On October 12, 1939 President Roosevelt authorized the government funding of atomic research. In February 1940, the Uranium Committee granted Enrico Fermi and Leo Szilard a contract to build a reactor at Columbia University. The experiment began at 9:45 A.M. on December 2, 1942. Fermi ordered the ZIP and all control rods, except one removed from the pile. George Weil operated the remaining rod by hand. Fermi ordered the removing of the final control rod a foot at a time. At 3 P.M., Fermi asked Weil to remove the control rod the final distance to engage the complete reaction. At 3:42 P.M. Fermi concluded that full critically had been achieved and ordered the ZIP in. On April 25th, 1986 the World's worst nuclear power accident occurred at Chernobyl in
At four in the morning on March 28, 1979, a malfunction in the cooling system at the Three Mile Island Nuclear Generating Station led to the most serious commercial nuclear accident in US history and paved the way for reforms in the way nuclear power plants are operated and regulated. It also made Americans question the safety of nuclear power, during routine maintenance, an automatically operated valve in the Unit 2 reactor closed when it should not have most likely due to either a mechanical or electrical failure. This shut off the water supply to the system that cools down the reactor core and prevented the steam generators from removing heat. Automated systems then shut down the reactor core. That should have been the end of the accident, but it was not.
Chernobyl Accident
Design Fault In The Reactor - The reactor used at Chernobyl suffers from instability at low power and may experience a rapid , uncontrollable power increase. Other reactor types have this problem they incorporate design features to stop instability from occurring. The cause of this instability is:
Water is a better coolant than steam
The water acts as a moderator and neutron absorber (slowing down the reaction) while steam does not.
Excess steam pockets in the RBMK design lead to increased power generation this is known as a positive void coefficient. This excess power causes additional heating thus producing more steam and means less neutron absorption causing the problem to escalate. This all happens very rapidly and if it is not stopped quickly it is very hard to stop as it supplies itself.
Violation Of Procedures - While running a test of the reactor numerous safety procedure were violated by the station technicians.
Only 6 - 8 control rods were used during the test despite there been a standard operating order stating that a minimum of 30 rods were required to retain control.
The reactor's emergency cooling system was disabled.
Communications Breakdown - The test was carried out without a proper exchange of information between the team in charge of the test and personnel responsible for the operation of the nuclear reactor.
Three Mile Island
