The DMS is a typical simplified BWR and was proposed by Hitachi, Ltd (Kawabata et al., 2008) in cooperation with the JAPC. The targets for the design are the same as in the IMR and are summarized in Table 19.1. A schematic view of the reactor is shown in Figure 19.4 and its major specifications are summarized in Table 19.4.

Containment

vessel

Reactor

vessel

Main

steam

line

The core is shortened and cooled by the natural circulation of the coolant without the recirculation pumps. One of the characteristic features for the system simplification for this concept is elimination of the steam-water separator and dryer, by introducing a gravity separation mechanism for the steam-water separation process. Therefore, the reactor pressure vessel is simplified and compact.

The power output is 428 MWe. The average discharge burnup is 45 GW d/t and the refueling interval is 24 months. The effective length of the core is shortened to 2 m to increase the driving force for the natural circulation core cooling. The system pressure is 7.2 MPa and is the same pressure as in the normal BWR. For the safety system design, the DMS employs a simplified ECCS with passive accumulator system, and hence, eliminated the high pressure core flooder (HPCF) system and decreased about 60% of the reactor core isolation cooling (RCIC) system capacity.