Safety evaluation of MHTGR licensing basis accident scenarios

Abstract

LIST OF FIGURES xv LIST OF TABLES xix A draft of the report was reviewed by Drs. James G. Guppy and Gregory J. Van Tuyle at BNL and Dr. Peter Williams at the NRC. Early drafts of the report were typed by Mrs. Amalia Ruggiero. The final draft and final report were typed by Mrs. Linda Hanlon. The author gratefully acknowledges all of the help and support he received.-xx i-* Time at which heat leaving vessel exceeds decay heat, i.e., net cooldown of reactor vessel and internals begins.

THATCH: A computer code for modelling thermal networks of high- temperature gas-cooled nuclear reactors

“…For fin spacing of about 10 cm and 15 cm fin lengths, at an RCCs panel radius of about 3.4 m, the curvature effects are indeed small. The effect of axial radiation was found to be very small in the reactor cavity (Kroeger, 1989) and would be even less at the temperature levels within the RCCS channels.…”

“…The reaction rates were raised up by one order and down by two orders. The result for several very conservative air ingress transients during core-heatup transients showed that the effect of ali these variations on the amount of graphite oxidized was negligible, because essentially ali oxygen entering the core will react and the amount of carbon oxidized is limited by the gas flow through the core, which remains small due to its long and narrow coolant passages [Kroeger, 1989].…”

“…In its recent version, the code has been applied extensively to model various transients in the commercial modular HTGR (MHTGR) [Kroeger, 1989], under funding by the Nuclear Regulatory Commission. A detailed description of the MHTGR canbe found in a concept description report [Bechtel National, 1986].…”

HTGR Dust Safety Issues and Needs for Research and Development

“…Other safety issues related to graphite oxidation include production of combustible gases (Kroeger 1989;Palmer, Sibulkin, Strehlow, & Yang 1978) and liberation of FPs. Provided circulating quantities of dust are indeed small, these issues are only important for structural graphite, not dust.…”