Tokyo Electric Power Co. (Tepco), the operator of the stricken Fukushima No. 1 Nuclear Power Station, has been insisting that the culprit that caused the nuclear crisis was the huge tsunami that hit the plant after the March 11 earthquake. But evidence is mounting that the meltdown at the nuclear power plant was actually caused by the earthquake itself.
According to a science journalist well versed in the matter, Tepco is afraid that if the earthquake were to be determined as the direct cause of the accident, the government would have to review its quake-resistance standards completely, which in turn would delay by years the resumption of the operation of existing nuclear power stations that are suspended currently due to regular inspections.
The journalist is Mitsuhiko Tanaka, formerly with Babcock-Hitachi K.K. as an engineer responsible for designing the pressure vessel for the No. 4 reactor at the ill-fated Fukushima nuclear plant.
He says if the earthquake caused the damage to the plumbing, leading to a “loss-of-coolant accident (LOCA)” in which vaporized coolant gushed into the containment building from the damaged piping, an entirely new problem — “vulnerability to earthquake resistance of the nuclear reactor’s core structure” — would surface and that this will require a total review of the government’s safety standards for nuclear power plants in Japan, which is quite frequently hit by earthquakes.
Such a review will require a number of years of study, making it impossible to restart the now suspended nuclear power stations next year as Tepco hopes.
What puzzles Tanaka most is why the emergency condensers, which turn vaporized coolant (steam) into water and are supposed to lower both the pressure and temperature of the reactor, were not operating at the time of the accident although the condensers have the capability of functioning even when electricity becomes unavailable.
It is highly probable, he says, that the plumbing linked with the condensers was damaged by the earthquake, causing water or vapor to leak out, thus leading to the nonfunctioning of the condensers.
In a report released on May 23, Tepco said it stopped the emergency condensers after the quake occurred but before the tsunami hit the plant so that the temperature of the pressure vessel would not change by more than 55 degrees Celsius per hour. This, it said, was strictly in accordance with the instructions contained in the operating manual.
When a Diet committee looking into the incident asked Tepco to submit a copy of the manual, most pages of the documents so submitted were “blacked out,” as the company alleged they contained trade secrets which it did not want to go into the public domain.
Totally dissatisfied, the committee issued another order to Tepco to submit the whole manual in its original form, to which the company complied on Oct. 24. This led journalist Tanaka to come to the conclusion that the utility was not telling the truth.
He said the 55-C-per-hour is a figure used in ordinary plants in a non-emergency situation to keep piping in a good condition and that the figure should not be used in an emergency. He pointed out that the manual says that the figure is something that should be followed in operations just prior to a cold shutdown of a reactor, not immediately after a problem has arisen.
At a news conference on May 15, Tepco said that according to its simulation, the meltdown at the No. 1 reactor of the nuclear power plant happened about 15 hours after the earthquake because the tsunami destroyed all electricity supply sources and the water level in the reactor lowered rapidly. But Tanaka says that the simulation is far different from the actually measured water level and pressure.
A rapid increase in the pressure inside the containment vessel is especially unnatural. Although the simulation report says that the pressure inside the containment vessel shot up to more than seven times standard atmospheric pressure around 5:40 a.m. on March 12, or about 15 hours after the quake, the fact is that the pressure had already risen to six times the standard at 12:12 a.m. on March 12 — five to six hours before the time given by the simulation report.
Simulation data calculated by a computer can be manipulated easily depending on the types of input. Tanaka suspects that Tepco cooked up simulation results to suit its own purposes in an attempt to deceive the public.
Atsuo Watanabe, former designer of containment vessels at Toshiba Corp., said on Oct. 26 that the most fundamental cause of the Fukushima plant fiasco probably lay in the blind acceptance of the safety standards adopted in the United States, which did not take into consideration all potential consequences from earthquakes.
The reactors damaged at Fukushima were of the GE Mark 1 type designed and built by General Electric Co. He pointed out that in the U.S., there is no need to consider the combination of an earthquake and a loss-of-coolant accident caused by broken piping, adding that it is reasonable to assume that the earthquake and loss of coolant occurred simultaneously at Fukushima No. 1.
Perhaps it was against such a background that Tepco blacked out crucial matters in the operational manual of the reactors, as there are 10 other GE Mark 1 type reactors in Japan.
These and other scientific findings have given rise to serious suspicion of Tepco’s claim that the crisis at the nuclear power plant was caused by the tsunami, and not by the earthquake. And a view that blames the tremor as the true culprit is becoming more and more trusted.
It is imperative that the special investigative committee recently created within the Diet undertake thorough inquiry into the real cause of the accidents. The panel must force those Tepco employees who have worked on the spot to testify, even though the company has so far obstinately opposed such testimonies.
Should the government decide to permit the resumption of nuclear power stations in various parts of the country by blindly accepting assertions coming from Tepco, the whole nation would face uneasiness in preventing another calamity in the future and would fail to fulfill its accountability to the whole world, which is watching whether Japan will conduct a thorough investigation to determine the true cause of the Fukushima disaster.
This is an abridged translation of an article from the December issue of Sentaku, a monthly magazine covering Japan’s political, social and economic scenes.