1. 1 Nuclear emergency management: taking the right decisions with uncertain models Catrinel Turcanu, Johan Camps & Benny Carlé cturcanu@sckcen.becturcanu@sckcen.be / jcamps@sckcen.bejcamps@sckcen.be Society and Policy Support Institute Environment, Health and Safety Belgian Nuclear Research Centre Workshop “All models are wrong…”, Groningen, 14-16/03/2011

2. 2 Outline Context Nuclear emergency model uncertainties Conclusions Model for evaluation of nuclear emergencies for the Doel NPP site

3. 3 Nuclear emergencies & models Atmospheric transport and dispersion models (concentrations, deposition) Dose models (dose adults, children, thyroid,.) Food models (concentrations, dose) … Use of models for the protection of people in emergency situations & preparedness phase:

4. 4 rain Wash-out Irradiation shielding Ingestion Irradiation Inhalation Dry deposition Inversion layer Plume rise Height-dependent wind velocity Atmospheric turbulence The modelling problem:

5. 5 How are decisions taken? Legislation Reference band of dose values – calculated based on model predictions (or measurements or both) Action levels on specific actions (Belgian levels) New recommendations: 20-100 mSv/y, all pathways Range ≠ uncertainty !

6. 6 Uncertainties Modelling assumptions Simplifications of reality Parameter uncertainty Calibration of model parameters Input data Meteorology Source term

7. 7 Source models: Torben Mikkelsen, Risø Average plume Meandering plume Fluctuating plume Uncertainties from modelling assumptions simple complex Best estimate Conservative calculation

8. 8 Model intercomparison Standard conditions Experimentally validated: factor 2-3 within experiments

9. 9 Model intercomparison Very specific conditions

10. 10 Model intercomparison realistic scenario Noodplan Doel JRODOS Rimpuff (ARGOS) TIC [Bq s/m 3 ] same color scale

11. 11 Potential problems related to the resolution of the calculation grid For the same scenario: Inner grid cell: 1 km Inner grid cell: 100m  no sheltering  sheltering >1km

12. 12 Source: Florian Gering Parameter uncertainty: Cs-137 in milk days after deposition

13. 13 Model uncertainties in radiological assessments Malcolm Crick, IAEA Source: Malcolm Crick

14. 14 Source: Marc de Cort Uncertainties in input data (1): meteorology

15. 15 with on-site single rain gauge data with multiple rain gauge data With rain-radar data Uncertainties in the input data (2) Example: Input data precipitation

16. 16 Effect of conservative approach for treatment of rain

17. 17 Example: conservative approach Tihange, core melt, rupture primary circuit Standard weather conditions

18. 18 Example: conservative approach Tihange, partial core melt, rupture primary circuit Standard weather conditions

19. 19 Example: conservative approach Tihange, core melt, rupture primary circuit unstable weather conditions

20. 20 Conclusions Complex problem Often models extended beyond validated range Difficult to obtain realistic uncertainties on calculations Even more difficult to communicate these uncertainties to decision-makers Best estimate often replaced by conservative approach But … conservative estimates may lead to unfeasible countermeasures