Month: April 2009

The IRIS Reactor Technical Data and Specifications

Information presented in this article is based on publicly available data of the IRIS reactor project, as properly cited from the original sources. This article is NOT part of the official IRIS project led by Westinghouse. For more reliable information, the reader should refer to any official websites and information sources of the IRIS project and/or the IRIS consortium. All trademarks and registered trademarks shown in this article are the property of their respective owners.

General Plant Data
Core thermal power 1000 MWt [ref.2-page35]
Power Plant Net Output 335 MWe [ref.2-page35]
Nuclear Steam Supply System
Number of coolant loops Integral RCS [ref.2-page35]
Steam temperature/pressure 317/5.8 °C/MPa [ref.2-page35]
Feedwater temperature/pressure 224/6.4 °C/MPa [ref.2-page35]
Reactor Coolant System
Total core flow rate 36000 kg/s [ref.3-page53]
Primary coolant flow rate 4700 kg/s [ref.2-page35]
Reactor operating pressure 15.5 MPa [ref.2-page35]
Core inlet temperature 292 °C [ref.2-page35]
Core (riser) outlet temperature 330 °C [ref.2-page35]
Reactor Core
Fuel assembly total length 5.207 m [ref.2-page35]
Fuel inventory 48.5 tU [ref.2-page35]
Average linear heat rate 10.0 kW/m [ref.2-page35]
Average core power density (volumetric) 51.26 kW/l [ref.2-page35]
Specific power
(= core thermal power/fuel inventory)
20.6186 kW/kg-HM
Fuel material Sintered UO2 [ref.2-page35]
Westinghouse standard PWR fuel
Fuel average density 96% Theoretical Density [ref.3-page203]
UO2-TD = 10.96 g/cc
Rod array Square
17×17 XL [ref.2-page38,ref.5-page155]
Number of fuel assemblies 89 [ref.2-page35]
Number of fuel rods/assembly 264 [ref.2-page35]
Fuel pellet diameter 8.19 mm [ref.1-page634]
Pellet-clad gap 0.082 mm [ref.1-page634]
Clad thickness 0.572 mm [ref.1-page634]
Outer diameter of fuel rods 9.5 mm [ref.2-page35,ref.5-page155]
Pitch (center-to-center) 12.54 mm [ref.1-page634]
P/D 1.32 [ref.3-page34]
Average H/HM ratio
(Hydrogen to Heavy Metal ratio)
3.4 [ref.3-page34]
Volume fractions 33.50% fuel
54.92% moderator
11.58% structure
Volume ratios fuel-to-moderator: 0.6099
moderator-to-fuel: 1.6396
Enrichment 4.95 Wt % U-235 [ref.2-page35]
Coolant average density 0.7295 g/cc [ref.6-page31]
0.727664 g/cc (calculated from enrichment and H/HM data)
Equilibrium cycle length 30-48 months [ref.2-page35]
Average discharge burnup 60 000 MWd/tU [ref.2-page35]
Reactor Pressure Vessel
Cylindrical shell inner diameter 6.21 m [ref.2-page35]
Wall thickness of cylindrical shell 28.5 cm [ref.2-page35]
Total height (including clossure head) 22.2 m [ref.5-page154]
Active core height (core barrel) 426.7 cm [ref.5-page156]
Active core inner diameter (core barrel) 241.27 cm [ref7-page45]
calculated from core thermal power, power density, and active core height
Active core outer diameter (core barrel) 285 cm [ref.5-page157]
Steam Generators
Type Vertical, helical coil tube bundle, once-through, superheated [ref.2-page35]
Number 8 [ref.2-page35]
Thermal capacity (each SG) 125 MWt [ref.2-page35]
Number of heat exchanger tubes (each SG) 656 [ref.2-page35]
Reactor Coolant Pump
Type Spool type, fully immersed [ref.2-page35]
Number 8 [ref.2-page35]
Pump head 19.8 m [ref.2-page35]
Primary Containment
Type Pressure suppression, steel [ref.2-page35]
Geometry Spherical, 25 m diameter [ref.2-page35]
Design pressure/temperature 1300/200 kPa/°C [ref.2-page35]


  1. Duderstadt, James J. and Louis J. Hamilton. (1976), Nuclear Reactor Analysis, John Wiley & Sons, Inc, New York.
  2. IRIS@NuclearNews
  3. MIT Master Thesis – Thermal Hydraulic Performance Analysis of a Small Integral PWR Core
  4. J-NucEngDes – Carelli – The exciting journey of designing an advanced reactor
  5. J-NucEngDes – Carelli et al. – The design and safety features of the IRIS reactor
  6. Data from US NRC
  7. Reactor dosimetry in the 21st century

Useful links

Related post:

Standard PWR nuclear fuel assembly (17×17) technical specification


PWR 17x17 FA

Geometry Square 17×17 matrix
Fuel assembly dimension Square 214 x 214 mm
Composition per assembly Total: 289Fuel: 264

Control rod guide thimble: 24

Instrumentation thimble: 1

Fuel material UO2 (U235,U238,Oxygen)
Cladding material Zircaloy-4
98.23 weight % zirconium with 1.45% tin, 0.21% iron, 0.1% chromium, and
0.01% hafnium
Gap filler Helium gas
Fuel average density 95 – 96% Theoretical Density
UO2-TD = 10.96 g/cc
Moderator (coolant) light water (H2O)
average density 0.7295 gr/cc
H/HM ratio
(hydrogen to heavy metal ratio)
1.7 – 3.4 (depends on enrichment level)
Enrichment 2.5 – 5 Wt % U235
Fuel pellet diameter 8.19 mm
Pellet-clad gap 0.082 mm
Clad thickness 0.572 mm
Outer diameter of fuel rods 9.5 mm
Pitch (center-to-center) 12.54 mm
P/D 1.32

Related Links

Citing Articles

A simple 2D Computational Fluid Dynamics (CFD) code

Here is an example of 2D Computational Fluid Dynamics (CFD) code, the governing equations are the non-compressible Navier-Stokes equations. The code was written in C language, created by Professor Takayuki Aoki from TokyoTech GSIC.

  • download the code here, extract, compile and run it on UNIX/LINUX platform, make sure that gcc and ImageMagick are correctly installed on your system
  • learn more about CFD from TokyoTech OCW here
  • See some results on YouTube here

You might also like this article: Free Time CFD Coding