CFD analysis of core melt spreading on the reactor cavity floor using ANSYS CFX code

• Published in: Nuclear engineering and design 2012-08, Vol.249, p.90-96
• Main Authors: Yeon, Wan-Sik, Bang, Kwang-Hyun, Choi, Youngjo, Kim, Yong Soo, Lee, Jaegon
• Format: Article
• Language: English
• Subjects: Applied sciences; Controled nuclear fusion plants; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Fuels; Holes; Installations for energy generation and conversion: thermal and electrical energy; Melts; Nuclear engineering; Nuclear fuels; Nuclear power generation; Nuclear reactor components; Nuclear reactors; Spreading; Spreads
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2011.08.047

► Spreading of core melt on nuclear reactor cavity is calculated using ANSYS CFX. ► Thermal radiation and viscosity of liquid–solid mixture of the melt are modeled. ► The code is validated with FARO and VULCANO spreading experiments. ► Calculation of a full-scale cavity shows the spreading completes within a minute. In the very unlikely event of a severe reactor accident involving core melt and reactor pressure vessel failure, it is important to provide an accident management strategy that would allow the molten core material to cool down, resolidify and bring the core debris to a coolable state for Light Water Reactors (LWRs). One approach to achieve a coolable state is to quench the core melt after its relocation from the reactor pressure vessel into the reactor cavity. This approach typically requires a large cavity floor area on which a large amount of core melt spreads well and forms a shallow melt thickness for small thermal resistance across the melt pool. Spreading of high temperature (∼3000K), low superheat (∼200K) core melt over a wide cavity floor has been a key question to the success of the ex-vessel core coolability. A computational model for the melt spreading requires a multiphase treatment of liquid melt, solidified melt, and air. Also solidification and thermal radiation physics should be included. This paper reports the approach and computational model development to simulate core melt spreading on the reactor cavity using ANSYS-CFX code. Solidification and thermal radiation heat transfer were modeled in the code and analyses of the FARO and VULCANO spreading experiments have been carried out to check the validity of the model. The calculation of 100 tons of core melt spreading over the full scale reactor cavity (6m×16m) showed that the melt spread was completed within a minute.