Are molten salt nuclear reactors safer and cleaner?

SAMOFAR (Safety Assessment of the Molten Salt Fast Reactor) is a €5 million European Union programme involving 11 partners from both science and industry. Lead researcher and Professor of Nuclear Reactor Physics at TU Delft, Jan-Leen Kloosterman, explained the advantages of molten salt reactors over the currently used solid fuel reactors: “In solid fuel reactors, the fuel rods are cooled from the outside, but the disadvantage is that if an accident happens and you can’t cool the fuel, it could melt releasing radioactive fission products. In molten salt reactors, the uranium and thorium fuel is dissolved in the coolant so it’s one medium and therefore you never have the problem of melting fuel and release of fission products.”

Molten salt reactors are built a bit like a bath with a drain and a ‘plug’ at the bottom. “The so-called ‘freeze plug’ is solid salt cooled from the outside,” said Kloosterman. “So if the power fails, for example because of a tsunami like we saw in Fukushima, cooling stops and the freeze plug melts due to the heat from the reactor core, allowing the fuel to flow into the safety-tanks underneath the reactor core.”

Molten salt nuclear technology has been around since the 1960s; but it was soon superseded by fast-breeder nuclear reactors fuelled with uranium and plutonium. However concerns about the health and environmental effects of nuclear fission by-product, plutonium, as well as its potential to be used in nuclear weapons, has got people thinking about molten salt reactors again.

The SAMOFAR programme will concentrate on molten salt reactors using thorium, a relatively cheap and abundant fuel: “And if you use thorium, you don’t produce plutonium which needs to be safely stored for hundreds of thousands of years,” explained Kloosterman.

It will be at least 25 years before there is an operational molten salt reactor in Europe, estimates Kloosterman, but the programme aims to have a large-scale demonstration facility by 2025. “In the meantime, the main purpose of SAMOFAR is to prove that all these safety-related principles really work in the experimental facilities.”