LCC Quick Notes, Nuclear SBO (Station Black Out) Mitigation
An Effective Means to Mitigate Fukushima-Type Event SBO
The US Nuclear Regulatory Commission (NRC) through the efforts of the Near-Term Task Force on the Fukushima Event has identified SBO mitigation as a major corrective action to harden operating nuclear power plants against greater than design basis environmental seismic, flooding, and terrorist attack. The NRC further recommends a "Defense in Depth" approach to mitigating such events.
LCC has developed (Patent Pending) a new technology which in itself provides a high level of SBO mitigation at a practical investment cost. The new technology consists of a Variable Speed, Constant Output Permanent Magnet Generator (PMG) which may be coupled to nuclear safety related pump turbine drives and fully power the respective turbine digital controls, electric governor valve operators, and operator control station equipment independent of external power feeds. This design overcomes traditional PMG limitations to single generation speeds and allows full operation power feed from 500 to 5000 RPM of turbine speed.
EXISTING DESIGN VULNERABILITY
Existing original designs and proposed digital upgrade system designs retain SBO vulnerability by requiring station AC electrical power or standby battery bank DC or inverted AC power to remain in control of the safety related steam turbine driven pumps. The SBO condition removes these electrical power sources either coincident with the damaging event or within a period of hours if the battery bank is undamaged. Plant specifications differ, but vital battery capacity ranges from less than eight hours to thirty-two hours at operating plants. Since reactor core cooling requirements extend for weeks, additional mitigating measures are necessary.
Diagram, Original External-Powered Controls
Diagram, PMG-Powered Controls
STANDBY PUMP LIMITATIONS
The placement of diesel powered portable pumps either on site or within short range transport having engineered water sources, suction line designs, discharge line designs, and fueling support represents one defense strategy. However, coincidental damage to the portable equipment by the SBO initiating event cannot be assumed absent in a practical risk assessment. Transport requirements for remote pump storage also depend upon secure storage, routine availability testing, and a functioning infrastructure for delivery. These are far too many assumptions to qualify standby portable pumps as a full corrective action.
Seismic re-qualifications to higher standards are also being examined for standby power feed equipment, conduit and cable runs which may prove costly to implement in operating plants.
LCC PMG POWER SOLUTION
While much has been discussed on the subject of SBO Mitigation, the LCC PMG represents a true corrective action solution.
The PMG self-powered system adds the key mitigation factor for a defense-in-depth corrective action by eliminating the need for any external electrical power feeds to the turbine controls and controlling instruments. The PMG may also be redundant, and controls may auction PMG power with external feeds with a final alignment based upon individual application risk analysis. The LCC PMG solution also has the following advantages:
► Costs are not significantly higher than external powered digital control system upgrades which have been advised as recommended by many groups due to the obsolescence, poor operating record, and lack of spare parts availability of the original turbine control systems.
► The modification package is limited to the SRT front pedestal area and does not involve major plant design changes, thus keeping costs down.
► Packages include higher seismic, temperature, EMI/RFI, and Radiation qualifications than original plant design basis EQ based upon highly successful LCC systems installed on very similar US Navy Nuclear Aircraft Carriers.
► Orders in 2011 result in 2013 year outage installations.
Link to TEG-5-Series Nuclear Turbine Controls
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