Primary coolant chemistry of the Peach Bottom and Fort St. Vrain high-temperature gas-cooled reactors

The chemical impurities in the primary coolants of the Peach Bottom and Fort St. Vrain reactors are discussed. The impurity mixtures in the two plants were quite different because the sources of the impurities were different. In the Peach Bottom reactor, the impurities were dominated by H2 and CH4, which are decomposition products of oil. In the Fort St. Vrain reactor, there were high levels of CO, CO2, and H2O. Although oil ingress at Peach Bottom created carbon deposits on virtually all surfaces, its effect on reactor operation was negligible. Slow outgassing of water from the thermal insulation at Fort St. Vrain caused delays in reactor startup. The overall graphite oxidation in both plants was negligible