Although most nuclear power plants were designed as baseload power plants, today, the utilities have had to implement or improve the maneuverability capabilities of their NPPs to be able to adapt the electricity supply to daily, seasonal, or other variations in power demand.
Nuclear power plants may take many hours, if not days, to startup or change their power output. Modern power plants can operate as load-following power plants and alter their output to meet varying demands. But baseload operation is the most economical and technically simple mode of operation. It is primarily because they require a long period to heat up the nuclear steam supply system and the turbine-generator to operating temperature. From this point of view, power plant generally is divided into two basic categories:
- Base Load Power Plant
- Load Following Power Plant
Base Load Power Plant
In general, nuclear power plants (NPPs) have been considered as baseload sources of electricity as they rely on technology with low variable costs and high fixed costs. This is the most economical and technically simple mode of operation. In this mode, power changes are limited to frequency regulation for grid stability purposes and shutdowns for safety purposes. Different plants and technologies may have differing capacities to power changes on demand. Baseload power plants are generally run at close to maximum output (100% of rated power) continuously (apart from maintenance refueling outages). During refueling, every 12 to 18 months, some of the fuel – usually one-third or one-quarter of the core – is replaced by fresh fuel assemblies. After refueling, the reactor is usually started up and operated again at nominal power.
Although most nuclear power plants were designed as baseload power plants, today, the utilities have had to implement or improve the maneuverability capabilities of their NPPs to be able to adapt the electricity supply to daily, seasonal, or other variations in power demand. The share of nuclear power in the national electricity mix of some countries has become large due to the significant increase in renewable energy sources.