Tangki pendingin merupakan salah satu bagian dari fasilitas FASSIP-02 Test Loop Strand yang merupakan sistem pendingin untuk melepaskan panas ke lingkungan. Fasilitas eksperimental skala besar FASSIP-02 Test Loop Strand dibangun untuk pengembangan sistem keamanan berbasis pendinginan pasif yang memanfaatkan aliran sirkulasi alami. Salah satu hal yang menarik untuk dibahas adalah proses pemanasan, tunak, dan pendinginan yang terjadi pada bagian pendinginan selama percobaan. Tujuan dari penelitian ini adalah untuk mendapatkan karakteristik historis dari perubahan suhu selama proses transien pemanasan, keadaan tunak, dan transien pendinginan di bagian pendinginan. Metode penelitian dilakukan secara eksperimental dengan perubahan kondisi awal setting temperatur air pada bagian pemanasan bervariasi dari 40 0C, 50 0C dan 60 0C. Semua pengukuran dilakukan selama 24 jam menggunakan sistem akuisisi data instrumentasi nasional dengan sampling rate 1 data per detik. Percobaan dilakukan dengan cara memanaskan suhu air di dalam heater sampai mencapai setting suhu yang ditentukan, kemudian mempertahankan suhu pada keadaan tunak selama 5 jam. Selanjutnya, daya listrik ke pemanas dimatikan dan sistem dibiarkan dingin secara alami saat merekam data. Hasil yang diperoleh setelah data percobaan diolah dengan program grafik Orgin 8, dimana diperoleh waktu yang diperlukan untuk mencapai kondisi tunak pada berbagai temperatur 40 0C, 50 0C dan 60 0C adalah 1291 detik, 2392 detik dan 3504 detik, masing-masing. Perubahan temperatur antara inlet dan outlet pada cooler berturut-turut adalah 5,43 0C, 9,67 0C dan 12,62 0C.   ABSTRACT The cooling tank is one part of the FASSIP-02 Test Loop Strand facility which is a cooling system to release heat to the environment. The FASSIP-02 Test Loop Strand large-scale experimental facility was built for the development of passive cooling based safety systems utilizing natural circulating flows. One of the interesting things to discuss is the heating, steady and cooling proCesses that occur in the cooling section during the experiment. The aim of the study was to obtain historical characteristics of temperature changes during the heating transient proCess, steady state and cooling transients in the cooling section. The research method was carried out experimentally with changes in the initial conditions of setting water temperature in the heating section variation from 40 0C, 50 0C and 60 0C. All measurements were carried out for 24 hours using the national instrumensasit data acquisition system with a sampling rate of 1 data per second. The experiment was carried out by heating the water temperature in the heater until it reached the specified temperature setting, then maintaining the temperature at steady state for 5 hours. Next, the electrical power to the heater is turned off and the system is allowed to cool naturally while recording data. The results obtained after the experimental data were proCessed with the Orgin 8 graph program, where it was obtained that the time required to reach steady conditions at various temperatures of 40 0C, 50 0C and 60 0C were 1291 seconds, 2392 seconds and 3504 seconds, respectively. Changes in temperature between the inlet and outlet in the cooler are 5.43 0C, 9.67 0C and 12.62 0C, respectively.

FASSIP-01 rectangular loop is a facility which owned by PTKRN-BATAN that used for observe the phenomenon of natural circulation in large-scale. This natural circulation phenomenon will be applied as a passive cooling system in nuclear power plant that will be built up in Indonesia. Some FASSIP-01 experiments have done before, but those experiments show that the fluid flow in FASSIP-01 is not in optimal conditions because there are some errors happened and causes some losses. The second modification of FASSIP-01 rectangular loop has purpose to minimize losses happened in previous modification of FASSIP-01. The purpose of this research is to know the characteristics of flow and the trend of the data from the flow in FASSIP-01 mod.2 rectangular loop before do experiments. Simulations is done by using 2-dimensional images and varying the heating temperature at 353,15 K and 363,15 K and the cooler at temperatures of 278.15 K, 283.15 K, 288.15 K and 293.15 K. Based on the simulation results it is known that the velocity flow rate will increase if the temperature in the heating tank is increased, but will decrease if the temperature in the cooling tank is increased. The results of the calculation of the Reynold Number and Nusselt Number based on the velocity flow rate are 2973,668 the lowest and 5775,356 the highest and for the Nusselt number  obtained 17,36 and the highest is 28,091.