Thursday, 20 July 2017

Options for Tackling Climate Change


Dear Michel,
In a brief conversation the other day you expressed the commonly held view that nuclear power is unacceptable due to the very long-lived waste that it creates. I anticipate that you are also concerned about safety and the risk of contaminating the environment as a result of a release of radioactive material. I don’t have sufficiently good French to sustain a discussion on this complex issue, which is also for many people a very emotional topic, and so I said little or nothing, but I've finally decided that I wish to express my views on the subject. 

Climate Change - Conservation is not Enough
I’m sure that we can both agree that climate change is the single most serious challenge facing the world today. The question is: what is the best way of tackling the problem of rising energy demand at the same time as limiting the emission of man-made greenhouse gases, principally carbon dioxide? 

Whilst we can make progress within developed economies by improvements in efficiency, conservation and demand management, the net result of these measures will be grossly insufficient to counter the legitimate requirement for more energy from developing economies. In this video “The Magic Washing Machine” by Hans Rosling (now sadly deceased) he explains why we in the developed world have no right to tell people in developing economies that they can’t use more energy because of Climate Change.



The Role of Renewables
So as well as conservation measures what is the best way forward?  Clearly renewables have a significant part to play in the future of energy production and they are getting cheaper but they are still being subsidized. 

Power generation from wind and solar energy is, however, based on diffuse energy sources and is consequently land hungry. The graphic below illustrates the areas required for different energy sources for a generation capacity of 1000MW. The units are in square miles.  In terms of area, a gas fired plant would be comparable with a nuclear power station and a coal fired plant would be a little bigger due to the space required for stockpiling coal and ash.


In addition at the time when demand peaks on cold winter eveningswhen there is no sunlight, if there is also no wind, both solar and wind generation will be unproductive. 

Depending on location, wind power is normally expected to have a 30-50% production factor but like solar it can be unproductive for days. 

Solar photo-voltaic panels produce most efficiently in hot sunny places, like sparsely inhabited deserts.  Long transmission lines, with their associated costs and losses, would then be needed to deliver the power to centres of population. In some locations this may be an economic proposition if geo-political constraints involving distance and international borders can be overcome. 

Both solar and wind are highly variable and cannot provide continuous reliable power. Electricity utility operators therefore have to predict the weather conditions, and hence the output from renewables, in order to schedule the right mix of flexible and inflexible power generation capacity from different types of generators and thus meet the demand. If there is an unpredictable drop in output from renewables then flexible generation capacity must be quickly brought on line. Electricity from flexible sources commands a much higher price in wholesale electricity markets than that from inflexible base load plants, so getting this right is therefore important for both utility companies and consumers. This paper from the US National Renewable Energy Laboratory explains the problem in detail.

So as the proportion of total generating capacity that wind and solar power occupy increases, there is either a need for grid scale energy storage or backup power supply systems, or both, to satisfy the demand when renewables can't. 

Energy Storage
There are many ways of storing and recovering energy. The one we are most familiar with is the use of batteries.

The following graphic, which plots energy density in MJoules/litre against MJoules/kg, puts into context the energy density of Lithium Ion and Zinc-Air batteries relative to other substances. The significance of energy density is that gasoline, for example, effectively stores about 50 times more energy per kg than lithium ion batteries. 

Battery storage technology is developing slowly; but batteries are still expensive and have a limited life. In my view both energy density and longevity would need to improve by at least one or possibly two orders of magnitude before the use of batteries would become economic on a grid scale.



Other energy storage systems are being proposed and investigated, and some may be promising in the long term, but most are not yet proven to be economically viable or available for widespread deployment. 

An interesting example is the idea that, when required, electricity could be fed back into the grid from the batteries in electric vehicles: and therefore at some future date a large battery storage capacity would be available to smooth out shortfalls between generating capacity and demand. It's unclear how this would be managed, but it would probably need an infrastructure that had connection points at the majority of parking places, as well as some form of metering that credited the vehicle owner if stored electricity that had already been paid for was drawn out of the vehicle's batteries. These connection points, or the vehicles themselves, would also need to be equipped with inverters capable of converting DC battery current into AC power synchronised with the grid.

An exception that has been proved to be viable for energy storage is pumped hydroelectricity, which has had plants in operation for decades.  They require two large lakes, one several tens of metres above the other. Water is pumped up when electricity costs are low and released through turbines to generate electricity when required. But, due to pump/turbine efficiencies and the two way conversion, the electricity recovered is only about 70-80% of the electricity input. The opportunities for such installations are few, and so far they have only been used for providing flexible power at peak times when the feed-in price for electricity is high. There are ten such schemes under construction in Europe totalling 1,339MW of capacity. To put this into context, the total energy consumption of the 28 EU countries in 2015 was 12,609,246,000MWh equivalent to a continuous consumption of 1,439,411MW and the schemes under construction add less than 0.1% of this as storage capacity.

Other Renewables
Except in particular locations bio-fuels are heavy consumers of agricultural land and are unlikely to provide more than marginal amounts of electricity on a global scale but they have a role to play. In Brazil, for example, they are successfully replacing fossil fuels for vehicles with blends of gasoline and ethanol derived from sugar cane. Biodiesel, in various blends, is established in North America and Europe. Biofuels are being encouraged by the EU but there are concerns that by displacing food production from agricultural land to forests, which are net absorbers of CO2, the production of biofuels could actually release more carbon dioxide than they save.

Tidal power could also contribute more to renewable energy production, and some plants have been in operation since the 1960's, but tidal barrages and lagoons have an impact on ecosystems and the energy generated is on a lunar cycle which does not coincide with diurnal demand. There are few suitable sites in North America, China or India and its contribution is likely to be marginal.

Although there are opportunities for improving output by replacing old machinery, and also by installing small scale plants, hydro-electricity is largely fully developed in Europe, the USA and some parts of Asia.

My conclusion is that, in the absence of economic grid scale energy storage technologies, over any specific 24 hour period, renewables can only satisfy a proportion of the total energy demand on any supply grid.

Backup Power
Backup power production capacity is therefore necessary to supply the demand for energy when wind and solar can’t and, because it takes time to bring generating capacity on line, some backup systems have to be kept running even when the demand is being satisfied by renewables.  

Under the German EnergieWende, in which it is intended to move away from fossil fuels and nuclear power to a low carbon energy economy, they have been running lignite and hard coal fired power plants (red and dark green) to replace the energy generated by nuclear plants (lime green) which have been taken out of service, and to provide backup to wind and solar (blue). During the last few years the consumption of gas (yellow) has also been reduced: so the increase in energy from renewable sources has been offset by the reduction in the least carbon dioxide producing sources i.e. nuclear and gas.









Coal is the most polluting of all the fuel options since, due to lower efficiencies, legacy plants produce more carbon dioxide per MWh than other fossil fuels and release, into the environment pollutants: including particulates; sulphur and nitrogen oxides; and ash. The latter contains uranium and is 100 times more radioactive than nuclear waste. It also contains heavy metals which will never decay and become less polluting. This ash is typically dumped or stockpiled with minimal control and has caused serious ash-slides. The horrific air pollution in China also dramatically illustrates the results of burning coal and is responsible for many premature deaths

There is a debate in Germany about the phasing out of coal but the government has made no definite commitment as yet. It will clearly be very difficult to phase out both nuclear and coal fired generation which represent more than 50% of current capacity.

Another effect of relying more and more on renewables has occurred in Germany on some sunny and windy days. Because German law forces the Grid to accept renewable energy in preference to that from fossil fuels, and electricity production from fossil fuels cannot easily be ramped down, on occasions the price of electricity has become negative in response to an over-supply, meaning that commercial consumers are being paid to burn more electricity!

In effect the German EnergieWende amounts to an experiment on a national scale.

More recently gas and oil have become cheaper internationally, as a result of fracking and the exploitation of shale oil in the USA, but gas and oil, while more efficient and less polluting than coal, still produce carbon dioxide.

Environmentalists for Nuclear and Renewables
So what would it really take to limit or even reverse climate change if today's renewable technologies by themselves aren't enough? Ross Koningstein and David Fork are engineers at Google, who worked together on the bold renewable energy initiative known as "RE>C"  Their research led them to think that a new technology is required, which will disrupt the existing status quo, but they don't specify which, or deal with the need to act now and not wait in the hope that some new technology will emerge.

Taking all this into account I've come to the conclusion that, alongside renewables, the only energy production technology that is available to be deployed on a global scale over the next twenty to thirty years, which will not contribute to climate change, is nuclear power.

In this video James Hansen explains why he has reached the same conclusion.



Other environmentalists also expand on their reasons for changing their view of nuclear power in this video.



So, together with a growing community of engineers, scientists and environmental campaigners, I am proposing nuclear power alongside renewables as the future for reducing carbon emissions.

But Not Pressurized Water Reactors!
I am, however, not happy that solid fuel pressurized light water reactors (PWRs), the most common type of reactor currently in service, are the best option for the future other than as a short term stop-gap solution. They represent a design that dates from the late 1960's and there has been little improvement since then. 

I don’t like the fact that, in order to generate high temperature steam at around 300 deg C, PWRs run at a pressure of over 300 bars and therefore present an inherent risk of explosion. To guard against a reactor vessel failure they need enormous reinforced concrete containment vessels. They burn enriched uranium fuel which generates waste with very long lived radioactive transuranics and other isotopes. Also they can only burn a small proportion of this fuel before the fuel rods deteriorate and must be replaced. 

Another major concern is that, when a reactor shuts down unexpectedly, they need backup power supplies in order to run pumps and therefore maintain the cooling needed to remove the heat from radioactive decay. This was what failed at Fukushima Daiichi, where the backup generators were in a location which was only designed to resist a 3 metre tsunami.

Other types of reactor like the liquid metal fast breeder, which typically use molten sodium as the coolant medium have other disadvantages. Sodium metal in liquid form is a good coolant, which operates at higher temperatures and lower pressures than water, but it reacts with air and violently reacts with water. These types of reactors also have a positive temperature coefficient of reactivity, meaning that as the temperature rises nuclear reactions increase and create more heat.  If there is a power failure, and the circulation of coolant stops, they are therefore inherently unstable.

Nuclear Safety
In spite of all these objections and the age of most of the plants currently in use, on a global scale, there have been very few incidents involving nuclear reactors which have had major consequences, and two of those were at plants with fundamental design flaws. At Chernobyl, where 64 people died of acute radiation sickness after emergency work, the reactors were never provided with containment vessels and at Fukushima Daiichi the backup power plant was located such that it was flooded by the tsunami that also killed over 20,000 people. At Three Mile Island operators did not react appropriately when a pilot valve failed and, by sticking open, allowed coolant to escape. This fault had occurred on 11 previous occasions. 

Estimates of future deaths related to radiation exposure from these accidental releases of radioactive material vary widely depending on their source, methods used and the assumptions made. For example for Chernobyl in 2006 the WHO estimate of radiation related premature deaths was 4,000 whereas the Greenpeace estimate was 200,000! In 2008 another WHO report urged caution in the development and use of projections (paragraph 110). 

These estimates, and the methods used to prepare them, are controversial and a full discussion would occupy too much space in this context, as would an examination of the number of fatalities in other industries associated with energy production, like coal mining. The specific point I wish to make is that much safer nuclear options are available than those which are currently in operation and these will be discussed below. 

Liquid Fuelled Reactors for Safer Nuclear Electricity
In view of these potential safety issues a shift away from PWR’s and fast breeders designed in the 60's and 70's towards inherently safe plants would be very welcome. Ideally these should: 
  • operate at atmospheric pressure and so couldn’t explode; 
  • be unable to overheat or meltdown; 
  • be designed to be walk away safe in the event of power failure; 
  • have a negative temperature coefficient of reactivity; 
  • allow load following and rapid output changes;
  • produce much less waste with a much shorter radio-active half-life.  
Of the various proposed Generation IV nuclear reactor designs there is one which fulfills all of these criteria, the liquid fuelled thorium reactor (LFTR).

On 14th July 2011, thanks to Ken Pottinger (now also sadly deceased) I became aware of an alternative to current PWR technologies, which is based on liquid fuelled thorium reactors and the Molten Salt Reactor Experiment. At the time I had no idea that nuclear reactors could have many design variants and even work in the liquid phase.  I spent several days researching the topic and wrote this piece on my blog summarizing my findings. A prototype molten salt reactor, operating at atmospheric pressure, ran at Oak Ridge National Nuclear Laboratory (ORNL) in the 60’s and this film, made at the time, shows how this pilot scale plant was designed, built and operated.


The Molten Salt Reactor Experiment ran for more than 13,000 hours at full power, without significant materials problems, and successfully demonstrated the viability of the concept. To turn it into a commercial product there is more development work needed on the optimization of the waste processing stages, and also on the materials necessary to resist the high temperature and intense radiation environment over the long term. At the time that the project was shut down, ORNL had already started to work on these areas. We are fortunate that the work on the MSRE at Oak Ridge was very fully documented and these documents are in the public domain.

Kirk Sorensen has been actively promoting this technology and he explains in this video how he came to rediscover molten salt reactors and Thorium as an alternative fuel.


What About Nuclear Waste?
But your specific concern was with the management of nuclear waste from PWR’s running on the Uranium 235/238 fuel cycle. 

The composition of nuclear waste depends on the fuel used in the reactor and the degree to which the fuel is burned. Solid fuel reactors can only burn about 1% of the fuel contained in their fuel rods which have to be replaced every 18 months.

Liquid fuelled reactors can burn a much larger percentage of their fuel than solid fuelled reactors because it is so much easier to remove gaseous fission products like Xenon 137, which poison nuclear reactions by absorbing neutrons. Also by incorporating on-line processing to remove waste from a side stream of the main molten salt fuel, there is no need to shut down the reactor to change fuel rods. Therefore, for the same amount of energy generated, molten salt reactors can produce 35 times less waste. 

LFTR versions running on Thorium also produce waste with a much shorter half-life of 300 years as opposed to tens of thousands of years. This very clear video, again from Kirk Sorensen with others, explains how fission products are created and what they can be used for.


In this rather more detailed video Kirk Sorensen projects forward the results of radioactive decay over time on waste from the Uranium 235/238 fuel cycle. He expands on the idea of recycling nuclear waste and asks, is it really all waste? 


But as he says you can also dispose of waste from PWR’s using liquid fuelled waste burning reactors. Leslie Dewan explains how in this video.


Energy Cheaper Than Coal
But without internationally agreed and binding carbon taxes, which would make fossil fuels more expensive, safer nuclear power just won't happen unless it is cheaper than other options. Robert Hargraves puts forward the argument that in order to replace fossil fuel burning power plants you must be able to generate electricity by low carbon methods at an overall cost less than that of fossil fuels. 
In this detailed talk he examines the costs of generating electricity from different sources including wind and solar. He also proposes using liquid fuelled reactors and points out that the higher operating temperatures of such reactors offer higher power generation efficiencies.


If you’ve got this far you are probably suffering from information overload but congratulations on your persistence! I hope that you are now beginning to question the dogmatic opinions of anti-nuclear campaigners because there are plenty of numbers and facts which support the statements above.

Why Hasn't it Been Developed Before?
When I first researched liquid fuelled reactors burning thorium I found it hard not to think that there was something that was being hidden from me. Such as some reasons that explained why such obviously better technology hadn’t been developed! Finally I was convinced that there isn’t anything of the sort and the reasons why it has languished for 60 years are almost entirely political in origin. This google tech talk, again by Kirk Sorensen, explains the background. 



Where Will Safer Nuclear Power Happen First?
This brings me finally to the current political environment. 

With an American President in place who doesn’t believe in man-made climate change, and the need to reduce carbon emissions, there is little or zero chance of any US government support for this technology, at least for the next few years. It’s a complex subject difficult to explain to non-specialists, or the general public, and can’t be fitted into a few tweets for people with short attention spans or other priorities. 

There are numerous privately funded companies which have announced programmes to develop liquid fuelled reactors. It remains to be seen whether this multi-pronged effort can surmount the burdensome costs and difficulties that will arise when they submit their designs for approval by regulatory agencies which are entirely unfamiliar with this technology. In the case of the USA, and at the risk of being called negative, it seems to me unlikely that these companies can persuade regulatory agencies to reduce the estimated one to two billion dollar cost and ten year timescale that the US Government Audit Office currently estimates it would take to certify and license a fundamentally new design. Faced with this private investors just won't bother or, if they are really keen, they will migrate to jurisdictions which are more welcoming.

There are research programmes in several countries, including France, and the International Atomic Energy Agency technical meeting on the status of molten salt reactors in 2016 represents a good summary of recent progress. It's also clear from these proceedings that the only government which is investing serious effort and resources in molten salt reactors is China. They will be the first to recreate the Molten Salt Reactor Experiment and develop it further. They will then patent their designs and sell them internationally. I wish them every success!

A bientôt
John


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