1. International Atomic Energy Agency ASSESSMENT OF OCCUPATIONAL EXPOSURE DUE TO EXTERNAL RADIATION SOURCES AND INTAKES OF RADIONUCLIDES Accident Dosimetry

2. International Atomic Energy Agency Accident Dosimetry - Unit objectives The objective of this unit is to provide an overview of measurement techniques that can be used for accident dosimetry. It describes post event information, retrospective dosimetry and dose reconstruction. The unit addresses use of biological and physical accident dosimetry techniques, using accident histories as examples. At the completion of this unit, the student should understand what dosimetric methods can be applied following an accident caused by overexposure due to external radiation and/or intake of radionuclides.

3. International Atomic Energy Agency Accident Dosimetry - Module Outline l Introduction Post Event Information Requirements Dose Reconstruction and Retrospective Dosimetry Post Event and Follow-up Monitoring l Biological and Physical Dosimetry l Selected Accident Histories l Accident Preparation l Management of Overexposed Workers

4. International Atomic Energy Agency Introduction

5. International Atomic Energy Agency Accident “Any unintended event, including operating errors, equipment failures or other mishaps, the consequences or potential consequences of which are not negligible from the point of view of protection or safety.” BSS Glossary

6. International Atomic Energy Agency IAEA Accident response experience Under the 1986 Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency, the IAEA: l makes available appropriate resources for emergency response, l promptly transmits requests for assistance to other States or international organizations which may possess necessary resources, and l may co-ordinate assistance at the international level

7. International Atomic Energy Agency IAEA Accident response experience l Chernobyl was the most serious accident in Agency history. l IAEA has been involved in investigation of a number of other accidents involving. u loss of control or misuse of radioactive sources, u errors in medical treatment, or u accidental exposure in irradiation facilities.

8. International Atomic Energy Agency Several situations contribute to accidents 1Operational error or equipment failure when transferring large sources; 2Interlock failure on high dose rate equipment; 3Radiography sources left unshielded; 4Equipment failure or operational errors in nuclear facilities. 5Medical misuse of sources; and 6Criticalities

9. International Atomic Energy Agency Accidents with ”clinical consequences”* Persons Activity affected Nuclear fuel cycle245 Industrial uses of radiation 94 Medical uses of radiation 18 Tertiary education and accelerators 19 Other344 Total720 * From 2000 UNSCEAR Report (1975 through 1994)

10. International Atomic Energy Agency Post Event Information Requirements

11. International Atomic Energy Agency Introduction There could be situations involving the use of radiation sources or radioactive material in which the operational controls break down Accidents or incidents may result in overexposure caused by the radioactive source and/or releases of radioactive materials into the working environment with the potential for high doses to the workforce

12. International Atomic Energy Agency Accidents – Medical treatment first After an accident, the radiological consequences may be complicated by trauma or other health effects incurred by workers Treatment of injuries, especially those that are potentially life threatening, generally takes priority over radiological operations Post-accident exposure assessment should be conducted when the situation has been brought under control.

13. International Atomic Energy Agency Post-accident – Gather key information Information is necessary for; Exposure assessment Medical assessment, to guide medical treatment of the victim (which may include chelation therapy or wound excision) Accident reconstruction Long term medical follow-up of victims

14. International Atomic Energy Agency Post-accident – Gather key information When exposure assessment starts, get as much information as possible Example - information is needed on; u Time and nature of the incident u Radiation sources, radionuclides involved u Personal dosimeters readings u Measurements on working environment u Measurements of body activity and timing of bioassay samples

15. International Atomic Energy Agency Post-accident information gathering Accidents or incidents can result in high committed effective doses (  dose limits) Site, individual and material specific data are normally needed for exposure assessment Necessary data include information on; u External dosimetry results, u Distribution of radioactivity in the container, u Position of the source module(s) and of exposed individuals relative to the source and any shielding during the accident, u Durations of exposure for each position.

16. International Atomic Energy Agency Post-accident information gathering Necessary data also includes information on; u Chemical and physical forms of the radionuclide(s), u Particle size, u Airborne concentrations, u Surface contamination levels, u Retention characteristics in the individual affected, u Nose blows, face wipes and other skin contamination levels.

17. International Atomic Energy Agency Post-accident information gathering Data may seem inconsistent or contradictory, Adequate dose assessments can be made only after; u Considering all of the data, u Resolving the sources of inconsistency as far as is possible, and u Deciding most likely and worst scenarios for exposure and magnitude of intake

18. International Atomic Energy Agency Dose Reconstruction and Retrospective Dosimetry

19. International Atomic Energy Agency Dose reconstruction and retrospective dosimetry may be conducted for several reasons: l To provide input to the clinical prognosis, especially in anticipating difficulties in medical management associated with bone marrow depression; l To provide data to help improve the understanding of the effects in man of acute exposure to high doses of radiation; l Epidemiological studies; and l Litigation

20. International Atomic Energy Agency Dose Reconstruction Dose reconstruction may be considered to be the process of assessment, or confirmation or revision of previous assessment of acute or chronic radiation exposures to individuals, groups or populations.

21. International Atomic Energy Agency Dose reconstruction may be required in a variety of situations l Acute accidental exposure. u Irradiation facility accidents u Stolen or lost sources u Criticality accidents u Reactor accidents l Suspected chronic overexposure of public groups or populations. l Occupational exposure reassessment.

22. International Atomic Energy Agency Retrospective dosimetry Retrospective dosimetry consists of the measurements conducted for dose reconstruction purposes when information provided by conventional dosimetry methods is inadequate or unavailable.

23. International Atomic Energy Agency Obtain accident dosimetry from various sources l Personal dosimeters, l Assessment of radionuclide intake by direct and/or indirect measurement methods, l Biological indicators using the patient’s body tissues, l Physical methods using body tissues, clothing or samples from the accident scene, l Accident simulation, l Mathematical dose reconstruction.

24. International Atomic Energy Agency Post Event and Follow-up Monitoring (in case of radionuclide intake)

25. International Atomic Energy Agency Recommended procedures for monitoring NO Later actions (see below) Dose estimate based on ICRP models Low level of internal contamination Low level monitoring if possible & justified Later actions

26. International Atomic Energy Agency External contamination interference Radiological characteristics of the radionuclides determine whether direct, indirect, or both methods should be used If there is external contamination with gamma emitters, direct measurements should normally be delayed until decontamination This 1) prevents interference with the measurement and 2) avoids contamination of the direct measurement facility

27. International Atomic Energy Agency External contamination interference If urgency of assessment precludes complete decontamination, wrap the individual in a sheet to minimize contamination of the facility Such initial direct measurement results are upper limits for the body content More measurements would be needed after further decontamination External α or β contamination won’t normally interfere with direct measurements, unless bremsstrahlung is produced by the betas

28. International Atomic Energy Agency Other concerns External contamination will not interfere with indirect methods However, care must be taken to avoid transfer of contamination to excreta samples Rarely, intakes may be so high that special techniques to avoid interference with equipment response, e.g. excessive electronic dead times

29. International Atomic Energy Agency Mobile Direct Measurement Facilities

30. International Atomic Energy Agency Mobile Direct Measurement Facilities

31. International Atomic Energy Agency Analysis of excreta Analyses of samples of urine and faeces should be considered to verify the intake These results may be difficult to interpret, because of; Possible multiple routes of intake and Imprecise about radionuclide transfer to the blood

32. International Atomic Energy Agency Analysis of excreta Early excreta results are generally not useful for intake assessment because of the delay between intake and excretion (particularly true for faecal excretion). Early detection of radioactivity in urine can be a useful indication of the material solubility and potential for effective treatment. Nevertheless, all excreta should be collected following an accident or incident Excreta analyses can be the only reliable method of assessing intakes if high external contamination interfere with direct measurements.

33. International Atomic Energy Agency Blood sampling Emphasize non-invasive procedures. Invasive procedures such as blood sampling are usually justified only in accident situations in which large intakes may have occurred Blood sampling can provide data on the solubility and biokinetics Has limited value for quantitative intake estimates because of rapid clearance of most radionuclides to other tissues

34. International Atomic Energy Agency Workplace monitoring samples Workplace monitoring samples, e.g. u Air filters u Surface contamination wipes, Should be analysed to determine; u Radionuclides involved u Isotopic ratios, and u Physicochemical characteristics

35. International Atomic Energy Agency Follow-up monitoring Direct and indirect follow-up measurements should be conducted at reasonable intervals for an extended period after an accident These results will help in establishing the biological half-lives of radionuclides in the body tissues and their excretion rates This, in turn, can help to improve the accuracy of dose assessment.

36. International Atomic Energy Agency Follow-up monitoring Excreta samples should be collected and analyzed until a reasonable estimate can be made of the temporal pattern of excretion If decorporation therapy, e.g. chelating agents, is used, sampling should continue to determine the effectiveness of the treatment Once excretion patterns have stabilized, individual samples collected during the day may be combined into 24-hour samples, and appropriate aliquots taken for analysis

37. International Atomic Energy Agency Biological Dosimetry

38. International Atomic Energy Agency Biological techniques for accident dosimetry l Chromosome aberrations. l Fluorescence In Situ Hybridization (FISH). l Glycophorin A (GPA). l Premature Chromosome Condensation (PCC).

39. International Atomic Energy Agency Chromosome aberration analysis l Normal human cell contains 46 chromosomes. l Two sets of 23 different chromosomes. l Each set is derived from a different parent. l Each chromosome has two thin strands of genetic material, joined at a single point called the centromere. l Radiation can cause breaks in these strands: u single strand breaks. u double strand breaks.

40. International Atomic Energy Agency Chromosome aberration analysis l Breaks can persist as fragments or recombine. l Abnormal recombinations can be detected. l A fragment without centromere attaches at the ends, forming a circle or ring. l Two damaged chromosomes can combine, with two centromeres – a dicentric. l Frequencies of fragments, rings and dicentrics depends on the levels of radiation and L.E.T.

41. International Atomic Energy Agency Chromosome aberration analysis l Culture blood sample for several hours. l Sample is processed and prepared on microscope slides. l Individual cell chromosomes can be identified under a high power microscope. l Number of aberrations in a fixed number of cells are tallied and compared with dose response curves.

42. International Atomic Energy Agency Chromosomes aberrations after exposure Dicentric Ring

43. International Atomic Energy Agency FISH dosimetry l FISH measures chromosome damage. l Detecting broken pieces of chromosomes in lymphocytes that rejoin in a mismatched way. l The number of reciprocal translocations is proportional to exposure at low doses. l The frequency of reciprocal translocations is stable with time.

44. International Atomic Energy Agency FISH dosimetry

45. International Atomic Energy Agency Glycophorin A (GPA) l GPA assay measures gene changes in red blood cells. l Flow cytometry is used to study millions of cells. l Cells are stained with color-coded antibodies specific to the M and N gene forms. GPA molecule

46. International Atomic Energy Agency Premature Chromosome Condensation l Radiation induces different types of DNA lesions. l Double-strand breaks are the most important for induction of chromosomal aberrations. l Visualization of initial radiation induced chromosome damage in the interphase nucleus became possible with PCC.

47. International Atomic Energy Agency Premature Chromosome Condensation It is possible to distinguish chromosomes at different stages of the cell cycle. PCC provides information on: The initial level of chromosome breakage produced in interphase immediately after irradiation, and The rate and extent of chromosome break repair following exposure.

48. International Atomic Energy Agency Physical Dosimetry

49. International Atomic Energy Agency Physical techniques for accident dosimetry l Electron Paramagnetic Resonance (EPR) l Thermoluminescence (TL) l Optically Stimulated Luminescence (OSL) l Chemiluminescence l Lyoluminescence l Neutron induced activity (criticalities) u Blood [ 23 Na (n,  ) 24 Na] u Hair [ 32 P (n,p) 32 S] u Clothing, jewelry, etc [various]

50. International Atomic Energy Agency Electron Paramagnetic Resonance (EPR) After exposure to radiation, the number of unpaired electrons in some materials increases. A strong magnetic field is applied to material containing paramagnetic species. Individual magnetic moments can be oriented either parallel or anti-parallel to the field. Distinct energy levels for the unpaired electrons are created. Result is net absorption of microwaves.

51. International Atomic Energy Agency Electron Paramagnetic Resonance (EPR) Energy-level Diagram For Two Spin States as a Function of Applied Field B

52. International Atomic Energy Agency Exposure orientation with physical dosimetry

53. International Atomic Energy Agency Selected Accident Histories

54. International Atomic Energy Agency Goiânia, Brazil, 1987 l Loss of control of a large 137 Cs source. l Source stolen for scrap metal, container opened. l Result - severe, widespread contamination. l About 250 people exposed, 4 fatalities. l 150 of people have been followed. l Dose reconstruction methods: u Whole body counting and bioassay u Chromosome aberration. u Spatial dose reconstruction conducted based on contamination measurements.

55. International Atomic Energy Agency Radioactive material accidents can cover large areas

56. International Atomic Energy Agency Irradiation Facility Accidents l Workers bypassed protective measures. t El Salvador, San Salvador, February, 1989 t Soreq, Israel, June, 1990 t Nesvizh, Belarus, October, 1991 l Workers exposed to 1.25 MeV photons from 60 Co irradiators. l 5 people overexposed, one fatality in each accident. Retrospective dosimetry techniques used: t Chromosome aberration analysis. t Spatial dose reconstruction was using TL. t EPR measurements (bone, clothing, teeth, t nail clippings)

57. International Atomic Energy Agency Accidental exposures usually very non-uniform

58. International Atomic Energy Agency Hanoi, Viet Nam, 1992 l Hands exposed to high intensity 15 MeV. l Result: amputation of two fingers l E.P.R. used on bone from the amputated finger and shirt material. l Chromosome aberration analysis. l Spatial dose reconstruction performed using TLD and Fricke dosimeters.

59. International Atomic Energy Agency Extreme geometry dependence

60. International Atomic Energy Agency Extreme geometry dependence

61. International Atomic Energy Agency Tammiku, Estonia, 1994 l High intensity 137 Cs source. l Three brothers removed a metal source container from a waste repository. l During the removal, the source fell out, it was put in a pocket, and taken home. l 18 people exposed, with one fatality. l Dosimetry complex. Retrospective dosimetry: u Spatial dose reconstruction using TL & OSL, u EPR and chemiluminescence, u Biological dosimetry techniques.

62. International Atomic Energy Agency Criticality accident summary TypeNumber SignificantFatalities Exposures Process systems 8 38 2 Fissile solution systems 5 1 0 Bare and reflected 11 10 2 metal systems Moderated metal and11 29 2 metal oxide systems Miscellaneous systems 6 6 0 TOTAL41 846

63. International Atomic Energy Agency Accident Preparation

64. International Atomic Energy Agency For well organized post accident response l Anticipate the accident possibilities l Establish a plan of action. l Plan early actions to be taken. l Early detailed accident information is needed: u Description of the geometry of exposure u Exposure time u Estimated source strength, u Estimated release of radioactive material.

65. International Atomic Energy Agency Early information is crucial l Accident information and personal items should accompany the patient. l These items may be used for dose estimation. l The importance of early information is highlighted in the Nesvizh report.

66. International Atomic Energy Agency Special monitoring of accidental exposures l If a dose > the annual dose limits, equivalent (organ) dose is more important than effective (whole body) dose. l Anticipate accident possibilities in dosimeter selection. l Monitoring of accidental exposures requires special attention to dosimeter design l Use of special measurement techniques should address accident characteristics.

67. International Atomic Energy Agency Accident dosimetry l Personnel dosimeters should provide photon doses  10 Gy. l Alarm dosimeters (or dose ratemeters) can prevent serious exposures. l Reliability is more important than accuracy for alarm dosimeters. l Prevention is better than dose assessment.

68. International Atomic Energy Agency Management of Overexposed Workers

69. International Atomic Energy Agency Management of overexposed workers l Have plans to handle possible overexposure; l Address of overexposed worker management and possible health consequences; l Plans should specify actions to be taken; l Management should allocate resources to carry out those actions.

70. International Atomic Energy Agency Management of overexposed workers l Act promptly after a suspected overexposure; l Begin an investigation, to assess the dose(s) received by the worker(s); l Investigation should include, u reading of personal dosimeters u information from instruments; and u in the case of internal exposure, direct or indirect monitoring, as appropriate.

71. International Atomic Energy Agency Management of overexposed workers l Doses near dose limits do not require special medical action. l Special dose assessments are needed at much higher levels. l Special measurements could involve biological dosimetry.

72. International Atomic Energy Agency Management of overexposed workers l Further medical steps may then be necessary. l Treatment of high dose exposures should address adverse health effects, particularly deterministic. l Dose reduction measures may be warranted after significant intake of radioactive material.

73. International Atomic Energy Agency Management of overexposed workers l Actions to be taken depends on, u radionuclide, u magnitude of dose commitment, and u efficiency and risk of the protective measure; l Act only when dose reduction outweighs side effects; l Actions include decorporation of actinides by DTPA, forced diuresis after 3 H intake, and excision of contaminated wounds.

74. 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 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, Indirect Methods for Assessing Intakes of Radionuclides Causing Occupational Exposure, Safety Guide, Safety Reports Series No. 18, ISBN 92-0-100600-4 (2000) INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of Doses to the Public from Ingested Radionuclides, Safety Reports Series No. 14, ISBN 92-0-100899-6 (1999) INTERNATIONAL ATOMIC ENERGY AGENCY, Radiological Protection for Medical Exposure to Ionizing Radiation Safety Guide, Safety Standards Series No. RS-G-1.5 (2002) International Atomic Energy Agency, Compendium of Neutron Spectra in Criticality Accident Dosimetry, Technical Reports Series No. 180 (1978). International Atomic Energy Agency, Dosimetry for Criticality Accidents: A Manual, Technical Reports Series No. 211 (1982).

75. International Atomic Energy Agency References International Atomic Energy Agency, The International Chernobyl Project: Technical Report, ISBN 92- 0-129191-4 (1991). International Atomic Energy Agency, The Radiological Accident in Goiânia, ISBN 92-0-129088-8 (1988). International Atomic Energy Agency, The Radiological Accident in San Salvador, ISBN 92-0-129090-X (1990). International Atomic Energy Agency, The Radiological Accident in Soreq, ISBN 92-0-101693-X (1993). International Atomic Energy Agency, The Radiological Accident at the Irradiation Facility in Nesvizh, ISBN 92-0-101396-5 (1996). International Atomic Energy Agency, An Electron Accelerator Accident in Hanoi, Viet Nam, ISBN 92-0- 100496-6 (1996). International Atomic Energy Agency, Dosimetric and Medical Aspects of the Radiological Accident in Goiânia in 1997, IAEA TECDOC Series No. 1009 (1998). International Atomic Energy Agency, The Radiological Accident in the Reprocessing Plant at Tomsk, ISBN 92-0-103798-8 (1998). International Atomic Energy Agency, The Radiological Accident in Tammiku, ISBN 92-0-100698-5 (1998). International Atomic Energy Agency, Accidental Overexposure of Radiotherapy Patients in San José, Costa Rica, ISBN 92-0-102098-8 (1998). International Atomic Energy Agency, Report on the Preliminary Fact Finding Mission Following the Accident at the Nuclear Fuel Processing Facility in Tokaimura, Japan, IAEA-TOAC (1999).

76. International Atomic Energy Agency References International Atomic Energy Agency, The Radiological Accident in Gilan, ISBN 92-0-110502-9(2002) International Atomic Energy Agency, The Radiological Accident in Samut Prakarn, ISBN 92-0-110902-4 (2002). International Atomic Energy Agency, Investigation of an Accidental Exposure of Radiotherapy Patients in Panama, ISBN 92-0-101701-4 (2002). International Commission on Radiation Units and Measurements, Retrospective Assessment of Exposure to Ionising Radiation. ICRU Report 68, [Journal of the ICRU Volume 2, No 2] (2002) United Nations Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionizing Radiation, Volume 1: Sources, (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 Atomic Energy Agency, Cytogenetic Analysis for Radiation Dose Assessment A Manual Details, Technical Reports Series No. 405 (2001). International Atomic Energy Agency, The Criticality Accident in Sarov, ISBN 92-0-100101-0 (2001). International Atomic Energy Agency, Follow-up of Delayed Health Consequences of Acute Accidental Radiation Exposure. Lessons to be Learned from Their Medical Management, IAEA TECDOC Series No. 1300, (2002) International Atomic Energy Agency, Use of Electron Paramagnetic Resonance Dosimetry with Tooth Enamel for Retrospective Dose Assessment, IAEA TECDOC Series No. 1331 (2002). INTERNATIONAL ATOMIC ENERGY AGENCY, Rapid Monitoring of Groups of Internally Contaminated People following a Radiation Accident, IAEA TECDOC 746 (1994).