Accident Experience with Light Water Reactors

Accident Experience with Light Water Reactors 

The Rasmussen Report analyzed the Browns Ferry incident in an 

The occurrence which has generated more public concern than any other is the well-known Three Mile Island accident. The reactor involved was the second unit of two located on an island in the Susquehanna River, near Harrisburg, Pennsylvania. The layout of the reactor circuit and ancillary systems is shown in Fig. 12.14. The sequence of events leading to the accident is given below. 

on 28 March 1979, the main feedwater pumps tripped this in itself was not an unexpected or particularly unusual event, and resulted in an automatic shutdown of the turbine it also caused the emergency feedwater pumps to start up, as they were designed to do. Unknown to the plant operators, however, the block valves on both of the emergency feedwater lines had inadvertently been left closed, so that no water was able to reach the steam generators. 

With the reactor shut down and the PORV open, the pressure in the primary circuit fell. The PORV was designed to close automatically when the pressure dropped to 2205 psi, which it did 13 s after the initial feedwater pump trip. Although the control room panel indicated that the valve had closed, it had in fact stuck open, so that the coolant was draining off into the reactor s let down system. This was to continue for almost two and a half hours before the circuit was eventually sealed by the closure of a backup valve. 

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Accident Experience with Light Water Reactors... 

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