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Chernobyl Disaster

Chernobyl Disaster. Saurabh Bhavsar Ameya Borwankar Akshay Chaubal Rohan Chaukulkar. Chernobyl Nuclear Power Plant. There were four reactors Reactor type was RBMK-1000 Capacity of each reactor was 1 GW. What was it ?.

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Chernobyl Disaster

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  1. Chernobyl Disaster Saurabh Bhavsar Ameya Borwankar Akshay Chaubal Rohan Chaukulkar

  2. Chernobyl Nuclear Power Plant • There were four reactors • Reactor type was RBMK-1000 • Capacity of each reactor was 1 GW

  3. What was it ? • Nuclear accident in the Reactor 4 of the Chernobyl Nuclear Power Plant in Ukraine • Worst Nuclear disaster in history in terms of the amount of radioactive material released • 30 people died including 28 from radiation exposure.

  4. Reactor Schematic

  5. Reasons for the failure • Flawed reactor design and Corruption • Inadequately trained personnel • Lack of proper regard for safety

  6. Improper Design • The reactor was designed such that it needed coolant even when not actively operating. • The reactor had a dangerously large positive void coefficient (measurement of how the reactor responds to increased steam formation in the water coolant). Chernobyl's RBMK reactor, however, used solid graphite as a neutron moderator to slow down the neutrons, and neutron-absorbing water to cool the core. Thus neutrons are slowed down even if steam bubbles form in the water. • When the rods are initially inserted into the reactor, the graphite ends displace some coolant. This greatly increases the rate of the fission reaction, since graphite is a more potent neutron moderator. Thus for the first few seconds of control rod activation, reactor power output is increased, rather than reduced as desired. This behavior is counter-intuitive and was not known to the reactor operators. • Co-current flow versus cross flow • Lack of secure containment

  7. Reactor Schematic

  8. Corruption • It was a design requirement that the rotational momentum of the steam turbine, as it spun down, could be used to generate electricity to run the cooling water pumps to bridge the power gap. • The test had not been completed successfully by March 1984 when the unit was brought into commercial operation ahead of schedule and celebrated as a "labour victory". • Under pressure, the director of the Chernobyl station Viktor Bryukhanov signed an acceptance document in order to declare that works planned for that year had been fulfilled. Had he not done so, thousands of workers, engineers and his own superiors would have lost bonuses, awards and other extras. Records were falsified to hide this fact.

  9. Reactor Schematic

  10. Inadequately Trained Operators • The day shift had been instructed in advance about the test and was familiar with procedures. A special team of electrical engineers was present to test the new voltage regulating system. • Delay • The night shift was not prepared to carry out the experiment • But it was still carried out • The operators seem to have been unaware of the xenon poisoning

  11. Reactor Schematic

  12. Lack of proper regard for safety • Switching off emergency cooling system • Use of higher than safe cooling water flow rate • Manual removal of control rods • Disabling of the automatic shut down system • A combustible material had been used in the construction of the roof of the reactor building and the turbine hall • The readings of another dosimeter were dismissed under the assumption that the new dosimeter must have been defective.

  13. Sequence of events • Excessive insertion of control rods • Excessive removal of control rods even more than the operating levels • Commencement of the test at low levels of power generation • Excessive water flow rate used • Experiment started • Rise in temperature

  14. Sequence of events • SCRAM started • Displacement of coolant due to control rods • Excessive temperature • Fracture of fuel rods • Control rods stuck • Reactor thermal output 30 GW (10 times normal)

  15. Sequence of events • Sudden increase in steam pressure • Bursting of cooling water pipes • Reactor Lid blown off • Explosion of either hydrogen or the graphite

  16. Fallout • Workers made to stay trying to pump water into the reactor • Smoke and steam carry the radioactive material • Firefighters not told that reactor had blown up so they too had radiation exposure • Cloud of radioactive material that scattered the material (about 10 tons of it)

  17. Fallout • An authoritative multi-agency study ( including IAEA and WHO) published in 2006 quantified the effects. Overall some 56 people were killed or have subsequently died, including the 9 children from thyroid cancer - which could have been avoided. • Among some 600,000 workers exposed in the first year, the possible increase in cancer deaths "due to this radiation exposure might be up to a few percent. This might eventually represent up to four thousand fatal cancers in addition to the approximately 100,000 fatal cancers to be expected due to all other causes in this population."

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