Session: 11-02 Severe accident mitigation phenomena

Paper Number: 134633

134633 - Numerical Study on the Operational Behavior of Catalytic Components With Spherical Packed Bed Structures 

Abstract: 

In order to effectively mitigate the potential risk of hydrogen explosions in severe accidents, Passive Autocatalytic Recombiners (PARs) have become widely employed in the containment of nuclear power plants in recent years. In the catalyst section of PAR, the amount of removed hydrogen is a crucial parameter for evaluating its operational behavior. However, the hydrogen removal capacity of PARs based on traditional structures is relatively limited, necessitating the development of more efficient catalytic components designs to cope with rapid hydrogen release during severe accident conditions. Catalytic components with spherical packed bed structures, characterized by a larger catalytic specific surface area, show significant potential to enhance the hydrogen removal capability of PARs.

This paper aims to analyze the operational behavior of catalytic components based on different spherical bed packed structures. Three typical structured packing forms are considered: simple cubic (SC), body center cubic (BCC) and face center cubic (FCC) arrangements of packed catalytic spheres. The models of catalytic components were constructed using the CFD software STAR-CCM+. To simulate the detailed process of the hydrogen catalytic oxidation over platinum (Pt), the elementary reaction mechanism was employed as the reaction kinetics model to define involved gas and surface species, reaction equations, Arrhenius formula coefficients of multiply reactions, and thermodynamic polynomial parameters by inserting relative CHEMKIN format input cards. All the inlet conditions were maintained as constants, and the gas-solid interfaces covered platinum with the same catalyst site density (2.72×10⁻⁸ kmol/m²). It should be noted that the possible gas-phase combustion of hydrogen oxidation is disregarded in the tests.

An analysis of multiply physical fields provides comprehensive insights into the reaction process occurring within catalytic components. The results indicate that hydrogen removal efficiencies at the outlets for the SC, BCC, and FCC arrangements of packed catalytic spheres are 81.46%, 99.09%, and 99.87%, respectively. Notably, the FCC packing exhibits the highest hydrogen removal capability, while the SC packing eliminates the lowest amount of hydrogen among the three structures. In addition, the SC, BCC, and FCC packings demonstrate a sequential increase in outlet gas phase temperature and velocity. This phenomenon is attributed to the corresponding rise in mass flow rates at the outlets of the three structures, resulting in more hydrogen could react on the catalytic surface. However, the most complex structure of the FCC packing also introduces the highest flow resistance, demanding a greater supply of hydrogen to release additional reaction heat and sustain continuous gas flow.

Presenting Author: Tianming Man Harbin Engineering University

Presenting Author Biography: The Ph.D student of Heilongjiang Provincial Key Laboratory of Nuclear Power System & Equipment in Harbin Engineering University, major in hydrogen mitigation in severe accident in the containment.

Authors:

Tianming Man Harbin Engineering University
Zehua Guo Harbin Engineering University
Ming Ding Harbin Engineering University
Wenkai Liang Tsinghua University