Over the last decade, several computational methods have been developed and used to examine reactor flow transients caused by pump outage. The variations in system character which have been analyzed are sufficiently diverse that it appears worthwhile to compile them into a single report.

Limitations on the maximum temperature of the pile moderator have been imposed to prevent or control the gasification reaction of the graphite stack with the pile gas atmosphere. An uncontrolled reaction would cause a loss of structural strength, density, and thermal conductivity and would thus result in an unnecessary shortening of the effective operating life of the HAPO piles. Numerous studies have been made to define the rates of reaction of the pile stack with various components of the pile gas and the influence on these rates of various pile operating conditions. Based on these studies, maximum graphite temperature has been so restricted that after 10 years of pile operation the graphic stack has sustained less than 1% oxidation (based on recent experimental data). As pile power levels increased, the maximum graphite temperature has also increased and will increase still more as present and future power level programs are completed. In order to evaluate the effect on the graphite stack of the present programs, and to some extent determine the feasibility of future programs, a more realistic approach to the question of structural integrity and oxidation versus pile life is necessary. It is the purpose of this report to summarize …