Despite the orders of Masao Yoshida, head of the Fukushima No. 1 nuclear power plant, venting of reactors and injections of water did not proceed smoothly in the early stage of the crisis, documents showed.
Despite the orders of Masao Yoshida, head of the Fukushima No. 1 nuclear power plant, venting of reactors and injections of water did not proceed smoothly in the early stage of the crisis, documents showed.
Fearing reactor core damage could lead to a serious accident, Yoshida started issuing instructions to prepare pumping in water to the No. 1 and No. 2 reactors around 90 minutes after all power sources to the reactors were lost by 3:40 p.m. on March 11, according to the internal documents of Tokyo Electric Power Co.
His orders were in accordance with procedures prepared to deal with serious accidents. But the work ran into a number of problems, some of them unexplained in the documents.
The documents, obtained by The Asahi Shimbun, said an increase in radiation levels at the reactor buildings made it impossible for workers to enter those buildings. The papers also cited damage to equipment from hydrogen explosions at neighboring reactor buildings.
The documents provide a timeline of events from 2:46 p.m. on March 11 when the magnitude-9.0 Great East Japan Earthquake struck, and include the explosions that occurred at the No. 1 to No. 3 reactors until March 15.
The documents are believed to have been based on records kept by plant workers and subsequent questioning of those workers by TEPCO officials.
TEPCO officials analyzed data that remained in the central control rooms of the reactors and released their findings in May.
A report on the venting and water-pumping operations was supposed to have been released at a June 15 news conference after being submitted to the Nuclear and Industrial Safety Agency (NISA).
However, a number of sources said the release of the report was canceled shortly before the news conference because approval from the Prime Minister's Official Residence could not be obtained.
The documents are expected to be submitted to the government-appointed panel established to investigate the causes and evaluate the measures taken to deal with the Fukushima nuclear accident.
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NO. 1 REACTOR
At the No. 1 reactor, the water level and other conditions at the core could not be confirmed from about 4:30 p.m. on March 11.
Yoshida concluded there was the possibility of a serious accident occurring.
At 5:12 p.m., he gave instructions to consider methods for pumping in water, including the use of firefighting pipes and firefighting vehicles that had been installed to deal with serious accidents.
However, by the night of March 11, high levels of radiation prevented workers from entering the No. 1 reactor building. The increase was likely due to leakage of radiation from the core.
The pumping in of fresh water using the firefighting pipes only began at 5:46 a.m. on March 12, about 12 hours later.
After pumping in 80 tons of fresh water over nine hours, the water supply ran out. Yoshida then gave instructions to pump in seawater at 2:54 p.m.
At 3:36 p.m., a power source was restored from a generator vehicle and preparations were completed to begin pumping in water mixed with boric acid.
However, an explosion occurred at that time in the reactor building. As a result, the power source equipment that had been prepared and the hoses used to pump in seawater were rendered inoperable.
Timeline for No. 1 reactor
March 11
3:37 p.m.: All AC power sources lost
5:12 p.m.: Yoshida gives instructions to consider methods for pumping in water to reactor core by using firefighting pipes and firefighting vehicles installed as measures to deal with serious accidents
9:51 p.m.: Rising radiation levels lead to ban on entering reactor building
March 12
12:06 a.m.: Yoshida gives instructions to prepare for venting because of increased pressure within containment vessel
5:46 a.m.: Work begins to pump in fresh water to reactor core through firefighting pipes using firefighting vehicles
9:04 a.m.: Workers head to plant site to operate vents
9:15 a.m.: Venting valves of containment vessel opened manually
10:17 a.m.: Venting valves operated from central control room
2:30 p.m.: Judgment made that venting worked because pressure within containment vessel decreased
3:36 p.m.: Explosion in reactor building
7:04 p.m.: Work begins to pump in seawater to reactor core through firefighting pipes using firefighting vehicles
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NO. 2 REACTOR
Yoshida also gave instructions from an early stage for the No. 2 reactor.
At 5:12 p.m. on March 11, the same time for the No. 1 reactor, he gave instructions to begin considering methods for pumping in water because he determined there was a possibility of the situation escalating into a serious accident.
He told workers at 5:30 p.m. on March 12 to prepare venting operations. That instruction came after confirmation was made that all residents near the plant had completed their evacuation.
Yoshida gave the order to begin venting about 16 hours later on the morning of March 13. He also gave instructions to prepare for the pumping of seawater, rather than fresh water, and implemented measures to deal with the situation.
However, after 11 a.m. on March 14, one valve used in venting would not open due to a hydrogen explosion at the No. 3 reactor. Moreover, hoses to pump water using firefighting vehicles were damaged and could not be used.
The pumping in of seawater using the firefighting vehicle started from that night after preparations were completed a second time.
Venting began after midnight March 14, but around 6 a.m. on March 15, an explosion was heard from near the suppression pool.
Timeline for No. 2 reactor
March 11
3:41 p.m.: All AC power sources lost
4:36 p.m.: Water level within core cannot be confirmed and pumping conditions uncertain
5:12 p.m.: Yoshida gives instructions to consider methods for pumping in water to reactor core to deal with serious accidents
March 12
12:30 a.m.: Evacuation of nearby residents based on central government instructions confirmed
1:30 a.m.: Request made to prime minister and NISA for approval to begin venting
5:30 p.m.: Yoshida gives instruction to begin preparations for venting operation
March 13
10:15 a.m.: Yoshida gives instructions to begin venting
12:05 p.m.: Yoshida gives instructions to prepare use of seawater
March 14
11:01 a.m.: One venting valve does not open because of explosion at No. 3 reactor building. Firefighting vehicle hoses also damaged
7:54 p.m.: Work begins to pump in seawater using firefighting vehicle
March 15
Past 6 a.m.: Explosion heard near suppression pool
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NO. 3 REACTOR
For the No. 3 reactor, Yoshida gave instructions to begin preparations for venting at 5:30 p.m. on March 12. That was two hours after an explosion in the No. 1 reactor building.
As part of efforts to minimize damage from the accident, Prime Minister Naoto Kan gave instructions at 6:25 p.m. to evacuate residents living within a 20-kilometer radius of the Fukushima plant.
However, Yoshida did not give instructions to complete the preparations for venting until 5:15 a.m. on March 13, about 12 hours later.
There are no records that specifically describe what type of work related to venting was conducted during that half-day period.
About an hour earlier, the water level in the reactor core fell and the top of the fuel rods likely became exposed.
The internal documents also describe the problems encountered in the unfamiliar venting process.
At 11:17 a.m. on March 13, the venting valve closed because the air cylinder that moves the valve lost pressure. The valve was only opened an hour or so later at 12:30 p.m. after the air cylinder was replaced.
Timeline for No. 3 reactor
March 11
3:38 p.m.: All AC power sources lost
March 12
11:36 a.m.: Remote-controlled cooling system stops
5:30 p.m.: Yoshida gives instructions to begin preparations for venting operation
March 13
2:42 a.m.: High-pressure pumping cooling system stops
5:15 a.m.: Yoshida gives instructions to complete preparations for venting
8:41 a.m.: Venting begins
Around 9:20 a.m.: Pressure in upper part of containment vessel decreases due to venting
9:25 a.m.: Work begins to pump in fresh water to core from firefighting vehicles using firefighting pipes
10:30 a.m.: Yoshida gives instructions to also consider pumping in seawater
Around 1:10 p.m.: Work begins to pump in seawater to core from firefighting vehicles
March 14
5:20 a.m.: Venting begins
11:01 a.m.: Explosion in reactor building. Pumping of seawater stops due to damage to firefighting vehicles
Around 4:30 p.m.: Pumping of seawater to core resumes