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

Abstract

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.