Plastics and Rubbish

In the current “atmosphere” of climate change, politicians are taking more notice of the environment, to which as a sceptic I notice they are not prepared to do a lot about it. Part of the problem is following the “swing to the right” in the 1980s, politicians have taken notice of Reagan’s assertion that the government is the problem, so they have all settled down to not doing very much, and they have shown some skill at doing very little. “Leave it to the market” has a complication: the market is there to facilitate trade in which all the participants wish to offer something that customers want and they make a profit while doing it. The environment is not a customer in the usual sense and it does not pay, so “the market” has no direct interest in it.

There is no one answer to any of these problems. There is no silver bullet. What we have to do is chip away at these problems, and one that indicates the nature of the problem is plastics. In New Zealand the government has decided that plastic bags are bad for the environment, so the single use bags are no longer used in supermarkets. One can argue whether that is good for the environment, but it is clear that the wilful throwing away of plastics and their subsequent degradation is bad for it. And while the disposable bag has been banned here, rubbish still has a lot of plastics in it, and that will continue to degrade. If it were buried deep in some mine it probably would not matter, but it is not. So why don’t we recycle them?

Then first reason is there are so many variations of them and they do not dissolve in each other. You can emulsify a mix, but the material has poor strength because there is very little binding at the interface of the tiny droplets. That is because they have smooth surfaces, like the interface between oil and water. If the object is big enough this does not matter so much, thus you can make reasonable fence posts out of recycled plastics, but there really is a limit to the market for fence posts.

The reason they do not dissolve in each other comes from thermodynamics. For something to happen, such as polymer A dissolving in polymer B, the change (indicated by the symbol Δ) in what is called the free energy ΔG has to be negative. (The reason it is negative is convention; the reason it is called “free” has nothing to do with price – it is not free in that sense.) To account for the process, we use an equation

            ΔG = ΔH -T ΔS

ΔH reflects the change of energy between each molecule in its own material and in solution of the other material. As a general rule, molecules favour having their own kind nearby, especially if they are longer because the longer they are the interactions per atom are constant for other molecules of the same material, but other molecules do not pack as well. Thinking of oil and water, the big problem for solution is that water, the solvent, has hydrogen bonds that make water molecules stick together. The longer the polymer, per molecule that enhances the effect. Think of one polymer molecule has to dislodge a very large number of solvent molecules. ΔS is the entropy and it increases as the degree of randomness increases. Solution is more random per molecule, so whether something dissolves is a battle between whether the randomness per molecule can overcome the attractions between the same kind. The longer the polymer, the less randomness is introduced and the greater any difference in energy between same and dissolved. So the longer the polymers, the less likely they are to dissolve in each other which, as an aside, is why you get so much variety in minerals. Long chain silicates that can alter their associate ions like to phase separate.

So we cannot recycle, and they are useless? Well, no. At the very least we can use them for energy. My preference is to turn them, and all the organic material in municipal refuse, into hydrocarbons. During the 1970s oil crises the engineering was completed to build a demonstration plant for the city of Worcester in Massachusetts. It never went ahead because as the cartel broke ranks and oil prices dropped, converting wastes to hydrocarbon fuels made no economic sense. However, if we want to reduce the use of fossil fuels, it makes a lot of sense to the environment, IF we are prepared to pay the extra price. Every litre of fuel from waste we make is a litre of refined crude we do not have to use, and we will have to keep our vehicle fleet going for quite some time. The basic problem is we have to develop the technology because the engineering data for that previous attempt is presumably lost, and in any case, that was for a demonstration plant, which is always built on the basis that more engineering questions remain. As an aside, water at about 360 degrees Centigrade has lost its hydrogen bonding preference and the temperature increase means oil dissolves in water.

The alternative is to burn it and make electricity. I am less keen on this, even though we can purchase plants to do that right now. The reason is simple. The combustion will release more gases into the atmosphere. The CO2 is irrelevant as both do that, but the liquefaction approach sends nitrogen containing material out as water soluble material which could, if the liquids were treated appropriately, be used as a fertilizer, whereas in combustion they go out the chimney as nitric oxide or even worse, as cyanides. But it is still better to do something with it than simply fill up local valleys.

One final point. I saw an item where some environmentalist was condemning a UK thermal plant that used biomass arguing it put out MORE CO2 per MW of power than coal. That may be the case because you can make coal burn hotter and the second law of thermodynamics means you can extract more energy in the form of work. (Mind you, I have my doubts since the electricity is generated from steam.) However, the criticism shows the inability to understand calculus. What is important is not the emissions right now, but those integrated over time. The biomass got its carbon from the atmosphere say forty years ago, and if you wish to sustain this exercise you plant trees that recover that CO2 over the next forty years. Burn coal and you are burning carbon that has been locked away from the last few million years.

The Fusion Energy Dream

One of the most attractive options for our energy future is nuclear fusion, where we can turn hydrogen into helium. Nuclear fusion works, even on Earth, as we can see when a hydrogen bomb goes off. The available energy is huge. Nuclear fusion will solve our energy crisis, we have been told, and it will be available in forty years. That is what we were told about 60 years ago, and you will usually hear the same forty year prediction now!

Nuclear fusion, you will be told, is what powers the sun, however we won’t be doing what the sun does any time soon. You may guess there is a problem in that the sun is not a spectacular hydrogen bomb. What the sun does is to squeeze hydrogen atoms together to make the lightest isotope of helium, i.e. ²He. This is extremely unstable, and the electric forces will push the protons apart in an extremely short time, like a billionth of a billionth of a second might be the longest it can last, and probably not that long. However, if it can acquire an electron, or eject a positron, before it decays it turns into deuterium, which is a proton and a neutron. (The sun also uses a carbon-oxygen cycle to convert hydrogen to helium.) The difficult thing that a star does, and what we will not do anytime soon, is to make neutrons (as opposed to freeing them).

The deuterium can then fuse to make helium, usually first with another proton to make ³He, and then maybe with another to make ⁴He. Each fusion makes a huge amount of energy, and the star works because the immense pressure at the centre allows the occasional making of deuterium in any small volume. You may be surprised by the use of the word “occasional”; the reason the sun gives off so much energy is simply that it is so big. Occasional is good. The huge amount of energy released relieves some of the pressure caused by the gravity, and this allows the star to live a very long time. At the end of a sufficiently large star’s life, the gravity allows the material to compress sufficiently that carbon and oxygen atoms fuse, and this gives of so much energy that the increase in pressure causes  the reaction  to go out of control and you have a supernova. A bang is not good.

The Lawrence Livermore National Laboratory has been working on fusion, and has claimed a breakthrough. Their process involves firing 192 laser beams onto a hollow target about 1 cm high and a diameter of a few millimeters, which is apparently called a hohlraum. This has an inner lining of gold, and contains helium gas, while at the centre is a tiny capsule filled with deuterium/tritium, the hydrogen atoms with one or two neutrons in addition to the required proton. The lasers heat the hohlraum so that the gold coating gives off a flux of Xrays. The Xrays heat the capsule causing material on the outside to fly off at speeds of hundreds of kilometers per second. Conservation of momentum leads to the implosion of the capsule, which gives, hopefully, high enough temperatures and pressures to fuse the hydrogen isotopes.

So what could go wrong? The problem is the symmetry of the pressure. Suppose you had a spherical-shaped bag of gel that was mainly water, and, say, the size of a football and you wanted to squeeze all the water out to get a sphere that only contained the gelling solid. The difficulty is that the pressure of a fluid inside a container is equal in all directions (leaving aside the effects of gravity). If you squeeze harder in one place than another, the pressure relays the extra force per unit area to one where the external pressure is weaker, and your ball expands in that direction. You are fighting jelly! Obviously, the physics of such fluids gets very complicated. Everyone knows what is required, but nobody knows how to fill the requirement. When something is unequal in different places, the effects are predictably undesirable, but stopping them from being unequal is not so easy.

The first progress was apparently to make the laser pulses more energetic at the beginning. The net result was to get up to 17 kJ of fusion energy per pulse, an improvement on their original 10 kJ. The latest success produced 1.3 MJ, which was equivalent to 10 quadrillion watts of fusion power for a 100 trillionth of a second. An energy generation of 1.3 MJ from such a small vessel may seem a genuine achievement, and it is, but there is further to go. The problem is that the energy input to the lasers was 1.9 MJ per pulse. It should be realised that that energy is not lost. It is still there so the actual output of a pulse would be 3.2 MJ of energy. The problem is that the output includes the kinetic energy of the neutrons etc produced, and it is always as heat whereas the input energy was from electricity, and we have not included the losses of power when converting electricity to laser output. Converting that heat to electricity will lose quite a bit, depending on how it is done. If you use the heat to boil water the losses are usually around 65%. In my novels I suggest using the magnetohydrodynamic effect that gets electricity out of the high velocity of the particles in the plasma. This has been made to work on plasmas made by burning fossil fuels, which doubles the efficiency of the usual approach, but controlling plasmas from nuclear fusion would be far more difficult. Again, very easy to do in theory; very much less so in practice. However, the challenge is there. If we can get sustained ignition, as opposed to such a short pulse, the amount of energy available is huge.

Sustained fusion means the energy emitted from the reaction is sufficient to keep it going with fresh material injected as opposed to having to set up containers in containers at the dead centre of a multiple laser pulse. Now, the plasma at over 100,000,000 degrees Centigrade should be sufficient to keep the fusion going. Of course that will involve even more problems: how to contain a plasma at that temperature; how to get the fuel into the reaction without melting then feed tubes or dissipating the hydrogen; how to get the energy out in a usable form; how to cool the plasma sufficiently? Many questions; few answers.

What to do about Climate Change

As noted in my previous post, the IPCC report on climate change is out. If you look at the technical report, it starts with pages of corrections. I would have thought that in these days the use of a word processor could permit the changes to be made immediately, but what do I know? Anyway, what are the conclusions? As far as I can make out, they have spent an enormous effort measuring greenhouse gas emissions and modelling, and have concluded that greenhouse gases are the cause of our problem and if we stopped emitting right now, totally, things would not get appreciably worse than they are now over the next century. As far as I can make out, that is it. They argue that CO2 emissions give a linear effect and for every trillion tonnes emitted, temperatures will rise by 0.45 Centigrade degrees, with a fairly high error margin. So we have to stop emitting.

The problem is, can we? In NZ we have a very high fraction of our electricity from renewable sources and we recently had a night of brown-outs in one region. It was the coldest night of the year, there was a storm over most of the country, but oddly enough there was hardly any wind at a wind farm. A large hydro station went out as well because the storm blew weeds into an intake and the station had to shut down and clean it out. The point is that when electricity generation is a commercial venture, it is not in the generating companies’ interests to have a whole lot of spare capacity and it make no sense to tear down what is working well and making money to spend a lot replacing it. So, the policy of using what we have means we are stuck where we are. China has announced, according to our news, that its coal-fired power stations will maximise and plateau their output of CO2 in about ten years. We have no chance of zero emissions in the foreseeable future. Politicians and environmentalists can dream on but there is too much inertia in an economy. Like a battleship steering straight for the wharf, the inevitable will happen.

Is there a solution? My opinion is, if you have to persist in reducing the heat being radiated to space, the best option is to stop letting so much energy from the sun into the system. The simplest experiment I can think of is to put huge amounts of finely dispersed white material, like the silica a volcano puts up, over the North Polar regions each summer to reflect sunlight back to space. If we can stop as much winter ice melting, we would be on the way to stop the potential overturn of the Gulf Stream and stop the Northern Siberian methane emissions. Just maybe this would also encourage more snow in the winter as the dust falls out.

Then obvious question is, how permanent would such a dispersion be? The short answer is, I don’t know, and it may be difficult to predict because of what is called the Arctic oscillation. When that is in a positive phase it appears that winds tend to circulate over the poles, so it may be possible to maintain dust over summer. It is less clear what happens in the negative phase. However, either way someone needs to calculate how much light has to be blocked to stop the Arctic (and Antarctic) warming. Maybe such a scheme would not be practical, but unless we at least make an effort to find out, we are in trouble.

This raises the question of who pays? In my opinion, every country with a port benefits if we can stop major sea level rising, so all should. Of course, we shall find that not all are cooperative. A further problem is that the outcome is somewhat unpredictable. The dust only has to last during the late spring and summer, because the objective is to reflect sunlight. For the period when the sun is absent it is irrelevant. We would also have to be sure the dust was not hazardous to health but we have lived through volcanic eruptions that have caused major lowering of the temperature world-wide so there will be suitable material.

There will always be some who lose on the deal. The suggestion of putting the dust over the Arctic would make the weather less pleasant in Murmansk, Fairbanks, Yukon, etc, but it would only return it to what it used to be. It is less clear what it would do elsewhere. If the arctic became colder, presumably there would be colder winter storms in more temperate regions. However, it might be better that we manage the climate than then planet does, thus if the Gulf Stream went, Europe would suffer both rising sea levels and temperatures and weather more like that of Kerguelen. In my opinion, it is worth trying.

But what is the betting any proposal for geoengineering has no show of getting off the ground? The politically correct want to solve the problem by everyone giving up something, they have not done the sums to estimate the consequences, and worse, some will give things up but enough won’t so that such sacrifices will be totally ineffective. We have the tragedy of the commons: if some are not going to cooperate and the scheme hence must fail, why should you even try? We need to find ways of reducing emissions other than by stopping an activity, as opposed to the emission.

The Non-Green Internet

Did you know that by reading this you are contributing to climate change. Oops! Seriously, it is claimed that by 2025 the internet will use a fifth of the world’s electricity, assuming no massive increase in the use of electric transport. And before you decide to stop reading this to save the climate, apart from the use of your computer, you make no difference whether you read it or not. On the other hand, apparently Bitcoin mining consumes the total electricity consumption of Switzerland, so steady on there. The infrastructure for the internet is always on, and the messages you send make no difference. Sorry but you cannot save the world by not sending that email, and of course had you posted a physical letter, there would have been significant greenhouse gas emissions from getting the letter from your desk to wherever.

People that store their work in the cloud do contribute. A major data centre consumes about 30 GWh per year, and the UK has about 450 data centres. After all, all this rubbish we write and record has to be stored somewhere. That raises the question, how many data centres will have to be built? These centres are where the “cloud” resides, and if everyone is busy filling them up, what happens when it is no longer so easy to build more? How long can we continue recording everything?

How much has to be recorded for posterity? All those pointless Facebook posts that make pointless comments (rude or otherwise) or show a few emoticons. If they were deleted after a few weeks, would anyone notice? The problem then, of course, is, who decides? Notice the recent fuss about Trump not being allowed to tweet. In my opinion, if they had done that to him when he became President he would have been more effective but that is another matter. The problem is, when you appoint a “Great Deleter” you open up so many cans of worms it is not funny. Some of what we store will be of interest historically, perhaps especially Trump’s tweets. Right now photos recovered from long ago fascinate many of us. I know that I recently downloaded a whole lot of photos of the area where my mother grew up, and where, still a long time ago, I drove her back to have a look around. So for me, it was of interest to hear her say what was there, where, and now be able to see it. Quite simply, in two lifetimes everything has changed remarkably, and what was there is no longer, other than in memories, and memories die. Also, storing photos in data centres takes up much less space than storing hard copies. Of the hard copies left, many have been lost, but how much of what is stored digitally will be available in a hundred years?

Much of what is stored digitally may become unreadable. In the scientific community, for example, the Royal Society for Chemistry has noted that computations carried out in the last century often use code that nobody now understands. Some of us have computer files written many years ago, but unless they were updated and converted into new formats they are unreadable other than on an ancient computer. Back to electricity, either we can go into our shell and try to live like the Amish, do something about electricity generation, or be like politicians and make encouraging speeches and hope all gets well. Apparently, Facebook, Apple, Google and others have committed to using 100% renewable electricity (although when is another question) and Microsoft claims that by 2050 it will have removed all the carbon emissions it has ever produced. These are noble aspirations, but so far, according to Greenpeace, only about 20% of the electricity used by the world’s data centres is renewable. Further, the data centres run uniform power consumption over the entire time. Solar is of little use during the night, and wind power fails when the wind is not blowing. If we rely heavily on such renewables, what happens when there are blackouts? And, of course, there is the question of the non-renewable resources used to build the computers in the cloud. So no, I do not think anyone will be reading my blogs in a hundred years. However, we should make more effort to generate electricity more sustainably. Unless we solve the fusion problem, I favour the liquid salt thorium-type reactor.

Climate Change and International Transport

You probably feel that in terms of pollution and transport, shipping is one of the good guys. Think again. According to the Economist (March 11, 2017) the emissions of nitrogen and sulphur oxides from 15 of the world’s largest ships match those from all the cars on the planet. If the shipping industry were a country, it would rank as the sixth largest carbon dioxide emitter. Apparently 90%  of trade is seaborne, and in 2018, 90,000 ships burn two billion barrels of the dirtiest fuel oil, and contribute 2 – 3% of the world’s total greenhouse emissions. And shipping is excluded from the Paris agreement on climate change. (Exactly how they wangled that is unclear.) The International Maritime Organization wants to cut emissions by 50% by 2050, but prior to COVID-19, economic growth led to predictions of a six-fold increase by then!

Part of the problem is the fuel: heavy bunker oil, which is what is left over after refining takes everything else it can use. Apparently it contains 3,500 times as much sulphur as diesel fuel does. Currently, the sale of these high sulphur fuels has been banned, and sulphur content must be reduced to 0.5% (down from 3.5%) and some ships have been fitted with expensive scrubbers to remove pollutants. That may seem great until you realize 80% of these scrubbers simply dump the scrubbed material, a carcinogenic mix of various pollutants, into the sea. They also increase fuel consumption by about 2%, thus increasing carbon dioxide missions.

On the 19th February, 2020, the Royal Society put out a document advocating ammonia as a zero-carbon fuel, and suggested that the maritime industry could be an early adopter. What do you think of that?

First, ammonia is currently made by compressing nitrogen and hydrogen at higher temperatures over a catalyst (The Haber process). The compression requires electricity, and the hydrogen is made by steam reforming natural gas, which is not carbon free, however it could be made by electrolysing water, which would be a use for “green” electricity”. The making of hydrogen this way may well be sound, but running the Haber process probably is not. The problem with this process is it really has to be carried out continuously, and solar energy is not available at night, and the wind does not always blow. However, leaving that aside, that part of the scheme is plausible. Ammonia can be burnt in a motor, or more efficiently in a fuel cell to make electricity. If you could make this work there are some ships that use diesel to make electricity to power motors, so that might work. Ammonia has an energy content of 3 kWh/litre (liquid hydrogen is 2/3 this) while heavy fuel oil has an energy content of 10 kWh/l. The energy efficiency of converting combustion energy to work is much higher in a fuel cell.

Of course by now you will have all worked out why this concept is a non-starter. The problem is the ship, its fuel tanks and motors, are part of the construction and are deep within the ship. The cost of conversion would be horrendous so it is most unlikely to happen. Equally, if we were serious about climate change, we could convert ships to use nuclear power. Various navies around the world have shown how this can be done safely. Don’t hold your breath waiting for the environmentalists to endorse that idea.

However, converting to nuclear power has the same problem as converting to ammonia: a huge part of the ship has to be demolished and rebuilt, so that is a non-starter. So there is no way out? Not necessarily.  I have currently been spending my lockdown writing a chapter for a book in a series on hydrothermal treatment of algae. Now the interesting thing about the resultant biocrude is that while you can make very high octane petrol and high cetane diesel, there is a residue of heavy viscous fluid that can be mainly free of sulphur and nitrogen. What on earth could you do with that? It is a thick viscous oil, surprisingly like heavy bunker oil. Any guesses as to what I might be tempted to recommend?

Aircraft and Carbon Dioxide Emissions

Climate change requires significant changes to our lifestyle, and one of the more tricky problems to solve is air travel. Interestingly, you will find many environmentalists always telling everyone to cycle, but then spend tens of thousands of air miles going to environmental conferences. So, what can we do?

One solution is to reduce air travel. And there is no need in principle to adopt Greta Thunberg’s solution of sailing over the Atlantic. With a bit of investment, high speed rail can get you between the centres of reasonably close cities faster than aircraft, when you include the time taken to get to and from airports, and time wasted at airports. We can also reduce travel, but only so far. At first sight, things like conferences can be held online, but there are two difficulties: time-zone differences encourage doing something else, and second, the major benefit from conferences is not listening to set talks, but rather meeting people outside the formal program. For business, facing each other is a far improved way of negotiating because the real signals are unspoken. 

Some airlines are trying to improve their environmental credentials by planting trees to compensate for the carbon dioxide they emit. That is very noble of them, but apart from the fact it is their money doing it (and often it is not – it is the passengers who feel conscious stricken to donate more money for planting) it is something that should be done anyway. 

There has been talk of building electric aircraft. My personal opinion is this is not the solution. The problem is in terms of unit weight, jet fuel contains at least thirty times the energy density of the best batteries available. Even worse, for jet fuel, as you go further, you get lighter, but not with batteries. You could make a large aircraft fly, say, 1,000 to 2,000 km, as long as you did not want to carry much in the way of passengers or cargo. With thirty times the fuel weight for a long distance flight your aircraft would never get off the ground. However, the Israeli firm Eviation has developed a small electric aircraft for a load of 9 persons (plus two crew) powered by 920 kWh batteries with operating costs estimated at $200/hr. The range is about 540 nautical miles, or about 1,000 km. That could work for small regional flights, and it will be available soon.

Another option to be offered by Airbus is the E-Fan-X project. They will take a BAe 146 craft, which usually carries about 100 passengers, and which usually is powered by four Honeywell turbofan engines, and replace one of the inner ones with an electric-driven 2 MW propulsion fan motor. The idea is the takeoff, where the most power is required will use the normal jets, but the electric motor can manage the cruise. 

An alternative is to reduce fuel consumption. One possibility is the so-called blended wing, which is being looked at by NASA. This works; an example is the B2 bomber, however while it reduces fuel consumption by 20% it is most unlikely to come into commercial use any time soon. One reason is that there is probably no commercial airport that could accommodate the radically different design. It would also have to have extensive examination because so far the design has only had military applications, in which only very specific loads are involved. In principle, this, and other designs can reduce kerosene usage, but only by so much. Maybe overall, 25% is achievable, which does not solve anything.

Uranium 235 has an energy density that leaves kerosene for cold, but which airport wants it, and would you board it anyway? It could presumably be made to work, but I can’t see it happening anytime soon because nobody will take the associated political risk.

That leaves hydrogen. 1 kg of liquid hydrogen can provide the same energy as 3 kg of kerosene, so weight is not the problem, but keeping it cold enough and maintaining pressure will add weight. It cannot be stored in the aircraft wings because of the volatility. To keep it cold it is desirable to have minimum surface area of the tank. However, it is reasonably clean burning, giving only water and some nitrogen oxides. For a Boeing 747-400 aircraft, the full fuel load is 90 tonne less, but because the tanks have to be in the fuselage, they occupy about 30% of the passenger space.

That may work for the future, but the only real way to power current aircraft is to burn hydrocarbon fuel. More on that next week.

Molten Salt Nuclear Reactors

In the previous post, I outlined two reasons why nuclear power is overlooked, if not shunned, despite the fact it will clearly reduce greenhouse gas emissions. I discussed wastes as a problem, and while they are a problem, as I tried to show they are in principle reasonably easily dealt with. There is a need for more work and there are difficulties, but there is no reason this problem cannot be overcome. The other reason is the danger of the Chernobyl/Fukushima type explosion. In the case of Chernobyl, it needed a frightening number of totally stupid decisions to be made, and you might expect that since it was a training exercise there would be people there who knew what they were doing to supervise. But no, and worse, the operating instructions were unintelligible, having been amended with strike-outs and hand-written “corrections” that nobody could understand. You might have thought the supervisor would check to see everything was available and correct before starting, but as I noted, there has never been a shortage of stupidity.

The nuclear reaction, which generates the heat, is initiated by a fissile nucleus absorbing a neutron and splitting, and then keeping going by providing more neutrons. These neutrons either split further fissile nuclei, such as 235U, or they get absorbed by something else, such as 238U, which converts that nucleus to something else, in this case eventually 239Pu. The splitting of nuclei produces the heat, and to run at constant temperature, it is necessary to have a means of removing that amount of heat continuously. The rate of neutron absorption is determined by the “concentration” of fissile material and the amount of neutrons absorbed by something else, such as water, graphite and a number of other materials. The disaster happens when the reaction goes too quickly, and there is too much heat generated for the cooling medium. The metal melts and drips to the bottom of the reactor, where it flows together to form a large blob that is out of the cooling circuit. As the amount builds up it gets hotter and hotter, and we have a disaster.

The idea of the molten salt reactor is there are no metal rods. The material can be put in as a salt in solution, so the concentration automatically determines the operating temperature. The reactor can be moderated with graphite, beryllium oxide, or a number of others, or it can be run unmoderated. Temperatures can get up to 1400 degrees C, which, from basic thermodynamics, gives exceptional power efficiency, and finally, reactors can be relatively small. The initial design was apparently for aircraft propulsion, and you guessed it: bombers. The salts are usually fluorides because low-valence fluorides boil at very high temperatures, they are poor neutron absorbers, and their chemical bonds are exceptionally strong, which limits corrosion, and they are exceptionally inert chemically. In one sense they are extremely safe, although since beryllium fluoride is often used, its extreme toxicity requires careful handling. But the big main advantage of this sort of reactor, besides avoiding the meltdown, is it burns actinides and so if it makes plutonium, that is added to the fuel. More energy! It also burns some of the fission wastes, and such burning of wastes also releases energy. It can be powered by thorium (with some uranium to get the starting neutrons) which does not make anything suitable for making bombs. Further, the fission products in the thorium cycle have far shorter half-lives. Research on this started in the 1960s and essentially stopped. Guess why! There are other fourth generation reactors being designed, and some nuclear engineers may well disagree with my preference, but it is imperative, in my opinion, that we adopt some. We badly need some means of generating large amounts of electricity without burning fossil fuels. Whatever we decide to do, while the physics is well understood, the engineering may not be, and this must be solved if we are to avoid a planet-wide overheating. The politicians have to ensure this job gets done.

Nuclear Waste Management

It is now generally recognized (apart from a few recidivists and those with deep investment in the fossil fuel industries) that we have to find alternatives to fossil fuels as energy sources. There is great enthusiasm for solar and wind power, despite the obvious shortcomings for total replacement that are generally overlooked, but one of the obvious replacements, nuclear power, is shunned. There are two reasons: the danger of reactor explosions, such as at Chernobyl and Fukushima, both of which were caused by stupidity, which, unfortunately, is never in short supply, and the hazard of nuclear waste. Whether we can get around stupidity is debatable, but we should be able to design so that the effects are minimal. In this post I want to think about nuclear waste, and I am going to mainly consider the current standard reactor process. However, I argue the main problem is social: people are so against nuclear power it is difficult to get the required programs implemented.

The usual waste is extremely dangerous, and comprises two subsets: fissioned products, which tend to have shorter half-lives, e.g. strontium ninety has a half-life of 29.1 years, and actinides, which have longer half-lives, the plutonium 239 has a half-life of 24,000 years. Because of the latter, very long storage is required, and the usual thought is it has to be stored for a minimum of 100,000 years. My personal view is that is far too short if plutonium is present. If we are going to bury this, we need geological structures that will remain unchanged for that length of time. The amount of waste is fortunately not excessive; a plant that produces 1 GW (and earns more than $1 million/day) apparently produces 20 t/day. The good news is that there are plenty of rock formations that have not changed in 100 million years, so the problem now is to put the waste down in a form that will stay where you put it.

The waste comes out in small ceramic pellets that have been heated at several hundred degrees Centigrade for a number of years. They are tough and can be dumped right then. The usual next step is to encase the radioactive nuclides in molten glass, which is then put into a stainless steel container, which is then put into a copper container. Provided there is no oxygen or sulphur-containing gas, copper simply does not react with anything found naturally in rock. The container then goes into a repository at a depth of several hundred meters in a hard rock, and that is further surrounded by bentonite clay, which is water-tight. 

That is the ideal. Unfortunately, so far there appear to be no such operational depositories, so the waste is buried in somewhat less desirable ways. There is a further problem in that a clay cannot be water-tight forever, and water-tightness may be a problem. A recent report (https://www.nature.com/articles/s41563-019-0579-x) has indicated a possible flaw that may make it necessary to revisit the current storage. When the glass or ceramic is placed in the steel cannister, as it cools a thin gap is created. If water gets into this gap, corrosion might occur, and if it does, the water gets progressively more acid, and that acid might start leaching waste. This is possible because when the waste is vitrified, it is distributed through the glass and some is at the glass surface. In my opinion there are various ways around this. The most obvious is to have only glass on the surface following vitrification, and that may mean two processes, the gap can be enclosed with silicone, and perhaps the steel could be enclosed in molten basalt. I do not know the answers, but I am reasonably convinced there is an answer.

We can do more. Reprocessing recovers plutonium and unburnt uranium, and it is possible to recover more fuel than you started with. This is because the initial fuel is uranium 235, but it would be surrounded by much more uranium 238; this is what absorbs a neutron and converts to plutonium 239. There will also be other useful radioactive isotopes there, such as americium for fire alarms, cobalt sixty for medical use, but of course there will remain a lot of rather noxious material. Most of the rest can be transmuted into more harmless material by irradiating them. Simple, so why don’t we do it? The basic reason is that most of the reactors currently used are of the light-water kind, and these cannot easily be so used. 

Different reactor designs can help the problem. Most current ones use a moderator to slow the neutrons. The advantages of this are stated to be that the required enrichment of uranium is much lower, and the plants are cheaper. The alternative of using fast neutrons (and no moderator) produce much less transuranic waste because the actinides are fissionable with fast neutrons. Paradoxically, Iran’s higher enrichment program could be used in fast neutron reactors and it would be much harder for them to produce bombs, but this seems not to be considered by the anti-Iran brigade. Molten salt reactors are claimed to produce less than one thousandth of the actinides. The actinides are the longest living waste, and they tend to be highly poisonous as well. So why are moderated reactors the predominant reactor? Possibly because they yield far more plutonium, and that is needed for bombs by the nuclear powers. It is alleged they are also cheaper. However, burning off these nuclides economically and safely is some distance away. It would involve a lot of money to set things up, and it would be preferable to develop much better robotic technology because you do not want to expose workers to the radiation while doing the processing. There is a further problem. If you have a large number of countries with nuclear power plants, using current technology, you have a large number of countries producing plutonium. The prospect of rogue countries developing bombs to blast out their neighbours is a deep problem, but there are ways around that. Unfortunately, that involves a somewhat radical change in the way some countries play politics.

Forests versus Fossil Fuels – a Debate on Effectiveness

The use of biomass for fuel has been advocated as a means of reducing carbon dioxide emissions, but some have argued it does nothing of the sort. There was a recent article in Physics World that discusses this issue, and here is a summary. First, the logic behind the case is simple. The carbon in trees all comes from the air. When the plant dies, it rots, releasing energy to the rotting agents, and much of the carbon is released back into the air. Burning it merely intercepts that cycle and gives the use of the energy to us as opposed to the microbes. A thermal power station in North Yorkshire is now burning enough biomass to generate 12% of the UK’s renewable energy. The power station claims it has changed from being one of the largest CO2 emitters in Europe to supporting the largest decarbonization project in Europe. So what could be wrong? 

My first response is that other than a short-term fix, burning it in a thermal power station is wrong because the biomass is more valuable for generating liquid fuels, for which there is no alternative. There are many alternative ways of generating electricity, and the electricity demand is so high that alternatives are going to be needed. There is no obvious replacement for liquid fuels in air transport, although the technology to make such fuels is yet to be developed properly. 

So, what can the critics carp on about? There were two criticisms about the calculated savings being based on the assumptions: (a) the CO2 released is immediately captured by growing plants, and (b) the biomass would have rotted and put its carbon back into the atmosphere anyway. The first is patently wrong, but so what? The critics claim it takes time for the CO2 to be reabsorbed, and that depends on fresh forest, or regrowth of the current forest. So replanting is obviously important, but equally there is quite some time used up in carbon reabsorption. According to the critics, this takes between 40 and a hundred years, then it is found that because biomass is a less energy-dense material during combustion, compared with coal you actually increase the CO2 emissions in the short-term. The reabsorption requires new forest to replace the old.

The next counter-argument was that the block should not be counted, but rather the landscape – if you only harvest 1% of the forest, the remaining 99% is busily absorbing carbon dioxide. The counter to that is that it would have been doing that anyway. The next objection is that older forests absorb carbon over a much longer period, and sequester more carbon than younger stands. Further, the wood that rots in the soil feeds microbes that otherwise will be eating their way through stored carbon in the soil. The problem is not so much that regrowth does not absorb carbon dioxide, but rather it does not reabsorb it fast enough to be meaningful for climate change.

Let us consider the options where we either do it or we do not. If we do, assume we replant the same area, and fresh vegetation is sufficient to maintain the soil carbon. In year 1 we release x t CO2. After year 40, say, it has been all absorbed, but we burn again and release x t CO2. By year 80, it is all reabsorbed, so we burn again. There is a net x t CO2 in the air. Had we not done this, in each of years 1, 40 and 80 we burn kx t CO2, giving us now 3kx t CO2, where k is some number <1 to counter the greater efficiency of burning coal. Within this scenario eventually the biofuel must save CO2. That we could burn coal and plant fresh forests is irrelevant because in the above scenario we only replace what was there. We can always plant fresh forest.

Planting more works in both options. This is a bit oversimplified, but it is aimed to show that you have to integrate what happens over sufficient time to eliminate the effect of non-smoothness in the functions, and count everything. In my example above it could be argued I do not know whether there will be a reduction in soil carbon, but if that is troublesome, at least we have focused attention on what we need to know. It is putting numbers on a closed system, even if idealized, that shows the key facts in their proper light. 

Transport System Fuel. Some passing Comments

In the previous series of posts, I have discussed the question of how we should power our transport systems that currently rely on fossil fuels, and since this will be a brief post, because I have been at a conference for most of this week, I thought it would be useful to have a summary. There are two basic objectives: ensure that there are economic transport options, and reduce the damage we have caused to the environment. The latter one is important in that we must not simply move the problem.

At this stage we can envisage two types of power: heat/combustion and electrical. The combustion source of power is what we have developed from oil, and many of the motors, especially the spark ignition motors, have been designed to optimise the amount of the oil that can be so used. The compression of most spark ignition engines is considerably lower than it could be if the octane rating was higher. These motors will be with us for some time; a car bought now will probably still be on the road in twenty years so what do we do? We shall probably continue with oil, but biofuels do offer an alternative. Some people say biofuels themselves have a net CO2 output in their manufacture. Maybe, but it is not necessary; the main reason would be that the emphasis is put onto producing the appropriate liquids because they are worth more than process heat. Process heating can be provided from a number of other sources. The advantages of biofuels are they power existing vehicles, they can be CO2 neutral, or fairly close to it, we can design the system so it produces aircraft fuel and there is really no alternative for air transport, and there are no recycling problems following usage. The major disadvantages are that the necessary technology has not really been scaled up so a lot of work is required, it will always be more expensive than oil until oil supplies run down so there is a poor economic reason to do this unless missions are taxed, and the use of the land for biofuels will put pressure on food production. The answers are straightforward: do the development work, use the tax system to change the economic bias, and use biomass from the oceans.

There are alternatives, mainly gases, but again, most of them involve carbon. These could be made by reducing CO2, presumably through using photolysis of water (thus a sort of synthetic photosynthesis) or through electricity and to get the scale we really need a very significant source of electricity. Nuclear power, or better still, fusion energy would work, but nuclear power has a relative disappointing reputation, and fusion power is still a dream. Hydrazine would make a truly interesting fuel, although its toxicity would not endear it to many. Hydrogen can work well for buses, etc, that have direct city routes.

Electricity can be delivered by direct lines (the preferred option for trains, trams, etc.), but otherwise it must be by batteries or fuel cells. The two are conceptually very similar. Both depend on a chemical reaction that can be very loosely described as “burning” something but generating electricity instead of heat. In the fuel cell, the material being “burnt” is added from somewhere else, and the oxidising agent, which may be air, must also be added. In the battery, nothing is added, and when what is there is used, it is regenerated by charging.

Something like lithium is almost certainly restricted to batteries because it is highly reactive. Lithium fires are very difficult to put out. The lithium ion battery is the only one that has been developed to a reasonable level, and part of the reason for that is that the original market was for mobile phones and laptops. There are potential shortages of materials for lithium ion batteries, but they would never cut in for those original uses. However, as shown in my previous post, recycling of lithium ion batteries will be very difficult to solve the problem for motor vehicle batteries. One alternative for batteries is sodium, obtainable from salt, and no chance of shortage.

The fuel cell offers some different options. A lot has been made of hydrogen as the fuel of the future, and some buses use it in California. It can be used in a combustion motor, but the efficiencies are much better for fuel cells. The technology is here, and hydrogen-powered fuel cell cars can be purchased, and these can manage 500 km on  single charge, and can totally refuel in about 5 minutes. The problem again is, hydrogen refuelling is harder to find. Methanol would be easier to distribute, but methanol fuel cells as of yet cannot sustain a high power take-off. Ammonia fuel cells are claimed to work almost as well as hydrogen and would be the cheapest to operate. Another possibility I advocated in one of my SF novels is the aluminium/chlorine cell, as aluminium is cheap, although chlorine is a little more dangerous.

My conclusions:

(a)  We need a lot more research because most options are not sufficiently well developed,

(b)  None will out-compete oil for price. For domestic transport, taxes on oil are already there, so the competitors need this tax to not apply

(c)  We need biofuels, if for no other reason that maintaining existing vehicles and air transport

(d)  Such biofuel must come at least partly from the ocean,

(e)  We need an alternative to the lithium ion battery,

(f)  We badly need more research on different fuel cells, especially something like the ammonia cell.

Yes, I gree that is a little superficial, but I have been at a conference, and gave two presentations. I need to come back down a little 🙂