Translated by: Ivayla Veleva
Published On: 23/08/2021

More than a decade after the closure of the Mihama NPP, the plant’s third reactor was officially restarted on Wednesday, 10 a.m., June 23, 2021.


The plant is located two hours from the major southern cities of Osaka and Kyoto and is operated by Kansai Electronic Power.


This is the oldest reactor (1976), which was put into operation after the catastrophic accident in Fukushima. Energy experts warn that history could repeat itself, and locals are also worried. In comparison, the Fukushima nuclear power plant was put into operation in 1971, and its reactors were 40 years old at the time of the collapse on March 11, 2011, when under the influence of unforeseen natural disasters, the plant crashed and caused death. to nearly 20,000 people in northeastern Japan.


Mihama’s owners have managed to extend the life of the reactor by investing 165 billion yen ($ 1.51 billion) in repairing infrastructure, electronics, replacing cables and gaskets according to the latest post-disaster safety standards (Fukushima), which are resistant to high temperature in case of accident and fire. By law, 40-year-old reactors can be upgraded and, if approved by a commission, run for an additional 20 years. The reactors in Mihama have been closed for more than a decade, and now the life of the reactor will be extended until 2036.


Speaking to Reuters, Tatsujiro Suzuki, a former deputy chairman of the Japanese government’s Atomic Energy Commission, said he had doubts about the approval process for restarting the Kansai reactor.


“The industry and the government do not seem to have learned anything from Fukushima,” said Suzuki, who is currently an adviser to the parliamentary nuclear safety committee.


Suzuki cited a 2019 scandal that revealed that Kansai Electronic executives were pocketing more than $ 3.2 million in gifts from city officials who host the company’s nuclear power plants.


“They haven’t changed despite the scandal, that’s my impression,” Suzuki told Reuters.


With the restart of this reactor, Japan has a total of ten operating nuclear reactors with a total capacity of 7,886 MW.


The 2004 incident was not the first to hit the plant, but before what happened in Fukushima in 2011, it was considered the worst in Japan. The first incident occurred on February 9, 1991, when the plant’s second reactor failed due to an improperly installed part designed to protect the cooling pipe from excessive vibration. As a result of this error, the pipe is sprayed due to the friction created and insignificant amounts of radiation are released into nature. While no one was injured in the first incident, the same is not true for the second. All eleven people who were in the turbine hall at the time were seriously injured. Some of them get severe burns on the body as a result of direct contact with the steam, while others inhale it and this severely damages their lungs. One of the victims died at the hospital with over 80% burns on her body. There were a total of five deaths.

The cause of this incident was the sudden bursting of a pipe carrying water under pressure to the secondary circuit of the power plant after it passed through the turbine and the heat exchanger and before it returned to the steam generator (see photos and circuit diagram below). The pipe bursts suddenly, releasing a huge amount of pressurized steam into the room in seconds.


When the reactor was operating at full capacity, this steam would be at a temperature of 195 ° C, at a pressure of 12.7 atmospheres (about 180 psi); we were told that at the time of the incident the temperature was 140 ° C and the pressure 9 atmospheres, but this information has not been confirmed.


The pipe in question is made of black steel, which corrodes easily and would now be replaced by steel. The real problem was in the thickness of its wall, which was originally 10 mm, and in order to work safely it was necessary not to thin more than 4.7 mm; but, as can be seen from the photos, it is completely eroded and 1.4 to 1.5 mm thick. In order to reach such a disastrous situation, a mistake was made either at the engineering design stage, where the corrosion phenomenon was underestimated or neglected (similar pipes in newer nuclear power plants are now made of stainless steel and not black steel); or in a routine check. Periodic inspections performed properly using ultrasonic instruments, which are widely used at the moment, would reveal the weakened condition of this tube. Major inspections of nuclear power plants are usually carried out every 10 years. This means that for the 28-year period of activity, until the time of the accident, the reactors had to be subject to at least two major inspections. According to unconfirmed data, this pipe has not been inspected once since the reactor was put into operation.


During a press conference in Mihama after the 2004 incident, Koji Ebisuzaki, director of quality control, said “We are responsible” Haruo Nakano, a spokesman for KEPCO, the company that owns and operates the plant, said: “We have made visual checks but we have never used ultrasound. “Although ultrasonic inspections of this type of equipment were not mandatory, they are the only way to detect internal corrosion.


The basic principles of nuclear safety nevertheless played their role effectively to prevent a major accident: level and backup safety systems installed at different levels shut down the reactor automatically and immediately, without any other incidents, despite the extremely rare nature of the event and the severity of the situation.


No radioactivity was released into the environment during the 2004 incident. It was not nuclear, but industrial – it could happen in any power plant, whether it was nuclear energy or burning fossil fuels.


So far, nine appeals from Fukui, Shiga and Kyoto prefectures have been filed in Osaka Municipal Court against the reopening of the third reactor at the Mihama NPP. Civic consciousness has the power to demand control, but this can only be done through purposeful and concrete actions. We can only hope that large corporations will not gamble with the lives of their workers and the local population because the consequences of careless management of such massive power plants could have potentially catastrophic consequences.

Translation and proofreading made possible with the volunteer help of Maia Cygielska.