14.4. A commercial nuclear power plant station usually consists of one or more generating units connected to the utility’s electrical distribution grid, which is also supplied by other units at various locations. Intercon­nections with grids of neighboring utilities are also provided to meet emer­gency requirements as well as to provide a means to purchase or sell energy. In dispatching load to generating units, the utility’s objective is to provide electricity to its customers by operating individual units in such a manner that generating costs will be minimal.

14.5. As pointed out in §10.99 and §10.106, the capital costs of the entire utility system must be paid on a unit time basis, whether or not an individual generating unit is operating. However, fuel is expended only when a unit is operating and the rate of expenditure for a given power level depends on the efficiency of the generating unit. Therefore, neglecting transmission considerations, it is cost-effective to dispatch the grid electrical load so that the most efficient plants operate as much as possible. The load changes during the course of a day, being lightest during the late night and early morning hours. Also, there are seasonal changes with peak loads occurring during hot weather when many air-conditioning units are oper­ating. Thus, the most fuel-efficient units will be operated as much as pos­sible to meet the constant base load, while less efficient units will be as­signed to operate as needed to meet the variable peak load. As a result of balancing capital and fuel costs, it is common practice to use low-capital — cost but fuel-inefficient gas turbine generators to meet the peak loads of shortest duration, while high-capital-cost but fuel-efficient nuclear units are base-loaded.