Patent Number: 
Section: claims

1. A reactor containment vessel vent system that reduces pressure in a reactor containment vessel by releasing gas in the reactor containment vessel to the atmosphere, the reactor containment vessel vent system, comprising:a vent line that forms a vent gas flow path through which vent gas is discharged from the reactor containment vessel and released to the atmosphere;a noble gas filter provided at a downstream portion of the vent line, the noble gas filter allowing at least steam to pass through and not allowing radioactive noble gases to pass through among the vent gas;a return pipe that directly connects a portion of the vent line that is immediately upstream of the noble gas filter and the reactor containment vessel;an intermediate vessel provided on the return pipe, in which gas containing the radioactive noble gases that cannot permeate the noble gas filter flows and is stored; anda bypass pipe that returns condensed water condensed in the intermediate vessel to the vent line on an upstream side of the noble gas filter. 2. The reactor containment vessel vent system according to claim 1, whereina steam trap is provided on the bypass pipe. 3. The reactor containment vessel vent system according to claim 1, whereina non-condensable gas collection system that collects non-condensable gases is provided on the return pipe at a portion that connects the immediate upstream portion of the noble gas filter and the intermediate vessel. 4. The reactor containment vessel vent system according to claim 3, whereinthe non-condensable gas collection system includesa pipe portion in which the return pipe at the portion that connects the immediate upstream portion of the noble gas filter and the intermediate vessel is substantially vertical, anda cylindrical pipe jacket that surrounds an outer peripheral portion of the pipe portion that is substantially vertical, anda gap through which air or water can flow is provided between the outer peripheral portion of the pipe portion and the pipe jacket.