A better understanding on the phenomenon of natural circulation flow for cooling systems is necessary prior to improving the safety of nuclear power plant, not only in normal operation but also in accident conditions. One way to understand this phenomenon is by analyzing the Nusselt number in various geometrical dimensions through experimentation. The purpose of this study is to understand natural circulation phenomenon in transient condition by varying height differences between heater and cooler. To achieve this purpose, an experiment apparatus called NC-Queen was developed and arranged to enable three variations of height differences between heater and cooler, i.e., 1.4 m, 1.0 m, and 0.3 m. It is made of a stainless steel tube with a diameter of 1 inch, arranged in rectangular shape 6.4 m in length, and uses water as coolant. The initial temperature of the heater was set at 90 °C. The Nusselt number was obtained by calculating the flow rate as a function of transient temperature. The results confirm that height differences affect thermal properties and flow region based kinetics characteristics of water. In initial condition, decreasing height difference from 1.4 m to 1.0 m resulted in flow rate reduction of 16.7 %, while decreasing height difference from 1.4 m to 0.3 m resulted in a 39.1 % flow rate reduction. In final condition, the flow rate reductions were 75 % and 82.6 %, respectively. Meanwhile, in initial condition, the Nusselt number for height difference reduction from 1.4 m to 1.0 m and from 1.4 m to 0.3 m decreased by 30.5 % and 74.6 %, respectively, while for final condition, the Nusselt number decreased by 11.9 % and 67.4 %, respectively. The new constants in relationship between Nusselt number and the height difference are a = 20.06 and b = 0.56. The dominance of turbulent flow provides a good safety margin with indications of the large amount of heat released.

No abstract

ABSTRAKReactor Cavity Cooling System (RCCS) adalah salah satu sistem keselamatan pada Reaktor Daya Non Komersial (RDNK). Untuk mensimulasikan keadaaan tersebut, dibuat prototype Heater Element System (HES) yang merupakan sistem pemanas listrik dan berfungsi untuk memberikan kalor pada simulator dinding RPV (wall) seperti pada acuan RPV tipe HTGR. Tujuan penelitian adalah untuk memperoleh karakteristik temperatur selama pemanasan prototype HES hingga mencapai temperature 400°C berdasarkan posisi vertikal dan horizontal HES. Metode pengamatan dilakukan dengan menggunakan kamera infra merah NEC tipe TH9100ML sebagai alat ukur temperatur dan alat visualisasi ditribusi temperatur. Hasil pengamatan menunjukkan, bahwa kehilangan kalor pada prototipe HES pada posisi vertikal lebih kecil dibandingankan pada posisi horizontal hal ini disebabkan karena luas permukaan pada posisi horizontal sebesar 7,260 cm2 lebih memungkinkan untuk kehilangan kalor lebih besar. Posisi vertikal temperatur yang dicapai pada wall prototipe HES lebih tinggi dibandingkan pada posisi horizontal.Kata Kunci: RCCS, Heater Element System, kamera infra merah, temperatur ABSTRACTReactor Cavity Cooling System (RCCS) is one of the safety systems in Non-Commercial Power Reactors (RDNK). To simulate this situation, a prototype Heater Element System (HES) was made using electric heating system as a heat sources and it serves to provide radiation heat to the RPV wall simulator as the reference of the RPV of HTGR type. The purpose of this study was to obtain the temperature characteristics during the heating of the HES prototype to reach temperatures of 400°C base on HES position, horizontal and vertical positions. The observation method was carried out using a TH9100ML infrared camera NEC type as a temperature measurement and a temperature distribution base on visualization. The observations show that the heat loss in the HES prototype in the vertical position is smaller than in the horizontal position because this is because the surface area in the horizontal position 7.260 cm2 is more likely to lose more heat. The vertical position the temperature achieved on the HES prototype wall is higher than in the horizontal position.Keywords: RCCS, Heater Element System, infrared camera, temperature