The Great East Japan Earthquake and tsunami that occurred five months ago and the ensuing nuclear crisis have reminded the public that natural disasters are unpredictable and that an accident at a nuclear power station could cause irreparable damage to extensive areas.
Risks of serious accidents at nuclear power plants cannot be overlooked in quake-prone Japan. We have proposed that an order of priority for shutting down nuclear plants be set based on their danger, and that the number of such power stations be gradually decreased.
To do so, it is necessary to closely assess the risks of each nuclear power plant.
The massive tsunami generated by the March 11 quake triggered a serious crisis at the Fukushima No. 1 Nuclear Power Plant run by Tokyo Electric Power Co. It is necessary to verify how far human factors — such as the insufficiency of the plant’s preparedness for a serious disaster and a delay in the plant operator’s initial response to the disaster — contributed to the nuclear crisis. Still, it must be kept in mind that all nuclear power plants in Japan are at risk of being badly damaged by earthquakes and tsunami.
Chubu Electric Power Co. has shut down its Hamaoka Nuclear Power Plant in Shizuoka Prefecture, as we had called for, at the strong urging of the central government. The utility and the government should further consider dismantling the plant in view of the inability to predict how much damage will be caused by an earthquake in the Tokai region, which is feared to devastate central Japan.
Numerous members of the public are worried about risks involving aging nuclear reactors. The service life of nuclear reactors is not covered by domestic law. Nuclear reactors must be evaluated after 30 years of operation to see if they have passed their service life, but they often continue to be used for another decade or two. The reasons behind such service life extensions are difficulties in finding locations to build new nuclear plants and power suppliers’ attempts to lessen their financial burdens.
However, there are serious problems involving such aging nuclear power plants. Newly developed technology can hardly be utilized to solve safety problems involving the design of aging reactors and entire nuclear power plants. The age-related degradation involving buildings housing such complexes is feared to be overlooked.
Fukushima plant’s No. 1 to 4 reactors, which had been in operation for 33 to 40 years, are Mark I reactors that U.S.-based General Electric developed in the 1960s. Risks involving Mark I reactors have been pointed out even in the United States.
The ongoing crisis at the Fukushima No. 1 plant may be attributable to its old design. Its key devices were situated in locations where they could be easily hit by tsunami and there were reportedly problems involving the venting of the reactors.
Of the 54 nuclear reactors across the country, 16 have been in operation for between 30 and 39 years and three have been in operation for 40 or more years. Aging reactors, particularly those that have been in use for at least 40 years, should be shut down and dismantled. Furthermore, whether to dismantle those that have been operated for more than 30 years and less than 40 years should be determined after examining whether their condition has deteriorated because of age.
Even keeping the risks of large earthquakes in mind, we have pointed out that it is unrealistic to immediately shut down all existing nuclear power plants.
Still, it is highly questionable to continue the construction of nuclear power plants that are already under way. The construction work should be suspended to assess the risks. The planned construction of new nuclear power plants should be frozen and whether to go ahead with the construction should depend on an overall nuclear power policy that the government will work out.
In conducting assessments of nuclear power plants, risks must not be deliberately underestimated in order to give the green light to their operations. Instead, the government and power suppliers must judge whether to approve operations at such power stations strictly based on the results of their risk assessments.
The ongoing Fukushima nuclear crisis has also uncovered risks involving spent nuclear fuel pools that have no protection barriers. Thorough safety measures must be taken to ensure the safety of such pools.
As the core of its nuclear power policy, Japan has promoted the nuclear fuel cycle program — in which plutonium is extracted from spent nuclear fuel and used in fast-breeder nuclear reactors.
However, serious doubts have been raised over the feasibility and safety of nuclear fuel cycle systems since long before the Fukushima crisis. Prospects for operations at the nuclear fuel reprocessing plant in Rokkasho, Aomori Prefecture, and the “Monju” prototype fast-breeder nuclear reactor in Tsuruga, Fukui Prefecture — the two key facilities in the program — remain unclear because of repeated technical problems.
The reprocessing plant was originally scheduled to be completed in 1997, but its completion has already been postponed 18 times, and costs for its construction have increased nearly three-fold. The Monju reactor was shut down because of a blaze that occurred immediately after the start of its operations. It developed trouble again immediately after the resumption of its operations last year — 14 1/2 years after the fire. The schedule to put fast-breeder nuclear reactors into commercial use has been delayed whenever a plan is announced. The feasibility of these reactors is highly doubtful.
Last month, the government announced its policy of decreasing Japan’s reliance on nuclear power plants for domestic electric power. In view of this new policy, the government should quickly abandon its nuclear fuel cycle program. Funds set aside for the program should rather be used for efforts to bring the Fukushima No. 1 plant under control.
Nuclear fuel spent at nuclear power stations should be disposed of without being reused. Regardless of whether it is reprocessed, it is difficult to find a final disposal site. Still, if the number of nuclear plants decreases, the accumulation of spent fuel will also slow down.
Even if Japan abandons nuclear fuel cycle systems, the amount of plutonium reprocessed both domestically and overseas is estimated to surpass 40 metric tons. Measures to process such a massive volume of plutonium should be worked out at an early date from the viewpoint of nuclear non-proliferation.
Many experts have expressed grave concern that expertise will be lost if Japan decreases its dependence on nuclear power stations and abandons its nuclear fuel cycle program. It is necessary to develop and secure a certain number of experts if Japan seeks to safely and efficiently dismantle nuclear reactors while continuing to operate a certain number of nuclear power plants for now.
For example, how about setting up a research base in Fukushima to develop technology for ensuring nuclear power safety, dismantling reactors, radiation management and decontaminating radioactive substances, and attracting experts from all over the world to the facility? Knowledge and technology developed there should be fully used on a global scale.
The importance of technology for the safe management of nuclear reactors and dismantling reactors will increase globally. It is the responsibility of Japan, which caused the nuclear accident, to make effective use of its experience from the crisis.