Archive for February, 2015

Could molten salts do for low carbon energy what it did for aluminium?

Posted by Laurence Watson on February 17th, 2015

Sodium Nitrate Salt

Sodium Nitrate salt crystals – by Ondřej Mangl via Wikimedia Commons

In the 1800’s if you wanted to impress your dinner guests you dusted off the aluminium tableware – it was a metal once valued more highly than platinum. That was until American and French engineers Charles Martin Hall and Paul Heroult discovered if you used molten salts in the process for extracting the metal from its ore, you dramatically reduced the costs of production. Today aluminium is so cheap that we use it to wrap our sandwiches. A light and corrosion resistant metal, it has also revolutionised countless industries including aircraft design, helping to make flying affordable enough for us all to enjoy.

In order to keep within a reasonable carbon emissions budget, avoiding risks of greater than 2 degrees global warming, we will need to see a massive scaling up of zero carbon technologies and fast. However, it’s still not yet clear which low carbon technologies are going to be able to deliver reliable power at an affordable cost. Could molten salts do for low carbon power what they did for aluminium production?

Molten salts and solar energy

Mirrors reflecting sunlight at a CSP plant

Compact Linear Fresnel Reflectors – mirrors reflecting sunlight onto structure containing molten salts – from Flickr

Molten salts are already used today as the storage medium for Concentrated Solar Power. The huge arrays of parabolic mirrors currently cropping up in deserted parts of the planet, concentrate the suns rays at a tower filled with molten salts. Salts have a high melting point, which mean they are ideal for absorbing the intense heat of the sun’s rays and for storing that heat even when the sun isn’t shining. A heat exchanger then transfers the heat (using water or heated air) to the turbines to make electricity. Concentrated solar power, in countries where it is viable, offer the tantalising prospect of energy from solar 24/7, making it a reliable form of base-load renewable energy. One of the key limiting factors aside from geography, however, is the availability of the particular type of salts being used today. This is a new source of demand for chemicals at an industrial scale and the supply chain has not yet been established so the cost of procuring the salts is currently very high. Salts are, however, very abundant and if CSP technologies take off there is nothing to stop costs tumbling, if and when chemical companies have the confidence to invest in increased production.

Molten salts and grid storage

Germany’s largest aluminium producer, Trimet Aluminium SE, is exploring how to make best use of the large amounts of molten salts it keeps on site for the electrolysis process. By varying the aluminium production rate at its Essen plant, Trimet can store a lot of energy – up to 3,360MWh over two days – to take advantage of the volatile power prices due to intermittent renewables. Using the plant as a virtual battery could pave the way for more of the same, providing the large amounts of grid storage needed to accommodate more renewables.

Molten salts and nuclear power

Molten salts could also be instrumental to a breakthrough in nuclear power. In the 1960’s, at Oak Ridge laboratories in Tennessee, a team of engineers prototyped a nuclear reactor that used salts instead of water to cool the reactor and transport the heat. They were trying to find a reactor that was inherently safe and realised that unlike water salts could tolerate the extreme heat from a nuclear reactor very well, removing the need to keep coolants under pressure, vastly simplifying things and reducing the risk of accident. The Molten Salt Reactor Experiment (MSRE) has become one of the most talked about alternative nuclear reactor designs in recent years – thanks in no small part to the work of ex-NASA engineer Kirk Sorensen who unearthed reams of information about the MSRE and the men behind it making it available on the web. The question is, dogged by high costs and a legacy of rare but nevertheless significant accidents, can the nuclear industry be persuaded to look again at reactors using molten salts? There is already research underway in the US and China and even a small under-funded effort in the EU. Several new start-ups have emerged relatively recently. If the early promise of molten salts can be properly exploited they could offer a much simpler alternative to today’s reactors – helping nuclear to live up to its true potential in the fight against climate change.


The last area where molten salts could have a role to play is in Carbon Capture and Storage. Even though we are burning fossil fuels at an alarming rate, we are not going to run out of them any time soon. If we want to stay within a safe global temperature increase we will have to stick to a carbon budget of emissions that is fast running out. Either the fossil fuels will need to stay in the ground or, if they are dug up, they will need to be burned in a way that captures and stores the greenhouse gas pollutants. The CCS plants being built today use solvents to scrub out the unwanted gases, which are then concentrated ready for transportation and permanent storage (in, for example, depleted gas fields or saline aquifers). However, there is another way of scrubbing CO2 from flue gases that is currently being explored in the lab and that is to bubble it through molten salts containing a metal anode and cathode. Add an electrical charge and the carbon then plates itself out onto the metal rods giving a pure form of carbon – a useful commodity that could be sold. This form of CCS requires energy to run it since reversing the combustion process, which creates the CO2, cannot be done without additional energy being used. However, the prize of being able to harvest pure carbon – a commodity much in demand for a range of applications including electric vehicle batteries – could mean the economics stack up especially if the extra energy to power the process is being harnessed from waste heat, new kinds of nuclear batteries, and renewables.

The UK has a proud heritage of research in molten salts and there are academic networks like the REFINE consortium and the RSC’s Molten Salts Discussion Group devoted to the subject with scientists from numerous Universities participating. If we want to be at the cutting edge of low carbon technology development we should seriously consider how to increase support for molten salts research and stimulate more commercial investment in the field.

We have no doubt that human ingenuity will crack the challenge of delivering large scale, reliable low carbon energy – the question is whether we do it quickly enough to avoid locking ourselves in to runaway climate change. Our industrial chemists could hold the key and it is high time we supported them in the task of developing the technologies we so urgently need.

Nuclear risk and regulation – time for a rethink?

Posted by Laurence Watson on February 6th, 2015

Nuclear fear – by Me2 on Flickr

Is nuclear over-regulated due to public fear and misconceptions of risks?

“Nuclear power seems to be being singled out for treatment that is not necessarily commensurate with the scale of risk. I say that because, in aggregate, as US climate scientist James Hansen often points out that nuclear has a massively beneficial impact on health in terms of lives saved from avoiding air pollution… There is a need for a public discourse about our perception of risk.”

– Baroness Worthington

Our patron, Baroness Worthington, recently brought up an important point in a debate in the House of Lords about  the formal regulatory process justifying consideration of the Advanced Boiling Water Reactor for deployment in the UK, which Hitachi-GE Nuclear Energy Ltd and Horizon Nuclear Power have proposed to construct at Wylfa and Oldbury. The regulatory justification is just part of the broad legal basis that needs to be covered when planning a new nuclear reactor.

Baroness Verma, the Parliamentary Under Secretary of State for Energy and Climate Change noted in reply that “the sector by its very nature is heavily regulated, and rightly so in order to build confidence”. But why does ionizing radiation receive such special treatment when it comes to assessing risk and if excessive regulation to build public confidence is slowing the development of nuclear power should we look at it again, especially in the context of the growing threats of climate change and air pollution?

Understanding relative doses

The EPR regulatory justification document (2010) describes some of the issues and factors at work when it comes to regulation around ionising radiation.

“The overall average annual dose to a member of the public from all sources of radioactivity is 2.7 millisieverts (a measure of dose and abbreviated as mSv) per year. Of this, about 84% is from natural sources, about 15% from medical procedures and about 1% from all other sources, including existing nuclear power stations….[exposure to radiation from these other sources] is limited to 1 mSv per year.”

“But the regulatory regime goes further than the legal 1 mSv limit. It requires operators to use BAT (Best Available Techniques) and ensure that the resulting exposures are below the statutory limits and as low as reasonably achievable (ALARA) [emphasis ours].

However, while the Health Protection Agency describes the increased risk of cancers from 1mSv as undetectable from background levels, the document goes on to say:

“The maximum occupational dose limit which applies to people at work is 20 mSv per year.”

So, while nuclear plants contribute a very small fraction of radiation exposure and are required to minimise this amount as far as is ‘reasonably’ possible, workers can be exposed to more than twenty times this amount. A chest CT scan will give you 6.6mSv. This great video on the most radioactive places around the world covers the workers and places most highly exposed – the very worst place might surprise you.

Wade Allison, Emeritus Professor of Physics at the University of Oxford writes in his book ‘Radiation and Reason’ that health risks from ionising radiation have been overestimated, and that the body does not have a linear response to ionising radiation.

The Linear No-Threshold (LNT) assessment of dosage to risk declares that as a certain dose of ionising radiation results in an increased chance cancer in a proportion of a population, this proportion will stay constant even if the dose becomes very small. If LNT is not correct for ionising radiation, then proceeding on the basis of ALARA (as low as reasonably achievable) is not an appropriate practice for regulation.

As Baroness Worthington pointed out, James Hansen among others has estimated the benefits of nuclear power from decreased air pollution, as well as avoided carbon emissions. Climate scientists have written en masse to call for more nuclear power. It is clear that in their minds the relatively small risks associated with nuclear power are vastly outweighed by the risks associated with continued dependence on unabated fossil fuels for our energy. It is therefore high time we had an informed public debate about these relative risks and looked again at the nuclear regulatory regime in light of our most recent understandings of risk.    

Fortunately Baroness Verma the Government’s Energy Minister in the Lords appears to agree with us as she ended the debate saying:

“I also agree that the discussions need to be much fuller and more informed, and of course I hope that we will take the opportunity to open that debate going forward…

I accept that what we do not want to do is single out a sector which is helping us to meet our carbon targets. We should not overly prescribe for one sector against others.”

So it appears that whichever party wins in the UK elections in May of this year it might herald the start of a debate about nuclear power, risk and regulation that is long overdue. We will be working hard to make sure that happens.

The recent film Pandora’s Promise does an excellent job of covering nuclear fear-mongering (if you haven’t seen it, it’s available on itunes and soon to be on Netflix). Many myths and scares have muddied the debate about realistic safety concerns.

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