Recent research led by L. Berti from the Department of Civil and Industrial Engineering at the University of Pisa has shed light on the critical safety systems of the International Thermonuclear Experimental Reactor (ITER). The study, published in the journal Nuclear Fusion, focuses on the Vacuum Vessel Pressure Suppression System (VVPSS), which is designed to manage potential Loss of Coolant Accidents (LOCAs) within the reactor. This is particularly important as it helps prevent dangerous increases in internal pressure that could compromise the reactor’s primary confinement barrier.
One of the unique aspects of this research is its exploration of steam condensation at sub-atmospheric pressures, a scenario that differs from the typical conditions found in nuclear fission reactors. Through an extensive experimental program using reduced-scale rigs, the team observed unstable condensation regimes at steam mass flow rates of about 500 grams per second, which is only 10% of the maximum rate expected during serious accidents. These unstable regimes led to significant vibrations within the experimental setup, phenomena known as “Chugging” or Condensation Induced Water Hammer.
Berti’s team utilized video analysis to assess the dynamics of bubble collapse and the characteristics of steam jets, correlating these observations with data from accelerometers. This detailed analysis allowed them to better understand the behavior of steam and water interactions under these specific conditions. Notably, the research highlighted the positive role of non-condensable gases (NCGs) in mitigating the adverse effects of unstable condensation. “The NCG inhibits the occurrences of Water Hammer inside the sparger and eliminates thermal stratification inside the water pool, increasing the turbulence,” Berti noted.
The implications of this research extend beyond the laboratory. As the energy sector increasingly turns to nuclear fusion as a viable alternative to traditional energy sources, understanding and improving safety systems like the VVPSS becomes paramount. The findings could lead to enhanced designs for future fusion reactors, potentially lowering the risks associated with coolant losses and improving overall reactor efficiency.
With ITER poised to be a cornerstone of future energy generation, advancements in safety systems not only bolster public confidence but also present commercial opportunities for companies involved in nuclear technology and safety engineering. As the world seeks cleaner and more sustainable energy sources, the insights from this study could play a crucial role in the successful deployment of fusion energy on a commercial scale.
