The NuScale design (45 MWe per module) employs natural circulation in its primary system where the core heats the water, causing it to rise through a central hot leg where it then enters the upper plenum and is cooled by a helical coil steam generator. Upon cooling it then proceeds down a cold leg downcomer where it is returned to the core. Because of this unique design, NuScale has developed an integral systems test facility, the NuScale integral scaled test (NIST) facility [14, 15] to obtain data on its natural circulation design feature. Figure 14.8 is an illustration of the NIST facility.

The NIST was built on the Oregon State University (OSU) campus and originally developed and constructed in the 2000-2003 timeframe by OSU, Idaho National Laboratory, and NEXANT-Bechtel. NuScale has leased the facility since 2008 and has made a number of proprietary modifications to the NIST configuration to match the current NuScale design. The objective of the testing at NIST to generate well-scaled thermal-hydraulic data for system characterization and safety code validation while also providing a platform for the design and test of plant operational procedures, control logic schemes and to inform safety methodology development. Additional testing is to include LOCA, non-LOCA, flow stability, and startup testing.