Chemical Forms of Important Fission Products in the Primary Circuit of HTR-PM Under the Condition of Equilibrium Core: From Methodology to Preliminary Results

In this paper, the methodology of studying the chemical forms of important fission products (FPs) in the primary circuit of a pebble-bed modular high-temperature gas-cooled reactor (HTR-PM) is given, and the chemical forms of important FPs cesium (Cs), strontium (Sr), argentum (Ag), iodine (I), and corresponding amounts are calculated under the condition of equilibrium core of HTR-PM considering the O₂ impurity in the helium coolant of the primary circuit. It is shown that for the Cs element, Cs₂O₂ and Cs₂O may undergo a phase transformation between their nongaseous state and gaseous state, respectively, and for the Sr element, the conversion from SrO₂ to SrO is obvious with the increase of temperature. In contrast, the reaction between Ag and O reacts thoroughly, and AgO is very stable under different temperature conditions. There is a turning point in the chemical reaction between Cs and I with the increase of temperature, which illustrates that there exists competition between the I-Cs reaction and the O-Cs reaction. These results provide clear chemical form information of the important FPs in the primary circuit, which is significant to understanding the chemical reaction behavior of radionuclides in HTR-PM.