Failure in a Turbine of a Power Plant
A catastrophic failure of the low pressure turbine followed by fire and flooding severely damaged the generator. The main turbine automatically tripped due to an erroneous mechanical over speed signal caused by high vibrations. The reactor, which was operating at 93 percent power, received an automatic scram signal triggered by the turbine trip. The high vibration was caused by catastrophic failure of the turbine blades. Ejected blade parts ripped through the turbine casing and severed condenser tubes and other piping. The rupture of piping supplying hydrogen gas to the generator for cooling caused a fire. While a source (EcoWatch, see reference) speaks of a 'large fire" and reports that "The plants fire brigade took 37 minutes to muster, dress and enter the turbine building to fight the fire. Their efforts were hindered by numerous communication problems", another source (ch2bc) mentions only that the hydrogen fire "was put out with a hand held fire extinguisher. "
Event Date
December 25, 1993
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The immediate cause was high vibration and sudden failure of the turbine blades. According the "List of nuclear power accidents by country" provided by Wikipedia, the main turbine experienced this major failure due to improper maintenance. https://en.wikipedia.org/wiki/List_of_nuclear_power_accidents_by_country (accessed November 2020).All other sources available do not report any root cause.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
steam turbine, generator, cooling system
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
According to ch2bc (see references), "The accident happened without any warning. "
Currency
Lessons Learned
Lessons Learned
Regular maintenance and inspection could have helped to prevent such catastrophic turbine failure.
Event Nature
Emergency Action
The reactor scrammed. Safety systems functioned properly. Some sources reported the lack of emergency procedure in case of water flooding.
Release Type
Release Substance
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
US Nuclear Regulation Commission Report of 4 January 1994 https://www.nrc.gov/docs/ML2005/ML20059E689.pdf (accessed November 2020)
NRC report on ENVIRONMENTAL ASSESSMENT AND FINDING OF NO SIGNIFICANT IMPACT, July 29, 1994;
https://www.nrc.gov/docs/ML0207/ML020730333.pdf
(accessed November 2020)
NUREG-0090 Vol. 16, No. 4
Report to Congress on Abnormal Occurrences