Nuclear power’s thermodynamic flaw

After the CSIRO once again demonstrated that nuclear is not the way forward, we revisit an article first published in Ecolibrium, in which Clive Broadbent, L.AIRAH, raises further concerns about the proposed use of nuclear energy.

I wrote this piece after reading an article by Ian Kenins that bravely critiques the use of nuclear power stations (zero greenhouse emissions quoted) to replace our ageing fossil fuel-powered ones (highly polluting). To date, the debate has been mainly around political, safety and economic aspects, but there is also a need to discuss the thermodynamic consequences of nuclear power.

These physical processes are inescapably subject to the first and second laws of thermodynamics: energy may be transformed, but it is always conserved, and the ability to harness that energy is never 100 per cent. Humanity seeks to use the resources at its disposal to bring order to a system that continues to increase in what is called entropy, or disorder.

One way to achieve some order from disorder is by using energy to perform useful work. Such is the case with power stations, which, while improving order in a localised setting, unfortunately increase the disorder over the wider planet.

The principles of power generation

In present-day central power stations, electrical energy output is derived from the combustion of coal to produce steam in boiler plants. At high temperatures and pressures, that steam drives turbines connected to electricity generators. The steam is then condensed back to water, cooled in cooling towers, and the process repeats, although some (hot) water is lost as evaporation, necessitating makeup from sources such as ponds or rivers.

We know that this process generates unwanted pollutants such as furnace ash, chemically contaminated water, and microbial growths in the heated water. It also creates excess heat. While the first and second laws of thermodynamics essentially describe the transfer of energy from heat (boiler plant) into work (at the turbines), those emissions also include the rejection of all the heat produced in the process. That dissipated heat energy has to go somewhere. And it does – to the environment.

A thermodynamic conundrum

Let’s look at the numbers. The power station process – transforming potential energy from the fuel source into kinetic energy or useful work at the turbine/generators – has a usual process efficiency of around 35 per cent, which means some 65 per cent is lost as waste heat. But if we want to think holistically about global warming rather than just the greenhouse gas component, we need to recognise that, in fact, 100 per cent of that energy will eventually be transferred to the environment.

Nuclear power stations operate in a similar manner to coal-fired ones despite using a different fuel. These plants also need the heat produced from the fuel to produce steam, and they use the same kit as coal-fired plants do. Rejected heat from nuclear stations also passes through to the natural environment (largely within cooling towers).

The process efficiency of a nuclear plant is similar to that of a coal-fired plant, with around 35 per cent of energy being useful. And as is the case with coal power, 100 per cent of energy is eventually transferred into the surrounding environment. This undermines nuclear power’s claims of being “zero-emission”. In terms of lowering global warming effects, nuclear power does nothing; it simply rejects heat to the environment, just as coal power does.

Contrast this with the use of solar and wind renewables. Solar is fuelled by the sun and wind by the earth’s rotation. No water is involved, and no global warming is produced, other than what occurs naturally. The superior option is as clear as day.