Section 4
COMMERCIAL LIGHT WATER
REACTORS

4.1 INTRODUCTION

General trends in occupational radiation
exposures at commercial nuclear power
reactors are best evaluated within the context of
other pertinent information. In this section, some
of the tables and appendices that summarize
dose data also show the type, capacity, amount
of electricity generated, and age of the reactor.
Dose data are then presented as a function of
these data.
4.2 DEFINITION OF TERMS
AND SOURCES OF DATA
4.2.1 Number ofReactors
The number of reactors shown in Tables 4.1,
4.2, and 4.3 is the number of BWRs, PWRs,
and LWRs that were in commercial operation
during the year listed. This is the number of
reactors on which the average number of
individuals with measurable dose and average
collective dose per reactor is based. Excluded
are reactors that had not yet completed a first
full year of commercial operation and those
reactors that have been permanently defueled.
The date that each reactor was declared to be
in commercial operation was taken from Ref. 15.
Three Mile Island (TMI) Unit 2 was included
in the compilation of data for commercially
operating reactors from 1975 through 1988
and has not been included in the data analyses
since 1988. Three Mile Island Unit 1 and TMI
Unit 2 reported data separately beginning in
1986, but since 2001, the dose breakdowns
for TMI Unit 2 have been reported with those
for TMI Unit 1, as there is very little dose from
activities at TMI Unit 2.

There were no changes to the count of
operating reactors in 2010. The number of
operating BWRs remains the same as in 2009
at 35, and the number of operating PWRs
remains the same at 69. The dose information
for these reactors and for others that are no
longer in commercial operation is listed at the
end of Appendix B.
4.2.2 Electric Energy Generated
The electric energy generated in megawatt
years (MW-yr) each year by each reactor is
graphically represented in Appendix D. This
number was obtained by dividing the megawatt
hours of electricity annually produced by each
facility by 8,760, the number of hours in the
year, except for leap years, when the number
is 8,784 hours. The number of megawatt hours
of electricity produced each year was obtained
from Ref. 15.
For the years 1973 to 1996, the electricity
generated is the gross electricity output of the
reactor. For 1997 to 2010, the number reflects
the net electricity produced, which is the gross
electricity minus the amount the plant uses
for operations. This change is the result of a
change in NRC power generation reporting
requirements. The electricity generated (in
MW-yr) that is presented in Tables 4.1, 4.2, and
4.3 is the summation of electricity generated
by the number of reactors included in each
year. These sums are divided by the number
of operating reactors included in each year to
yield the average amount of electric energy
generated per reactor, which is also shown in
Tables 4.1, 4.2, and 4.3.

NUREG-0713

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