An extremely serious situation ensues at the number 2 reactor in the Fukushima No 1 nuclear plant. At 23:20, 14 March 2011, local time, the nuclear fuel rods have been completely exposed, despite an earlier effort to pump in sea water.
According to the press and official sources (with some links: the linked pages are in Japanese), the chronology of the events surrounding this reactor is as follows. All times are local, and there are some differences in the times depending on the source, which means that this article is subject to corrections at later points (major changes are noted in the time stamp). Please note that this concerns the no 2 reactor, not the no 3 reactor where there was a hydrogen explosion earlier on 14 March, or the no 1 reactor, which had a hyrogen explosion on 12 March.
14 March 2011
13:25 — Tokyo Electric Power Company (TEPCO) reports the situation as an emergency to the state. The cooling system ceased work, and the water level had dropped.
16:34 — TEPCO prepares to pump in sea water.
17:17 — The fuel rods (3.7m tall) started to be exposed.
18:06 — Pressure relief valve opened; water level recovered.
18:22 — The fuel rods are completely exposed.
18:24 — Sea water pumped in.
[Time unclear] — Workers missed that the fuel for the pumps had run out. There was a 3-minute period when no sea water was being pumped in.
20:37 — TEPCO prepares to release steam to the outside.
23:20 — The water level had recovered for a while, but has lowered again, exposing the fuel rods totally. According to TEPCO, the pressure relief valves linking the pressure vessel and the containment vessel were closed, which made pumping sea water impossible, and leading to rising pressure inside the reactor. The company is planning to relieve pressure by opening a valve that links the containment vessel to the outside. Steam thereby released will contain radiation.
15 March 2011
00:02 — TEPCO releases steam from the containment vessel to the outside.
03:00 — The fuel rods are still totally exposed. Sea water is being pumped in, but the water level has not risen.
[05:35 — Press conference] — Sea water is being pumped in, however, the situation has not yet been stabilized.
06:14 [Information made available at 08:09 on the Nuclear and Industrial Safety Agency website, and subsequent press reports] — A large explosion noise is heard at the no 2 reactor. The suppression chamber may be damaged. (Source: http://kinkyu.nisa.go.jp/kinkyu/2011/03/post-94.html) As such, there is likely to be damage to the containment vessel. The personnel at the plant are evacuated, except for 50 workers who are needed to pump in the water.
[06:43 — Press conference] — The suppression pool (i.e. the suppression chamber) in the no 2 reactor is damaged. There has been no dramatic increase in the radiation levels near the plant. (Tweet: http://twitter.com/Kantei_Saigai/statuses/47416147573882880/) It is unclear whether the government was aware of the explosion noise at 06:10 mentioned above, though it does mention the damage to the suppression chamber / pool.
08:31 — Very high radiation detected at the main gate of the plant: 8,217μSv/h (the figure was 965μSv/h at 07:00).
[08:52 — Reported by Yomiuri — http://www.yomiuri.co.jp/national/news/20110315-OYT1T00172.htm] — The water level has recovered: 2.8m of the fuel rods are still exposed.
10:22 — Extremely high radiation detected at the no 3 reactor: 400,000μSv/h
11:00 — People are ordered to stay inside within a 30 km radius. At some point past 11:00 a fire starts at the no 4 reactor. This reactor was not in operation, but stored spent fuel rods.
11:25 — 1.2m of the fuel rods are still exposed.
13:00 — 1.7m of the fuel rods are still exposed.
TEPCO and the government have been criticized for the way in which the information regarding the nuclear reactors in Fukushima has been handled so far. They certainly deserve such criticisms, since too little information is made public a little too late.
An increase in the radiation level has been detected beyond the 30 km radius of the plant, however, it does not affect health. People are asked to remain calm.