Day 1.5 Avci 060710 - Radiation Overview - International ... · U.S. Environmental Protection Agency’s Federal Guidance ... Radiation Health Risk Assessment Overview, continued

June 2010 | Argonne National Laboratory, USA

Radiation Overview

Dr. Halil AvciArgonne National Laboratory


ENVIRONET Environmental Remediation Training Course

2

Outline Radiation Basics

Sources of Radiation– Naturally occurring– Anthropogenic

Site Contamination– Contaminated media (soil, groundwater, surface water, buildings)– Sources of contamination

Radiation Dose and Risk

Radiation Health Risk Assessment Overview

Site Releases and Dose Standards



3

Radiation Basics – The Atom and Radioactivity

Electrons

Nucleus: Contains protons and neutrons

• Stable Nuclei – low energy state

• Unstable Nuclei – high energy state

- Emits radiation



4

Radiation Basics – Radiation Types of Concern

Paper

Glass

Lead

Alpha Particles () --2 protons & 2 neutrons

Beta Particles () –an electron (from the nucleus)

Gamma Rays () --high-energy electromagnetic radiation



5

Radiation Basics – Measurement of Radiation

Alpha, beta, and gamma radiation emitted by radioactive materials can be measured directly using hand held or laboratory equipment.



6

Radiation Basics – Activity and Half-Life

Activity – rate of decay of a radioactive material– Units: Curie (Ci) [3.7 × 1010 decays/s] and Becquerel (Bq) [1 decay/s]

Half-life – amount of time required to reduce the amount of radioactive material by 50%

Decay rate of radioactivity: After ten half-lives, the level of radiation is reduced to one thousandth

Time: two three four five six seven eight nineonehalf-life



7

8.06 × 10-6

(2.18 × 10-16)1.24 × 105

(4.59 × 1015)8.04 dIodine-131

0.0115(3.12 × 10-13)

86.6(3.20 × 1012)

30.17 yrCesium-137

2.97 × 106

(8.04 × 10-5)3.36 × 10-7

(1.24 × 104)4.47 × 109 yrUranium-238

g/Ci (g/Bq)Ci/g (Bq/g)Half-LifeRadionuclide

Mass per Unit Activity

Activity per Unit Mass(Specific Activity)

Activity = (Number of radioactive atoms) × 0.693/half-life

Note: for a given quantity of material, the longer the half-life, the less radioactive is the material. Conversely, for a given radioactivity, the longer the half-life, the greater is the quantity of the material.

Radiation Basics – Activity and Half-Life, continued



8

Radiation Basics – Decay “Chains”

Radioactive elements tend to decay into other radioactive elements – decay chains

Decay chains end in a stable element

Most decay chains are short

Some decay chains are very long

When successive members of a decay chain have the same activity, they are said to be in secular equilibrium



9

Example – Uranium Decay Series

Uranium-238*

Thorium-234*

Uranium-234*

Thorium-230*

Radium-226*

Radon-222*

Polonium-218

Lead-214*

Bismuth-214*

Polonium-214*

Lead-210*

Bismuth-210

Polonium-210*

Lead-206 (stable)

22 years27 minutes

140 days160 micro-seconds

5 days20 minutes

3.1minutes

3.8 days

1,600 years

77,000 years

240,000 years1.2 minutes

24 days

4.5 billionyears Protactinium-234*

NOTES:Only the dominant decay mode

is shown.The times shown are half-lives.The symbols and indicate

alpha and beta decay.An asterisk indicates that the

isotope is also a gammaemitter.



10

Sources of Radiation Natural Background (e.g., cosmic rays, radionuclides in soil and

geologic media, radon)

Naturally Occurring Radioactive Material (NORM)– Sometimes referred to as Technologically Enhanced Naturally

Occurring Radioactive Material (TENORM)

Anthropogenic– Weapons Programs(*)

– Nuclear Power(*)

– Radioisotope Applications(*)

• Medical• Industrial• Research

(*) Over the entire life-cycle of programs and applications



11

Site Contamination Contaminated Media

– Soil– Groundwater– Surface water– Building materials

• Surface contamination• Volume contamination

Sources of Contamination– Legacy waste disposal practices– Accidents– Normal operational releases– Abandoned facilities



12

Radiation Dose

Radiation deposits energy when it interacts with matter; the amount deposited is called “dose.”

Biological material (cells) can absorb energy from radiation, leading to ionization, excitation, or cell damage.

Depending on the type of radiation, the dose can be localized tospecific organs, or distributed across the whole body.

Unlike radiation itself, dose cannot be measured directly. It is a calculated quantity.



13

Common Radiation Dose Terms

Absorbed Dose (Rad or Gray): amount of energy deposited per unit mass of material (The U.S. uses rad and the international community uses Gray, 1 Gray = 100 rads)

Dose Equivalent (Rem or Sievert): measures of the biological effectiveness of the incident radiation (The U.S. uses rem and the International community uses Sievert (Sv); 1 Sievert = 100 rems.)– For gamma and beta radiation: 1 rad = 1 rem = 0.01 Sv– For alpha radiation: 1 rad = 20 rems = 0.2 Sv

– 1 mrem = 0.001 rem; 1 mSv = 0.001 Sv



14



15

*

(*) Ubiquitous background consists of inhalation of radon and thoron (2.28 mSv), external space (0.33 mSv), ingestion (0.29 mSv), and external terrestrial (0.21 mSv)



16

What Health Effects Can Result from Radiation Exposure? Detrimental effects of ionizing radiation include:

– Carcinogenesis (can cause cancer)– Mutagenesis (can cause mutations in cells)– Teratogenesis (can cause birth defects)– Acute toxicity (can kill you)

Large doses of radiation (600,000 to 1,000,000 mrem) can cause severe health effects, including death.

At normal environmental and occupational levels, the most important effect is the increase in the potential for developing a latent fatal cancer. (Latent means the cancer manifests itself later in life, long [often years] after the exposure to radiation occurs.)



17

Health effects are fairly well characterized for high doses of most types of radiation.

Health effects are estimated from people with high exposures:– Atomic bomb survivors– Uranium miners– Medical treatments

Effects from low-level exposures are extrapolated from those seen at high doses.

Radiation Health Effects

Bottom line: we know fairly well what happens at high doses; we estimate what happens at low doses.



18

Linear Extrapolation of Dose-Response RelationshipR

espo

nse

Doses We Are Interested In

Where We Have Data

••

•

Dose



19

Radiation Health Risk Assessment Overview

Potential receptors and exposure scenarios

Pathways analysis

Dose estimates

Risk estimates



20

inhalation

incidental ingestion

dermal contact food ingestion

inhalationdermal contact

Source Release Transport Exposures Intakes/Doses

Toxicity DataEstimated

Risks

incidental ingestion

dermal contactdrinking water ingestion

air transport

biouptakesurface water transport

groundwater transport

leaching to groundwater

deposition

Environmental Pathways from a Contaminated Site to Receptors



21

Radiation Health Risk Assessment Overview, continued


Pathways analysis– Concentrations of radionuclides at the point of receptors

Dose estimates

Risk estimates



22

Exposure Routes for Radionuclides

Inhalation

Ingestion

External Exposure

• Soil• Water• Food

• Gases• Airborne dust

• Soil• Air• Water

Exposure point concentration



23

Dose Estimates from Exposure-Point Concentrations

For inhalation and ingestion– Dose = Intake × Dose Conversion Factor (DCF)

– Intake = Amount of radionuclide inhaled or ingested (Ci or Bq)• For inhalation:

Intake = (Concentration of radionuclide in air in Ci/ft3 or Bq/m3) ×(breathing rate in ft3/s or m3/s) × (exposure duration in s)

• For ingestion:Intake = (concentration of radionuclide in food or water in Ci/lb or Bq/kg) × (consumption rate of water or food in lb/day or kg/day) × (exposure duration in day)

– DCF is obtained from literature (e.g., ICRP 26/30 or the U.S. Environmental Protection Agency’s Federal Guidance Report (FGR) No. 11)

• Units are rem/Ci or Sv/Bq



24

Dose Estimates from Exposure-Point Concentrations, continued

For external exposure– Dose = Concentration × DCFe × exposure duration

– Concentration = Concentration of radionuclide in exposed media• Air: Ci/ft3 or Bq/m3

• Water: Ci/ft3 or Bq/m3

• Ground Surface: Ci/ft2 or Bq/m2

• Soil: Ci/ft3 or Bq/m3

– DCFe is obtained from literature (e.g., ICRP 26/30 or FGR No.12) in units of

• Air: rem per Ci sec per ft3 or Sv per Bq s per m3

• Water: rem per Ci sec per ft3 or Sv per Bq s per m3

• Ground Surface: rem per Ci sec per ft2 or Sv per Bq s per m2

• Soil: rem per Ci sec per ft3 or Sv per Bq s per m3



25

Dose Estimates from Exposure-Point Concentrations, continued

DCFs can be organ-specific (e.g., lung, red bone marrow, bone surfaces, thyroid, gonads, breast) or whole body.

Doses are calculated for each radionuclide and each exposure route (inhalation, ingestion, external).

Total dose is the sum of doses from all radionuclides and exposure routes.



26

Inhalation– Concentration of Radionuclide 1 in air = 105 Bq/m3

– Breathing rate = 8,400 m3/yr = 2.7 × 10-3 m3/s– Exposure duration = 2 hr = 7,200 s– Intake = (106 Bq/m3) × (2.7 × 10-3 m3/s) × (7,200 s) = 1.9 × 106 Bq– DCF for inhalation = 1 × 10-10 Sv/Bq– Inhalation dose from Radionuclide 1 = (1.9 × 106 Bq ) × (1 × 10-10 Sv/Bq) = 1.9 × 10-4 Sv

Ingestion– Concentration of Radionuclide 2 in tomatoes = 103 Bq/kg– Consumption rate = 0.5 kg tomatoes/day– Exposure duration = 10 days– Intake = (103 Bq/kg ) × (0.5 kg/d)*10 d = 5 × 103 Bq– DCF for ingestion = 5 × 10-9 Sv/Bq– Ingestion dose from Radionuclide 2 = (5 × 103 Bq ) × (5 × 10-9 Sv/Bq ) = 2.5 × 10-5 Sv

Dose Estimates from Exposure-Point Concentrations –Example Calculations



27

External Exposure– Concentration of Radionuclide 1 on ground surface = 106 Bq/m2

– Exposure duration = 105 s– DCF = 1 × 10-17 Sv/Bq s per m2

– Dose from external exposure to Radionuclide 1 = (106 Bq/m2 ) × (105 s ) ×(1 × 10-17 Sv/Bq s m-2 ) = 10-6 Sv

Total Dose assuming the same individual is exposed to Radionuclide 1 through inhalation and external exposure and Radionuclide 2 through ingestion

– Total Dose = 1.9 × 10-4 Sv + 2.5 × 10-5 Sv + 10-6 Sv = 2.16 × 10-4 Sv

Dose Estimates from Exposure-Point Concentrations –Example Calculations, continued



28

Radiation Health Risk Assessment Overview, continued


Pathways analysis– Concentrations of radionuclides at the point of receptors

Dose estimates

Risk estimates



29

Radiation Health Risk Estimates Radiation cancer health risks (in terms of mortality [death] and morbidity

[incidence]) can be calculated using radionuclide-specific risk coefficients (also called slope factors) developed by the U.S. EPA (similar to the way dose conversion factors are used to calculate dose).

– EPA’s risk coefficients are given in FGR No. 13. They are given in units of risk per Bq inhaled or ingested (for internal exposures), and in units of risk per Bq-s per m3 for submersion, Bq-s per m2 for ground surface, and Bq-s per kg for soil contamination (external exposures).

Often the risk is calculated by applying a dose-to-risk conversion factor to the total whole body dose.



30

Radiation Health Risk Estimates, continued Dose-to-risk conversion factors are developed by international organizations

(such as the United Nations Scientific Committee on the Effects of Atomic Radiation [UNSCEAR] and the International Commission on Radiation Protection [ICRP]) and adopted by national organizations.

Dose-to-risk coefficients used for workers are generally lower than the coefficients used for the general public (e.g., ICRP Publication 60 gives 4 × 10-4 per person-rem [4 × 10-2 per person-Sv] for workers, and 5 × 10-4

per person-rem (5 × 10-2 per person-Sv] for general public for cancer mortality).

There is a lot of uncertainty in risk coefficients and dose-to-risk conversion factors.



31

Radiation Health Risk Estimates – Example Calculation

Assume – Dose = 2.2 × 10-4 Sv– Dose-to-Risk Conversion Factor for Cancer Mortality = 5 × 10-2 per

person-Sv

– Risk of Cancer Mortality = (2.2 × 10-4 Sv) × (5 × 10-2 /Sv) = 1 × 10-5



32

Concepts of Clearance, Exclusion, and Exemption (Source: ANSI/HPS N13.12-1999 and IAEA Safety Guide RS-G-1.7)

Clearance: Removal of items or materials that may contain residual levels of radioactive materials within authorized practices from any further control of any kind. Clearance implies that the subject materials or objects were under regulatory control.

Exclusion: Designation by a regulatory authority that the magnitude or likelihood of an exposure is essentially unamenable to control through requirements of a standard and such exposures are outside the scope of standards, e.g., exposure from 40K in the body, from cosmic radiation at the surface of the earth and from unmodified concentrations of radionuclides in most raw materials.

Exemption: Designation by a regulatory authority that specified uses of radioactive materials or sources of radiation are not subject to regulatory control because the radiation risks to individuals and the collective radiological impact are sufficiently low.



33

Standards and Generic Guidelines for Exemption of Radium-and Thorium-Contaminated Sites in the United States

U.S. EPA standards for remediation of uranium mill tailings sites (40 CFR 192.12):– Remedial actions shall be conducted so as to provide reasonable

assurance that, as a result of residual radioactive materials from any designated processing site:

(a) The concentration of radium-226 in land averaged over any area of 100square meters shall not exceed the background level by more than—

1) 5 pCi/g (0.185 Bq/g), averaged over the first 15 cm of soil below the surface, and

2) 15 pCi/g (0.555 Bq/g), averaged over 15-cm-thick layers of soil more than 15 cm below the surface.

U.S. Department of Energy (DOE) has generic guidelines for remediation of radium- and thorium-contaminated sites (DOE Order 5400.5) that are similar to the EPA standards for uranium mill tailings sites.



34

Site Release Options

Any use (no restrictions on the use of the property; cleared, exempt, or excluded)

Limited use (e.g., industrial, recreational – access to the site is not controlled)

Restricted use (access to the site is controlled)



35

Site Release and Dose Standards

Site release is based on some primary dose criterion. The primary dose criterion used by most nationalities and organizations is

100 mrem/yr (1 mSv/yr) from all practices (as recommended by ICRP Publication 60).

– U.S. Nuclear Regulatory Commission uses 25 mrem/yr (0.25 mSv/yr) for license termination

– U.S. EPA uses 10-4 to 10-6 risk for Superfund sites instead of dose

Radionuclide-specific activity concentrations are derived based on certain future use of the site (e.g., residential, industrial, recreational, controlled access) that correspond to the dose criterion.

The site is remediated to achieve the derived concentration levels. The dose criterion used for exclusion and exemption is generally 1 mrem/yr

(10 micro Sv/yr). Screening level activity concentrations are developed for exclusion or exemption (see for example ANSI/HPS N13.12-1999 and IAEA Safety Guide RS-G-1.7).

Documents

Day 1.5 Avci 060710 - Radiation Overview - International ... · U.S. Environmental Protection Agency’s Federal Guidance ... Radiation Health Risk Assessment Overview, continued