The uranium that makes conventional nuclear power possible has a number of significant disadvantages. For one thing, uranium reactors generate large quantities of waste. Much of this remains dangerous for thousands of years, and a proportion of it can be used to produce weapons-grade plutonium. A second issue is that uranium is a comparatively scarce material, which exists in significant quantities in only a small number of countries. The theoretical risk of giant explosions caused by uranium reactors is a further concern.

For all of these reasons, a growing number of scientists and energy experts believe that the world should switch from uranium to thorium as its primary nuclear fuel. Compared to uranium, thorium is far more abundant as well as much more energy-dense. In addition, the waste products generated by thorium are virtually impossible to turn into plutonium – and they remain dangerous for hundred of years rather than thousands.

There are a number of different ways to use thorium to produce electricity. In Manchester, Kirk Sorensen made the case for liquid-fluoride reactors. This technology was developed by the US military in the 1950s and 1960s and was shown to have many benefits. For example, reactors of this type can be smaller than conventional uranium reactors, partly thanks to their low-pressure operation. Despite its early promise, research into liquid-fluoride thorium reactors was abandoned – the most likely reason being that the technology offered no potential for producing nuclear weapons.

Sorensen estimates that between 5,000-6,000 tonnes of thorium could produce as much energy as the world currently consumes each year.

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