Editing IPCC:AR6/WGIII/Chapter-6 (section)

==== 6.4.2.4 Nuclear Energy ====

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Nuclear power can deliver low-carbon energy at scale ( ''high confidence'' ). Doing so will require improvements in managing construction of reactor designs that hold the promise of lower costs and broader use ( ''medium confidence'' ). At the same time, nuclear power continues to be affected by cost overruns, high upfront investment needs, challenges with final disposal of radioactive waste, and varying public acceptance and political support levels ( ''high confidence'' ).

There are sufficient resources for substantially increasing nuclear deployment ( ''medium confidence'' ). Estimates for identified uranium resources have been increasing steadily over the years. Conventional uranium resources have been estimated to be sufficient for over 130 years of supply at current levels of use; 100 years were estimated in 2009 ( [[#Hahn--1983|Hahn 1983]] ; [[#NEA/IAEA--2021|NEA/IAEA 2021]] ). In the case of future uranium resource scarcity, thorium or recycling of spent fuel might be used as alternatives. Interest in these alternatives has waned with better understanding of uranium deposits, their availability, and low prices ( [[#IAEA--2005|IAEA 2005]] ; OECD NEA 2015).

There are several possible nuclear technology options for the period from 2030 to 2050 ( ''medium confidence'' ). In addition to electricity, nuclear can also be used to produce low-carbon hydrogen and freshwater ( [[#Kavvadias--2014|Kavvadias and Khamis 2014]] ; [[#Kayfeci--2019|Kayfeci et al. 2019]] ).

• '''Large reactors.''' The nuclear industry has entered a new phase of reactor construction, based on evolutionary designs. These reactors achieve improvements over previous designs through small to moderate modifications, including improved redundancy, increased application of passive safety features, and significant improvements to containment design to reduce the risk of a major accident ( [[#MIT--2018|MIT 2018]] ). Examples include European – EPR, Korean – APR1400, USA – AP1000, Chinese – HPR1000 or Russian – VVER-1200.

'''•''' '''Long-term operation (LTO) of the current fleet.''' Continued production from nuclear power will depend in part on life extensions of the existing fleet. By the end of 2020, two-thirds of nuclear power reactors will have been operational for over 30 years. The design lifetime of most of existing reactors is 30–40 years. Engineering assessments have established that reactors can operate safely for longer if key replaceable components (e.g., steam generator, mechanical and electrical equipment, instrumentation and control parts) are changed or refurbished ( [[#IAEA--2018|IAEA 2018]] ). The first lifetime extension considered in most of the countries typically is 10–20 years ( [[#IEA--2020j|IEA 2020j]] ).

• '''Small modular reactors (SMR).''' There are more than 70 SMR designs at different stages of consideration and development, from the conceptual phase to licensing and construction of first-of-a-kind facilities ( [[#IAEA--2020|IAEA 2020]] ). Due to smaller unit sizes, the SMRs are expected to have lower total investment costs, although the cost per unit of generation might be higher than conventional large reactors ( [[#Mignacca--2020|Mignacca and Locatelli 2020]] ). Modularity and off-site pre-production may allow greater efficiency in construction, shorter delivery times, and overall cost optimisation ( [[#IEA--2019c|IEA 2019c]] ). SMR designs aim to offer an increased load-following capability that makes them suitable to operate in smaller systems and in systems with increasing shares of VRE sources. Their market development by the early 2030s will strongly depend on the successful deployment of prototypes during the 2020s.

Nuclear power costs vary substantially across countries ( ''high confidence'' ). First-of-a-kind projects under construction in Northern America and Europe have been marked by delays and costs overruns ( [[#Berthelemy--2015|Berthelemy and Rangel 2015]] ). Construction times have exceeded 13–15 years and cost has surpassed three to four times initial budget estimates ( [[#IEA--2020j|IEA 2020j]] ). In contrast, most of the recent projects in Eastern Asia (with construction starts from 2012) were implemented within five to six years (IAEA 2021). In addition to region-specific factors, future nuclear costs will depend on the ability to benefit from the accumulated experience in controlling the main drivers of cost. These cost drivers fall into four categories: design maturity; project management; regulatory stability and predictability; and multi-unit and series effects ( [[#NEA--2020|NEA 2020]] ). With lessons learned from first-of-a-kind projects, the cost of electricity for new builds are expected to be in the range of USD42–102 MWh –1 depending on the region ( [[#IEA--2020j|IEA 2020j]] ).

Lifetime extensions are significantly cheaper than new builds and cost competitive with other low-carbon technologies. The overnight cost of lifetime extensions is estimated in the range of USD390–630 kWe –1 for Europe and North America, and the LCOE in the range of USD30–36 MWh –1 for extensions of 10–20 years ( [[#IEA--2020j|IEA 2020j]] ).

Cost-cutting opportunities, such as design standardisation and innovations in construction approaches, are expected to make SMRs competitive against large reactors by 2040 ( [[#Rubio--2016|Rubio and Tricot 2016]] ) ( ''medium confidence'' ). As SMRs are under development, there is substantial uncertainty regarding the construction costs. Vendors have estimated first-of-a-kind LCOEs at USD131–190 MWh –1 . Effects of learning for nth-of-a-kind SMR are anticipated to reduce the first-of-a-kind LCOE by 19–32%.

Despite low probabilities, the potential for major nuclear accidents exists, and the radiation exposure impacts could be large and long-lasting ( [[#Steinhauser--2014|Steinhauser et al. 2014]] ). However, new reactor designs with passive and enhanced safety systems reduce the risk of such accidents significantly ( ''high confidence'' ). The (normal) activity of a nuclear reactor results in low volumes of radioactive waste, which requires strictly controlled and regulated disposal. On a global scale, roughly 421 kt of spent nuclear fuel have been produced since 1971 (IEA 2014). Out of this volume, 2–3% is high-level radioactive waste, which presents challenges in terms of radiotoxicity and decay longevity, and ultimately entails permanent disposal.

Nuclear energy is found to be favourable regarding land occupation ( [[#Cheng--2017|Cheng and Hammond 2017]] ; [[#Luderer--2019|Luderer et al. 2019]] ) and ecological impacts ( [[#Brook--2015|Brook and Bradshaw 2015]] ; [[#Gibon--2017|Gibon et al. 2017]] ). Similarly, bulk material requirements per unit of energy produced are low (e.g., aluminum, copper, iron, rare earth metals) ( [[#Vidal--2013|Vidal et al. 2013]] ; [[#Luderer--2019|Luderer et al. 2019]] ). Water-intensive inland nuclear power plants may contribute to localised water stress and competition for water uses. The choice of cooling systems (closed-loop instead of once-through) can significantly moderate withdrawal rates of freshwater ( [[#Meldrum--2013|Meldrum et al. 2013]] ; [[#Fricko--2016|Fricko et al. 2016]] ; [[#Mouratiadou--2016|Mouratiadou et al. 2016]] ; [[#Jin--2019|Jin et al. 2019]] ). Reactors situated on the seashore are not affected by water scarcity issues ( [[#Abousahl--2021|Abousahl et al. 2021]] ). Lifecycle analysis (LCA) studies suggest that the overall impacts on human health (in terms of disability adjusted life years (DALYs)) from the normal operation of nuclear power plants are substantially lower than those caused by fossil fuel technologies and are comparable to renewable energy sources ( [[#Treyer--2014|Treyer et al. 2014]] ; [[#Gibon--2017|Gibon et al. 2017]] ).

Nuclear power continues to suffer from limited public and political support in some countries ( ''high confidence'' ). Public support for nuclear energy is consistently lower than for renewable energy and natural gas, and in many countries as low as support for energy from coal and oil ( [[#Corner--2011|Corner et al. 2011]] ; [[#Pampel--2011|Pampel 2011]] ; [[#Hobman--2013|Hobman and Ashworth 2013]] ). The major nuclear accidents (i.e., Three Mile Island, Chernobyl, and Fukushima) decreased public support ( [[#Poortinga--2013|Poortinga et al. 2013]] ; [[#Bird--2014|Bird et al. 2014]] ). The public remains concerned about the safety risks of nuclear power plants and radioactive materials ( [[#Pampel--2011|Pampel 2011]] ; [[#Bird--2014|Bird et al. 2014]] ; [[#Tsujikawa--2016|Tsujikawa et al. 2016]] ). At the same time, some groups see nuclear energy as a reliable energy source, beneficial for the economy and helpful in climate change mitigation. Public support for nuclear energy is higher when people are concerned about energy security, including concerns about the availability of energy and high energy prices (Groot et al. 2013; [[#Gupta--2019b|Gupta et al. 2019b]] ), and when they expect local benefit ( [[#Wang--2020c|Wang et al. 2020c]] ). Public support also increases when trust in managing bodies is higher ( [[#de%20Groot--2011|de Groot and Steg 2011]] ). Similarly, transparent and participative decision-making processes enhance perceived procedural fairness and public support ( [[#Sjoberg--2004|Sjoberg 2004]] ).

Because of the sheer scale of the investment required (individual projects can exceed USD10 billion in value), nearly 90% of nuclear power plants under construction are run by state-owned or controlled companies, with governments assuming significant part of the risks and costs. For countries that choose nuclear power in their energy portfolio, stable political conditions and support, clear regulatory regimes, and adequate financial framework are crucial for successful and efficient implementation.

Many countries have adopted technology-specific policies for low-carbon energy courses, and these policies influence the competitiveness of nuclear power. For example, feed-in-tariffs and feed-in premiums for renewables widely applied in the EU ( [[#Kitzing--2012|Kitzing et al. 2012]] ) or renewable portfolio standards in the USA ( [[#Barbose--2016|Barbose et al. 2016]] ) impact wholesale electricity price (leading occasionally to low or even negative prices), which affects the revenues of existing nuclear and other plants ( [[#Bruninx--2013|Bruninx et al. 2013]] ; [[#Newbery--2018|Newbery et al. 2018]] ; [[#Lesser--2019|Lesser 2019]] ).

Nuclear power’s long-term viability may hinge on demonstrating to the public and investors that there is a long-term solution to spent nuclear fuel. Evidence from countries steadily progressing towards first final disposals – Finland, Sweden and France – suggests that broad political support, coherent nuclear waste policies, and a well-managed, consensus-based decision-making process are critical for accelerating this process ( [[#Metlay--2016|Metlay 2016]] ). Proliferation concerns surrounding nuclear power are related to fuel cycle (i.e., uranium enrichment and spent fuel processing). These processes are implemented in a very limited number of countries following strict national and internationals norms and rules, such as the International Atomic Energy Agency (IAEA) guidelines, treaties and conventions. Most of the countries that might introduce nuclear power in the future for their climate change mitigation benefits do not envision developing their own full fuel cycle, significantly reducing any risks that might be linked to proliferation ( [[#IAEA--2014|IAEA 2014]] , 2019).

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