[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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