RIS 2004-01, Withdrawn NRC Regulatory Issue Summary 2004-001: Method for Estimating Effective Dose Equivalent from External Radiation Sources Using Two Dosimeters
| ML040420042 | |
| Person / Time | |
|---|---|
| Issue date: | 02/17/2004 |
| From: | Beckner W D, Miller C L NRC/NMSS/IMNS, NRC/NRR/DIPM/IROB |
| To: | |
| Pederson R, NRR/DIPM, 415-3162 | |
| References | |
| RIS-04-001 | |
| Download: ML040420042 (9) | |
Withdrawn NRC Regulatory Issue Summary 2004-01, "Method of Estimating Effective Does Equivalent from External Radiation Sources Using Two Dosimeters," dated February 17, 2004, has been withdrawn. ADAMS Accession Number: ML040420042 See Federal Register notice dated October 25, 2016 81 FR 73448 UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, DC 20555-0001February 17, 2004NRC REGULATORY ISSUE SUMMARY 2004-01METHOD FOR ESTIMATING EFFECTIVE DOSE EQUIVALENT FROM EXTERNAL RADIATION SOURCES USING TWO DOSIMETERS
ADDRESSEES
All U.S. Nuclear Regulatory Commission (NRC) licensees.
INTENT
NRC is issuing this regulatory issue summary (RIS) to provide guidance on an approved two-dosimeter monitoring method for estimating effective dose equivalent (EDE) from external radiation exposures. This EDE can be used instead of the deep dose equivalent (DDE) in complying with certain NRC regulatory requirements. This RIS requires no action or written response on the part of an addressee.
BACKGROUND
Total effective dose equivalent (TEDE) is used in 10 CFR Part 20 to specify dose limits foroccupationally exposed workers and for members of the public. Other requirements (in Part 20
and other parts of NRC's regulations), such as the criteria for license termination, are also specified in terms of the TEDE. Since EDE cannot be directly measured, Part 20 defines TEDE
as "the sum of the deep-dose equivalent (for external exposures) and the committed effective dose equivalent (for internal exposures)." Part 20 goes on to specify that this DDE be measured at the part of the whole body with the highest exposure. This DDE can be directly measured with available dosimeters and, in most exposure situations, provides a reasonable, conservative, and often the best estimate for EDE from external sources (EDEex). However, innonuniform exposure situations, such as from a directional source, DDE measured at the part of the whole body with the highest exposure can be an overly conservative estimate.The NRC recently published RIS 2003-04 to encourage licensees to use the EDEex fordetermining TEDE whenever the dose from external sources is calculated instead of measured with personal dosimeters. The RIS discusses the limitations on, and the regulatory basis for, substituting the EDEex for DDE in determining compliance with TEDE-based regulatoryrequirements. Estimating EDEex from dosimeter readings is very dependent on exposuregeometry. Therefore, RIS 2003-04 noted that methods for estimating TEDE from an EDEex determined from dosimeter readings must be approved by the NRC. RIS 2003-04 also noted that NRC approved the use of a two-dosimeter method for estimating effective dose equivalent at Entergy sites (Reference 1). This RIS describes the exposure situations in which NRC would regard the use of a monitoringmethod to estimate EDEex as appropriate and acceptable for estimating TEDE. This RIS doesnot affect the definition of other non-TEDE limits or criteria in Part 20.
SUMMARY OF ISSUE
SUse of Effective Dose EquivalentThe NRC has approved a method for estimating EDEex from external photon exposuresituations. The guidance in this RIS is based on the review and approval of the exemption for Entergy (Reference 1). This method uses two dosimeter readings and is based on research conducted by the ElectricPower Research Institute (EPRI). The EPRI work (References 2, 3, and 4) indicates that a single dosimeter, calibrated to read DDE and worn on the chest, provides a reasonably accurate estimate of EDEex when the individual is exposed to a number of randomly distributedradiation sources during the monitoring period. This is consistent with current allowable dosimetry practices and requires no special approval. However, for nonuniform exposures, such as from directional radiation fields or point sources, EDEex can be estimated from areading of a dosimeter worn on the front (Rfront) of the trunk of the body, combined with thereading of a dosimeter worn on the back (Rback) of the trunk of the body. EPRI gives two algorithms for combining the dosimeter results:
1.Mean Method (not approved for use at this time)The first algorithm is a simple, unweighted, average (MEAN) of the two dosimeterreadings. The MEAN is equal to 1/2 (Rfront + Rback).The EPRI technical reports state that the nonweighted average does not always give aconservative result. Since no method is provided to identify when the simple average gives nonconservative results, this algorithm is not approved for use at this time.2.Weighted MethodThe second algorithm, which was the subject of the Entergy exemption, is a weightedaverage algorithm such thatEDEex = 1/2 (Hi + MEAN)where Hi is the higher of Rfront or Rback . A mathematically simpler form of this weighted algorithm isEDEex = 3/4 Hi + 1/4 Lo where Hi is the higher of Rfront or Rback and Lo is the lower of Rfront or Rback. The data presented in the EPRI technical reports (references 1 and 2) indicate that thisweighted two-dosimeter algorithm provides a reasonably conservative estimate of EDEex. Therefore, only the weighted two-dosimeter algorithm is approved for use at this time forexposures in a nonuniform field. An exemption from Part 20 is not needed if the guidance in this RIS is followed fordetermining external exposures. Footnote 2 in the Organ Dose Weighting Factors table in
10 CFR 20.1003 permits the use of weighting factors to determine external exposures without case-by-case approvals when specific NRC guidance has been issued. This RIS constitutes such guidance for using the above weighted method for determining the external exposure from direct dosimeter measurements. When using this two dosimeter method, TEDE is the sum of the EDEex (for external exposures) and the committed effective dose equivalent (for internalexposures). The requirement in 10 CFR 20.1201(c) that the assigned DDE be measured at the highest exposed part of the whole body, does not apply when EDEex is used in place of DDE todemonstrate compliance with TEDE based requirements.The use of this two-dosimeter method may not eliminate the current practice of monitoringwhole-body exposure with multiple dosimeters to determine the highest exposed part of the whole body. It should be noted that 10 CFR Part 20.1201(a) and (c) still require doses to be measured at specific body locations for demonstrating compliance with the non-TEDE dose limits (i.e., dose to the lens of the eye, skin of the whole body and extremities, or the total organ dose). Licensees will, most likely, need to provide additional dosimeters if monitoring is required by 10 CFR 20.1502, to demonstrate compliance with any of these non-TEDE dose limits. See Regulatory Guide 8.34 for guidance on meeting the monitoring requirements of
10 CFR 20.1502.Additional Issues and LimitationsLicensees may use this weighted two-dosimeter method for determining EDEex, and estimatingTEDE, from external photon exposures without applying for further approval from the NRC,
subject to the following limitations:1.Partial-body irradiations (i.e., exposure geometries that preferentially shield thedosimeters) could bias the EPRI method results in the nonconservative direction.
Licensees must ensure that dosimeters are worn so that at least one of the two dosimeters "sees" the major source, or sources, of radiation (one dosimeter will normallybe shielded from a source by the body). In other words, the radiological work will be conducted and the dosimeters worn in such a way 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.2.This method for estimating EDEex from dosimeter readings is not valid for exposuresituations where the individual is immersed in a shielding material (i.e., diving operations). Large dose-rate gradients resulting from such immersions over the space occupied by the body can bias the two-dosimeter results.3.Only dosimeters that have demonstrated angular response characteristics at least asgood as those specified in Reference 5 are to be used. If the dosimeter's responsedecreases more rapidly than EDEex, as the angle of incident radiation increases, theresulting EDEex estimate will be biased in the nonconservative direction. .This method for estimating EDEex from two-dosimeter readings is not applicable toexposure situations where the sources of radiation are nearer than 12 inches (30 cm)
from the surface of the body. This is the closest distance that the two-dosimeter algorithm has been demonstrated to provide conservative results for discrete (point)
radiation sources. 5.The use of monitoring methods for estimating EDEex from exposure to point sources(i.e., hot particles) on, or near the surface of the body is outside the scope of this approval. Tables 5 though 7 in Reference 3 provide some calculated EDEex valuesresulting from exposure to point sources in contact with the torso of the body. However, the information provided in these tables does not bound all of the pertinent point source exposure situations. Licensees using the weighted methodology need to maintain sufficient records to demonstratethat the above limitations were met.CONCLUSIONSThe weighted two-dosimeter algorithm described in this RIS provides an acceptablyconservative estimate of EDEex. The TEDE based on EDEex using this algorithm in accordancewith its associated limitations is acceptable.When recording or reporting doses in situations in which the EDEex is assessed instead of theDDE, the value of the EDEex is entered in place of the DDE in recording or reporting forms suchas NRC Forms 4 or 5.REFERENCES1.Exemption from the Requirements of 10 CFR Part 20, Section 20.1003 Definition ofTotal Effective Dose Equivalent issued to 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 , 67 FR 58826 (September 18, 2002) (ML022550559).2. EPRI Technical Report TR-101909, Volume 1, February 1993.
3.EPRI Technical Report TR-101909, Volume 2, June 1995.
4.EPRI Implementation Guide TR-109446, September 1998.
5.Xu, X. G.; Reese, W. D.; and Poston, J. W. , "A Study of the Angular DependenceProblem In Effective Dose Equivalent Assessment," Health Physics, Volume 68., No. 2,February 1995, pp. 214-224.
BACKFIT DISCUSSION
This RIS does not require any action or written response or require any modification to plantstructures, systems, components, or design; therefore, the staff did not perform a backfit analysis.FEDERAL REGISTER NOTICEA notice of opportunity for public comment was published in the Federal Register on July 24,2003 (Vol. 68, No. 142, pp. 43769-43771).
PAPERWORK REDUCTION ACT STATEMENT
This RIS does not request any information collection.This RIS requires no action or written response on the part of an addressee.
If you have any questions about this RIS, please contact the persons listed below or theappropriate Office of Nuclear Reactor Regulation project manager. /RA//RA/Charles L. Miller, DirectorWilliam D. Beckner, Chief Division of Industrial andReactor Operations Branch Medical Nuclear SafetyDivision of Inspection Program Management Office of Nuclear Material SafetyOffice of Nuclear Reactor Regulation and SafeguardsTechnical Contacts:Roger Pedersen, NRRSami Sherbini, NMSS301-415-3162301-415-7853 E-mail: rlp1@nrc.govE-mail: sxs2@nrc.govAttachment: List of Recently Issued NRC Regulatory Issue Summaries
BACKFIT DISCUSSION
This RIS does not require any action or written response or require any modification to plantstructures, systems, components, or design; therefore, the staff did not perform a backfit analysis.FEDERAL REGISTER NOTICEA notice of opportunity for public comment was published in the Federal Register on July 24,2003 (Vol. 68, No. 142, pp. 43769-43771).
PAPERWORK REDUCTION ACT STATEMENT
This RIS does not request any information collection.This RIS requires no action or written response on the part of an addressee.
If you have any questions about this RIS, please contact the persons listed below or theappropriate Office of Nuclear Reactor Regulation project manager. /RA//RA/Charles L. Miller, DirectorWilliam D. Beckner, Chief Division of Industrial andReactor Operations Branch Medical Nuclear SafetyDivision of Inspection Program Management Office of Nuclear Material SafetyOffice of Nuclear Reactor Regulation and SafeguardsTechnical Contacts:Roger Pedersen, NRRSami Sherbini, NMSS301-415-3162301-415-7853 E-mail: rlp1@nrc.govE-mail: sxs2@nrc.govAttachment: List of Recently Issued NRC Regulatory Issue SummariesDISTRIBUTION:ADAMS
RIS File*See previous concurrenceDOCUMENT NAME: C:\ORPCheckout\FileNET\ML040420042.wpdOFFICEOES:IROB:DIPMTech EditorIMNS:NMSSIMNS:MNSSIEHB:DIPMIOLB:DIPMNAMECDPetronePKleene*SSherbini*PKHolohan*RLPedersen*EWeiss*DATE / /12/19/200301/21/2004 / /200401/14/200401/14/2004OFFICEC:IQMB:DIPMOGCD:NMSSSC:OES:IROB:DIPMC:IROB:DIPMNAMETRQuay*CLMillerTReisWDBecknerDATE01/21/200402/04/2004 / /200402/11/200402/17/2004OFFICIAL RECORD COPY
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