Bottom reflector esp. for pebble bed reactor - has vertical gas ducts of small dia. at top leading into fewer larger ducts below

摘要

A bottom reflector for a gas-cooled nuclear reactor of the pebble bed type is composed of vertical graphite columns of hexagonal cross-section, each divided several times into separate blocks or layers one above another. The columns contain vertical bores for cooling gas and one or more fuel element discharge ducts. Those vertical bores (35) which intersect the top (inclined) face (20) of the bottom reflector continue down only a limited distance below this top face and then lead into other bores (38) of considerably larger dia. Pref., the bores of smaller dia (35) are limited to the uppermost graphite block (30) of a column (26). Pref. also, the top and bottom ends of the large dia. bores (38), occupying the remaining block of the column, have an increased dia. pref. in the form of a conical divergence. Used for a gas-cooled nuclear reactor comprising a core composed of numerous spherical fuel elements. The arrangement enable the flow resistance to the hot gas passing downwards through the ducts in the bottom reflector to be considerably reduced, while still maintaining the small dia. in the upper part of the reflector, which is necessitated by the size of the spherical fuel elements.