A system comprising a reactor containment vessel and a treatment facility; the system being characterized by a non-sliding butterfly valve for a high radiation environment including a valve box having a flow passage, a plate-shaped valve body that opens and closes the flow passage, and a rotatable valve shaft that engages with the valve body to pivot the valve body, the butterfly valve comprising: a valve body-side valve seat section provided in an outer peripheral portion of the valve body; a valve box-side valve seat section provided in the valve box; and a valve movement mechanism that moves the valve body in an extending direction of the flow passage along with rotation of the valve shaft between a blocking position at which the valve body-side valve seat section and the valve box-side valve seat section are in contact with each other to close the flow passage and an open position at which the valve body-side valve seat section and the valve box-side valve seat section are separated from each other to open the flow passage, wherein the valve body side valve seat section and the valve box-side valve seat section are not in contact with each other when the valve body pivots from the open position and when the valve body pivots to the open position; wherein the valve body-side valve seat section is provided in an annular shape in such a manner that an outer diameter of the valve body-side valve seat section increases from one end portion toward the other end portion in a direction that extends from the valve body to the valve movement mechanism opposite to a flow direction of a fluid, and the valve body-side valve seat section is formed of a laminated material composed of alternatingly stacked a plurality of plates made of stainless steel and a plurality of plates made of expanded graphite, wherein the system comprises a pipe, a driving unit, a decelerator disposed in the driving unit, a motor and a remote manual operation unit, wherein the butterfly valve is arranged in the pipe connecting the reactor containment vessel adapted to be disposed inside a reactor building and the treatment facility adapted to be disposed outside the reactor building and being configured to adjust pressure inside the reactor containment vessel, and wherein the valve shaft that drives the valve body while engaging with the valve body is connected to the decelerator in the driving unit and the valve shaft is configured to be rotated by the operating force given from the motor to the decelerator in the driving unit and the operating force input to the remote manual operation unit adapted to be disposed outside the reactor building and transmitted to the decelerator in the driving unit. a valve body-side valve seat section provided in an outer peripheral portion of the valve body; a valve box-side valve seat section provided in the valve box; and a valve movement mechanism that moves the valve body in an extending direction of the flow passage along with rotation of the valve shaft between a blocking position at which the valve body-side valve seat section and the valve box-side valve seat section are in contact with each other to close the flow passage and an open position at which the valve body-side valve seat section and the valve box-side valve seat section are separated from each other to open the flow passage, wherein the valve body side valve seat section and the valve box-side valve seat section are not in contact with each other when the valve body pivots from the open position and when the valve body pivots to the open position; wherein the valve body-side valve seat section is provided in an annular shape in such a manner that an outer diameter of the valve body-side valve seat section increases from one end portion toward the other end portion in a direction that extends from the valve body to the valve movement mechanism opposite to a flow direction of a fluid, and the valve body-side valve seat section is formed of a laminated material composed of alternatingly stacked a plurality of plates made of stainless steel and a plurality of plates made of expanded graphite, wherein the system comprises a pipe, a driving unit, a decelerator disposed in the driving unit, a motor and a remote manual operation unit, wherein the butterfly valve is arranged in the pipe connecting the reactor containment vessel adapted to be disposed inside a reactor building and the treatment facility adapted to be disposed outside the reactor building and being configured to adjust pressure inside the reactor containment vessel, and wherein the valve shaft that drives the valve body while engaging with the valve body is connected to the decelerator in the driving unit and the valve shaft is configured to be rotated by the operating force given from the motor to the decelerator in the driving unit and the operating force input to the remote manual operation unit adapted to be disposed outside the reactor building and transmitted to the decelerator in the driving unit.