“Overview of Level 3 PSA”

1. IAEA Training Course on Safety Assessmentof NPPs to Assist Decision Making “Overview of Level 3 PSA” Workshop Information Lecturer Lesson IV 3_4 IAEA Workshop City , CountryXX - XX Month, Year

2. Level 3 PSA • LEVEL 3 PSA = the assessment of off-site consequences leading, together with the results of Level 2 analysis, to estimates of risk to the public. • Provides insights into the relative importance of accident prevention and mitigative measures in terms of the adverse consequences for the health and the public and the contamination of land, air, water and foodstuffs. • Provides insights into the relative effectiveness of emergency response planning aspects of off-site accident management, and into the economic impacts. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

3. Sampling of meteorological data Meteorological data Radionuclide release data Atmospheric dispersion and deposition Dose conversion factors Dose evaluation for each exposure pathway Counter-measures Estimation of health effects Population and agricultular data Risk conversion factors Estimation of economic consequences Economic data Level 3 PSA - Basic Elements of Probabilistic Consequence Analysis IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

4. Level 3 PSAProbabilistic Consequence Analysis • LEVEL 3 PSA = Probabilistic Consequence Analysis (PCA). • PCA conducted using the variety of PCA codes addressing models for different phenomena, e.g. • atmospheric dispersion • deposition of airborne material • resuspension • migration through food-chains • pathways to humans and health effects • economic effects • various meteorological sampling techniques IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

5. Level 3 PSA Process: Inputs The starting points for consequence assessment are the postulated radionuclide releases to the environment from Level 2 PSA (STCs): • quantity of isotopic composition of released radionuclides • their physical and chemical characteristics • heat content of the plume • time profile of the release • release height and building dimensions • frequency of occurence of the release category IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

6. Level 3 PSA Process: Inputs (Cont.) OTHER PCA CODE INPUTS • Meteorological data and its sampling • Population data • Agricultural production data • Land data • Food distribution data • Economic data • Countermeasures • Short-term: sheltering, evacuation, iodine tablets... • Long-term: relocation, land decontamination, food bans... IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

7. Level 3 PSA Process: Calculation Steps • Atmospheric dispersion: • release of the plume • direction and dispersion of the plume • surface deposition • Calculation of dose: • external dose (cloud, ground) • inhalation • ingestion • Calculation of health effects: Deterministic and stochastic. Early and late. • Calculation of economic consequences. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

8. Meteorological Sampling and Result Measure Calculation • The consequences of a given accident release at a given location vary with the meteotrological conditions and the wind direction • Calculation steps are repeated many times using sampled meteorological data • Result measures calculated on a (r, ) grid around a release location (containment) • Large number of different weather conditions may exist è Distribution of resulting measures at each grid element è Mean value for each grid element • Mean values can be averaged over all directions of the wind rose è Mean result may be presented as f (distance from release point) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

9. CCDF - Complementary Cumulative Distribution Function Why use the CCDF? • Weather conditions affect results • The mean summarizes the results fromall meteorologicalsamples • Need to see the variation due to weather conditions • Relating the variation to probability of weather conditions è understanding of results IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

10. CCDF - Complementary Cumulative Distribution Function CCDF: How is it calculated? • Results (e.g., number of early fatalities) calculated for each meteorological condition (sample) are binned (grouped) • Each sample has a probability of occurence • Sum of probabilities of samples in a bin è probability of that bin • Probability of bin x release frequency è frequency of bin • A point of a CCDF curve can show: • Conditional probability of the corresponding consequence value or a greater value, given a release has occurred • Frequency of the corresponding consequence occurring or being exceeded (this result takes into account the release frequencies) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

11. Examples of Level 3 PSA Results - Early Fatalities This figure presents the calculated curve for “early fatalities” showing four statistical measures and one individual observation for Surry NPP (NUREG-1150 Vol.2) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

12. This figure presents the calculated curve for “latent cancer fatalities” showing four statistical measures and one individual observation for Surry NPP (NUREG-1150 Vol.2) Examples of Level 3 PSA Results - Latent Cancer Fatalities IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

13. Examples of Level 3 PSA Results - Contribution of PDSs to Risk IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

14. Examples of Level 3 PSA Results - Contribution of Containment Failure Bins to Risk IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

15. Probabilistic Consequence Assessment (PCA) Codes • COSYMA (CEC, late 80s) • MACCS (U.S. NRC, late 80s) • CONDOR (UK) • OSCAAR (Japan) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

16. Emergency Planning WHAT? • Development of strategies to protect the public in situations of severe reactor accident WHY? • During the first hours of an accident at a NPP, critical decisions may be necessary concerning actions to protect the public • In the long term, balanced protective actions will be required in order to protect the public USE OF PSA? • Emergency plans and emergency preparedness should be fully related to the actual understanding of the severe accident effects and their consequences IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

17. Countermeasures or Protective Actions • PCA codes allow the specification of a wide range of emergency actions, and criteria for imposing and withdrawing the actions • Short-Term: To reduce the doses from the early exposures pathways • Evacuation • Sheltering • Iodine tablets • Decontamination of people • Long-Term: To reduce chronic exposure to radiation • Relocation • Land decontamination • Food bans • Other long-term countermeasures (generally not modelled in PCA codes): Changes to agricultural practices, deep ploughing, alternative feed, caesium binders, alternative crops, alternative production, etc. IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

18. Effectiveness of Emergency Response Actions (Examples) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

19. Effectiveness of Emergency Response Actions (Examples) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

20. References • IAEA Safety Series No. 50-P-12 "Procedures for Conducting Probabilistic Safety Assessments in Nuclear Power Plants (Level 3)" • NUREG-1150-Vol 2 "Severe Accident Risk: An Assessment for Five U.S. Nuclear Power Plants" (1990) IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making