...At exactly 46 minutes and 46 seconds past 2 p.m. on March 11 -- just after the magnitude 9.0 earthquake had struck off the northeast coast of Japan -- reactors No. 1-3 began emergency shut-down procedures (reactors No. 4-6 were not operating). However, as the reactors were shutting down, the plant log reveals workers were being bombarded with alarms for control rod insertions in each reactor, water level fluctuations, and other details of a nuclear plant swinging into crisis-response mode.
According to the TEPCO documents, the tsunami hit at about 3:30 p.m., cutting all power at the plant. In response, at about 5 p.m. TEPCO ordered power-source trucks to head to the plant from its branches nearby. However, "the trucks were unable to make progress due to road damage and traffic jams," a report included in the documents states. Unable to get the trucks to the Fukushima plant, at 6:20 p.m., TEPCO requested neighboring Tohoku Electric Power Co. to send some in their stead.
The Tohoku Electric trucks did not arrive at the plant until about 11 p.m., but faced with "the dark, pools of tsunami water, missing manhole covers on the road, and debris everywhere hindering progress," workers found hooking up the necessary power cables extremely difficult, according to a report from around dawn on March 12. Power was finally restored to the plant at about 3 p.m., but at 3:36 p.m. a massive hydrogen explosion in the No.1 reactor building destroyed the newly laid cables, cutting power once more.
Meanwhile, workers inside the plant were trying to vent the No. 1 reactor to relieve pressure building in the reactor vessel. Reports made as the crisis went on show workers tried to vent the reactor manually at about 9:15 p.m. on March 11 but soon had to stop, with an entry at about 9:30 p.m. stating, "We tried the operation onsite, but the radiation dose was so high we gave up." The venting operation was eventually completed, but not until 10:17 p.m.
What the workers were doing between 9:30 p.m. and 10:17 p.m., however, is not revealed in the TEPCO documents, and a TEPCO representative told reporters, "We don't know what kind of risk assessment led the workers to try again."
However, an entry for 9:51 p.m. in the plant duty log also released by TEPCO states: "No entry permitted" to the No. 1 reactor building due to high radiation -- an order that photos of memos on the plant's central control room whiteboard show came directly from TEPCO President Masataka Shimizu. The high radiation that led to the no-entry order furthermore lends support to the theory that a core meltdown began soon after the tsunami struck...