WO 07-0013, Operating Corporation, Application to Use Weighting Factors for External Exposure

Operating Corporation, Application to Use Weighting Factors for External Exposure

ML071790404
Person / Time
Site:	Wolf Creek
Issue date:	06/22/2007
From:	Hedges S Wolf Creek
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
WO 07-0013
Download: ML071790404 (7)

Text

W#LF CREEK NUCLEAR OPERATING CORPORATION Stephen E. Hedges June 22, 2007 Vice President Operations and Plant Manager WO 07-0013 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Subject:

Docket No. 50-482: Application to Use Weighting Factors for External Exposure Gentlemen:

Pursuant to 10 CFR 20.1003, "Weighting factor WT," Wolf Creek Nuclear Operating Corporation (WCNOC) hereby requests approval to use weighting factors provided in the American National Standard Institute (ANSI) HPS N13.41-1997 (the Standard) for external.

radiation exposures when demonstrating compliance with total effective dose equivalent (TEDE), based on requirements in Part 20 to Title 10 of the Code of Federal Regulations (10 CFR).

As described in Attachment I, use of the weighting factors would improve assessment of occupational dose to individuals from exposure to highly non-uniform radiation fields. The technical basis for this application is the consensus technical standard approved the American National Standards Institute- Accredited HPS N13 Committee. The Standard is practical and consistent with the organ or tissue weighting factors in 10 CFR 20.1003.

WCNOC requests approval of this proposed amendment by March 3, 2008, i.e., prior to Refueling Outage 16, which is scheduled to start in March 2008. Approval of this request is not required to conduct the outage or to restart the unit following the outage. Once approved, the request will be implemented within 90 days of approval.

P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNET

WO 07-0013 Page 2 Attachment II provides a list of commitments from this application. If you have any questions concerning this matter, please contact me at (620) 364-4190, or Mr. Kevin Moles at (620) 364-4126.

Sincerely, .

E. Hedges SEH/rlt Attachment cc: J. N. Donohew (NRC), w/a V. G. Gaddy (NRC), w/a B. S. Mallett (NRC), w/a Senior Resident Inspector (NRC), w/a

Attachment I to WO 07-0013 Page 1 of 4 Application to Use Weighting Factors for. External Exposure

1.0 INTRODUCTION

1.1 PURPOSE Pursuant to 10 CFR 20.1003, "Weighting factor WT," Wolf Creek Nuclear Operating Corporation (WCNOC) hereby requests approval to use weighting factors provided in the American National Standard Institute (ANSI) HPS N13.41-1997 (the Standard) for external radiation exposures when demonstrating compliance with total effective dose equivalent (TEDE), based on requirements in Part 20 to Title 10 of the Code of Federal Regulations (10 CFR).

Specifically, WCNOC requests approval to calculate the external dose quantity effective dose equivalent (EDE) using the compartments, compartment factors, and method of summation specified in ANSI/HPS N13.41-1997, "Criteria for Performing Multiple Dosimetry," approved December 1996. The assigned EDE is the sum of each dosimeter measurement modified by its appropriate weighting factor. EDE will be used in place of deep dose equivalent (DDE) in the calculation of total effective dose equivalent (TEDE).

This request does not seek approval to use Section 4 "Criteria for When to Use Multiple Dosimeters," or Section 5.5, "Alternatives to the Use of Multiple Dosimeters" of the Standard.

1.2 REGULATORY EVALUATION

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 its 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 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). Therefore, the ICRP 26 recommendations are based on controlling the sum of the risk weighted doses to selected organs.

Effective dose equivalent (EDE or HE) is defined in 10 CFR 20.1003 as "the sum of the products of the dose equivalent to the organ or tissue (HT) and the weighting factors (WT) applicable to each of the body organs or tissues that are irradiated (HE = Y-WTHT)."

For the purposes of implementing workplace controls, and due to the difference in dosimetry, 10 CFR Part 20 breaks this EDE into two components: (1) dose resulting from radioactive sources internal to the body, and (2) dose resulting from sources external to the body. Dose limits and other requirements in Part 20 are based on the sum of these external and internal exposures. For radioactive material taken into the body, the occupational dose limit is based on the resulting dose equivalent integrated over 50 years, or committed effective dose equivalent (CEDE).

WO 07-0013 Page 2 of 4 The TEDE is defined in 10 CFR 20.1003 as the "sum of the deep-dose equivalent (for external exposures) and the committed effective dose equivalent (for internal exposures)."

TEDE = deep-dose equivalent (DDE) + ZWTHT, 50 (CEDE)

The organ WT 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. However, measuring the dose to the various organs and tissues with a dosimeter worn outside the body presents some practical difficulties.

If the body is irradiated uniformly, the external component of TEDE can be determined with a single DDE measurement on any part of the whole body. This conservative approach to determining TEDE can be overly conservative for extremely non-uniform-irradiations (i.e., when only a small portion of the whole body is irradiated). As discussed in NRC Regulatory Issue Summaries 2002-06, "Evaluating Occupational Dose for Individuals Exposed to NRC-Licensed Material and Medical X-Rays," 2003-04, "Use of the Effective Dose Equivalent in Place of the Deep Dose Equivalent in Dose Assessments," and 2004-01, "Method for Estimating Effective Dose Equivalent from External Radiation Sources Using Two Dosimeters," the NRC has approved several methods for determining external EDE (EDEex), and has encouraged the use of EDEex, in place of DDE for demonstrating compliance with the TEDE requirements in 10 CFR Part 20.

To ensure a conservative determination of TEDE, 10 CFR 20.1201(c) requires that the DDE component be determined from the part of the whole body receiving the highest exposure.

Thus, if the body is not irradiated uniformly, a single dose measurement cannot determine the dose to the various organs and tissues for an accurate determination of the EDEex. Footnote 2 to the "Organ Dose Weighting Factors" table in 10 CFR 20.1003 states that "for the purpose of weighting the external whole body dose (for adding to the internal dose), a single weighting factor, of WT = 1.0, has been specified. The use of other weighting factors for external exposure will be approved on a case-by-case basis until such time as specific guidance is issued." The above standard, ANSI/HPS N13.41, provides weighting factors that can be utilized when multiple dosimeters are used to measure the external dose received by an individual.

2.0 TECHNICAL JUSTIFICATION 2.1 IMPROVED ASSESSMENT OF DOSE In uniform radiation fields, the dosimeter used to measure whole body dose is typically worn on the chest. The dosimeter measures radiation exposure using an operational dose quantity called DDE.

When the radiation field is highly non-uniform, either the chest dosimeter is moved to the part of the whole body expected to receive the highest dose or additional dosimeters are worn so that the highest whole body dose can be measured.

Difficulties arise because the annual occupational dose limit is based on the stochastic risk from whole body exposure, which is related to the dose quantity EDE. While the use of DDE as a surrogate quantity to approximate EDE works well in uniform radiation fields, in highly non-

WO 07-0013 Page 3 of 4 uniform radiation fields, a more accurate estimate of EDE is needed to improve the assessment of occupational dose.

2.2 COMPARTMENT FACTORS ANSI/HPS N13.41 provides a method for estimating EDE, based on using multiple dosimeters at specific areas of the body. The whole body is divided into seven areas called "compartments." Each compartment, or composite compartment, is monitored separately. The results of the dose measurements for each compartment are weighted with an associated compartment factor." A compartment factor "relates the fractional risk to the organs underlying the measurement location to the total risk from uniform irradiation of the whole body.." The resulting weighted doses are then summed to determine the EDEex, for the whole body.

ANSI/HPS N13.41, Appendix A describes how the 10 CFR 20 organ or tissue weighting factors are apportioned to each compartment based on the associated underlying organs and tissues.

The resulting compartment factors used to calculate EDEex, are listed below:

ANSI/HPS N13.41 COMPARTMENT FACTORS Compartment Name Compartment Factor Head and neck 0.10 Thorax, above the diaphragm 0.38 Abdomen, including the pelvis 0.50 Upper right arm 0.005 Upper left arm 0.005 Right thigh 0.005 Left thigh 0.005 2.3 DOSIMETER SELECTION AND PLACEMENT NRC Inspection Procedure 71121, "Occupational Radiation Safety," Attachment 71121.01, "Access Control to Radiologically Significant Areas," dated 03/06/02, Section 03.04(c),

"Dosimeter selection and placement criteria," provides suitable criteria for assuring compliance with Part 20.1201(c). These criteria provide for monitoring the part of the body expected to receive the highest dose.

WCNOC will monitor the part of the whole body within each compartment (and/or composite compartment) that receives the highest dose. WCNOC procedure RPP 03-106, "Use of Special Dosimetry," provides guidance for determining dosimeter selection and placement and will be revised consistent with that found in NRC Inspection Procedure Attachment 71121.01, dated 03/06/02. WCNOC procedure RPP 03-0405, "Exposure History Files," provides guidance for tracking and reporting of individual's radiation exposure and will be revised such that the EDEex (when used) will be reported in place of the DDE, as discussed in NRC. Regulatory Issue Summary 2004-01.

WO 07-0013 Page 4 of 4 Consistent with WCNOC's current practice, a single chest dosimeter will measure the dose to both the thorax and abdomen compartments. The combined compartments will be called the chest compartment.

National Voluntary Laboratory Accreditation Program (NVLAP) accredited dosimeters will be worn at the same whole body locations after the application is approved as they are today.

Because we will continue to monitor the part of the body expected to receive the highest dose, the dosimeter orientation toward the source will not change. Therefore, there are no new challenges to the dosimeter's angular response characteristics resulting from approval of this application.

2.4 DOSE ASSIGNMENT Based on the NRC's approval of this request, WCNOC will account for dose consistent with the guidance of the standard as follows:

The DDE for each compartment will be determined from dosimeters worn at that location.

When no dosimeter is worn at a particular compartment, the DDE will be determined from the dosimeter positioned where the exposure is judged to be similar. The assigned EDE will be the sum of each DDE measurement multiplied by its appropriate compartment factor.

The assigned lens dose equivalent (LDE) will be the higher of the head or chest dosimeters. The assigned shallow dose equivalent (SDE) will be the highest of any whole body dosimeter.

2.5 PRECEDENCE The NRC approved a similar change for the Entergy Operations, Inc. fleet (Arkansas Nuclear One, Unit 1 and Unit 2, James A. Fitzpatrick Nuclear Power Plant, Grand Gulf Nuclear Station, Unit 1, Indian Point Nuclear Generating Units Nos. 2 and 3, Pilgrim Nuclear Power Station, River Bend Station, Unit 1, Vermont Yankee Nuclear Power Station, and Waterford Steam Electric Station, Unit 3) by letter dated October 2, 2006. Additionally, a similar change was approved for Southern California Edison Company's San Onofre Nuclear Generating Station by letter dated May 10, 2005.

2.6 CONCLUSION

Accurate assessment of occupational dose from external sources of radiation in highly non-uniform radiation fields requires a method for assessing EDE. Use of the proposed weighting factors will improve the accuracy of WCNOC's assessment of occupational dose.

WCNOC requests approval to assess EDE based on the consensus technical standard, ANSI/HPS N13.41. This standard was approved by the American National Standards Institute -

Accredited HPS N13 Committee on 20 June 1996. At the time of balloting, the HPS N13 Committee membership included representatives from the NRC and the National Council on Radiation Protection and Measurements.

The use of multiple dosimeters to monitor the part of the whole body expected to receive the highest dose will utilize criteria for dosimeter selection and placement consistent with current NRC inspection procedures.

Attachment II to WO 07-0013 Page 1 of 1 LIST OF COMMITMENTS The following table identifies those actions committed to by Wolf Creek Nuclear Operating Corporation in this document. Any other statements in this letter are provided for information purposes and are not considered regulatory commitments. Please direct questions regarding these commitments to Mr. Kevin Moles, Manager Regulatory Affairs at Wolf Creek Generating Station, (620) 364-4126.

REGULATORY COMMITMENT DUE DATE WCNOC will monitor the part of the whole body within each Within 90 days of compartment (and/or composite compartment) that receives the approval highest dose. WCNOC procedure, RPP 03-106, "Use of Special Dosimetry," provides guidance for determining dosimeter selection and placement and will be revised consistent with that found in NRC Inspection Procedure Attachment 71121.01, dated 03/06/02.

WCNOC procedure RPP 03-0405, "Exposure History Files," Within 90 days of provides guidance for tracking and reporting of individual's approval radiation exposure and will be revised such that the EDEex (when used) will be reported in place of the DDE, as discussed in NRC Regulatory Issue Summary 2004-01.

Based on the NRC's approval of this request, WCNOC will Within 90 days of account for dose consistent with the guidance of the standard as approval follows:

The DDE for each compartment will be determined from dosimeters worn at that location. When no dosimeter is worn at a particular compartment, the DDE will be determined from the dosimeter positioned where the exposure is judged to be similar. The assigned EDE will be the sum of each DDE measurement multiplied by its appropriate compartment factor.

The assigned lens dose equivalent (LDE) will be the higher of the head or chest dosimeters. The assigned shallow dose equivalent (SDE) will be the highest of any whole body dosimeter.