ML003739554

1993/07/31-Regulatory Guide 8.9 (Revision 1), Acceptable Concepts, Models, Equations, and Assumptions for a Bioassay Program

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Issue date:	07/31/1993
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Revision 1 U.S. NUCLEAR REGULATORY COMMISSION July 1993 REGULATORY GUIDE OFFICE OF NUCLEAR REGULATORY RESEARCH REGULATORY GUIDE 8.9 (Draft was issued as DG-8009)

ACCEPTABLE CONCEPTS, MODELS, EQUATIONS, AND ASSUMPTIONS FOR A BIOASSAY PROGRAM A. INTRODUCTION approaches for determining intake and calculating a dose have been developed. For certain unusual cir-Section 20.1204 of 10 CFR Part 20, "Standards cumstances, such as exposures at or near the limits, for Protection Against Radiation," requires that each special consideration may need to be given to the spe-licensee, when required by 10 CFR 20.1502, take cifics of an individual's retention and excretion in de-suitable and timely measurements of quantities of termining the intake. It is not the intent of this regula-radionuclides in the body, quantities of radionuclides tory guide to constrain licensees from performing excreted from the body, concentrations of radioactive more detailed analyses when the licensee determines materials in the air in the work area, or any combina- that the magnitude of the exposure warrants further tion of such measurements as may be necessary for investigation.

detection and assessment of individual intakes of radioactive material. Furthermore, 10 CFR 20.1204 This guide describes practical and consistent (c) (1) allows for the use of specific information on methods acceptable to the NRC staff for estimating the physical and biochemical properties of the radio- intake of radionuclides using bioassay measurements.

active material deposited in the body in determining Alternative methods acceptable to the NRC staff are an individual's internal dose. Also, as stated in in ICRP Report No. 54, "Individual Monitoring for 10 CFR 20.1703(a)(3)(ii), if respiratory protection Intake of Radionuclides by Workers: Design and In-equipment is used to limit intakes of airborne radio- terpretation" (Ref. 1), and NCRP Report No. 87, active material, the licensee's respiratory protection "Use of Bioassay Procedures for Assessment of Inter-program is to include bioassay measurements, as nal Radionuclide Deposition" (Ref. 2).

appropriate, to evaluate actual intakes of airborne activity. Any information collection activities mentioned Because of differences in physical properties and in this regulatory guide are contained as requirements in 10 CFR Part 20, which provides the regulatory ba-metabolic processes, each individual's dose resulting sis for this guide. The information collection require-from an exposure is unique. In other words, the same ments in 10 CFR Part 20 have been approved by the exposure to multiple individuals will cause different Office of Management and Budget, Approval No.

doses to each individual. However, for the purpose of demonstrating compliance with dose limits, standard 3150-00 14.

Written comments may be submitted to the Regulatory Publications USNRC REGULATORY GUIDES Branch, DFIPS, ADM, U.S. Nuclear Regulatory commission, Washing-pub- ton, DC 20555.

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experience.

_ I ir B. DISCUSSION ent. In addition, the particulars of the exposure situ-ation, such as particle size distribution, will affect the Bioassay measurements include the analysis of ra-lung compartment deposition fractions and the resul-dioactive material in body organs or in the whole tant biological clearances. For example, particles body (in vivo measurements) and in biological mate-larger than 20 gm AMAD1 will deposit mainly in the rial excreted, eliminated, or otherwise removed from naso-pharyngeal (N-P) region and tend to show bio-the body (in vitro measurements). The in vivo meas-logical retention and excretion characteristics more urements are made using a whole body counter, thy-typical of an ingestion intake than of an inhalation roid counter, lung counter, or other similar device.

intake of the default 1 gm AMAD. These character-The in vitro measurements involve collection of urine, istics are due to the fact that a large fraction of parti-feces, or tissue samples that are measured directly, or cles deposited in the N-P region is cleared by the after radiochemical separation, by gamma spectrome-ciliated epithelial cells to the throat and subsequently try, or by alpha or beta counting of the separated ra-swallowed, thereby appearing to be an ingestion in-dionuclide as appropriate.

take. Fitting an individual's bioassay measurement ICRP Publication 30, "Limits for Intakes of Radi- data for a particular exposure situation to the stan-onuclides by Workers" (with accompanying addenda) dard modeling will, however, provide reasonably ac-(Ref. 3), has been used by the NRC as the basis for curate estimates for most situations.

its annual limits on intake (ALI) and derived air con- This guide contains methods for evaluating bioas-centrations (DAC) listed in Appendix B to say data that will result in calculated intakes that are

§§ 20.1001 through 20.2401. Likewise, the modeling acceptable to the NRC staff for evaluating compliance in ICRP-30 serves as the basis for interpreting the with the occupational dose limits of 10 CFR 20.1202.

bioassay measurements in NUREG/CR-4884, "Inter- Examples of specific exposure situations and the pretation of Bioassay Measurements" (Ref. 4). Since physical and biochemical processes considered in the the issuance of ICRP-30 (Ref. 3), improvements in assessment of the exposures are in Appendix A to this the metabolic modeling for a few radionuclides have guide. Additional information on bioassay measure-resulted in dosimetric modeling equally acceptable to ments, interpretation of bioassay data, and bioassay the NRC staff. For example, a model developed by program components can be found in ICRP-30 (Ref.

Jones (Ref. 5) provides acceptable estimates of uri- 3), ICRP-54 (Ref. 1), NCRP-87 (Ref. 2), and nary fractional excretions of plutonium. Also, a trit- NUREG/CR-4884 (Ref. 4).

ium metabolic model developed by Johnson and The following terms, which have not been de-Dunford (Ref. 6) provides acceptable (and often im-fined in 10 CFR 20.1003, have been used in this proved) estimates of time-dependent tritium excre-guide.

tion. As additional research is conducted, it is ex-pected that refinements in the metabolic modeling Evaluation Level-The level at which an intake will further improve the methods available for corre- should be evaluated beyond the initial bioassay meas-lating bioassay measurements to actual intake and the urement. The evaluation level is 0.02 times the an-resultant dose to an individual. nual limit on intake (ALI), which is equivalent to 40 derived air concentration (DAC) hours.

Metabolic modeling, such as that presented in Excretion Fraction-The fraction of the intake ICRP-30 (Ref. 3) and ICRP-54 (Ref. 1), has been that has been excreted by the body at time (t) follow-used for evaluating bioassay measurements through ing the intake.

the development of time-dependent values for the bodily retention or excretion (or both) of the ingested Intake Retention Fraction-The fraction of the or inhaled radioactive material. NUREG/CR-4884 intake that is retained in the body at time (t) follow-(Ref. 4) presents a comprehensive set of data on in- ing the intake.

take retention and excretion fractions developed Investigation Level-The level at which an intake from these models. These data, and the accompany- should be investigated. The investigation level is any ing description of the modeling and methods, provide intake greater than or equal to 0. 1 times the annual useful information for using bioassay measurements to limit on intake (ALI).

estimate intake. In addition, ICRP-54 (Ref. 1) pre- C. REGULATORY POSITION sents metabolic models accompanied by data and fig-ures of bodily retention and excretion for many of the NOTE: The regulatory positions in this regulatory radionuclides of importance to NRC licensees. guide supersede the information contained in NRC IE Information Notice No. 82-18, "Assessment of In-ICRP-30 (Ref. 3) and ICRP-54 (Ref. 1) are takes of Radioactive Material by Workers."

based on general considerations (i.e., standard chemical forms and standard man or woman meta- 'Activity Median Aerodynamic Diameter (AMAD): The di-bolic modeling). Each individual's physiological char- ameter of a unit density sphere with the same terminal settling velocity in air as that of an aerosol particle whose activity is acteristics and biochemical processes may be differ- the median for the entire aerosol.

8.9-2

1. AVAILABILITY OF BIOASSAY SERVICES determined on an a priori basis, considering the likely exposure of the individual. In determining the work-The purposes of bioassay measurements are to er's likely exposure, consider such information as the confirm the adequacy of radiological controls and to worker's access, work practices, measured levels of determine compliance with the occupational dose lim-airborne radioactive material, and exposure time. Pe-its. Bioassay services should be available if the types riodic measurements should be made when the cumu-and quantities of radioactive material licensed for use lative exposure to airborne radioactivity, since the at the facility could, under normal operational occur-most recent bioassay measurement, is > 0.02 ALI (40 rences, result in airborne levels in normally occupied DAC hours). Noble gases and airborne particulates areas exceeding DACs. Provisions should be made for with a radioactive half-life less than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> should be the collection of appropriate samples, analysis of bio-excluded from the evaluation since external exposure assay samples, and evaluation of the results of these is generally controlling for these radionuclides.

analyses to determine intakes.

As a minimum, periodic measurements should be

2. FREQUENCY OF REQUIRED BIOASSAY conducted annually. Periodic measurements provide MEASUREMENTS additional information on any long-term accumula-Determining the appropriate frequency of routine tion and retention of radioactive material in the body, bioassay measurements depends upon the exposure especially for exposures to concentrations of airborne potential and the physical and chemical characteris- radioactive material below monitoring thresholds.

tics of the radioactive material and the route of entry 2.1.3 Termination Measurements to the body. Elements that should be considered in-clude (1) the potential exposure of the individual, (2) When an individual is no longer subject to the the retention and excretion characteristics of the radi- bioassay program, because of termination of employ-onuclide, (3) the sensitivity of the measurement tech- ment or change in employment status, termination nique, and (4) the acceptable uncertainty in the esti- bioassay measurement should be made, when practi-mate of intake and committed dose equivalent. Bioas- cable, to ensure that any unknown intakes are quan-say measurements used for demonstrating compliance tified (see Example 2 in Appendix A to this guide).

with the occupational dose limits should be conducted 2.2 Special Monitoring often enough to identify and quantify potential expo- Because of uncertainty in the time of intakes and sures and resultant intakes that, during any year, are the absence of other data related to the exposure likely to collectively exceed 0.1 times the ALL.2 (e.g., physical and chemical forms, exposure dura-Two separate categories of bioassay measure- tion), correlating positive results to actual intakes for ments further determine the frequency and scope of routine measurements can sometimes be difficult.

measurements: routine measurements and special Abnormal and inadvertent intakes from situations measurements. such as a failed respiratory protective device, inade-quate engineering controls, inadvertent ingestion, 2.1 Routine Measurements contamination of a wound, or skin absorption 3 should Routine measurements include baseline measure- be evaluated on a case-by-case basis. Circumstances ments, periodic measurements, and termination that should be considered when determining whether measurements. These measurements should be con- potential intakes should be evaluated include:

ducted to confirm that appropriate controls exist and

• The presence of unusually high levels of facial to assess dose. and/or nasal contamination, 2.1.1 Baseline Measurements

• Entry into airborne radioactivity areas without An individual's baseline measurement of radioac- appropriate exposure controls, tive material within the body should be conducted

• Operational events with a reasonable likelihood prior to initial work activities that involve exposure to that a worker was exposed to unknown quanti-radiation or radioactive materials, for which monitor- ties of airborne radioactive material (e.g., loss of ing is required. system or container integrity),

2.1.2 Periodic Measurements

• Known or suspected incidents of a worker ingest-ing radioactive material, In addition to the baseline measurements, peri-odic bioassay measurements should be performed.

• Incidents that result in contamination of wounds The frequency of periodic measurements should be or other skin absorptions,

• Evidence of damage to or failure of a respiratory protective device.

2 The 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- 3The skin absorption of airborne tritium has been included in ceed 10% of the applicable limit (i.e., intakes likely to exceed the determination of its ALI and DAC values for occupational 0.1 ALI for adults). inhalation exposures in Appendix B to §§20.1001-20.2401.

8.9-3

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2.3 Estimating Intakes-Evaluation and Investi- posure generally provide reliable estimates of intakes gation Levels for most gamma emitting radionuclides. In vitro Licensees should estimate the intake for any bio- measurements should be used for radionuclides that assay measurement that indicates internally deposited emit little or no gamma radiation. However, in vitro radioactive material resulting from licensed activities. urine or fecal measurements for the first voiding fol-The scope of the evaluation should be commensurate lowing exposure, while providing important informa-with the potential magnitude of the intake. For indi- tion for assessing potential significance, do not gener-vidual exposures with an estimate of intake less than ally represent equilibrium conditions and thereby 0.02 ALI, minimum bioassay measurements are ade- should not be relied upon in evaluating actual intakes.

quate to provide a reasonable approximation of in- ICRP Publication 54 (Ref. 1) and NCRP Report No.

take. Repeated follow-up measurements or additional 87 (Ref. 2) provide guidance acceptable to the NRC exposure data reviews are not necessary, provided a staff for determining the types of bioassay measure-reasonable estimate of the actual intake can be made ments that should be made considering the physical based on available data. 4 and biological characteristics of the radioactive material.

2.3.1 Evaluation Level

4. INTERPRETATION OF BIOASSAY MEAS-For very small intakes, a single bioassay measure- UREMENTS ment is generally adequate to estimate intake. 5 For intakes that represent a significant contribution to The specific scope and depth of the evaluation of dose, other available data should be evaluated. If in- bioassay measurements, as discussed in Regulatory itial bioassay measurements indicate that an intake is Position 2.3, depends on the potential significance of greater than an evaluation level of 0.02 ALI, addi- the intake. The methods presented below are accept-tional available data, such as airborne measurements able to the NRC staff for correlating bioassay meas-or additional bioassay measurements, should be used urements to estimates of intakes for the purpose of to obtain the best estimate of actual intake. demonstrating compliance with the occupational dose limits of 10 CFR 20.1201.

2.3.2 Investigation Level 4.1 Time of Exposure For single intakes that are greater than 10% of the ALI, a thorough investigation of the exposure Accurate estimation of intake from bioassay should be made. Therefore, if a potential intake ex- measurements is dependent upon knowledge of time ceeds an investigation level of 0.1 ALI, multiple bio- of intake. Generally, the time of intake is known con-assay measurements and an evaluation of available sidering work activities and other monitoring data, workplace monitoring data should be conducted. If such as air sample data. Therefore, the time of intake practical, daily measurements should be made until a will be known for all but unusual situations. When the pattern of bodily retention and excretion can be es- time of intake cannot be determined from monitoring tablished. Such a determination is feasible after as data, it can often be determined from information few as three measurements; however, physiologically provided by the individual. When information is in-related variations and uncertainties require that meas- sufficient to determine the time of intake, it is accept-urements be continued over a longer period of time in able to assume that the intake occurred at the mid-some cases. For potential intakes near or exceeding point of the time period since the last bioassay meas-the ALIs, the bioassay data evaluations should con- urement. This initial assumption should be refined by sider any additional data on the physical and chemi- using any available information such as the individu-cal characteristics and the exposed individual's physi- al's work schedule, facility operations data, historical cal and biokinetic processes, air monitoring data, and the effective half-life of the radionuclides detected (see Example 2 of Appen-

3. TYPE OF MEASUREMENTS dix A).

Characteristics such as mode of intake, uptake, 4.2 Acceptable Biokinetic Models and excretion and mode of radioactive decay should be considered in selecting the most effective and reli- Determining a worker's intake from bioassay able types of measurements. For example, in vivo measurements involves comparing the measured bod-lung or total body measurements shortly following ex- ily retention or excretion to a tabulated value. The models and methods used for evaluating bioassay measurements should provide a reasonable assess-4 The purpose of this guidance is to describe the scope of the ment of the worker's exposure. For intakes that are a bioassay measurements that should be considered for assess-ing intakes. It is not intended to limit the types of reviews that small fraction of the limit, greater inaccuracy in the may be warranted for assessing the overall significance of an estimate of intake can be accepted without significant intake.

impact on the overall assessment of a worker's dose.

5For radionuclides that are difficult to detect, such as alpha emitters, a single measurement may not be adequate to deter- However, for annual exposures for which monitoring mine intakes. is 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.

4.3 Intake Retention and Excretion Fractions Variations from predicted retention and excre-for Calculating Intakes tion for specific individuals can be expected. Excre-tion of radionuclides may be influenced by the work- ICRP-54 (Ref. 1) presents urinary excretion and er's diet, health condition, age, level of physical and fecal excretion equations as a function of time follow-metabolic activity, or physiological characteristics. ing intake for a number of radionuclides. By differen-The lung deposition and clearance of the inhaled ra- tiating these equations, intake retention functions can dionuclide, the particle size distribution,-and the time be derived. The solution of these equations over a of the excretion also influence the excretion rate of range of times allows the development of tabulated radionuclides. intake retention and excretion fractions. The intake retention fractions 6 (IRFs) contained in NUREG/

Important considerations for evaluating bioassay CR-4884 (Ref. 4) were developed in this manner and measurements include: represent an acceptable basis for correlating bioassay

• Appropriate measurement technique (in vivo or measurements to estimates of intake. To apply the in vitro) based on radionuclide decay character- use of IRFs for calculating an individual's radionu-istics (i.e., types of radiation emitted) and clide intake from a single bioassay measurement, di-biokinetic characteristics (i.e., systemic uptake vide the total activity in 24-hour urine, 24-hour feces, and retention and urine and fecal excretion frac- accumulated urine, or accumulated feces, 7 or the ia-tions), dionuclide content in the total body, systemic organs, lungs, nasal passages, or GI tract, by the appropriate

• The effects of diuretics or chelation to reduce IRF value in NUREG/CR-4884.

systemic uptake and tQ increase excretion or ex-cretion rates, Equation 1 demonstrates this method:

• Representativeness of measurements such as I = A (t) 24-hour or accumulated urine or fecal measure- Equation 1 IRF(t) ments,

• The appropriate lung clearance class (D, W, or where:

Y), if known (see definition of class in 10 CFR 20.1003). If no information on the biological be- I = Estimate of intake with units the havior or chemical form is available, the most same as A(t),

restrictive clearance class relevant for the par- A (t) = Numerical value of the bioassay ticular element should be assumed (i.e., that measurement obtained at time t (de-class that gives the lowest value of ALI), cay corrected to time of sampling for

• Particle size distribution, in vitro measurements) with appro-priate units (jiCi, Bq, or jig).

• Chemical toxicity as in the case of uranium (see 10 CFR 20.1201(e)). IRF(t) = Intake retention fraction correspond-ing to type of measurement for time t The metabolic models in ICRP-30 and accompa- after estimated time of intake, nying addenda (Ref. 3) and ICRP-54 (Ref. 1) pre-4.3.1 Evaluating Spot Samples sent acceptable bases for estimating intake from bio-assay measurements. Other acceptable models are the If the total urine or feces is not collected for the tritium model developed by Johnson and Dunford 24-hour period, the following equations may be used (Ref. 6) and the plutonium urinary excretion model to estimate the total activity excreted or eliminated developed by Jones (Ref. 5). over the 24-hour period based on less frequent sam-pling (spot samples).

The use of computer codes that apply these mod-els is also acceptable for evaluating bioassay measure- AAj = Ci E(ti-ti-1 ) Equation 2 ments provided it can be demonstrated through docu-mented testing that the models and methods em- Ai= AA, + AA 2, + ... AAj Equation 3 ployed provide results that are consistent with the ac-ceptable models. There are several commercially 6 available computer codes for interpreting bioassay For purposes of this guide and the application of the data from NUREG/CR-4884, the parameter IRF denotes both intake re-measurements; these codes may be used as long as tention fractions and intake excretion fractions.

the software application is based on acceptable mod- 7 The term "24-hour urine" means the total urine output col-els and provides results that correctly implement the lected over a 24-hour period, and the term "24-hour feces" means the total feces output collected over a 24-hour period.

models. No specific computer codes are endorsed by "Accumulated urine" and "accumulated feces" mean the total the NRC staff. Licensees are responsible for ensuring output since time of exposure.

8.9-5

_- - Li i where: Logarithmic interpolation should be used for in-terpolating retention and excretion fractions (see Ex-AAi = Activity or amount of radioactive ma- ample 2 in Appendix A). For example, using the terial in sample i NUREG/CR-4884 (Ref. 4) data, an IRF value for 2.8 i = The sequence number of the sample days post-intake should be calculated by a logarith-mic interpolation between the 2-day and the 3-day CQ = The radionuclide concentration in IRF values.

urine (activity/liter) or feces (activity/

gram) of sample i, decay corrected to Examples of the application of intake retention and excretion fractions based on the NUREG/

the time of sampling CR-4884 data set are provided in Appendix A.

E = Daily excretion rate (use measured 4.3.2 Evaluating Multiple Bioassay Meas-rates when available, or assume val- urements ues of 1.4 liters/day for urine and When multiple bioassay measurements are made, 135 grams/day for feces for standard man or 1.0 liter/day for urine and a statistical evaluation of the data should be per-formed. Numerous statistical methods are available 110 grams/day for feces for standard for evaluating multiple measurements, but the results woman) will be no better than the reliability of the data set.

ti = The time (days) after intake that Measurements that are suspect or known to be inac-sample i is collected curate should be excluded from the analysis. Addi-tional measurements should be used for obtaining an Ai = Total activity excreted or eliminated appropriate data set. For the evaluation of multiple up to time ti measurements, NUREG/CR-4884 (Ref. 4) recom-This method is applicable only if spot samples are mends the use of unweighted, minimized chi-squared collected with a frequency that is consistent with the statistics, assuming all variances are the same (i.e., a significance of changes in the excretion rates. In gen- least squares fit). This method is acceptable to the eral, spot samples should be collected frequently NRC staff; it is simple and straightforward for evaluat-enough that there is no more than a 30% increase in ing multiple bioassay measurements. The equation is the IRFs between bioassay measurements. For exam- as follows:

ple, if the IRF for accumulated urine increases at a rate of 30% per day, spot samples should be collected =- IRFi(t) x Ai(t) Equation 5 1,__

daily. If the rate is 10% per day, collecting spot sam- 2:j IRFi(t) 2 ples once every 3 days would be adequate. Also, the Other statistical analyses of the data may provide rapid clearance and excretion of inhaled particles a better fit of the data, considering the particulars of from the N-P region of the lung makes it important the measurements. For example, a minimized chi-that at least one spot sample be collected within the squared fit weighted by the inverse of the variance first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after exposure. Otherwise, the reliability may be used. Several methods are available for esti-of using accumulated samples and excretion fractions mating the variance of measurements. One approach, for calculating intakes should be examined; calcula-applicable to radioactivity measurements, is to assume tions based on spot samples correlated to 24-hour that the variance is proportional to the value of the samples may provide better estimates.

measurement itself. Another is the assumption that For spot samples used to estimate an equivalent the variance is proportional to the expected value 24-hour sample, correcting for abnormal conditions (Ref. 7).

of high or low fluid intake or excessive loss of fluids In selecting the statistical method to be used for by perspiration may be warranted. NCRP-87 (Ref. 2) evaluating multiple measurements, consideration presents the following method based on a relationship should be given to available information, particularly between the specific gravity (sp. gr.) of the sample to observed variability of the data and reliability of indi-the average specific gravity of urine (1.024 g/ml). vidual measurements. Other statistical methods are 1.024 - I (g/ml) acceptable to the NRC staff provided it can be dem-corr. conc. = meas. conc. onstrated that the results provide reasonable estimates meas. sp. gr. - 1 (g/ml) of intake.

Equation 4 4.4 Adjusting Intake Estimates for Multiple and An alternative to this method is a correction Continuous Intakes based 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

A (t) = Amount of activity in compartment allow for the individual quantification of each expo- or whole body at time t following on-sure. As a general rule, if intakes are separated in set of intake time so that the retained or eliminated fraction from an earlier intake is less than 10% of the retention or T = Duration of intake (exposure time excretion fraction for the next intake, each intake period) may be evaluated separately without regard to any previous intakes. t = Time from onset of intake to time of measurement Continual intakes that are distributed equally in IRF(u) = Intake retention fraction at time u in size and time may be approximated using a relation-compartment or whole body for a ship based on time integration of the IRF. The total intake is estimated by dividing the measured activity single intake of a radionuclide by the appropriate time-integrated retention or excre- u = Variable time between integration tion fraction. An example using the IRF values from limits NUREG/CR-4884 (Ref. 4) would be to perform a numerical integration over the individual IRF values n = number of increments covering the time period of interest. Any one of a number of standard integration techniques, including numerical and analytical solutions, can be used. For The number of increments to be used for a nu-example, using the trapezoidal rule (see Example 7 in merical integration should be selected to minimize Appendix A) yields the following method: unnecessary errors associated with the particulars of the IRF values over which the integration is being per-For bioassay measurements taken during an ex- formed. In general, errors associated with the inte-posure time interval, the equation is: gration technique used should be limited to less than 10%.

I A(t) X T for t < T Equation 6 4.5 Correcting Intake Estimates for Particle Size Differences f IRF(u) du 0 The models used for deriving intake retention and excretion fractions, such as those in NUREG/

Using the trapezoidal rule to solve Equation 6 CR-4884, are typically based on 1-micrometer activ-ity median aerodynamic diameter (AMAD) particles.

yields the following approximation:

It is acceptable to correct intake estimates for parti-Equation 7 cles of different sizes. These corrections often help A(t) x T x n explain retention or excretion rates different from IRF(t) + IRF(t = 0.1 days)

IRF(un-i )

those expected, such as would occur for larger parti-

+ IRF(ul) + .**+

cles preferentially deposited in the upper region of t X L2 the respiratory tract (N-P region) with more rapid clearance times; Guidance for determining AMADs is For bioassay measurements taken after an expo- provided in Regulatory Guide 8.25, "Air Sampling in sure interval, the equation is: the Workplace" (Ref. 8).

Equation 10, taken from Appendix B to A(t) X T for t > T Equation 8 NUREG/CR-4884 (Ref. 4), should be used for revis-T IRF (u) du ing the totaf body IRFs in NUREG/CR-4884 to parti-cle size distributions between 0.1 to 20 pirm AMAD.

t-T Equation 10 Likewise, Equation 8 may be approximated using the trapezoidal rule, which yields Equation 9:

I =

IRFAMAD

= IRF1 IRF~),Ip"I E H50TWT TH50TWT DN-P(AMAD)

DN..p(l pum)

A(t) X n HSOTWT DT-B(AMAD)

[IRF(t - T) + IRF(t) + IRF(ul) + ... + IkF(un1i)J B TH50TWT DT-B ( Ym) where: HSOTWT Dp(AMAD)1 fTHpXTWT Dp(1 pM)

I = Total intake during period T 8.9-7

where: Table 1 Aerosol AMAD IRFAMAD = IRF for the activity median 0.2 Am 0.5 gm 0.7 Aim 1.0 Am aerodynamic diameter (AMAD) of interest DN-P 0.05 0.16 0.23 0.30 IRF1Im = Total body IRF for inhala- DT-B 0.08 0.08 0.08 0.08 tion of 1 Aim AMAD aero- Dp 0.50 0.35 0.30 0.25 sols (these IRFs are given Total in Appendix B to NUREG/ Deposition 0.63 0.59 0.61 0.63 CR-4884 (Ref. 4))

2.0 jim 5.0 jm 7.0 jm 10.0 jim

= Summation over all tissues (and organs) T DN-P 0.50 0.74 0.81 0.87 N-P, T-B, P DT-B 0.08 0.08 0.08 0.08

= The compartments or re-gions of deposition of the 0.17 0.09 0.07 0.05 respiratory tract: the Total nasopharyngeal passage re- Deposition 0.75 0.91 0.96 1.00 gion (N-P), the tracheobronchial region (T-B), and the pulmonary Equation 10, for revising the IRF for different region (P) particle sizes, is applicable for the total body IRF.

ICRP-54 (Ref. 1) provides graphs of IRF values for fN-P,T, fT-BT, fPT = The fraction of committed 0.1 Am, 1 gim, and 10 jim AMAD particles for other dose equivalent in the tis- tissues and excreta. Intake retention and excretion sue T resulting from depo- functions are derived for other AMAD particles sition in the N-P, T-B, and based on the acceptable biokinetic modeling as dis-P regions, respectively. cussed in Regulatory Positions 4.2 and 4.3.

(Values for individual radi-It is acceptable to take into account particle size onuclides are contained in distribution and its effect on lung deposition and the Supplements to Part 1 transfer in evaluating an individual's dose. ICRP-30 of ICRP-30 (Ref. 3).)

(Ref. 3) (with supplements) provides data and meth-ods for use in evaluating the lung deposition and re-H50T = Committed dose equivalent sultant doses for particle sizes between 0.1 and 20 gim for tissue (or organ) T per AMAD. For particles with AMADs greater than 20 unit intake gm, complete deposition in the N-P region can be assumed.

WT = Tissue (or organ) weighting It is acceptable to compare the estimate of intake factor, from 10 CFR for different particle sizes with the ALIs in Appendix 20.1003 B to §§20.1001-20.2401 for demonstrating compli-ance with intake limits. The ALIs are based on a par-DN-P, DT-B, Dp ticle size of 1 micrometer. However, modifying the

= Regional deposition frac-ALI values for different particle size distributions re-tions for an aerosol enter-ing the respiratory system. quires prior NRC approval (10 CFR 2 0.1 2 04(c) (2)).

(Values presented in Table 4.6 Use of Individual Specific Biokinetic Model-1 below.) ing Individual specific retention and excretion rates Equation 10 may not provide valid corrections may be used in developing biokinetic models that for time periods shortly following intakes. The time differ from the reference man modeling (10 CFR after intake for which Equation 10 begins to yield sat- 20.1204(c)). The quality and quantity of data used isfactory results is less than 1 day for Class D com- for this type of individual specific modeling should be pounds. For Class W compounds, this time is about 7 sufficient to justify the revised model. Licensees days following intake, and for Class Y compounds, should not attempt to develop individual specific re-about 9 days following intake. tention and excretion fractions in the absence of ac-8.9-8

tual biochemical and particle size information. Indi- 20.2103(b), and 20.2106(a). For additional informa-vidual specific modeling is not required but may be tion on recordkeeping and reporting occupational ex-developed; the modeling as presented above in Regu- posure data, including intakes, refer to Revision 1 of latory Position 4.2 is acceptable for evaluating regula- Regulatory Guide 8.7, "Instructions for Recording tory compliance. and Reporting Occupational Radiation Exposure Data" (Ref. 10).

5. CALCULATING DOSE FROM ESTIMATES OF INTAKE D. IMPLEMENTATION Regulatory Guide 8.34, "Monitoring Criteria and The purpose of this section is to provide informa-Methods To Calculate Occupational Radiation tion to applicants and licensees regarding the NRC Doses" (Ref. 9), contains additional guidance on de- staff's plans for using this regulatory guide.

termining doses based on calculated intakes once the intake is determined. Except in those cases in which an applicant pro-poses an acceptable alternative method for complying

6. RECORDKEEPING with specified portions of the Commission's regula-Records of measurement data, calculations of in- tions, the methods described in this guide will used by takes, and methods for calculating dose must be the NRC staff for evaluating compliance with 10 CFR maintained as required by 10 CFR 20.1204(c), 20.1001-20.2401.

8.9-9

REFERENCES

1. International Commission on Radiological Pro-tection, "Individual Monitoring for Intake of 5. S. R. Jones, "Derivation and Validation of a Uri-Radionuclides by Workers: Design and Interpre- nary Excretion Function for Plutonium Applica-tation," ICRP Publication 54, Pergamon Press, ble Over Ten Years Post Intake," Radiation Pro-tection Dosimetry, Volume 11, No. 1, 1985.

New York, 1988.

2. National Council on Radiation Protection and 6. J. R. Johnson and D. W. Dunford, GENMOD-Measurements, "Use of Bioassay Procedures for A Programfor Internal Dosimetry Calculations, Assessment of Internal Radionuclide Deposi- AECL-9434, Chalk River Nuclear Laboratories, tion," NCRP Report No. 87, February 1987. Chalk River, Ontario, 1987.

3. International Commission on Radiological Pro- 7. K. W. Skrable et al., "Intake Retention Func-tection, "Limits for Intakes of Radionuclides by tions and Their Applications to Bioassay and the Workers," ICRP Publication 30, Part 1, and Estimation of Internal Radiation Doses," Health ICRP Publication 30, Supplement to Part 1, Ap- Physics Journal, Volume 55, No. 6, 1988.

pendix A, Pergamon Press, New York, 1978. 8. U.S. Nuclear Regulatory Commission, "Air Sam-

4. E. T. Lessard et al., "Interpretation of Bioassay pling in the Workplace," Regulatory Guide Measurements," U.S. Nuclear Regulatory Com- 8.25,* Revision 1, June 1992.

mission, NUREG/CR-48 84,

• July 1987. 9. U.S. Nuclear Regulatory Commission, "Monitor-ing Criteria and Methods To Calculate Occupa-tional Radiation Doses," Regulatory Guide

'Copies may be purchased at current rates from the U. S. Gov- 8.34," July 1992.

ernment Printing Office, Post Office Box 37082, Washing-ton, DC 20013-7082 (telephone (202) 512-2249 or (202) 10. U.S. Nuclear Regulatory. Commission, "Instruc-512-2171; or from the National Technical Information Serv- tions for Recording and Reporting Occupational ice by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161. Radiation Exposure Data," Regulatory Guide 8.7, 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-

• Correct intake estimates for particle size differ-tion and excretion functions for calculating intakes ences.

based on bioassay measurements. The data used for these examples are taken from NUREG/CR-4884, The examples in this appendix are:

"Interpretation of Bioassay Measurements." These Calculating Intake Following an Inadver-Example 1:

examples do not illustrate the use of all possible bio- tent Exposure Based on a Single Bioassay assay or health physics measurements that may be Measurement available (e.g., excreta and air sampling measure-ments) during a specific exposure incident. The pur- Example 2: Calculating Intake with Unknown Time of pose of these examples is not to define the total scope Intake of a bioassay program, rather, these examples dem-onstrate the use of the calculational techniques pre- Example 3: Using Multiple Measurements To Calcu-sented in Regulatory Position 4 of the guide for corre- late Intake lating measurements to intake. The examples demon-strate the use of retention and excretion fractions to: Example 4: Uranium Intake

• Estimate intake from one or several bioassay Example 5: Comparison of Air Sampling and Bioassay measurements, Measurement Results

• Adjust intake estimates for multiple or continu-ous intakes, and Example 6: Correcting Intake Estimates for Particle Size Difference

• E. T. Lessard et al., "Interpretation of Bioassay Measure- Example 7: Adjusting Intake Estimates for Multiple ments," U.S. Nuclear Regulatory Comrmission, NUREG/

CR-4884, July 1987. and Continual Intakes A-1

EXAMPLE 1 Calculating Intake Following an Inadvertent Exposure Based on a Single Bioassay Measurement Determination that Intake Occurred where:

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

Material," 10 CFR 35.315 (a) (8) requires licensees to A (t) = Thyroid content at time (t) of meas-perform thyroid burden measurements for all occupationally exposed individuals who were involved urement in the preparation or administration of therapeutic IRF(t) = Intake retention fraction for meas-dosages of 131I. These measurements are to be per- ured 1311 at time interval (t) after es-formed within 3 days following the preparation or ad- timated time of intake.

ministration.

The table of thyroid IRF values for 131I is found In this example, the required bioassay measure- on page B-103 of NUREG/CR-4884. The IRF value ments are conducted for all involved individuals fol- at time after intake of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (t=24 hours) is 0. 133.

lowing a therapy patient iodination. It is identified that the technologist who prepared the dose has a measured thyroid content of 0.080 pLCi of 131I. It is Substituting the measured thyroid content and the corresponding thyroid IRF value into the above determined that the technologist most likely received equation and solving yields the following:

an inhalation intake when a difficulty was encoun-tered during the preparation of the dosage. The time of the measurement is determined to be 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> af- 0.080 AuCi I= = 0-60 uCi (2.2 E + 4 Bq) ter the estimated time of intake. 0.133 Evaluation Procedure As discussed in Regulatory Position 2.3, if a bio-assay measurement indicates that the potential intake is greater than the evaluation level of 0.02 AL!,

The lung clearance class for all chemical com- additional exposure data or additional bioassay meas-pounds of iodine is Class D. Since no information is urements should be examined for determining the available on particle size distribution, a 1 gm AMAD best estimate of intake. The ALI for Class D 131I is particle size must be assumed. Using Equation 1 from 5E+1 ACi* (from Appendix B to Regulatory Position 4.3 for estimating intake from a §§20.1001-20.2401); therefore, the evaluation level single bioassay measurement, the intake can be esti- is 1 gCi (0.02 times the ALI value of 5E+1 gCi).

mated as follows: Since the estimated intake is less than this level, no further evaluation is warranted.

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

A-2

EXAMPLE 2 Calculating Intake with Unknown Time of Intake Determination that Intake Occurred Substituting the measured body content and the corresponding IRF value into the above equation and solving yields the following:

While conducting a routine termination bioassay measurement of a maintenance worker at a nuclear power plant, a whole body content of 0.40 ,uCi of 0.40 ,uCi I= = 6.26,uCi 60Co was measured. Since the worker had entered a 6.39E- 2 contaminated area earlier in the day, she was in-structed to shower and don disposable coveralls to en- The ALI for Class W 60 Co is 2E+2 gCi; there-sure that no external contamination of her skin or fore, the evaluation level is 2E+2 gCi times 0.02 or clothing was present. A second bioassay measurement 4 giCi. Since the calculated intake is greater than the was conducted and a whole body content of 0.40 ,uCi 4 jiCi evaluation level, additional information should of 60 Co was confirmed. Routine surveys show that be sought.

60 Co at this facility is generally Class W.

As part of the additional review, the health phys-ics supervisor conducted a further review of the indi-Evaluation Procedure vidual worker's activities in an attempt to determine the actual time of exposure. A review of air sample The health physics supervisor was notified. In an data and worker access failed to indicate any abnor-attempt to determine the cause and time of exposure, mal exposure conditions. For unknown situations, the an examination was conducted of plant survey data, exposed individual is most often the best source of including airborne activity measurements for areas of information when attempting to define the exposure the plant where she had recently worked. This exa- conditions. The individual may remember unusual mination failed to identify a source of exposure; all circumstances that at the time may have seemed ac-areas to which the maintenance worker had access ceptable, but upon further examination could have over the past several days were found to be minimally resulted in the unexpected exposure. In this case, the contaminated and no elevated levels of airborne ra- maintenance worker remembered breaching a con-dioactive material had been experienced. This infor- taminated system to remove a leaking valve. The sys-mation, in addition to the determination that the tem was supposed to have been depressurized and worker was not externally contaminated, indicated drained. However, she remembered that when the that the intake did not occur during the past several system was breached, a slight pressure relief was ex-days. In the absence of any other information, the perienced and a small amount of water was drained.

licensee assumed that the intake occurred at the mid- Following a review of the Radiation Work Permit point in the time since the worker's last bioassay (RWP) log and the containment entry log, it was de-measurement. This assumption allows for an initial as- termined that this incident occurred 28 days prior to sessment of the potential significance of the intake, In the measured body content. Prior to and since that this case, the most recent bioassay measurement was time, her other work activities have been in areas conducted 6 months (180 days) before, which repre- only moderately contaminated; an additional intake sented her initial baseline measurement at the time of would have been unlikely. Based on these data, the hire. Using these assumptions, the calculation of in- most likely time of intake was determined to have oc-take is as follows: curred during the contaminated system breach 28 days before.

The appropriate IRF values for this exposure I A (t) should be for a time of 28 days post-intake. Also, the IRF(t) "total body" IRF values should be used, since the body content has been determined by an ih vivo total body measurement. A 28-day IRF value is calculated where: by performing a logarithmic interpolation between the I = Estimate of intake in units the same 20-day value and the 30-day value.

as A(t)

A (t) = Whole body content at time (t) of IRF (day X) = exp[ In (IRF(day Z)) - In (IRF(day measurement x[ (R (day Z) -(day Y) )

IRF(t) = Intake Retention Fraction for meas-ured 6 0Co at time interval t after esti- x (day X - day Y) +Iin (IRF (day Y))]

mated time of intake (half of 6 months or 90 days)

A-3

I-where: Substituting this interpolated IRF value into the IRF (day X) = Interpolated IRF value, calculated equation for calculating intake and solving yields:

at day X, which lies between two IRF values occurring at days Y and Z; in this case, X = 28 days, Y = 20 days, and Z = 30 days IRF (day Y) = IRF value occurring at day Y, in 0.126

= 3.17 ACi (11.7 E+4 Bq)

IRF (day Z) = IRF value occurring at day Z, in this example, 30 days Solving this interpolation yields: Since this calculated intake was less than the evaluation level (i.e., less than 0.02 times the ALI value of 2E+2 uCi for 1 gm AMAD, Class W, 6 0 Co),

and the data reviews did not indicate any other IRF (28 days) = expIY'1 (IRF(30 days)) - In (IRF(20 days))

[Lt 30 days- 20 days ) source of exposure, no further evaluation is war-ranted. However, had this calculated intake exceeded the evaluation level of 4 gCi, additional bioassay X (28 days - 20 days) In (IRF (20 days))1 measurements over the next several days should be considered. If the licensee had previously determined that monitoring for internal exposure was required

= ex[( In (0.123)-In (0.140) X 8 das+ n(0 1402 pursuant to 10 CFR 20.1502(b), this intake would

= 10 days J have been recorded in the worker's exposure records and provided to the worker as a part of her termina-

= 0.126 tion exposure report, for which NRC Form 5 may be used.

A-4

EXAMPLE 3 Using Multiple Measurements To Calculate Intake Determination that Intake Occurred where:

A laboratory worker accidentally breaks a flask containing a volatile compound of 32p, The worker I = Estimate of the 32p intake exits the work area. Contaminated nasal smears indi-cate that the worker may have received an acute in- IRF(t) = Excretion fraction for 24-hour urine halation intake. The results of work area air sampling measurements are reviewed, indicating increased air- collected 2 days post-intake, which borne levels. Bioassay measurements are initiated to equals 4.17E-02 (see NUREG/

assess the actual intake. CR-4884, page B-25)

Evaluation Procedure A(t) = 1.5 gCi, value of the second-day From a review of the biokinetics for inhalation 24-hour urine sample intakes of 32p, it is determined that urine sample col-lection followed by liquid scintillation detection would provide the best bioassay data for calculating intake. The ALI value for inhalation intakes of Class D For the particular 3 2 P compound involved, the appro- compound of 32P is 9E+2 gCi. The initial estimate of priate lung clearance class is Class D. Also, lacking intake of 36 ACi exceeds the evaluation level of 0.02 other data, a particle size distribution of 1 gim AMAD ALI, which is the recommended level above which must be assumed. multiple bioassay measurements should be considered The first voiding is analyzed and the results verify for assessing actual intake. Follow-up measurements the occurrence of an intake. However, because of the are made. By examining the tabulated IRF values for particular characteristics of the sample (e.g., collec- 24-hour urine for 32P, the RSO determines that tion time relative to time of exposure), the results are 24-hour urine samples should be collected for the not considered reliable for calculating an intake. 10th and 20th day.

Follow-up 24-hour urine samples are collected. The results of a second-day 24-hour sample indicate a to-tal activity of 1.50 jiCi, decay corrected from the time Note: Daily measurements should be considered the sample is counted to the end of the 24-hour sam- if the initial assessment indicates an intake greater ple collection period. Using Equation 1 from Regula- than the investigation level of 0.1 ALI. The time peri-tory Position 4.3, an initial estimate of the intake is ods above were selected for purposes of demonstrat-calculated as follows: ing the calculational method. In actuality, one would typically examine the third-day results before decid-ing on the need and frequency of additional measure-A (t) ments.

IRF(t) 1.50 uCi The following table summarizes the results of the 4.17E - 02 24-hour urine sample measurements, the correspond-ing IRF value from NUREG/CR-4884, and the calcu-

= 36 uCi (1.3E + 6 Bq) lated intake based on the individual measurements using 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 36 10 1.3E-1 4.34 E-3 30 20 6.OE-2 1.55 E-3 39 A-5

The best estimate of intake is calculated using Equa- If the licensee has previously determined that tion 5 from Regulatory Position 4.3.1 to obtain the esti- monitoring for internal exposure pursuant to 10 CFR mate of the intake. This estimate is calculated from the 20.1502(b) is required, the data and results of this bioassay measurements obtained on three different days evaluation are placed in the worker's exposure following the incident: records and included on the worker's NRC Form 5 report. I I= , IRFI x Al a IRF2 (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 32 I = 36 pCi (1. 3E - 6 Bq ) p A-6

EXAMPLE 4 Uranium Intake Determination that Intake Occurred E = Daily excretion rate of 1.4 liter/day for urine for reference man (refer-An accident at a facility that produces UF6 (ura- ence woman rate is 1.0 liter/day) nium hexafluoride) results in a worker being exposed to an unknown concentration of UF6 with a natural ti = Time (in days) after intake to when uranium isotopic distribution. Based on information the first sample was taken in Appendix B to §§20.1001-20.2401, the UF 6 is = Time (in days) after intake to when identified as an inhalation lung Class D compound.

the previous sample was taken (0 days in this case)

Evaluation Procedure The accumulation for the second sample is calcu-The health physics supervisor examines the sig- lated in a similar manner:

nificance of the exposure. Based on potential air-borne radioactive material levels, it is determined that bioassay measurements should be conducted. Exam- AA 2 = C2 x E x (t2 -t 2 1 )

ining the biokinetics and decay characteristics for ura-nium isotopes, the health physics supervisor deter- =210 x 1.4 x (2.4-1.8) mines that urine sample collection and analysis should be performed. = 176 fg Spot urine samples are collected over the follow- Accumulation for the final sample is similarly cal-ing few days with the results presented in the follow- culated.

ing table.

Concentration AA 3 = C3 x E x (t 3 -t 3 1a)

Time of Sample of Uranium in Urine (Days Post-Intake) (Wg/l) = 140 x 1.4 x (3.0-2.4) 1.8 460 = 118 Mg 2.4 210 3.0 140 The accumulated urine through the third spot sample collected on day 3 is calculated by summing Using the results of the spot samples, accumu-all the accumulations.

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- An = AA1 +AA 2 + AA3 sented in units of micrograms per liter, Because of the long half-lives of uranium isotopes, decay correction = 1,160 + 176 + 118 to time of sampling is not required.

= 1, 4 5 0 zg Using Equation 2, the amount of uranium in the first sample is calculated as follows:

where:

AA, = Cl x E x (ti -ti1 1 ) A3 = Accumulated activity up to time, t, of the third sample collected on the

=460 x 1.4 x (1.8-0) third day post-intake

= 1160 ug Using the calculation for accumulated urine activ-ity, the intake may be calculated by applying the method of Equation 1 from Regulatory Position 4.3.

where: The IRF for this calculation would be that for the ac-AA, = Activity or amount of uranium in the cumulated urine for uranium, Class D, from Appen-first sample dix B to NUREG/CR-4884 (page B-163). Because of the long radiological half-lives, the IRFs for all the C1 = Concentration of uranium in the first uranium isotopes are essentially the same; the values sample for 23 8U have been used for this example.

A-7

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

= 1, 450 Activity = U(weight) x gCi/g conversion 0.291 = 4,980 ,ug x 0.35 gCi/g x 1E-06 g/g

= 1.7E-03 gCi (64 Bq) U-234

= 4, 980 Ag

= 4,980 gg x 0.015 gCi/g x 1E-06 g/pLg where: = 7.5E-05 giCi (2.8 Bq) U-235 I = Estimate of intake with units the = 4,980 gg x 0.33 jiCi/g x IE-06 g/j~g same as A(t) = 1.6E-03 gCi (61 Bq) U-238 IRF(t) = Intake retention fraction for ura-nium, Class D inhalation for the ac- These calculated activity intakes for the uranium cumulated urine in the third day fol- isotopes are much less than the evaluation level of 0.02 ALI, at which additional evaluations (e.g.,

lowing time of intake measurements) should be considered. Therefore, A(t) = Value of the calculated accumulated considering the significance of the radiation exposure, urine based on the three spot samples the bioassay measurements conducted provide an Gig) adequate basis for calculation of the intake.

A conversion from a mass (g+/-g) to activity (,uCi) A separate limit of 10 milligrams in a week for for the different percentages of the uranium isotopes soluble uranium is contained in 10 CFR 20.1201(e) can be performed based on isotopic specific activity. and Appendix B to §§20.1001-20.2401. This limit is Natural uranium is composed of three isotopes: 234U based on the chemical toxicity, which should be at 0.0056% atom abundance, 235U at 0.72%, and evaluated in addition to the radiation exposure. The 238 U at 99.274%. Based on these abundances and the above evaluation determines that the total intake was radioactive decay constants for these isotopes, the 4,980 jig (4.98 mg). Therefore, the 10 mg/wk limit of corresponding weight to activity conversion factors 10 CFR 20.1201(e) was not exceeded.

I A-8

EXAMPLE 5 Comparison of Air Sampling and Bioassay Measurement Results Determination that Intake Occurred compounds of cesium (refer to Appendix B to

§§20.1001-20.2401). The table of inhalation IRFs During fabrication of a 137Cs source, the airborne for 137Cs may be found on page B-111 of NUREG/

radioactive material levels to which the worker is ex- CR-4884. The IRF value for the total body, 0.8 day posed are sampled, using a continuous low-volume air after intake, is 6.26E-01. Substituting these values sampler. At the end of the 8-hour shift, the technolo- into Equation 1, the calculation of the intake is:

gist counts the filter and calculates that the average airborne activity during the sample period was 5.4E-7 iCi/ml (20,000 Bq/m3 ) of 13 7Cs. The elevated levels I A(t)

IRF (t) are unexpected and the health physicist compares the measured levels with the 137 Cs Class D DAC value from Appendix B to §§20.1001-20.2401. The 8-hour 0.21 M 0 34 uCi (12, 400 Bq) average concentration is 9 times the DAC value for

-1=

137Cs of 6E-8 gCi/ml. The worker was not wearing a 6.26 E -01 respiratory protective device during the fabrication The two calculated estimates of 137Cs intake are process as elevated airborne radioactive material lev- significantly different. The health physicist discusses els were not anticipated. the work activities leading to the exposure with the The health physicist evaluates the significance of individual and determines that the differences could the exposure by calculating the intake (based on the be attributable to several factors:

air sample data) and comparing the result with the

• A difference in the breathing rate assumed for ALI value for 137Cs from Appendix B to reference man and that of the worker,

§§20.1001-20.2401 (137 Cs, inhalation ALI = 200 Aci).

• A difference in the concentrations of airborne radioactive material as sampled by the low-As a first approximation, the health physicist as- volume sampler and the levels as breathed by the sumes that the worker was exposed to the average worker. These differences could be due to the airborne 137 Cs concentration represented by the activ- location of the sampler and the worker relative ity on the air sampler filter for the entire 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> of to the source of airborne material and the direc-the work shift. A worker breathing rate of 1.2 m3! tion of air flow, and hour (light work activity) is also assumed. The follow-

• A difference in exposure time assumed for the ing intake is calculated: worker (i.e., the actual exposure was less than the full 8-hour shift).

Intake = 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> X 1.2 IE6-m hours ml m3 The available data cannot resolve the difference between the air sampling results and the in vivo bioas-

= 5.2 /uCi(1.9E5 Bq) say analysis: additional bioassay measurements and a review of the worker's exposure relative to the This calculated intake is greater than the evalu- workplace ambient air sampling should be conducted ation level of 0.02 ALI. The health physicist orders to resolve the difference.

an in vivo bioassay measurement to be performed on the worker. The estimate to be used as the dose of record should be the value considered to better represent the Evaluation Procedure actual exposure situation. In general, bioassay meas-urements will provide better estimates of actual The in vivo measurement is performed the fol- worker intakes, provided the data are of sufficient lowing morning, approximately 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> after the es- quality. Air sampling results typically represent only timated time of intake. Since the exposure time spans an approximation of the level of radioactive material an 8-hour work period and time-dependent airborne in the air breathed by the worker. Appropriately col-activities are unknown, the worker's exposure is as- lected and analyzed, bioassay results can provide a sumed to have occurred at the midpoint in the 8-hour better indication of actual intakes.

shift. The results indicate a total body activity of 0.21 ACi of '3 7 Cs. The -corresponding intake may be esti- This example does not address the health physics mated by using Equation 1 from Regulatory Position issues concerning the elevated airborne levels and po-4.3. Inhalation Class D is assigned for all chemical 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 retention Evaluation Procedure fractions (in NUREG/CR-4884) are based on a 1-jim AMAD particle size distribution. Rarely (if ever) will the actual distribution of airborne particulates be The IRF may be adjusted for a 2.0-jim AMAD completely characteristic of 1-jm AMAD particles. particle size using Equation 10 of Regulatory Position Evaluating different particle size distributions can as- 4.5. The approximation relationship of this equation sist in explaining retention and excretion rates that is applicable to the total body IRFs for particle sizes are different than would be expected, based on the between 0.1 jim and 20 jim AMAD.

standard modeling (see 10 CFR 20.1204(c)(1)).

Values for DN-P, DT-B, and Dp derived from the In this example, it is assumed that the actual par- data in Part 1 of ICRP Publication 30 (pages 24 and ticle size distribution has been determined to be char- 25) are presented in the following table. (Note: the acterized as a 2-jpm AMAD of Class W compound of deposition fractions presented in Table B.8.1 of 60 Co. It is assumed that the intake occurred 20 days NUREG/CR-4884 (page B-801) contains errors and before the bioassay measurements were made. should not be used.)

Table 6A. Regional Deposition Fractions for Aerosol with AMADs Between 0.2 and 10 jm 0.2 jm 0.5 jm 0.7 jm 1.0 jim DN-P 0.05 0.16 0.23 0.30 DT-B 0.08 0.08 0.08 0.08 Dp 0.50 0.35 0.30 0.25 Total Deposition 0.63 0.59 0.61 0.63 2.0 Am 5.0 Am 7.0 jm 10.0 jim DN-P 0.50 0.74 0.81 0.87 DT-B 0.08 0.08 0.08 0.08 Dpo 0.17 0.09 0.07 0.05 Total Deposition 0.75 0.91 0.96 1.00 The values of fN-P,T, fT-B,T, and fPT for Class W centages and must be converted to decimal fractions 6°Co needed for Equation 10 are listed in the Supple- before use. The decimal fractions for each tissue, ment to Part 1 of ICRP Publication 30 on page 40. along with its weighting factor and committed dose These values in ICRP Publication 30 are given as per- equivalent factor, are presented in the following table.

Table 6B. Input Values HSOT (per unit intake) *`

Tissue fN-PT fT-B,T, fP,T War (Sv/Bq)

Gonads 0.35 0.21 0.44 0.25 4.OE-09 Breast 0.19 0.17 0.64 0.15 4.2E-09 Red Marrow 0.20 0.17 0.63 0.12 4.2E-09 Lungs 0.02 0.02 0.96 0.12 3.6E-08 Thyroid 0.03 Bone Surface 0.03 LLI Wall 0.45 0.15 0.40 0.06 8.2E-09 Liver 0.21 0.19 0.60 0.06 9.2E-09 Remainder 0.10 0.09 0.81 0.06 8.OE-09 Tissue weighting factors from 10 CFR 20.1003.

Committed dose equivalent per unit intake.

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

DN-P(AMAD)

IRF(AmAD) = IRF(LIM)': T H50TWT DN-P( lgm)

TH50TWT DT-B (AMAD)

+ fT-B,T H50TWT DT-B (O1m) tTH5OTVW

'IH50T'A Dp(AMAD)

+ fP,T H50TWT "TH50TWI Dp(lgm) J Substituting input values from the table into the . The above method for revising the IRF for differ-above equation results in the following: ent particle sizes, is applicable for the total body IRF.

ICRP-54 provides graphs of IRF values for 0.1 gIm, 1 Total Body IRF(2 gm) gm, and 10 gm AMAD particles for other tissues and at 20 days after intake = 8.5 E-02 excreta.

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

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EXAMPLE 7 Adjusting Intake Estimates for Multiple and Continual Intakes The following is a simplified example showing the t = Time from onset of intake to time of application of the numerical integration of IRFs over measurement a continual exposure period. It is recognized that most exposure situations do not involve chronic expo- u = Variable time between integration sures to airborne radioactive material; most intakes limits can be reasonably characterized as acute exposures.

However, when exposures extend over a longer pe- IRF(u) = Intake retention fraction at time u in riod of time (i.e., more than a few days) it may be compartment or whole body for a necessary to adjust the IRFs, which are based on sin- single intake of a radionuclide gle acute intakes, to account for the extended expo- n = Number of increments sure period.

For this example, the time interval values are:

Urinalysis performed on a Friday indicated an uptake of 3 H for a worker. It was determined that the T = 5 days (period of intake) worker was continually exposed to 3 H as HTO (water vapor) for the 5 work days of the prior week (i.e., t = 11 days (number of days following Monday through Friday of the previous week). Re- onset of intake) sults of the 24-hour urine sample reveal 10 g.Ci (3.7E+05 Bq) of 3 H. The integration period is for the time (t-T) to t; therefore the interval consists of a total of 6 days. For Evaluation Procedure the numerical integration, the 6-day time interval has been divided into 6 equal 1-day increments.

Since the exposure occurred over an extended period of time and the measurement was taken after The IRF values for the calculation, taken from the exposure interval, the methods of Equation 9 NUREG/CR-4884 (page B-711), are listed in the from Regulatory Position 4.4 should be used. following table. If IRF values are not presented for the day of interest, a logarithmic interpolation should be performed to calculate the value.

Time Intervals from A(t) n (t-T) to t IRF

[IRF(t - T) + IRF(t) + IRF(u!) + ... d IRF(u,-j (in 1-day Increments) (24-hr Urine) 6 2.85E-02 7 2.66E-02 where:

8 2.48E-02 A (t) = Amount of activity in compartment or whole body at time t following on- 9 2.31E-02 set of intake 10 2.16E-02 I = Total intake during period T 11 2.02E-02 T = Duration of intake (exposure time Substituting the IRFs and the interval length into period) the above equation yields:

I 10, Ci x 6

[ 5; 2 E 2.85E - 02 + 2.02E - 02

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

_ 2 5.OE+02,uCi (1.8E+07 Bq)

This calculated intake is less than 0.02 ALI for necessary to determine the intake. However, addi-3 H (i.e., 500 jiCi < 0.02 times the ALI value of 8E4 tional radiation safety measures may be needed to gCi). Additional bioassay measurements would not be evaluate the incident and prevent future occurrences.

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REGULATORY ANALYSIS A separate regulatory analysis was not prepared implemented by the guide. A copy of the "Regulatory for this regulatory guide. The regulatory analysis Analysis for the Revision of 10 CFR Part 20" prepared for 10 CFR Part 20, "Standards for (PNL-67 12, November 1988), is available for Protection Against Radiation" (56 FR 23360), inspection and copying for a fee at the NRC Public provides the regulatory basis for this guide and Document Room, 2120 L Street NW., Washington, examines the costs and benefits of the rule as DC, as an enclosure to Part 20.

on recycled paper Federal Recycling Program RA-1

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