1. INTRODUCTION OF PASSIVE SAFETY AND NATURAL CIRCULATION CHARACTERISTICS FOR AC600/1000

1.1. Main design characteristics of AC600/1000

145 fuel assembly and 3658 mm active section core is used in AC600. 177 fuel assembly and 4267mm active section core is used in AC1000. Neutron instrumentation system inserts into core from top of pressure vessel so that there is not any penetration in the bottom head of reactor pressure vessel. Steel water reflector is used to save neutron and to reduce neutron fluency on wall of reactor pressure vessel. Modularization construction, advanced digital instrumentation and control system are considered in AC600/1000 design. Passive safety systems including passive emergency residual heat removal, passive safety injection and passive containment cooling sub-systems are very important for AC600/1000 design.

No any penetration below top of reactor core is useful to reduce core melt frequency. Integral reactor top structure and large size reactor vessel are also used in AC600/1000 design. The inner diameters of reactor pressure vessels are 4000mm for AC600 and 4340 mm for AC1000. Low power density of reactor core, low neutron leakage, 80% stainless steel +20% water reflector and large size reactor pressure vessel are able to assure 60 year life time of plant. Gray rods are used in AC600/1000 to achieve daily load follow. Linear power density of core is 134.2/140W/cm for AC600/1000 respectively, much lower than current PWR nuclear power plant so that AC600/1000 reactor core has larger safety margin.