U.S. NUCLEAR REGULATORY COMMISSION Revision 1July 1 993

REGULATORY GUIDEOFFICE OF NUCLEAR REGULATORY RESEARCH

REGULATORY GUIDE 8.9(Draft was issued as DG-8009)

ACCEPTABLE CONCEPTS, MODELS, EQUATIONS, ANDASSUMPTIONS FOR A BIOASSAY PROGRAM

A. INTRODUCTION

Section 20.1204 of 10 CFR Part 20, "Standards

for Protection Against Radiation," requires that each

licensee, when required by 10 CFR 20.1502, take

suitable and timely measurements of quantities of

radionuclides in the body, quantities of radionuclides

excreted from the body, concentrations of radioactive

materials in the air in the work area, or any combina-

tion of such measurements as may be necessary for

detection and assessment of individual intakes of

radioactive material. Furthermore, 10 CFR 20.1204

(c) (1) allows for the use of specific information on

the physical and biochemical properties of the radio-

active material deposited in the body in determining

an individual's internal dose. Also, as stated in

10 CFR 20.1703(a)(3)(ii), if respiratory protection

equipment is used to limit intakes of airborne radio-

active material, the licensee's respiratory protection

program is to include bioassay measurements, as

appropriate, to evaluate actual intakes of airborne

activity.

Because of differences in physical properties and

metabolic processes, each individual's dose resulting

from an exposure is unique. In other words, the same

exposure to multiple individuals will cause different

doses to each individual. However, for the purpose of

demonstrating compliance with dose limits, standard

approaches for determining intake and calculating a

dose have been developed. For certain unusual cir-

cumstances, such as exposures at or near the limits,

special consideration may need to be given to the spe-

cifics of an individual's retention and excretion in de-

termining the intake. It is not the intent of this regula-

tory guide to constrain licensees from performing

more detailed analyses when the licensee determines

that the magnitude of the exposure warrants further

investigation.

This guide describes practical and consistent

methods acceptable to the NRC staff for estimating

intake of radionuclides using bioassay measurements.

Alternative methods acceptable to the NRC staff are

in ICRP Report No. 54, "Individual Monitoring for

Intake of Radionuclides by Workers: Design and In-

terpretation" (Ref. 1), and NCRP Report No. 87,

"Use of Bioassay Procedures for Assessment of Inter-

nal Radionuclide Deposition" (Ref. 2).

Any information collection activities mentioned

in this regulatory guide are contained as requirements

in 10 CFR Part 20, which provides the regulatory ba-

sis for this guide. The information collection require-

ments in 10 CFR Part 20 have been approved by the

Office of Management and Budget, Approval No.

3150-00 14.

USNRC REGULATORY GUIDES

Regulatory Guides are issued to describe and make available to the pub-

lic such information as methods acceptable to the NRC staff for imple-

menting specific parts of the Commission' s regulations, techniques

used by the staff in evaluating specific problems or postulated acci-

dents, and data needed by the NRC staff In its review of applications for

permits and licenses. Regulatory Guides are not substitutes for regula-

tions, and compliance with them is not required. Methods and solutions

different from those set out in the guides will be acceptable If they pro-

vide a basis for the findings requisite to the issuance or continuance of a

permit or license by the Commission.

This guide was issued after consideration of comments received from

the public. Comments and suggestions for improvements in these

guides are encouraged at all times, and guides will be revised, as ap-

propriate, to accommodate comments and to reflect new information or

experience.

Written comments may be submitted to the Regulatory PublicationsBranch, DFIPS, ADM, U.S. Nuclear Regulatory commission, Washing-ton, DC 20555.

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_ I ir

B. DISCUSSION

Bioassay measurements include the analysis of ra-dioactive material in body organs or in the wholebody (in vivo measurements) and in biological mate-rial excreted, eliminated, or otherwise removed fromthe body (in vitro measurements). The in vivo meas-urements are made using a whole body counter, thy-roid counter, lung counter, or other similar device.The in vitro measurements involve collection of urine,feces, or tissue samples that are measured directly, orafter radiochemical separation, by gamma spectrome-try, or by alpha or beta counting of the separated ra-dionuclide as appropriate.

ICRP Publication 30, "Limits for Intakes of Radi-onuclides by Workers" (with accompanying addenda)(Ref. 3), has been used by the NRC as the basis forits annual limits on intake (ALI) and derived air con-centrations (DAC) listed in Appendix B to§§ 20.1001 through 20.2401. Likewise, the modelingin ICRP-30 serves as the basis for interpreting thebioassay measurements in NUREG/CR-4884, "Inter-pretation of Bioassay Measurements" (Ref. 4). Sincethe issuance of ICRP-30 (Ref. 3), improvements inthe metabolic modeling for a few radionuclides haveresulted in dosimetric modeling equally acceptable tothe NRC staff. For example, a model developed byJones (Ref. 5) provides acceptable estimates of uri-nary fractional excretions of plutonium. Also, a trit-ium metabolic model developed by Johnson andDunford (Ref. 6) provides acceptable (and often im-proved) estimates of time-dependent tritium excre-tion. As additional research is conducted, it is ex-pected that refinements in the metabolic modelingwill further improve the methods available for corre-lating bioassay measurements to actual intake and theresultant dose to an individual.

Metabolic modeling, such as that presented inICRP-30 (Ref. 3) and ICRP-54 (Ref. 1), has beenused for evaluating bioassay measurements throughthe development of time-dependent values for thebodily retention or excretion (or both) of the ingestedor inhaled radioactive material. NUREG/CR-4884(Ref. 4) presents a comprehensive set of data on in-take retention and excretion fractions developedfrom these models. These data, and the accompany-ing description of the modeling and methods, provideuseful information for using bioassay measurements toestimate intake. In addition, ICRP-54 (Ref. 1) pre-sents metabolic models accompanied by data and fig-ures of bodily retention and excretion for many of theradionuclides of importance to NRC licensees.

ICRP-30 (Ref. 3) and ICRP-54 (Ref. 1) arebased on general considerations (i.e., standardchemical forms and standard man or woman meta-bolic modeling). Each individual's physiological char-acteristics and biochemical processes may be differ-

ent. In addition, the particulars of the exposure situ-ation, such as particle size distribution, will affect thelung compartment deposition fractions and the resul-tant biological clearances. For example, particleslarger than 20 gm AMAD1 will deposit mainly in thenaso-pharyngeal (N-P) region and tend to show bio-logical retention and excretion characteristics moretypical of an ingestion intake than of an inhalationintake of the default 1 gm AMAD. These character-istics are due to the fact that a large fraction of parti-cles deposited in the N-P region is cleared by theciliated epithelial cells to the throat and subsequentlyswallowed, thereby appearing to be an ingestion in-take. Fitting an individual's bioassay measurementdata for a particular exposure situation to the stan-dard modeling will, however, provide reasonably ac-curate estimates for most situations.

This guide contains methods for evaluating bioas-say data that will result in calculated intakes that areacceptable to the NRC staff for evaluating compliancewith the occupational dose limits of 10 CFR 20.1202.Examples of specific exposure situations and thephysical and biochemical processes considered in theassessment of the exposures are in Appendix A to thisguide. Additional information on bioassay measure-ments, interpretation of bioassay data, and bioassayprogram components can be found in ICRP-30 (Ref.3), ICRP-54 (Ref. 1), NCRP-87 (Ref. 2), andNUREG/CR-4884 (Ref. 4).

The following terms, which have not been de-fined in 10 CFR 20.1003, have been used in thisguide.

Evaluation Level-The level at which an intakeshould be evaluated beyond the initial bioassay meas-urement. The evaluation level is 0.02 times the an-nual limit on intake (ALI), which is equivalent to 40derived air concentration (DAC) hours.

Excretion Fraction-The fraction of the intakethat has been excreted by the body at time (t) follow-ing the intake.

Intake Retention Fraction-The fraction of theintake that is retained in the body at time (t) follow-ing the intake.

Investigation Level-The level at which an intakeshould be investigated. The investigation level is anyintake greater than or equal to 0. 1 times the annuallimit on intake (ALI).

C. REGULATORY POSITIONNOTE: The regulatory positions in this regulatory

guide supersede the information contained in NRC IEInformation Notice No. 82-18, "Assessment of In-takes of Radioactive Material by Workers."

'Activity Median Aerodynamic Diameter (AMAD): The di-ameter of a unit density sphere with the same terminal settlingvelocity in air as that of an aerosol particle whose activity isthe median for the entire aerosol.

8.9-2

1. AVAILABILITY OF BIOASSAY SERVICES

The purposes of bioassay measurements are toconfirm the adequacy of radiological controls and todetermine compliance with the occupational dose lim-its. Bioassay services should be available if the typesand quantities of radioactive material licensed for useat the facility could, under normal operational occur-rences, result in airborne levels in normally occupiedareas exceeding DACs. Provisions should be made forthe collection of appropriate samples, analysis of bio-assay samples, and evaluation of the results of theseanalyses to determine intakes.

2. FREQUENCY OF REQUIRED BIOASSAYMEASUREMENTS

Determining the appropriate frequency of routinebioassay measurements depends upon the exposurepotential and the physical and chemical characteris-tics of the radioactive material and the route of entryto the body. Elements that should be considered in-clude (1) the potential exposure of the individual, (2)the retention and excretion characteristics of the radi-onuclide, (3) the sensitivity of the measurement tech-nique, and (4) the acceptable uncertainty in the esti-mate of intake and committed dose equivalent. Bioas-say measurements used for demonstrating compliancewith the occupational dose limits should be conductedoften enough to identify and quantify potential expo-sures and resultant intakes that, during any year, arelikely to collectively exceed 0.1 times the ALL.2

Two separate categories of bioassay measure-ments further determine the frequency and scope ofmeasurements: routine measurements and specialmeasurements.

2.1 Routine Measurements

Routine measurements include baseline measure-ments, periodic measurements, and terminationmeasurements. These measurements should be con-ducted to confirm that appropriate controls exist andto assess dose.

2.1.1 Baseline Measurements

An individual's baseline measurement of radioac-tive material within the body should be conductedprior to initial work activities that involve exposure toradiation or radioactive materials, for which monitor-ing is required.

2.1.2 Periodic Measurements

In addition to the baseline measurements, peri-odic bioassay measurements should be performed.The frequency of periodic measurements should be

2The 10% ALI criterion is consistent with 10 CFR 20.1502(b),which requires licensees to monitor intakes and assess occu-pational doses for exposed individuals who are likely to ex-ceed 10% of the applicable limit (i.e., intakes likely to exceed0.1 ALI for adults).

determined on an a priori basis, considering the likelyexposure of the individual. In determining the work-er's likely exposure, consider such information as theworker's access, work practices, measured levels ofairborne radioactive material, and exposure time. Pe-riodic measurements should be made when the cumu-lative exposure to airborne radioactivity, since themost recent bioassay measurement, is > 0.02 ALI (40DAC hours). Noble gases and airborne particulateswith a radioactive half-life less than 2 hours should beexcluded from the evaluation since external exposureis generally controlling for these radionuclides.

As a minimum, periodic measurements should beconducted annually. Periodic measurements provideadditional information on any long-term accumula-tion and retention of radioactive material in the body,especially for exposures to concentrations of airborneradioactive material below monitoring thresholds.

2.1.3 Termination Measurements

When an individual is no longer subject to thebioassay program, because of termination of employ-ment or change in employment status, terminationbioassay measurement should be made, when practi-cable, to ensure that any unknown intakes are quan-tified (see Example 2 in Appendix A to this guide).

2.2 Special Monitoring

Because of uncertainty in the time of intakes andthe absence of other data related to the exposure(e.g., physical and chemical forms, exposure dura-tion), correlating positive results to actual intakes forroutine measurements can sometimes be difficult.Abnormal and inadvertent intakes from situationssuch as a failed respiratory protective device, inade-quate engineering controls, inadvertent ingestion,contamination of a wound, or skin absorption 3 shouldbe evaluated on a case-by-case basis. Circumstancesthat should be considered when determining whetherpotential intakes should be evaluated include:

* The presence of unusually high levels of facialand/or nasal contamination,

* Entry into airborne radioactivity areas withoutappropriate exposure controls,

* Operational events with a reasonable likelihoodthat a worker was exposed to unknown quanti-ties of airborne radioactive material (e.g., loss ofsystem or container integrity),

* Known or suspected incidents of a worker ingest-ing radioactive material,

* Incidents that result in contamination of woundsor other skin absorptions,

* Evidence of damage to or failure of a respiratoryprotective device.

3The skin absorption of airborne tritium has been included inthe determination of its ALI and DAC values for occupationalinhalation exposures in Appendix B to §§20.1001-20.2401.

8.9-3

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2.3 Estimating Intakes-Evaluation and Investi-gation Levels

Licensees should estimate the intake for any bio-assay measurement that indicates internally depositedradioactive material resulting from licensed activities.The scope of the evaluation should be commensuratewith the potential magnitude of the intake. For indi-vidual exposures with an estimate of intake less than0.02 ALI, minimum bioassay measurements are ade-quate to provide a reasonable approximation of in-take. Repeated follow-up measurements or additionalexposure data reviews are not necessary, provided areasonable estimate of the actual intake can be madebased on available data.4

2.3.1 Evaluation Level

For very small intakes, a single bioassay measure-ment is generally adequate to estimate intake. 5 Forintakes that represent a significant contribution todose, other available data should be evaluated. If in-itial bioassay measurements indicate that an intake isgreater than an evaluation level of 0.02 ALI, addi-tional available data, such as airborne measurementsor additional bioassay measurements, should be usedto obtain the best estimate of actual intake.

2.3.2 Investigation Level

For single intakes that are greater than 10% ofthe ALI, a thorough investigation of the exposureshould be made. Therefore, if a potential intake ex-ceeds an investigation level of 0.1 ALI, multiple bio-assay measurements and an evaluation of availableworkplace monitoring data should be conducted. Ifpractical, daily measurements should be made until apattern of bodily retention and excretion can be es-tablished. Such a determination is feasible after asfew as three measurements; however, physiologicallyrelated variations and uncertainties require that meas-urements be continued over a longer period of time insome cases. For potential intakes near or exceedingthe ALIs, the bioassay data evaluations should con-sider any additional data on the physical and chemi-cal characteristics and the exposed individual's physi-cal and biokinetic processes,

3. TYPE OF MEASUREMENTS

Characteristics such as mode of intake, uptake,and excretion and mode of radioactive decay shouldbe considered in selecting the most effective and reli-able types of measurements. For example, in vivolung or total body measurements shortly following ex-

4The purpose of this guidance is to describe the scope of thebioassay measurements that should be considered for assess-ing intakes. It is not intended to limit the types of reviews thatmay be warranted for assessing the overall significance of anintake.

5For radionuclides that are difficult to detect, such as alphaemitters, a single measurement may not be adequate to deter-mine intakes.

posure generally provide reliable estimates of intakesfor most gamma emitting radionuclides. In vitromeasurements should be used for radionuclides thatemit little or no gamma radiation. However, in vitrourine or fecal measurements for the first voiding fol-lowing exposure, while providing important informa-tion for assessing potential significance, do not gener-ally represent equilibrium conditions and therebyshould not be relied upon in evaluating actual intakes.ICRP Publication 54 (Ref. 1) and NCRP Report No.87 (Ref. 2) provide guidance acceptable to the NRCstaff for determining the types of bioassay measure-ments that should be made considering the physicaland biological characteristics of the radioactivematerial.

4. INTERPRETATION OF BIOASSAY MEAS-UREMENTS

The specific scope and depth of the evaluation ofbioassay measurements, as discussed in RegulatoryPosition 2.3, depends on the potential significance ofthe intake. The methods presented below are accept-able to the NRC staff for correlating bioassay meas-urements to estimates of intakes for the purpose ofdemonstrating compliance with the occupational doselimits of 10 CFR 20.1201.

4.1 Time of Exposure

Accurate estimation of intake from bioassaymeasurements is dependent upon knowledge of timeof intake. Generally, the time of intake is known con-sidering work activities and other monitoring data,such as air sample data. Therefore, the time of intakewill be known for all but unusual situations. When thetime of intake cannot be determined from monitoringdata, it can often be determined from informationprovided by the individual. When information is in-sufficient to determine the time of intake, it is accept-able to assume that the intake occurred at the mid-point of the time period since the last bioassay meas-urement. This initial assumption should be refined byusing any available information such as the individu-al's work schedule, facility operations data, historicalair monitoring data, and the effective half-life of theradionuclides detected (see Example 2 of Appen-dix A).

4.2 Acceptable Biokinetic Models

Determining a worker's intake from bioassaymeasurements involves comparing the measured bod-ily retention or excretion to a tabulated value. Themodels and methods used for evaluating bioassaymeasurements should provide a reasonable assess-ment of the worker's exposure. For intakes that are asmall fraction of the limit, greater inaccuracy in theestimate of intake can be accepted without significantimpact on the overall assessment of a worker's dose.However, for annual exposures for which monitoringis required by 10 CFR 20.1502(b), these methods

8.9-4

should not lead to significant underestimation or that computer codes are appropriate for use in their

overestimation of the actual intake. . particular circumstances.

Variations from predicted retention and excre-tion for specific individuals can be expected. Excre-tion of radionuclides may be influenced by the work-er's diet, health condition, age, level of physical andmetabolic activity, or physiological characteristics.The lung deposition and clearance of the inhaled ra-dionuclide, the particle size distribution,-and the timeof the excretion also influence the excretion rate ofradionuclides.

Important considerations for evaluating bioassaymeasurements include:

* Appropriate measurement technique (in vivo orin vitro) based on radionuclide decay character-istics (i.e., types of radiation emitted) andbiokinetic characteristics (i.e., systemic uptakeand retention and urine and fecal excretion frac-tions),

* The effects of diuretics or chelation to reducesystemic uptake and tQ increase excretion or ex-cretion rates,

* Representativeness of measurements such as24-hour or accumulated urine or fecal measure-ments,

* The appropriate lung clearance class (D, W, orY), if known (see definition of class in 10 CFR20.1003). If no information on the biological be-havior or chemical form is available, the mostrestrictive clearance class relevant for the par-ticular element should be assumed (i.e., thatclass that gives the lowest value of ALI),

* Particle size distribution,

* Chemical toxicity as in the case of uranium (see10 CFR 20.1201(e)).

The metabolic models in ICRP-30 and accompa-nying addenda (Ref. 3) and ICRP-54 (Ref. 1) pre-sent acceptable bases for estimating intake from bio-assay measurements. Other acceptable models are thetritium model developed by Johnson and Dunford(Ref. 6) and the plutonium urinary excretion modeldeveloped by Jones (Ref. 5).

The use of computer codes that apply these mod-els is also acceptable for evaluating bioassay measure-ments provided it can be demonstrated through docu-mented testing that the models and methods em-ployed provide results that are consistent with the ac-ceptable models. There are several commerciallyavailable computer codes for interpreting bioassaymeasurements; these codes may be used as long asthe software application is based on acceptable mod-els and provides results that correctly implement themodels. No specific computer codes are endorsed bythe NRC staff. Licensees are responsible for ensuring

4.3 Intake Retention and Excretion Fractionsfor Calculating Intakes

ICRP-54 (Ref. 1) presents urinary excretion andfecal excretion equations as a function of time follow-ing intake for a number of radionuclides. By differen-tiating these equations, intake retention functions canbe derived. The solution of these equations over arange of times allows the development of tabulatedintake retention and excretion fractions. The intakeretention fractions 6 (IRFs) contained in NUREG/CR-4884 (Ref. 4) were developed in this manner andrepresent an acceptable basis for correlating bioassaymeasurements to estimates of intake. To apply theuse of IRFs for calculating an individual's radionu-clide intake from a single bioassay measurement, di-vide the total activity in 24-hour urine, 24-hour feces,accumulated urine, or accumulated feces,7 or the ia-dionuclide content in the total body, systemic organs,lungs, nasal passages, or GI tract, by the appropriateIRF value in NUREG/CR-4884.

Equation 1 demonstrates this method:

I = A (t)IRF(t) Equation 1

where:

I = Estimate of intake with units thesame as A(t),

A (t) = Numerical value of the bioassaymeasurement obtained at time t (de-cay corrected to time of sampling forin vitro measurements) with appro-priate units (jiCi, Bq, or jig).

IRF(t) = Intake retention fraction correspond-ing to type of measurement for time tafter estimated time of intake,

4.3.1 Evaluating Spot Samples

If the total urine or feces is not collected for the24-hour period, the following equations may be usedto estimate the total activity excreted or eliminatedover the 24-hour period based on less frequent sam-pling (spot samples).

AAj = Ci E(ti-ti-1 )

Ai= AA, + AA 2, + ... AAj

Equation 2

Equation 3

6 For purposes of this guide and the application of the data fromNUREG/CR-4884, the parameter IRF denotes both intake re-tention fractions and intake excretion fractions.

7 The term "24-hour urine" means the total urine output col-lected over a 24-hour period, and the term "24-hour feces"means the total feces output collected over a 24-hour period."Accumulated urine" and "accumulated feces" mean the totaloutput since time of exposure.

8.9-5

_ L i - - i

where:

AAi = Activity or amount of radioactive ma-terial in sample i

i = The sequence number of the sample

CQ = The radionuclide concentration inurine (activity/liter) or feces (activity/gram) of sample i, decay corrected tothe time of sampling

E = Daily excretion rate (use measuredrates when available, or assume val-ues of 1.4 liters/day for urine and135 grams/day for feces for standardman or 1.0 liter/day for urine and110 grams/day for feces for standardwoman)

ti = The time (days) after intake thatsample i is collected

Ai = Total activity excreted or eliminatedup to time ti

This method is applicable only if spot samples arecollected with a frequency that is consistent with thesignificance of changes in the excretion rates. In gen-eral, spot samples should be collected frequentlyenough that there is no more than a 30% increase inthe IRFs between bioassay measurements. For exam-ple, if the IRF for accumulated urine increases at arate of 30% per day, spot samples should be collecteddaily. If the rate is 10% per day, collecting spot sam-ples once every 3 days would be adequate. Also, therapid clearance and excretion of inhaled particlesfrom the N-P region of the lung makes it importantthat at least one spot sample be collected within thefirst 24 hours after exposure. Otherwise, the reliabilityof using accumulated samples and excretion fractionsfor calculating intakes should be examined; calcula-tions based on spot samples correlated to 24-hoursamples may provide better estimates.

For spot samples used to estimate an equivalent24-hour sample, correcting for abnormal conditionsof high or low fluid intake or excessive loss of fluidsby perspiration may be warranted. NCRP-87 (Ref. 2)presents the following method based on a relationshipbetween the specific gravity (sp. gr.) of the sample tothe average specific gravity of urine (1.024 g/ml).

Logarithmic interpolation should be used for in-terpolating retention and excretion fractions (see Ex-ample 2 in Appendix A). For example, using theNUREG/CR-4884 (Ref. 4) data, an IRF value for 2.8days post-intake should be calculated by a logarith-mic interpolation between the 2-day and the 3-dayIRF values.

Examples of the application of intake retentionand excretion fractions based on the NUREG/CR-4884 data set are provided in Appendix A.

4.3.2 Evaluating Multiple Bioassay Meas-urements

When multiple bioassay measurements are made,a statistical evaluation of the data should be per-formed. Numerous statistical methods are availablefor evaluating multiple measurements, but the resultswill be no better than the reliability of the data set.Measurements that are suspect or known to be inac-curate should be excluded from the analysis. Addi-tional measurements should be used for obtaining anappropriate data set. For the evaluation of multiplemeasurements, NUREG/CR-4884 (Ref. 4) recom-mends the use of unweighted, minimized chi-squaredstatistics, assuming all variances are the same (i.e., aleast squares fit). This method is acceptable to theNRC staff; it is simple and straightforward for evaluat-ing multiple bioassay measurements. The equation isas follows:

1,__-= IRFi(t) x Ai(t)

2:j IRFi(t) 2Equation 5

Other statistical analyses of the data may providea better fit of the data, considering the particulars ofthe measurements. For example, a minimized chi-squared fit weighted by the inverse of the variancemay be used. Several methods are available for esti-mating the variance of measurements. One approach,applicable to radioactivity measurements, is to assumethat the variance is proportional to the value of themeasurement itself. Another is the assumption thatthe variance is proportional to the expected value(Ref. 7).

In selecting the statistical method to be used forevaluating multiple measurements, considerationshould be given to available information, particularlyobserved variability of the data and reliability of indi-vidual measurements. Other statistical methods areacceptable to the NRC staff provided it can be dem-onstrated that the results provide reasonable estimatesof intake.

corr. conc. = meas. conc.1.024 - I (g/ml)

meas. sp. gr. - 1 (g/ml)

Equation 4 4.4 Adjusting Intake Estimates for Multiple and

An alternative to this method is a correction Continuous Intakesbased on the expected creatine excretion rate of 1.7 In practice, a worker may receive repeated expo-grams/day for men and 1.0 grams/day for women. sures to the same radionuclide over a period of time.Refer to NCRP-87 (Ref. 2) for additional informa- These intakes should be treated as separate acute in-tion. takes if measurements collected through the period

8.9-6

allow for the individual quantification of each expo-

sure. As a general rule, if intakes are separated in

time so that the retained or eliminated fraction from

an earlier intake is less than 10% of the retention or

excretion fraction for the next intake, each intake

may be evaluated separately without regard to any

previous intakes.

Continual intakes that are distributed equally in

size and time may be approximated using a relation-

ship based on time integration of the IRF. The total

intake is estimated by dividing the measured activity

by the appropriate time-integrated retention or excre-

tion fraction. An example using the IRF values from

NUREG/CR-4884 (Ref. 4) would be to perform a

numerical integration over the individual IRF values

covering the time period of interest. Any one of a

number of standard integration techniques, including

numerical and analytical solutions, can be used. For

example, using the trapezoidal rule (see Example 7 in

Appendix A) yields the following method:

For bioassay measurements taken during an ex-

posure time interval, the equation is:

I A(t) X T for t < T Equation 6

f IRF(u) du

0

Using the trapezoidal rule to solve Equation 6

yields the following approximation:

Equation 7

A(t) x T x n

IRF(t) + IRF(t = 0.1 days)t X L2 + IRF(ul) + .**+ IRF(un-i )

For bioassay measurements taken after an expo-

sure interval, the equation is:

A(t) X T for t > T Equation 8

T IRF (u) du

t-T

A (t) = Amount of activity in compartmentor whole body at time t following on-

set of intake

T = Duration of intake (exposure timeperiod)

t = Time from onset of intake to time of

measurement

IRF(u) = Intake retention fraction at time u incompartment or whole body for asingle intake of a radionuclide

u = Variable time between integration

limits

n = number of increments

The number of increments to be used for a nu-

merical integration should be selected to minimize

unnecessary errors associated with the particulars of

the IRF values over which the integration is being per-

formed. In general, errors associated with the inte-

gration technique used should be limited to less

than 10%.

4.5 Correcting Intake Estimates for Particle SizeDifferences

The models used for deriving intake retention

and excretion fractions, such as those in NUREG/CR-4884, are typically based on 1-micrometer activ-

ity median aerodynamic diameter (AMAD) particles.

It is acceptable to correct intake estimates for parti-

cles of different sizes. These corrections often help

explain retention or excretion rates different from

those expected, such as would occur for larger parti-

cles preferentially deposited in the upper region of

the respiratory tract (N-P region) with more rapid

clearance times; Guidance for determining AMADs is

provided in Regulatory Guide 8.25, "Air Sampling in

the Workplace" (Ref. 8).

Equation 10, taken from Appendix B to

NUREG/CR-4884 (Ref. 4), should be used for revis-

ing the totaf body IRFs in NUREG/CR-4884 to parti-

cle size distributions between 0.1 to 20 pirm AMAD.

Equation 10

I IRFAMAD = E H50TWT DN-P(AMAD)IRF~),Ip"I = IRF1 TH50TWT DN..p(l pum)

Likewise, Equation 8 may be approximated using

the trapezoidal rule, which yields Equation 9:

A(t) X n

[IRF(t - T) + IRF(t) + IRF(ul) + ... + IkF(un1i)J HSOTWT DT-B(AMAD)

B TH50TWT DT-B ( Ym)

where:

I = Total intake during period T

HSOTWT Dp(AMAD)1

fTHpXTWT Dp(1 pM)

8.9-7

where: Table 1Aerosol AMAD

0.2 Am 0.5 gm 0.7 Aim 1.0 AmIRFAMAD = IRF for the activity medianaerodynamic diameter(AMAD) of interest

IRF1Im = Total body IRF for inhala-tion of 1 Aim AMAD aero-sols (these IRFs are givenin Appendix B to NUREG/CR-4884 (Ref. 4))

= Summation over all tissues(and organs) T

DN-P

DT-B

Dp

TotalDeposition

0.05 0.16 0.23 0.30

0.08 0.08 0.08 0.08

0.50 0.35 0.30 0.25

0.63 0.59 0.61 0.63

2.0 jim 5.0 jm 7.0 jm 10.0 jim

DN-P

DT-BN-P, T-B, P = The compartments or re-gions of deposition of therespiratory tract: thenasopharyngeal passage re-gion (N-P), thetracheobronchial region(T-B), and the pulmonaryregion (P)

fN-P,T, fT-BT, fPT = The fraction of committeddose equivalent in the tis-sue T resulting from depo-sition in the N-P, T-B, andP regions, respectively.(Values for individual radi-onuclides are contained inthe Supplements to Part 1of ICRP-30 (Ref. 3).)

H50T = Committed dose equivalentfor tissue (or organ) T perunit intake

0.50 0.74 0.81 0.87

0.08 0.08 0.08 0.08

0.17 0.09 0.07 0.05Total

Deposition 0.75 0.91 0.96 1.00

Equation 10, for revising the IRF for differentparticle sizes, is applicable for the total body IRF.ICRP-54 (Ref. 1) provides graphs of IRF values for0. 1 Am, 1 gim, and 10 jim AMAD particles for othertissues and excreta. Intake retention and excretionfunctions are derived for other AMAD particlesbased on the acceptable biokinetic modeling as dis-cussed in Regulatory Positions 4.2 and 4.3.

It is acceptable to take into account particle sizedistribution and its effect on lung deposition andtransfer in evaluating an individual's dose. ICRP-30(Ref. 3) (with supplements) provides data and meth-ods for use in evaluating the lung deposition and re-sultant doses for particle sizes between 0.1 and 20 gimAMAD. For particles with AMADs greater than 20gm, complete deposition in the N-P region can beassumed.

WT

DN-P, DT-B, Dp

= Tissue (or organ) weightingfactor, from 10 CFR20.1003

= Regional deposition frac-tions for an aerosol enter-ing the respiratory system.(Values presented in Table1 below.)

It is acceptable to compare the estimate of intakefor different particle sizes with the ALIs in AppendixB to §§20.1001-20.2401 for demonstrating compli-ance with intake limits. The ALIs are based on a par-ticle size of 1 micrometer. However, modifying theALI values for different particle size distributions re-quires prior NRC approval (10 CFR 2 0.12 04(c) (2)).4.6 Use of Individual Specific Biokinetic Model-

ing

Individual specific retention and excretion ratesmay be used in developing biokinetic models thatdiffer from the reference man modeling (10 CFR20.1204(c)). The quality and quantity of data usedfor this type of individual specific modeling should besufficient to justify the revised model. Licenseesshould not attempt to develop individual specific re-tention and excretion fractions in the absence of ac-

Equation 10 may not provide valid correctionsfor time periods shortly following intakes. The timeafter intake for which Equation 10 begins to yield sat-isfactory results is less than 1 day for Class D com-pounds. For Class W compounds, this time is about 7days following intake, and for Class Y compounds,about 9 days following intake.

8.9-8

tual biochemical and particle size information. Indi-vidual specific modeling is not required but may bedeveloped; the modeling as presented above in Regu-latory Position 4.2 is acceptable for evaluating regula-tory compliance.

5. CALCULATING DOSE FROM ESTIMATESOF INTAKE

Regulatory Guide 8.34, "Monitoring Criteria andMethods To Calculate Occupational RadiationDoses" (Ref. 9), contains additional guidance on de-termining doses based on calculated intakes once theintake is determined.

6. RECORDKEEPING

Records of measurement data, calculations of in-takes, and methods for calculating dose must bemaintained as required by 10 CFR 20.1204(c),

20.2103(b), and 20.2106(a). For additional informa-tion on recordkeeping and reporting occupational ex-posure data, including intakes, refer to Revision 1 ofRegulatory Guide 8.7, "Instructions for Recordingand Reporting Occupational Radiation ExposureData" (Ref. 10).

D. IMPLEMENTATION

The purpose of this section is to provide informa-tion to applicants and licensees regarding the NRCstaff's plans for using this regulatory guide.

Except in those cases in which an applicant pro-poses an acceptable alternative method for complyingwith specified portions of the Commission's regula-tions, the methods described in this guide will used bythe NRC staff for evaluating compliance with 10 CFR20.1001-20.2401.

8.9-9

REFERENCES

1. International Commission on Radiological Pro-tection, "Individual Monitoring for Intake ofRadionuclides by Workers: Design and Interpre-tation," ICRP Publication 54, Pergamon Press,New York, 1988.

2. National Council on Radiation Protection andMeasurements, "Use of Bioassay Procedures forAssessment of Internal Radionuclide Deposi-tion," NCRP Report No. 87, February 1987.

3. International Commission on Radiological Pro-tection, "Limits for Intakes of Radionuclides byWorkers," ICRP Publication 30, Part 1, andICRP Publication 30, Supplement to Part 1, Ap-pendix A, Pergamon Press, New York, 1978.

4. E. T. Lessard et al., "Interpretation of BioassayMeasurements," U.S. Nuclear Regulatory Com-mission, NUREG/CR-48 84, * July 1987.

'Copies may be purchased at current rates from the U. S. Gov-ernment Printing Office, Post Office Box 37082, Washing-ton, DC 20013-7082 (telephone (202) 512-2249 or (202)512-2171; or from the National Technical Information Serv-ice by writing NTIS at 5285 Port Royal Road, Springfield,VA 22161.

5. S. R. Jones, "Derivation and Validation of a Uri-nary Excretion Function for Plutonium Applica-ble Over Ten Years Post Intake," Radiation Pro-tection Dosimetry, Volume 11, No. 1, 1985.

6. J. R. Johnson and D. W. Dunford, GENMOD-A Program for Internal Dosimetry Calculations,AECL-9434, Chalk River Nuclear Laboratories,Chalk River, Ontario, 1987.

7. K. W. Skrable et al., "Intake Retention Func-tions and Their Applications to Bioassay and theEstimation of Internal Radiation Doses," HealthPhysics Journal, Volume 55, No. 6, 1988.

8. U.S. Nuclear Regulatory Commission, "Air Sam-pling in the Workplace," Regulatory Guide8.25,* Revision 1, June 1992.

9. U.S. Nuclear Regulatory Commission, "Monitor-ing Criteria and Methods To Calculate Occupa-tional Radiation Doses," Regulatory Guide8.34," July 1992.

10. U.S. Nuclear Regulatory. Commission, "Instruc-tions for Recording and Reporting OccupationalRadiation Exposure Data," Regulatory Guide8.7, Revision 1,* June 1992.

8.9-10

APPENDIX A

EXAMPLES OF THE USE OF INTAKE RETENTION FRACTIONS

The following examples illustrate the use of reten-tion and excretion functions for calculating intakesbased on bioassay measurements. The data used forthese examples are taken from NUREG/CR-4884,"Interpretation of Bioassay Measurements." Theseexamples do not illustrate the use of all possible bio-assay or health physics measurements that may beavailable (e.g., excreta and air sampling measure-ments) during a specific exposure incident. The pur-pose of these examples is not to define the total scopeof a bioassay program, rather, these examples dem-onstrate the use of the calculational techniques pre-sented in Regulatory Position 4 of the guide for corre-lating measurements to intake. The examples demon-strate the use of retention and excretion fractions to:

* Estimate intake from one or several bioassaymeasurements,

* Adjust intake estimates for multiple or continu-ous intakes, and

*E. T. Lessard et al., "Interpretation of Bioassay Measure-ments," U.S. Nuclear Regulatory Comrmission, NUREG/CR-4884, July 1987.

* Correct intake estimates for particle size differ-ences.

The examples in this appendix are:

Example 1: Calculating Intake Following an Inadver-tent Exposure Based on a Single BioassayMeasurement

Example 2: Calculating Intake with Unknown Time ofIntake

Example 3: Using Multiple Measurements To Calcu-late Intake

Example 4: Uranium Intake

Example 5: Comparison of Air Sampling and BioassayMeasurement Results

Example 6: Correcting Intake Estimates for ParticleSize Difference

Example 7: Adjusting Intake Estimates for Multipleand Continual Intakes

A-1

EXAMPLE 1

Calculating Intake Following an Inadvertent ExposureBased on a Single Bioassay Measurement

Determination that Intake Occurred where:

I = Estimate of intake in the same unitsas for A(t)In 10 CFR Part 35, "Medical Use of Byproduct

Material," 10 CFR 35.315 (a) (8) requires licensees toperform thyroid burden measurements for alloccupationally exposed individuals who were involvedin the preparation or administration of therapeuticdosages of 131I. These measurements are to be per-formed within 3 days following the preparation or ad-ministration.

In this example, the required bioassay measure-ments are conducted for all involved individuals fol-lowing a therapy patient iodination. It is identifiedthat the technologist who prepared the dose has ameasured thyroid content of 0.080 pLCi of 131I. It isdetermined that the technologist most likely receivedan inhalation intake when a difficulty was encoun-tered during the preparation of the dosage. The timeof the measurement is determined to be 24 hours af-ter the estimated time of intake.

Evaluation Procedure

The lung clearance class for all chemical com-pounds of iodine is Class D. Since no information isavailable on particle size distribution, a 1 gm AMADparticle size must be assumed. Using Equation 1 fromRegulatory Position 4.3 for estimating intake from asingle bioassay measurement, the intake can be esti-mated as follows:

A (t) = Thyroid content at time (t) of meas-urement

IRF(t) = Intake retention fraction for meas-ured 1311 at time interval (t) after es-timated time of intake.

The table of thyroid IRF values for 131I is foundon page B-103 of NUREG/CR-4884. The IRF valueat time after intake of 24 hours (t=24 hours) is 0. 133.

Substituting the measured thyroid content andthe corresponding thyroid IRF value into the aboveequation and solving yields the following:

0.080 AuCiI = = 0-60 uCi (2.2 E + 4 Bq)0.133

As discussed in Regulatory Position 2.3, if a bio-assay measurement indicates that the potential intakeis greater than the evaluation level of 0.02 AL!,additional exposure data or additional bioassay meas-urements should be examined for determining thebest estimate of intake. The ALI for Class D 131I is5E+1 ACi* (from Appendix B to§§20.1001-20.2401); therefore, the evaluation levelis 1 gCi (0.02 times the ALI value of 5E+1 gCi).Since the estimated intake is less than this level, nofurther evaluation is warranted.

A(t)IRF(t)

.*Since the tables in NUREG/CR-4884 are given in specialunits (rad, rem, and curie), this guide presents special unitsfollowed by SI units in parentheses.

A-2

EXAMPLE 2

Calculating Intake with Unknown Time of Intake

Determination that Intake Occurred

While conducting a routine termination bioassaymeasurement of a maintenance worker at a nuclearpower plant, a whole body content of 0.40 ,uCi of60Co was measured. Since the worker had entered acontaminated area earlier in the day, she was in-structed to shower and don disposable coveralls to en-sure that no external contamination of her skin orclothing was present. A second bioassay measurementwas conducted and a whole body content of 0.40 ,uCiof 60 Co was confirmed. Routine surveys show that6 0Co at this facility is generally Class W.

Evaluation Procedure

The health physics supervisor was notified. In anattempt to determine the cause and time of exposure,an examination was conducted of plant survey data,including airborne activity measurements for areas ofthe plant where she had recently worked. This exa-mination failed to identify a source of exposure; allareas to which the maintenance worker had accessover the past several days were found to be minimallycontaminated and no elevated levels of airborne ra-dioactive material had been experienced. This infor-mation, in addition to the determination that theworker was not externally contaminated, indicatedthat the intake did not occur during the past severaldays. In the absence of any other information, thelicensee assumed that the intake occurred at the mid-point in the time since the worker's last bioassaymeasurement. This assumption allows for an initial as-sessment of the potential significance of the intake, Inthis case, the most recent bioassay measurement wasconducted 6 months (180 days) before, which repre-sented her initial baseline measurement at the time ofhire. Using these assumptions, the calculation of in-take is as follows:

I A (t)IRF(t)

where:

I = Estimate of intake in units the sameas A(t)

Substituting the measured body content and thecorresponding IRF value into the above equation andsolving yields the following:

0.40 ,uCiI = = 6.26,uCi

6.39E- 2

The ALI for Class W 60Co is 2E+2 gCi; there-fore, the evaluation level is 2E+2 gCi times 0.02 or4 giCi. Since the calculated intake is greater than the4 jiCi evaluation level, additional information shouldbe sought.

As part of the additional review, the health phys-ics supervisor conducted a further review of the indi-vidual worker's activities in an attempt to determinethe actual time of exposure. A review of air sampledata and worker access failed to indicate any abnor-mal exposure conditions. For unknown situations, theexposed individual is most often the best source ofinformation when attempting to define the exposureconditions. The individual may remember unusualcircumstances that at the time may have seemed ac-ceptable, but upon further examination could haveresulted in the unexpected exposure. In this case, themaintenance worker remembered breaching a con-taminated system to remove a leaking valve. The sys-tem was supposed to have been depressurized anddrained. However, she remembered that when thesystem was breached, a slight pressure relief was ex-perienced and a small amount of water was drained.Following a review of the Radiation Work Permit(RWP) log and the containment entry log, it was de-termined that this incident occurred 28 days prior tothe measured body content. Prior to and since thattime, her other work activities have been in areasonly moderately contaminated; an additional intakewould have been unlikely. Based on these data, themost likely time of intake was determined to have oc-curred during the contaminated system breach 28days before.

The appropriate IRF values for this exposureshould be for a time of 28 days post-intake. Also, the"total body" IRF values should be used, since thebody content has been determined by an ih vivo totalbody measurement. A 28-day IRF value is calculatedby performing a logarithmic interpolation between the20-day value and the 30-day value.

A (t) = Whole body content at time (t) ofmeasurement

IRF (day X) = exp[ In (IRF(day Z)) - In (IRF(day

x[ (R (day Z) -(day Y) )

x (day X - day Y) +Iin (IRF (day Y))]

IRF(t) = Intake Retention Fraction for meas-ured 6 0Co at time interval t after esti-mated time of intake (half of 6months or 90 days)

A-3

I-

where:

IRF (day X) =

IRF (day Y) =

IRF (day Z) =

Substituting this interpolated IRF value into theInterpolated IRF value, calculated equation for calculating intake and solving yields:at day X, which lies between twoIRF values occurring at days Y andZ; in this case, X = 28 days, Y = 20days, and Z = 30 days

IRF value occurring at day Y, in 0.126

= 3.17 ACi (11.7 E+4 Bq)IRF value occurring at day Z, inthis example, 30 days

Solving this interpolation yields:

IRF (28 days) = expIY'1 (IRF(30 days)) - In (IRF(20 days))[Lt 30 days- 20 days )

X (28 days - 20 days) In (IRF (20 days))1

= ex[( In (0.123)-In (0.140) X 8 das+ n(0 1402= 10 days J

= 0.126

Since this calculated intake was less than theevaluation level (i.e., less than 0.02 times the ALIvalue of 2E+2 uCi for 1 gm AMAD, Class W, 6 0 Co),and the data reviews did not indicate any othersource of exposure, no further evaluation is war-ranted. However, had this calculated intake exceededthe evaluation level of 4 gCi, additional bioassaymeasurements over the next several days should beconsidered. If the licensee had previously determinedthat monitoring for internal exposure was requiredpursuant to 10 CFR 20.1502(b), this intake wouldhave been recorded in the worker's exposure recordsand provided to the worker as a part of her termina-tion exposure report, for which NRC Form 5 may beused.

A-4

EXAMPLE 3

Using Multiple Measurements To Calculate Intake

Determination that Intake Occurred where:

A laboratory worker accidentally breaks a flaskcontaining a volatile compound of 32p, The workerexits the work area. Contaminated nasal smears indi-cate that the worker may have received an acute in-halation intake. The results of work area air samplingmeasurements are reviewed, indicating increased air-borne levels. Bioassay measurements are initiated toassess the actual intake.

Evaluation Procedure

From a review of the biokinetics for inhalationintakes of 32p, it is determined that urine sample col-lection followed by liquid scintillation detection wouldprovide the best bioassay data for calculating intake.For the particular 3 2 P compound involved, the appro-priate lung clearance class is Class D. Also, lackingother data, a particle size distribution of 1 gim AMADmust be assumed.

The first voiding is analyzed and the results verifythe occurrence of an intake. However, because of theparticular characteristics of the sample (e.g., collec-tion time relative to time of exposure), the results arenot considered reliable for calculating an intake.Follow-up 24-hour urine samples are collected. Theresults of a second-day 24-hour sample indicate a to-tal activity of 1.50 jiCi, decay corrected from the timethe sample is counted to the end of the 24-hour sam-ple collection period. Using Equation 1 from Regula-tory Position 4.3, an initial estimate of the intake iscalculated as follows:

A (t)IRF(t)

1.50 uCi4.17E - 02

= 36 uCi (1.3E + 6 Bq)

I = Estimate of the 32p intake

IRF(t) = Excretion fraction for 24-hour urinecollected 2 days post-intake, whichequals 4.17E-02 (see NUREG/CR-4884, page B-25)

A(t) = 1.5 gCi, value of the second-day24-hour urine sample

The ALI value for inhalation intakes of Class Dcompound of 32P is 9E+2 gCi. The initial estimate ofintake of 36 ACi exceeds the evaluation level of 0.02ALI, which is the recommended level above whichmultiple bioassay measurements should be consideredfor assessing actual intake. Follow-up measurementsare made. By examining the tabulated IRF values for24-hour urine for 32P, the RSO determines that24-hour urine samples should be collected for the10th and 20th day.

Note: Daily measurements should be consideredif the initial assessment indicates an intake greaterthan the investigation level of 0.1 ALI. The time peri-ods above were selected for purposes of demonstrat-ing the calculational method. In actuality, one wouldtypically examine the third-day results before decid-ing on the need and frequency of additional measure-ments.

The following table summarizes the results of the24-hour urine sample measurements, the correspond-ing IRF value from NUREG/CR-4884, and the calcu-lated intake based on the individual measurementsusing the above method.

Table 3A. Calculated Intake

(t;) (Ai) (IJ)Time After Decay-Corrected Estimated Intake

Intake Activity in 24-Hour Based on Single(Days) Urine Sample (jiCi) IRF Samples (jiCi)

2 1.5E+0 4.17 E-2 3610 1.3E-1 4.34 E-3 3020 6.OE-2 1.55 E-3 39

A-5

The best estimate of intake is calculated using Equa-tion 5 from Regulatory Position 4.3.1 to obtain the esti-mate of the intake. This estimate is calculated from thebioassay measurements obtained on three different daysfollowing the incident:

I = , IRFI x Al

a IRF2

If the licensee has previously determined thatmonitoring for internal exposure pursuant to 10 CFR20.1502(b) is required, the data and results of thisevaluation are placed in the worker's exposurerecords and included on the worker's NRC Form 5report. I

(4.17E-2 X 1.5) +(4.34E-3 X 1.3E-I) +(1.55E-3 x 6.OE-2)1= (4.I7E-2)2 + (4.34B-3) 2 + (1.55E-3)2

I = 36 pCi (1. 3E - 6 Bq ) 32 p

A-6

EXAMPLE 4

Uranium Intake

Determination that Intake Occurred E

An accident at a facility that produces UF6 (ura-nium hexafluoride) results in a worker being exposedto an unknown concentration of UF6 with a naturaluranium isotopic distribution. Based on informationin Appendix B to §§20.1001-20.2401, the UF 6 isidentified as an inhalation lung Class D compound.

Evaluation Procedure

The health physics supervisor examines the sig-nificance of the exposure. Based on potential air-borne radioactive material levels, it is determined thatbioassay measurements should be conducted. Exam-ining the biokinetics and decay characteristics for ura-nium isotopes, the health physics supervisor deter-mines that urine sample collection and analysisshould be performed.

Spot urine samples are collected over the follow-ing few days with the results presented in the follow-ing table.

= Daily excretion rate of 1.4 liter/dayfor urine for reference man (refer-ence woman rate is 1.0 liter/day)

= Time (in days) after intake to whenthe first sample was taken

ti

= Time (in days) after intake to whenthe previous sample was taken (0days in this case)

The accumulation for the second sample is calcu-lated in a similar manner:

AA2 = C2 x E x (t2 -t 2 1 )

=210 x 1.4 x (2.4-1.8)

= 176 fg

Accumulation for the final sample is similarly cal-culated.

Time of Sample(Days Post-Intake)

Concentrationof Uranium in Urine

(Wg/l)

AA 3 = C3 x E x (t 3 -t 3 a1 )

= 140 x 1.4 x (3.0-2.4)

1.82.43.0

460210140

Using the results of the spot samples, accumu-lated urine activities can be calculated using Equa-tions 2 and 3 from Regulatory Position 4.3. The con-centration of uranium in the urine samples is pre-sented in units of micrograms per liter, Because of thelong half-lives of uranium isotopes, decay correctionto time of sampling is not required.

Using Equation 2, the amount of uranium in thefirst sample is calculated as follows:

AA, = Cl x E x (ti -ti1 1 )

=460 x 1.4 x (1.8-0)

= 118 Mg

The accumulated urine through the third spotsample collected on day 3 is calculated by summingall the accumulations.

An = AA1 +AA 2 + AA3

= 1,160 + 176 + 118

= 1, 4 5 0 zg

where:

A3 = Accumulated activity up to time, t, ofthe third sample collected on thethird day post-intake

= 1160 ug

where:

AA, = Activity or amount of uranium in thefirst sample

C1 = Concentration of uranium in the firstsample

Using the calculation for accumulated urine activ-ity, the intake may be calculated by applying themethod of Equation 1 from Regulatory Position 4.3.The IRF for this calculation would be that for the ac-cumulated urine for uranium, Class D, from Appen-dix B to NUREG/CR-4884 (page B-163). Because ofthe long radiological half-lives, the IRFs for all theuranium isotopes are essentially the same; the valuesfor 23 8U have been used for this example.

A-7

A(t)IRF(t)

= 1, 4500.291

= 4, 980 Ag

where:

I = Estimate of intake with units thesame as A(t)

IRF(t) = Intake retention fraction for ura-nium, Class D inhalation for the ac-cumulated urine in the third day fol-lowing time of intake

A(t) = Value of the calculated accumulatedurine based on the three spot samples

Gig)

A conversion from a mass (g±g) to activity (,uCi)for the different percentages of the uranium isotopescan be performed based on isotopic specific activity.Natural uranium is composed of three isotopes: 234Uat 0.0056% atom abundance, 235U at 0.72%, and2 3 8 U at 99.274%. Based on these abundances and theradioactive decay constants for these isotopes, thecorresponding weight to activity conversion factors

are 3.5E-01 ACi/g for 234U, 1.5E-2 gCi/g for 235U,and 3.3E-01 j±Ci/g for 238U. Using these conversions,the following activity intakes are calculated:

Activity = U(weight) x gCi/g conversion

= 4,980 ,ug x 0.35 gCi/g x 1E-06 g/g= 1.7E-03 gCi (64 Bq) U-234

= 4,980 gg x 0.015 gCi/g x 1E-06 g/pLg= 7.5E-05 giCi (2.8 Bq) U-235

= 4,980 gg x 0.33 jiCi/g x IE-06 g/j~g= 1.6E-03 gCi (61 Bq) U-238

These calculated activity intakes for the uraniumisotopes are much less than the evaluation level of0.02 ALI, at which additional evaluations (e.g.,measurements) should be considered. Therefore,considering the significance of the radiation exposure,the bioassay measurements conducted provide anadequate basis for calculation of the intake.

A separate limit of 10 milligrams in a week forsoluble uranium is contained in 10 CFR 20.1201(e)and Appendix B to §§20.1001-20.2401. This limit isbased on the chemical toxicity, which should beevaluated in addition to the radiation exposure. Theabove evaluation determines that the total intake was4,980 jig (4.98 mg). Therefore, the 10 mg/wk limit of10 CFR 20.1201(e) was not exceeded.

I

A-8

EXAMPLE 5

Comparison of Air Sampling and Bioassay Measurement Results

Determination that Intake Occurred

During fabrication of a 137Cs source, the airborneradioactive material levels to which the worker is ex-posed are sampled, using a continuous low-volume airsampler. At the end of the 8-hour shift, the technolo-gist counts the filter and calculates that the averageairborne activity during the sample period was 5.4E-7

iCi/ml (20,000 Bq/m3) of 137Cs. The elevated levelsare unexpected and the health physicist compares themeasured levels with the 137Cs Class D DAC valuefrom Appendix B to §§20.1001-20.2401. The 8-houraverage concentration is 9 times the DAC value for137Cs of 6E-8 gCi/ml. The worker was not wearing arespiratory protective device during the fabricationprocess as elevated airborne radioactive material lev-els were not anticipated.

The health physicist evaluates the significance ofthe exposure by calculating the intake (based on theair sample data) and comparing the result with theALI value for 137Cs from Appendix B to§§20.1001-20.2401 (137Cs, inhalation ALI = 200Aci).

As a first approximation, the health physicist as-sumes that the worker was exposed to the averageairborne 137Cs concentration represented by the activ-ity on the air sampler filter for the entire 8 hours ofthe work shift. A worker breathing rate of 1.2 m3!hour (light work activity) is also assumed. The follow-ing intake is calculated:

Intake = 8 hours X 1.2 IE6- mhours ml m3

= 5.2 /uCi(1.9E5 Bq)

This calculated intake is greater than the evalu-ation level of 0.02 ALI. The health physicist ordersan in vivo bioassay measurement to be performed onthe worker.

Evaluation Procedure

The in vivo measurement is performed the fol-lowing morning, approximately 20 hours after the es-timated time of intake. Since the exposure time spansan 8-hour work period and time-dependent airborneactivities are unknown, the worker's exposure is as-sumed to have occurred at the midpoint in the 8-hourshift. The results indicate a total body activity of 0.21ACi of '37Cs. The -corresponding intake may be esti-mated by using Equation 1 from Regulatory Position4.3. Inhalation Class D is assigned for all chemical

compounds of cesium (refer to Appendix B to§§20.1001-20.2401). The table of inhalation IRFsfor 137Cs may be found on page B-111 of NUREG/CR-4884. The IRF value for the total body, 0.8 dayafter intake, is 6.26E-01. Substituting these valuesinto Equation 1, the calculation of the intake is:

I A(t)IRF (t)

0.21 M -1= 0 34 uCi (12, 400 Bq)6.26 E -01

The two calculated estimates of 137Cs intake aresignificantly different. The health physicist discussesthe work activities leading to the exposure with theindividual and determines that the differences couldbe attributable to several factors:

* A difference in the breathing rate assumed forreference man and that of the worker,

* A difference in the concentrations of airborneradioactive material as sampled by the low-volume sampler and the levels as breathed by theworker. These differences could be due to thelocation of the sampler and the worker relativeto the source of airborne material and the direc-tion of air flow, and

* A difference in exposure time assumed for theworker (i.e., the actual exposure was less thanthe full 8-hour shift).

The available data cannot resolve the differencebetween the air sampling results and the in vivo bioas-say analysis: additional bioassay measurements and areview of the worker's exposure relative to theworkplace ambient air sampling should be conductedto resolve the difference.

The estimate to be used as the dose of recordshould be the value considered to better represent theactual exposure situation. In general, bioassay meas-urements will provide better estimates of actualworker intakes, provided the data are of sufficientquality. Air sampling results typically represent onlyan approximation of the level of radioactive materialin the air breathed by the worker. Appropriately col-lected and analyzed, bioassay results can provide abetter indication of actual intakes.

This example does not address the health physicsissues concerning the elevated airborne levels and po-tential worker exposure to levels greater than DACs.

A-9

EXAMPLE 6

Correcting Intake Estimates for Particle Size Difference

Annual limits on intake and the intake retentionfractions (in NUREG/CR-4884) are based on a 1-jimAMAD particle size distribution. Rarely (if ever) willthe actual distribution of airborne particulates becompletely characteristic of 1-jm AMAD particles.Evaluating different particle size distributions can as-sist in explaining retention and excretion rates thatare different than would be expected, based on thestandard modeling (see 10 CFR 20.1204(c)(1)).

In this example, it is assumed that the actual par-ticle size distribution has been determined to be char-acterized as a 2-jpm AMAD of Class W compound of60 Co. It is assumed that the intake occurred 20 daysbefore the bioassay measurements were made.

Evaluation Procedure

The IRF may be adjusted for a 2.0-jim AMADparticle size using Equation 10 of Regulatory Position4.5. The approximation relationship of this equationis applicable to the total body IRFs for particle sizesbetween 0.1 jim and 20 jim AMAD.

Values for DN-P, DT-B, and Dp derived from thedata in Part 1 of ICRP Publication 30 (pages 24 and25) are presented in the following table. (Note: thedeposition fractions presented in Table B.8.1 ofNUREG/CR-4884 (page B-801) contains errors andshould not be used.)

Table 6A. Regional Deposition Fractions for Aerosol with AMADs Between 0.2 and 10 jm

DN-P

DT-BDp

Total Deposition

DN-P

DT-B

DpoTotal Deposition

0.2 jm

0.05

0.08

0.50

0.63

2.0 Am

0.50

0.08

0.17

0.75

0.5 jm

0.160.08

0.35

0.59

5.0 Am

0.74

0.08

0.09

0.91

0.7 jm

0.230.08

0.30

0.61

7.0 jm

0.81

0.08

0.07

0.96

1.0 jim

0.300.08

0.25

0.6310.0 jim

0.87

0.08

0.05

1.00

The values of fN-P,T, fT-B,T, and fPT for Class W6°Co needed for Equation 10 are listed in the Supple-ment to Part 1 of ICRP Publication 30 on page 40.These values in ICRP Publication 30 are given as per-

centages and must be converted to decimal fractionsbefore use. The decimal fractions for each tissue,along with its weighting factor and committed doseequivalent factor, are presented in the following table.

Table 6B. Input Values

Tissue

GonadsBreastRed MarrowLungsThyroidBone SurfaceLLI WallLiverRemainder

fN-PT

0.350.190.200.02

fT-B,T,

0.210.170.170.02

fP,T War

0.440.640.630.96

0.250.150.120.120.030.030.060.060.06

HSOT (per unit intake) * ̀

(Sv/Bq)

4.OE-094.2E-094.2E-093.6E-08

0.450.210.10

0.15

0.190.09

0.400.600.81

8.2E-099.2E-098.OE-09

Tissue weighting factors from 10 CFR 20.1003.Committed dose equivalent per unit intake.

A-10

The following equation is used to estimate theIRF for 2-gm particles.

IRF(AmAD) = IRF(LIM)': T H50TWT

TH50TWT

+ fT-B,T H50TWT

tTH5OTVW

'IH50T'A

+ fP,T H50TWT

"TH50TWI

Substituting input values from the table into theabove equation results in the following:

Total Body IRF(2 gm)at 20 days after intake = 8.5 E-02

This IRF could be used to estimate intakes as il-lustrated in previous examples.

DN-P(AMAD)

DN-P( lgm)

DT-B (AMAD)

DT-B (O1m)

Dp(AMAD)Dp(lgm) J

. The above method for revising the IRF for differ-ent particle sizes, is applicable for the total body IRF.ICRP-54 provides graphs of IRF values for 0.1 gIm, 1gm, and 10 gm AMAD particles for other tissues andexcreta.

A-11

EXAMPLE 7

Adjusting Intake Estimates for Multiple and Continual Intakes

The following is a simplified example showing theapplication of the numerical integration of IRFs overa continual exposure period. It is recognized thatmost exposure situations do not involve chronic expo-sures to airborne radioactive material; most intakescan be reasonably characterized as acute exposures.However, when exposures extend over a longer pe-riod of time (i.e., more than a few days) it may benecessary to adjust the IRFs, which are based on sin-gle acute intakes, to account for the extended expo-sure period.

Urinalysis performed on a Friday indicated anuptake of 3 H for a worker. It was determined that theworker was continually exposed to 3 H as HTO (watervapor) for the 5 work days of the prior week (i.e.,Monday through Friday of the previous week). Re-sults of the 24-hour urine sample reveal 10 g.Ci(3.7E+05 Bq) of 3 H.

Evaluation Procedure

Since the exposure occurred over an extendedperiod of time and the measurement was taken afterthe exposure interval, the methods of Equation 9from Regulatory Position 4.4 should be used.

t = Time from onset of intake to time ofmeasurement

u = Variable time between integrationlimits

IRF(u) = Intake retention fraction at time u incompartment or whole body for asingle intake of a radionuclide

n = Number of increments

For this example, the time interval values are:

T = 5 days (period of intake)

t = 11 days (number of days followingonset of intake)

The integration period is for the time (t-T) to t;therefore the interval consists of a total of 6 days. Forthe numerical integration, the 6-day time interval hasbeen divided into 6 equal 1-day increments.

The IRF values for the calculation, taken fromNUREG/CR-4884 (page B-711), are listed in thefollowing table. If IRF values are not presented forthe day of interest, a logarithmic interpolation shouldbe performed to calculate the value.

A(t) n

[IRF(t - T) + IRF(t) + IRF(u!) + ... d IRF(u,-j

Time Intervals from(t-T) to t

(in 1-day Increments)

6

7

IRF(24-hr Urine)

2.85E-02

where:

A (t)

I

T

8= Amount of activity in compartment

or whole body at time t following on-set of intake

= Total intake during period T

= Duration of intake (exposure timeperiod)

9

2.66E-02

2.48E-02

2.31E-02

2.16E-02

2.02E-02

10

11

Substituting the IRFs and the interval length intothe above equation yields:

I [ 5; 2 E2.85E - 02 + 2.02E - 02

_ 2

10, Ci x 6

+ 2.66E-02 + 2.48E-02 + 2.31E1-02 + 2.16E-02]

5.OE+02,uCi (1.8E+07 Bq)

This calculated intake is less than 0.02 ALI for3H (i.e., 500 jiCi < 0.02 times the ALI value of 8E4gCi). Additional bioassay measurements would not be

necessary to determine the intake. However, addi-tional radiation safety measures may be needed toevaluate the incident and prevent future occurrences.

A-12

REGULATORY ANALYSIS

A separate regulatory analysis was not preparedfor this regulatory guide. The regulatory analysisprepared for 10 CFR Part 20, "Standards forProtection Against Radiation" (56 FR 23360),provides the regulatory basis for this guide andexamines the costs and benefits of the rule as

implemented by the guide. A copy of the "RegulatoryAnalysis for the Revision of 10 CFR Part 20"(PNL-67 12, November 1988), is available forinspection and copying for a fee at the NRC PublicDocument Room, 2120 L Street NW., Washington,DC, as an enclosure to Part 20.

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