This significant increase in the generating costs of oil-fired plants is presently being reflected in electric bills via the "fuel adjustment allowances". Any increased use of oil-fired plants can only make the costs of electricity even higher. Clearly, nuclear power is the most economic bulk electricity supplier primarily due to its relative insensitivity to fuel costs.

The issue of nuclear plant reliability has become important as a concerned public attempts to form an opinion regarding the use of nuclear reactors for electric generating stations. The call for a nuclear moratorium is usually preceded by the claim that nuclear power is not only unsafe and unnecessary, but that it is unreliable as well. Referen Reference is often made to a May 1973 article in 19 the Wall Street Journal that stated that "the most dependable feature of nuclear power plants is their unreliability".

Clearly, some nuclear power plants have not operated as reliably as their owners would have liked. There have been problems. The record is clear that the reliability of nuclear power plants has been lower than anticipated over the first one to three years of commercial operation. However, the record is also clear on at least two other counts. First, nuclear plants have been generally as reliable as fossil plants of approximately the same size. Second, the reliability of nuclear generating stations usually increases substantially after the station has been operating for a few years. The facts regarding nuclear plant operation do not support the contention that reactors are unreliable devices.

The following points need to be understood:

1. One of the best guides to generating plant reliability

Nuclear and fossil plant operating statistics used in calculating the availability numbers in this section were collected from the Edison Electric Institute and the Nuclear Assurance Corporation plant data files.

2.

in current use is a number called plant availability.
Plant availability indicates the portion of time during
a given period that the plant is available for use.
Availability factors are thus one measure of the plant's
ability to provide electrical energy. If a plant must
be taken off the line because of the failure of one of its
components, its availability is adversely affected.

In general, there is a greater disparity in plant avail-
ability between large and small fossil stations than be-
tween fossil and nuclear stations of approximately the
same size. During the years from 1960 to 1972, total
plant availability of fossil units between 60 and 90
megawatts in size averaged about 92 percent, whereas
fossil units 600 megawatts or more averaged about 73 per-
cent. Of the 29 nuclear plants operating at the end of
1972, half were larger than 600 megawatts and currently
ordered nuclear plants are typically twice that size.
In general, nuclear plant availability has been in the
range of 68 to 70 percent. Reactor availability (the
availability of just the reactor rather than the entire
plant) from 1960 to 1972 averaged about 76 percent.

Additionally, examples can be found where nuclear plants are more reliable than fossil plants of comparable size. Commonwealth Edison in Chicago, which runs 25 percent of the nuclear capacity in the country, found that during the 12-month period ending November 30, 1973, their

VII. Power Plant Reliability*

The issue of nuclear plant reliability has become important as a concerned public attempts to form an opinion regarding the use of nuclear reactors for electric generating stations. The call for a nuclear moratorium is usually preceded by the claim that nuclear power is not only unsafe and unnecessary, but that it is unreliable as well. Reference is often made to a May 1973 article in 19

the Wall Street Journal that stated that "the most dependable feature of nuclear power plants is their unreliability".

Clearly, some nuclear power plants have not operated as reliably as their owners would have liked. There have been problems. The record is clear that the reliability of nuclear power plants has been lower than anticipated over the first one to three years of commercial operation. However, the record is also clear on at least two other counts. First, nuclear plants have been generally as reliable as fossil plants of approximately the same size. Second, the reliability of nuclear generating stations usually increases substantially after the station has been operating for a few years. The facts regarding nuclear plant operation do not support the contention that reactors are unreliable devices.

The following points need to be understood:

1. One of the best guides to generating plant reliability

Nuclear and fossil plant operating statistics used in calculating the availability numbers in this section were collected from the Edison Electric Institute and the Nuclear Assurance Corporation plant data files.