1. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Design Basis Accidents (DBA) M. T. Porfiri – ENEA UTFUS-TECN (Frascati) Seminar – Safety in Nuclear Fusion Plants La Sapienza University Rome – 24 April 2015

2. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Outline  Safety Analysis “ Course ” : Deterministic Assessment  DBA: definition  General Safety Objectives: ITER case  Project Environmental Release Guidelines: ITER case  DBAs: ITER case  Release fraction in incidents: ITER case  Release fraction in accidents: ITER case  Example: LOCA in Divertor cooling loop 2/15

3. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Glossary ACP Activated Corrosion Products DBADesign Basis Accident DCF Dose Conversion Factor DVDivertor EPR European Pressurized Reactor EST Environmental Source Term FWFirst Wall FMEAFailure Mode and Effects Analysis ISSIsotope Separation System ITERInternational Tokamak Experimental Reactor HTSHeat Transfer System HXHeat Exchange LOOPLoss Of Offsite Power PFCPlasma Facing Component PIE Postulated Initiating Event PST Process Source Term TFToroidal Field VVVacuum Vessel 3/15

4. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 (Courtesy of S. Ciattaglia) Safety Analysis “ Course ” : Deterministic Assessment 4/15 SOURCE TERMS ASSESSMENT Normalworking conditions Occupational dose IE AS Thermodynamic transients Aerosols and H3 transport Containments Release from the plant DCF Overall Plant Analysis FFMEA Radioactive waste Operational&Decomm waste Identification&classification Management On-site Recycling Final disosal Effluents PST EST DCF man*Sv/y dose/sequence to MEI frequency*dose Quantity and waste categories mSv/y SOURCE TERMS Normalworking conditions Occupational dose PIE Thermodynamic transients Aerosols and H3 transport Confinements Release from the plant DCF Overall Plant Safety Analysis FMEA Radioactive waste Operational&Decomm waste Identification&classification Management On site Recycling Final disposal Effluents PST EST DCF person*Sv/y dose/sequence to Public frequency*dose Quantity and waste categories mSv/y

5. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 DBA: definition A Design Basis Accident is a postulated accident that a nuclear facility must be designed and built to withstand without loss to the systems, structures, and components necessary to ensure public health and safety [NRC]. They are classified as incidents and accidents, according to the frequency of occurrency. The methodologies to be used for the DBAs analysis must be conservative. That means they use pessimistic or worst-case assumptions and models. Most of the analyses presented to regulatory bodies follow this approach. 5/15

6. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 ITER case 6/15 Central Solenoid Outer Intercoil Structure Toroidal Field Coils Poloidal Field Coils Machine Gravity Supports Blanket Modules Vacuum Vessel Cryostat Port Plug (Radiofrequency Heating) Divertor Torus Cryopump

7. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 General Safety Objectives: ITER case General safety objectives For personnelFor the public and environment Situations in design basis Normal situations ALARA, and in any case less than: Maximum individual dose ≤ 10 mSv/yr Average individual dose ≤ 2.5 mSv/yr Collective annual dose ≤ 500 mSv*p/yr Releases less than the limits authorised for the installation, Impact as low as reasonably achievable and in any case less than: ≤ 0.1 mSv/yr Incidental situations As low as reasonably achievable and in any case less than: 10 mSv per incident Release per incident less than the annual limits authorised for the installation. [i.e. 0.1 mSv per incident] Accidental situations Take into account the constraints related to the management of the accident and post-accident situation No immediate or deferred counter-measures (confinement, evacuation) < 10 mSv No restriction of consumption of animal or vegetable products Situations beyond design basis Hypothetical accidents No cliff-edge effect; possible counter-measures limited in time and space 7/15

8. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Project Environmental Release Guidelines: ITER case 8/15

9. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 DBAs: ITER case (1) 9/15

10. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 DBAs: ITER case (2) 10/15

11. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Release fraction in incidents: ITER case 11/15 Margins against Project Environmental Release Guidelines for Reference Events. Sum of Tritium, Activated Dust and Activation Corrosion Product Releases

12. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Release fraction in accidents: ITER case 12/15 Margins against Project Environmental Release Guidelines for Reference Events. Sum of Tritium, Activated Dust and Activation Corrosion Product Releases

13. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Example: LOCA in Divertor cooling loop (1) 13/15 -The accident postulated is a double ended pipe rupture in a large diameter pipe, at the pump inlet of the DV (divertor)/LIM (limiter) primary coolant loop. -The coolant leak pressurises the vault. -The Fusion Power Shutdown System (FPSS) will stop plasma burn in three seconds. -This results in a plasma disruption that delivers 0.4 GJ of energy to the DV. -The high stress conditions of the divertor plates are postulated to result in an in-vessel leak for a break on the DV/LIM HTS loop. -The DV/LIM HTS coolant in-leakage pressurises the VV and, when VV pressure exceeds 110 kPa, the bleed lines to VVPSS and to drain tank open. -In the mean time, the vault is pressurised and a high vault atmosphere pressure signal (the set point is at 105 kPa) triggers the isolation of the vault. -When the VV pressure exceeds 150 kPa the rupture disks open towards the Vacuum Vessel Suppression System.

14. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 Example: LOCA in Divertor cooling loop (2) 14/15 The chemical reactions between the steam and the PFC protective materials produce an amount of H2 far from the explosion risk (4kg).

15. Seminar: Safety in Nuclear Fusion Plants - La Sapienza University (Rome) – 24 April 2015 15/15 Mobilised Inventory Release path, transport of inventory Release amount Total release Tritium TCWS vault >> environment (before vault isolation) 4.1*10 -7 g-T Tritium: controlled release 4.1*10 -7 g-T uncontrolled 6.5*10 -2 g-T total release 6.5*10 -2 g-T Dust: uncontrolled 1.7*10 -2 g total release 1.7*10 -2 g ACP: controlled release 1.7*10 -7 g uncontrolled 0.27 g total release 0.27 g TCWS vault >> environment (after vault isolation) 6.5*10 -2 g- T Dust TCWS vault >> environment (before vault isolation) No release TCWS vault >> environment (after vault isolation) 17 mg ACP TCWS vault >> environment (before vault isolation) 1.7 *10 -7 g TCWS vault >> environment (after vault isolation) 270 mg Example: LOCA in Divertor cooling loop (3)