United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

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 §R/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


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).

Page Last Reviewed/Updated Thursday, March 29, 2012