The Nuclear Regulation Authority has adopted a draft certification that the No. 1 and No. 2 reactors at Kansai Electric Power Co.’s Takahama nuclear power plant in Fukui Prefecture meet the post-Fukushima nuclear safety standards — effectively giving its basic safety clearance for reactors that have already passed the legal threshold of 40 years in operation. Pending additional procedures, the two reactors may become the first to have their operation extended beyond the 40-year limit set after the 2011 disaster at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear power plant. The NRA’s decision risks undermining the rule that reactors, in principle, be decommissioned after they have been in operation for 40 years.

The law regulating nuclear reactors was revised in 2012 — under the previous Democratic Party of Japan-led government — to establish the rule prohibiting reactors from being operated for more than 40 years. But it also allowed a one-off extension of up to 20 more years upon receiving a safety clearance from the NRA, which the following year put into force more stringent safety standards on nuclear power plants.

The rule set a grace period for power firms to get the NRA’s nod for the extension — up to this July for the two aging Takahama reactors. Eleven reactors — five that have passed or were nearing the 40-year period, along with the six at Tepco’s Fukushima No. 1 plant — have since been decommissioned.

True, the 40-year rule is not based on objective scientific grounds that prove or disprove the safety of reactors after a certain period in operation. But it must not be forgotten that the rule was introduced from the standpoint of ensuring safety in view of the following fact: if the inside of a reactor’s pressure vessel, which is made of steel, is irradiated by neutrons for a long time, its resistance to destruction weakens as its viscosity lowers. The 40-year rule should be upheld as a reasonable criteria that uses prudence on the safe side. The one-off extension for up to 20 years was allowed in view of overseas trends, in particular practices in the United States. But the government at the time of the rule’s introduction was saying an extension of a reactor’s operation beyond 40 years should be “the rarest of exceptions.”

What NRA chief Shunichi Tanaka said in adopting the draft certification for the Takahama reactors — that power companies can overcome the technical problems of aging reactors by spending money on renovating their facilities — can have the effect of turning an extension of the life of reactors beyond 40 years into a normalcy, rather than an exception. Even though the Abe administration has reversed the DPJ-led government’s policy of seeking a phaseout of nuclear power by the 2030s, it has not revised the 2012 legal provision and the 40-year rule remains in place.

The administration of Prime Minister Shinzo Abe, which seeks to reactivate idled nuclear power plants once they have cleared the NRA’s screening, also says the government will aim to reduce the nation’s reliance on nuclear power “as much as possible” through energy conservation, introduction of more renewable energy sources and greater efficiency of thermal power plants. But the administration’s energy mix outlook — which estimates the share of nuclear power in the nation’s electricity generation at 20 to 22 percent in fiscal 2030 — assumes that several reactors will be operated beyond the 40-year limit. Since construction of new nuclear power plants will remain effectively difficult given post-Fukushima public sentiment, the share of nuclear power in fiscal 2030 will likely be around 15 percent at most if all existing reactors have been reactivated — unless some aging reactors are run for more than 40 years.

In March last year, Kansai Electric asked the NRA to screen not only the two Takahama reactors but also the No. 3 reactor at its Mihama plant, also in Fukui Prefecture, for operation beyond the 40-year limit. The Mihama reactor will reach the 40-year limit this December. These reactors represent three of the five Kansai Electric reactors that are more than 30 years old. The utility has reasons to seek extension of the life of its aging reactors. Highly dependent on nuclear power before the 2011 Fukushima disaster, the company’s finances have been severely strained by the cost of imported fuel to run its thermal power plants to make up for the shutdown of its nuclear power plants.

To get permission for extending the operation of the aging Takahama reactors, Kansai Electric will need to reinforce them by upgrading 1,300 km of cables (either replacing them with ones made of new materials or covering old cables with fire-proof sheets), building a concrete dome above the pressure vessels and constructing an emergency commanding center and a seismic isolation building, among others. But the pressure vessels, which may have suffered embrittlement due to bombardment by neutrons, cannot be reinforced or replaced.

The NRA’s Tanaka noted that Kansai Electric will be spending roughly half of expense of building a new reactor on renovating the two aging reactors. Completion of the renovation work, estimated to cost some ¥200 billion, is expected to take more than three years even if the NRA’s nod is given by July. Kansai Electric apparently thinks that the expense still makes business sense — since restarting the two reactors at Takahama, which have higher output capacity than other aging reactors that have been decommissioned, are expected to improve its earnings by ¥9 billion each month.

Japan currently has 43 nuclear power reactors — 18 of which are more than 30 years old. If the 40-year rule is strictly applied, their number will gradually decline. This conforms not only to the government’s policy of reducing Japan’s reliance on nuclear power but also to the popular wishes as expressed in media opinion polls, in many of which a majority of respondents oppose the restart of idled reactors and want nuclear power to account for less of the nation’s electricity supply than envisaged by the government. The NRA should uphold the 40-year rule to cut the weight of nuclear power as well as to ensure safety of reactors.

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