The Foreign Ministry had simulated a possible attack on nuclear plants in 1984 that included a scenario in which all power sources were lost--as occurred at the Fukushima No. 1 nuclear plant--but chose to keep the results confidential, The Asahi Shimbun learned.
The Foreign Ministry had simulated a possible attack on nuclear plants in 1984 that included a scenario in which all power sources were lost--as occurred at the Fukushima No. 1 nuclear plant--but chose to keep the results confidential, The Asahi Shimbun learned.
If the ministry report had been shared with many officials in the government, it could have helped to raise attention to the need to prepare for a possible nuclear power station blackout.
The ongoing nuclear crisis was triggered by a complete loss of the electricity grid, emergency diesel generators and depletion of backup batteries in the March 11 Great East Japan Earthquake and tsunami. Pumps for cooling water were also broken down in the disaster.
The report on the study of possible attacks on nuclear facilities and projected damages, compiled in February 1984, was obtained by The Asahi Shimbun.
It is the first of its kind known to have been compiled by the government. The report's first scenario anticipated that a complete loss of power sources would lead to a situation where damaged fuel rods would fall to the bottom of the containment vessel, breaching the vessel. That would result in the leakage of radioactive materials into the atmosphere. The report also projected that a hydrogen explosion would likely be triggered.
This is precisely what occurred in the No. 1 and No. 3 reactors at the Fukushima No. 1 nuclear plant.
The station blackout scenario came to be discussed in the 1990s and later in Japan. But no adequate measures were taken to address the possibility.
Tetsuya Endo, who was involved in the compilation of the report as an official at the ministry's division handling affairs related to the United Nations, said the report was designed to be just a reference for the ministry.
"No measures were taken for nuclear facilities" to improve safeguards, Endo said.
The report projected up to 18,000 deaths from acute radiation exposure in an attack on a nuclear reactor that damages the containment vessel and the cooling system, resulting in a meltdown and immediate release of radioactive materials into the air.
But the ministry decided not to disclose results of the study, even to the prime minister's office, fearing it could inflame the anti-nuclear power movement.
The United States and European countries carry out contingency drills based on studies simulating terror attacks on nuclear power plants.
The ministry commissioned the study to the Japan Institute of International Studies, a private organization, after the global community was shaken by Israel's bombing of a research nuclear facility in Iraq in 1981.
The attack did not lead to a leak of radioactive materials because the nuclear reactor was under construction at the time.
Japan at that time had 20 nuclear reactors operating.
Under the study, three scenarios were explored: 1) a complete loss of power from the grid and from backup diesel generators; 2) a complete loss of power and ability to cool a reactor after an attack by a powerful bomb that destroyed a containment vessel; 3) destruction of not only the containment vessel but also the pressure vessel in an attack by a guided bomb with extremely high targeting accuracy.
The scenarios did not envisage any specific nuclear power plants in Japan.
In the second scenario, the study set the amount of leaked radioactive materials at more than 100 times the figure in the accident at the Fukushima No. 1 nuclear power plant to project the number of deaths and injuries.
These numbers were arrived at under various weather conditions based on the 1982 U.S. technical guide for development of reactor site criteria, which assessed the safety of a nuclear reactor.
The U.S. document was used because the distribution of the population given in the report was similar to Japanese communities hosting nuclear plants.
The Japanese report concluded that under the second scenario, up to 18,000 people could be killed unless people evacuated immediately, and the average death toll would be about 3,600.
It also projected that on average, a radius of 30 kilometers would be rendered uninhabitable. In the worst-case scenario, a radius of 87 km would have to be abandoned.
For the third scenario, the report stated that (the situation) "would likely be harsher."
However, the report on the country's study of possible attack on a nuclear plant was never made public.
An official at the ministry's disarmament division who was in charge of the report stated in the report that the document was for internal use only, given the possible "impact on the anti-nuclear power movement."
The ministry made 50 copies of the report for its officials.
Copies were never submitted to the prime minister's office and the Japan Atomic Energy Commission, a panel tasked to formulate Japan's policy of research, development and use of nuclear power and established under the Cabinet Office.
An official at the ministry's Arms Control and Disarmament Division admitted the existence of the study, but added that few details are available.
"I have no knowledge of circumstances at that time since related documents are no longer kept," the official said.
Hisashi Ninokata, professor of reactor engineering at Tokyo Institute of Technology, said that an attack against a nuclear reactor should be acknowledged as an inherent risk to the safety of the facility.
"Many researchers, worrying about reinvigorating anti-nuclear power movement, argued that a severe accident resulting from a terror attack would be unlikely in Japan," he said. "But the government should explain the danger and safeguard measures to the public by admitting that an attack (on a nuclear reactor) is a risk involved."
(This article was written by Takuya Suzuki, Kyohei Matsuda, Eisuke Sasaki and Kazuo Yamagishi.)