[Federal Register Volume 68, Number 177 (Friday, September 12, 2003)]
[Notices]
[Pages 53755-53758]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-23255]


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NUCLEAR REGULATORY COMMISSION

[Docket No. 50-285]


Omaha Public Power District, Fort Calhoun Station, Unit 1; 
Exemption

1.0 Background

    The Omaha Public Power District (the licensee) is the holder of 
Facility Operating License No. DPR-40 which authorizes operation of the 
Fort Calhoun Station, Unit 1 (FCS). The license provides, among other 
things, that the facility is subject to all rules, regulations, and 
orders of the U.S. Nuclear Regulatory Commission (NRC, the Commission) 
now or hereafter in effect.
    The facility consists of a pressurized water reactor located in 
Washington County in Nebraska.

2.0 Request/Action

    Title 10 of the Code of Federal Regulations (10 CFR), part 20, 
section 20.1003 states that the definition of total effective dose 
equivalent (TEDE) is the sum of the deep-dose equivalent (for external 
exposures) and the committed effective dose equivalent (for internal 
exposures). The proposed exemption would change the definition of TEDE 
to mean the sum of the effective dose equivalent or the deep-dose 
equivalent (for external exposures) and the committed effective dose 
equivalent (for internal exposures). The licensee requests the 
exemption because the current method of calculating TEDE, under certain 
conditions (such as when there is a non-uniform exposure), can 
significantly overestimate the dose received.

[[Page 53756]]

    In summary, the licensee's application dated January 8, 2003, 
requests an exemption from the 10 CFR 20.1003 definition of TEDE.

3.0 Discussion

    Pursuant to 10 CFR 20.2301, the Commission may, upon application by 
a licensee or upon its own initiative, grant exemptions from the 
requirements of 10 CFR part 20 if it determines the exemptions are 
authorized by law and would not result in undue hazard to life or 
property.
    The staff examined the licensee's rationale to support the 
exemption request and concluded that the new method for calculating 
TEDE, under certain conditions, is a more accurate means of estimating 
worker radiation exposure and therefore would not result in undue 
hazard to the workers. The basis for this follows.

4.0 Regulatory Evaluation

    By letter dated January 8, 2003, the licensee requested an 
exemption from the current definition, and the approval to use an 
alternate definition of TEDE. The licensee requested that the 
definition of TEDE, as used in 10 CFR 20.1003 (i.e., for the purpose of 
complying with the dose recording requirements, dose reporting 
requirements, or the dose limits), be changed to mean the sum of the 
effective dose equivalent or the deep dose equivalent (for external 
exposures), and the committed effective dose equivalent (for internal 
exposures). The licensee also requested approval to use a method for 
estimating the effective dose equivalent for external exposures 
(EDEex) published by the Electric Power Research Institute 
(EPRI) in Technical Report TR-101909, Volumes 1 and 2, and 
Implementation Guide TR-109446. The effect of granting this request 
would be to allow the licensee the option to control TEDE using 
EDEex in those cases where it is a more accurate predictor 
of the risk from occupational radiation exposure.
    The radiation protection approach and dose limits contained in 10 
CFR part 20 are based on the recommendations of the International 
Commission on Radiation Protection (ICRP) in their 1977 publication No. 
26 (ICRP 26). For stochastic effects, the ICRP-recommended dose 
limitation is based on the principle that the risk should be equal, 
whether the whole body is irradiated uniformly or whether there is non-
uniform irradiation (such as when radioactive materials are taken into 
the body and, depending on their physical and chemical properties, 
concentrate in certain tissues and organs). This condition will be met 
if

[Sigma]T[omega]THT<=Hwb
,L

where WT is a weighting factor representing the 
proportions of the stochastic risk resulting from tissue (T) 
to the total risk, when the whole body is irradiated uniformly; HT 
is the annual dose equivalent in tissue (T); and Hwb,L 
is the recommended annual dose-equivalent limit for uniform irradiation 
of the whole body, namely 5 rem (50 mSv). The 
sum[Sigma][omega]TWTTHT is called effective dose 
equivalent (EDE). The values for [omega]T are given in ICRP 
26, for the various tissues (T), and are codified in 10 CFR 
part 20.
    For the purposes of implementing workplace controls, and due to the 
difference in dosimetry, 10 CFR part 20 breaks this total EDE, or TEDE, 
into two components: (1) dose resulting from radioactive sources 
internal to the body, and (2) dose resulting from sources external to 
the body. For radioactive material taken into the body, the 
occupational dose limit is based on the resulting dose equivalent 
integrated over 50 years (H50) of exposure such that

[Sigma]T[omega]TH50, T 
<=Hwb,L.

This quantity 
[Sigma]T[omega]TH50,T is 
called the committed effective does equivalent (CEDE) in 10 CFR part 
20.
    Demonstrating compliance with the dose limits from internal 
exposures is accomplished using direct measurements of concentrations 
of radioactivity in the air in the work areas, or quantities of 
radionuclides in the body, or quantities of radionuclides excreted from 
the body, or a combination of these. Having determined the quantities 
of radionuclides present or taken into the body, these can be compared 
to secondary or tertiary limits (e.g., annual limits on intake or 
derived air concentrations) listed in Appendix B to 10 CFR part 20. 
These secondary and tertiary limits have been calculated using standard 
assumptions of the physical and chemical forms of the radionuclides, 
the standard physiological parameters from the Reference Man, and the 
bio-kinetic models adopted in ICRP 26. Alternatively, the regulations 
allow the licensee to adjust certain of these standard assumptions and 
calculate CEDE directly, using appropriate models.
    The normal practice for determining radiation dose from external 
sources is to measure the radiation intensity at the surface of the 
body with a monitoring device (dosimeter) calibrated to read in terms 
of a tissue dose equivalent at a specified tissue depth. In 1991, when 
10 CFR part 20 was revised to adopt the ICRP 26 recommendations on 
limits and controls, there was little guidance on how to determine the 
dose to the several tissues necessary to calculate EDEex. It 
is impractical to separately monitor (or measure) the dose received by 
the various organs and tissues that contribute to TEDE. As a practical, 
conservative simplification, 10 CFR part 20 limits the dose from 
external sources in terms of deep dose equivalent (DDE). The DDE is the 
dose equivalent at a tissue depth of one centimeter, and is required 
(by 10 CFR part 20.1201(c)) to be determined for the part of the body 
receiving the highest exposure. The TEDE annual limit is met if

DDE + [Sigma]T[omega]TH50,T 
<= 5 rem (50 mSv).

In addition to the annual limit on TEDE, 10 CFR part 20 provides a non-
stochastic annual limit of 50 rem (0.5 Sv) for each individual tissue 
such that

DDE + H50, T<= 50 rem (0.50 Sv)

for all tissues except the skin and lens of the eye.
    Using the highest DDE, to bound the individual tissue doses from 
radioactive sources outside the body, generally results in a slightly 
conservative estimate of EDEex from uniform exposures. 
However, it can be overly conservative for non-uniform exposure 
situations. Since many high-dose jobs at nuclear power plants are 
performed under non-uniform exposure conditions, this can lead to a 
significant overestimation of the actual TEDE dose, and the risk, to 
the workers. To address this issue, the licensee has requested approval 
to provide a more accurate dose assessment by replacing DDE with 
EDEex when calculating TEDE from non-uniform exposures, 
where the EDEex is determined with a method developed by 
EPRI.
    In developing this method, the EPRI investigators used mathematical 
equations developed by Cristy and Eckerman to model standard, adult 
human male and female subjects (phantoms). The Monte Carlo radiation 
transport computer code MCNP was used to calculate the dose to 
individual tissues modeled in the phantoms, and simulated dosimeter 
readings, for a range of different exposure geometries. Dosimeters with 
an isotropic response were modeled at several locations on the surface 
of the phantoms. Both broad beam and point radiation sources (with 
selected photon energies) were considered. Indicated doses (e.g., 
simulated dosimeter readings) and the actual EDEex (e.g., 
the sum of the products of the calculated phantom tissue doses and 
their respective ICRP 26 weighting factors) were calculated for

[[Page 53757]]

photons incident on the phantoms from various locations. Empirical 
algorithms were developed to relate the EDEex resulting from 
the full range of exposure situations to the indicated doses that could 
be measured at the surface of the body. Two algorithms were developed 
to estimate EDEex from just two dosimeters worn on the trunk 
of the whole body (front and back, respectively). The first algorithm 
is a simple, non-weighted averaging of the front and back dosimeter 
readings. The second algorithm weights the higher of the two dosimeter 
readings.

5.0 Technical Evaluation

    The staff reviewed the technical descriptions of the EPRI method 
for estimating EDEex; the resulting data and conclusions 
contained in Technical Report TR-101909, Volumes 1 and 2; 
Implementation Guide TR-109446 and the supporting technical papers 
published by the principal EPRI investigators. The staff also performed 
independent calculations to verify a sampling of the results tabulated 
in these documents.
    The EPRI work indicates that a single dosimeter (calibrated to read 
DDE), 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. The alternate definition of TEDE requested, would 
allow the licensee the option to monitor worker dose with a single DDE 
measurement as currently required, or to control TEDE using 
EDEex (as determined by the EPRI two badge method) in 
situations where monitoring the highest DDE would require moving, or 
supplementing, the single badge.
    The data presented in the EPRI reports indicate that the weighted 
two-dosimeter algorithm provides a reasonably conservative estimate of 
EDEex. However, the non-weighted algorithm does not always 
give a conservative result. The licensee has stated that it will only 
use the weighted two-dosimeter algorithm such that;

EDEex = \1/2\ (MAX + \1/2\ (Rfront + 
Rback))

where Rfront is the reading of the dosimeter on the front of 
the body, Rback is the reading of the dosimeter on the back 
of the body, and MAX is the higher of the front or back dosimeter 
readings.
    Additional issues and limitations noted in the staff's review are 
included in the following paragraphs.
    Partial-body irradiations, that preferentially shield the 
dosimeter, could bias the EPRI method results in the non-conservative 
direction. The licensee has stated that they will ensure that the 
dosimeters are worn so that at least one of the two badges ``sees'' the 
source(s) of radiation. 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) not cast over other 
portions of the whole body.
    Isotropic dosimeters (e.g., dosimeters that respond independently 
of the angle of the incident radiation) are impractical and not widely 
available commercially. Therefore, the licensee must implement the EPRI 
method using dosimeters that will have an angular dependent response. 
If the dosimeter reading decreases more rapidly than EDEex, 
with increasing exposure angle, the resulting EDEex estimate 
will be biased in the non-conservative direction. The EPRI principle 
investigators have addressed this issue of angular dependance in their 
published technical paper entitled ``A Study of the Angular Dependence 
Problem In Effective Dose Equivalent Assessment'' (Health Physics 
Volume 68. No. 2, February 1995, pp. 214-224). The licensee has stated 
that the dosimeters used to estimate EDEex will have 
demonstrated angular response characteristics at least as good as that 
specified in this technical paper. In addition, the dosimeters will be 
calibrated to indicate DDE at the monitored location, to ensure their 
readings reflect electronic equilibrium conditions.
    The EPRI 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. Tables 5 thru 7 in EPRI TR-101909, Volume 2, provide calculated 
EDEex values resulting from exposure to point sources in 
contact with the torso of the body. However, the staff review 
determined that the information provided in these tables does not bound 
all of the pertinent point source exposure situations. The licensee has 
stated that the use of EDEex, to determine compliance with 
the TEDE limit, resulting from point sources (i.e., hot particles) on, 
or near the surface of the body, is outside the scope of this request.
    Table 8 in TR-101909, Volume 2, provides a summary of the 
EDEex, and dosimeter (front and back) readings calculated 
for parallel beams and point sources used to develop the EPRI 
algorithms. However, the magnitude of the units for the parallel beam 
dose factors listed are low by five orders of magnitude (e.g., ``E-15 
rad-cm squared per photon'' instead of the correct ``E-10 rad-cm 
squared per photon''). This error does not effect the conclusions drawn 
from the data. However, the specific dose factors listed in Table 8 
should not be used to calculate EDEex.
    When EDE is used to calculate TEDE under the revised definition, 
the requirement in 10 CFR part 20.1201(c), that DDE be determined for 
the part of the body receiving the highest exposure, is not applicable. 
However, when TEDE is calculated using the DDE (i.e., from a single 
dosimeter reading), 10 CFR 20.1201(c) does apply.
    The exemption applies only to the definition (and methods for 
calculating) TEDE . It does not modify the dose limits for any 
individual organ or tissue, or the methods for complying, specified in 
10 CFR part 20 (i.e., 10 CFR 20.1201(a)(1)(ii), (a)(2) and 10 CFR 
20.1208). The licensee is still required to provide surveys and 
monitoring necessary to demonstrate compliance with these requirements.

6.0 Evaluation Summary

    The staff concludes that calculating TEDE using EDEex as 
proposed by the licensee in place of DDE provides a more accurate 
estimate of the risk associated with the radiation exposures 
experienced by radiation workers at a nuclear power plant. 
Additionally, the staff finds that the proposal to limit TEDE such that

EDEex + CEDE <= 5 rem

is consistent with the basis for the limits in 10 CFR part 20. 
Therefore, subject to the limitations noted above and agreed to by the 
licensee, defining TEDE to mean the sum of EDEex or DDE (for 
external exposures) and CEDE (for internal exposures), in lieu of the 
current 10 CFR 20.1003 definition, is acceptable.
    Additionally, the staff concludes that the methods for estimating 
EDEex described in EPRI Technical Report TR-101909, Volumes 
1 and 2, and Implementation Guide TR-109446 are based on sound 
technical principles. The proposed EPRI weighted, two-dosimeter 
algorithm provides an acceptably conservative estimate of 
EDEex with a degree of certainty that is comparable to that 
inherent in the methods allowed by 10 CFR part 20 for estimating CEDE. 
Therefore, subject to the limitations noted above, using the EPRI 
weighted, two-dosimeter algorithm so that

EDEex = \1/2\ (MAX + \1/2\ Rfront + 
Rback))


[[Page 53758]]


for the purposes of demonstrating compliance with 10 CFR 20.1003 is 
acceptable.

7.0 Conclusion

    Accordingly, the Commission has determined that, pursuant to 10 CFR 
20.2301, the exemption is authorized by law and would not result in 
undue hazard to life or property. Therefore, the Commission hereby 
grants Omaha Public Power District an exemption from the requirements 
of 10 CFR 20.1003 for Fort Calhoun Station, Unit 1. The exemption 
changes the definition of TEDE to mean the sum of EDEex or 
DDE (for external exposures) and CEDE (for internal exposures). This 
exemption is granted to allow the licensee the option to monitor worker 
dose using EDEex based on the following conditions:
    1. Only the EPRI weighted, two-dosimeter algorithm will be used 
such that

EDEex = \1/2\ (MAX + \1/2\ Rfront + 
Rback))

where Rfront is the reading of the dosimeter on the front of 
the body, Rback is the reading of the dosimeter on the back 
of the body, and MAX is the higher of the front or back dosimeter 
readings.
    2. 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.
    3. The dosimeters used to estimate EDEex will have 
demonstrated angular response characteristics at least as good as that 
specified in the technical paper entitled, ``A Study of the Angular 
Dependence Problem In Effective Dose Equivalent Assessment'' (Health 
Physics Volume 68. No. 2, February 1995, pp. 214-224). Also, the 
dosimeters will be calibrated to indicate DDE at the monitored 
location, to ensure their readings reflect electronic equilibrium 
conditions.
    4. The EPRI 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.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will not have a significant effect on the 
quality of the human environment(68 FR 52801).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 8th day of September, 2003.
    For the Nuclear Regulatory Commission.
Eric J. Leeds,
Acting Director, Division of Licensing Project Management, Office of 
Nuclear Reactor Regulation.
[FR Doc. 03-23255 Filed 9-11-03; 8:45 am]
BILLING CODE 7590-01-P