M. Kimura, J. Ishikawa and T. Homma Nuclear Safety Research Center

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. Background • 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 (NSC’s Guideline on emergency preparedness) • No practical guidance for protective measure strategy

3. Objectives • 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

4. CURRENT Meteorologicaldata HEINPUT PopulationAgriculturaldata DOSDAC Meteorologicalsampling Healtheffect MS HE Protectivemeasure Earlyexposure Sourceterm Atmosphericdispersion EARLY PM Deposition Economicloss ADD Chronicexposure ECONO HINAN CHRONIC OSCAAR module Preprocessor code Accident Consequence Model • OSCAAR (Off-Site Consequence Analysis of Atmospheric Releases of radionuclides)

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. GUT or LUNG, Y1 GUT or LUNG, Y 1 1.0 INORGANIC IODINE, Y2 INORGANIC IODINE, Y 2 0.8 s s r r 2 2 2 2 0.6 Reduction factor (Intake of stable iodine/ No measurement) BLADDER BLADDER THYROID, Y3 THYROID, Y 3 EXCRETA EXCRETA 0.4 ORGANIC IODINE, Y4 ORGANIC 0.2 IODINE, Y 4 0.0 -80 -60 -40 -20 0 20 40 : the rate of uptake of radioactive and stable iodine by the thyroid Time (h) before or after an intake of radioiodine : the rate constant for uptake or excretion of iodine from each compartment Metabolic Model of Iodine Johnson model (1981) Reduction in the committed thyroid dose to man (for adult, 100mg)

7. ▲ JAEA evaluation Source Term Development Release fraction of iodine ● 環境へのヨウ素の放出割合 □ Relative failure frequency (from INS/M03-22) 発生頻度/全格納容器破損頻度 BWR5/Mk-II 0 0 10 10 -1 -1 10 10 -2 -2 10 10 -3 -3 10 10 -4 -4 10 10 :Relative failure frequency (each / all containment failure scenarios) ●: Release fraction of Iodine -5 -5 10 10 -6 -6 10 10 -7 -7 10 10 -8 -8 10 10 -9 -9 10 10 -10 -10 10 10 V-ν TB-δ AE-δ TW-θ TB-μ TB-σ TC-θ TB-α AE-α TBU-μ TBU-σ TBU-δ TBU-α TQUX-μ TQUX-σ TQUV-δ TQUX-δ TB-υ-l AE-ψ-l TQUV-α TQUX-α AE-υ-l TBU-υ-l TBU-ψ-l TQUX-υ-l TQUV-υ-l TQUV-ψ-l 　・10-1 Iodine release fraction　：Energetic events, Overpressure, ISLOCA 　・10-5～10-4：Containment vent 　・10-7～10-8：Termination

8. Source Term Development (Cont’d) ●Release time (hr) □Relative failure frequency (from INS/M03-22) ▲JAEA evaluation ●:Release time (hr) :Relative failure frequency (each / all containment failure scenarios)

9. Source terms and PM strategy Three source term scenarios 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)

10. Steps for Consequence Evaluation • 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 (NSC’s 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 • Calculation of maximum dose ateach 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 Find a maximum dose at each distance and each weather sequence

11. 95% Met 95% Met 50% Met 50% Met Evacuation Stable iodine • Thyroid dose (Sv) • Effective dose (Sv) Sheltering Distance from the release point (km) Distance from the release point (km) Large Early Release • Effect of the reduction for the thyroid dosedue to the delay of evacuation and SI intake • Effect of the reduction for the effective dosedue to protective measures • 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).

12. 95% Met 95% Met 50% Met 50% Met Evacuation • Effective dose (Sv) Stable iodine • Thyroid dose (Sv) Sheltering Distance from the release point (km) Distance from the release point (km) Large Late Release • Effect of the reduction for the thyroid dosedue to protective measures • Effect of the reduction for the effective dosedue to protective measures • 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.

13. 95% Met 50% Met Evacuation Stable iodine • Thyroid dose (Sv) • Effective dose (Sv) Sheltering Distance from the release point (km) Distance from the release point (km) Control Release • Effect of the reduction for the thyroid dosedue to sheltering and intake of stable iodine • Effective dose for distance from the release point • 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.

14. Conclusions • 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.