Small nuclear reactor researchers eye up alternatives to traditional technology

While pressurised water reactors cooled by light water (LPWRs) are likely to be the first small modular reactors (SMRs) deployed commercially, they are by no means the only type of SMR under development. Several research groups and private companies are also looking at alternative nuclear technologies for their potential in smaller reactors.

These alternative reactors generally belong to the category known as Generation IV. Because they are at an earlier stage of development, they are unlikely to be ready for deployment until the 2030s or 2040s.

Stable salt reactor

One reactor under development by UK private company Moltex Energy is called the stable salt reactor (SSR). As the name implies, this technology uses a flowing molten salt as a key component of the reactor, but it is quite different from the liquid fluoride thorium reactor (LFTR) normally associated with molten salt technology.

While an LFTR uses nuclear fuel dissolved in the molten salt and flowing around the reactor, in the SSR the fuel is stationary and held in fuel rods as in a conventional reactor. The fuel – based on typical low-enriched uranium, or even derived from spent fuel currently treated as waste – is dissolved in a molten salt, which Moltex claims improves the burn-up rate. The fuel rods are submerged in a different molten salt, which acts as the primary coolant in the reactor. One important factor in the safety of the SSR is that fission products caesium and iodine, which are produced in gaseous form in water-cooled reactors, remain bound in non-volatile salts within the fuel assembly.