4S reactor

Our design efforts to satisfy these conditions have resulted in the development of the Super Safe, Small and Simple (4S) fast reactor with an electric power output of 50 There are several advantages of the 4S reactor ... 

The 4S reactor assembly and plant design are shown in Fig. 1 and Fig. 2, respectively. The diameter of the reactor vessel is 2.5 m and the area of the nuclear building is 26m x 16m, thus requiring only a small ground space. 

Finally, the author would like to emphasize the need for worldwide cooperation on the development of the 4S reactor. 

The 4S reactor employs a burnup control system with an annular reflector in place of the control rod and its living mechanism. Burnup control by vertical movement of the annular reflector eliminates the necessity for complicated control rod operations. 

The MBRU-12 has maintained a conservative approach, providing for the shuffling of fuel under a closed guard vessel cover, which could help achieve early market availability. The 4S reactor, however, incorporates a small-diameter core of high neutron leakage rate with moving reflector control of bum-up reactivity loss, as a way to assure negative sodium void worth under all conditions. The reflector in the 4S is located outside the core and the power control is executed via the feedwater control from the steam-water power circuit. Some further related R D is required on these features (ANNEX XIV). 

Collaboration among ANL in the USA and CRIEPI and Toshiba in Japan related to the ENHS R D is being carried out. The CRIEPI and Toshiba effort is focused on the 4S reactor design (ANNEX XIV) important elements of which were adopted for the ENHS reactor concept. 

Figure XIV-3 shows a general view of the 4S reactor for a 50 MW(e) plant although the size and dimensions differ from those of the reactor for a lOMW(e) plant, nearly all basic concepts are the same, except that the primary reactor cooling system (PRACS) is used in the 50 MW(e) design instead of the IRACS in the 10 MW(e) design.

A summary of the neutron-physical characteristics of the 4S reactor is provided in Table XIV-2. 

In the 4S design, the reactor building is isolated horizontally by seismic isolators. The design standard already exists for such isolators for nuclear power plants (NPPs) in Japan [XIV-8]. The thin reactor shape results in a higher characteristic frequency therefore, the 4S reactor could be rigid against vertical shock. 

XTV-2] MATSUMIYA, H., et al.. Development of a reflector drive mechanism using magnetic repulsion force for 4S Reactor, ANS Winter Meeting (Paper presented at meeting in Washington, D C., Nov. 12-16, 2000). 

XIV-4] KOBAYASHI, Y., et al., A study of magnetic impact type micro-stepping actuator to drive large payload reflector for 4S reactor, IMECE2004-59372, 2004 ASME International Mechanical Engineering Congress and RD D Expo (Anaheim CA, USA, Nov. 13-19, 2004). 

The abovementioned design features of the 4S-LMR are also viewed as necessary conditions for plant installation at remote locations in developing or developed countries. Specifically, these features contribute to achieving a simplified reactor design, with the per-output weight of stmctural materials in the 4S reactor being lower than in a typical large reactor. 

The 4S reactor is designed to apply a reactivity control system with a movable annular reflector replacing the control rods and driving mechanisms, which traditionally require frequent maintenance. If applied, control rods would have to be replaced a number of times during the long core lifetime. 

XXIII-8] NISHI, Y., et al., A new concept of the 4S reactor and thermal hydraulic characteristics, ICONE-12 (Proc. 12 Int. Conf on Nuclear Engineering, Arlington, April 25-29, 2004X ICONE 12-49257. 

The images of 4S reactor has been used by using Courtesy of Toshiba Corporation. The author... 

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