The past nine months have been an urgent wake-up call for the UK and the wider world. Russia’s invasion of Ukraine has highlighted the importance of energy security and its effect on prices. Meanwhile, the worsening climate crisis is focusing more and more attention on the pressing need for clean and affordable energy.

But there is a potential solution to these problems – the FLEX molten salt reactor (MSR) currently being developed by MoltexFLEX. It is vital that the UK supports this ground-breaking solution.

Although conventional nuclear plants have provided reliable, low carbon electricity for decades, they face two principal challenges, which the FLEX reactor is designed to overcome – cost and time.

In recent years, operating costs for conventional nuclear energy have increased on average worldwide, from $96/MWh in 2010 to $155/MWh in 2019. The global energy crisis and spiralling gas prices have put that rise into stark context, with conventional nuclear plants offering increased security but not affordability.

Moreover, conventional nuclear plants require large capital expenditure and take significant time to build. According to the World Nuclear Association and the International Atomic Energy Agency, the median construction period in 2020 was in excess of seven years.

Nuclear remains essential to the decarbonisation of the global economy, but the big question for nuclear energy providers is: How do we make it more affordable in the long term?

Molten salt solution
The answer is molten salt technology. While the use of molten salt to fuel and cool a nuclear reactor is not a new idea (many of the benefits were first realised in the 1950s), MoltexFLEX is employing the concept in a revolutionary new way.

Conventional MSRs mix the fuel with the coolant and require a complex system of pumps, pipework and heat exchangers to safely contain the highly radioactive salt – an extremely challenging engineering problem. By contrast, the FLEX reactor keeps the radioactive fuel salt in dedicated tubes separate from the coolant salt and needs no moving parts, relying on convection rather than pumps for coolant circulation. This is a far simpler design – and further enhances the inherent safety of an MSR.

The removal of pumps means that the FLEX reactor operates at low pressure, so it does not need a large, expensive concrete and steel containment structure like conventional plants. Also, it is a modular design, allowing most components to be factory-produced and transported to site, minimising onsite work and slashing construction time. What’s more, it can run for 16–25 years before needing refuelling, so there is very little operator input and low operating costs.

All this means this new reactor could produce electricity below $40/MWh, therefore solving the problem of affordability.

Load-following operation
Another less frequently discussed problem is the growing need for reliable energy sources that can work flexibly in tandem with intermittent renewables. As the world transitions to a zero carbon energy mix, and global demand for electricity grows faster than renewables can supply, this will only become more apparent. But the FLEX reactor has been designed to cope with this and can provide the versatility to perfectly complement wind and solar.

The FLEX reactor is a simple device that produces heat when needed and quietly idles otherwise. The reactor’s ability to load follow – in other words, to adjust its power output – allows it to readily adjust in response to demand. In contrast, this can be complicated and uneconomic for conventional nuclear plants.

But the reactor shows its true versatility when combined with Moltex’s ‘GridReserve’ thermal storage technology. This once again uses molten salt to store the heat produced by the reactor and can be used on demand to generate steam to drive conventional turbines. A site hosting a fleet configuration of 32 FLEX reactors, each producing 16 MWe, can be coupled with a GridReserve to generate 1,500 MWe for eight hours over the course of a day.

This makes the FLEX reactor a readily scalable way to back up intermittent renewable energy. In a future energy system, this will be crucial.

A further bonus is that the FLEX reactor generates heat at 750°C, which can be employed in a wide variety of downstream decarbonisation applications – including high temperature electrolysis to efficiently produce clean hydrogen for use in industry or fuel cells in heavy transport.

MoltexFLEX is on track to deploy its first reactor in the UK by the end of the decade, with subsequent reactors being rolled out in the 2030s.

The technology being developed by MoltexFLEX is key to unlocking affordable advanced nuclear technologies in the UK. The new reactor combines the affordability of molten salts with essential flexibility. We need to back molten salt technologies – one of the most realistic ways of reaching net zero.

The views and opinions expressed in this article are strictly those of the author only and are not necessarily given or endorsed by or on behalf of the Energy Institute.