International Atomic Energy Agency Criteria for the Need for Monitoring ASSESSMENT OF OCCUPATIONAL EXPOSURE DUE TO INTAKES OF RADIONUCLIDES

International Atomic Energy Agency Criteria for the Need for Monitoring – Unit Objectives The objective of this unit is to review the principles and criteria used to determine the need for monitoring for internal exposure assessment. The unit covers quantities and units for internal dosimetry, how to select the appropriate monitoring methods, and provides suggested criteria for monitoring. At the completion of this unit, the student should understand how to establish the need for individual and workplace monitoring for internal contamination.

International Atomic Energy Agency Criteria for the Need for Monitoring – Unit Outline l Dosimetric quantities l Monitoring programme l Suggested criteria to define the need for monitoring. u Need for monitoring u Examples of monitoring cases

International Atomic Energy Agency Dosimetric Quantities

International Atomic Energy Agency Quantities for internal dose assessment Physical quantities - Directly measurable. Protection quantities - Defined for dose limitation purposes, but not directly measurable. Operational quantities - Measurable for demonstration of compliance with dose limits.

International Atomic Energy Agency The fundamental dosimetric quantity absorbed dose, D, is defined as: D = de / dm where de is the mean energy imparted by ionizing radiation to matter in a volume element and dm is the mass of matter in the volume element. The energy can be averaged over any defined volume, the average dose being equal to the total energy imparted in the volume divided by the mass in the volume. The SI unit of absorbed dose is the joule per kilogram (J/kg), termed the gray (Gy). Absorbed dose, D

International Atomic Energy Agency Primary physical quantities are not used directly for dose limitation The same dose levels of different radiations (ie photons and neutrons) do not have the same level of biological effect  Radiation weighting factor, w R (related to radiation quality) Different body tissues have different biological sensitivities to the same radiation type and dose  Tissue weighting factor, w T

International Atomic Energy Agency ICRP has defined Protection Quantities for dose limitation Effective dose Used for the whole body Equivalent dose Used for individual tissues or organs

International Atomic Energy Agency Multipliers of the equivalent dose to an organ or tissue to account for the different sensitivities to the induction of stochastic effects of radiation. Tissue or organ w T Tissue or organw T Gonads0.20Bone marrow (red)0.12 Colon0.12Lung 0.12 Stomach0.12Bladder 0.05 Breast 0.05Liver 0.05 Oesophagus0.05Thyroid 0.05 Skin 0.01Bone surface 0.01 Remainder0.05TOTAL1.00 Tissue weighting factors

International Atomic Energy Agency Radiation weighting factors, w R 1 Type and energy ranges Radiation weighting factor, w R Photons, all energies Electrons and muons, all energies Neutrons, energy < 10 keV 10 keV to 100 keV 100 keV to 2 MeV > 2 MeV to 20 MeV > 20 MeV Protons, other than recoil protons, energy > 2 MeV Alpha particles, fission fragments, heavy nuclei 20 1)All values relate to the radiation incident on the body, or, for internal sources, emitted from the source.

International Atomic Energy Agency Equivalent dose, H T,R The absorbed dose in an organ or tissue multiplied by the relevant radiation weighting factor w R : H T,R = w R · D T,R where D T,R is the average absorbed dose in the organ or tissue T, and w R is the radiation weighting factor for radiation R.

International Atomic Energy Agency Equivalent dose, H T When the radiation field is composed of different radiation types with different values of w R the equivalent dose is: H T = w R · D T,R The unit of equivalent dose is J/kg, termed the Sievert (Sv). R

International Atomic Energy Agency Effective dose, E T A summation of the tissue equivalent doses, each multiplied by the appropriate tissue weighting factor: E = w T ·H T where H T is the equivalent dose in tissue T and w T is the tissue weighting factor for tissue T. T

International Atomic Energy Agency Committed Effective Dose Internal exposure continues for some time after intake. Actual exposure duration depends on the radionuclide. The exposure is said to be “committed”. Assess the committed effective dose over a 50 year period.

International Atomic Energy Agency Operational quantity for internal dose assessment Intake - The activity of a radionuclide taken into the body To determine the committed effective dose from an estimated intake the dose coefficient for radionuclide j by ingestion, e(g) j,ing inhalation, e(g) j,inh

International Atomic Energy Agency Intake vs. Uptake Do not confuse intake with uptake! Uptake “The processes by which radionuclides enter the body fluids from the respiratory tract or gastrointestinal tract or through the skin, or the fraction of an intake that enters the body fluids by these processes.” (RS-G-1.2) It is the remaining uptake activity, or excreted that is measured through direct and indirect methods to establish intake

International Atomic Energy Agency Intakes corresponding to Limits Given:  Exposure from a single radionuclide  Exposure by inhalation or ingestion  No external exposure  Relevant effective dose limit, L Intake I j,L corresponding to L is given by: where e(g) j is the relevant dose coefficient.

International Atomic Energy Agency Intake Fraction Intake fraction, m(t), The amount of material remaining or being excreted from the body at time, t, after intake divided by the intake quantity. The intake fraction depends on: the radionuclide, its chemical and physical form, the route of intake, time after intake

International Atomic Energy Agency Derived Air Concentration Derived air concentration (DAC) The concentration of airborne activity (in Bq/m 3 ) that would result in the limit on intake of I j,inh,L by a worker exposed continuously at that level for one year.

International Atomic Energy Agency Example of DAC DAC = I j,inh,L / (2000 * 1.2) Assume airborne 137 Cs with a 5 μm AMAD. e(g) inh = 6.7 E-9 Sv/Bq Annual dose limit = 20 mSv = 0.02 Sv I j,inh,L = 0.02 / 6.7 E-9 = 3 E+6 Bq DAC = 3E+6/ (2000*1.2) = 1.3 E+3 Bq/m 3

International Atomic Energy Agency The measured airborne activity concentration, expressed as a fraction of the DAC, multiplied by the exposure time in hours gives an estimate of intake expressed in DAC·h. Example: 1 week at the 0.1 DAC would be 4 DAC·h, or an intake of 4/2400 = I j,inh,L DAC·h corresponds to an intake of I j,inh,L. Use of DAC·h

International Atomic Energy Agency Monitoring Programme

International Atomic Energy Agency Need for monitoring specified in the BSS The Basic Safety Standards require that: “For any worker who is normally employed in a controlled area, or who occasionally works in a controlled area and may receive significant occupational exposure, individual monitoring shall be undertaken where appropriate, adequate and feasible.” Para. I.33

International Atomic Energy Agency Monitoring programme Direct measurement techniques: Measurements of radionuclides in the whole body or specific organs; Indirect measurement techniques: Measurements of radionuclides in biological samples, such as excreta or breath; and/or Measurement of radionuclides in physical samples: filters from air samplers, or smears.

International Atomic Energy Agency Monitoring programme measurements Used to calculate the radionuclide intake, Multiply intake by the appropriate dose coefficient, e(g) j,ing or e(g) j,inh, Result leads to an estimate of committed effective dose.

International Atomic Energy Agency Selection of the monitoring approach Depends on the: amount of radioactive material radionuclide(s) involved, physical and chemical form of the radioactive material, type of containment used, operations performed, and general working conditions.

International Atomic Energy Agency Examples of work environments include, Handling of large quantities of gaseous or volatile materials, e.g. 3 H in large scale production processes, in heavy water reactors and in luminizing; Processing of plutonium and other transuranic elements; Mining, milling and processing of thorium ores, and the use of thorium and its compounds.

International Atomic Energy Agency Other workplace examples Mining, milling and refining of high grade uranium ores; Processing of natural and slightly enriched uranium, and reactor fuel fabrication; Bulk production of radioisotopes;

International Atomic Energy Agency Further workplace examples Working in mines and other workplaces where radon levels exceed a specified action level; Handling of large quantities of radiopharmaceuticals, such as 131 I for therapy; and Maintenance of reactors, which can lead to exposure due to fission and activation products.

International Atomic Energy Agency Suggested Criteria for Individual Monitoring

International Atomic Energy Agency Need for monitoring depends on exposure potential * * ISO/TC 85/SC 2/WG13/SG1, Monitoring of Workers Occupationally Exposed to a Risk of Internal Contamination with Radioactive Material

International Atomic Energy Agency Individual monitoring is based on exposure potential. l Committed effective dose of  1 mSv in a year? l Consider various factors, including: u The physical form safety factor f fs, u The handling safety factor f hs, u The protection safety factor f ps. l Material form (e.g. volatile liquid, powder) may be taken into account both directly (i.e., f fs ) and indirectly, through the protective measures being taken (i.e. f hs and/or f ps )

International Atomic Energy Agency Physical form safety factor f fs Based on the physical and chemical properties of the material being handled. In the majority of cases, should be given a value of 0.01.

International Atomic Energy Agency Handling safety factor f hs Based on experience of the operation being performed and the form of the material.

International Atomic Energy Agency Handling safety factors, f hs Storage (stock solution)0.01 Very simple wet operations0.1 Normal chemical operations1 Complex wet operations (spills)10 Simple dry operations10 Handling of volatile compounds100 Dry and dusty operations100

International Atomic Energy Agency Protection safety factor f ps Based on the use of permanent laboratory protective equipment (e.g. glove box, fume hood). Open bench operations1 Fume hood0.1 Glove box0.01

International Atomic Energy Agency Specific radionuclide ‘decision factor’ d j = (A j e(g) j,inh f fs f hs f ps ) / A j - cumulative activity of radionuclide j in the workplace over a year, e(g) j,inh - inhalation dose coefficient (Sv/Bq) for inhalation of radionuclide j, conversion from Sv to mSv.

International Atomic Energy Agency decision factor Cumulative decision factor l Cumulative decision factor, D, for all radionuclides in the workplace; l If D is 1 or higher, a need for individual monitoring would be indicated, l If D is less than 1, individual monitoring may not be necessary.

International Atomic Energy Agency Use of decision factor - an example l Single radionuclide handled on the open bench (f ps = 1). l Normal chemical operations (f hs = 1). l Default value of f fs = l For d j = 1, A j = 0.1/e(g) j,inh l I j,inh,L = 0.02/e(g) I,inh l A i = 5 I j,inh,L

International Atomic Energy Agency More than one radionuclide in the workplace? Decisions to conduct individual monitoring for the separate radionuclides may be based on the following criteria: All radionuclides for which d j  1 shall be monitored; l When D  1, radionuclides for which d j  0.3 should be monitored; and l Monitoring of radionuclides for which d j is much less than 0.1 is unnecessary.

International Atomic Energy Agency Workplace example l Insoluble Pu-239 l Normal chemical operations in a fume hood. l Default AMAD for workplaces of 5 µm. l Values of f fs, f hs, and f ps are taken to be 0.01, 1.0, and 0.1, respectively. l Then:

International Atomic Energy Agency Workplace example Pu l Individual monitoring would be required if A Pu239, the activity of 239 Pu, is greater than: l Otherwise, individual monitoring would not be required.

International Atomic Energy Agency Workplace example Pu Cs l Cs-137 is handled in the same workplace, l d Pu239 remains the same, and l Decision factor for Cs-137 is given by: l where A Cs137 is the activity of Cs-137 present in the workplace.

International Atomic Energy Agency Workplace example Pu Cs l If: l Individual monitoring should be performed for any nuclide for which, d j  0.3, for: u Pu-239 if A Pu239 is greater than 36 kBq, u Cs-137 if A Cs137 is greater than 45,000 kBq. l Individual monitoring is unnecessary for Pu- 239 if A Pu239 is much less than 12 kBq and for Cs-137 if A Cs137 is much less than 15,000 kBq.

International Atomic Energy Agency References FOOD 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 (1999). INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of Occupational Exposure Due to Intakes of Radionuclides, Safety Guide No. RS-G-1.2, ISBN (1999). INTERNATIONAL ATOMIC ENERGY AGENCY, Indirect Methods for Assessing Intakes of Radionuclides Causing Occupational Exposure, Safety Guide, Safety Reports Series No. 18, ISBN (2002). 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).