To enhance the thermal safety in case of station blackout, a wickless-heat pipe is proposed as an alternative passive cooling system technology to remove decay heat generation in the nuclear spent fuel storage pool. The objectives of this research are to investigate the heat transfer phenomena in vertical straight wicklessheat pipe using Graphene nanofluid working fluid and to study the effect of Graphene nanofluid on the vertical straight wickless-heat pipe thermal performance. The investigation was conducted in 6 meters height and 0.1016 m inside diameter of vertical straight wickless-heat pipe. In this research, the Graphene nanofluid with 1 % of weight concentration was used as working fluid. The effect of working fluid filling ratio, evaporator heat load, and coolant volumetric flow rate on the water jacket were studied. The results showed that the heat transfer phenomena, which were indicated by an overshoot, zigzag, and stable state, were observed. Based on thermal resistance obtained, it was shown that the vertical straight wickless-heat pipe charged with the Graphene nanofluid has a lower thermal resistance compared to one with demineralized water. The thermal resistance of vertical straight wickless-heat pipe using Graphene nanofluid and demineralized water were 0.015 °C/W and 0.016 °C/W, respectively. While the best thermal performance was achieved at a filing ratio of 80 %, higher heat load, and higher coolant volumetric flow rate. It can be concluded that Graphene nanofluid could enhance the thermal performance of vertical straight wickless-heat pipe.

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Abstract. After Fukushima Dai-ichi nuclear power reactor accident, spent fuel in spent fuel storage pool (SFSP) became an important thing to pay attention to, due to its decay heat release. If station blackout occurred, the active system for SFSP cooling system will experience malfunction to remove the product of decay heat. To keep spent fuel safe, heat pipe as passive cooling system device can be used to remove spent fuel decay heat even if the active cooling system failed. Heat pipe with 6 m on length will be proposed as apassive cooling system in SFSP. For that, it is necessary to analyze the effect of Graphene nano-fluid as heat pipe working fluid. The objective of this research is to know the effect on Graphene nano-fluid to enhance the heat pipe thermal performance and to know the heat transfer phenomena inside the heat pipe based on Graphene nano-fluid. Graphene nano-fluid with 1% weight concentration was used as working fluid with filling ratio of 80%. The experimental investigation is conducted with varying the evaporator heat load of 1000, 1500, 2000, and 2500 W. Water as coolant flows in thecondenser with aconstant volumetric flow rate of 8 L/min. The experiment results show that there was anovershoot, zigzag and stable phenomena inside the heat pipe. The thermal resistance of heat pipe is obtained at 0.015 o C/W. The use of Graphene nano-fluid as working fluid can enhance the heat pipe thermal performance significantly and can be used as an alternative working fluid in heat pipe for thepassive cooling system in SFSP of nuclear power plant.

Kejadian station blackout (SBO) pada PLTN Fukushima Daiichi pada Maret 2011 di Jepang menjadi latar belakang yang penting untuk kegiatan penelitian tentang sistem pendinginan pasif pada teknologi keselamatan reaktor nuklir. Pengaruh perubahan densitas fluida di daerah panas menimbulkan gaya apung (buoyancy force) dan pengaruh perubahan densitas fluida pada keadaan dingin menimbulkan gaya gravitasi (gravitational force) sehingga terjadi sirkulasi alam pada fluida kerja (air) di sepanjang untai. Tujuan penelitian dilakukan untuk mengetahui unjuk kerja Heating Tank Section (HTS) yang dilengkapinya dengan keterbaruan berupa helical heat exchanger. Penelitian dilakukan secara eksperimental berdasarkan variasi setting temperatur air dalam tangki pemanas dan daya listrik di heater (variasi tegangan regulator). Berdasarkan hasil perhitungan efisiensi pada HTS (εH) dengan keterbaruan yang dimilikinya memiliki rentang 45,48% - 99,41% dengan efisiensi ratarata 82,58%. Efisiensi yang cukup tinggi pada HTS ini menunjukkan bahwa adanya keterbaruan penukar kalor helical meningkatkan unjuk kerja pemanasan HTS pada fasilitas Untai FASSIP-03 NT.