Nuclear Power Revisited

We face some major energy policy choices, and a need to move away from fossil fuels, with nuclear energy and renewables often being presented as solutions, but also as polar opposites.

Assuming energy demand can be managed appropriately, it seems likely that renewables can supply all human energy needs. So why is there still support for nuclear power?

The simple answer is that it is well established with powerful supporters, and it does deliver energy, about 11% of global electricity, with relatively low carbon emissions and relatively reliably. These ‘relative’ qualifications are however important in making comparisons with renewables. The load factors for UK nuclear plants have been rather poor in recent year, around 60%, due in part to unplanned shut downs, so that wind turbines, with load factors of 30-40%, depending on location, do not look look too bad by comparison.  Higher nuclear load factors are now more common in the UK and elsewhere, and new plants may be able to get to 90%, but wind technology is also improving, with offshore load factors being higher. 

Nuclear will no doubt always win on this measure, but the comparison turns in favour of wind when we look at the embedded energy and the Energy Return on Energy Invested ratio. It is around 15:1 for nuclear plants and up to 80:1 for wind turbines on good sites: www.routledge.com/books/details/9781849710732/. The figures for wind and other renewables are likely to improve, while those for nuclear are likely to get worse as reserves of high grade uranium ore deplete. More energy is then needed to mine and process the ore to make reactor fuel. Renewables like wind and solar do not need any fuel. Given that most of the energy used for the nuclear fuel production still comes from fossil sources (e.g. diesel for strip mining bulldozers and trucks in remote areas), emissions will rise as ore quality drops. At present carbon emissions for the nuclear cycle are said to be similar to those for some renewables (though views differ), but, unless nuclear and/or renewable energy can be used for fuel processing, they will rise to be much more, with, in any case, ever diminishing energy returns on energy investment: www.wiseinternational.org/nuclear-energy/studies-reports

The economics of nuclear suffer not just from the need to supply fuel but also due to the need to deal with wastes, as well as the cost of maintaining safety and security, problems which are either absent or relatively small for most renewables. At present, in the UK, on shore wind projects are going ahead with strike prices much lower than proposed new nuclear projects. Some PV solar projects are also cheaper and both are likely to be substantially cheaper in the years ahead as they move down their learning curves. By contrast nuclear costs appear to be continually rising, with in effect negative learning curves, at least in the US and France:  www.sciencedirect.com/science/article/pii/S0301421513011440 

That may not always be the case everywhere, as was claimed recently: www.sciencedirect.com/science/article/pii/S0301421516300106  

Though that study has been challenged as unrepresentative and flawed: www.sciencedirect.com/science/article/pii/S0301421516301690 www.sciencedirect.com/science/article/pii/S0301421516301549

It may be that new nuclear technology will emerge that improves on this situation, but that is far from certain. Some want to look again at fast breeder reactors and the use of molten fluoride/thorium systems, but there are many unknowns. Certainly early breeder and experimental thorium reactors proved to have problems: http://thebulletin.org/thorium-wonder-fuel-wasnt7156 . New technology may limit some of the problems, but the economics are unclear, and, even if prototypes prove to be viable, commercial-scale projects are likely to be decades away. Some also look to the idea of developing new types of small reactors. In the past attempts have been made to improve the economics of nuclear plants by going for larger scale units, with little success. There would seem to be no reason why going for smaller scale units would be any more successful: http://ieer.org/wp/wp-content/uploads/2013/08/SmallModularReactors.RevisedSept2013.pdf www.sciencedirect.com/science/article/pii/S0301421513011440

Fusion remains the ultimate dream. If it can be successfully developed, it would avoid the fuel resource limits of fission: without breeders, there is not enough uranium to run fission plants for more than a few decades, depending on the number of plants in operation. However, despite very large scale funding, there is some way to go to viable fusion technology, and, although break-through are always possible, at present it seems that, even if all goes well with experimental tests, workable commercial-scale fusion reactors will not be available until the second half of this century.

Moreover, even if it can be developed successfully, fusion may have limits. Quite apart from the unknown cost, there would be safety and security issues. Plasma based fusion plants would contain radioactive tritium gas at very high temperatures, and there is a risk of leaks or even explosive loss of containment.  They may not generate very long lived radioactive wastes, but activated components would have to be stripped out regularly and stored somewhere. Fusion reactors are likely to need lithium, to make tritium, and reserves of that are finite, and are already in demand for the batteries of electric vehicles. Looking far ahead, it may be possible to find fuel for fusion plants on the asteroids or elsewhere in the solar system. That is fortunate since, if we are to engage in extensive interplanetary travel, we may need fusion energy for propulsion. For the nearer future however, on earth, fusion seems almost totally irrelevant. Unlike renewables, which are available now, for the foreseeable future it can make no contribution to dealing with the urgent problem of climate change. 

Why not both?

While that may be true, couldn’t nuclear fission support renewables, at least in the interim while fusion and/or more renewables are developed longer term? This seem unlikely on any significant scale for a range of practical reasons. Nuclear plants are usually run 24/7 to recoup their high capital costs, although their output can be varied to some extent, so in theory they might be able to balance the variable output from renewables. In practice however this would be difficult for the regular short variations associated with renewables: there are operational and safety constraints limiting nuclear plants to relative slow, infrequent ramping up and down. Some of them can follow the slow daily cycles in demand, but they could not balance the rapid and frequent, minute by minute, variations in wind and solar availability.  Basically, they are inflexible. So rather than complementing renewables, they can play no real role in flexible energy system that will be needed. 

Maintaining costly nuclear plants to provide back up when wind and solar were low for long periods would clearly not make sense since there are other much cheaper options for that occasional standby role. Moreover, if there was a large nuclear element on the grid, then at times of low demand (at night in summer), its input to the grid would conflict with any renewable energy input that was available. One or other, or both, would have to give way, dumping power wastefully. It is conceivable that storage and exports could compensate for this and that smaller more variable nuclear plants may emerge, possible feeding waste heat to nearby users, although there would be safety and security issues with locating mini-nuclear plants in or near cites, as has been proposed. For the present, the current generation of large inflexible, usually remotely sited, nuclear plants and widely distributed variable renewables do not fit well together on the same grid. The two options are not compatible at large scale.

Carbon Capture

It has always seemed a long shot- capturing and storing carbon dioxide to reduce climate impacts. But a range of technologies now are being developed which some see as viable.  The most advanced are those that capture CO2 from power station exhausts. An early variant of this idea was tested by MIT and involved feeding captured CO2 to a bioreactor where it was absorbed by fast growing biomass- algae: http://web.mit.edu/erc/spotlights/alg-all.html. So that could be used as a fuel, in which case this was a pioneering version of what is now called Carbon Capture and Utilisation - CCU. More recent CCU developments have involved using captured CO2 and hydrogen gas to make syngases and fuels, the hydrogen being produced by electrolysis of water using surplus power from wind or PV. Power to Gas (P2G) and Power to Liquid (P2L) system are emerging in Germany, producing  methane for injection into the gas main, or synfuels for vehicle use: www.audi-mediaservices.com/publish/ms/content/en/public/pressemitteilungen/2014/11/14/new_audi_e-fuels_project.html  and : www.sciencealert.com/audi-have-successfully-made-diesel-fuel-from-air-and-water  Alternatively, the hydrogen/syngasses can be stored and then used for power production when there is a lull and /or high demand for power, this offering a way to balance the variable output from renewables: www.dw.de/power-to-gas-may-solve-renewables-storage-challenge/a-17754416/

The concentration of CO2 in power plant exhaust is very much higher than that in the air, but some think that the later can also be used, either for storage in some chemical form, or to make fuels, as with the ‘air capture’ system being developed with support from Bill Gates: www.sciencealert.com/scientists-are-building-a-system-that-could-turn-atmospheric-co2-into-fuel  The advantage of air capture is that it can be done anywhere there is room for the plants. Not everyone is convinced CCU for fuel production will be economically viable without more effort: http://pubs.rsc.org/en/content/articlelanding/2015/ee/c4ee04117h#!divAbstract  However there are obvious attractions in being able to make synfuels, and also some clever new ideas for producing other high value materials, like carbon nano-fibres: www.acs.org/content/acs/en/pressroom/newsreleases/2015/august/co2.html

While CCU is moving ahead, so is the more conventional approach- simple Carbon Capture and Storage(CCS) as discussed in an earlier post in this Renew Extra series. The attraction here is that CCS can allow for the continued use of fossil fuels for electricity production, with the resultant CO2 being stored deep underground, for example in empty oil and gas wells. There is some symmetry in this since that’s where the oil and gas came from, and in fact inert gas injection is already used in Enhanced Oil Recovery to squeeze out the last of the resource. In theory the compressed CO2 should stay safely stored since it simply replaces the geologically trapped fossil resources that had remained secure for millennia until the artesian well cap was breached for extraction. Some may also bond with rock strata to form new solid deposits. However, there are worries about storage in other locations, for example in open aquifers, particularly if these were on land rather than offshore. Sudden release of large amounts of CO2 could be very hazardous to health if the cloud spread to areas of human habitation: when cool CO2, is heavier than air so it could produced a suffocating blanket of gas. 

So far most of the new developments have focused on the capture phase. It is sometimes claimed that very high percentages of the power plant CO2 can be captured, but it has to be remembered that there are energy costs in doing this, as well as further energy costs associated with compression and then transmission to the storage site. As a result, since extra energy will have to be supplied to meet this needs, the net CO2 reduction will be reduced maybe to 60-70% depending on, amongst other things, the transmission distance.  And the cost, already high, will be increased.

So far progress has not been spectacular – despite there being some major programmes. The UKs £1bn CCS programme took a long time to get started, with two pilot projects being chosen. There had been disagreements about the focus. Some said that the more advanced pre-combustion carbon capture approach was the best option, and that gas CCS was the way ahead. In the event, for one of the chosen projects, the UK backed an oxyfuel power coal fired plant at the Drax site in Yorkshire- the White Rose project. http://www.whiteroseccs.co.uk/

Oxygen injection prior to combustion increases the proportion of CO2 in the flue gas, to improve capture efficiency. But it is expensive to do this, and, with the future of government support for CCS in doubt, last year the Drax company pulled out if it. The aim had been to transport the captured CO2 via the proposed Yorkshire and Humber CCS Cross Country Pipeline, a project being developed by National Grid, for storage offshore in deep saline formations under the southern North Sea. But now it all seems doubtful- given the governments sudden decision, last November, to abandon the £1bn competition entirely. That raised some protest- DRAX had already been hit by government cuts back for biomass conversion projects. http://www.theguardian.com/environment/2015/nov/25/uk-cancels-pioneering-1bn-carbon-capture-and-storage-competition

This decision will also impact on the second project chosen, a post-combustion carbon dioxide capture technology from a gas fired CCGT plant at the existing Peterhead gas power station in Aberdeenshire, led by Shell and SSE. The aim was use an amine based capture system, plus conditioning and compression of the captured CO2, which would then be transferred as dense phase CO2 by subsea pipeline to the existing Goldeneye gas platform in the central North Sea, where it would be injected into the depleted Goldeneye gas reservoir for permanent storage, at a depth of over 2.5 km below sea level. Once the required volume of CO2 had been injected (1 million tones p.a. over 15 year was expected) it was planned to monitor the reservoir pressure build-up for 3 years, and to leave the Goldeneye Platform in place. After that the platform would be decommissioned. Post-closure handover to a ‘competent management authority’ would follow the reservoir tests.

As can be seen the technology is complex and extended, and there are risks.  In the UK, CO2 is classed by the Health and Safety Executive (HSE) as a ‘substance hazardous to health’. The HSE says that: ‘In CCS operations it is likely that CO2 will be handled close to, or above, its critical pressure (73.82 bara) where many of its properties are similar to that of a liquid. In this state it is often referred to as ‘dense phase’, whereas above critical temperature (31.04°C) and pressure it is referred to as ‘supercritical’. Significant hazards associated with dense phase or supercritical CO2 arise when pressure falls suddenly or is lost completely.  However, the HSE says that where the risks are properly controlled the likelihood of a major hazard incident is expected to be very low, as in other similar processes in the energy, chemical and pipeline industries. In its insurance review, Shell say ‘many of the risks involved in CCS are not that different from a typical Upstream Oil & Gas project (although the process of extraction is reversed) and are closely aligned with those of Enhanced Oil Recovery (EOR) projects in which Shell and various partners have been involved over the past 20 years’, but note that, at Goldeneye, ‘due to integrity issues and CO2 phase behaviour management, it is not possible to use the wells without any modification.’ www.gov.uk/government/publications/carbon-capture-and-storage-knowledge-sharing-commercial-project-management-and-lessons-learned

For now, CCS seems to be stalled in the UK. It is possible that other companies will step in, but CCS is expensive and the money is evidently no longer there.  Some see CCS as vital and urgent, and so there may still be pressure to push ahead : www.eti.co.uk/carbon-capture-and-storage-building-the-uk-carbon-capture-and-storage-sector-by-2030/  New ideas have emerged which might improve its economics: www.chemengonline.com/modified-mofs-cut-carbon-capture-costs-half/  http://actu.epfl.ch/news/a-cost-effective-and-energy-efficient-approach-to-/  and www.myscience.org/news/2015/study_suggests_method_is_rock_solid_for_storing_carbon_dioxide_deep_underground-2015-imperial

However, there is clearly still a way to go, and in principle it might be argued that CCU is better than CCS, since it offers a fuel, and CCS does seem a little inelegant- stuffing a pollutant underground and hoping it will stay there, all so that we can continue to use fossil fuels for a while longer, while avoiding some of their emission impacts.  Some hope that the development of CCS for fossil fuel use will just be a first stage, to be followed by BECCS- biomass energy with Carbon Capture, which could give us a negative carbon option- sucking CO2 from the air. Direct Air Capture (with storage) would also do that, but some say what's wrong with reafforestation- growing more trees.  That could be the fastest, easiest and most cost-effective option for post-emission atmospheric CO2 reduction: www.smithschool.ox.ac.uk/research-programmes/stranded-assets/Stranded%20Carbon%20Assets%20and%20NETs%20-%2006.02.15.pdf

Though trees aren’t a permanent carbon store (they die, rot and can burn), and as mentioned in an earlier post in this Renew Extra series, pulling CO2 out of the air may not work- it may be replaced by excess CO2 outgassed from the seas. So we would also have to remove that. So carbon capture, by whatever means, does seem to be a limited option and the various technical fixes are not a long-term solution.  Even BECCs would need large areas of biomass (and CO2 storage) to make a significant impact. Instead we should deal with the problem at source and switch to using non-fossil fuels as fast as possible. 

*For a useful review of negative carbon options see: www.carbonbrief.org/in-depth-experts-assess-the-feasibility-of-negative-emissions