The individual containment vessels of the NuScale design sit in a common open external tank referred to as the reactor pool. The NuScale containment conforms tightly to the reactor vessel without room for any additional water tanks. The NuScale reactor pool provides the emergency heat sink function provided by the internal RWST in other iPWR designs. In addition, the NuScale reactor pool provides an additional barrier to fission product release (NuScale, 2012).

The NuScale containment is maintained under a vacuum to enhance its heat transfer characteristics. Equipment to draw and maintain the vacuum will be required.

5.3.2 Control room habitability equipment

Current large PWRs require equipment to maintain control room habitability following an accident or toxic gas release. The iPWR designs have the same need for this function. While large PWRs can rely on safety-related AC-backed equipment to function in a long-term manner, the iPWR designs rely on passive systems designed to last at least 72 hours. This typically requires the use of batteries and compressed air systems dedicated to this purpose.