[Federal Register Volume 68, Number 142 (Thursday, July 24, 2003)]
[Notices]
[Pages 43769-43771]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-18688]
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NUCLEAR REGULATORY COMMISSION
Proposed Generic Communication Method For Estimating Effective
Dose Equivalent From External Radiation Sources Using Two Dosimeters
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of opportunity for public comment.
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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is proposing to
issue a Regulatory Issue Summary (RIS) which approves and provides
guidance on a two dosimeter monitoring method that can be used by
licensees for estimating effective dose equivalent (EDE) from external
radiation exposures. The NRC is seeking comment from interested parties
on the clarity and utility of the guidance contained in the proposed
RIS. In particular, comment is requested on the following questions:
1. Is the two dosimeter method a technically acceptable alternative
to the current practice of estimating EDE from deep dose equivalent
(DDE)?
2. Is the NRC use of a RIS to approve the two dosimeter method
acceptable under the existing regulations?
3. Are algorithms that attempt to provide better estimates of the
effective dose equivalent by using more than one dosimeter of
importance to your industry?
4. Do you believe that this and similar algorithms, many of which
were described in NCRP Publication 122, are sufficiently technically
developed to serve as a basis for dosimetry of record?
5. Is the discussion of the issues provided in the RIS sufficiently
detailed to provide a background for the reasons for approving the EPRI
method generically?
6. Should different or more detailed guidance be provided in an NRC
Regulatory Guide or generic communication?
7. Should the definition of the total effective dose equivalent
(TEDE) in part 20 be revised to replace the deep dose equivalent with
the effective dose equivalent, and make that quantity more consistent
with national and international definitions?
8. To what extent should accuracy replace conservatism as the goal
for personnel monitoring?
The NRC will consider the comments received in its final evaluation
of the proposed RIS.
This Federal Register notice is available through the NRC's
Agencywide Documents Access and Management System (ADAMS) under
accession number ML031980001.
DATES: Comment period expires September 22, 2003. Comments submitted
after this date will be considered if it is practical to do so, but
assurance of consideration cannot be given except for comments received
on or before this date.
ADDRESSES: Submit written comments to the Chief, Rules and Directives
Branch, Division of Administrative Services, Office of Administration,
U.S. Nuclear Regulatory Commission, Mail Stop T6-D59, Washington, DC
20555-0001, and cite the publication date and page number of this
Federal Register notice. Written comments may also be delivered to NRC
Headquarters, 11545 Rockville Pike (Room T-6D59), Rockville, Maryland,
between 7:30 a.m. and 4:15 p.m. on Federal workdays.
FOR FURTHER INFORMATION CONTACT: Sami Sherbini at (301) 415-7853 or by
e-mail to [email protected], or Roger Pedersen at (301) 415-3162 or by e-
mail to [email protected].
SUPPLEMENTARY INFORMATION:
Draft Regulatory Issue Summary Method For Estimating Effective Dose
Equivalent From External Radiation Sources Using Two Dosimeters
Addressees
All U.S. Nuclear Regulatory Commission (NRC) licensees.
Intent
NRC is issuing this regulatory issue summary (RIS) to provide
guidance on an approved two-dosimeter monitoring method for estimating
effective dose equivalent (EDE) from external radiation exposures. This
EDE can be used instead of the deep dose equivalent (DDE) in complying
with NRC regulatory requirements.
Background
Total effective dose equivalent (TEDE) is used in 10 CFR part 20
(part 20) to specify dose limits for occupationally exposed workers,
and for members of the public. Other requirements (in part 20 and other
parts of NRC's regulations), such as the criteria for license
termination, are also specified in terms of the TEDE. Since EDE cannot
be directly measured, part 20 defines TEDE as ``the sum of the deep-
dose equivalent (for external exposures) and the committed effective
dose equivalent (for internal exposures).'' Part 20 goes on to specify
that this DDE be measured at the part of the whole body with the
highest exposure. This DDE can be directly measured with available
dosimeters, and, in most exposure situations, provides a reasonable,
conservative, and often the best, estimate for EDE from
[[Page 43770]]
external sources (EDEex). However, in non-uniform exposure
situations, such as from a directional source, DDE measured at the part
of the whole body with the highest exposure can be an overly
conservative estimate.
The NRC recently published RIS 2003-04 to encourage licensees to
use the EDEex for determining TEDE whenever the dose from
external sources is calculated instead of measured with personnel
dosimetry. The RIS discusses the limitations on, and the regulatory
basis for, substituting the EDEex for DDE in determining
compliance with TEDE based regulatory requirements. Estimating
EDEex from dosimeter readings is very dependent on exposure
geometry. Therefore, RIS 2003-04 also noted that methods for estimating
TEDE from an EDEex determined from dosimeter readings, must
be approved by the NRC. The 2003-04 RIS also noted that NRC approved
the use of a two dosimeter method for estimating effective dose
equivalent at Entergy sites (Reference 1).
This RIS describes the exposure situations in which NRC would
regard the use of a monitoring method to estimate EDEex as
appropriate and acceptable for estimating TEDE. This RIS does not
affect the definition of other non-TEDE limits or criteria in part 20.
Summary of Issues
Use of Effective Dose Equivalent
The NRC has approved a method for estimating EDEex from
external photon exposure situations. The guidance in this RIS is based
on the review and approval of the exemption for Entergy (Reference 1).
This method uses two dosimeter readings and is based on research
conducted by the Electric Power Research Institute (EPRI). The EPRI
work (References 2, 3, and 4) indicates that a single dosimeter,
calibrated to read DDE and worn on the chest, provides a reasonably
accurate estimate of EDEex when the individual is exposed to
a number of randomly distributed radiation sources during the
monitoring period. This is consistent with current allowable dosimetry
practices and requires no special approval. However, for nonuniform
exposures, such as from directional radiation fields or point sources,
EDEex can be estimated from a reading of a dosimeter worn on
the front (Rfront ) of the trunk of the body, combined with
the reading of a dosimeter worn on the back (Rback) of the
trunk of the body.
Two algorithms are given by EPRI for combining the dosimeter
results:
9. Mean Method:
The first algorithm is a simple, un-weighted, average (MEAN) of the
two dosimeter readings. The MEAN is equal to \1/2\ (Rfront +
Rback).
The EPRI technical reports state that the non-weighted average does
not always give a conservative result. Since no method is provided to
identify when the simple average gives non-conservative results, this
algorithm is not approved for use at this time.
10. Weighted Method:
The second algorithm, which was the subject of the Entergy
exemption, is a weighted average algorithm such that:
EDEex = \1/2\(Hi + MEAN)
Where Hi is the higher of Rfront or Rback.
A mathematically simpler form of this weighted algorithm is:
EDEex = 3/4Hi + 1/4Lo
Where Hi is the higher of Rfront or Rback and Lo
is the lower of Rfront or Rback.
The data presented in the EPRI technical reports (references 1 and
2) indicate that this weighted two-dosimeter algorithm provides a
reasonably conservative estimate of EDEex. Therefore, only
the weighted two-dosimeter algorithm is approved for use at this time
for exposures in a non-uniform field.
As a result of NRC approving the above weighted method, monitoring
the DDE at the part of the body receiving the highest exposure as
provided in 10 CFR 20.1201(c) is not needed for determining compliance
with TEDE based requirements when the weighted method is used subject
to the limitations which are set out below. This is because Footnote 2
in the ``Organ Dose Weighting Factors'' table in 10 CFR 20.1003,
permits the use of weighting factors to determine external exposures
without case-by-case approvals when specific NRC guidance has been
issued. This RIS constitutes such guidance for using the above weighted
method for determining the external exposure from weighted dosimeters
measuring direct DDE. An exemption from part 20 is not needed if the
guidance in this RIS is followed for determining external exposures.
However, 10 CFR 20.1201(c) still applies to the DDE required to be used
in complying with the organ dose limit in 10 CFR 20.1201(a)(1)(ii).
Additional Issues and Limitations
Licensees may, subject to the following limitations, use this
weighted two-dosimeter method for determining EDEex, and
estimating TEDE, from external photon exposures without applying for
further approval from the NRC.
Partial-body irradiations (i.e., exposure geometries that
preferentially shield the dosimeters) could bias the EPRI method
results in the non-conservative direction. Licensees must ensure that
dosimeters are worn so that at least one of the two dosimeters ``sees''
the major source, or sources, of radiation (one dosimeter will normally
be shielded from a source by the body). In other words, the
radiological work will be conducted and the dosimeters worn in such a
way, so that no shielding material is present between the radioactive
source(s) and the whole body, that would cast a shadow on the
dosimeter(s) and not over other portions of the whole body.
This method for estimating EDEex from dosimeter
readings, is not valid for exposure situations where the individual is
immersed in a shielding material (i.e., diving operations). Large dose-
rate gradients resulting from such immersions over the space occupied
by the body can bias the two dosimeter results.
Only dosimeters that have demonstrated angular response
characteristics at least as good as those specified in Reference 5, are
to be used. If the dosimeter's response decreases more rapidly than
EDEex, as the angle of incident radiation increases, the
resulting EDEex estimate will be biased in the non-
conservative direction. In addition, the dosimeters should be
calibrated to indicate DDE at the monitored location to ensure their
readings reflect electronic equilibrium conditions.
This method for estimating EDEex from two dosimeter
readings is not applicable to exposure situations where the sources of
radiation are nearer than 12 inches (30 cm) from the surface of the
body. This is the closest distance that the two-dosimeter algorithm has
been demonstrated to provide conservative results for discrete (point)
radiation sources.
The use of monitoring methods for estimating EDEex, from
exposure to point sources (i.e., hot particles) on, or near the surface
of the body, is outside the scope of this approval. Tables 5 through 7,
in Reference 3, provide some calculated EDEex values
resulting from exposure to point sources in contact with the torso of
the body. However, the information provided in these tables does not
bound all of the pertinent point source exposure situations.
Licensees using the weighted methodology need to maintain
sufficient records to demonstrate the above limitations were satisfied.
[[Page 43771]]
Conclusions
The weighted two-dosimeter algorithm, described in this RIS,
provides an acceptably conservative estimate of EDEex. The
TEDE based on EDEex using this algorithm in accordance with
its associated limitations is acceptable.
When recording or reporting doses in situations in which the
EDEex is assessed instead of the DDE, the value of the
EDEex is entered in place of the DDE in recording or
reporting forms, such as NRC Forms 4 or 5.
References
1. Exemption from the Requirements of 10 CFR part 20, Sec.
20.1003 Definition of Total Effective Dose Equivalent issued to
Arkansas Nuclear One, Units 1 and 2; Grand Gulf Nuclear Station;
Indian Point Nuclear Station, Units 1, 2 and 3; James A. Fitzpatrick
Nuclear Power Plant; Pilgrim Nuclear Power Station; River Bend
Station; Vermont Yankee Nuclear Power Plant; and Waterford Steam
Electric Station, Unit 3, 67 FR 58826 (September 18, 2002)
(ML022550559).
2. EPRI Technical Report TR-101909, Volume 1, February 1993.
3. EPRI Technical Report TR-101909, Volume 2, June 1995.
4. EPRI Implementation Guide TR-109446, September 1998.
5. Xu, X. G.; Reese, W. D.; and Poston, J. W. , ``A Study of the
Angular Dependence Problem In Effective Dose Equivalent
Assessment'', Health Physics, Volume 68., No. 2, February 1995, pp.
214-224.
Backfit Discussion
This RIS does not require any action nor written response nor
require any modification to plant structures, systems, components, or
design; therefore, the staff did not perform a backfit analysis.
Federal Register Notice
A notice of opportunity for public comment was published in the
Federal Register.
Paperwork Reduction Act Statement
This RIS does not require any action nor written response nor
require any modification to plant structures, systems, components, or
design; therefore, the staff did not perform a backfit analysis.
Paperwork Reduction Act Statement
This RIS does not request any information collection.
End of Draft Regulatory Issue Summary
Documents may be examined, and/or copied for a fee, at the NRC's
Public Document Room at One White Flint North, 11555 Rockville Pike
(first floor), Rockville, Maryland. Publicly available records will be
accessible electronically from the Agencywide Documents Access and
Management System (ADAMS) Public Electronic Reading Room on the
Internet at the NRC Web site, http://www.nrc.gov/NRC/ADAMS/index.html.
If you do not have access to ADAMS or if you have problems in accessing
the documents in ADAMS, contact the NRC Public Document Room (PDR)
reference staff at 1-800-397-4209 or 301-415-4737 or by e-mail to
[email protected].
Dated at Rockville, Maryland, this 14th day of July 2003.
For the Nuclear Regulatory Commission.
William D. Beckner,
Branch Chief, Reactor Operations Branch, Division of Inspection Program
Management, Office of Nuclear Reactor Regulation.
[FR Doc. 03-18688 Filed 7-23-03; 8:45 am]
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