Nuclear Energy - December 1998

Monthly Energy Review, March, 1999

In December 1998, U.S. nuclear generating units produced a total of 62 net terawatthours (billion kilowatthours) of electricity, 13 percent higher than in December 1997. Nuclear units generated at an average capacity factor of 86.5 percent, 11.7 percentage points higher than in December 1997. Nuclear power supplied 23.4 percent of the total electric utility-generated electricity in December 1998 compared with 20.7 in December 1997.

On December 31, 1998, there were 104 operable nuclear generating units in the United States, with a collective net summer capability of 96.6 million kilowatts of electricity.

Of the 104 operable units, 8 units generated no electricity during the month because of maintenance, refueling, or repair outage. By comparison, a total of 75 units were reported operating at 90 percent of capacity or more in December. Of these 75 units, a total of 37 operated at 100 percent or greater (based on net summer capability).

In addition, there were 3 other units with construction permits, although construction for all 3 units has been halted. The design capacity of the 3 units with construction permits was 3.6 million kilowatts.

Nuclear Energy Notes

1. In 1998 EIA undertook a major revision of the data categories in Table 8.2 to make them more relevant to current conditions and trends in the U.S. commercial nuclear electric power industry. To acquire the data for the revised categories it was necessary to develop a reactor unit database employing different sources than those used previously for Table 8.2 and still used for Table 8.1. Because of differences in definitions and tally protocols, the year-by-year tallies of operable reactors in the two databases diverge in some years, although this divergence does not change the overall trends.

The data in Table 8.2 apply to commercial nuclear power units, which means that the units contributed power to the commercial electricity grid whether or not they were owned by an electric utility. A total of 259 units ever ordered was identified. (Many of the orders were placed before 1973 and thus do not appear in the table. Annual data on orders and other characteristics from 1953 forward can be found in EIA's Annual Energy Review 1997, Tables 9.1 and 9.2.) Although most orders were placed by electric utilities, several units are or were ordered, owned, and operated wholly or in part by the Federal government, including BONUS (Boiling Nuclear Superheater Power Station), Elk River, Experimental Breeder Reactor 2, Hallam, Hanford N, Piqua, and Shippingport.

A reactor is generally defined as operable in Table 8.2 while it possessed a full-power license from the Nuclear Regulatory Commission or its predecessor the Atomic Energy Commission, or equivalent permission to operate, at the end of the year or month shown. The definition is liberal in that it does not exclude units retaining full-power licenses during long, non-routine shutdowns that for a time rendered them unable to generate electricity. For example:

   * In 1985 the five then-active Tennessee Valley Authority units (Browns
   Ferry 1, 2, and 3 and Sequoyah 1 and 2) were shut down under a regulatory
   forced outage. Browns Ferry 1 remains shut down and has been defueled,
   while the other units were idle for several years, restarting in 1991,
   1995, 1988, and 1988, respectively. All five units are counted as operable
   during the shutdowns.

   * Shippingport was shut down from 1974 through 1976 for conversion to a
   light-water breeder reactor, but is counted as operable from 1957 until its
   retirement in 1982.

   * Calvert Cliffs 2 was shut down in 1989 and 1990 for replacement of
   pressurizer heater sleeves but is counted as operable during those years.

Exceptions to the definition are Shoreham and Three Mile Island 2. Shoreham was granted a full-power license in April 1989, but was shut down two months later and never restarted. In 1991, the license was changed to Possession Only. Although not operable at the end of the year, Shoreham is treated as operable during 1989 and shut down in 1990, because counting it as operable and shut down in the same year would introduce a statistical discrepancy in the tallies. A major accident closed Three Mile Island 2 in 1979, and although the unit retained its full-power license for several years, it is considered permanently shut down since that year.

2. Capacity: Nuclear generating units may have more than one type of net capacity rating, including the following:

(a) Net Summer Capability--The steady hourly output that generating equipment is expected to supply to system load, exclusive of auxiliary power, as demonstrated by test at the time of summer peak demand. Auxiliary power of a typical nuclear power plant is about 5 percent of gross generation.

(b) Net Design Capacity or Net Design Electrical Rating (DER)--The nominal net electrical output of a unit, specified by the utility and used for plant design. The monthly capacity factors are computed as the actual monthly generation divided by the maximum possible generation for that month. The maximum possible generation is the number of hours in the month multiplied by the net summer capability at the end of the month. That fraction is then multiplied by 100 to obtain a percentage. Annual capacity factors are averages of the monthly values for that year.