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Consideration of Off-site Emergency Planning and Response using Probabilistic Accident Consequence Assessment Models M. Kimura, J. Ishikawa and T. Homma.

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Presentation on theme: "Consideration of Off-site Emergency Planning and Response using Probabilistic Accident Consequence Assessment Models M. Kimura, J. Ishikawa and T. Homma."— Presentation transcript:

1 Consideration of Off-site Emergency Planning and Response using Probabilistic Accident Consequence Assessment Models M. Kimura, J. Ishikawa and T. Homma Nuclear Safety Research Center Japan Atomic Energy Agency (JAEA) NREP Conference, April 22, 2009

2 2 IAEA Safety Requirements (GS-R-2, 2002) Safety Guide (GS-G-2.1, 2007) – Management approach – Practical goals (8 goals) Prevent the occurrence of deterministic health effects Prevent, to the extent practicable, the occurrence of stochastic health effects – Intervention principles – Efficient and cost-effective system ICRP (Publ.103, 2007) – Optimization of overall strategy Japan (NSCs Guideline on emergency preparedness) – No practical guidance for protective measure strategy Background

3 3 Perform a risk informed analysis of protective measures using Level 3PSA code (OSCAAR), in order to formulate the technical basis for the effective strategy of protective measures –Introduce a metabolic model of iodine to accurately evaluate the effect of reducing thyroid dose by administration of stable iodine –Combination of protective measures, sheltering and evacuation with administration of stable iodine Objectives

4 4 Accident Consequence Model OSCAAR (Off-Site Consequence Analysis of Atmospheric Releases of radionuclides) OSCAAR module Preprocessor code

5 5 Models of OSCAAR Atmospheric Dispersion and Deposition Multi-puff trajectory model with two scale wind fields Take account of temporal changes in weather conditions and variable long duration releases Meteorological Sampling Stratified sampling scheme appropriate for use with the trajectory dispersion model was designed and developed Select a representative sample of weather sequences for analysis Exposure Pathways Realistic estimates for all possible exposure pathways with protective measures with simple models such as sheltering, evacuation, relocation and food ban –Shielding and filtering factors for sheltering –Radial evacuation

6 6 Metabolic Model of Iodine GUT or LUNG, Y 1 THYROID, Y 3 ORGANIC IODINE, Y 4 BLADDER EXCRETA INORGANIC IODINE, Y 2 s 2 r 2 GUT or LUNG, Y1 THYROID, Y3 ORGANIC IODINE, Y4 BLADDER EXCRETA INORGANIC IODINE, Y2 s 2 r 2 Johnson model (1981) Reduction in the committed thyroid dose to man (for adult, 100mg) Reduction in the committed thyroid dose to man (for adult, 100mg) : the rate of uptake of radioactive and stable iodine by the thyroid : the rate constant for uptake or excretion of iodine from each compartment Time (h) before or after an intake of radioiodine Reduction factor (Intake of stable iodine/ No measurement)

7 7 Source Term Development Iodine release fraction Energetic events, Overpressure, ISLOCA Containment vent Termination / :Relative failure frequency (each / all containment failure scenarios) TQUV-αTQUX-α TB-α TBU-α AE-α TQUX-μ TB-μ TBU-μ TQUX-σ TB-σ TBU-σ TQUV-δTQUX-δ TB-δ TBU-δ AE-δTW-θTC-θ V-ν TQUV-υ-lTQUX-υ-l TB-υ-l TBU-υ-l AE-υ-l TQUV-ψ-l TBU-ψ-l AE-ψ-l BWR5/Mk-II : Release fraction of Iodine Relative failure frequency (from INS/M03-22) JAEA evaluation Release fraction of iodine

8 8 Release time (hr) Relative failure frequency (from INS/M03-22) : Release time (hr) JAEA evaluation Source Term Development (Contd) :Relative failure frequency (each / all containment failure scenarios)

9 9 Strategies of protective measures Large early release: precautionary evacuation with stable iodine intake Large late release: evacuation and sheltering with stable iodine intake Control release: sheltering with stable iodine intake Site data A reference site is assumed to be located at a coastal area facing the Pacific Ocean (JAEA site at Tokai) Source terms and PM strategy Release scenario Release time (hr after scram) Duration of release (hr) Release fraction of iodine (%) Large early release Large late release Control release Three source term scenarios

10 10 Calculation of dose from each pathway and time-dependent iodine concentrations in air at receptor points using OSCAAR 248 weather sequences selected by a stratified sampling method Calculation of dose reduction effects by various combinations of protective measures Intervention levels for implementing each protective measure (NSCs Guideline) Sheltering 10 mSv, Evacuation 50 mSv effective dose Administration of stable iodine 100 mSv (thyroid equivalent dose for infants) Inhalation dose due to isotope iodine based on I-131~135 contents in thyroid using Johnson model Steps for Consequence Evaluation Find a maximum dose at each distance and each weather sequence Calculation of maximum dose at each distance from the site and its probability of weather sequence Probability of exceeding a specific dose level Dose at each distance from the site at a specific cumulative probability of weather sequences

11 11 For large early release, precautionary evacuation is needed before the start of release. It is important to develop the preparedness action before occurring accident (e.g. EAL: emergency action level, PAZ: precautionary action zone) Early stable iodine intake can be very effective to reduce the thyroid dose for the people within about 20 km from the site even the delay of evacuation (consideration of distribution method). For large early release, precautionary evacuation is needed before the start of release. It is important to develop the preparedness action before occurring accident (e.g. EAL: emergency action level, PAZ: precautionary action zone) Early stable iodine intake can be very effective to reduce the thyroid dose for the people within about 20 km from the site even the delay of evacuation (consideration of distribution method). Large Early Release Distance from the release point (km) Effective dose (Sv) 95% Met 50% Met Sheltering Evacuation Distance from the release point (km) Thyroid dose (Sv) 95% Met 50% Met Stable iodine Effect of the reduction for the effective dose due to protective measures Effect of the reduction for the thyroid dose due to the delay of evacuation and SI intake

12 12 For large late release, evacuation and sheltering areas can be decided to consider weather conditions at the time of accident. In this scenario, evacuation and sheltering area are unlikely to occur beyond 20 km and 50 km. Sheltering or evacuation with administration of stable iodine is very important to reduce the thyroid dose. For large late release, evacuation and sheltering areas can be decided to consider weather conditions at the time of accident. In this scenario, evacuation and sheltering area are unlikely to occur beyond 20 km and 50 km. Sheltering or evacuation with administration of stable iodine is very important to reduce the thyroid dose. Large Late Release Distance from the release point (km) Thyroid dose (Sv) 95% Met 50% Met Stable iodine Distance from the release point (km) Effective dose (Sv) 95% Met 50% Met Sheltering Evacuation Effect of the reduction for the effective dose due to protective measures Effect of the reduction for the thyroid dose due to protective measures

13 13 For control release, evacuation area is unlikely to occur beyond a few kilometers and sheltering area is unlikely to occur beyond about 10 km. For very severe weather conditions, sheltering with stable iodine intake is needed. For control release, evacuation area is unlikely to occur beyond a few kilometers and sheltering area is unlikely to occur beyond about 10 km. For very severe weather conditions, sheltering with stable iodine intake is needed. Control Release Effective dose (Sv) Distance from the release point (km) Sheltering Evacuation Distance from the release point (km) Thyroid dose (Sv) 95% Met 50% Met Stable iodine Effective dose for distance from the release point Effect of the reduction for the thyroid dose due to sheltering and intake of stable iodine

14 14 For the representative source terms, the preliminary analysis has been performed using the probabilistic accident consequence model (OSCAAR) to evaluate the effectiveness of protective action strategy involving a combination of evacuation, sheltering and administration of stable iodine. The study indicated following findings for three release scenarios. Large early release Precautionary evacuation is needed before the start of release. Early stable iodine intake can be very effective to reduce the thyroid dose even the delay of evacuation. It is important to develop the preparedness action before occurring accident (e.g. EAL, PAZ, method for distribution of stable iodine). Large late release Evacuation and sheltering areas can be decided to consider weather conditions at the time of accident. Sheltering or evacuation with administration of stable iodine is very important to reduce the thyroid dose. Control release Evacuation area is unlikely to occur beyond a few kilometers and sheltering area is unlikely to occur beyond about 10 km. For very severe weather conditions, sheltering with stable iodine intake is needed. Conclusions


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