Prairie Island (USA)

Map of Prairie Island

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2 * PWR 520 MW constructed by Westinghouse; operation since 1973/74

Facilities in Prairie Island

plantreactor typconstruction startoperation startshut down
Prairie Island-1PWR19681973
Prairie Island-2PWR19691974

100 workers were slightly contaminated due to a release of radioactive gas. At the time of the incident the reactor had been disconnected from the net because of maintenance works. No gas was lost to the ambient, the workers showed only radiation values of 10 bis 20 Millirem as they have been wearing protective suits.
The gas accidently wasn't directed through the provided filter.


High temperatures, 100 km/h winds, and cooling tower problems are causing headaches for Northern States Power Co.`s Prairie Island Plant.
The two units were, and are, operating, but with only two of four cooling towers in service. A section of one of the forced air cooling towers collapsed in May. An inspection of the other three turned up structural problems at one, and it was taken out of service. Iron rot on the galvanized bolts used in tower construction is a possible cause of the problem.
The harsh weather also knocked out many of the public alert sirens around Prairie Island. The plant lost the use of 39% of the sirens.


Loss of shutdown cooling during reactor vessel drainout; Core exit temperature rose approximately 90 ° in 20 min. Unit was in cold shutdown and workers were lowering the water level in the RPV to prepare for inservice inspection of the SG. Because of inaccurate water level instrumentation readings, the level fell below what was intended, causing loss of suction in the RHR suction line and cavitation of the RHR pump. Workers stopped the pump and starting charging pump to refill the RPV. The RHR was down for 20 minutes, the temperature rose to around 105°C. Because of the low pressure the water would have started boiling off in just 5 more minutes.


Second of two puzzling scrams led to shutdown of the unit; first was Dec.21. both scrams followed indications of negative flux rate in the core, an asymmetrical power geometry caused by the sudden dropping of one or more control rods. both events were compounded by a simultaneous loss of power to both RC pumps and the main condenser circulation pumps, as result of a seperate breaker failure.