Small, simple and safereactor is an interesting alternative in supplying energy for eastern part of Indonesia. For this purpose, theSmall Simple Safe Reactor (SSSR) is designed. This design is based on PWR design buth with a greatsimplification so it can be build based of the capability of the exsisting Indonesian industry. SSSR isdesigned deliver 50 MWth thermal energy output which will be used to produce electricity and / or freshwater via sea water desalination. SSSR design adopts integral concept in which the reactor core and theheat exchangers are located inside the reactor vessel. SSSR also uses natural circulation. The designoperation pressure is less then half of the normal operating pressure of PWR. The EGGS, RHS and SOSare combined Multi Purpose Water Pool System (MPWPS) which can operate passively at all transientconditions. All piping system outside the reactor vessel other than secondary (working) fluid piping areeliminated. All of these features will simplify the design and increase if safety characteristic (simple andsafe concept). SSSR uses U02 fuel pellets inside zirkaloy 4 cladding which are arranged in a 61 rodhexagonal fuel assembly which consists of 48 fuel rods, 6 burnable poison rods (BPR), 6 control rod guidetimbles dan 1 instrimentation channels located at the central of fuel assembly. SSSR core consists of dari60 periferal fuel assembly (0,4 % Gd02 at BPR) dan 61 central fuel assembly (4 % Gd02 at BPR) withactive height of aktif 1.4 m and diameter of 1.3 m. Reflektor BeO with the thich of 20 cm is assembled atouter side of the cores, while BeO pellets are added until 20 em hight at the top and botton edge of the fuelrods. The coolant is light water. The fuel has uniform initial enrichment of 7.2 % U-235. The core isoperated in batch mode (without fuel suffling) from BoL to EoL. This study focuses in neutronics aspectcalculation which is done using SRAG 2005 computer code. The calculation results show that the core canbe operated along 10 years with the value of k = 1.07 at BoL and 1.01 at EoL, and has negative values offuel temperature coefficient and void moderator coefficient along the core lifetime. Thus it can beconcluded that the SSSR core design is safe in neutronic aspectKev words: integral concept, natural circulation, small, simple and safe reactor. Andang Widi Harto; Program Studi Teknik Nuklir, Jurusan Teknik Fisika, Fakultas Teknik UGM