For nearly 70 years nuclear power has been touted by governments the world over as a safe clean renewable source of energy: a clean environmentally friendly carbon neutral source of renewable energy that will fulfil our energy requirements well into the future, and aid us in our move away from dependence on fossil fuels. In a world where devastating climate change and the effects of it are increasingly visible, we are constantly told that nuclear power is the only reasonable alternative to fossil fuels and that this is how we should tackle climate change. This is absolute nonsense. It is a very dangerous route to take for all sorts of reasons. In order to challenge this view it is important to understand the fundamentals of nuclear power and how it works.
How does nuclear power work?
In the nuclear generation process a radioactive metal called uranium, in pellet form, from Uranium-235 is placed inside the reactor core. To control the emission of harmful radiation, these pellets are coated with a ceramic of uranium oxide. The atoms from the Uranium-235 undergo a chain reaction within the core, which splits the atoms. This splitting of the atoms is known as nuclear fission. Heat and radiation are the by-products produced during this process. By splitting the atoms of normally unstable Uranium-235, the metal undergoes a chemical change and becomes a different, more stable element.(1)
The heat and radiation produced by this nuclear fission process begins to heat the water. The water used in this process has a dual purpose. Firstly, it acts as a coolant for the reactor core to prevent overheating. Secondly it acts as a medium with which to carry away the heat and steam. This steam is what drives the turbines, which in turn generate electricity. Water flows constantly within and around the reactor core. Normally there are two sets of pipes, four pipes in total. These are the flow and return pipes. The flow pipes transmit fresh cold water to the tanks, while the return pipes carry away the hot water and steam that drives the turbines. While the hot water is contained within the reactor it is under extreme pressure which prevents this water boiling. As this hot water leaves the pressurised vessel it boils rapidly producing the steam which drives the turbines.
Primarily there are four different types of nuclear power plants. (2)
- Pressurized Water Reactors (PWR’s)– In a PWR the water used as coolant is separate to the water used to generate steam and to drive a turbine.
- Boiling Water Reactors (BWR’s) – The water from the reactor is converted into steam and used to directly drive the generator turbine.
- High Temperature Gas Cooled Reactors (HTGC’s) – High Temperature gas cooled reactors operate at higher temperatures than PWRs and use gas as the primary coolant.
- Heavy Water Reactors (HWR’s) – Heavy Water reactors are similar to PWRs but use water enriched with a Hydrogen isotope as the coolant.
Energy density of various energy sources
While not in any way advocating the use of nuclear power as a viable alternative to fossil fuels it is important to understand why it may seem an attractive source of energy to some people. This view has gained traction in recent years because of the increasing understanding and realisation of the effects of climate change. Before getting into why this is not an alternative to fossil fuel, certain aspects of power generation must be understood. Different fuel sources will have a different energy density. For instance, when paper is burned it will not produce the same quantity of heat energy as say petroleum. When referring to renewables such as solar powerthey are described by their power densities. This means how much power in Watts can be provided per square metre of PV panel. See below charts for comparison of energy densities and power densities of different energy sources.(3)