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The severe accidents management system prevents and mitigates SAs, and maintains containment integrity. It is designed to meet the procedural requirements and criteria of U.S. NRC regulations, including the post Three Mile Island (TMI) requirements for new plants as reflected in 10 CFR 50.34 (f) and SECY-93-087. This system includes a large dry pre-stressed concrete containment, Hydrogen Management System (HMS), large reactor cavity and core debris chamber, Cavity Flooding System (CFS), In-Vessel corium Retention and External Reactor Vessel Cooling System (IVR-ERVCS), Safety Depressurization and Vent System (SDVS), Emergency Containment Spray Backup System (ECSBS), and Severe Accidents Management Procedure (SAMP).

Hydrogen Mitigation System

The Hydrogen Mitigation System (HMS) consists of 26 Passive Auto-catalytic Recombiners (PARs) and 10 glow plug igniters. The capacity of the HMS is designed to accommodate the hydrogen production from a 100% metal-water reaction of fuel cladding and to limit the average hydrogen concentration in containment below 10% in accordance with 10 CFR 50.34 (f) for a degraded core accident.
PAR images
Igniter images

Reactor Cavity Design

The reactor cavity adopts a core debris chamber, which is designed to have a heat transfer area of corium more than 0.02㎡/MWt. The flow path of the reactor cavity is designed to be convoluted to hinder the transfer of core debris to the upper containment chamber. This design prevents Direct Containment Heating (DCH) by core debris.
Reactor Cavity images

Cavity Flooding System

The APR1400 has two strategies for cooling the molten core: Ex-Vessel Cooling (EVC) and In-Vessel Retention (IVR). The Cavity Flooding System (CFS) supplies the coolant for ex-vessel cooling and consists of two trains connected with IRWST and two isolation valves that are installed in each line. When the two isolation valves are opened during SAs, the cavity cooling water is supplied from the IRWST to the reactor cavity by gravity. The CFS cools down core debris in the reactor cavity, scrubs fission product releases, and mitigates Molten Corium Concrete Interaction (MCCI).
Cavity Flooding System and IVR-ERVCS images

In-Vessel Corium Retention through External Reactor Vessel Cooling System

The in-vessel corium retention and external reactor vessel cooling system retains the molten core in the reactor vessel by cooling the external surface of reactor vessel. This system submerges the reactor vessel bottom head before molten core moves to the bottom head. Cooling water is supplied from the IRWST by a Shutdown Cooling Pump (SCP) and a Boric Acid Makeup Pump (BAMP). This system maintains the integrity of the reactor vessel and reduces the threat of containment integrity.

Emergency Containment Spray Backup System

The Emergency Containment Spray Backup System (ECSBS) provides long-term cooling by supplying spray water within the containment for 48 hours so that the containment temperature and pressure are reduced during SAs. This system consists of a spray nozzle, piping and containment penetration. Spray water is supplied by external pump from a temporary external water source. The ECSBS contributes to ensuring the integrity of containment.