La Salle (USA)

Map of La Salle

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2 * 1100 MW BWR units constructed by General Electric; grid connection in 1985 and 1989

Facilities in La Salle

plantreactor typconstruction startoperation startshut down
La Salle-1BWR19731982
La Salle-2BWR19731984


"While shutting down Unit 1 IAW LGP-2-1 with the main turbine off line the plant experienced a turbine control system (EHC) malfunction. This resulted in opening all main turbine bypass valves and subsequent reactor low pressure condition. The low pressure condition resulted in a closure of all main steam isolation valves (MSIV's) and automatic reactor scram. Three rods failed to indicate fully inserted on the scram. Plant emergency operating procedures were entered. All ECCS and plant systems operated as expected. All control rods are fully inserted and the ATWS emergency operating procedure has been exited."

The main turbine had been taken off line prior to this event and shutdown was being conducted with heat removal on the bypass valves. Pressure control is currently by using the steam line drains with the Safety Relief Valves in manual. Level is being maintained using normal feedwater. The electrical grid is stable though the plant is not yet on backfeed. Diesel generators are operable.
(source: NRC)


loss of offsite power -> scram due to a failure of auxiliary transformer; emerg. power supply operated properly


Following a reactor trip, the FW pump turbines could not be tripped automatically or manually. The MSIVs were manually closed by operators to secure the pumps.


Main turbine trip caused by URturbine thrust bearing wear detector. The signal was a false alarm but it led to a scram following the turbine trip. the FW pumps responded as they should, pouring water into the reactor. but operators could not shut the pumps down from control room, 1 of the pumps was shut manually, but operators had trouble to shut the 2. manually from pump area, too; Instrumentation & alarm systems for the safety and relief valves also malfunctioned: valves worked controlling pressure, and venting steam into the suppression pool, but when the event was over the instruments showed the valves were still open when, in fact, they were closed.


loose connection discovered on the HPCS systems´ battery


RCIC failure during test: pressure differential switch failed because of a torn diaphragm


RCIC system failure: during test: steam line high flow isolation switch failed, because of a torn diaphragm -> switch would not have isolated the outboard containment isolation valve during a steam line break


Fault on unit 2 auxiliary transformer ( exploded due to inernal fault) resulted in unit 1 reactor trip with subsequent equipment failures (due to spurious signals caused by undervoltage): instrument air, process computer, CREV; AIT to site


Fault on auxiliary transformer (failed lightning arrestor), caused trip of unit 1.


Unstable core power oscillations resulted from an ATWS trip of both recirculation pumps (cold water inflow scram at 118% power).