Two circuit pressurised water reactor with isolating steam valves - has paralleled steam mains to prevent safety valve blowing

摘要

A steam supply system for a pressurised water reactor comprises =1 steam main which leads from each steam generator, inside the containment, to a T-branch outside the containment, each arm of the branch containing a safety valve; there is also an isolating valve downstream of the branch. There are two such steam mains leading from each steam generator out through the containment; outside the containment, each of these steam mains has a T-branch followed by an isolating valve and each branch leads to a safety valve; downstream of the isolating valves all the steam mains are cross-connected. If oen external isolating valve accidentally jams or closes, the safety valves upstream of it do not blow off, possibly contaminating the surrounding atmosphere if the steam is contaminated, but instead the steam flows through the other steam main from the same steam generating unit.