International Atomic Energy Agency Individual Dose Assessment ASSESSMENT OF OCCUPATIONAL EXPOSURE DUE TO INTAKE OF RADIONUCLIDES
Jan 17, 2018
International Atomic Energy Agency
Individual Dose Assessment
ASSESSMENT OF OCCUPATIONAL EXPOSURE DUE TO INTAKE OF
RADIONUCLIDES
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Individual Dose Assessment – Unit Objectives
The objective of this unit is to provide an overview of the use monitoring measurement to assess the exposure from internally deposited radionuclides. It includes a discussion of the use of material and individual specific data to improve dose estimates, and the role of task and special monitoring in assessment of internal exposure.At the completion of the unit, the student should understand the principles involved in dose assessment, and how to apply these principles.
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Individual Dose Assessment – Unit Outline
Introduction Need for Monitoring Routine Monitoring Programme Design Methods of Measurement Monitoring Frequency Reference Levels Use of Material & Individual Specific Data Task Related Monitoring Special Monitoring
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IntroductionIntroduction
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Monitoring objective
The general objective of operational monitoring programmes is the assessment of workplace conditions and individual exposures
The assessment of doses to workers routinely or potentially exposed to radiation through intakes of radioactive material constitutes an integral part of any radiation protection programme and helps to ensure acceptably safe and satisfactory radiological conditions in the workplace
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Individual monitoring methods
Individual monitoring for intakes is done by: Direct methods
Whole body counting Organ counting (e.g. thyroid or lung
monitoring) Indirect methods
Analysis of samples of excreta Analysis of selected body fluids or tissues Personal air samplers is also used
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Workplace monitoring
Workplace monitoring is used in many situations involving radionuclide exposure
May be used to demonstrate satisfactory working conditions or where individual monitoring may not be sufficient
May be appropriate when contamination levels are low, for example in a research laboratory using small quantities of radioactive tracers
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Monitoring techniques for internal dose estimation
Monitoring for radionuclide intake dose estimation may include one or more techniques:
Sequential measurement of radionuclides in the whole body or in specific organs;
Measurement of radionuclides in biological samples such as excreta or breath;
Measurement of radionuclides in physical samples such as filters from personal or fixed air samplers, or surface smears.
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Determination of committed effective dose
Measurements are used to determine intake The intake, multiplied by the dose coefficient,
gives an estimate of committed effective dose Dose coefficients have been calculated by the
ICRP and are given in the BSS In some situations, direct measurements may
be used to determine whole body or individual organ dose rates directly
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AMAD (activity median aerodynamic diameter)
The aerodynamic diameter of an airborne particle is the diameter that a sphere of unit density would need to have in order to have the same terminal velocity when settling in air as the particle of interest.
The thermodynamic diameter is the diameter that a sphere of unit density would need to have in order to have the same diffusion coefficient in air as the particle of interest.
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DOSE COEFFICIENTS FOR SELECTED RADIONUCLIDES
Radionuclide
Inhalation Ingestion
Type /form (a)e(g)inh (Sv/Bq)
f1 e(g)ing (Sv/Bq)AMAD = 1μm AMAD = 5μm
H-3 HTO (c) 1.8 E-11(b) 1 1.8 E-11
OBT 4.1 E-11(b) 1 4.2 E-11
Gas 1.8 E-15(b)
C-14 Vapour 5.8 E-10(b) 1 5.8 E-10
CO2 6.2 E-12(b)
CO 8.0 E-13(b)
P-32 F 8.0 E-10 1.1 E-09 0.8 2.3 E-10
M 3.2 E-09 2.9 E-09
Fe-55 F 7.7 E-10 9.2 E-10 0.1 3.3 E-10
M 3.7 E-10 3.3 E-10
Fe-59 F 2.2 E-09 3.0 E-09 0.1 1.8 E-09
M 3.5 E-09 3.2 E-09
Co-60 M 9.6 E-09 7.1 E-09 0.1 3.4 E-09
S 2.9 E-08 1.7 E-08 0.05 2.5 E-09
Sr-85 F 3.9 E-10 5.6 E-10 0.3 5.6 E-10
S 7.7 E-10 6.4 E-10 0.01 3.3 E-10
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Need for Monitoring
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Designation of workplace areas
Determination of the need for monitoring begins with designation of workplace areas
Supervised areas
Controlled areas
Area designation is based on knowledge of workplace conditions and the potential for worker exposure
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Designation of workplace areas
A worker should be enrolled in an internal exposure monitoring programme when there is a likelihood of an intake that exceeds a predetermined level
Guidance on the designation of areas is given in the Guide on Occupational Exposure
If operational procedures are set up to prevent or reduce the possibility of intake, a controlled area will, in general, need to be established
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Establishing the need for monitoring
Individual or area monitoring need depends on: Amount of radioactive material present Radionuclide(s) involved Physical and chemical form Type of containment used Operations performed and General working conditions
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Establishing the need for monitoring
Examples:
Workers handling sealed sources, or unsealed sources in reliable containment, may need to be monitored for external exposure, but not necessarily for internal exposure
Workers handling radionuclides such as tritium, I-125 or Pu-239 may need monitoring for internal exposure, but not for external exposure
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To monitor or not to monitor?
The decision to conduct intake monitoring may not be simple
Routine monitoring only for: Workers in controlled areas Contamination control and When significant intakes can be expected
From experience, if a C.E.D. > 1 mSv is unlikely, Individual monitoring may be unnecessary Workplace monitoring may be in order
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Situations that may call for monitoringSituations that may call for monitoring
Some situations where routine individual monitoring may be appropriate include:
Handling of large quantities of gaseous or volatile materials, e.g. 3H and its compounds in;
Large scale production processes Heavy water reactors and Luminizing;
Processing of plutonium and other transuranic elements;
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Situations that may call for monitoringSituations that may call for monitoring
Mining, milling and processing of thorium ores Use of thorium and its compounds – can lead
to exposure from radioactive dusts, and thoron (Rn-220) and its progeny);
Mining, milling and refining of high grade uranium ores;
Processing of natural and slightly enriched uranium, and reactor fuel fabrication;
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Situations that may call for monitoringSituations that may call for monitoring
Bulk production of radioisotopes; Working in mines and other workplaces where
radon levels exceed a specified action level; Handling radiopharmaceuticals, such as I-131
for therapy, in large quantities; Reactor maintenance exposure due to
fission and activation products
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Individual vs. Workplace monitoring
Individual monitoring may not be feasible for some radionuclides because of: Radiation type(s) emitted and Detection sensitivity of monitoring methods
In such situations, reliance must be placed on workplace monitoring
However, for some radionuclides, e.g. 3H, individual monitoring may be more sensitive than workplace monitoring
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Monitoring for new operations
Individual monitoring is likely to be needed for new operations
As experience in the workplace is accumulated, the need for routine individual monitoring should be kept under review
Workplace monitoring may be found to be sufficient for radiological protection purposes
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Routine Monitoring Programme Design
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Consider monitoring limitationsConsider monitoring limitations
Monitoring conducted on a fixed schedule for selected workers is routine monitoring
Internal exposure monitoring has several limitations
These limitations should be considered in the design of an adequate monitoring programme
Monitoring does not measure directly the committed effective dose to the individual
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Internal exposure monitoring limitations
Monitoring does not measure directly the committed effective dose to the individual
Biokinetic models are needed to: determine activity in the body from excreta
sample activity levels, determine intake from body content, calculate the committed effective dose
from the estimated intake
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Further internal monitoring limitations
Measurements may be subject to interference from other radionuclides present in the body:
Natural 40K present naturally
Cs-137 from global fallout
Uranium naturally present in the diet
Radiopharmaceuticals administered for diagnostic or therapeutic purposes
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Interference from “background” radionuclides
Establish the radionuclide body content from previous intakes
Particularly important when the non-occupational intakes are elevated, e.g. in mining areas high domestic radon exposure
Workers should have bioassay measurements before working with radioactive materials to establish a ‘background’ level.
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Interference from Radiopharmaceuticals
Radiopharmaceuticals can interfere with bioassays for some time after administration
Duration of interference depends on: Properties of the agent administered and Radionuclides present at the workplace
Request workers to report administration of radiopharmaceuticals
It can then be determined if adequate internal monitoring can be performed
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Internal exposure monitoring limitations
The results of an individual monitoring programme for the estimation of chronic intakes might depend on the time at which the monitoring is performed
For certain radionuclides with a significant early clearance component of excretion, there may be a significant difference between measurements taken before and after the weekend
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Internal exposure monitoring limitations
For nuclides with long effective half-lives, the amount present in the body and the amount excreted depend on, and will increase with, the number of years for which the worker has been exposed
In general, the retained activity from previous years’ intakes should be taken to be part of the background for the current year
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Timing of measurements is important
Results for the estimation of chronic intakes can depend on when the monitoring is done
If radionuclides have a significant early clearance, difference between pre- and post-weekend measurements may be significant
These should be reviewed individually if chronic exposure is possible
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Timing of measurements is important
If nuclides have long effective half-lives, Amount present in the body and Amount excreted
depend on the number of years for which the worker has been exposed
These amounts may increase with exposure Retained activity from previous years’ intakes
should generally be taken to be part of the background for the current year
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Internal exposure monitoring limitations
The analytical methods used for individual monitoring sometimes do not have adequate sensitivity to detect the activity levels of interest
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Air and surface monitoring
Analytical methods may not have adequate sensitivity
A system of workplace and personnel monitoring may be needed to determine radionuclide intake quantities
Fixed or personal air samplers (PASs) may be used to determine the airborne concentrations of radioactive material
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Air and surface monitoring
Air sampling results, together with standard or site specific assumptions: Physical and chemical form of the material Breathing rate and Worker exposure time
to estimate inhalation intakes Surface monitoring may also indicate intake
potential or need for detailed area monitoring But, models for estimating intake from surface
contamination are particularly uncertain
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Methods of Measurement
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Direct vs. Indirect measurements
Radionuclide intake can be determined by either direct or indirect measurement methods
Direct measurement of photons is also referred to as body activity measurements, whole body monitoring or whole body counting
Indirect measurements include activity in either biological or physical samples
Each type has advantages and disadvantages The selection of over than another depends on
the nature of the radiation to be measured
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Direct measurements
Direct methods are useful only for those radionuclides which emit photons: Of sufficient energy, and In sufficient numbers, To escape from the body and Be measured by an external detector
Direct measurements are particularly useful for fission and activation products
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Direct measurements Radionuclides which do not emit energetic
photons (e.g. 3H, 14C, 90Sr-90Y) can usually be measured only by indirect methods
Pu-239 emits weak x-rays and may be measured by either method
Some higher energy beta emitters, e.g. 32P or 90Sr-90Y, can sometimes be measured ‘directly’ via the bremsstrahlung produced
These measurements have a relatively high minimum detectable activities and are not usually employed for routine monitoring
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Direct measurements
Direct measurements: Rapid Convenient Can estimate activity in the whole body or
a defined part of the body Less dependent on biokinetic models than
indirect monitoring
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Direct measurements
May have greater calibration uncertainties, especially for low energy photon emitters
May require the worker to be removed from work involving radiation exposure for the period over which the retention characteristics are measured
Often need special, well shielded, and expensive facilities and equipment.
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Direct measurements – Qualitative applications
Useful in qualitative and quantitative determinations of radionuclides
Can assist in identifying the mode of intake by determining the distribution of activity
Sequential measurements can reveal activity redistribution and give information about the total body retention and biokinetics
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Indirect measurements
Generally interfere less with workers duties However, require access to a radiochemical
analytical laboratory Analytical laboratory may also be used for
measuring environmental samples Perform high level (e.g. reactor water
chemistry) and low level (e.g. bioassay or environmental samples) work in separate laboratories
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Indirect measurements - Excreta
Excreta measurements determine the rate of loss of radioactive materials from the body by a particular route
Must be related to body content and intake by a biokinetic model
Radiochemical analyses low detection levels sensitive detection of body activity
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Indirect measurements – Air samples
Can be difficult to interpret - air concentration may not represent breathing zone
Personal air sampler (PAS) placed on the worker’s lapel or protective headgear can collect more representative samples
Sample comprising only a few particles still a problem
Air concentrations + breathing rates + measured exposure times = estimated intake
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Indirect measurements – Air samples
Use of PASs only estimates intake Cannot be used to refine a dose estimate based
on individual retention characteristics PAS measurements cannot be repeated Can provide intake estimates for nuclides such
as 14C (particulate), 239Pu, 232Th and 235U, when other methods may have sufficient sensitivity
Interpretation depends on the dose coefficients and the derived air concentration (DACs)
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Particles size is important
Particle size influences deposition of inhaledparticulates in the respiratory tract
Correct interpretation of bioassay and dose assessment depends on particle size data
Determine airborne particle size distribution using cascade impactors or other methods
BB
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Al
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0.1 1 10 100AMAD (m)
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0.01
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on (%
) ET1
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Particles size is important
Measurements should, at least, include the concentration of the respirable fraction
Some models for interpreting PAS results discriminate against non-respirable particles
Dose assessment improves with more site and material specific information
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Measurement detection limits
Measurement methods have limits of detection arising from: Naturally occurring radioactive materials Statistical fluctuations in counting rates,
and Factors related to sample preparation and
analysis Minimum significant activity (MSA) and
minimum detectable activity (MDA)will be discussed in another unit
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Monitoring Frequency
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Individual monitoring frequency
BSS:
“The nature, frequency and precision of individual monitoring shall be determined with consideration of the magnitude and possible fluctuations of exposure levels and the likelihood and magnitude of potential exposures.”
Characterize the workplace to determine the appropriate frequency and type of monitoring!
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Individual monitoring frequency
Identify radionuclides in use and determine their chemical and physical forms
Consider possible changes of these forms under accident conditions;
e.g. the release of uranium hexafluoride into the atmosphere results in the production of HF and uranyl fluoride
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Individual monitoring frequency
Chemical and physical forms (e.g. particle size) determine material behaviour on intake and biokinetics in the body
These in turn determine the excretion routes and rates, and hence the type of excreta samples to be collected and their frequency
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Proper frequency minimizes intake uncertainty
Set bioassay sampling schedules to minimize intake estimate uncertainties due to the unknown time of an intake, i.e. If acute intake occurs immediately after
previous assay, Assuming intake at the monitoring period
midpoint underestimates the intake Monitoring period should be short enough that
the underestimate factor of 3
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Determining the monitoring frequency
Monitoring period, ΔT, depends on: Radionuclide retention, R(t) Radionuclide clearance, E(t) Sensitivity of the measurement process, i.e
measurement MDA Acceptable uncertainty Committed effective dose, e(50)
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Determining the monitoring frequency
For in vivo measurementse(50) MDA/R(ΔT) 365/ΔT ≤ 1 mSv/year
For in vitro measurementse(50) MDA/E(ΔT) 365/ΔT ≤ 1 mSv/year
Maximum overestimation shouldn’t exceed 3 If exposure occurs at ΔT/2, this means;
R(1)/R(ΔT/2) ≤ 3E(1)/E(ΔT/2) ≤ 3
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Recommended maximum time intervals for routine monitoring
In vitro measurements In vivo measurements Isotope Type Urine (days) Whole Body (days) Thyroid (days) 3H HTO 30 - - 14C Organic 30 - - Dioxide 180 32P F 30 - - 35S F 15 - - 36Cl F 30 - - 51Cr F (15) 15 - 54Mn M - 90 - 59Fe M - 90 - 57Co S (180) 180 - 58Co S (180) 180 - 60Co S (180) 180 - 89Sr F, S 60 - 90Sr F, S 180 - 110mAg S - 180 - 125I F (90) - 90 131I F (15) - 15 137Cs F (180) 180 - 147Pm S 180 - 226Ra M 180
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Suggested maximum time intervals for routine monitoring for uranium compounds
Material Type* Urine (days)
Faeces (days)
Lungs (days)
Natural / Depleted U F and M 90 Uranium hexafluoride F 90 Uranium peroxide F 30 Uranium nitrate F 30 Ammonium diuranate F 30 - - Uranium tetrafluoride M 90 180 180 Uranium trioxide M 90 180 180 Uranium octoxide S 90 180 180 Uranium dioxide S 90 180 180
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Suggested maximum time intervals for routine monitoring for actinide compounds
Isotope Type Urine (days)
Faeces (days)
Lungs (days)
228Th S 180 180 - 232Th S 180 180 - 237Np M 180 180 - 238Pu S 180 365 - 239Pu S 180 365 - 241Am M 180 365 180 244Cm M 180 365 -
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Recommended monitoring interval tolerances
Unreasonable to expect bioassay measurements to be preformed on exact schedule
Monitoring interval - Days Tolerance - Days15 230 460 790 14
180 30365 30
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Schedule to avoid missing an intake
Schedule monitoring to ensure an intake above a predetermined level is not ‘missed’
Intake could be missed if, As a result of clearance, Body content or daily excretion Declines to a level below the minimum
significant activity of the measurement During the time between intake and
measurement
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Schedule to avoid missing an intake
m(t) - Fraction of an intake in the body (direct measurement) or being excreted from the body for indirect measurement, depends on:
Physical half-life
Biokinetics of the radionuclide, and
Is a function of the time since intake
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Schedule to avoid missing an intake
An intake I and the resulting committed effective dose E(50) would be missed if,
I m(t) is less than the MSA
Monitoring frequency should be set so that intakes corresponding to more than 5% of the annual dose limit are not missed.
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Monitoring frequency depends on sensitivity
Monitoring frequency is largely driven by the sensitivity of the measurement technique
Measurement techniques should be as sensitive as possible
However, associated costs - Most sensitive techniques Frequent monitoring measurements
should be balanced against risk doses are underestimated or missed
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Additional methods for better sensitivity
Measurement method and frequency should detect intakes a specified dose limit fraction
Goal cannot be realized because: Lack of analytical sensitivity Unacceptably long counting times Short sampling intervals required for
excreta collection Additional methods – e.g. improved workplace
monitoring and personal air sampling - should be used for adequate worker protection
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Use of Reference Levels
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Reference levels
Reference levels are helpful in management of operations
Expressed in terms of measured quantities or other quantities to which measured quantities can be related
If exceeded, take specified action or decision Reference levels usually based on committed
effective dose E(50) for radionuclide intake
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Reference levels
Appropriate dose limit fraction corresponding to each reference level should be established
Take other sources of exposure into account
Recording Levels and Investigation Levels relevant to internal contamination monitoring for occupational exposures.
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Recording level
Defined as “a level of dose, exposure or intake specified by the regulatory authority at or above which values of dose, exposure or intake received by workers are to be entered in their individual exposure records”
Example - RL for a radionuclide intake set to correspond to a committed effective dose of 1 mSv (0.001 Sv) from a year’s intakes
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Recording level
For N monitoring periods per year, the recording level for intake of radionuclide j in a monitoring period would be given by:
jj )g(Ne
.RL 0010
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Investigation level
Is “the value of a quantity such as effective dose, intake or contamination per unit area or volume at or above which an investigation should be conducted”
Investigation level for radionuclide intake - A value of committed effective dose above which monitoring results justify further investigation
Set by management, depends on programme objectives and type of investigation to be done
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Investigation level
For routine monitoring, the investigation level for a radionuclide intake is set in relation to: Type and frequency of monitoring Expected level and variability of intakes
Numerical value of the investigation level depends on conditions in the workplace
Investigation level may be set for; Individuals in a particular operation, or Individuals within a workplace without
reference to a particular operation
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Investigation level – An example
Routine operation with routine monitoring IL set at a committed effective dose of 5
mSv (0.005 Sv) from a year’s intakes For N monitoring periods per year, the IL (in
Bq) for the intake of any radionuclide j in any monitoring period is:
where e(g)j is the dose coefficient for inhalation or ingestion
jj )g(Ne
.IL 0050
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Derived levels
Measured quantities are radionuclide activities in the body or excreta samples
It is convenient to establish reference levels for the measurement results themselves
These are termed derived investigation levels (DILs) and derived recording levels (DRLs)
Measurement results that imply radionuclide intakes or committed effective doses at the corresponding reference levels
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Derived levels
Derived investigation and recording levels are calculated separately for each radionuclide
Specific to the radiochemical form in the workplace Are a function of time since intake For the previous examples,
)t(m
)g(Ne.DIL
jj 0
0050
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Derived recording level
t0 (time elapsed between intake and bioassay) is usually set as 365/2N days - assumes that intake occurs at the mid-point of the monitoring period, and
)t(m)g(Ne
.DRLj
j 00010
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Derived levels
Measurement result should always be maintained in the radiation monitoring records for the workplace and for the individual
For worker exposure to external radiation or to multiple radionuclides, management may need to reduce the derived levels for individual radionuclides appropriately.
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Use of Material and Individual Specific Data
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Biokinetic models
Biokinetic models for most radionuclides Developed by the ICRP Use reference parameter values Are based on Reference Man data, and Observed radionuclide behaviour in
humans and animals Have been developed for defined chemical
forms of radionuclides, and Are generally used for planning purposes
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Biokinetic models
Characterize particular workplace conditions to determine forms actually present
In some circumstances, the chemical or physical forms of the radionuclides will not correspond to the reference biokinetic models
Then, material specific models may need to be developed
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Specific biokinetic models
For small intakes are small, i.e. a few per cent of the dose limit, reference models are probably good enough
If the intake estimate 1/4 dose limit, model parameters for; Specific material(s), and Individual(s)
may be needed for better estimate of the committed effective dose
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Specific biokinetic models
Specific models can be developed from sequential direct and indirect measurements of the exposed workers
Analysis of workplace air and surface contamination samples can also assist in the interpretation of bioassay measurements
Example - Measure 241Am/ 239,240Pu from direct lung measurement of 241Am to assess plutonium intakes or inhaled particle solubility
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Need for specific information
Common example – aerosol particle size a worker would likely inhale differs significantly from ICRP 5 μm AMAD default value
Fractions of inhaled materials deposited in various regions of the respiratory tract would have to be determined from the ICRP respiratory tract model, and
An appropriate dose coefficient calculated
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Need for specific information
More specific information may also be needed on the material solubility characteristics
Can be obtained from experimental studies in animals or by in vitro solubility studies
Retrospective determination of particle characteristics may be difficult
Consideration should be given to obtaining material specific information when setting up worker monitoring programmes
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Individual variability
There are differences between individuals in excretion rates and other biokinetic parameters for the same intake
Individual variability may be more significant than the differences between generic and individual specific biokinetic models
Excreta sample collection periods should be sufficiently long to reduce this variability, e.g. 24 hours for urine and 72 hours for faeces
Use of individual specific model parameters should be rare under routine circumstances.
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Task Related Monitoring
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Task related monitoring is,
Not routine, i.e. it is not regularly scheduled Conducted to provide information about a
particular operation, and give a basis for decisions on the conduct of the operation
Useful when short term procedure conditions would be unsatisfactory for long term use
Usually conducted the same as routine monitoring, unless the circumstances of the operation dictate otherwise
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Special Monitoring
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Special monitoring
May be necessary as a result of; Known or suspected exposures An unusual incident,
e.g. loss of containment of radioactive materials as indicated by an air or surface sample, or
Following an accident
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Special monitoring
Usually prompted by a result of a routine bioassay measurement that exceeds the derived investigation level
It may also result from occasional samples such as nose blows, swipes or other monitoring.
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Special monitoring
Measurement techniques for special monitoring usually the same as routine measurement
However, improved sensitivity or a faster processing time may be needed
Advise the laboratory that the sample analysis or the direct measurement has priority over routine measurements, and
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Recommended methods for special monitoring after inhalation
In vitro measurements In vivo measurements nasal Urine Faeces Organ
Isotope NB EA Spot sample 24 h 72 h WB Th
3H ** ** 14C ** ** * 32P ** * 35S ** * 51Cr ** ** ** 54Mn ** ** ** ** 59Fe ** ** ** 58, 60Co ** ** ** ** 90Sr ** ** 110mAg ** ** ** ** 125, 131I ** ** ** 137Cs ** ** * ** 147Pm ** ** 226Ra ** ** Legend ** Recommended * Supplementary
NB: Nose blow EA: Expired air WB: Whole body Th: Thyroid
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Recommended methods for special monitoring after inhalation
In vitro measurements In vivo measurements
nasal Urine Faeces Isotope Nose
blow Spot
sample 24 h 72 h Lung Natural / Depleted U ** ** ** * Uranium hexafluoride ** ** ** Uranium peroxide ** ** ** Uranium nitrate ** ** ** Ammonium diuranate ** ** ** Uranium tetrafluoride ** ** ** * * Uranium trioxide ** ** ** * * Uranium octoxide ** ** ** ** Uranium dioxide ** ** ** **
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Recommended methods for special monitoring after inhalation
Legend NB: Nose blow EA: Expired air
In vitro measurements
nasal Urine Faeces In vivo
measurements
Isotope NB EA 24 h 72 h Lung 228Th ** ** ** ** 232Th ** * ** ** 237Np ** ** ** 238Pu ** ** ** 239Pu ** ** ** 241Am ** ** ** ** 244cm ** ** **
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Special monitoring
The frequency of follow-up monitoring may be changed
Inform the laboratory that samples may have a higher than normal level of activity
The measurement technique can be tailored to the special monitoring situation, and
Necessary precautions may be taken to prevent contamination of other samples
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ReferencesFOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOUR ORGANISATION, OECD NUCLEAR ENERGY AGENCY, PAN AMERICAN HEALTH ORGANIZATION, WORLD HEALTH ORGANIZATION, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115, IAEA, Vienna (1996).
INTERNATIONAL ATOMIC ENERGY AGENCY, Occupational Radiation Protection, Safety Guide No. RS-G-1.1, ISBN 92-0-102299-9 (1999).
INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of Occupational Exposure Due to Intakes of Radionuclides, Safety Guide No. RS-G-1.2, ISBN 92-0-101999-8 (1999).
INTERNATIONAL ATOMIC ENERGY AGENCY, Direct Methods for Measuring Radionuclides in the Human Body, Safety Series No. 114, IAEA, Vienna (1996).
INTERNATIONAL ATOMIC ENERGY AGENCY, Indirect Methods for Assessing Intakes of Radionuclides Causing Occupational Exposure, Safety Guide, Safety Reports Series No. 18, ISBN 92-0-100600-4 (2000).
INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Direct Determination of the Body Content Of Radionuclides, ICRU Report 69, Journal of the ICRU Volume 3, No 1, (2003).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Individual Monitoring for Internal Exposure of Workers: Replacement of ICRP Publication 54, ICRP Publication 78, Annals of the ICRP 27(3-4), Pergamon Press, Oxford (1997).
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ReferencesFOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOUR ORGANISATION, OECD NUCLEAR ENERGY AGENCY, PAN AMERICAN HEALTH ORGANIZATION, WORLD HEALTH ORGANIZATION, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115, IAEA, Vienna (1996).
INTERNATIONAL ATOMIC ENERGY AGENCY, Occupational Radiation Protection, Safety Guide No. RS-G-1.1, ISBN 92-0-102299-9 (1999).
INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of Occupational Exposure Due to Intakes of Radionuclides, Safety Guide No. RS-G-1.2, ISBN 92-0-101999-8 (1999).
INTERNATIONAL ATOMIC ENERGY AGENCY, Direct Methods for Measuring Radionuclides in the Human Body, Safety Series No. 114, IAEA, Vienna (1996).
INTERNATIONAL ATOMIC ENERGY AGENCY, Indirect Methods for Assessing Intakes of Radionuclides Causing Occupational Exposure, Safety Guide, Safety Reports Series No. 18, ISBN 92-0-100600-4 (2000).
INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Direct Determination of the Body Content Of Radionuclides, ICRU Report 69, Journal of the ICRU Volume 3, No 1, (2003).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Individual Monitoring for Internal Exposure of Workers: Replacement of ICRP Publication 54, ICRP Publication 78, Annals of the ICRP 27(3-4), Pergamon Press, Oxford (1997).