02-23691. Entergy Operations, Inc., Entergy Nuclear Operations, Inc., 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 ...

1.0 Background

Entergy Operations, Inc. and Entergy Nuclear Operations, Inc. (the licensees) are the holders of Renewed Facility Operating License No. DPR-51; Facility Operating License Nos. NPF-6 and NPF-29; Provisional Operating License No. DPR-5; and Facility Operating License Nos. DPR-26, DPR-64, DPR-59, DPR-35, NPF-47, DPR-28, and NPF-38, which authorize operation of 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. The licenses provide, among other things, that the facilities are subject to all rules, regulations, and orders of the U.S. Nuclear Regulatory Commission (NRC, the Commission) now or hereafter in effect.

The facilities consist of pressurized and boiling water reactors located in Pope County, Arkansas; Claiborne County, Mississippi; Westchester County, New York; Oswego County, New York; Plymouth County, Massachusetts; West Felciana Parish, Louisiana; Windham County, Vermont; and Saint Charles Parish, Louisiana. (The operating authority of Provisional Operating License No. DPR-5 for Indian Point Nuclear Station, Unit 1, was revoked by Commission Order dated June 19, 1980).

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, can significantly overestimate the dose received.

In summary, the licensee's application dated July 20, 2001, as supplemented by letter dated June 13, 2002, 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 is as follows.

4.0 Regulatory Evaluation

By letter dated July 20, 2001, as supplemented by letter dated June 13, 2002, the licensee requested an exemption from the current definition, and the approval to use an alternate definition, of TEDE in 10 CFR 20.1003. 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 (EDE_ex) published by the Electric Power Research Institute (EPRI) in Technical Report TR-101909, Volumes 1 and 2, and the Implementation Guide TR-109446. (These EPRI documents were provided on the docket as enclosures to a previous May 1, 2001, application from the licensee, which was superseded by the July 20, 2001, application). The effect of granting this request would be to allow the licensee the option to control TEDE using EDE_ex 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

Σ_Tω_T H_T≤H_wb,L

where ω_T 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; H_T is the annual dose equivalent in tissue (T); and H_wb.L is the recommended annual dose-equivalent limit for uniform irradiation of the whole body, namely 5 rem (50 mSv). The sum Σ_Tω_T H_T is called effective dose equivalent (EDE). The values for ω_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

Σ_Tω_T H_50,T≤H_wb,L

This quantity Σ_Tω_T H_50,T is called the Committed Effective Dose 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 common 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 EDE_ex. 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 + Σ_Tω_T H_50,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 + H_50,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 EDE_ex 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 EDE_ex when calculating TEDE from non-uniform exposures, where the EDE_ex is determined with a method developed by the 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 EDE_ex (e.g., the sum of the products of the calculated phantom tissue doses and their respective ICRP 26 weighting factors) were calculated for photons incident on the phantoms from various locations. Empirical algorithms were developed to relate the EDE_ex 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 EDE_ex 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 EDE_ex; the resulting data and conclusions contained in Technical Report TR-101909, Volumes 1 and 2; the Implementation Guide TR-109446; and 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.

Table 8 in TR-101909, Volume 2, provides a summary of the EDE_ex and dosimeter (front and back) readings calculated for parallel beams and point sources used to develop the EPRI algorithms. The staff noted that the magnitude of the units for the parallel beam dose factors listed in Table 8 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”). The licensee verified, in its June 13, 2002, supplemental letter, that this is a typographical error in the EPRI document. However, this error does not affect the conclusions drawn from the data. The licensee has stated that they will not use the specific dose factors listed in Table 8 to calculate EDE_ex.

The EPRI work indicates that a single dosimeter (calibrated to read DDE) worn on the chest provides a reasonably accurate estimate of EDE_ex 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 EDE_ex (as determined by the EPRI two-badge method). This would benefit the licensee 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 EDE_ex. 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

EDE_ex = 1/2 (MAX + 1/2 (R_front + R_back))

where R_front is the reading of the dosimeter on the front of the body, R_back 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) and not 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 EDE_ex, with increasing exposure angle, the resulting EDE_ex 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 EDE_ex 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 EDE_ex 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 EDE_ex 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 EDE_ex 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.

The exemption applies only to the TEDE definition and calculations. It does not modify the dose limits for any individual organ or tissue specified in, or method for complying with, 10 CFR Part 20. Also, when DDE is used to calculate TEDE under the revised definition, the requirement that it be for the part of the body receiving the highest exposure in 10 CFR 20.1201(c) is applicable.

6.0 Evaluation Summary

The staff concludes that calculating TEDE using this EDE_ex 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

EDE_ex + CEDE ≤ 5 rem

is consistent with the basis for the limits in 10 CFR Part 20. Therefore, subject to the limitations noted above, defining TEDE to mean the sum of EDE_ex 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 EDE_ex 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 EDE_ex 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

EDE_ex = 1/2 (MAX + 1/2 (R_front + R_back))

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 Entergy Operations, Inc. and Entergy Nuclear Operations, Inc. an exemption from the requirements of 10 CFR 20.1003 for 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. The exemption changes the definition of TEDE to mean the sum of EDE_ex 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 EDE_ex based on the following conditions:

1. Only the EPRI weighted, two-dosimeter algorithm will be used such that

EDE_ex = 1/2 (MAX + 1/2 (R_front + R_back))

where R_front is the reading of the dosimeter on the front of the body, R_back 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 EDE_ex 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 EDE_ex 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 (67 FR 56603, dated September 4, 2002).

This exemption is effective upon issuance.

Dated at Rockville, Maryland, this 12th day of September 2002.

For the Nuclear Regulatory Commission.

Bruce A. Boger,

Director, Division of Inspection Program Management, Office of Nuclear Reactor Regulation.