ML043630036
| ML043630036 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/20/2004 |
| From: | Scherer A Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML043630036 (6) | |
Text
SOUTHERN CALIFORNIA A. Edward Scherer EDISON Manager of Nuclear Regulatory Affairs An EDISON INTFR.ATIONALD Company December 20, 2004 U.S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555-0001
Subject:
Docket Nos. 50-361, 50-362 and 50-206 Application to Use Weighting Factors for External Exposure
Dear Sir or Madam:
Pursuant to 10 CFR Part 20.1003, 'Weighting factor Wr," Southern California Edison (SCE) is requesting approval to use weighting factors for calculating external whole body dose. The application is provided as an enclosure to this letter.
Specifically, SCE requests approval to apply the weighting factors specified in the consensus technical standard, American National Standards Institute, HPS N13.41-1997, "Criteria for Performing Multiple Dosimetry" to assign Total Effective Dose Equivalent from external sources of radiation.
As described in the application, approval 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 by the American National Standards Institute - Accredited HPS N1 3 Committee. The standard is practical and consistent with the organ or tissue weighting factors in 10 CFR Part 20.1003.
Barb P.O. Box 128 San Clemente, CA 92674-0128 949-368-7501 Fax 949-368-7575
Document Control Desk December 20, 2004 If you have any questions, please contact Mike Russell at (949) 368-7638.
Sincerely,
Enclosure:
Application to Use Weighting Factors for External Exposure cc: w/enclosure B. S. Mallett, Regional Administrator, NRC Region IV D. B. Spitzberg, NRC Region IV, San Onofre Unit 1 M. P. Shannon, NRC Region IV,San Onofre Units 2 & 3 B. M. Pham, NRC Project Manager, San Onofre Units 2, and 3 J. C. Shepherd, NRC Project Manager, San Onofre Unit I C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 and 3 A. T. Gody, Chief, Operations Section, NRC Region IV
ENCLOSURE APPLICATION TO USE WEIGHTING FACTORS FOR EXTERNAL EXPOSURE
1.0 INTRODUCTION
........................................ .1 1.1 PURPOSE ......................................... 1
1.2 REGULATORY EVALUATION
......................................... 1 2.0 TECHNICAL JUSTIFICATION ......................................... 1 2.1 IMPROVED ASSESSMENT OF DOSE ......................................... 1 2.2 COMPARTMENT FACTORS ......................................... 2 2.3 CHEST COMPARTMENT ......................................... 2 2.4 DOSIMETER SELECTION AND PLACEMENT ......................................... 3 2.5 DOSE ASSIGNMENT ......................................... 3
2.6 CONCLUSION
......................................... 3
Application to Use Weighting Factors For External Exposure Page 1
1.0 INTRODUCTION
1.1 PURPOSE Pursuant to 10 CFR Part 20.1003, uWeighting factor WT," Southern California Edison (SCE) requests approval to use weighting factors for calculating external whole body dose.
Specifically, SCE requests approval to use weighting factors specified in HPS N13.41 (HPS N13.41-1997, "Criteria for Performing Multiple Dosimetry",
Approved December 1996. American National Standards Institute, Inc.) for assessing effective dose equivalent (EDE) based on direct measurement of external exposures using personnel dosimeters. The assigned EDE is the sum of each dosimeter measurement modified by its appropriate weighting factor.
1.2 REGULATORY EVALUATION
Dose limits in 10 CFR Part 20 are specified in the dose quantity total effective dose equivalent (TEDE). TEDE is defined in 20.1003 as the sum of the external dose quantity called deep dose equivalent (DDE) plus the internal dose quantity called committed effective dose equivalent.
Footnote 2, in the Organ Dose Weighting Factors' table in 10 CFR 20.1003, permits the use of weighting factors for external exposure with prior NRC approval. SCE seeks NRC approval to use weighting factors to calculate the external exposure quantity EDE and to use EDE in place of DDE in the calculation of TEDE.
2.0 TECHNICAL JUSTIFICATION 2.1 IMPROVED ASSESSMENT OF DOSE In uniform radiation fields, the dosimeter used to measure whole body dose is 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-uniform radiation fields, a more
a;.
Application to Use Weighting Factors for External Exposure Page 2 accurate estimate of EDE is needed to improve the assessment of occupational dose.
2.2 COMPARTMENT FACTORS HPS N13.41 provides a method for assessing EDE based on measurements of DDE at specific areas of the body called 'compartments" and applying appropriate weighting factors called 'compartment factors". 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."
HPS N13.41, Appendix A describes how the 10 CFR Part 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 EDE are listed below:
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 CHEST COMPARTMENT Consistent with SCE'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.
Application to Use Weighting Factors for External Exposure Page 3 2.4 DOSIMETER SELECTION AND PLACEMENT NRC Inspection Procedure 71121.01, 'Access Control To Radiologically Significant Areas" issue date 03/06/02, Section 03.04(c) uDosimeter selection and placement criteria," will be used to provide adequate criteria for monitoring the part of the body expected to receive the highest dose.
2.5 DOSE ASSIGNMENT The DDE for each compartment will be determined from dosimeters worn at that location. When no dosimeter is worn at a particular compartment, 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.
2.6 CONCLUSION
Accurate assessment of occupational dose from external sources of radiation in highly non-uniform radiation fields requires a method for assessing EDE. NRC approval of this application will improve the accuracy of licensee assessment of occupational dose.
SCE will assess EDE based on the consensus technical standard, 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 Commiftee membership included representatives from the Nuclear Regulatory Commission and the National Council on Radiation Protection and Measurements.
The HPS N13.41 consensus technical standard has previously been approved for use by the NRC for evaluating occupational dose to medical personnel wearing lead aprons in Regulatory Issue Summary 2002-06, 'Evaluation Occupational Dose for Individuals Exposed to NRC-Licensed Material and Medical X-Rays," dated April 16, 2002.
The proposed method will monitor the part of the whole body expected to receive the highest dose using the criteria for dosimeter selection and placement found in current NRC inspection procedures.