“While I was with Tokyo Electric Power Co. (Tepco), a question was raised internally as to whether or not the measuring pipe installed at the Fukushima No. 1 nuclear power plant, the diameter of which is about the same as that of a human thumb, can withstand an earthquake. But Tepco has yet to make clear whether or not the March 2011 earthquake damaged that pipe,” says Toshio Kimura, a former Tepco plant engineer.
Kimura, 49, who served the company for 17 years from 1983 to 2000 and worked at Fukushima No. 1 for 12 years, is strongly of the view that pipes in the plant were damaged seriously by the quake before a subsequent tsunami struck the plant.
He thus casts doubt on Tepco’s position that the tsunami caused loss of all the power sources, thus leading to the disaster. He says, “An effective means of determining the true cause of the accident would have been to analyze recorded data related to transient phenomena — data that show what happened near the reactor cores. Even though more than two years have passed since the disaster, however, Tepco has only released partial data.
“So I demanded that Tepco release the relevant data. It made public the data on Aug. 19 for the first time.” But it was found later that the data did not represent the whole data.
In September, Kimura prepared a report titled “Leakage from the piping in the Fukushima No. 1 nuclear power plant caused by vibrations from the earthquake.”
The transient phenomena recorder records various measurements in a nuclear power plant at every one-hundredth of one second. It accumulates such data as a reactor’s output, pressure and temperature and coolant’s flowing volume. Analysis of these data makes it possible to accurately identify “process behaviors” or what is happening in an nuclear reactor.
Specifically the analysis clarifies the time sequences of a process like, for example, a pump having stopped first, causing a coolant flow to decline, then lowering the water level and raising the reactor core temperature.
For Kimura, Tepco’s failure to release these data for such a long time looked only too unnatural.
In analyzing the data, Kimura took special note of the fact that natural circulation of coolant stopped. Along with an isolation condenser, natural circulation of coolant constitutes the “lifeline” in case loss of all the power sources occurs. Even if a primary loop recirculation pump, which pumps coolant water into the reactor core, stops functioning due to loss of all the power sources, natural circulation of coolant is supposed to maintain 10 percent of normal core flow of coolant.
Analysis of the data showed, however, that immediately after the earthquake hit, about 30 percent of coolant inside the core started flowing backwards and that after the coolant flow returned to the normal flow direction, the core flow fluctuated and eventually became less than zero. All these occurred before the nuclear power plant was struck by the tsunami.
Why is it that cooling by natural circulation of coolant became dysfunctional along with the isolation condenser right after the earthquake? Kimura believes that piping rupture was the very cause of the loss of these two “lifelines”
There are a couple of phenomena that seem to correspond to what Kimura believes happened. One is that a pump designed to draw up water from the bottom of the containment vessel seems to have been activated frequently, indicating that damage to piping caused coolant to leak and accumulate at the bottom of the vessel.
The other is that radioactive contamination was taking place at a much faster rate than was estimated by Tepco. A Tepco report said that the reactor water level reached the top of nuclear fuel approximately three hours after the earthquake, i.e., at around 5:46 p.m. (on March 11, 2011) and that radioactive vapor leakage from the containment vessel due to damage to the reactor core started afterward.
But the same report contained a contradictory statement that when a plant operator tried to enter into the reactor building at 5:19 p.m. on the same day, he had to give up because the dose of radioactivity was too high. This shows that the meltdown was taking place earlier than Tepco estimated. This corroborates Kimura’s inference that immediately after the earthquake, piping was damaged and coolant started leaking, thus rapidly lowering the reactor water level and igniting the meltdown.
Behind Tepco’s continued refusal to release all the data and to admit that the earthquake damaged the piping is a fear that serious doubts will arise about the safety of its Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture, which it hopes to restart as soon as possible. It has been known that at the time of the 2007 Chuetsu offshore earthquake, damage to piping due to the quake caused a fire at the nuclear power plant.
Niigata Gov. Hirohiko Izumida played a leading role in remedying the situation at the time. Because of this experience, he strongly demanded that Tepco construct pipes related to venting radioactive vapor underground to make it quake-proof.
Since the governor accepted Tepco’s proposal to build pipes for the second venting equipment underground in addition to the first venting equipment, whose pipes are built on the ground level, mass media reported that restart of the nuclear power plant is certain. But this is wrong. Izumida explained that Tepco’s proposal does not constitute a request for restart. The truth is that the hurdle for restart has been raised. The Niigata prefectural government has created a technical committee on nuclear plant safety. Among the subjects of discussion at the committee is “the impact of an earthquake on important equipment.”
If a theory that the earthquake damaged piping in the Fukushima No. 1 nuclear plant gains credibility during the discussions, Tepco will have to build underground pipes for the second venting equipment. This means that restart will be impossible until the completion of the quake-proof second venting equipment and that Tepco will have to push new measures to make the nuclear power plant quake-proof. Then financial institution may refuse to give new loans to Tepco or call on it to revise its management plan or resume discussions on resolution of Tepco. This is why Tepco will never accept the theory that the quake, not the tsunami, caused the Fukushima nuclear disaster.
Discussions at Niigata Prefecture’s technical committee on nuclear plant safety will have great impact on restart of not only the Kashiwazaki-Kariwa nuclear power plant but also other nuclear power plants in Japan. It likely will not be long before “lies” by Tepco are brought to light.
This is an abridged translation of an article from the November issue of Sentaku, a monthly magazine covering Japanese political, social and economic scenes.