Despite investigations by four special committees, key questions remain about the crisis at the Fukushima No. 1 nuclear power plant, the world's worst nuclear disaster since Chernobyl.

The committees, each set up by the government, the Diet, Tokyo Electric Power Co. and the private sector, have key differences in interpretations of events such as if TEPCO planned to abandon the facility at one point, if critical mistakes were made in cooling overheating reactors and what actually occurred in the No. 2 reactor.

So far, the first three committees have released reports but failed to paint a clear and definitive account of what actually transpired in the critical hours and days after the Great East Japan Earthquake and tsunami on March 11 damaged and swamped the plant, as the nuclear crisis quickly spiraled out of control.

The first committee was set up by the central government last summer as TEPCO was still trying to bring the overheating reactors into a state of cold shutdown.

The Investigation Committee on the Accident at the Fukushima Nuclear Power Stations is chaired by Yotaro Hatamura, a professor emeritus at the University of Tokyo noted for his work on the "science of failure." The committee released its interim report in December.

The committee indicated as the cause of the accident the tremendous lack of preparation by TEPCO and the Nuclear and Industrial Safety Agency (NISA) for the possibility of a severe accident caused by the loss of all power sources due to tsunami.

The committee focused on cooling operations at the No. 1 and No. 3 reactors in examining the response to the accident. The report also focused on the process that led to the failure to utilize the System for Prediction of Environmental Emergency Dose Information (SPEEDI) to guide the evacuation of local residents as well as the problems in transmitting information between the prime minister's office and TEPCO headquarters. The final report is expected in July.

The Independent Investigation Commission on the Fukushima Daiichi Nuclear Accident, a private-sector panel, released its final report in late February.

It conducted detailed interviews with about 20 politicians and specialists, including former Prime Minister Naoto Kan, Banri Kaieda, the then industry minister, and Haruki Madarame, chairman of the Nuclear Safety Commission of Japan. The committee also gained the cooperation of about 300 other individuals, but its requests for interviews with TEPCO executives were rejected.

The committee described TEPCO's lack of preparation for a severe accident as "systematic negligence" and also said the utility did not implement measures to deal with a severe accident as outlined by the International Atomic Energy Agency. The committee described Japan's nuclear safety regulations as "Galapagosized," a concept in Japan referring to a perceived tendency for some Japanese industries to isolate themselves from international standards like the isolated wildlife on the Galapagos Islands.

TEPCO also established its own investigative committee, the Fukushima Nuclear Accidents Investigation Committee, which released an interim report in December.

Many of the interpretations it made appear to defend what the utility had done until the accident. The panel said safety measures taken before the accident had passed inspections by the central government. The main cause of the accident was said to be the lack of preparation against a tsunami that exceeded prior assumptions.

The panel also concluded that the March 11, 2011, earthquake had not damaged equipment important from a safety standpoint. The final report is expected in June.

The fourth committee, the National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission, has the authority to force individuals to testify. Its report is expected to be released in June.

TEPCO planned total withdrawal?
One important point over which the three committees that have already released reports disagree is whether Masataka Shimizu, TEPCO president at the time of the nuclear accident, said that all workers would be evacuated from the Fukushima No. 1 nuclear plant.

While many government officials, including Kan, felt Shimizu said he intended to pull out all workers, the three committees have differing interpretations as to if he indeed intended to abandon the plant.

In its interim report, TEPCO's investigative committee said, "The gist of what we asked the prime minister's office is 'Because the situation at the plant is difficult, we want consideration to be given to temporarily evacuating workers who are not directly involved in the work when that need arises.' We never thought about (total withdrawal) nor asked that all workers be allowed to leave."

In the government panel's interim report, Masao Yoshida, the head of the Fukushima plant at the time, considered having only those workers needed to control the various functions at the plant remain and evacuating all others outside the plant site. That point was discussed and shared with TEPCO headquarters.

The panel also said that early on March 15, Shimizu called the head of NISA and other officials and said, "The situation at the No. 2 reactor is very severe and if the situation should worsen, I feel pulling out the workers is also possible."

Shimizu never clearly said that the workers needed to control the plant would remain, as that was taken as a natural precondition, according to the government committee.

Meanwhile, Cabinet ministers began considering from early on March 15 what to do in the event TEPCO pulled its workers out. While the government panel said Shimizu might not have been clear in his instructions, it never went to the extent of saying he asked to evacuate all workers.

On the other hand, the private-sector panel took the position that there was the possibility that Shimizu made the request to pull out all workers.

One point the panel used to back that view is the phone calls Shimizu made to Kaieda and Yukio Edano, the then chief Cabinet secretary.

Kaieda was asked about the possibility of evacuating workers from the Fukushima No. 1 nuclear plant to the Fukushima No. 2 nuclear plant because of the increased possibility for an explosion at the No. 2 reactor.

Kaieda rejected that request because he felt it was a proposal to pull out all workers. Shimizu made a similar call to Edano and when he hesitated, the TEPCO president said, "The on-site situation cannot be maintained much longer."

The private-sector panel also pointed to the failure of TEPCO to clearly state how many workers would be needed to remain at the plant. It also referred to the government panel's report that stated that many government officials took the TEPCO request to mean it wanted all workers pulled out and stated that there was insufficient support for TEPCO's argument that its request was made on the precondition that necessary workers would remain at the plant.

The panel also said Kan's strong demand of TEPCO officials to keep workers at the plant was effective in pressing the utility to remain at the plant.

Mistakes in coolings operations?
The focus of the investigative committees when they examined the response to the nuclear accident was the cooling operations for the No. 1 and No. 3 reactors. The government panel pointed out problems in what plant workers did as well as in the transmission of information.

The panel pointed to the delay among plant workers and officials as well as those at TEPCO headquarters in realizing that the isolation condensers (IC) in the No. 1 reactor had stopped functioning shortly after the plant was inundated by the tsunami. That oversight led to a delay in implementing alternative cooling measures and might have worsened the situation, according to the government panel.

An IC works by cooling steam from the reactor core by passing it through piping in a tank filled with water. The steam is reverted to water and pumped back into the core. When its power source is lost, separation valves in the piping automatically close to prevent radioactive materials from leaking into the atmosphere.

Although the ICs automatically began operating immediately after the earthquake struck, the valves shut when the mechanism lost all sources of power slightly past 3:30 p.m. on March 11 after the tsunami struck. Plant workers did not realize the valves were shut until about three hours after the ICs stopped working.

According to those individuals in the plant who responded to the accident, there was no one who had experience operating the ICs either during training exercises or inspections. Workers only had word-of-mouth information from those who had such experience.

The government panel's interim report pointed out, "That was extremely inappropriate for an operator of a nuclear power plant." The TEPCO panel did not find any human error in the handling of the cooling mechanisms.

Regarding the ICs for the No. 1 reactor, they automatically began operating after pressure in the reactor core increased at 2:52 p.m. on March 11, soon after the quake struck. However, because the pressure then decreased rapidly, a worker closed the valves and stopped the ICs 10 minutes after they began operating to avoid damage to the core. The utility's panel said that response was according to company manuals.

The panel also concluded that even if the ICs had not been stopped it would not have led to a statistically significant difference in the resulting situation in the core.

The private-sector panel pointed to the failure of plant workers to quickly pass on their concerns about the shutting of the separation valves in the ICs to those in charge of dealing with the accident at the plant.

There were also differences among the three committees in their interpretations of the cooling of the No. 3 reactor.

Early on March 13, a plant worker manually stopped the high pressure coolant injection (HPCI) system to avoid damage to the core. However, a report of that stoppage to plant officials and TEPCO headquarters was delayed by more than an hour. Alternative methods to pump in water to the core were also unsuccessful. Because the HPCI was not restarted, no water was pumped in for about seven hours and that could have led to further damage to the core.

The government panel said preparations should have been started for alternative cooling measures since the HPCI was only a stopgap measure. That failure along with the delay in sharing information was criticized by the government panel.

The HPCI operates on batteries and can pump in a large volume of water in a short time. It could have been used in the No. 3 reactor since the batteries were not flooded by the tsunami.

Although the TEPCO panel did not initially cover the HPCI in its interim report, TEPCO later compiled the results of an additional investigation. The later report said a plant worker manually stopped the HPCI due to concerns about equipment malfunctions. It also said plant officials shared in the strategy for alternative cooling once the HPCI was stopped.

The government panel did not recognize such sharing of information. It pointed out that if alternative cooling measures had been implemented earlier there was the possibility that damage to the core could have been reduced and the volume of radioactive materials spewed into the atmosphere could have been decreased.

What happened at the no. 2 reactor?
One point that none of the investigative committees has uncovered is the extent of damage to the No. 2 reactor. At a little after 6 a.m. on March 15, a number of workers at the Fukushima No. 1 plant heard the sound of a large impact.

At 6:18 a.m., during a teleconference with TEPCO headquarters, a plant official said that the sound might have been caused by the bottom of the suppression chamber of the No. 2 reactor falling.

At 6:50 a.m., a radiation level of 583 microsieverts per hour was recorded at the main gate to the plant about one kilometer from the No. 2 reactor building. That reading was about eight times the level recorded an hour earlier. At 9 a.m., a radiation level of 11,930 microsieverts was recorded, the highest for the entire accident.

The government panel report said, "(Fukushima plant chief) Yoshida felt some sort of explosion occurred in the containment vessel based on information received that a large impact was heard as well as information that the pressure in the suppression chamber of the No. 2 reactor was zero."

However, the TEPCO panel included an analysis of readings from seismographs at the Fukushima No. 1 plant. There were no observations of shaking caused by an explosion between 6 a.m. and 6:10 a.m. when the sound of an impact was heard at the No. 2 reactor. Shaking was recorded at 6:12 a.m. when an explosion likely occurred at the No. 4 reactor, according to the TEPCO panel.

The government panel also said the impact sound was likely caused by the explosion at the No. 4 reactor. The private-sector panel also rejected the notion that an explosion occurred at the No. 2 reactor.

The panels also could not explain what caused the high radiation levels. Although an explosion occurred at the No. 4 reactor, there were no fuel rods in the core because the reactor was undergoing periodic inspection. There was also no noticeable damage to the fuel in the storage pools.

The extent of damage to the containment vessel of the No. 2 reactor is unknown. Once that becomes clear it could be possible to point to the No. 2 reactor as the cause of the high radiation levels.

TEPCO used an industrial endoscope on March 26 to check the interior of the reactor. The water level was only about 60 centimeters from the bottom of the containment vessel, much lower than estimated. Water pumped into the reactor more than likely has leaked from damaged parts of the core. However, none of the panels have yet explained how that damage occurred.

(By Naoya Kon and Takashi Sugimoto, The Asahi Shimbun, 01/05/2012)