This Day in History – August 4

4 August 1956

 India’s first nuclear research reactor APSARA was commissioned.

What happened?

Bhabha Atomic Research Centre (BARC) commissioned APSARA, the first nuclear research reactor in India and also Asia.


  • On 4th August 1956, the nuclear reactor APSARA attained criticality at 3:45 PM. Criticality refers to the state of a nuclear reactor when the nuclear fission reaction becomes self-sustaining. This means that each fission reaction releases enough neutrons to sustain the chain reaction. This is an important milestone in the commissioning of a reactor.
  • APSARA was the first nuclear research reactor in India and also Asia.
  • Its design was conceptualized by Dr Homi Bhabha (the Father of Indian nuclear programme) in 1955.
  • The reactor was named APSARA and dedicated to the nation in 1957 by the then Prime Minister of India, Pandit Jawaharlal Nehru.
  • The reactor was built with assistance from the United Kingdom who provided the initial fuel.
  • APSARA was a pool-type reactor and uses 80% enriched uranium fuel.
  • With the commissioning of this reactor, India started producing radioisotopes. The knowledge and experience gained thereof has helped in the current infrastructure for producing and applying radioisotopes. Radioisotopes have found many applications in the field of medical diagnosis and therapy, sterilization of medical products, pipeline inspection, food preservation and so on.
  • Radioisotopes have also found use in agriculture. Scientists have been able to study growth simulation, storage effects post irradiation, role of induced radioactivity, the combined effects of neutron irradiation and chemical mutagens. This has significantly helped in developing disease-resistant and high-yielding crop varieties.
  • Experiments with APSARA on neutron induced fission, reactivity measurements, diffusion kinetics of fission product gases, neutron radiography, two phase flow visualization, radiation shielding and neutron detector development have led to major design inputs for the current generation of Prototype Fast Breeder Reactor, Pressurized Heavy Water Reactors and Advanced Heavy Water Reactor.
  • APSARA has also been instrumental in studies in basic sciences such as neutron scattering, neutron activation analysis and neutron and gamma-ray emission studies. This has aided in characterization of materials and in forensic investigations.
  • APSARA is located at BARC, Mumbai. It was permanently shut down in 2010.

APSARA nuclear reactor details:

  • Reactor type: Swimming pool type/ Thermal Reactor
  • Date of criticality: August 4, 1956
  • Reactor power: 1 MW
  • Fuel material: Enriched uranium – aluminium alloy
  • Fuel element: Plates
  • Fuel cladding: Aluminium alloy
  • Total weight of fuel: 4.5 kg
  • Core size: 560 mm X 560 mm X 615 mm(H)
  • Moderator: light water
  • Max Neutron Flux: 1013n/cm2/sec
  • Coolant: light water
  • Shut off rods: cadmium

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