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GENERIC MODELS FOR USE IN ASSESSING THE IMPACT OF

0,84

DISCHARGES OF RADIOACTIVE SUBSTANCES TO THE

229

stron

ENVIRONMENT

2486

International Atomic Energy Agency

2001

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CONTENTS

1. INTRODUCTION . 1

1.1. Background 1

1.2. Objectives . 2

1.3. Scope 2

1.4. Structure 3

2. PROCEDURES FOR SCREENING RADIONUCLIDE DISCHARGES . 4

2.1. Dose criteria and choice of model . 4

2.1.1. Reference level 5

2.2. General assessment approach 7

2.2.1. Estimation of the annual average discharge rate . 9

2.2.2. Estimation of environmental concentrations 10

2.2.2.1. Air and water . 10

2.2.2.2. Terrestrial and aquatic foods 10

2.2.3. Estimation of doses . 11

2.2.4. Screening estimates of collective dose . 11

3. ATMOSPHERIC DISPERSION . 12

3.1. Screening calculations 12

3.2. Features of the dispersion model 13

3.3. Building considerations . 14

3.4. Dispersion in the lee of an isolated point source, H > 2.5HB . 16

3.5. Dispersion in the lee of a building inside the wake zone 20

3.6. Dispersion in the lee of a building inside the cavity zone . 23

3.6.1. Source and receptor on same building surface . 24

3.6.2. Source and receptor not on same building surface 24

3.7. Default input data . 25

3.8. Plume depletion 26

3.9. Ground deposition . 26

3.10. Resuspension of deposited radionuclides 27

3.11. Estimates for area sources . 28

3.12. Uncertainty associated with these procedures 28

4. RADIONUCLIDE TRANSPORT IN SURFACE WATERS 29

4.1. Screening calculations 30

4.2. Features of models of dilution in surface waters 32

4.2.1. Sediment effects 32

4.2.2. Applicability and limitations of the models . 33

4.2.2.1. Conservatism . 33

4.3. Rivers 34

4.3.1. Basic river characteristics required for calculations . 34

4.3.1.1. Estimating a default value for the river flow rate 35

4.3.2. Calculation of radionuclide concentrations 35

4.3.2.1. Water usage on the river bank opposite to the radionuclide discharge point 35

4.3.2.2. Water usage on the same river bank as the radionuclide discharge point 36

4.4. Estuaries 39

4.4.1. Estuarine regions . 39

4.4.2. Basic estuarine characteristics required for calculation . 39

4.4.2.1. Estimating a default value for the river flow rate and tidal velocities . 40

4.4.3. Calculation of radionuclide concentrations 40

4.4.3.1. Water usage on the bank of the estuary opposite

to the radionuclide discharge point 40

4.4.3.2. Water usage upstream or downstream prior to complete mixing 42

4.4.3.3. Water usage upstream at a distance greater than Lu . 42

4.4.3.4. Water usage upstream at a distance less than Lu or downstream at a distance greater than

Lz . 42

4.5. Coastal waters 44

4.5.1. Coastal region modelling approach . 44

4.5.2. Basic coastal water characteristics 45

4.5.3. Radionuclide concentration estimate 45

4.6. Lakes and reservoirs . 47

4.6.1. Classification 47

4.6.2. Small lakes and reservoirs 47

4.6.2.1. Required parameters 47

4.6.2.2. Radionuclide concentration estimate 48

4.6.3. Large lakes . 49

4.6.3.1. Required parameters 51

4.6.3.2. Default lake flow velocity 51

4.6.3.3. Radionuclide concentration estimates . 51

4.7. Sediment effects 52

4.7.1. Sorption and retention . 52

4.7.2. Radionuclide concentration in water 53

4.7.3. Radionuclide concentration in suspended sediment . 54

4.7.4. Radionuclide concentration in bottom sediment 54

4.7.5. Radionuclide concentration in shore/beach sediment 57

4.8. Uncertainty 57

4.9. Radionuclides discharged to sewers 58

5. TRANSPORT OF RADIONUCLIDES THROUGH TERRESTRIAL AND AQUATIC FOOD CHAINS

5.1. Terrestrial food chain models 60

5.1.1. Concentrations in vegetation 60

5.1.1.1. Direct deposition on to plant surfaces . 63

5.1.1.2. Reduction of radionuclide concentrations from surfaces of vegetation . 63

5.1.1.3. Deposition on soil . 63

5.1.1.4. Reduction of radionuclide concentration in the soil surface 65

5.1.1.5. Uptake from soil by edible portions of vegetation and the implicit assumption of

inadvertent soil ingestion 65

5.1.1.6. Derivation of minimum values for Fv, 1 and Fv, 2 . 66

5.1.2. Concentrations in animal feed . 68

5.1.3. Intake of radionuclides by animals and transfer to milk and meat . 69

5.1.3.1. Concentration in milk . 69

5.1.3.2. Concentration in meat 70

5.1.4. (Semi-)natural terrestrial ecosystems 71

5.2. Aquatic food chain transport . 71

5.2.1. Basic model . 72

5.2.2. Bioaccumulation factor Bp 72

5.2.3. Adjustment of Bp for the effect of suspended sediment 74

5.2.4. Adjustment of Bp for caesium and strontium in freshwater fish . 74

5.2.5. Biota not included in this Safety Report 74

5.3. Uncertainty associated with these procedures 75

6. DOSIMETRIC, HABIT AND OTHER DATA FOR DOSE ESTIMATION 76

6.1. Estimation of total individual doses from a source . 76

6.2. Calculation of external doses from airborne radionuclides 77

6.3. Calculation of external doses from deposited activity 83

6.3.1. Estimating external doses from deposits 84

6.4. Calculation of external doses from activity in sediments 85

6.5. Calculation of internal doses due to intake by inhalation and ingestion 86

6.5.1. Irradiation from inhaled radionuclides . 86

6.5.2. Ingestion of radionuclides 92

6.6. Radiation doses from radionuclides in sewage sludge 94

6.6.1. External irradiation exposure 94

6.6.2. Inhalation of resuspended material 95

7. ESTIMATION OF COLLECTIVE DOSE FOR SCREENING PURPOSES . 95

7.1. Generic estimates of collective dose . 96

8. PROCEDURES TO FOLLOW WHEN ESTIMATED DOSES EXCEED THE SPECIFIED

REFERENCE LEVEL 97

8.1. An iterative approach to evaluation 107

8.1.1. Initial assessment steps 107

8.1.2. Re-evaluation of the input data . 107

8.1.2.1. Estimated discharge rate and conditions . 107

8.1.2.2. Exposure conditions 109

8.1.3. Final revised generic dose calculations . 110

8.2. Realistic dose assessments in consultation with qualified professionals using more accurate

models 110

REFERENCES 111

ANNEX I: SCREENING DOSE CALCULATION FACTORS 119

I-1. Screening factors (maximum annual dose per unit discharge concentration) 119

I-2. Generic factors (dose per unit discharge) . 123

I-2.1. Atmospheric discharges . 123

I-2.2. Liquid discharges 130

I-2.2.1. Discharge into a sewerage system . 130

I-2.2.2. Discharge into a river . 133

REFERENCE . 137

ANNEX II: RADIONUCLIDE HALF-LIVES AND DECAY CONSTANTS . 138

REFERENCE . 140

ANNEX III: SPECIAL CONSIDERATIONS FOR ASSESSMENT OF DISCHARGES OF TRITIUM

AND CARBON-14 . 141

III-1. Tritium . 141

III-2. Carbon-14 143

REFERENCES . 144

ANNEX IV: EXAMPLE CALCULATIONS . 145

IV-1. Example calculation for discharges to the atmosphere when H > 2.5HB 145

IV-1.1. Scenario description . 145

IV-1.2. Calculational procedure 145

IV-2. Example calculation for discharges to the atmosphere for receptors in the wake and cavity

zones . 146

IV-2.1. Scenario description . 146

IV-2.2. Calculational procedure 146