Fuel dissolved in salt: PSI video explains how a molten salt reactor works
The Paul Scherrer Institute shows the principle of the molten salt reactor in an animation. Together with Copenhagen Atomics it is preparing an experiment with a small reactor of this type.
Photo: PSI / Wikimedia Commons, CC BY-SA 4.0 (cropped and resized)
Video: YouTube · PSI Paul Scherrer Institut · youtube.com
The Paul Scherrer Institute (PSI), Switzerland's largest research institute for natural and engineering sciences, released an explainer video on molten salt reactors (MSR) on 14 October. Unlike in today's nuclear power plants, the fuel is not contained in solid fuel rods but dissolved in molten salt, which also carries the heat away as it circulates. Using the 'Onion Core' concept of the Danish company Copenhagen Atomics as an example, the animation explains how fuel salt, nuclear fission and the structure of the reactor core work together.
The video names safety characteristics and fuel flexibility among the advantages, and radioactive waste, material stability and complex licensing procedures as open problems. The background is a collaboration agreed by PSI and Copenhagen Atomics in July 2024: a thorium molten salt critical experiment is planned, which is also meant to provide openly available data for validating reactor simulations; as fuel, Copenhagen Atomics relies on a salt of lithium, thorium and low-enriched uranium fluoride.
According to the Swiss nuclear regulator ENSI, the container-sized reactor is to run for one month at one megawatt of thermal power on the PSI site in Villigen. PSI and Copenhagen Atomics are currently drafting the licensing documents; according to ENSI, they are to be submitted in the second half of 2026 at the earliest.