ML083020031

Application to Use Weighting Factors for External Exposure

ML083020031
Person / Time
Site:	Beaver Valley, Davis Besse, Perry
Issue date:	11/20/2008
From:	Russell Gibbs Plant Licensing Branch III
To:	Hagan J FirstEnergy Nuclear Operating Co
Gratton C, NRR, DORL, 415-1055
References
TAC MD8286, TAC MD8287, TAC MD8288, TAC MD8289
Download: ML083020031 (5)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 November 20, 2008 Mr. Joseph J. Hagan President and Chief Nuclear Officer FirstEnergy Nuclear Operating Company Mail Stop A-GO-19 76 South Main Street Akron, OH 44308

SUBJECT:

BEAVER VALLEY POWER STATION, UNIT NOS. 1 AND 2; DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO.1; AND PERRY NUCLEAR POWER PLANT, UNIT NO.1 - APPLICATION TO USE WEIGHTING FACTORS FOR EXTERNAL EXPOSURE. (TAC NOS. MD8286 THRU MD 8289)

Dear Mr. Hagan:

By the letter dated March 6, 2008, as supplemented by letter dated September 18, 2008, FirstEnergy Nuclear Operating Company (the licensee) requested approval by the Nuclear Regulatory Commission (NRC) for the use of the weighting factors listed in Table 1 of the American National Standard Institute HPS N13.41-1997, "Criteria for Performing Multiple Dosimetry," for external radiation exposures when demonstrating compliance with total effective dose equivalent, based on requirements in Title 10 of the Code of Federal Regulations, Part 20.

The licensee requested approval to use the weighting factors at Beaver Valley Power Station, Units 1 and 2, Davis-Besse Nuclear Power Station, Unit No.1, and Perry Nuclear Power Plant, Unit NO.1. ANSI/HPS N13.41-1997 was approved December 1996.

On the basis of its review, the NRC staff finds the licensee's request acceptable. The enclosed safety evaluation documents the findings. Please contact Christopher Gratton at (301) 415-1055, if you have any questions on this matter.

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Russell Gibbs, Chief Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-334, 50-412, 50-346, and 50-440

Enclosure:

Safety Evaluation cc: w/encl: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO APPROVAL TO USE EFFECTIVE DOSE EQUIVALENT WEIGHTING FACTORS FOR EXTERNAL RADIATION EXPOSURE FIRSTENERGY NUCLEAR OPERATING COMPANY BEAVER VALLEY POWER STATION. UNITS 1 AND 2 DAVIS-BESSE NUCLEAR POWER STATION. UNIT NO.1 PERRY NUCLEAR POWER PLANT, UNIT NO.1 DOCKET NOS. 50-334. 50-412. 50-346. AND 50-440

1.0 INTRODUCTION

By the letter dated March 6, 2008, as supplemented by letter dated September 18, 2008, FirstEnergy Nuclear Operating Company (the licensee) requested approval by the Nuclear Regulatory Commission (NRC) for the use of the weighting factors listed in Table 1 in the American National Standard Institute (ANSI) HPS N13.41-1997, "Criteria for Performing Multiple Dosimetry," for external radiation exposures when demonstrating compliance with total effective dose equivalent (TEDE), based on requirements in Title 10 of the Code of Federal Regulations (10 CFR), Part 20, for the Beaver Valley Power Station, Units 1 and 2, the Davis-Besse Nuclear Power Station, Unit No.1, and the Perry Nuclear Power Plant, Unit NO.1. ANSI/HPS 1\113.41-1997 was approved December 1996.

The licensee stated that accurate assessment of occupational exposure of workers from external sources of radiation in highly non-uniform radiation fields requires a method for assessing the effective dose equivalent (EDE) and that the use of the proposed weighting factors will improve the accuracy of the licensee's assessment of occupational exposure.

Therefore, the effect of granting this request would be to allow the licensee the option to control EDE using the weighted external exposure measurements in those cases where it is a more accurate predictor of the risk from occupational radiation exposure.

2.0 REGULATORY EVALUATION

Part 20 of 10 CFR defines EDE or HE as the sum of the products of the dose equivalent to each tissue (HT) and the weighting factors (WT) applicable to each of the body organs or tissues that are irradiated (HE = r T WT HT) ." Each tissue weighting factor is the proportion of the risk of stochastic effects resulting from the dose to that organ or tissue to the total risk of stochastic effects when the whole body is irradiated uniformly. The weighting factors are applicable to the organs and tissues whether the dose results from radiation sources internal or external to the body.

Enclosure

-2 For the purposes of implementing workplace controls, and due to the difference in dosimetry methods, 10 CFR Part 20 breaks EDE into two components, dose resulting from radioactive sources internal to the body, and dose resulting from sources external to the body. The doses from external and internal exposures are then summed to obtain the TEDE. Several dose limits (such as those in 20.1201 (a)(1)(i) and 20.1301 (a)) and other requirements in 10 CFR in Part 20 are based on TEDE.

As of February 15, 2008, 10 CFR 20.1003 defines TEDE as the "sum of the effective dose equivalent (for external exposures) and the committed EDE (for internal exposures)." The committed EDE is the sum of the products of the dose equivalents to each tissue, from radioactive material taken into the body, integrated over 50 years, and the weighting factor applicable to that tissue.

In most relatively uniform exposure situations, a single dosimeter, calibrated to measure deep dose equivalent (DOE), worn on the whole body, provides a reasonably accurate estimate of the EDE from external exposures (EDE ex) . If the body is not irradiated uniformly, a single dose measurement can not determine the dose to the various organs and tissues for an accurate determination of the EDEex* To insure a conservative TEDE determination, 10 CFR 20.1201 (c) requires that when external exposure is determined by measurement with an external monitoring device, the DOE, measured for the part of the body receiving the highest exposure, must be used in place of the EDEex, unless the EDEex is determined by a dosimetry method approved by the NRC.

Using DOE in place of EDEex can be overly conservative in extremely non-uniform irradiations (e.g., when only a small portion of the whole body is irradiated). As discussed in NRC Regulatory Issue Summaries 2002-06, 2003-04 and 2004-01, the NRC has approved several methods for determining EDEex, and has encouraged the use of EDE ex in place of DOE for demonstrating compliance with the TEDE requirements in 10 CFR Part 20.

3.0 TECHNICAL EVALUATION

The NRC staff has reviewed the technical approach for estimating EDEex provided in ANSI/HPS N13.41-1997. This multiple dosimetry method divides the whole body into seven separate compartments. Each compartment, or combined compartment (since the ANSI/HPS-N13.41 allows combining adjacent compartments), is monitored separately. The results of the dose measurement for each compartment are weighted with an associated "compartment factor." The resulting weighted doses are then summed to determine the EDE ex for the whole body.

The compartment factors are listed in Table 1 of the ANSI/HPS N13.41. The factor for each compartment was developed by summing the stochastic weighting factors given in 10 CFR Part 20 for all the organs located within that compartment. For each tissue that reside in more than one compartment (i.e., red bone marrow), the weighting factor was apportioned between the compartments based on the fraction of the total mass of the tissue residing in each, using the information in International Commission on Radiation Protection Publication 23.

-3 Fundamental to the ANSIIHPS N13.41 multiple dosimeter method of determining EDEex, are the assumptions that (1) the average dose to the tissues in each compartment can be reasonably measured (with one or more dosimeters), and (2) that the dose distribution across the compartment is sufficiently constant so that this average dose can be applied to each tissue in the compartment. The compartments defined in ANSI/HPS N13.41 are small enough so that under most exposure situations these assumptions are met and a single determination of DDE in each compartment is sufficient. However, this may not be the case in those unusual situations where a significant dose gradient exists across the compartment (particularly the thorax and abdomen compartments). In these cases, dosimeter placement in each compartment becomes critical to ensuring that the EDE ex is not underestimated.

To ensure that the estimates of EDE ex are conservative, the licensee has committed to measuring the dose to each compartment (and/or combined compartment) by locating the dosimeter, calibrated to DDE, at the highest exposed portion of that compartment. The dosimeter location for each compartment will be subject to the same criteria the licensee currently uses for demonstrating compliance with 10 CFR 20.1201 (c).

The licensee has stated that in uniform exposure situations, a single dosimeter placed between the wearer's head and waist, consistent with the licensee's current practice, will be used to monitor monitoring external exposure

4.0 CONCLUSION

The NRC staff concludes that the licensee's commitments to dose measurement using the multiple dosimetry method to determine EDE ex by applying the weighting factors listed in Table 1 of ANSI/HPS N13.41-1997, as discussed above in Section 3.0 of this report, is consistent with the ANSI/HPS standard and with the requirements of 10 CFR Part 20, and is therefore acceptable for the purposes of demonstrating compliance with the TEDE-based requirements in 10 CFR Part 20.

Principal Contributor: R. Pedersen, NRR Date: November 20, 2008

Mr. Joseph J. Hagan November 20,2008 President and Chief Nuclear Officer FirstEnergy Nuclear Operating Company Mail Stop A-GO-19 76 South Main Street Akron, OH 44308 SUB,JECT: BEAVER VALLEY POWER STATION, UNIT NOS. 1 AND 2; DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO.1; AND PERRY NUCLEAR POWER PLANT, UNIT NO.1 - APPLICATION TO USE WEIGHTING FACTORS FOR EXTERNAL EXPOSURE. (TAC NOS. MD8286 THRU MD 8289)

Dear Mr. Hagan:

By the letter dated March 6, 2008, as supplemented by letter dated September 18, 2008, FirstEnergy Nuclear Operating Company (the licensee) requested approval by the Nuclear Regulatory Commission (NRC) for the use of the weighting factors listed in Table 1 of the American National Standard Institute HPS N13.41-1997, "Criteria for Performing Multiple Dosimetry," for external radiation exposures when demonstrating compliance with total effective dose equivalent, based on requirements in Title 10 of the Code of Federal Regulations, Part 20.

The licensee requested approval to use the weighting factors at Beaver Valley Power Station, Units 1 and 2, Davis-Besse Nuclear Power Station, Unit No.1, and Perry Nuclear Power Plant, Unit No.1. ANSI/HPS 1\113.41-1997 was approved December 1996.

On the basis of its review, the NRC staff finds the licensee's request acceptable. The enclosed safety evaluation documents the findings. Please contact Christopher Gratton at (301) 415-1055, if you have any questions on this matter.

Sincerely, IRA!

Russell Gibbs, Chief Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-334, 50-412, 50-346, and 50-440

Enclosure:

Safety Evaluation cc w/encl: Distribution via Listserv DISTRIBUTION:

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