Saturday, March 14, 2009

Safe acceptable nuclear power? Here's a way...

Mephistopheles flying over Wittenberg, in a lithograph by Eugène Delacroix. Image credit: WikipediaUse now; pay later ... a Faustian pact with fossil fuels: Burning fossil fuel the way we do now could almost have been designed to seriously endanger humankind and myriads of other forms of life on this planet. You want climate chaos? Okay, just burn up all that coal, oil and gas as fast as you can and you'll get a climate guaranteed to cause a mass extinction which will likely include humans. Mephistopheles, to mix metaphors, gets his pound of flesh. Suffering and mega-death are part of the fossil fuel package, clearly visible to those who can see beyond the PR smoke of the fossil fuel industry. So can we have our energy cake and eat it too? Yes, if we eschew fossil fuels and look for alternatives.

Renewable energy gap: I'm enthusiastic about renewable energy. I've built an eco-cottage (massive insulation) and a passive-solar conservatory for heating my stone-built farmhouse. I'm about to install an air-source heat pump and, in a few months, I hope to set about the installation of a grid-connected 6kW Proven wind turbine. I live a simple, low energy life. I travel very little, never fly and burn wood grown on this farm in my woodburning stove . I also plant trees. And my aim? To be carbon neutral.

Most people can't do many of these sorts of things if they live in towns or cities. They need - and expect to have - electric energy available at the flick of a switch. So do I! So... can renewables like wind and solar power deliver the energy we need? Unfortunately, the answer - for the time being - is no and all the green bluster about solar, wind and waves being able to do it is just naive. In time - by which I mean decades - renewables could and should power the planet when we have built infrastructure like supergrids, vast solar arrays in the Sahara desert and so on. But for now, renewables provide just a few percent of total electric energy used. When the wind doesn't blow and the sun doesn't shine, they're useless. This winter, there have been weeks of cold grey weather without wind. The lights still work because of fossil fuel... and nuclear generation.

Choices: We all want the lights to work when we need them. Almost every modern gadget and convenience depends utterly on dependable electricity supply. So we have choices to make:
  1. carry on burning fossil fuels like there was no tomorrow... which there won't be
  2. eliminate fossil fuels as soon as possible whilst building up renewable supply systems
  3. build nuclear power stations to replace coal-fired plants as quickly as possible, whilst pursuing renewable generation also as fast as possible (part of the much vaunted Green New Deal which may or may not come to pass)

Option 1 means disaster and ought to be unacceptable to anyone who cares about the future for their children and the rest of life on our despoiled planet.

Option 2 means many years of unreliable electricity supply with frequent power cuts. It would work if everyone was prepared to undergo hardship: cold houses, no lights, no TV, no computers for much of the time. But almost everyone would find this unacceptable too

So we're left with Option 3. Nuclear power stations have been working away, generating reliable baseload power for many years. There have been serious problems and even a disaster or two, but modern designs have good safety records. Unlike coal, they almost never kill people.

Protests: It goes without saying that any attempt to build new nuclear plants in countries like Britain will result in massive protests. The reasons people protest against nuclear plants are well known and often justified. At the very least, the massive reactor containment structures are eyesores and at the end of the reactor's life will have to remain there for many decades while radiation levels decay sufficiently for dismantling. Then there's proliferation and the unsolved radioactive waste problem. These are genuine causes for concern.

Protests can and do delay construction, sometimes for years. We haven't got years to cut carbon emissions. So is there a way to make nuclear power more acceptable to people who would otherwise protest? And is there a way to make it even safer than it is now? I think there is...

Out of sight, out of mind: If you visit Llanberis in North Wales, you'll probably not be aware that there's a major power station there. Where is it? You can't see all the usual structures. The reason is because it is completely underground. So why not take that notion further? Why not build nuclear power plants underground too? The size of excavation needed for a nuclear plant is comparable to the Dinorwig pumped storage power station in Llanberis, as my drawing shows.
Size comparison between the Sizewell PWR and Dinorwig pumped storage excavations
Let's consider the advantages that underground construction would offer:


  1. because the containment is unbreachable (given proper choice of ground conditions, hydrogeology and rock types), reactor assemblies would be immune to military attack from the air and also from suicide bombers. Containment above ground could not withstand bunker-busting bombs or small nuclear devices, the latter possibly 'delivered' by suicide vehicle. In our dangerous world, these are possibilities
  2. such unbreachable containment is also immune to accidents, whether external (e.g. crashing airliners) or internal such as major loss of coolant (Three Mile Island) or even Chernobyl-style meltdown disasters. Building robust containment structures above ground is hardly cheap and uses a heck of a lot of greenhouse gas-emitting (in manufacture) steel and cement!
  3. virtually no decomissioning costs: you could more or less just walk away and slam the door. Monitoring would be needed, as for underground nuclear waste repositories, but because nothing irradiated is above ground, access would only need to be minimal. In addition, there would be no need ever to remove irradiated fuel assemblies unless the fuel is to be reprocessed. When the reactor reaches the end of its operating lifetime, the whole facility could be sealed, complete with its spent fuel.
  4. there will be protests at each and every new surface nuclear build with endless public enquiries because of protests. Underground plants would demolish most of the objections. Public acceptance and planning consent should be straightforward since there wouldn't be much surface infrastructure to object to. Most of the usual public fears and objections would cease to be serious issues. It also means that off-the-shelf reactor designs (like the PWRs used throughout France and the most of the USA) could be built even though they might not be as potentially safe as so-called 'fourth generation' reactors, because of the additional safety conferred by underground plants. Waiting for unproven safer designs could lose us another decade.


Cost: I have no idea how much underground siting would add to a budget. But if you take into account minimised decommissioning costs (not historically factored in to the cost of nuclear power as we are now finding out) and spent fuel disposal possibilities, I would guess that it would be completely viable.The economics are only artificially marginal because there's no carbon tax. Anyway, what price security and safety? And if a power utility wanted to re-use as much of the infrastructure as possible at the close of the first reactor's design life, it could just dig another chamber and build its new (improved) reactor next door. Power lines, turbines, transformers etc. all remain to be used again

So far as I know, no-one has ever tried costing it. As my drawing (above) shows, the actual reactor vessel and primary heat exchangers are really quite small structures because of the high power density which nuclear generation allows. So the chamber would be no larger than many others routinely built for different purposes. The reactor assembly could even be built in a modified abandoned mine (e.g. salt mine). Of course, any such underground site depends on there being a cooling source nearby (river, lake, sea) for condensing steam from the turbines. All the non-radioactive sections of the plant could be above ground to reduce costs.

Location: Finding suitable underground conditions, especially in flatter rainy areas with fast-moving groundwater circulation, could be a problem. A Llanberis-like site could, in theory, be ideal because the excavations could be made within the steep valley side so that any groundwater would drain out by gravity. And just outside are two deep lakes (see Cooling, below).

Cooling: Like any steam-driven turbines, cool water is needed both for raising steam and for condensing it. There's no reason for the turbines and cooling systems to be located underground since these aren't in contact with radioactive parts of the circuit. So much of the plant could, like conventional plants, be located by a river or the sea.

So... if we are to have nuclear fission generation on a larger scale to tide us over until fusion power and renewables come to our rescue, why not build all nuclear plants underground? I think this reasonable question deserves a reasonable answer.

Further reading: You may like to look at Nuclear power... safe underground and The Future of Nuclear Power, both in this blog series.

Tuesday, March 10, 2009

Four-minute guide to the science of climate change

Everyone’s heard that the planet’s climate is changing but is it true that the planet is warming? What’s the evidence? If there’s an unusually cold winter, isn’t that evidence of global cooling? Many people are sceptical and a little confused. Is global warming just another scare story put about by green eco-nutters? It’s more comforting to believe that everything’s fine and we can carry on as usual. But an unpalatable truth is that the global economic system depends almost totally on cheap fossil fuels – coal, oil, natural gas – to power industry, transport, modern consumerist lifestyles and provide employment. Taking action to reduce the greenhouse gases (GHGs) - which science says cause climate change - will mean drastically cutting back on using these fuels. There’s trouble ahead. So it is reasonable to question how we know climate change really is happening. Mitigation and adaptation will dramatically change our lifestyles, though not necessarily for the worse. So what really is the evidence for climate change? This 4-minute guide summarises it.

Climate and the weather: There is now a mass of evidence that climate is changing fast. Confusion arises because most people don’t appreciate the difference between weather and climate. A cold winter in north Europe doesn’t mean that the climate is cooling: there’s a lot of natural variation year by year and always has been. Climate is about averaging the weather’s variations around the planet over a number of years and looking for a global trend. And there is a trend: temperatures are increasing. The planet is getting hotter and the rate looks set to accelerate.

The evidence comes from careful observations by scientists from many different disciplines over many years. Many lines of evidence can actually be seen happening:
  • Ice sheets and glaciers are melting everywhere and there are many dramatic before and after photos which illustrate this
  • The area covered by floating sea ice in the Arctic is reducing rapidly
  • Permafrost in the Arctic is melting, releasing methane, a potent greenhouse gas (an example of a dangerous ‘positive’ feedback)
  • The lower atmosphere (troposphere) is becoming warmer
  • Sea levels and ocean temperatures are rising (see below)
  • Species of animals and plants are ‘migrating’ to higher latitudes because their home ranges are becoming too warm for them. Diseases are also expanding their range and affecting crops and trees as well as people
  • Coral reefs are being killed by the hotter waters. Corals are not only beautiful to look at, they are nursery grounds to myriads of marine species (and sometimes called ‘the rainforests of the sea’.) The planet needs its corals because they sequester carbon from carbon dioxide (CO2) to build their skeletons out of a hard, white mineral called calcium carbonate so, like trees, they are ‘carbon sinks’
  • The oceans are absorbing much of the CO2 but as they do so, they are becoming more acidic. This is affecting all kinds of marine life which build their shells out of calcium carbonate. The mineral dissolves in weak acid so acidification means that corals and shells won’t be able to grow, triggering all kinds of knock-on effects in the marine food chain.
Predicting the future: Global Climate Models Climate scientists have developed computer models to predict future climate. They know these are generally accurate because they can successfully be used to predict known past climate by checking their predictions against actual observations (see below). The models allow scientists to predict how the climate will change over the next few decades and are a cornerstone of periodic updates from the Intergovernmental Panel on Climate Change (IPCC) on global climate change.

How can scientists investigate past climates accurately? One way is to examine drill cores taken from ice sheets like those covering Antarctica and Greenland. Past climates can be reconstructed effectively using the records of former atmosphere composition and precipitation preserved in the ice. What’s more, they can be cross-checked using actual historical records and other ‘proxy’ observations such as tree-rings, isotope analysis and radiometric dating. Importantly, the ice cores contain a record of CO2 levels which are higher now than at any time in the last 700,000 years. One well-known result of using all these different methods to assess past climates is the hockey stick graph in which numerous different lines of evidence broadly agree that temperatures have over recent decades started on a steep upward trend. It is not a uniform upward movement because of complex atmosphere-ocean oscillations, the best-known of which is El Niño.

One prediction made by the computer models is that the Arctic and Antarctic will warm faster than the rest of the world. Evidence is coming in that not only is this happening but, alarmingly, it’s happening even faster than predicted because of positive feedbacks. Other predictions show droughts and desert areas increasing (particularly in Australia) and more violent weather patterns with poor countries particularly vulnerable (especially much of Africa). Tropical forests - normally massive carbon 'sinks' (the trees absorb CO2 from the air and transform it into wood, so locking up the carbon) – are today being logged and burned to make way for farming and biofuel plantations, releasing vast quantities of CO2 into the air. As if that wasn’t enough, the models predict drying and major die-off of the Amazon rainforests and increase in wildfires in these former sanctuaries of biodiversity.

The main concern is that rising global temperatures will trigger ‘tipping points’ where GHG inputs reach a critical level, causing a major climate ‘flip’ which could be extremely hostile to much of life – including humans. We know from the distant past that major climate change events can and do occur. One of these, almost certainly caused by GHGs from stupendous volcanic eruptions, wiped out 90 per cent of life on the planet. This mass extinction event occurred around 250 million years ago and was probably worsened by ‘tipping points’ such as major methane releases from methane clathrates. (Today’s oceans host vast deposits of clathrates.) We know of 5 mass extinctions from the geological record and we are now causing the sixth.

How warming happens: the greenhouse effect If you enter a greenhouse on a sunny day, it’s hot because the sun’s heat is trapped by the glass. Carbon dioxide (and other gases like methane, nitrous oxide and ozone-killer CFCs) are called greenhouse gases because they, like the glass in a greenhouse, trap some of the sun’s heat. Without the greenhouse ‘blanket’, the planet would radiate most of this heat back into space. As more GHGs gush into the atmosphere from power station chimneys, farming and car tailpipes, it’s rather like adding double glazing to the greenhouse: more heat is trapped. Most of this heat is absorbed by the world’s oceans so they, like the air, are getting hotter.

The bathtub effect: Without the greenhouse effect, life on Earth wouldn’t exist. Some GHGs are essential to keep the planet habitable, but humans are grossly overdoing it. Imagine a bath (which represents the atmosphere) with the taps full on and gushing water (representing GHGs pouring into the atmosphere). There’s no plug so water is also draining from the plughole (representing carbon ‘sinks’ like the oceans and forests which both naturally absorb CO2). In a stable system, the amount of water coming in is roughly balanced by the amount flowing out: the carbon cycle. But we’ve upset the system by pouring increasing amounts of ‘water’ into the ‘bathtub’ so the tub is filling up and will soon overflow. The ‘carbon sinks’ drain is overwhelmed so the planet heats up. This is well explained by the Bathtub simulator. Before people began to burn fossil-fuel in the 19th century, CO2 levels – even during warm periods - were below 300 parts per million (ppm). During ice ages, they fell to less than 200ppm. Since the industrial revolution, they have risen ever faster, particularly in the last decade and now stand at 387. Actual warming closely mirrors this rise.

Sea level rise: Warmer water expands so sea levels go up. But sea levels also rise because of all the melting glaciers and ice sheets around the world. In fact, the rapid melting of almost all the world’s glaciers is one of the most scary indicators that the climate is warming. Sea levels have been rising by about 2mm each year for the last century but this is predicted to greatly increase, causing large scale flooding of many low lying populated areas. The IPCC in their latest (2007) report predict about half a metre of further sea level rise though more recent research suggests double that amount.

This guide to the scientific evidence for climate change and the predictions science can make is deliberately very brief. Below is a list of sources of further information if you want to follow anything up.

The Royal Society has produced
this overview of the current state of scientific understanding of climate change to help non-experts better understand some of the debates in this complex area of science.

New Scientist's
guide to climate change, global warming and greenhouse gases with many other interesting links and news stories.

‘Understanding and Responding to Climate Change’ Downloadable PDF document from the US National Academies. Excellent guide with clear explanations and many images. A free printed version is also available.

RealClimate Climate science blog written by climate scientists with many useful short guides e.g. ‘Highlight’ (right column, scroll down)

Climate change for kids, explained by OneWorld’s Tiki the Penguin

guide to climate change exposes the reality that global warming will impact poorer countries harder and sooner than the richer countries which are responsible.