Nuclear reactor boiler with two safety valves - each with isolator, one isolator always being open

摘要

A nuclear reactor possesses a secondary containment in which a steam generating unit is housed; a steam line leading from this unit comprises a safety valve and in total there are two safety valves connected to the steam generating unit. Upstream of each safety valve there is a cut-off valve, these two cut-off valves being so interlocked in their drives that when one of them is closed the other is open, so that one safety valve is always operational. Should the safety valve in the steam line open, for example as a result of a failure of the turbine, then that branch can be safely cut out of the system by closing the associated cut-off valve upstream of it. When this is done, the automatic interlock between the two cut-off valves ensures that the other is still open and that therefore the second safety valve is still operational.