|A cutaway of the travelling wave reactor (Image: TerraPower)|
Initially developed in the 1950s, the TWR design resurfaced in the early 1990s, and was later patented by Intellectual Ventures, the company from which TerraPower was spun out of. The TWR is a liquid sodium-cooled fast reactor that uses depleted or natural uranium as fuel.
The core design of the original TWR concept envisages a moving region, or 'wave', in which the uranium is bred progressively into plutonium, which is the actual fuel that undergoes fission. However, in mid-2011 TerraPower announced a change of design to a standing wave reactor in order to address the problem of cooling a moving region. The current design would start the fission reaction at the centre of the reactor core, where the breeding stays, while fresh fuel from the outer edge of the core is progressively moved to the central region, as used fuel is moved out of the centre to the periphery.
TerraPower plans to build a 600 MWe demonstration plant, known as the TWR-P, by 2018-2022 followed by larger commercial plants of 1150 MWe from the late 2020s.
B&W is also actively marketing a new reactor design of its own - the 180 MWe mPower. The company pointed out that its own mPower reactor is based on pressurized water reactor technology using standard enriched uranium as fuel, whereas TerraPower's TWR "is a larger reactor based on Generation IV technology and designed to use depleted uranium as fuel." (World Nuclear News, 2/18/2014)