Question 428: 10 CFR 20.2102 (a) requires the use of the
units curie, rad, rem, including multiples and
subdivisions, on records required by Part 20. May a
licensee continue to use roentgen-based units (e.g., R, mR,
R/h, mR/h) in exposure control, radiation survey, and
instrument and dosimeter calibration records without
conversion to rad or rem, provided that assessed doses for
individuals are recorded in units of rad or rem?
Background: The purpose in asking this question is to
establish whether or not the units of measurement specified
in 10 CFR 20.2101 (a) -- curie, rad, rem, and multiples and
subdivisions -- must appear in all records required by Part
20 or only in those records that specifically deal with
activity, absorbed dose, or dose equivalent. The intent is
to be scientifically correct in recording exposure rate
measurements made with radiation survey instruments and
estimates of exposure obtained with direct-reading
dosimeters and to avoid unnecessary changes to existing
recordkeeping practices. Nuclear fuel cycle, radiography,
medical, well-logging, and low-level waste licensees
perform hundreds of thousands of radiation surveys each
year with instruments that are calibrated for exposure rate
and that read out in units of µR/h, mR/h, or R/h. Thousands
of workers at nuclear power plants and licensed
radiographers wear direct-reading dosimeters that are
calibrated for exposure and that display mR or R. These
radiation surveys and dosimeters are used to estimate
exposure rates and exposures for the purpose of controlling
individual doses, but they are not normally used to assess
dose equivalent. Therefore, it is not normally necessary
to convert roentgen-based units to rad or rem in records of
surveys and dosimeter readings. Rather than change the
hundreds of forms, survey maps, logs and calibration sheets
that are used at a facility to record exposure control
data, radiation surveys, and calibrations, each licensee
would prefer to continue recording radiation levels and
exposures in roentgen-based units and to explain the
relationship of these units to rem in a single program
document, such as the facility's radiation protection plan.
An example of such an explanation for a nuclear power plant
is "exposures and exposure rates measured and recorded in
roentgen-based units are numerically equal to or greater
than deep-dose equivalent rates in rem-based units for the
x-ray and gamma radiation energies normally present in
locations other than inside or near open reactor plant
components." The use of a single program statement would
permit a licensee to record what was actually measured in
the true units of measurement. This approach to recording
exposures and exposure rates appears to be consistent with
10 CFR 20.2101 (a), which implicitly prohibits the use of
the SI units becquerel, gray, and sievert, but which does
not prohibit the use of roentgen and other appropriate
units when measuring and recording quantities other than
activity, absorbed dose, and dose equivalent. It is also
consistent with the use of roentgen-based units in 10 CFR
Part 34 (§§34.21, 34.24, 34.33) and in 10 CFR Part 39
(§§39.33).
Answer: Yes, except that the "assessed doses for
individuals" must be recorded and reported in terms of dose
equivalent quantities in units of rem for demonstrating
compliance with the limits of Part 20.
As indicated in the background to the question, 10 CFR
20.2101 (a) prescribes the units to be used for the
quantities activity, absorbed dose, and dose equivalent on
records required by Part 20. 10 CFR 20.2101 (a) also
requires that each licensee clearly indicate the units of
all quantities on records required by Part 20. The
roentgen is a unit for the quantity exposure; it is not a
unit for the quantities absorbed dose or dose equivalent.
Thus the use of this quantity and unit are not inconsistent
with the requirements of 10 CFR 20.2101 (a). However, the
quantity exposure and its unit roentgen are commonly used
as surrogates for the quantity absorbed dose and the unit
rad or the quantity dose equivalent and the unit rem. When
this is the case for use of the quantity exposure and its
unit roentgen on records required by Part 20, the
quantitative relationship between exposure (roentgen) and
absorbed dose rad) or dose equivalent (rem) must be clearly
documented and understood by individuals using these
quantities and units in meeting the requirements of Part
20. The documentation of this relationship may be in the
licensee's "radiation protection plan" or other radiation
protection program document (s), including survey
procedures; it is not necessary that this relationship
(e.g., conversion factor) appear on each form, map, or log
used in surveys and calibrations. It may be assumed that
one roentgen equals one rem, or a more accurate conversion
factor may be used. The relationship between exposure
roentgen} and absorbed dose (rad) or dose equivalent (rem)
should also be included in the instruction (training) of
individuals who make the measurements of exposure (in
roentgen units), and records of those measurements, that
are required by Part 20.
Note: The answer to Question 96 (a) has been revised to be
consistent with the answer above. Questions and answers
116 and 117 and answers also discuss dose quantities and
units to be used in records. (References: 10 CFR 20.2101,
10 CFR 20.1003; 10 CFR 34.21, 34.24, 34.33; 10 CFR 39.33).