Environmental Health Physics

Transcription

1 Environmental Health Physics Jeffrey J. Whicker Bill Eisele Mike McNaughton U N C L A S S I F I E D

2 Environmental health physics combines with many other scientific fields to protect people and the environment from radiation in a balanced way. ECOLOGY HEALTH PHYSICS Env. Health Physics NUCLEAR TECHNOLOGY GEOCHEMISTRY ENVIRONMENTAL ENGINEERING RADIATION BIOLOGY AG. SCIENCE ATMOS SCIENCE U N C L A S S I F I E D Slide 2

3 What do environmental health physicists do? Protection of environment and public through assessment of radiation dose to human and non-human biota Emergency response and counter measures: Remediation of contaminated lands Providing scientific information about radiation and risk to the public (interface with the social sciences) U N C L A S S I F I E D Slide 3

4 Env. HP applications: Assessment of radiation dose to human and non-human biota Assessment of current and future dose Provide information to public Demonstrate regulatory compliance U N C L A S S I F I E D Slide 4

5 Biota dose assessment: Who cares about radiation protection for earthworms anyway? Some reasons: Value for protection of the environment and ensuring ecosystem health and productivity Assessment and restricting radioactivity levels in human (and non-human) dose pathways Regulatory/legal reasons U N C L A S S I F I E D Slide 5

6 Env. HP applications to emergency response and counter measures: Initial dispersion and deposition modeling Dose assessments Protective action decisions: shelter in place, evacuation, decontamination Soil conditioning (plowing, treatment, etc.) Foodstuff controls (decisions for distribution, feeding supplements) Vulnerability assessments and preparation U N C L A S S I F I E D Slide 6

7 Environmental health physics applications for remediation of contaminated lands Science-based balance between risk and financial and ecological costs Clean up required Level (Bq g -1 ) Isolate and Monitor No Action Required $Cost Size of Contaminated Area (m 2 ) U N C L A S S I F I E D Slide 7

8 Models are a main tool used by environmental health physicists for prediction of concentrations/ dose/ risk/ transport Very useful, often conservative, but not necessarily accurate Equilibrium-based models Assume steady-state conditions, but transport processes are dynamic and dependent on numerous factors Mostly not mechanistic Site-specific information is often not available (i.e., k d ) Site-specific predictions are rarely validated in practice, but lots of nice work has been done elsewhere U N C L A S S I F I E D Slide 8

9 Common models and information used at LANL for dose assessment: Air Dispersion CAP88 Gaussian dispersion and dose assessment (individual and population dose) Hotspot- Gaussian dispersion after accidents (fire, explosions, etc.) NARAC- Complex terrain dispersion with current meteorology Pathway Dose Assessment RESRAD family of codes Dose models (e.g., ICRP 72 dose conversion coefficients for public) EPA Exposure Factors Handbook (e.g., soil ingestion, indoor/outdoor occupancy factors, food consumption rates, etc.) Special applications: GoldSim- Stochastic modeling of exposures; Groundwater modeling; MCNP U N C L A S S I F I E D Slide 9

10 Dose (mrem) Dose assessments and results are evaluated in context of dose limits and regional background radiation for public communication Public Dose Limits (mrem/yr) All pathway dose 100 Air pathway 10 Water pathway mrem/year Year U N C L A S S I F I E D Slide 10

11 Cosmic radiation- Solar radiation and beyond U N C L A S S I F I E D Slide 11

12 Protons and alpha particles enter atmosphere creating a cosmic shower U N C L A S S I F I E D Slide 12

13 Type of radiation with altitude LA County Graph from UNSCEAR 2000 U N C L A S S I F I E D Slide 13

14 External dose rate (mrem/yr) Effective doses from cosmic radiation in Los Alamos County Dose rate from cosmic radiation as a function of elevation in LA County- Calculations from CARI-6 model most populated cities in US Unshielded Mean ± 2 std Unshielded dose rate Shielded dose rate Elevation (ft) U N C L A S S I F I E D Slide 14

15 Cosmogenic Radionuclides- a very small contribution to overall radiation dose Major long-lived cosmogenically produced radionuclides (lifetime and reaction) Carbon-14 (5730 a): 14 N(n, p), 12 C (Neutron activation) Radionuclide Annual Effective Dose (mrem y -1 ) Sodium-22 (2.6 a) (Spallation of Ar) Tritium (12.3 a): 14 N(n, 3 H), 12 C (Spallation) Beryllium-7 (53.3 d) (Spallation N and O) C Na H Beryllium-10 (1.6E6 a): 14 N(n,p α), 10 Be (Spallation) Chlorine-36 (3E5 a) (Activation 35 Cl ) Argon-39 (269 a) (Activation 38 Ar ) U N C L A S S I F I E D Slide 15

16 Radiation exposure from terrestrial sources -primordial radionuclides in soils and rocks 232 Th 40 K 238 U, 235 U U N C L A S S I F I E D Slide 16

17 Primary exposure pathways for terrestrial radionuclides in soil and building materials Inhalation of Rn/Th decay progeny Building materials Gamma Beta Gamma Beta Radon/Thoron gas evolve 40 K 238 U, 232 Th decay progeny U N C L A S S I F I E D Slide 17

18 Terrestrial External Effective Dose Rates for Outdoor Exposure Soil Concentrations Radionuclide LA County (Bq/kg) World-wide (Bq/kg) U Th K Effective Dose Units Effective Dose Rates* LA County World-wide msv/yr mrem/yr 12 6 *Equations from UNSCEAR 2000: DR ngy / hr) C C C *0.604 air ( K 40 U 238 Th 232 EDR( msv / yr) DRair ( ngy / hr)*8760( hr / yr)*0.2*0.7( Sv / Gy)*10 ( Gy msv / ngy Sv) 6 U N C L A S S I F I E D Slide 18

19 But, we are what we eat, so we are radioactive as well, K-40, and the Th- 232 and U-238 series Ingestion Doses Radionuclides Effective Dose (mrem yr -1 ) K Th and 238 U series 13 Total 28 U N C L A S S I F I E D Slide 19

20 LA County radon concentrations compared to U.S. values U.S. Median 14 and 2 GSD Count Result (pci/l) U N C L A S S I F I E D Slide 20

21 Mean effective doses from Rn in LA County slightly higher than U.S. values, but great variability Statistic LA County (mrem/yr) U.S. Pop. (mrem/yr) a Mean ± 1 Std 269 ± ± 390 Median 2.5 Percentile 97.5 Percentile a From NCRP 160 U N C L A S S I F I E D Slide 21

22 Integration of environmental and occupational health physics: environmental radon in the workplace Workforce in the US is about 146 million workers 200 billion person-hours per year (Dept of Labor 2008) Many of these hours are spent indoors justifying measurements of indoor air quality, including radon Much less is known about Rn levels in the workplace than homes U N C L A S S I F I E D Slide 22

23 Counts Only a few Pu particles are needed to result in a significant dose, but there is more to the story: There is usually much more radon progeny in plutonium facilities 4000 There is 1000 Times More Radon Than Plutonium Pre-Release Post-Release Po Po DAC-h Pu-239 on a typical radon background Alpha Particle Energy Graph courtesy of David Wannigman, LANL U N C L A S S I F I E D Slide 23

24 Collective effective dose rate comparison for LANL workers Radiological Workers Office Workers Individual effective dose rate (2008): Average radiological worker ~0.4 msv y -1 Top radiological workers ~5.8 msv yr -1 Collective effective dose: 0.4 msv * 2,000 persons = 800 person-msv Individual effective dose rate from radon: Average office worker ~0.3 msv y -1 Top office worker ~1.1 msv yr -1 Collective effective dose: 0.3 msv * 12,000 persons = 3600 person-msv (about 4.5 times the radiation workers) U N C L A S S I F I E D Slide 24

25 Collective effective dose evaluations for public: Off-site LANL radiation emissions vs radon 2007 collective dose from LANL emissions for population 80 km radius from LANL 3.6 person-msv Estimates of the average annual collective dose from radon for residents within 80 km radius of LANL (assume all are office workers) Exposure at home 3 msv * 280,000 persons = 840,000 person-msv Factor of ~233,000 times higher for public radon dose (barely regulated) verses LANL emissions (heavily regulated) U N C L A S S I F I E D Slide 25

26 Radiologically-based medical procedures: NCRP 160 has changed our conception of background radiation exposure levels Conventional radiography CT Scans U N C L A S S I F I E D Slide 26

27 Radiologically-based medical procedures con t: Nuclear Medicine phosphate compound labeled with ( 99m Tc) Interventional Fluoroscopy U N C L A S S I F I E D Slide 27

28 msv per procedure Estimated annual number of medical procedures in Los Alamos County by procedure type (accounting for age, insurance coverage, and state-wide rates) and dose per procedure type Annual Number of Procedures Dose per Procedure Dose per procedure Conventional Radiography 1004 Interventional Fluoroscopy Computed Tomography 1121 Nuclear Medicine Conventional Radiography Interventional Fluoroscopy Computed Tomography Nuclear Medicine U N C L A S S I F I E D Slide 28

29 Average LA resident dose (mrem/yr) Sum = 291 mrem per year, close to the 300 mrem/yr in U.S. (NCRP 160)- Increasing ~ 10%/year Conventional Radiography Interventional Fluoroscopy Computed Tomography Nuclear Medicine U N C L A S S I F I E D Slide 29

30 Additional man-made Sources of radiation dose Global Fallout (10 mrem/yr) Industrial Sources (1mrem/yr) LANL (<5 mrem/yr) U N C L A S S I F I E D Slide 30

31 Distinguishing LANL Pu from global fallout: Pu isotope ratio vs Pu activity in Pajarito Plateau sediments Pu/ 239 Pu/ 239 Pu Pu Atom Ratio RG RG S RG M RG S RG RG Upper Limit of O M RG Fallout Pu Activity c M c c c c c c c C LA LA LA Plutonium from Northern N.M. Fallout (Based on 240 Pu/ 239 Pu Atom Ratio) Possible LANL Influence LANL Influence Likely LA LA LALA LA e -6 4e -5 4e -4 4e -3 4e -2 4e Pu Pu Activity (pci/g) (Bq/g) U N C L A S S I F I E D

32 Downstream changes in plutonium atom ratios in Pueblo/Los Alamos Canyon Pu/ 239 Pu Atom Ratios in Sediments Northern N.M. Fallout ( 240 Pu/ 239 Pu) 240 Pu/ 239 Pu Atom Ratio Possible LANL Influence Likely LANL Influence Modern LANL 240 Pu/ 239 Pu Pre-1960s LANL 240 Pu/ 239 Pu Distance From Source (km) U N C L A S S I F I E D

33 Effective Dose Rate (mrem/yr) Total of radiation dose for average LA County resident- 775 mrem/yr LANL Operations Global Fallout Medical Inhalation-Radon Ingestion Terrestrial-indoor Terrestrial-outdoor Cosmogenic Cosmic Effective Dose U N C L A S S I F I E D Slide 33

34 In the end, acute events (e.g., accidents, natural disasters, etc.) could result in much greater dose than routine/controlled releases Public dose limit Lethal Dose (50%) MEI dose for fire at TA Start of acute effects/vomiting, hair loss Radiation worker limit 5000 Resident near Chernoybl 2000 Pack a day smoker 1300 Average background dose Dose (mrem/yr) U N C L A S S I F I E D Slide 34

35 Dose based on Air Samples (mrem) Specific example: Peak dose during shutdown of operations at MDA-B during Las Conchas fire, maybe driven by ventilation shutdown. Unexpected upset conditions drive dose in many cases Time Profile of Dose at Sampler 317 Operations shut down during Las Conchas fire week Sampling Periods U N C L A S S I F I E D Slide 35

36 Conclusions Environmental health physicist integrates many disciplines and tries to balance risk with cost/policy/public perception/etc.. A millirem is not a millirem In the end, we in Los Alamos receive more radiation dose than the average person in United States Higher doses in cosmic, terrestrial, and radon are main reasons for the higher doses Average radiation doses in LA County much higher than 5 to 10 years ago because of increased medical exposures- CT scans in particluar Background + medical exposures >>> bigger than LANL-derived dosesthis is important for perspective and public communication U N C L A S S I F I E D Slide 36

37 Thank you for your attention! U N C L A S S I F I E D Slide 37