The vast majority of operating reactors, commercial and military, use light (normal) water as the primary reactor coolant. Given the extensive operational experience with light-water reactors (LWRs), it is the technology of choice for reactor vendors who want to get their product to market quickly and for potential customers who are concerned about investment risk. Thirteen of the 22 SMR designs presented in this chapter are based on LWR technology. Although they all share a common coolant choice, other design features are quite varied. Overall configurations include traditional loop design, compact loop design in which the external vessels are flanged directly to the reactor pressure vessel, and integral system design in which most or all of the primary system components are located within the reactor pressure vessel. Individual module output capacities range from 8 to 300 MWe and plant-level strategies range from using a single reactor per plant to as many as 12 reactors per plant. Also, the plants may be sited on land, operated on floating barges or submerged below the ocean surface.

Table 2.1 provides a summary of the LWR-based SMR designs described in the following sections.