The supercritical sater-cooled reactor (SCWR) is a high-temperature, high — pressure water-cooled reactor, which operates above the thermodynamic critical point of water (above 374 °C, 22.1 MPa) (Fig. 13.10) . SCWRs are based on existing advanced Gen III water-cooled reactors as well as developments in supercritical water power cycle technology in such sectors as the coal industry. SCWRs are basically LWRs operating at higher pressure and temperatures with a direct, once-through cycle. The coolant remains single-phase through the system. There is no need for recirculation using jet pumps, pressurizer systems, steam generators, separators and driers, which results in plant simplification, albeit at the expense of increased temperature and pressure. The major components of the power conversion cycle external to the reactor vessel are similar to supercritical fossil-fired boilers.

The SCWR uses either pressure vessel or pressure tube boundaries for the supercritical water in the core (Starflinger et al., 2008) (see Fig. 13.11). The higher of the two outlet temperatures, 625 °C, affords a thermal efficiency approaching 50%, which compares very favourably to the ~33% efficiency of today’s LWRs. The high-pressure single-phase coolant provides another advantage over current technology, because it circumvents the need for steam generators and allows the use of an off-the-shelf advanced power turbine. Combined, these factors could potentially reduce capital costs by up to 40%. The main advantage of the SCWR is thus a lower operating cost because of higher thermal efficiency and a simpler

design made possible by the use of a well-established, high-temperature, single­phase coolant.

It is hoped that SCWRs will support the next generation of baseload electricity suppliers. The overall GIF plan for the SCWR is to complete the operation of a fuelled loop test by about 2015, with a view to construction of a prototype sometime after 2020. The SCWR can be designed as a fast or thermal reactor with a closed or once-through fuel cycle. In addition, pressure-vessel or pressure-tube designs offer a number of design options that have the potential to meet the GIF’s criteria (Khartabil, 2009) (see Table 13.7).

Research in developing the technology will need to focus on areas such as safety, sustainability, proliferation resistance and physical protection (Khartabil, 2009). A key challenge is the selection of materials for the core components (a replacement will be needed for Zircaloy cladding for example) and in demonstrating core power stability; thermal-hydraulics data will be needed to design and license the reactor (Khartabil, 2009; Abram and Ion, 2008). Material selection for the reactor core (fuel cladding and other components) will need to take account of creep, oxidation and stress corrosion data.

13.11 SCWR pressure vessel baseline alternative (Starflinger et al., 2008).