Dirty bomb event in urban environment radiation exposure of public and emergency personnel

Transcription

1 Dirty bomb event in urban environment radiation exposure of public and emergency personnel 1. Introduction 2. Radiological dispersion device information 3. Contamination levels in urban environment 4. Exposure pathways for personnel and public 5. Airborne respirable particulate from resuspension processes (research results) 6. Contamination examples: Cs 137 (gamma), Sr 90 (beta), Pu 238 (alpha) emitters 7. Estimates of exposure from passing cloud 8. Conclusions 1

2 Dirty bomb event in urban environment radiation exposure of public and emergency personnel 1. Introduction Conventional bombs are frequent in terroristic and criminal scene. Conceivable threat is combination of explosives and radionuclides as means to generate airborne radioactive material and to disperse over a larger area. In urban environment possible result: casualties from bomb explosion, contamination, radiation exposure, fear or panic, local disruption of normal life, economic consequences Competent authorities and safety and emergency institutions have to be prepared for this threat and develop plans to deal with such emergency exposure situations : Emergency preparedness The purpose of my presentation to give some background information, to illustrate the conceivable radiological situations, potential exposure of public and of emergency personnel and to address some emergency actions and protection of emergency personnel 2

3 2. Radiological dispersion device information (1) Experimental and analytical investigations (e.g. High Consequence Assessment and Technology Program, Sandia National Laboratories, F.T. Harper et al., USA), IAEA, other national safety institutions) Radionuclides of concern are related to radiological properties and possible availability of higher activity sources Various constructions of a dirty bomb can be imagined as combination of explosive and radioactive material with the intention of airborne dispersal of radioactive particulates. Of special concern is particulate with respirable particle sizes < 10 µm AED (inhalation hazard) F. Lange, ConRad

4 2. Radiological dispersion device information (2) Candidate radionuclide Predominant radiation Co 60 X metal Sr 90 X ceramic Cs 137 X salt I 192 X metal Ra 226 X salt Pu 238 X ceramic F. Lange, ConRad 2013 Typical solid material property Am 241 X Pressed ceramic powder, sintered ceramic pellets Cf 252 X ceramic Effect of explosive and device construction: Material dependent fracture behaviour, resulting particle size distribution, generation of larger fragments and of respirable particulate (< 10 µm AED) Bomb fragments ballistic flight, circumferential distribution, mainly within ~100 m radius Particulates > 10 µm may also become airborne, deposition velocity v d increases with (AED) 2, e.g. 100 µm particle has v d 0.3 m/s Airborne activity is transported in downwind direction by atmospheric dispersion 4

5 2. Radiological dispersion device (RDD) information (3) Statement: It is judged to be a reasonably cautious assumption that in case of a successful implementation of an RDD explosion not more than Bq of the radioactive material would be released and dispersed airborne as respirable particulate < 10 µm AED The following estimates regarding contamination levels, affected areas and radiation exposure of member of the public and emergency personnel via critical pathways are based on this assumption: Boundary conditions of RDD detonation and atmospheric dispersion modelling: Release of larger fragments, possibly radioactive, mainly within 100 m radius Bq airborne release of radioactive particulate with respirable particle sizes (< 10 µm AED,: 0-2,5 µm: 50 % and 2,5-10 µm : 50 % deposition velocity: v d = m/s Atmospheric dispersion conditions: neutral stability class D, moderate wind velocity: u= 2 m/s Location: urban environment F. Lange, ConRad

6 Dirty bomb event in urban environment radiation exposure of public and emergency personnel Contamination level depends on the airborne released activity and the size distribution of the particulate Assumed location of detonation: close to the ground in open air The blast leads to a larger volume of hot gases and entrained/immersed radioactive particulate, starting condition for atmospheric dispersion (particle simulation model) Larger fragments: ballistic flight, mainly distributed within 100 m radius The deposition velocity as function of aerodynamic diameter (AED) determines the rate of depletion from the passing cloud through dry (no rain) deposition of particulate matter and associated contamination pattern on surfaces AED [µm] Depostion velocity v d [m/s] < The heavy blast and larger impacting fragments can lead to severe injuries of persons nearby and can pose problems in treatment if radioactive F. Lange, ConRad

7 3. Contamination levels in urban environment: Result of atmospheric dispersion model LASAIR operated by Fed. Radiation Protection Office (BfS), courtesy H. Walter (1) Release Bq Respirable < 10 µm Explosive: 1 kg range neutral stability, u= 2 m/s deposition velocity: m/s 1000 m Contour line 10 4 Bq/m² (e.g. Cs 137 deposition level in Munich after Chernobyl accident: Bq/m²) 1000 m F. Lange, ConRad 2013 LASAIR is an advanced atmospheric dispersion model 7

8 Contamination levels in urban environment: Result of atmospheric dispersion model LASAIR operated by Fed. Radiation Protection Office (BfS), courtesy H. Walter (2) 1000 m F. Lange, ConRad

9 Contamination levels in urban environment: Result of atmospheric dispersion model LASAIR operated by Fed. Radiation Protection Office (BfS), courtesy H. Walter (3) Release Bq Respirable < 10 µm Explosive: 1 kg range Bq/m² 1000 m Bq/m² Bq/m² F. Lange, ConRad m neutral stability (D) u= 2 m/s deposition velocity v d = m/s 9

10 Radiation exposure after contamination event: public and emergency personnel (1) Radiation exposure, e.g. for first responders, after contamination event 1. External (direct) radiation: Gamma ( ) radiation (pentrating) effective dose [µsv, msv, Sv] Dose = dose rate [µsv/h, msv/h] exposure duration [h] Dose rate is easily measured and monitored by standard hand-held instruments Example: larger area with Cs 137 (strong gamma emitter) contamination of 10 6 Bq/m²: Dose rate 2 µsv/h Beta ( ) radiation skin dose effective dose (tissue weighting factor 0.01) Detection by contamination monitors as activity concentration on surfaces, e.g. counts per unit area, dose rate if radionuclide is known Contamination monitors are not standard equipment of emergency personnel Example: larger area with Sr 90 (high decay energy beta emitter) contamination of 10 6 Bq/m²: (effective) dose rate 33 µsv/h Alpha ( ) radiation: no external exposure, except for skin contamination of high decay energy emitters 10

11 Radiation exposure after contamination event: public and emergency personnel (2) Radiation exposure, e.g. for first responders, in early time after contamination event 2. Internal exposure from inhalation of respirable (< 10 µm) particulate Intake [Bq] = activity concentration in air [Bq/m³] exposure time t [s] breathing rate BR [m³/s] Effective dose= intake [Bq] dose coefficient [Sv/Bq] persons dwelling and operating in contaminated areas with airborne activity concentration resulting from various resuspension processes. (wind, walking, driving vehicles, contaminated clothing, etc) This exposure pathway requires quantative information about resuspension processes Other exposure pathways after contamination event can be controlled, e.g. skin contamination, or avoided, e.g. consumption of contaminated food. Note: Persons residing within the passing activity cloud from dirty bomb detonation could be exposed via inhalation during the short period of cloud passage and could become contaminated. These exposure pathways from the passing radioactive cloud could occur shortly after the release in downwind direction. They could hardly be avoided (the inhalation exposure will be shortly addressed here) 11

12 Resuspension data from experimental and analytical research work by Fraunhofer Institute ITEM (Prof. Dr. Wolfgang Koch), study contracts by Federal Ministry of Environment (BMU) and Federal Office for Radiation Protection In model experiments, wind resuspension rates of respirable particles and their time dependence after deposition on representatively contaminated urban surfaces were measured under real-life conditions, taking into account different weather conditions and countermeasures (fixation). In addition, data were generated to enable comprehensible and realistic modeling of the influence of particle resuspension caused by persons and responders themselves by walking movements and moving vehicles, both outdoors and in emergency stations. For early phase of radiological emergencies: exposure of emergency personnel has been modelled and estimated (scenario analyses) 12

13 Resuspension data from experimental and analytical research work by Fraunhofer Institute ITEM (Prof. Dr. Wolfgang Koch) Resuspension factor RF [1/m] = airborne activity concentration,[bq/m³] activity concentration on surface,[bq/m²] Resuspension rate RR [1/s] = resuspension flux density,[bq/m² s] activity concentration on surface, [Bq/m²] Resuspension rate = fraction of surface contamination released per unit time Also useful: Resuspended fraction RA [/] = fraction of surface contamination that becomes airborne by resuspension processes (e.g. from intermittent action such as walking persons and driving vehicles) F. Lange, ConRad

14 Resuspension data from experimental and analytical research work by Fraunhofer Institute ITEM (Prof. Dr. Wolfgang Koch) Measurement of various resuspension processes with emphasis on early phase after contamination Small channel apparatus with online detection of resuspended particles, particle size information 1. Continuous airflow to simulate acting wind Resuspension rates RR from wind for representative surfaces and particulate, emphasis on respirable dust (< 10 µm AED) dependence of RR from wind velocity and from time 2. Short airflow bursts to simulate conditions of high velocity air jets from persons walking (upstep+downstep motion) and from moving vehicles Model chamber (clean room) with measurement of airborne dust 1. to measure resuspension from contaminated clothing during typical activities 2. to determine resuspension from dust contamination on the ground by walking persons 14

15 Surfaces contaminated with particulate solid Indoor relevant Environment relevant Textile Tyvek Art slate road surface Natural slate Roof tile Glass wood road surface Sand-lime brick 15

16 Contamination Dry deposited particulate (non-fixed) Cerium oxide Silver Aluminum oxide Wet deposited particulate CsCl-droplets after drying 16

17 Wind resuspension: Time pattern Strong decrease of resuspension rate with time: R R A t RR A 1/t - Dependence from wind velocity u [m/s]: R R ~ (u) 2.5 (u < 10 m/s) Resuspension rate [1/h] 10 m/s 2 m/s Time [min] 17

18 Wind resuspension: time dependence up to 60 h Results of resuspension experiments with channel apparatus 1E-03 y = x Resuspension Rate RR [1/h] RR A t -1 Resupensionsrate [1/h] 1E-04 1E-05 R 2 = y = x R 2 = For longer times (up to 60 h) larger data scatter due to detection limits (counting statistics) Same time dependence 1E Zeit [h] Time [h] 18

19 Wind resuspension: transient (e.g. locally high air flow under shoe sole from walking or from moving vehicle) 20 m/s Transient wind gust; Duration: 3 s; Pause: 2 min 20 m/s Decrease following n -1.2, n>1 1 t 10 m/s Flow at 20 m/s suppresses resuspension when subsequently challenged with 10 m/s. 10 m/s Number of short wind pulses 19

20 Measurement of particle resuspension rate Measurement in model chamber (clean room) Simulation under real conditions Transferability of experiments with channel apparatus Realisation of human activities: walking, running,.. Gravity effects taken into account Direct Measurement of activity concentration as measure for inhalation doses. F. Lange, ConRad 2013 Dirty bomb event in urban 20

21 Wind resuspension: Fixation measures Natural Naturschiefer slate 2,91E-03 Spraying of water or glycerol Natural Naturschiefer slate/hh2o 2 O 3,26E-04 water mixture Natural Naturschiefer slate Glyc/H2O 2 O 3,06E-05 Sand-lime Kalksandstein brick Sand-lime Kalksandstein brick/h2o 2 O 3,16E-04 5,21E-02 Reduction in release; Efficiency factor: Sand-lime Kalksandstein brick Glyc/H2O 2 O 6,11E-05 Early fixation measures result Glass 5,13E-03 in efficient protection of first Glass/H H20 2 O 2,70E-04 responders and reduction of Glass Glyc/H2O 2 O 4,08E-05 spreading of contamination 1,00E-05 1,00E-03 1,00E-01 Resupension rate [1/h] (1-30 min) 21

22 Wind resuspension: Time pattern Resuspended fraction 9,0E-03 8,0E-03 7,0E-03 6,0E-03 5,0E-03 4,0E-03 3,0E-03 2,0E-03 1,0E-03 0,0E+00 u = 6 m/s differentiell kumulativ Arrival of first responders: 10 min after event Major part of inhalation dose within first hour Early personal protection and fixation measures for surface contamination effective First hour: RR = [1/h] 10th hour: RR = [1/h] Hours after event differential cumulative 22

23 Wind resuspension: Inhalation dose Activity concentration [Bq/m³] Contaminated area u labil unstable neutral stabil stable L Width of contaminated area, L [m] L 2 R R FK 2 dx z C Exp 2 u ( x) 2 ( x) 0 z z activity concentration in breathing height z = 1.5 m for u = 6 m/s RR = /h (10th hour) RR = /h (10th hour) Surface contamination ( dirty bomb ) SC = Bq/m² (respirable) Typ. value of resuspension factors in first hours: /m Inhaled activity : < 10 Bq in first hour < 0.5 Bq in 10th hour 23

24 Estimates of radiation exposure for emergency personnel operating within areas of high contamination levels of 10 6 Bq/m² Contamination 10 6 Bq/m² (respirable particle sizes < 10 µm) As representative radionuclides: Cs 137 (gamma), Sr 90 (beta), Pu 238 (alpha) For reasons of simplicity but still reasonable estimate for airborne activity in areas contaminated at a level of 10 6 Bq/m² wind resuspension at a rather high wind speed of 6 m/s at the ground is assumed: Cs 137: dose rate from groundshine = 2 µsv/h ( an additional contribution from deposited larger radioactive particles is possible) effective dose from inhalation of 10 Bq in first hour Eff. Dose = 10 Bq Sv/Bq (dose coefficient) = 0.4 µsv Eff. dose from inhalation of 0.5 Bq in 10th hour = 0.02 µsv Sr 90: effective dose from external radiation (groundshine): 33 µsv/h (no attenuating effects assumed, e.g. ground roughness, etc.) effective dose from inhalation of 10 Bq in first hour Eff. Dosis = 10 Bq Sv/Bq = 2 µsv Eff. dose from inhalation of 0.5 Bq in 10th hour = 0.1 µsv Pu 238: no external dose rate (with exception of skin contamination of high energy alpha emitter) effective dose from inhalation of 10 Bq in first hour Eff. Dosis = 10 Bq Sv/Bq (assumed as oxide) = 200 µsv Eff. dose from inhalation of 0.5 Bq in 10th hour = 10 µsv 24

25 Contamination levels in urban environment: Result of atmospheric dispersion model LASAIR operated by Fed. Radiation Protection Office (BfS), courtesy H. Walter (3) Release Bq Respirable < 10 µm Explosive: 1 kg range Bq/m² 1000 m Bq/m² Bq/m² F. Lange, ConRad m neutral stability (D) u= 2 m/s deposition velocity v d = m/s 25

26 Estimates of radiation exposure of persons residing in areas during passage of radioactive plume from dirty bomb release (1) Result of LASAIR calculation is deposition level F [Bq/m²] for a release of Q = 10 6 Bq of respirable particulate (< 10 µm AED) with a (dry) deposition velocity v d = 1.5 m/s F [Bq/m²] = Q [Bq] [s/m³] v d [m/s] [equ.1] where is the time-integrated air concentration The activity intake INT [Bq] via inhalation is given by: INT = Q [Bq] [s/m³] BR [m³/s] [equ. 2] Where BR is the breathing rate (BR m³/s for an adult, about 1 m³/h) Combining equation 1 and 2 1 INT [Bq] = (F/v d ) BR, i.e. given the contamination level F, deposition velocity v d and breathing rate BR the intake of a person during the passage of the radioactive cloud at such a location can be calculated: At a contamination level of 10 4 Bq/m² (according to LASAIR result) the intake via inhalation is Bq At a contamination level of 10 5 Bq/m² (according to LASAIR result) the intake via inhalation is Bq 26

27 Estimates of radiation exposure of persons residing in areas during passage of radioactive plume from dirty bomb release (2) Inhaled Activity [Bq] Cs Sv/Bq Sr Sv/Bq Pu 238 (oxide) Sv/Bq Contamination level Bq 80 µsv 400 µsv 40 msv Bq 800 µsv 4 msv 400 msv 10 4 Bq/m² 10 5 Bq/m² Based on the calculated deposion levels by LASAIR the corresponding inhalation doses (effective dose) during the passage of the radioactive cloud are estimated as orientation. Inhalation doses for a person that happens to be exposed to the passing cloud in a few hundred meters in downwind direction would be practically unavoidable (no warning time) In comparison doses from inhalation following resuspension are at a very low level. 27

28 8. Conclusions Some quantitative estimates of potential exposure of emergency personnel (first responders) and members of the public have been given when a severe contamination by malicious dispersal of respirable radioactive material has occurred External radiation exposure can be controlled with common dose rate and dose meters (gamma), more difficult is use of contamination monitors (beta, alpha) A recent study by Fraunhofer Institute ITEM on resuspension processes provides valuable data for radiological scenario analyses regarding inhalation and suppression of resuspension These results provide a quantitative basis to estimate exposure of emergency personell and for measures to reduce resuspension and for personal protection In case of such an RDD event protective actions by emergency personnel, contamination control, medical care, decontamination, return to normal living conditions would face many problems. The widespread fear of radioacticity and of ionizing radiation would very much complicate all remedial activities. Quantifying the expected radiation exposure and the associated health risk is one means for a more rational approach to such a situation 28