Standby Power

It is essential that nuclear plants have standby sources of electrical power to run critical equipment as a backup in case there is a loss of normal power. There are generally two sources of backup power - emergency diesel generators and station batteries. The typical plant has two or three large emergency diesel generators, each capable of supplying sufficient power to place the plant in a safe condition.

Station batteries are a secondary backup, providing DC or AC using inverters, to power essential components. Typical battery strings are either 60-cell 125 volt, or 120-cell 250 volt configurations. The lead-acid battery cells are quite large and heavy and are installed using seismically qualified racks designed specifically for this purpose.

Some sites also have smaller diesel generator sets known as station blackout or SBO diesels. SBO diesels are intended to power lights, fire pumps, and other emergency equipment, but are too small to power large plant loads. In the wake of the 2011 Fukushima Daiichi disaster, it is likely that SBO diesels will become a requirement for all nuclear plants.

NLI offers equipment in all areas of standby power. NLI has provided both emergency generators as well as smaller SBO diesels. In partnership with GNB, we supply station batteries to roughly half the nuclear plants in the US, and several overseas. We also supply safety-related battery chargers in partnership with both Power Conversion Products (PCP) and C&D Technologies. NLI even supplies seismically qualified battery racks.

As a leading supplier of low and medium voltage switchgear and breakers, NLI also can provide the entire electrical infrastructure necessary to distribute emergency power, including inverters to convert DC from batteries into AC.

Should plants be required to install SBO diesels, NLI is prepared to supply them. NLI recently supplied a 175kW diesel generator in a custom enclosure. The enclosure can withstand 180 mph winds and sits atop a 3,500 fuel tank that allows the generator to run at full power for seven days. NLI seismically tested the full-size diesel as part of the qualification process, which also included software V&V on the control systems.

NLI has also qualified and provided diesel fuel pumps as ASME III. NLI worked closely with the US manufacturer of these pumps and provided QA oversight of the manufacturing process. This process involved material controls, NDE, material testing, hydrostatic testing, and other fairly typical tests and inspections imposed by ASME. NLI was also responsible for documentation requirements such as the Code Data Report, Design Report, and Code Reconciliation. NLI also seismically qualified these pumps.