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Experiments in AHWR Critical Facility

An Advanced Heavy Water Reactor (AHWR) is designed in BARC to demonstrate commercial utilisation of thorium. Critical facility is a specially designed research reactor to experimentally verify the basic physics design parameters of AHWR and other advanced fuel cycle.

Experiments performed

  • Critical Facility went critical on 7th April, 2008. The observed critical height for the reference core configuration was 226.7 cm which agreed well with the estimated value of 226.5 cm.
  • Measurement of critical height for various cores
  • Calibration of reactivity devices
  • Level coefficient measurement
  • Neutron Spectrum measurement on central cluster
  • Cadmium ratio measurement at infinite dilution
  • Integral experiments with ThO2 -U mixed pin cluster and ThO2-PuO2 cluster
  • Fine structure flux measurement inside the central lattice of Nat. Uranium and thorium clusters.
  • Measurement of Moderator and Coolant Void Coefficient of reactivity
  • Measurement of Westcott Neutron Spectrum parameters in reference core of AHWR Critical Facility

Critical Facility for AHWR and 500 MWe PHWRs

  • India has large Thorium reserves.
  • The  long term Energy Needs of India require utilisation of the Thorium reserves.
  • Advanced Heavy Water Reactor (AHWR) using Thorium  is being developed at BARC
  • Critical facility is designed specifically for  validating the reactor physics design and nuclear data for AHWR

Salient Features

Nominal Reactor Fission Power

100 watts 
(Max Power 400 watts)

Thermal Neutron Flux
108 - 10 9n/cm2/sec (Average)
330 cm dia, 500 cm height
Variable Lattice pitch
Minimum 215 mm
Heavy water/ Light water
Shutdown system
a) 6 Cadmium shut off rods,
b) Moderator Dump

The Advanced Heavy Water Reactor (AHWR) Critical Facility is a specially designed research reactor to experimentally verify the basic physics design parameters of AHWR and other advanced fuel cycles. This facility became critical on 7th April, 2008 and will be of immense utility in demonstrating the commercial feasibility of thorium utilization.

Critical facility is a low power research reactor with a nominal power of 100 W.  The reactor tank of aluminium houses fuel assemblies and moderator heavy water.  A square box above the reactor tank houses the lattice girders from which the fuel assemblies are suspended. The lattice girders can be moved to vary the pitch. These lattice girders also support the reactor shutdown devices. The top of the square box is closed by a revolving floor, which also permits access to any of the lattice location for handling operations.

Reactor Core

Types of Cores in Critical Facility 

Reference Lattice Core (RLC)

  • 19 rod cluster of Natural Uranium
  • 61 lattice locations (6 for SORs)
  • 245 mm pitch


  • 54 pin AHWR (Th-Pu Oxide, Th-U233 Oxide) Clusters in 9 positions of RLC
  • 245 mm pitch

PHWR 540 MWe

  • 37 rod  standard fuel bundles per channel
  • 69 lattice locations (6 for SORs)
  • 286 mm pitch


Fuel Assembly