12.2.2 Heavy Water CANDU SCWR (Gen IV). The SCWR concept is also being considered as an evolution from CANDU reactor technology. As with the LWR systems, there is an aim to continually enhance the design and applications of the CANDU system. Thus, complementary to the SCWR loop concept described above, a channel design option with multi-stream products is also possible within the SCWR context. The CANDU SCWR concept is envisaged for flexibility of application, e. g. including electricity production, hydrogen generation (direct or indirect) and high-temperature process heat applications, depending on demand. It could also have desalination applications (Generation IV Seminar on Nuclear Energy Systems Research and Development, 2004; Duffey, 2004a, b). It is seen as part of the evolution towards the CANDU X system, sometimes referred to as a Generation V system. The CANDU X design could also be economically competitive. The main elements of the CANDU X system are described below. CANDUX. The CANDU X concept is another pressure tube reactor in the CANDU family of reactors. The design is being put forward by AECL in Canada. It has a flexible generating capacity, in the range 350-1150 MWe. This depends on the number of fuel channels in the plant.

The innovative features of the Mark 1 model include supercritical heavy water for the reactor coolant and supercritical light water for the turbine generator. The utilisation of supercritical water results in a significant increase in system pressure and temperature compared with earlier generation CANDU plants.

CANDU X retains the use of two passive shutdown systems as in current generation plants. There is also passive decay heat removal even if the reactor system is empty of coolant.

The CANDU X reactor possesses a number of the attributes expected from future generation systems. It has high efficiency due to increased core outlet temperature. There is flexibility in reactor power scale available through extensive modularity in design.

Regarding its fuel cycle and waste management concerns, the option to use thorium fertile material and slightly enriched fuels is available to reduce the level of minor actinides produced.

As for supercritical light water systems, the main applications would be for electricity generation. However, the high core outlet temperature increases the number of process heat applications that are possible. The temperature is higher than can be achieved by current water reactors but lower than can be achieved for HTRs and LMFRs. The attractiveness for process heat applications is particularly true for the smallest 350 MWe version.

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