Nuclear power |


The FLEX reactor – the next step in molten salt reactor evolution


Moltex Energy, the UK-based developer of molten salt nuclear technology, launched its subsidiary MoltexFLEX last autumn to work on its FLEX reactor – the latest application of the company’s platform stable salt reactor (SSR) design. MoltexFLEX CEO David Landon outlines the work being done to make it a reality


The FLEX reactor is the thermal spectrum version of Moltex Energy Limited’s globally patented SSR technology – it uses graphite as the moderator. The SSR technology (see MPS, January 2017, pp 22-26) is shared with MoltexFLEX’s sister company, Moltex Energy Canada, which is developing the fast spectrum version (the SSR-W) and the WAste To Stable Salt (WATSS) process that will produce the fuel for the reactor from recycled spent fuel.


SSRs are fundamentally unique in comparison with all other molten salt reactors in that they restrict the radioactive fuel salt to tubes similar to the fuel assemblies in conventional reactors. A separate, non-radioactive molten salt then transfers heat from the reactor core to heat exchangers.


In other molten salt reactors, where the fuel is also the coolant, the complex fuel salt circulation system – with pumps, filters, conditioning units and heat exchangers – is exposed to the radioactive fuel salt. This puts severe demands on those components and makes maintenance challenging, and these engineering challenges arguably represent the key reasons that these reactors are not currently used commercially.


Simple solution


The FLEX reactor is an evolution of the company’s earlier thermal spectrum design, the SSR-U. MoltexFLEX was launched in September 2022 in the UK to promote the FLEX design worldwide and develop SSR technology.


The FLEX reactor is designed with simplicity in mind. It is small and modular, allowing most components to be factory-produced, enabling transportability, reducing on-site work and speeding up construction, all of which minimise the overall costs. It is a low-pressure design that uses natural convection for all heat transfer – this removes the need for pumps or any other moving parts, and for expensive high pressure containment structures. Wherever possible, the FLEX reactor will use materials and technology already proven within the nuclear industry, making safety and design substantiation quicker and easier by eliminating the need for extensive research programmes.


MoltexFLEX’s key objective is to bring the FLEX reactor to market quickly, rapidly deploying fleets worldwide. This is one of the reasons for the selection of low-enriched uranium as a feedstock for the fuel – this material is available now and is


Site overview image. This artist’s impression shows a typical grid-scale array of FLEX reactors – the 32 buildings on the right. On the left, the blue GridReserve® tanks can be seen next to the turbine island. © MoltexFLEX


storage


generally accepted round the world without the development of new safeguard protocols. The company aims to produce its first-of-a-kind plant by the end of the decade.


The FLEX reactor is inherently and passively safe. The design philosophy centres on reducing or eliminating hazards through the fundamental characteristics of the technology, along with passive measures to manage residual risks. It relies on inherent safety features such as the containment of volatile fission products as salts within the fuel salt, and passive control systems such as the expansion and contraction of molten salt with temperature to insert or withdraw neutron poison from the core to control the reactor. This approach offers a considerable advantage over other reactor technologies, which rely far more heavily on active safety systems with complex backup systems to ensure reliability of operation.


The FLEX reactor has been developed to provide energy at a cost comparable to that of burning fossil fuels. Furthermore, its high temperature, 750°C, output offers the potential for higher-efficiency energy conversion as technologies such as supercritical CO2


turbines


mature. Given the vast challenge involved in deep decarbonisation, the ability to produce high temperature heat cost effectively will be as important as producing low-cost electricity.


Complements renewables The output temperature of the FLEX reactor enables cost-effective storage of thermal energy in the molten salt GridReserve®


or days. This energy can be released when 24 | April 2023| www.modernpowersystems.com


demand outstrips supply, enabling the FLEX and GridReserve®


renewable energy by rapidly responding to changes in demand and providing dispatchable generation to address dips in output. For technical and economic reasons, conventional nuclear plants are less able to provide this flexibility.


The FLEX reactor’s output heat can be directly used for on- and off-grid electricity generation or for downstream applications, including: direct heat for district heating or industrial processes (as much as two-thirds of all heat use in European industry is below 700°C); high-temperature electrolysis to produce clean hydrogen (the FLEX reactor can also support more efficient thermochemical production of hydrogen); and


as a power source for water desalination plants.


Additionally, the FLEX reactor can be reconfigured for marine applications, principally for ship propulsion.


Flexible in deployment system for hours


A FLEX reactor outputs 40 MWt, equivalent to 16 MWe; heat can be produced at a levelised cost of £10/MWh, whereas electricity can be produced at approximately £30/MWh. Each reactor has a ground footprint similar to that of a typical three- bedroom house. They can be deployed singly or in arrays of any number to provide energy at the gigawatt scale. For example, an array of 32 units may be deployed in combination with the GridReserve®


thermal storage facility to deliver 1.5 GWe for eight hours of peak demand.


system to complement intermittent


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47