ML080570154

Approval to Use Effective Dose Equivalent Weighting Factors for External Radiation Exposure

ML080570154
Person / Time
Site:	Summer
Issue date:	03/14/2008
From:	Melanie Wong NRC/NRR/ADRO/DORL/LPLII-1
To:	Archie J South Carolina Electric & Gas Co
Martin R, NRR/DORL, 415-1493
References
TAC MD8129
Download: ML080570154 (5)

Text

March 14, 2008 Mr. Jeffery B. Archie Vice President, Nuclear Operations South Carolina Electric & Gas Company Virgil C. Summer Nuclear Station Post Office Box 88 Jenkinsville, SC 29065

SUBJECT:

VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO. 1, APPROVAL TO USE EFFECTIVE DOSE EQUIVALENT WEIGHTING FACTORS FOR EXTERNAL RADIATION EXPOSURE (TAC NO. MD8129)

Dear Mr. Archie:

By letter dated February 19, 2008, the South Carolina Electric and Gas Company requested the U.S. Nuclear Regulatory Commission's (NRCs) approval for the use of the weighting factors provided in the American National Standard Institute standard HPS N13.41-1997 for external radiation exposures when demonstrating compliance with total effective dose equivalent, based on requirements in Part 20 of Title 10 of the Code of Federal Regulations (10 CFR) for the V. C.

Summer Nuclear Station. Authority to permit the use of other weighting factors than those in the 10 CFR 20.1003 table entitled "Organ Dose Weighting Factors" is in footnote 2 to the table.

Authority to approve a dosimetry method for determining the effective dose equivalent from external exposure, is in 10 CFR 20.1201(c).

On the basis of its review, the NRC staff finds your request acceptable. The enclosed safety evaluation documents the staffs findings.

Sincerely,

/RA/

Melanie C. Wong, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-395

Enclosure:

Safety Evaluation cc w/enclosure: See next page

March 14, 2008 Mr. Jeffery B. Archie Vice President, Nuclear Operations South Carolina Electric & Gas Company Virgil C. Summer Nuclear Station Post Office Box 88 Jenkinsville, SC 29065

SUBJECT:

VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO. 1, APPROVAL TO USE EFFECTIVE DOSE EQUIVALENT WEIGHTING FACTORS FOR EXTERNAL RADIATION EXPOSURE (TAC NO. MD8129)

Dear Mr. Archie:

By letter dated February 19, 2008, the South Carolina Electric and Gas Company requested the U.S. Nuclear Regulatory Commission's (NRCs) approval for the use of the weighting factors provided in the American National Standard Institute standard HPS N13.41-1997 for external radiation exposures when demonstrating compliance with total effective dose equivalent, based on requirements in Part 20 of Title 10 of the Code of Federal Regulations (10 CFR) for the V. C.

Summer Nuclear Station. Authority to permit the use of other weighting factors than those in the 10 CFR 20.1003 table entitled "Organ Dose Weighting Factors" is in footnote 2 to the table.

Authority to approve a dosimetry method for determining the effective dose equivalent from external exposure, is in 10 CFR 20.1201(c).

On the basis of its review, the NRC staff finds your request acceptable. The enclosed safety evaluation documents the staffs findings.

Sincerely,

/RA/

Melanie C. Wong, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-395

Enclosure:

Safety Evaluation cc w/enclosure: See next page DISTRIBUTION:

Public RidsAcrsAcnw&mMailCenter RidsOgcRp LPL2-1 R/F RPedersen, NRR RidsNrrDorlLp2-1 (MWong) RidsRgn2MailCenter (EGuthrie)

RidsNrrPMRMartin (hard copy) RidsNrrBTully (hard copy)

ADAMS No: ML080570154 OFFICE NRR/LPL2-1/PM NRR/LPL3-1/LA DIRS/IR OGC NLO NRR/LPL2-1/BC NAME RMartin BTully SGarry JAdler MWong DATE 03/14/08 03/14/08 02/27/08 03/11/08 03/14/08 OFFICIAL RECORD COPY

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO APPROVAL TO USE EFFECTIVE DOSE EQUIVALENT WEIGHTING FACTORS FOR EXTERNAL RADIATION EXPOSURE SOUTH CAROLINA ELECTRIC & GAS COMPANY SOUTH CAROLINA PUBLIC SERVICE AUTHORITY VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO. 1 DOCKET NO. 50-395

1.0 INTRODUCTION

By the application dated February 19, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML080530393), South Carolina Electric and Gas Company (the licensee) requested approval by the U.S. Nuclear Regulatory Commission (NRC) of 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, (the Standard) 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 V. C.

Summer Nuclear Station. The Standard 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 licensees 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 defines Effective Dose Equivalent (EDE or E) as the sum of the products of the dose equivalent to each tissue (T) and the weighting factors (T) applicable to each of the body organs or tissues that are irradiated (E = TTT ). 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.

For the purposes of implementing workplace controls, and due to the difference in dosimetry methods, 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 total effective dose equivalent TEDE. Several dose limits (such as those in 20.1201(a)(1)(i) and 20.1301(a)) and other requirements 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 effective dose equivalent (for internal exposures). The committed effective dose equivalent 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 (DDE), worn on the whole body, provides a reasonably accurate estimate of the EDE from external exposures (EDEex). 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 DDE, 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 DDE 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 EDEex in place of DDE for demonstrating compliance with the TEDE requirements in 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 EDEex 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 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.

Fundamental to the ANSI/HPS 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 EDEex is not underestimated.

To ensure that the estimates of EDEex 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 some exposure situations, one dosimeter may be provided for a combined thorax-abdomen compartment. In those cases, a combined weighting factor of 0.88 will be applied to the dosimeter results, consistent with ANSI/HPS N13.41.

4.0 CONCLUSION

S The NRC staff concludes that the licensees commitments to dose measurement using the multiple dosimetry method to determine EDEex 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 Contributors: R. Pedersen, NRR Date: March 14, 2008

Virgil C. Summer Nuclear Station cc:

Mr. R. J. White Nuclear CoordinatorS.C. Public Service Authority c/o Virgil C. Summer Nuclear StationPost Office Box 88, Mail Code 802 Jenkinsville, SC 29065 Resident Inspector/Summer NPS c/o U.S. Nuclear Regulatory Commission 576 Stairway Road Jenkinsville, SC 29065 Chairman, Fairfield County Council Drawer 60 Winnsboro, SC 29180 Mr. Henry Porter, Assistant Director Division of Waste Management Bureau of Land & Waste Management Dept. of Health & Environmental Control 2600 Bull Street Columbia, SC 29201 Mr. Thomas D. Gatlin, General Manager Nuclear Plant Operations South Carolina Electric & Gas Company Virgil C. Summer Nuclear Station Post Office Box 88, Mail Code 300 Jenkinsville, SC 29065 Mr. Bruce L. Thompson, Manager Nuclear Licensing South Carolina Electric & Gas Company Virgil C. Summer Nuclear Station Post Office Box 88, Mail Code 830 Jenkinsville, SC 29065 Ms. Kathryn M. Sutton Morgan, Lewis & Bockius LLP 111 Pennsylvania Avenue, NW.

Washington, DC 20004