1. Safety Considerations for the EU DCLL DEMO Blanket Dario Carloni 2nd EU-US DCLL Workshop 14-15th November 2014 UCLA

2. Overview The Strategy for ITER Future FPPs DEMO Blanket Open Issues

3. The strategy for ITER No in-vessel component is given any safety credit No safety function for in-vessel components In-vessel components regarded as “experimental” In safety analyses, in-vessel components always assumed to fail in an in-vessel incident/accident This puts additional burden on some ex-vessel components for the confinement function e.g. because in-vessel part of primary cooling loop is always considered failed, ex-vessel parts of the loop are first confinement barrier (up to and including first isolation valve) Some in-vessel components do have shielding function Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 3

4. Future Fusion Power Plant High availability will be essential interruptions to electricity generation unacceptable High reliability required of all components In-vessel components must not fail May be possible to give them full safety credit for the confinement function This would simplify part of the confinement strategy Can’t do this for DEMO. But how far can we go? Safety analysis must demonstrate that any IVC failure will not affect the safety function of other systems Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 4

5. Possible safety functions for in-vessel components Safety functions we might assign to IVCs: First confinement barrier Cannot be achieved with adequate reliability by some components (e.g. First Wall) Barrier to prevent propagation of accident e.g. blanket box, to avoid in-box LOCA pressurizing the vacuum vessel Barrier to avoid contact with certain fluids e.g. to avoid water reaching Be pebbles following divertor in-vessel LOCA Removal of decay heat following loss of cooling Shielding Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 5

6. General Requirements To protect every inventory of radioactive, toxic or hazardous material  to prevent mobilisation into rooms where personnel could be exposed  to prevent release to the environment that could lead to public exposure To meet DEMO general safety objectives in compliance with the environment in operational / accidental situation To reduce potential impacts to the extent reasonably practicable Confinement of Radioactivity

7. DCLL Tritium will be mostly present in the PbLi and a non-negligible amount may permeate into the He circuit Erosion/corrosion phenomena due to high metal velocity within the modules and manifolds Fouling High contamination Activation products, as Po-210 and Hg-203 (relatively volatile and highly radiotoxic) and Fe-55 or Mn-54 may be transported in the coolant Draining of the breeder blanket in accidental scenario not possible Confinement of Radioactivity

8. General Requirements DCLL To avoid over-pressurization of the VV  Pressure Suppression Systems / EV To avoid over-pressurization of the second confinement (EV/TB) He at 8 MPa nominal pressure with T Permeation against vacuum (PAV) for T extraction PbLi pressure is of vital importance since a sudden overpressure can cause the total damage of the PAV with consequences for safety. Confinement of Pressure

9. General Requirements DCLL Plasma/(first) wall interactions causing erosion on the first wall surface The plasma-facing side of the first wall should be plated with 2-3 mm tungsten The produced micron range dust could ignite under accidental oxidation conditions Exothermic reactions of PbLi with air and water may take place in accidental conditions LiM spill: several possible configurations of interactions should be addressed dependent on contact modes: LM droplets sprayed in water, LM veins in water, and steam/ water jets into LM If high LM oxidation takes place (case of Li in LM droplets, steam in LM loop) a high hydrogen production could occur hydrogen explosion Confinement of Chemical Energy

10. General Requirements DCLL Structural material shall remain below critical temperature values Redundancy by means of two or more circuits with the nominal working fluids will be investigated The main heat removal function from structural material will be provided by PbLi, while He will provide backup function, even split in two parallel circuits Redundancy Nevertheless, common cause failure of all circuits should be addressed, depending on the specific blanket design, when mature enough, similarly to old concept activities. Management of Long Term Heat Removal

11. DCLL blanket concept PbLi activation products (Po-210, Hg-203) Confinement Strategy

12. Open Issues The number of circuits will affect the fraction of total radioactive inventory assumed to be released in postulated accidents, as in-vessel LOCA, ex-vessel LOCA, etc.  to be decided basing on safety analyses Safety draining not available Passive pressure relief systems to be provided Interaction between He and PbLi during accidental scenario Safety function for breeding blanket, 0 barrier?

13. Thank you!

14. Objectives of DEMO confinement Internal hazards with potential radiological impact in case of accident To protect every inventory of radioactive, toxic or hazardous material  to prevent mobilisation into rooms where personnel could be exposed  to prevent release to the environment that could lead to public exposure To meet DEMO general safety objectives in compliance with the environment in operational / accidental situation To reduce potential impacts to the extent reasonably practicable internal fire internal explosion thermal releases plasma transients / disruption internal flooding missile effects and pipe whip Loss of Vacuum (LOV) mechanical risks chemical risks magnetic and electromagnetic risks

15. Passive safety methods Passive Containment Cooling System (PCCS)  meets the single-failure criteria and probabilistic risk assessments (PRA) used to verify reliability.  relies on heat removal only by naturally occurring forces such as gravity, natural circulation, condensation and evaporation to keep the containment within the design limits of pressure and temperature.  automatically activate in the unlikely event of a plant emergency.  can be applied for DEMO WCLL concept using water cooling. passive pressure relief systems and rupture panels  VV is connected to the VVPSS /EV by pressure relief devices with rupture disks.  pressure relief system to reduce overpressure of containment (HCPB, HCLL) For the DCLL concept interaction between He and PbLi ? Safety function for breeding blanket, 0 barrier? Confinement requirement due to different blanket concepts (e.g. He/PbLi interaction in the confinement of DCLL concept)

16. Options for confinement barriers Requirements of confinement barrier: SIC Fully and regularly inspectable. ITER Port Closure Plate: Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 16

17. In-box LOCA Scenarios To limit the in-box pressure a pressure relief valve outside the bioshield into a large volume in the building could be considered: HCPB: In the He purge gas loop this might be feasible. WCLL, HCLL, DCLL: In the LiPb loop a fast expansion of the liquid metal towards the relief valve will be prevented by MHD effects. Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 17

18. Consequences of assigning function to a component Safety function must be assured in all loading conditions within design basis (Cat.1 – Cat.4) Appropriate Codes and Standards must be used for design and fabrication (probably, “nuclear” codes) Materials must be fully characterized in all conditions (to Cat.4) and for full component lifetime including effects of irradiation, neutron damage, corrosion, etc. if not included in the Code, it may be adequate to develop DEMO Structural Design Criteria (SDC-IC), as at ITER Component will be classified Safety Important (SIC) high quality fabrication with inspections by safety authority in-service inspection requirements Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 18

19. Background In the event of a Loss of Coolant Accident (LOCA), escaping coolant may be radiologically contaminated contains permeated tritium, Activated Corrosion Products, sputtering products in case of in-vessel LOCA, may also carry substantial part of in- vessel tritium and active dust inventory Flow rate too high to send through detritiation systems and filters and then vent to environment Escaping coolant must be contained For water, can use suppression pool (like ITER) For helium, very large expansion volume may be needed For PPCS Model B (HCPB), 50,000 m 3 required. Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 19

20. PPCS approach Rupture disks connect Steam Generator Hall and Vacuum Vessel to Expansion Volumes Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 20

21. Options to consider for DEMO Segmenting He loops to limit maximum spill still need to consider multiple-loop LOCAs as beyond design basis event Isolation valves to limit spill can they close fast enough? dividing coolant flow into multiple pipes to reduce biggest leak size and thereby reduce maximum He flow rate Heat exchanger on duct entering Expansion Volume, to cool hot He and reduce peak pressure Use parts of building volumes as expansion volumes some large volumes available, but can they be leak-tight? may contaminate building rooms, but could they be used only in extremely unlikely events? Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 21

22. Further issue May need to consider simultaneous water and helium LOCA in-vessel (from divertor and blanket) May be design extension condition, but cannot be excluded How to separate, to condense steam and to cool and contain He? Neill Taylor | Safety/Designers meeting | KIT | 6 November 2014 | Page 22