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原子力発電の2030/2040年度の見通し、シナリオ別に見る現実性

Japan’s official nuclear targets for 2030 and 2040 can be met only under an extreme maximum scenario that assumes an implausibly broad restart and prolonged operation of reactors, leaving renewables as the realistic path for securing decarbonized electricity.

Renewable Energy Institute · 14 March 2025 · read the original in Japanese →

On February 18, 2025, the Japanese government indicated the direction of its future energy policy in the Seventh Basic Energy Plan, approved by the Cabinet. In the previous, sixth plan, it had pledged to reduce dependence on nuclear power as far as possible; in the seventh, it reversed course and declared that nuclear power would be used to the fullest extent. Despite the difference in wording, both plans assign too large a share to nuclear power. The sixth plan set a target of 20 to 22 percent in fiscal 2030; the seventh sets a target of 20 percent in fiscal 2040. The purpose of this column is to show whether that assumption is realistic.

To forecast the future of nuclear power generation in Japan, I analyzed four scenarios, “low,” “middle,” “high,” and “maximum,” based on the latest status of reactors around the country. The result makes clear that the national targets for fiscal 2030 and fiscal 2040 can be realized only under the ultimate “maximum” scenario. Calculated under the reasonable “middle” scenario, nuclear power’s share of total national electricity generation remains at 12 percent in fiscal 2030 and 7 to 8 percent in fiscal 2040.

More than 60 percent of reactors are in no condition to operate.運転可能な状況にはない原子炉が6割以上

As of March 14, 2025, Japan had a total of 33 reactors, with installed capacity amounting to 33 GW (gigawatts, or one million kilowatts). If the three reactors now under construction are added, the total becomes 36 reactors with 37 GW of installed capacity (Figure 1). In addition, 26 reactors have already been decommissioned.

Figure 1: Status of Japan’s reactors (as of March 14, 2025).図1：日本の原子炉の状況（2025年3月14日時点）

Of the 33 existing reactors, 14, with 13 GW of capacity, have been restarted. All are reactors that conform to the new regulatory standards for safety established in response to the March 2011 accident at the Fukushima Daiichi Nuclear Power Station. Half of these 14 reactors, seven in all, have been approved to operate beyond 40 years. The oldest among them is Unit 1 at the Takahama Power Station, with installed capacity of 826 MW (megawatts, or one thousand kilowatts), which has now been in operation for more than 50 years.

Three of the existing reactors, with 4 GW of capacity, have received approval to restart but have not in fact restarted. They are Units 6 and 7 at the Kashiwazaki-Kariwa Nuclear Power Station, each 1,356 MW, and Unit 2 at the Tokai Power Station, 1,100 MW. The two Kashiwazaki-Kariwa units face local opposition, and completion of their counterterrorism facilities, formally facilities for responding to specified serious accidents and other events, is expected to be delayed until August 2029 for Unit 7 and September 2031 for Unit 6. Tokai Unit 2 is scheduled to complete safety measures under the new regulatory standards in December 2026.

Another eight reactors, with 8 GW of capacity, have applications pending for restart. Units 2 at the Shika Nuclear Power Station, 1,206 MW, and Tsuruga Power Station, 1,160 MW, however, face serious difficulties. On January 1, 2024, the Noto Peninsula earthquake struck the Shika Nuclear Power Station. It is expected to take several years before the effects of the seismic zone can be assessed. Tsuruga Unit 2, meanwhile, received a disposition of non-approval from the Nuclear Regulation Authority on November 13, 2024, denying restart because an active fault lies directly beneath it.

The remaining eight existing reactors, with 8 GW of capacity, have not applied for conformity review under the new regulatory standards, even though more than ten years have passed since they ceased operation. Restarting these eight reactors is an extremely difficult prospect. In particular, at least one of Kashiwazaki-Kariwa Units 1 through 5, each 1,100 MW, is required to be decommissioned if Units 6 and 7 are restarted.

As for reactors under construction, the Oma Nuclear Power Station, 1,383 MW, and Unit 3 at the Shimane Nuclear Power Station, 1,373 MW, have already applied for conformity review under the new regulatory standards and could begin operating around fiscal 2030. Construction of Unit 1 at Tokyo Electric Power Company Holdings’ Higashidori Nuclear Power Station remains postponed indefinitely. Because foundation work has not begun on the concrete portion beneath the containment vessel, the base mat, the International Atomic Energy Agency does not regard this reactor as being under construction.

Analysis under four scenarios that assume uncertain conditions.不確実な状況を想定した4つのシナリオで分析

To forecast the future of nuclear power in Japan, it is necessary to formulate appropriate scenarios for reactors in a variety of circumstances. This column sets out four scenarios: “low,” “middle,” “high,” and “maximum.” The requirements for each scenario are shown in Table 1.

Table 1: Assumed scenarios and requirements for nuclear power generation in Japan.表1：日本の原子力発電の想定シナリオと要件

(2) On November 13, 2024, the Nuclear Regulation Authority issued a disposition of non-approval for the application concerning Tsuruga Unit 2.

(3) At least one of Kashiwazaki-Kariwa Units 1 through 5 is subject to decommissioning in connection with the restart of Units 6 and 7.

(4) Tokyo Electric Power Company’s Higashidori Unit 1 suspended construction work on March 11, 2011.

I will explain the important points regarding the scenarios above.

- Restart date (existing reactors): Based on the record of the 14 reactors that have restarted so far, approved reactors are assumed to restart three years after approval, and reactors with applications pending are assumed to restart six years after application. In the middle, high, and maximum scenarios, approved reactors and reactors with applications pending restart on April 1, 2030. In the maximum scenario, reactors that have not applied restart on April 1, 2040.

- Operating date (reactors under construction): Oma and Shimane Unit 3 may begin operating around fiscal 2030. In the high and maximum scenarios, they begin operating on April 1, 2030. In the maximum scenario, Tokyo Electric Power Company’s Higashidori Unit 1 begins operating on April 1, 2040.

- No new construction except reactors already under construction: Because new types of reactor, such as small modular reactors, have little record of construction or operation and no construction sites have been decided, the possibility that they can begin operation by fiscal 2040 is extremely small. No new construction is assumed under any of the scenarios.

- Reactor operating life and extensions: In Japan, a reactor operating license is for 40 years, with a further 20-year extension possible. In addition, when operation is suspended for a long period because of external factors, the period of suspension can be excluded. For example, a reactor that has been shut down for ten years because of earthquake effects or safety measures may be permitted to operate for a total of 70 years. Yet not a single reactor anywhere in the world has continued operating for 60 years. The longest is Unit 1 at Switzerland’s Beznau Power Station, 380 MW, which at present has operated for 55 years. Taking this point into account, the low and middle scenarios assume an operating life of 60 years, while the high and maximum scenarios add long suspension periods to those 60 years.

- Capacity factor: The capacity factor of restarted reactors, that is, the ratio of actual electricity generated to installed capacity multiplied by time, averaged 73.8 percent over the eight years from 2016 through 2023. The low scenario assumes 70 percent, the middle scenario 75 percent, and the high and maximum scenarios 80 percent.

Nuclear power generation is forecast to fall short of the government’s targets.原子力の発電電力量は政府の目標を下回る予測

On the basis of the four scenarios, I estimated the installed capacity of nuclear power generation from fiscal 2024 through fiscal 2050 (Figure 2). This column focuses on fiscal 2030 and fiscal 2040 and compares them with the government’s targets. The estimates from fiscal 2041 through fiscal 2050 are provided for reference.

Figure 2: Forecast of installed capacity for nuclear power generation in Japan.図2：日本の原子力発電の設備容量の予測

Looking more closely, under the low scenario capacity continues to decline from fiscal 2028 and reaches zero in fiscal 2045. Under the middle scenario, it is forecast to increase from 13 GW in fiscal 2024 to 17 GW in fiscal 2030. Once the 2030s begin, reactor operating lives expire one after another, and capacity falls to 13 GW by fiscal 2040.

Under the high scenario, installed capacity rises to 25 GW in fiscal 2030. This scenario assumes that a total of 25 reactors, including reactors that have not yet received approval for operating-life extensions, will continue operating beyond 60 years. It presupposes that not a single reactor will be decommissioned before fiscal 2045, and that all will continue to operate.

Under the maximum scenario, capacity increases to 28 GW in fiscal 2030 and to 36 GW in fiscal 2040. Even in this scenario, no reactor is decommissioned by the end of fiscal 2045.

On the basis of the forecasts above, I calculated nuclear power’s share of total national electricity generation (Figure 3). The Japanese government assumes total national electricity generation of 934 billion kWh (kilowatt-hours) in fiscal 2030 and 1.1 to 1.2 trillion kWh in fiscal 2040.

Figure 3: Share of nuclear power generation in Japan’s electricity mix.図3：日本の電源構成における原子力発電の比率

Except under the maximum scenario, the targets of 20 to 22 percent in fiscal 2030 and 20 percent in fiscal 2040 are not reached.

Even under the high scenario, in which 25 reactors operate at the elevated capacity factor of 80 percent, the fiscal 2030 target is missed, if only slightly. Even if each reactor continues operating for more than 60 years, the gap widens in fiscal 2040, falling 4 to 5 percentage points below the target.

Only the maximum scenario can achieve the fiscal 2040 target. It is a condition in which 32 of the 33 existing reactors are operating, excluding one of Kashiwazaki-Kariwa Units 1 through 5; all continue operating beyond 60 years; three newly built reactors also begin operation; and a total of 35 reactors operate at the elevated capacity factor of 80 percent. Such an assumption can fairly be said to be far removed from reality. It shows just how difficult achieving the government’s targets will be.

This result raises a major problem. If electricity generated from renewable energy does not exceed the government’s unambitious targets, 36 to 38 percent in fiscal 2030 and 40 to 50 percent in fiscal 2040, Japan will face a substantial shortage of decarbonized electricity.

In a situation where nuclear power generation is not expanding as expected, renewable energy still has ample room to grow. By revising its targets for the future electricity mix, the government can make the fullest possible use of renewable energy’s potential.