Analysis of Steam-Entry Experiments in the Phase-I GCFR Critical Assembly

摘要

The initial three-phase program of critical experiments conducted in behalf of design and safety evaluations for the 300-MW(e) GCFR demonstration plant included extensive studies of steam-entry effects. The report presents results of a General Atomic analysis of the simulated steam ingress experiments in a central 47-liter region of the 3150-liter-core Phase-I GCFR assembly. Investigations of differences in calculated steam worth due to variations in analytical techniques are reported, including methods for cross-section generation, adjustments for heterogeneity, neutron-streaming effects, group structure, and the use of various stages of perturbation theory. For each of the densities of steam simulated by CH sub 2 (up to the equivalent of 45 g/lter H sub 2 O in the ''coolant'' channels), the regeneration of cross-section sets for the zone fuel materials with the hydrogen-degraded spectra was found essential for obtaining reasonable agreement of calculated and measured flooding worths. Also, it was necessary to use exact perturbation theory methods, since first-order perturbation was found to be completely inappropriate with the 10- and 28-group structures employed. (ERA citation 03:040403)