Section III - Discussion
III. DISCUSSION
External dosimetry is the science dealing with measurement of a
radiation field incident to the body and the evaluation of the dose
equivalent resulting from energy deposited within the body by the
radiation. External dose is usually a derived or inferred quantity
since it is not possible to directly measure the exact dose to any organ
or tissue. Any measurement must be compared to a known quantity to
derive dose and dose equivalent.
10 CFR 835 contains requirements which affect external dosimetry
programs through-out DOE and DOE-contractor facilities. The salient
features are:
-- External dose equivalent to workers "shall" be computed and recorded
when monitored in accordance with 10 CFR 835.402(a) & 702(a) (also
RCM 722.4);
-- internal doses shall be added to external doses for the purposes of
demonstrating compliance with occupational dose limits and keeping
worker doses "as low as reasonably achievable" (ALARA)(10 CFR
835.703(a)). The quantity, total effective dose equivalent, is the
result of a methodology by which internal doses are added to
external doses on the basis of equal risk; and
-- monitoring in the workplace "shall" be routinely performed, as
necessary, to identify and control potential sources of radiation
exposures (10 CFR 835.401(b)) (also RCM 514.1, 514.3, 551.1 &
552.2).
10 CFR 835 states that the occupational exposure of general employees to
radiation or radioactive material resulting from routine DOE nuclear and
radiation activities "shall" not cause the following annual limits to be
exceeded: (1) A total effective dose equivalent from both internal and
external sources of 5 rems (0.05 Sv); (2) the sum of the dose equivalent
for external exposures and the committed dose equivalent to any organ
other than the lens of the eye of 50 rems (0.5 Sv); (3) a lens of the
eye dose equivalent of 15 rem (0.15 Sv); and (4) a shallow dose
equivalent of 50 rem ((0.5 Sv) to the skin or any extremity (10 CFR
835.202(a) and RCM 213.1 & Table 2-1). Note that Subpart N of 10 CFR
835 contains provisions for accidents and emergencies. These
requirements are not discussed in this IG with the exception that
Section IV.A.5. of this IG does briefly discusses nuclear accident
dosimetry.
Several limits other than those for general employees must be considered
in the design of an external dosimetry program. A limit of 0.5 rem
(0.005 Sv) dose equivalent for the period from conception to birth for
the embryo/fetus of a declared pregnant worker "shall" not be exceeded
and efforts "shall" be made to avoid substantial variation above a uniform
exposure rate that would satisfy the limit (i.e., 50 mrem (0.5 mSv) per
month to the declared pregnant worker)(10 CFR 835.206(a) & (b) and RCM
215 & Table 2-1). An annual limit of 0.1 rem (0.001 Sv) total
effective dose equivalent for minors accessing a DOE site or facility
(10 CFR 835.207 and RCM Table 2-1), members of the public entering a
controlled area (10 CFR 835.208 and RCM Table 2-1), and visitors (RCM
Table 2-1 and RCM 214) "shall" not be exceeded. All occupational exposure
received during the current year "shall" be included when demonstrating
compliance with the annual limits (10 CFR 835.202(b) and RCM 213.1).
Occupational dose evaluation and dose records "shall" not include
exposures from background, therapeutic and diag-nostic medical
radiation, and voluntary participation in medical research programs (10
CFR 835.202(c) and RCM Table 2-1, Note 3).
The RCM introduces additional controls:
-- Administrative control levels which are below dose limits of the
RCM and 10 CFR 835 (RCM 211);
-- the lifetime control level of N rem, where N is the individual's
age in years (RCM 212); and
-- special control levels for individualized exposure control (RCM
216).
The RCM establishes a DOE administrative control level of 2 rems (0.02
Sv) per year per person for all DOE activities and requires the
establishment of a facility administrative control level that is less
than the DOE administrative control level (RCM 211). The administrative
control levels apply to the total effective dose equivalent. The
lifetime control level applies to lifetime occupational radiation dose
which is the sum of all total effective dose equivalent values for each
year since January 1, 1989, plus the sum of external dose equivalent (or
deep dose equivalent) values and internal effective dose equivalent
values recorded prior to January 1, 1989. Special control levels apply
to total effective dose equivalent values and shall be established for
individuals who have a lifetime occupational dose, in rem, that exceeds
their age in years (RCM 216.1). Special control levels should be
considered for persons undergoing radiation therapy.
Radiation protection programs for limiting external exposures are based
on the DOE policy that administrative and engineering controls and
shielding material should be used to the extent reasonably achievable,
so that personnel are not exposed unnecessarily. It is nonetheless
recognized that low-level, chronic occupational exposures to external
ionizing radiation are difficult to avoid at some facilities, due to the
types of material handled or processed necessitating an external
dosimetry program at most DOE and DOE-contractor facilities.
10 CFR 835 was written to implement radiation protection standards that
are consistent with the Presidential approved guidance to Federal
Agencies, promulgated by the Environmental Protection Agency "Radiation
Protection Guidance to Federal Agencies for Occupational Exposure -
Recommendations Approved by the President" (EPA, 1987). It reflects many
of the scientific recommendations of the National Council on Radiation
Protection and Measurements (NCRP) and the International Commission on
Radiological Protection (ICRP). 10 CFR 835 contains primary limits for
exposure of workers to internal and external sources of ionizing
radiation and control of radiological conditions in the work place. The
primary annual limits are expressed in terms of total effective dose
equivalent (TEDE) to the whole body, lens of the eye dose equivalent,
shallow dose equivalent to any extremity or to the skin, and the sum of
the dose equivalent for external exposures and the committed dose
equivalent for internal exposures to any other individual organs or
tissues.
Personnel dosimeter measurements and associated external dose
evaluations are the primary method for demonstrating compliance with the
external component of dose limits for protecting workers. These
measurement systems shall also comply with the requirements of the
"Department of Energy Laboratory Accreditation Program for Personnel
Dosimetry" (DOELAP) (DOE, 1988a). (Extremity dosimeters are currently not
covered by an accreditation program.) In addition to individual dose
evaluations, collective dose, average worker dose, and maximum dose to a
worker should be determined and used to track the perform-ance of the
radiation protection program. Both area radiation monitoring and
personnel dosimeter results "shall" be used by a facility's radiation
protection organization to manage worker exposures to maintain them
below the limits and ALARA (10 CFR 835.1003(b) and RCM 511.1, 514.1 &
551.1).