For accident response, the PCCS provides long-term passive cooling capability fo r the containment using natural convection processes. Decay heat is rejected to isolation condenser pool and then to the atmosphere. No active pumps or diesels ate needed for the heat removal, resulting in no operator action requires for a t least three days.
Beyond three days, water makeup and other simple operator action are all that i s needed to continue passive cooling. This feature, together with drywell floodi ng for design-basis and severe-accident events, offers the potential for site ra diological consequences of design-basis and severe-accident events being a very s mall fraction of licensing limits.
For loss-os-coolant accidents(LOCAs), the supression pool absorbs blowdown energ y, the reactor is depressurized with a set off depressurization valves, the grav ity-driven cooling system floods the reactor, and the isolation condenser remove decay heat. Fission pproducts are retained in the supression pool and multiple barriers contain fission produscts inside the plant.
There is no containment flooding for most LOCAs. SBWR response to low-elevation LOCAs and severe accidents provides for lower drywell flooding.
Use of the PCCS, passivegravity-driven core cooling syste, and passive natural-c irculation air system providing habitability control for control room operators, allows elimination of emergency diesel generators, core cooling pumps. Thaat ul timately simplifies plant design and licensing, and reduces plant cost.