Session: 05-04: Nuclear Engineering and Safety Analysis

Paper Number: 136234

136234 - Experimental Investigation on the Heat Transfer Capacity of a Prototypically Long Straight Thermosiphon Bundle for Nuclear Spent Fuel Pool Passive Cooling 

Abstract: 

The importance of incorporating passive residual heat removal systems into the design of Nuclear Spent Fuel Pool (NSFP) heat removal systems has been highlighted by the lessons learned from the catastrophic event at the Fukushima Daiichi Nuclear Power Plant in 2011. Owing to the high heat transport capability of latent heat transfer, the simple design and reliable operation of two-phase closed thermosyphons (TPCT) has emerged as a promising solution to enhance nuclear power station safety by passively cooling NSFP during accidents or station blackouts. This paper presents experimental results of investigations on the heat transfer behaviour of a straight, 10-meter long TPCT pipe bundle (smooth tubes, working fluid water, 3 × 3 quadratic arrangement of tubes, vertical orientation), which has a 2-meter evaporator section and a 4-meter condenser section. The experiments were conducted at the test facility ATHOS (Atmospheric THermosyphon cOoling System) at the Institute of Nuclear Technology and Energy Systems, University of Stuttgart. The primary objective was to examine the heat transfer capacity under realistic thermal operating conditions by incorporating the heat supply from a heated water pool and the heat removal through convective airflow in a chimney. Prior testing at the test stand THOR (THermosyphon labORatory) with an 8-meter long TPCT showed that the optimal filling ratio for a 2 m evaporator section approached 30%. Thus, this filling ratio was selected as the optimal filling ratio for the 10-meter long TPCT pipe bundle. Experimental tests were conducted at NSFP operating temperatures of 45°C, 60°C, and 80°C (normal, abnormal, and accidental thermal conditions of NSFP) and heat-sink temperatures ranging from 5 to 30 °C and an average air velocity of 0.4 m/s. Results indicated that the heat transfer rate of the TPCT bundle was up to 8 kW at a water pool temperature of 80°C during long-term tests and that the TPCT operates at a water pool temperature of 45 °C, affirming the TPCT bundle's capability to provide efficient passive cooling for NSFPs. In addition, start-up experiments were conducted by increasing the water pool temperature from 30 to 80 °C. The results showed reliable operation of the TPCT bundle and confirmed the absence of non-condensable gases inside the TPCTs. Finally, the introduced improvement measures, such as the determination of the optimal filling ratio, degassing of the TPCTs, and increase in the evaporator section, showed an increase in the heat transfer rate of the TPCT bundle of up to approximately 30 % compared with previous studies.

Presenting Author: Sergio Iván Cáceres Castro Institute of Nuclear Technology and Energy Systems (IKE)

Presenting Author Biography: I currently serve as a Research Associate at the Institute of Nuclear Technology and Energy Systems, University of Stuttgart, since September 2020. My academic foundation was laid in Mechanical Engineering at the Universidad Industrial de Santander in Colombia from July 2009 to September 2013. Building on this, I pursued a Bachelor's in Energy Engineering at Hochschule Bremen, spanning from October 2013 to April 2017. This trajectory led me to the University of Stuttgart, where I earned a Master's in Energy Engineering from October 2017 to August 2020.

Authors:

Sergio Iván Cáceres Castro Institute of Nuclear Technology and Energy Systems (IKE)
Rudi Kulenovic Institute of Nuclear Technology and Energy Systems (IKE)
Jörg Starflinger Institute of Nuclear Technology and Energy Systems (IKE)