a sequence of physical events - Three Mile Island

oxygen in the presence of radiation. What was apparentlyignored by, or unknown to, some analystsis that when excess hydrogen is present, the reversereaction (recombination) takes place at amuch faster rate. Oxygen would thus be used upfaster than it was formed, and no oxygen (otherthan minute traces) could ever appear in the bubble.][By midnight on April 3, the decay power wasdown to about 5 MW. This is a power density(spread over the entire reactor core in its originalundamaged dimensions) of 2.9 watts per cubic inch.For comparison, a 60-watt light bulb producesabout 6 watts per cubic inch.]April 4,1979 to April 7,1979Degassing continued throughout April 4 and 5.The pressurizer was being periodically vented intothe reactor building.At 1:25 p.m. on April 6, reactor coolant pumpRC-P1A tripped. Pump RC-P2A was successfullystarted about 2 minutes later.At 8:00 p.m. on April 7, the RCS pressure wasslowly lowered to 400 psig.Stable conditions were established at 2:03 p.m.on April 27, 1979, when RC-P2A was stopped andnatural circulation was established in both steamgenerators. (Steam generator B was later isolated,and adequate natural circulation was continued withsteam generator A alone.) At that time, there wereminor transients on some core thermocouples,which subsequently settled down.The achievement of natural circulation ended thereal emergency phase of the accident, but otherproblems have remained. The reactor building washeavily contaminated with about 5 million gallons ofradioactive water, and the resulting waste disposalproblem has not yet been solved. (There were evena few areas in the auxiliary building showing higherthan normal radioactivity.) Perhaps most important,however, long term cooling of the badly damagedcore will be necessary.339