 2 did not explode after the earthquake and tsunami, because, it would appear, the panel worked and designed and responded to critical pressure levels by detaching from the structure. However, much radioactive steam, particularly in the early days of the incident, leaked out of the blowout panel opening, and the opening continues to be a main contributor to the total radioactivity releases on site. Now that the unit 2 reactor's temperature is under control, the opening is no longer necessary. A crane lifted a closure panel into a frame set against the side of the reactor building. The panel includes an access door.
New measurements of the level of radioactive contamination inside the unit 1 reactor building have been published. The latest readings, from February 14, cover mainly the third and fourth floors. They are generally much lower (half) than previous readings taken mostly in October 2011, although they do not update the first floor of the building, which has some of the highest readings. Measurements range from less than 1 mSv/hr to 45 mSv/hr. The building has been off-limits to human teams because of high levels of radiation.
