Distribution of plutonium and americium compounds in the combustion products of radioactive graphite in water vapor or air is analyzed. The study is carried out via thermodynamic analysis using the TERRA software package in a temperature range of 400÷3200 K. It is revealed that all carbon in water vapor passes into gas at temperatures above 900 K, and its transition temperature in air is 1000 K. Condensed plutonium compounds transform into vapor compounds in water vapor at temperatures above 1800 K and in air at 1700 K. Condensed americium compounds begin transforming into a vapor state at temperatures above 2000 K, and their transition temperature in air is 2200 K.