Recommendations on Long-term Use of Nuclear Energy in a Carbon-Neutral Japan


Mitsubishi Research Institute, Inc.

Tokyo, November 10, 2022—Mitsubishi Research Institute, Inc. published the English version of its proposal for the long-term use of nuclear energy based on its own calculations and independent surveys. The recommendations are in light of the growing global trend toward achieving carbon neutrality and a renewed awareness of the importance of energy security. The recommendations are as follows:

Energy risks revealed around the world: accelerating the move toward decarbonization and energy security at the same time

About two years have passed since former Prime Minister Suga declared at the end of October 2020 that Japan would become carbon neutral by 2050, and in that time the global trend toward decarbonization has greatly accelerated. On the other hand, the invasion of Ukraine in February 2022 exposed the risk of dependence on authoritarian countries for energy, and achieving decarbonization and energy security simultaneously has become a trend in the energy sector. As an example of this balancing act, a decision was made in July to include nuclear and natural gas in the EU taxonomy1 , suggesting the importance of having a variety of options for energy sources. Countries are also reviewing their energy policies, including the United Kingdom and France, which plan to build more nuclear power plants, and Germany, which plans to return to coal-fired power plants and to maintain in reserve some of its nuclear power plants that were to be decommissioned at the end of this year.

On November 4, 2022, we published the English version of our Social and Economic Impacts of Carbon Neutrality in 2050 report. The report defined four scenarios for Japan’s future through 2050 and proposed the direction that measures should take to achieve a smooth transition to a decarbonized society. This report states the importance of making clear that nuclear power will play a role in Japan’s long-term energy strategy. It elaborates on the need for Japan to maintain its nuclear-power related technologies and human resources, and innovate in nuclear power itself. The report speaks to the potential for using nuclear power in harmony with the large-scale uptake of renewable energy.

1:The EU taxonomy is a classification system, establishing a list of environmentally sustainable economic activities.

Securing diverse power supply is key for Japan: government takes step to build new plants

In Japan, where energy self-sufficiency is only about 10%, energy security is an important issue that will determine the fate of the nation. The power supply capacity in the eastern Japan area was greatly reduced by the Fukushima earthquake in March 2022, and demand for electricity increased significantly at the end of June due to unusually hot weather—both resulted in tight electricity supply. In addition, the invasion of Ukraine accelerated the rise of resource prices and exposed the risk of procuring energy supplies on the assumption of good relations with other countries, underscoring the importance of securing anew a diverse supply capacity. Electric power systems need to be flexible enough to handle rare events such as earthquakes and extreme weather. Japan’s own power system, which has been reliant upon renewable energy and thermal power sources in recent years, could have been more responsive if nuclear power, which features a different set of characteristics, had been in operation too. In light of these circumstances, at the GX Implementation Council2 in August, Prime Minister Kishida ordered for studies to be undertaken, including on "…the development and construction of next-generation advanced reactors…"

2:A meeting chaired by the Prime Minister to consider measures necessary to implement the transformation of the entire economic and social system, namely, GX (Green Transformation), by shifting the fossil-fuel-centric economic, social, and industrial structure present since the Industrial Revolution to one that is clean-energy centric.

Nuclear energy is an effective option: maintaining the domestic economy and industry, achieving reliable carbon neutrality, and guaranteeing a stable energy supply

Amidst uncertainty in the overseas procurement of resources and technology, and lacking an international power grid, Japan needs an optimal mix of energy from diverse power sources. This will enable it to simultaneously achieve energy security, carbon neutrality, and 3E (energy security, environmental sustainability, and economic efficiency) while maintaining the domestic economy and industry without lowering the standard of living.

Japan is now at a crossroads as to whether to include nuclear power as an option in its future energy mix. Japan needs to make swift progress in many venues: the maximum introduction of renewable energy accompanied by the development of innovative technologies such as solar and wind power generation and storage batteries; energy saving and electrification on the demand side; decarbonization of thermal power such as fuel conversion to hydrogen and ammonia; CCS (carbon dioxide capture and storage); and DAC (direct air capture). Yet there are challenges and uncertainties in the implementation of each of these.

As a response to this uncertainty, the use of nuclear energy, which has a technical track record, does not emit carbon dioxide when generating electricity, and is regarded as quasi-domestic energy, is an effective option. The ideal way of using nuclear power should be clarified based on both the risks inherent in nuclear power that cannot be completely eliminated and the risks that could arise in the face of uncertainty surrounding carbon neutrality and energy security in the case that nuclear power is not used.

We propose the following plan for the long-term use of nuclear energy.

  • Short-term: restart existing nuclear power plants that meet regulatory standards to contribute to the stable supply of electricity
  • Medium-term: sustain use of nuclear power until 2050—the only practical solution
  • Long-term: re-examine policy on the use of nuclear power for 2050 onward based on the outlook around 2040 for alternative decarbonization technologies and security trends
  • Additional considerations: as a tangible option moving forward, nuclear innovation should be promoted to the same degree as other technologies like hydrogen, ammonia, and CCS

If the future of nuclear energy is left to ambiguity now, its technology, human resources, and supply chain will be weakened and difficult to sustain until 2050. Without action, we risk losing the promising option of nuclear energy altogether.

Maintaining a base that enables nuclear power to account for at least 10 - 15% of power generation as of 2050

We estimated nuclear energy requirements as of 2050 from three perspectives: (1) compensating for uncertainties in the development of decarbonization technologies such as hydrogen and CCS, (2) diverse supply capacities, and (3) maintaining the nuclear safety base of technology and human resources. (1) In particular, if the implementation of hydrogen, ammonia, and CCS technologies is delayed, up to 40 - 50% of the electricity generated must be supplied by established sources such as nuclear power to supplement renewable energy—in reference to discussion at the national council (Supplement 1). (2) According to our calculations, even assuming the deployment of variable renewable energy, such as solar and wind power, a large amount of storage batteries, and a significant increase in the number of interconnection lines, which greatly exceed the council's reference values mentioned above, it would be difficult to meet electricity supply and demand solely with variable renewable energy. It would be necessary to maintain at least 10 - 15% of power with base load sources, including nuclear power. (3) According to a commissioned study we conducted, the maintenance of technology, human resources, and supply chain is necessary for the safe operation of nuclear power generation until 2050. In particular, with regard to the maintenance of technology, human resources, and supply chain related to design and advanced equipment manufacturing, the construction of nuclear reactors will be important not only for operation and maintenance but also for the succession of unique technology related to design and construction. For this, about one reactor will need to be constructed every few years3, 4. This, together with existing nuclear power plants, is equivalent to maintaining about 10 - 15% of the electricity. Taking into account (1) through (3) above, nuclear power will realistically have to cover at least 10 - 15% of the electricity generated in 2050.

Policy on the use of nuclear energy after 2050 needs to be reconsidered around 2040 in light of developments in other decarbonizing technologies, including further expansion of nuclear energy use itself if necessary, and the option of post-nuclear power, in other words stopping the use of nuclear power altogether. If a post-nuclear power scenario is a viable option around 2040, society will then be able to redefine how power plants in operation, under construction, or planned at the time should be used in order to make the option a reality.

3:Mitsubishi Research Institute, Inc. “Report on the domestic and foreign nuclear industry”,

4:The Japan Electrical Manufactures’ Association "4th Nuclear Subcommittee on Maintenance of Nuclear Technology and Human Resources",

Nuclear innovation as a long-term power option

As a power supply option beyond 2050, nuclear innovation technologies, along with other decarbonization technologies, could continue to make a significant contribution to carbon neutrality. In promoting the introduction of renewable energy to the maximum extent possible, it is important to consider the changing role of nuclear power and the timing of this change, assuming that it coexists with renewable energy, in order to promote the necessary development. For example, plans could be fleshed out such as the introduction of a small modular reactor with adjustable power for variable renewable energy around 2030, a high-temperature gas cooled reactor for large-scale domestic hydrogen production around 2040, and a fusion reactor for high safety and low environmental impact after 2050 with an eye toward replacing existing light water reactors.

Social acceptance of nuclear power is on the rise, but continuous efforts to improve safety and build trust are essential

According to the results of our own questionnaire survey of 30,000 people nationwide, the social acceptance of nuclear power is gradually increasing (Supplement 2), and nuclear power is seen as one of the energy sources that can be used to achieve both decarbonization and energy security, as well as a stable supply of electricity at present. However, there are inherent risks associated with the use of nuclear power, such as widespread environmental pollution that became apparent after the accident at the Fukushima Daiichi nuclear power plant. While we can say that safety has steadily improved due to the independence of regulatory bodies after the accident and the implementation of countermeasures to avoid severe accidents based on the new regulatory standards, we should never forget the feelings of those who were directly or indirectly affected by the accident. In light of the inherent risks of nuclear power, which will never reach zero, it is essential to continue to make efforts to improve safety and build trust, including improving the way operators approach nuclear power and addressing the risk of being targeted for attack in wartime.

Based on the recognition that safety and trust are different, we should focus on steady activities to foster trust

It goes without saying that the accident at the Fukushima Daiichi nuclear power plant damaged the public's trust in the nuclear industry, including nuclear power operators, manufacturers, and the government.

Trust has three main aspects. The first is competence, such as the ability of the nuclear industry to use nuclear technology safely. The second is motivation, such as whether the nuclear power industry complies with regulations and conducts business activities fairly and honestly. The third is value similarity, such as whether organizations and individuals in the nuclear power industry view the world from the same point of view as the rest of society, and whether the industry responds to the needs and wishes of society. Our own questionnaire survey on trust, conducted separately with 4,700 people nationwide, revealed that value similarity had a particularly strong influence in cases such as trust in the nuclear industry (Supplement 3). In other words, whether or not the nuclear power industry can properly understand and respond to society's wishes from the same point of view as society is important in building trust. On the other hand, public opinion spans the full spectrum from prioritizing safety above all else, to requests for electricity that is both inexpensive and stable. In light of this, the nuclear industry should not focus on measures aimed at building trust just for show, but rather on steady efforts to understand the thoughts and values of society and to demonstrate a willingness to respond appropriately to each. In other words, perfunctory initiatives that do not involve internal or substantive changes in the nuclear industry, such as changing the organization without changing the mindset of following precedent, will not foster trust. It goes without saying that the industry must make voluntary, autonomous, and continuous efforts to improve safety based on incorporating the latest knowledge and technological developments. The first step toward building trust should be to continuously demonstrate that as an industry all are sincere in efforts to accurately understand and appropriately respond to the diverse thoughts and values of society.

Existing and dormant issues must be resolved

Choosing to use nuclear power will require resolving various issues. Issues can be grouped into two types: those to be resolved regardless of nuclear-power use, and those to be resolved for the continuous use of nuclear-power. Among the former, the most important issue is the geological disposal of high-level radioactive waste. This is not a technical issue, but a society-wide issue, and society must take time for deep discussion on and work to make steady progress in specific issues such as regional and intergenerational equity and social, economic, and environmental impacts. On the other hand, if we choose to continue the use of nuclear power, we should consider as high priorities the weakening of the industrial base and a lack of successors for skills. Measures to enhance the attractiveness of the industry are also needed, such as promoting industrial enhancement measures using digital technology. In particular, if the government is to embark on construction of nuclear-power facilities in the future, it will be necessary to steadily address issues related to the state's responsibility, the difficulty of predicting future regulations on new reactors, the stable supply of uranium fuel, and the business viability of investment risks borne by the private sector and finances amid uncertainty.

These recommendations mark the start of continued work from the Mitsubishi Research Institute to conduct further research and form subsequent recommendations in fully addressing these important issues.


Supplement 1: Electricity supply outlook as of 2050 aimed at achieving carbon neutrality

  • National councils in Japan are discussing issues and initiatives assuming that, as of 2050, 50 - 60% of the energy will come from renewable sources and the rest from decarbonized thermal and nuclear power
  • Considering the uncertainty of technological development related to decarbonized thermal power (hydrogen, CCS, etc.), it is necessary for nuclear power, etc. to shoulder 40 - 50% of the energy mix
Figure 1: Estimates of installed power sources as of 2050 (council reference values)5
Estimates of installed power sources as of 2050 (council reference values)

5:Agency for Natural Resources and Energy, Study on Achieving Carbon Neutrality in 2050, May 13, 2021,

Supplement 2: Time series changes in the social acceptance of nuclear energy (our original questionnaire survey)

  • According to the results of a survey conducted via our consumer market forecasting system mif (FY 2022)6, the percentage of respondents who said it was better to use nuclear power positively and that it was better to use nuclear power increased in each age group over the past two years
  • Conversely, "better not to use" and "better not to use at all" declined in all age groups

6:Mitsubishi Research Institute's Consumer Market Forecast System (mif) 2022 Basic Survey
(Region: Nationwide, Target: Male and female, 20 - 69 years old, Method of survey: Web survey, Number of participants: 30,000, When: June 2022)

Figure 2: Consumer Market Forecast System mif Survey Results (FY 2022) (Excerpt)
Consumer Market Forecast System mif Survey Results (FY 2022) (Excerpt)

Supplement 3: Our nation-wide questionnaire on the three aspects of trust

Implementation method:

  • We surveyed a total of 4,700 citizens (100 from each prefecture) and measured their trust in nine nuclear power entities7 using a questionnaire
  • We used the assumption that trust is comprised of three aspects: competence, motivation, and value similarity,8 and set questions on a five-point scale, from “think so” to “don't think so”


  • Trust in nuclear power operators and manufacturers is at a moderate level among the nine entities
  • For all entities, value similarity has the strongest influence on trust, but value similarity is particularly prominent for nuclear power operators and manufacturers
Figure 3: Three Aspects of Trust
Three Aspects of Trust
Figure 4: Results of our questionnaire on trust (excerpt)
Results of our questionnaire on trust (excerpt)

7:Entities: research and international organizations, experts, nuclear power operators and manufacturers, host municipalities, the Nuclear Regulation Authority, the Ministry of Economy, Trade and Industry and the Agency for Natural Resources and Energy, the mass media, the courts and the Diet

8:Kazuya Nakayachi, 'The Classroom of Trust Studies' (Kodansha Gendai Shinsho), 2015

For Inquiry

Societal Safety and Industrial Innovation Division
Mitsubishi Research Institute, Inc.
10-3 Nagatacho 2-chome, Chiyoda-ku, Tokyo 100-8141, Japan