Regulatory Guide 8.14

Revison 1, Personnel Neutron Dosimeters.

ML13064A088
Person / Time
Issue date:	08/31/1977
From:	NRC/OSD, Office of Nuclear Regulatory Research
To:
References
RG-8.014, Rev 1
Download: ML13064A088 (3)

U.S. NUCLEAR REGULATORY COMMISSIONRevision IAugust 1977REGULATORY GUOIDEOFFICE OF STANDARDS DEVELOPMENTREGULATORY GUIDE 8.14PERSONNEL NEUTRON DOSIMETERSA. INTRODUCTIONSection 20.202, "Personnel Monitoring," of 10CFR Part 20, "Standards for Protection AgainstRadiation," requires that licensees supply personnelmonitoring equipment and require its use by specifiedindividuals. This guide provides guidance acceptableto the NRC staff on the use of personnel neutrondosimeters where exposure to neutrons occurs.B. DISCUSSIONThe American National Standards Institute hasapproved a standard entitled "Personnel NeutronDosimeters. (Neutron Energies Less than 20 MeV)"and designated ANSI N319-1976.' This standardgives performance criteria, use factors, and dosimetrysystem calibration criteria for neutron dosimetrysystems. Accuracy criteria are not included amongthe performance criteria, however.This guide supplements the standard by adding anaccuracy requirement. The guide also provides sub-stitutes for certain of the standard's performance re-quirements because data from a test performed by theBattelle Pacific Northwest Laboratory showed thatthe requirements of the standard could not be met byNTA film or thermoluminescence dosimeter systems.A copy of the Battelle data is available by writing tothe Occupational Health Standards Branch, Office ofStandards Development, U.S. Nuclear RegulatoryCommission, Washington, D.C. 20555.One problem in neutron dosimetry is that neutrondosimeters are less sensitive than gamma dosimeters.Section 20.202 of the NRC regulations requires per-sonnel monitoring if a worker is likely to receive a'Copies may be obtained from the American National StandardsInstitute, Inc., 1430 Broadway, New York, New York 10018.*Lines indicate substantive changes from previous issue.whole body dose of more than about 300 millirems ina quarter year. Many neutron dosimeters have dif-ficulty measuring neutron doses of this magnitude.The problem is even more severe in a mixed radiationfield where neutrons contribute only a portion of the300 millirems. Thus the regulations may require per-sonnel monitoring when the neutron dose is less than300 millirems in a quarter, but the standard only re-quires the dosimeters to detect 300 millirems perquarter (paragraph 4.1 of the standard). Thisproblem is discussed in regulatory position C.I.C. REGULATORY POSITIONANSI N319-1976, "Personnel Neutron Dosi-meters (Neutron Energies Less than 20 MeV),"'provides guidance acceptable to the NRC staff on theuse of personnel neutron dosimeters, as sup-plemented and modified below.1. When Neutron Dosimeters Should Be WornNeutron dosimeters should be worn whenever theneutron dose equivalent is likely to exceed 300 mremin a quarter (the minimum sensitivity required of aneutron dosimeter in paragraph 4.1 of the standard).If personnel monitoring is required by §20.202because of the total radiation exposure but theneutron dose equivalent is not likely to exceed 300mrem in a quarter, the following alternatives are ac-ceptable with regard to personnel neutron dosimetry:a. Using higher sensitivity dosimeters. The licenseemay use a dosimeter with a sensitivity greater thanthat required in the standard. Albedo neutrondosimeters generally are believed to be more sensitivethan required by the standard. Film may be accep-table if fading due to humidity can be controlled, ifthe neutron spectrum has a small proportion ofneutrons below the neutron energy threshold of thefilm (about 0.7 MeV), and if the tracks are countedon a large area of film.USNRC-REGULATORY GUIDES Comments shou!d be sent to the Secretary of the Commission, US. Nuclear Regs.latory Commission, Washington, D.C. 20555, Attention: Docketing and ServiceRegulatory Guides are issued to describe and make available to the public methods rranch.acceptable to the N RC staff of implementing specific Darts of the Commission'sreeulatio-s, to delineate techniques used by the staff in evaluating specific ,"roblemns The guides are issued in the following ton broad divisions:or Postut3ted accidents, or to provide guidance to applicants. Regulatory Guidesarc not subslitutes for regulations, and compliance with them is not required. 1. Power Reactors 6. ProductsMethods and soiullons diflerent from those set out in the nuides will be accept. 2. Research and Test Reactors 7. Transportationable if they provide a basis for the findings requisite to the isruance or continuance 3. Fuels and Materials Facilities 8. Occupational Healthof a permit or license by the Commission 4. Environmental end Siting 9. Antitrust Review5. Materials and Plant Protection 10. GeneralComments and suggestions for improvements in these guides ar. at all Requests for single copies of issued guides lwhich may be reoroduced) or for place-times; and guides will be revised, as appropriate, to accommodate cominents and rlent on an automatic dristribution fist tor single copies o! future guides in Specificto reflect new information or experience. This guide was revisad as a result of divisions should be made in writing to the US. Nuclear Regulatory Commission,substantive comment; receved from the Public and additional staff revyew. Washington. D.C. 20555, Attention: Director, Division of Document Contro b. Calculated neutron dose equivalent to supplementneutron dosimeter. A licensee may use a personnelneutron dosimeter but may substitute a calculatedneutron dose equivalent for the measured doseequivalent if the measured dose equivalent cannot bereliably determined because of the lack of sensitivityof the dosimeter. Calculated dose equivalents may bebased on measured neutron/gamma ratios or onneutron dose equivalents measured with portable orfixed monitoring instruments and known personneloccupancy times. More information on determiningneutron dose equivalents by neutron/gamma ratios isgiven in Regulatory Guide 8.4, "Direct-Reading andindirect-Reading Pocket Dosimeters."c. Calculated neutron dose equivalent in place ofneutron dosimeter. If the individual is not likely toreceive a neutron dose equivalent in excess of 100mrem in a quarter but wouid still have to have somesort of monitoring under §20.202 (e.g., gammamonitoring), a personnel neutron dosimeter may beomitted. The neutron dose equivalent should then beestimated by the methods in regulatory positionC.L.b above. This procedure is discussed in moredetail in regulatory position C.3 of Regulatory Guide8.4.d. Neutron dose equivalent much smaller than gam-ma dose equivalent. If the neutron whole body doseequivalent is not likely to exceed 10% of the gammaplus x-ray dose equivalent, neutron dosimeters maybe omitted and the neutron dose equivalent may beassumed equal to zero.e. Negligible neutron dose equivalent. If theneutron dose equivalent is not likely to exceed 30mrem per quarter, or 10 mrem per quarter for in-dividuals under 18 years of age, neutron dosimetersmay be omitted and the neutron dose equivalent as-sumed equal to zero. The determination that an in-dividual is not likely to receive a neutron doseequivalent of 30 mrem per quarter should not bebased on previous NTA film badge readings sinceNTA film is not suffficiently sensitive to detect thisdose equivalent rate.2. Performance RequirementsSection 4 of the standard contains -several perfor-mance requirements on the dosimetry system.Instead of paragraph 4.1 of the standard on lowerlimit of detection, the following should be used:"The lower limit of detection of the dosimetrysystem shall not exceed 300 mrem per quarter. Thequarterly lower limit of detection (LLD) in mrems atthe 95% confidence level is defined asLLD = 4.66/s Swhere N is the number of dosimetry exchange periodsin a quarter and S is the standard deviation of thenormal background in mrems for a single reading."(This definition of LLD was chosen to be consistentwith the NRC position previously stated in Tables 1and 3 of Regulatory Guide 4.8, "EnvironmentalTechnical Specifications for Nuclear Power Plants."The basis for the definition is given in USERDAreport HASL-300, p. D-08-01.)Instead of the 10% limit on the standard deviationin paragraph 4.4 of the standard on precision, a limitof 30% should be used.The following accuracy requirement should be ad-ded: "When exposed to an unmoderated californium-252 source; the average accuracy of a set of 10dosimeters exposed in the range from 100 mrems to 3rems should be +/-50%."The tests necessary to verify that the dosimetrysystem meets the requirements in the standard maybe performed by the licensee or by someone selectedby him. The tests may be performed on a system justonce to demonstrate that it can meet the require-ments of Section 4 of the standard.In the case of film, each different type of packagingshould be considered a different system to be testedseparately. Tests should also be repeated any timechanges are made in the dosimetry system (i.e.,processing the dosimeters differently). A licensee fol-lowing the recommendations of this guide shouldmaintain records to show that his neutron dosimetershave been tested and meet the perforrriance require-ments of Section 4 of the standard.3. Meeting the Fading Requirements of the Standard.To meet the fading requirements in paragraphs 5.3and 5.4 of the standard, the licensee should irradiatefour dosimeters with a neutron dose equivalent of atleast 0.5 rem. The dosimeters should then be storedfor an entire dosimeter exchange period at a humiditysimilar to that expected in normal use. Thedosimeters should then be read to verify that, on theaverage, they meet the fading criterion (paragraph 5.3of the standard). If humidity is a significant cause offading, the test should be performed during a periodof high humidity.4. Dosimetry System CalibrationSection 6 of the standard gives suggestions ondosimetry system calibration. Calibration ofdosimeter response may. be performed by the ex-posure of the dosimeter and a reference monitoringinstrument in the actual locations where significantneutron exposure occurs. The spherical (Hankins)"rem-meter," the Anderson-Braun rem counter, orother similar instruments may be -used as referencemonitoring instruments. These monitoring instruýments should be calibrated by sources whose calibra-tion is traceable to the National Bureau of Standards.I8. 14-2 Calibrations of dosimeter response may also beperformed by the dosimeter processor. The processorshould use a calibration factor applicable to the dosespectrum delivered to the individuals wearing thedosimeters. The calibration may be performed by thelicensee or by someone selected by him, and recordsdescribing the dosimeter calibration should be main-tained by the licensee. The dosimeter calibrationshould be repeated any time the licensee has reason tobelieve the neutron spectrum has changed and theprevious calibration might not be valid.5. Maintaining Body ContactAlbedo neutron systems usually require close bodycontact at all times during usage. Sizable errors canoccur if close body contact is not maintained. Albedoneutron dosimeters should have a means to maintainthis necessary close contact with the body.D. IMPLEMENTATIONThe purpose of this section is to provide informa-tion to applicants regarding the NRC staff's plans forusing this regulatory guide.Except in those cases in which the applicantproposes an acceptable alternative method for com-plying with §20.202 of the Commission's regulations,the method herein will be used in the evaluation ofsubmittals in connection with license applicationsdocketed after November 1, 1977.If an applicant wishes to use this regulatory guidein developing submittals for applications docketed onor before November 1, 1977, the pertinent portions ofthe application will be evaluated on the basis of thisguide.8.14-3