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What is the IPCC saying about Nuclear Power?

The globally recognised authority of organisations like the Intergovernmental Panel on Climate Change holds a lot of value for stakeholders whose causes encompass action on climate change, and claiming a degree of affiliation with it is invariably tempting.

from Overview to the IPCC First Assessment Report, 1990


Assessment Report 6 was released this year with much emphasis on the distinct benefits of dramatically reducing fossil fuel consumption within a decade. The Summary for Policymakers includes “deployment of low- or zero-emission technologies” as part of urgently-needed system transitions. The text belabours the potential for relatively low cost and rapid emissions reductions through solar and wind. This endorsement directly follows equally explicit reference to “carbon capture and storage usage on fossil fuel technology as part of net zero CO2 energy systems”. Among stakeholders engaged with amplifying the IPCC’s work, there are few groups who heartily applaud the latter along with the former.


Whether renewable-, fossil-based, or otherwise, the Summary for Policymakers notes that “almost all mitigation options face institutional barriers that need to be addressed to enable their application at scale.”


Nuclear energy isn’t directly mentioned. The first proper discussion of it is within Working Group III’s full report, section 6.4.2.4:

  • WG3 isn’t particularly concerned about fissile fuel reserves, noting the steady increase in known uranium reserves over time, in addition to the potential for used fuel recycling and thorium.

  • Energy from nuclear reactors will have applications for electricity, hydrogen production, and desalination.

  • Cost and build times can be high but WG3 describes how these can be controlled. Electricity supply prices from conventional new builds are estimated to be USD$42-102 per MWh. Crucial context is given several pages on by an indicative price of around US$70 per MWh for geothermal energy.

  • The minimal land footprint and bulk material intensity for reactors is noted positively, with water requirements significantly moderated by choice of cooling systems.

  • With high confidence, WG3 asserts that “nuclear power continues to suffer from limited public and political support in some countries”, which may be literally true, but not for the 13,500 citizens surveyed most recently across eight countries for Thirdway, ClearPath and RePlanet. In other countries, such as Austria, the political opposition to nuclear energy appears to be a self-reinforcing narrative more than anything scientific.

  • WG3 appears to be satisfied with international treaties and conventions as barriers to weapons diversion and proliferation.


Much of the reliable information references very recent reports from the IEA, the IAEA and the OECD-NEA.


As for nuclear waste, this section of the report says that “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”. Repurposing some of this sentence to say “broad political support, coherent climate-energy policies, and a well-managed, consensus-based decision-making process are critical for accelerating this process” then it sounds exactly like what determined national energy transitions to net zero emissions will need to be.


In contrast, the broader document is inconsistent on the topic. The assertion elsewhere that “larger-scale national nuclear generation does not tend to associate with significantly lower carbon emissions” represents an embarrassing error on WG3’s part, with the citation having been expertly dissected, every flaw of reasoning and arithmetic exposed, and the authors’ own data in fact demonstrating the opposite when properly analysed.

Other questions are prompted by the section on Illustrative Mitigation Pathways, where the changes in global primary energy supply for said pathways are visualised in Figure 3.8. Even bearing in mind the electrical efficiency advantages of various renewable energy sources, are pathways with distinctly lower future consumption (IMP-LD and IMP-SP in particular) truly illustrative?


Depending largely on one’s levels of optimism for humanity’s and earth’s future, the first pathway illustrating sensibly expanded energy usage in 2100 is IMP-NEG. This is a different proposition to the striking increases in biomass and (what is obviously) solar and wind. Meanwhile, there’s nuclear energy down there, putting in its best effort out of all the pathways. How much effort? Tracking down the IMP-Neg numbers in the Scenario Explorer reveals future capacity, relative to 2020, hitting 184% in 2050 and 544% by 2100 - the equivalent of around 700 and (eventually) 2,070 AP1000 reactors, respectively. Considering the long design lifetimes of modern reactors versus the gradual retirement of last century’s nuclear fleet, this will be a rough yearly average of 27 new units from now on.


Does thirty-odd gigawatts of fresh nuclear per year sound unrealistic? It’s already been done, briefly, in the 1980s, with 1960s technology. Nowadays, the global nuclear energy sector is looking at a build rate of 40 GW per year.


With regard to emissions, IMP-Neg projects 217 gCO2/kWh globally for electricity supply in 2030 (red circle).

Other pathways look lower, so is this ambitious? Emissions intensity was double that in 2022 after a decade of dismayingly slow decline. IMP-Neg implies an immediate, unprecedented acceleration of nearly six times faster.


IMP-Neg is just one pathway, regardless of how illustrative WG3 considers it to be. In Table 3.6 the AR6 scenarios database is organised by pathways which limit warming by 2100 to either 1.5C or 2C, with greater or lesser a) overshoot of emissions and b) modelled confidence.



First, note the median, lower quartile and upper quartile values for most fossil fuels without CCS, which are predominantly negative. Obviously, pathways for mitigating greenhouse gas production will involve reductions in coal, oil and gas emissions.

Now look at “Change in primary energy from nuclear”. The first and third columns, representing immediate action for 1.5C and 2C respectively, project a median of 35-40% more nuclear energy by 2030, and nearly a doubling in 2050. More importantly, the lower quartiles, although diminished, also indicate increases, and this holds true for all scenario classes in 2050. Below the lower quartile it’s likely that many pathways which forecast negative changes for nuclear energy are legitimate outliers. In contrast, pathways in which global nuclear energy must expand to nearly quadruple its present production fall within the interquartile range, rather than grouped above it with possible high-end outliers.


So, what does the IPCC say about nuclear? In summary, IPCC Working Group 3 has presented the following, well-referenced, information:

  • Nuclear energy technology can be built in a timely and affordable manner on small land footprints with small water and material requirements and without concern for fuel reserves.

  • Progress on the management of waste in a few countries is going well and informing the rest on successful future strategies, while weapons diversion is mitigated by existing international cooperation.

  • In the interquartile range – arguably the most representative – the most ambitious scenario classes project increasing nuclear energy generation through 2030 to 2050, and no decrease.


Additionally, the nuclear projection in the upper quartile of the highest ambition, lowest temperature pathways (1.5C, immediate action, with no or limited overshoot) is consistent with recently renewed and announced ambition by the nuclear energy sector’s representative organisations and industry partners.



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