Melted-core retention structure

The disclosed melted-core retention structure comprises the following inside a reactor vessel (1) that contains a reactor core: a bottom support plate (6), in which vertically-penetrating channel holes are formed, that is provided beneath the core and supports the core; a bottom support plate support (7) that is affixed to the reactor vessel (1) and supports the bottom support plate (6); a thermally-insulating spacer (10); a reticulated heat path (9) that is affixed to the bottom support plate support (7) with the thermally-insulating spacer (10) interposed therebetween and contacts the bottom support plate (6); and a vertical heat path (8) that extends downwards from the reticulated heat path (9). The reticulated heat path (9) and the vertical heat path (8) have higher coefficients of thermal conductivity than the thermally-insulating spacer (10).