Occupational Radiation Protection during High Exposure Operations

IAEA Training Material on Occupational Radiation Protection Occupational Radiation Protectionduring High Exposure Operations Lecture 9 Radioactive Sources to be Considered

Contents • Nuclear accident • Radiological accident

1. Nuclear accident Stages of emergency response At an early stage in a nuclear accident local public protective actions need to be taken promptly (normally within hours) are called urgent protective actions (evacuation, short term sheltering, etc.). Subsequent protective actions, such as relocation, carried out within days to weeks are called early protective actions. The division of an emergency into stages in pragmatic (useful for decision making) source characterization taking into account the levels of sources monitored on-site off-site during the accident. 3

Early stage In case of nuclear accident in a nuclear installation, dynamics of radioactive release and radionuclide dispersion over on-site and off-site would not be accurately predicted at the early stage of the accident. Urgent obligatory actions at that time could therefore be carried out in a temporal distribution of radioactivity. In early stage of a nuclear accident radiation monitoring are used for: • Identification of threats, reasons and their severity • Identification of uncontrollable source • Prediction of further dynamics and consequences for staff • Selection of adequate protective actions on-site during urgent emergency response • Justification of medical triage of injured staff 4

Early stage Radiological data to be used for the activities depends on a threat category. 5

Early stage Requirements to exercise regarding to source simulation are: • Exercise data should be no different from real data except for the fact that they are simulated • Compliance of topics and issues of training with emergency instruction and responsibilities of certain personnel in the case of an accident • Coverage of possible emergency situations stipulated in emergency plans of emergency response and protection of workers and rescuers. 6

Early stage Emergency planning category and exercise scenario 7

Whole term Subsequent to the early stage in a nuclear accident, spent nuclear fuel (SNF) management, isolation of damaged unit and decontamination become high priority objectives of emergency and recovery actions. 8

2. Radiological accident Uncontrolled dangerous source The categorization system is based on the concept of “dangerous sources” which are quantified in terms of “D values”. The D value is the radionuclide specific activity of a source which, if not under control, could cause severe deterministic effects for a range of scenarios that include both external exposure from an unshielded source and internal exposure following dispersion of the source material. • The D1-value is the activity of radionuclide in a source that, if uncontrolled but not dispersed, might result in an emergency that could cause severe deterministic health effects by external exposure • The D2-value is the activity of radionuclide in a source that, if uncontrolled and dispersed, might result in an emergency that could cause severe deterministic health effects by internal and external exposure • The D-value is the lowest-value of the D1 - and D2-values for a radionuclide 9

Minimal values of activity which can induce deterministic effects (D1-, D2-, D-values) 10

Uncontrolled dangerous source The IAEA has established 5 dangerous categories of sources corresponding to ratio activity of source to D-value, A/D: I A/D ≥ 1000 Extremely dangerous to the person II 1000 > A/D ≥ 10 Very dangerous to the person III 10 > A/D ≥ 1 Dangerous to the person IV 1 > A/D ≥ 0.01 Unlikely to be dangerous to the person V 0.01 > A/D Most unlikely to be dangerous to the person 11

IAEA’s Categorization of radioactive sources Radioisotope Thermoelectric Generator - RTGs Teletheraphy Irradiators Gamma-knife 12

IAEA’s Categorization of radioactive sources Industrial gamma Radiography H/M dose rate brachytherapy 13

IAEA’s Categorization of radioactive sources Fixed industrial gauges Well logging gauges 14

IAEA’s Categorization of radioactive sources Bone densitometers Portable gauges ; Static eliminators Low dose rate brachytherapy 15

IAEA’s Categorization of radioactive sources Electron capture devices Low dose rate brachytherapy X ray fluorescence devices 16

INES - The International Nuclear and Radiological Event Scale The INES Scale is a worldwide tool for communicating to the public in a consistent way the safety significance of nuclear and radiological events. Just like information on earthquakes or temperature would be difficult to understand without the Richter or Celsius scales, the INES Scale explains the significance of events from a range of activities, including industrial and medical use of radiation sources, operations at nuclear facilities and transport of radioactive material. Events are classified on the scale at seven levels: Levels 1–3 are called "incidents“ and Levels 4–7 "accidents". The scale is designed so that the severity of an event is about ten times greater for each increase in level on the scale. Events without safety significance are called “deviations” and are classified Below Scale / Level 0. 17

INES - The International Nuclear and Radiological Event Scale 18

Uncontrolled dangerous source For radiological emergencies an airborne release of radioactive material is of concern primarily if a dispersible dangerous source is contained in a fire or explosion. The distance at which such a release is hazardous depends on many factors such as the size of the source, the amount of material dispersed into the air, its dilution, the movement of the plume and the size and nature of the particles. These factor should also be taking into account during an emergency. For airborne release from facilities the significant pathways of exposure for personnel are mainly: • External gamma radiation from radioactive martial deposited on the ground, called ground shine • Inhalation of radioactive material contained in the plume • Deposition of radioactive material on the skin 23

INES scale application for release of radionuclide #n = 5 24

Uncontrolled dangerous source Radiation monitoring is carried out during emergency actions on site and on zones boundaries with the aim of preventing transfer of radionuclide, retrospective estimation of applied measures and prospective estimation of occupational doses for planned measures. Radiation monitoring is intended for also assessment of individual and collective doses, efficiency of emergency response and identification of involved persons needed in medical treatment or follow up. 25

Misuse of industrial and medical dangerous source In radiological accidents by the misuse of industrial/medical dangerous source the most important pathways of exposure are external exposure and inadvertent ingestion. For the radiological emergency due to misuse of industrial/medical dangerous source, emergent response for radiation protection and for retrieving the dangerous source should be planned in advance and conducted. Special investigation should be organized in a case of loss or theft of source. Members of searching team should be supplied by individual dose monitors, protective clothes, radiometric and dosimetric devices with wide range of radiation measurement, remote source catcher and shield container. 26

Transport accident of dangerous source Two typical situations can occur during transportation: • The movement of all radioactive materials according to standards of regulatory, administrative, safety and engineering controls • Either deliberate or inadvertent movements of radioactive materials outside of the regulatory and legal framework Regulations require that exposure from handling, storage and transport of radioactive material shall be kept as low as reasonably achievable taking into account social and economic factors. Also past events and their analysis should be useful for typical source considerations. Analysis of incidents and accidents has been based on the severity scale for radioactive material transport events developed for the IAEA’s transport Event Database EVTRAM. 27

Adoption of the INES scale for transport events 28

Transport accident of dangerous source When a radiation hazard is suspected or known, it is essential that an inner cordon be established around the radioactive source and all persons be evacuated from within the inner cordon control area. The inner cordon should be set up at a distance where the external dose rate level does not exceed 0.1 mSv/h. Airborne radioactivity should be measured or estimated in order to set up the area of inner cordon control. 29

Transport accident of dangerous source If the first responder encounters any of the following conditions, the scene is likely to require prompt radiological evaluation to assess the magnitude of the radiation hazards: • Radiation level greater than 0.1 mSv/h at distance of 1 m from a surface or object • The confirmed detection of neutron radiation that is not from a legal shipment of radioactive materials • Contamination indicated by loose, spilled or leaking radioactive materials The first responder should establish the location of the radioactive material. The next step is to identify the radioactive material. The topography of the scene is a critical factor in the determination of the most effective means of seizing the radioactive materials and bringing them under control. 30

Occupational Radiation Protection during High Exposure Operations