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Nuclear Energy

September 22, 2010 1 comment

In my science writing class, we’re reading a book called “Power to Save the World”, by Gwyneth Cravens. She’ll be visiting the school to give a talk on nuclear energy next week, but until then, here are some thoughts.

Nuclear Energy. We don’t have enough of it. It’s clean, efficient, and safe energy, which is something we could really use. The objections are fears of radiation, meltdown, weaponization, and the stability of the power grid. We’ll start with the pros:

Nuclear energy is a paradigm shift. It’s a quantum leap, if I may use that despicable idiom again. Let’s talk about thermodynamics. Energy is split into several types: There’s kinetic energy, which is what moving bodies have, and potential energy, which measures how much energy is ‘stored’ – usually due to gravity. Electrical power generation relies on conversion from kinetic energy to another type of potential energy: electrical potential energy. The simplest reactors convert the energy of a fast-moving river or winds into a spinning turbine, which creates electric potential energy. Then there’s internal energy. This comes in a few types. There’s thermal energy, which is the energy which turns most modern turbines. A difference in thermal energy causes a flow of mass – usually steam, sometimes water – which causes a turbine to turn. That thermal energy can be generated from another type of internal energy, chemical energy. This is the energy stored in chemical bonds, the interactions within a molecule but between atoms. Combustion of coal releases chemical energy.

The last type of internal energy is nuclear energy. This is the energy bound up inside individual atoms. We initially thought that atoms were the smallest level there was – the Greek work atomos means indivisible. We now know that we can ‘change’ atoms with nuclear reactions, just like we change molecules with chemical reactions. And while we can’t create energy, there are some reactions that release energy. Nuclear reactions are centered around iron – specifically iron-56. We can ‘fuse’ two atoms together, and as long as the result is lighter than iron-56, we gain energy in the process. In the same way, we can ‘fission’ an atom into two, and as long as the result is heavier than iron-56, we gain energy in the process. Modern reactors are based around fission, since it’s easier to control at reasonable conditions. Stars use fusion, which is only useful at extreme temperatures and pressures. Because the energy from fission comes from the bonds within a single atom, rather than the chemical bonds between atoms, we gain much more energy for an equivalent ‘number’ of reactions, or an equivalent mass.

Sometimes – usually, in fact – the reaction doesn’t quite work out evenly. There’s either one too many electron, or too many protons and neutrons, or just an excess of energy. These are the forms of radiation that scare people so much. A nuclear reactor does create these, but modern nuclear technology also encases the reactor in a containment shield, which would prevent the release of significant radiation. Chernobyl didn’t have this, which is why there were any deaths at all from that incident – but Chernobyl is a special case, we’ll talk about that in a bit. The truth is, we’re exposed to radiation every day – from the Earth, from the cosmos, from medical devices, from cigarette smoke, and even from conventional power plants. The difference with nuclear energy is that we can and do prevent that radiation from leaking out. We initially didn’t understand the radiation. We understand how radiation works, and have realized that the radiation that escapes a nuclear reactor is in fact a far lower dose than the average dose from the environment alone, and is even a lower dose than your average combustion plant. This kind of low-dose radiation hasn’t even been demonstrated to cause any harm at all – this is the subject of controversy right now. The Linear Non-Threshold group says that a low dose of radiation is just less dangerous, but still has some risk, while the other side says that sufficiently low doses cause no risk at all.

The other fear, apart from radiation and effects, is weaponization. People fear that any worker at a nuclear plant could easily grab components for a dirty bomb, or that the huge cooling silos would become the next target for a 9/11-like attack. However, the material inside a nuclear reactor, while dangerous, is not refined enough for a nuclear bomb. For that you need a different kind of equipment, that refines uranium rather than harness the energy of its decay. Dirty bombs don’t need highly refined uranium, but a dirty bomb is also not nearly as deadly as people seem to think – if the response was handled properly and radiation medication got to those who needed it, the radiation effects would have limited effects outside a certain radius. The dose you would receive decreases quickly with distance, and as long as you’re not right at the point of the explosion, moving indoors will limit your dose significantly, and having enough radiation meds, food, and water to last a few days brings your exposure down to a minimum.

So, Chernobyl. The Chernobyl Nuclear Power Plant was the worst-managed nuclear power plant that will ever exist. Never again will the mistakes made there occur again. The ‘containment vessel’ that is typically made of reinforced concrete or steel was practically worthless, the Ukranians put an incompetent plant manager in charge, who had already nearly destroyed another reactor, a previous failure had been covered up and mostly ignored, and the entire failure was caused by an unauthorized, ill-conceived, and improperly executed experiment. And despite such a confluence of idiocy and raw power, there were only 56 direct deaths, and the total number of deaths caused by the event was far lower than the two hundred thousand initially predicted.

Modern reactors have safeguards in place to actually shut down a reactor in a state of emergency. The system will ‘scram’ – immediately insert all of the control rods – if a runaway reaction is detected. Whereas in Chernobyl, they intentionally pulled all the control rods out in a foolish attempt to restore power after their failed experiment. You couldn’t cause a meltdown in a modern reactor with the safeguards in place even if you were trying.

Let’s talk about efficiency and waste. Nuclear energy, if used to power everything an average human would use for a lifetime, would create about a pound of slightly radioactive solid waste. Far less waste than coal and natural gas are pumping into the atmosphere. The radioactivity is rather weak, as the elements that are still present at that point have a rather long halflife, meaning they release radiation for a long time, but do so very slowly. We can contain these materials in a storage container practically indefinitely – we bury them underground, and they slowly die off and become inert. The supply of fuel to reactors is also much less mass than is required for a natural gas or coal reactor, meaning less tanker trucks or fuel pumps need to be run.

The generation process itself releases only steam, after it has cooled the reactor and fueled the turbine, and perhaps some warm and purified water into a nearby stream, depending on how the cooling system works for that type of plant – there are a few kinds, which use slightly different methods to turn the turbine. The actual products of the reaction, rather than being exhausted, are contained and can be refined and reused in certain types of reactors to minimize waste and improve efficiency.

France’s primary method of power generation is nuclear. When I asked the only Frenchman I know about that, my thermodynamics professor, Dr. Gallois, I expected his usual nationalist pride, but that isn’t what I got. I was surprised by his anti-nuclear reaction – although I have learned that many professors at this university are skeptical towards some of the more common scientific claims.

There is one problem with nuclear reactors: they don’t like to turn off. A natural gas reactor will gladly cold-start every morning and shutdown every evening, but a nuclear reactor has a somewhat slower process. A cold start can take a full day, or more. While a nuclear reactor can ‘tune’ its energy output to a certain degree, they can’t provide the instant power that we need to maintain our power grid on the timescale of less than a day – they’re useful for what’s called ‘base load’. They can run all the time, reduce power at night, run full during the day, except for an occasional maintenance period, and the extra energy usage during the day can be handled by conventional reactors for now, at least until we have a better way of storing energy at night and using it during the day.

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