Go contents Go main menu Go left menu

The APR1400's Nuclear Steam Supply System (NSSS) improves the reactor's safety and reliability by increasing the thermal margin and system capacity, and using more reliable components and materials on top of the advances in the safeguard system. In addition, a simplified reactor vessel head assembly has been implemented to enhance plant maintainability.

Major Design Features of the APR1400 NSSS

Nuclear Steam Supply System example images
  • 1 Reactor, 2 Steam Generator, 4 Reactor Coolant Pump, 1 Pressurizer
  • Reactor
    • Thermal Power: 4,000MWth
    • Hot Leg Temperature : 615°F
    • Thermal Margin: >10%
  • Steam Generator
    • Tube Material: Alloy 690
    • Plugging Margin: 10%
  • Pressurizer
    • Total Volume: 68m2
    • Pilot Operated Safety Relief Valves (POSRVs) for safe depressurization

Reactor Vessel

  • Vertical cylindrical shell & Hemispherical lower head, Hemispherical upper head
  • Forged surface & stainless steel lining
  • 4 inlet nozzles, 2 outlet nozzles & 4 Direct Vessel Injection (DVI) Nozzles
  • No weld seam in the core region shell
  • Reactor vessel internal structure consists of the core support barrel and upper guide structure
  • Integrated upper structure enables shortened refueling period, reduced occupational radiation exposure & simplified working procedures
Reactor Vessel example images

Steam Generator

  • 10% tube plugging margin
  • Reduced operating pressure/temperature & increased steam flow rate
  • Increase in heat transfer area to accommodate upgraded power and reduced Reactor Coolant System (RCS) temperature
  • Major design improvements
  • Modified primary outlet nozzle angle (45° → 40°) to improve mid-loop operation
  • Automatic control of steam generator water level for all operating ranges
  • Design improvement to prevent flow induced vibration
  • Alloy 690 TT tubes with improved corrosive resistance
  • Able to secure the steam generator dry-out time (20 minutes) against Total Loss Of Feed Water (TLOFW) accidents
Steam Generator example images


Several upgrades have been applied to the APR1400 to allow it to achieve higher performance including an improvement in the operational reliability and maintenance (4 Pressurizer Safety Valves (PSVs) + 2 Safety Depressurization (SDS) valves → 4 Pilot Operated Safety Relief Valves (POSRVs)), an increased pressurizer capacity, and improved capability against Reactor Coolant System (RCS) transients. The POSRV was designed to provide protection from too much pressure as well as safe depressurization, minimizing contamination in containment by discharging fluid in In-containment Refueling Water Storage Tank (IRWST) through the sparger.
Pressurizer example images

Reactor Coolant Pump

  • The four pump assemblies circulate reactor coolant from two steam generators to the reactor vessel and back to the steam generators
  • Centrifugal type
  • Vertical/Single stage impeller
  • Diffuser type
  • Bottom suction
  • Radial discharge nozzle
  • Rated Flowrate = 121,600 gpm, Rated Head = 360 ft
  • Speed : 1,190 RPM
Reactor Coolant Pump example images

Integrated Head Assembly

The Integrated Head Assembly (IHA) contains not only the Reactor Vessel (RV) upper head, Control Element Driving Mechanisms (CEDMs), heat junction thermocouples and head lift rig as in the OPR1000, but also the head area cable tray, missile shield, seismic restraints and the CEDM cooling fan and ducts, which now can be handled altogether as a package. The IHA also reduces the handling steps of the RV head area as well as the refueling time, resulting in lower radiation exposure to maintenance personnel and seismic loads on CEDM and cables.
Integrated Head Assembly  example images