‘Now, uranium, which is a metal mined from the earth, is made up of three different atoms; one of these is called U 235, and in U 235 the neutron particles are very active and a few are constantly flying out.’ A diagram illustrating what he said was projected onto a large screen behind him. ‘If one of these particles, which fly out at about twenty-five thousand miles per second, hits another U 235 atom, that atom will split into two, and sometimes three, separate atoms. It is that collision and that splitting of the atom that generates heat, just the way the banging of my fists does.’ He banged his fists again, more gently this time.

‘At the same time as splitting into two or three, more neutron particles fly out; if these particles can also be made to hit atoms, then we have what is known as a chain reaction.

‘Now the way we make this work for us is, in outline, very simple. Uranium is processed and refined and then put into metal tubes, which are called fuel rods. Several hundred rods are then inserted into what we call the core – you can think of it as being like the barrel of a revolver, the rods being the bullets. The rods are insulated from each other by what are called control rods, through which neutron particles cannot pass. As the control rods start to be withdrawn, the neutron particles start flying out and splitting the atoms in the other rods, and the fuel rods start to get very, very hot. The control rods are not withdrawn completely, but adjusted to maintain the temperature required.

‘The entire core is immersed in water; the water is kept under very high pressure to prevent it from boiling so that it will act as a coolant for the core – like a car’s radiator system. After the water leaves the core, heated to a temperature many times higher than boiling point, it is then converted into steam, which is then pushed through the turbines.

‘If anything goes wrong, the control rods are dropped straight back into the core and the reaction stops. The core, which you’ll see when we make our tour, is suspended above the ground, in its tank, with the control rods directly above it. The reason it is suspended above the ground is for ease of access to all parts of it. Almost all maintenance is done by remote control from outside the containment – that’s the name of the building in which the core is housed.’

Yeodall paused for some moments. He’d got through the toughest bit for his audience, but the easiest bit for him; he bit his lip, took a deep breath, and ploughed on.