A detailed analysis for the UN Economic Commission for Europe of the full life-time green house gas emissions from energy generation has surprisingly concluded that nuclear has the lowest- around a global average of 5 gm CO2 equivalent/kWh, with, it says ‘most of the emissions occurring in the front-end processes’ i.e. extraction, conversion, enrichment of uranium and fuel fabrication. It goes on ‘This value is comparable to the lower range of literature values because of the following assumptions: revised energy inputs for mining and milling, including electricity inputs for ISL [In Situ Leaching], centrifugation-only enrichment, longer life-time assumed for nuclear power plant (60 years instead of 40)’.
60 years is pretty optimistic, as, arguably, are some of the other assumptions for nuclear, while it is quite pessimistic on renewables, all of which it calculates emit more CO2 /kWh. The differences are only small at the low end of the range quoted for renewables, but they open up at the top end of the range, to 3 times more for onshore wind, nearly 5 times more for offshore wind and 17 times more for solar PV, all as compared with the lowest figure quoted for nuclear.
However, it is hard to make valid long term comparisons when looking at very different technologies deployed in very different circumstances and locations. For example, for load factors for wind and solar, it selects ‘average’ regional load factors, which may be a problem given that in practice they vary significantly from site to site, and over time. In any case, they are improving radically with the advent of new technology. Whereas the study is focused on 2020 and uses offshore wind load factor figures varying from 30-40%, we might expect 50% or even 60% to be more common soon, as larger floating devices are installed in windier areas further out to sea. That could have a big impact on the LCA score. So the study results may not be a very useful guide to the future. Impacts from the use of materials are also included, but it uses the IEA’s arguably high figures for wind (mostly for copper) and low figures for nuclear. So once again, the final results may be a little unreliable- particularly as guide to the future.
Nevertheless, for what it's worth, the rankings for renewables are as follows. For Solar technologies, GHG emissions are put at 27 to 122 g CO2 eq./kWh for solar thermal CSP, and 8.0–83 g CO2 eq./kWh for photovoltaics, with thin-film cells being lower-carbon than silicon-based PV. For wind power, GHG emissions are put at 7.8 to16 g CO2 eq./kWh for onshore, and 12 to 23g CO2 eq./kWh for offshore turbines. For hydro they are put at 6-147gCO2 eq./kWh, depending on size. By contrast, coal is of course very bad, at up to 1095g, gas is also pretty high (up to 513) even with CCS (221), but, at 5.1-6.4, nuclear comes out as the lowest.
The study was done by the Luxembourg Institute of Science and Technology (LIST) with back up from the UNECE Task Force on Carbon Neutrality and some data input on nuclear from the World Nuclear Association. Its life cycle GHG results are a long way from the results that have emerged from some other studies, especially those that take a whole system view of the total system/scenario impacts of using nuclear not renewables. For example, Prof. Mark Jacobson at Stanford says they are high, since ‘new nuclear power plants cost 2.3 to 7.4 times those of onshore wind or utility solar PV per kWh, take 5 to 17 years longer between planning and operation, and produce 9 to 37 times the emissions per kWh as wind’.
His point is that the high cost and slow deployment capability of nuclear means that, in a hypothetical high nuclear scenario, emissions/kWh would be much higher than in one using wind water and solar (WWS) renewables, so that ‘a fixed amount of money spent on a new nuclear plant means much less power generation, a much longer wait for power, and a much greater emission rate than the same money spent on WWS technologies’. And overall, he says emissions from new nuclear are 78 to 178 g-CO2/kWh, a far cry from the UNECE’s 5.1-6.4.
Given the ongoing row over the inclusion of nuclear in the European Commission's proposed new Sustainable Investment Taxonomy, we might also expect some reactions to this study, especially since the UNECE has form in this area: its Carbon Neutrality Toolkit and Nuclear Technology Brief are explicit about the presumed virtues/necessity of nuclear in averting climate change. Certainly the new UNECS study sticks to the view that the radiological health risks of nuclear are relatively low- lower than for coal and even geothermal. Plenty to discuss there! And its results for on land-use are also debatable. It says renewables all use more land space/MWh output than nuclear plants, but what about offshore projects?
Disagreements
Differing conclusions on nuclear versus renewables are not uncommon and some of them fed into to this study. It’s not just a matter of costs, on which the data for current technology is fairly clear- renewables win hands down. However, materials-related issues are less clear. As noted above, the IEA sees nuclear as having a relatively low requirements for materials compared to renewable, but there are rival views with nuclear also seen as relying on some key rare materials.
There are also other divergences of view. While most analysts accept that nuclear delivers a relatively poor Energy Return of Energy Invested (typically a 15:1 output/input ratio), there are disagreements about the EROEI figures for renewables- although all of them are better than nuclear, wind and hydro especially. As noted above, there are also disagreements about land-use. Clearly biomass is very land-use intense, solar thermal CSP too, but offshore wind, wave and tidal stream technologies use no land directly, neither does solar PV on roof tops. However, the UNECE study has nuclear beating all else in land use/kWh terms.
These and other divergent views feed into the wider battle over nuclear versus renewables, which continues in the UK and elsewhere, and is also shaped by rival strategic and political views - and differing technical and economic assessments of the viability of new nuclear, or, for that matter, the need for it. It can get a little tiring to keep going over the same ground- and I can say that authoritatively since I’m in the midst of doing an expanded update of the book I wrote for the Institute of Physics about nuclear power five years ago. But there’s no sign of the debate concluding….indeed it seems to spin around and around again. See my next post.
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