ENEA

1. ENEA Overview of the task and coordination: refined description of the accident sequences, reference data (AAS), work planM. T. Porfiri, T. Pinna Garching 9th October 2006 Meeting Safety assessment for EU TBM to support ITER Licensing Process

2. Outline • Coordination task scope • FMEA and postulated initiating events • Finished description of the accident sequences • Reference data • Schedule

3. Coordination task scope (1) 1. Study and analyses of all the existing design TBM documents Done 2. Revision of the existing accident analyses Done 3. Documentation of the inherent limitations and lacunas Within two months (December 06) from the kick off meeting including also the main outcomes of the FMEA, in order to justify the choice of the sequences selected for the accident analyses proposed 4.Discussion together with the Associations involved in the safety analyses for the refinement of the accidents to be analyzed Kick off meeting

4. Coordination task scope (2) 5. Verifications of the tools used (codes) for the analyses and a quality assurance procedure for the reproducibility of the results Decision during the kick off meeting 6. Preparation of a data base pulled out from the design to support the accident analyses, in order to avoid misleading in the data interpretation; In preparation, to be completed within November 2006 • Technical review of the results of the accident analyses performed in the frame of the current task. First results: January 07 Final results: April 07

5. HCPB: failure mode and effect analysis • The components of the TBM are on going to be analyzed with the FMEA methodology. • For each one of them, the possible failure modes that could occur in the different operating phases will evaluated. • For each failure mode will be pointed out: • failure causes and possible actions to prevent the failure, • consequences and actions to prevent and mitigate the consequences, • identification of the Postulated Initiating Events (PIEs) which include the failure. • This last attribute will be useful to individuate the set of PIEs to be taken into account in the deterministic transient analyses. • At present only the FMEA for HCPB is quite completed, while the HCLL FMEA is still on going.

6. HCPB: postulated initiating events (1)

7. HCPB: postulated initiating events (2)

8. Choice of accident analyses The accident analyses selected for the two models that are: • Ex-vessel LOCA+in-vessel LOVA for HCPB and • ex-vessel LOCA+in-vessel He, LiPb and water LOCA for HCLL have the scope to include the PIE detected by the Failure Mode and Effect Analysis. As example the PIE LBO1 LOCA Out-VV because large rupture of TBM cooling circuit pipe inside TWCS Room can be used.

9. From FMEA HCPB: LB01 description (1) A large LOCA out-vessel from the TBM HCS could be determined by a significant rupture in the cooling circuit from components located in the HCS room or in the piping running from the Port Cell to the HCS room (i.e.: service shaft and TWCS Room). The representative event here selected has been the break of a cooling pipe inside the TWCS Room (HCS zone). The following chain of consequences could follow the initiator: • Loss of He coolant into Vault • Pressurization of Vault • Release of Tritium contained in He coolant into Vault • Emptying of the TBM cooling loop and loss of heat removal capability • Overheating of TBM if the plasma is not promptly shutdown • Swelling of Ceramic Breeder and Be pebbles • Over thermo-mechanical stress on BU, Grid, Caps and FSW structures

10. From FMEA HCPB: LB01 description (2) • Ingress of air in TBM box cooling channels when the pressure in cooling circuit gets room pressure • Be-air and Be-water (moisture contained in air) reactions if coolant channels inside the box lost their integrity because thermo-mechanical stress, particularly, if the plasma is not shutdown. In such a case, the following aggravating failures could follow: - H2 production - Possible H2 explosion inside the box • Possible break of TBM box • Ingress of He (i.e.: some coolant not yet discharged from the loop and purge gas) and air (from the external break) into VV • Plasma disruption if it has not been actively or passively (plasma poisoning due to armour material evaporation) shutdown • VV pressurisation

11. From FMEA HCPB: LB01 description (3) • Opening of bleed lines towards VVPSS when VV pressure gets 80 kPa and opening of lines to drain tank when p>110kPa • Release of radioactive products contained in VV (tritium & dusts) to VVPSS • Release of radioactive products contained in VV (tritium & dusts) to TWCS Room if VV pressure overcomes room pressure • Loss of Be pebbles into VV due to dynamic effects (e.g. VV suction, He flowing) caused by the FW rupture. In this case, it is also worthwhile to remark that the loosing of pebbles inside the VV makes more complicated recovery actions inside the VV to clean vacuum chamber before restart. Consequences that could reduce plant availability • Aggravating consequences could occur in case of rupture in other water cooled PFCs due to disruption • Increase of ORE for recovery actions.

12. Finished description of the accident sequences The AAS document used for GSSR has been adopted as a template to describe the accident sequences and all the connected information as: • Event Sequence • System Assumptions • Confinement assumptions • Analysis Methodology • Results They are in the linked documents: HCPB accident - AAS.doc, HCLL accident - AAS.doc

13. Accident description for HCLL TBM Ex-vessel LOCA+in-vessel He, LiPB and water LOCA • The detection of the ex-vessel LOCA fails to trigger the Fusion Power Shutdown System (FPSS) Modest inventories of radioactive material • Consequent melting of the TBM wall structure and LiPb spreading in VV • Water and steam enter the VV from the FW cooling loop 0. Initiating event: break in the ex-vessel He cooling loop

14. HCLL TBM general scheme for ex-vessel LOCA+in-vessel He, LiPB and water LOCA • VV pressurizes and the reaction between lithium lead and water produces hydrogen. • The release of tritium and aerosols from the VV and the TBM box can occur through the TBM cooling loop bypass generated between VV and external zone (TCWS vault). 6. Either because the exit of H2 in the cooling room through the by bypass or, the ingress of air in the VV after differential pressure inversion, hydrogen/oxygen explosion can be possible.

15. Accident description for HCPBEx-vessel LOCA+in-vessel LOVA • The detection of the ex-vessel LOCA fails to trigger the Fusion Power Shutdown System (FPSS) • Melting and/or thermal-mechanical stresses on the box structure occurs • He ingress in the VV will cause the plasma disruption • Box structures containing lithium orthosilicate and beryllium pebbles can loose their integrity 0. Initiating event: break in the ex-vessel He cooling loop 5.After differential pressure inversion the gases (air, He) in the VV and in TBM flow towards outside through the TBM cooling loop bypass and tritium and dust can be transported from the gas stream and released in the external zones.

16. Reference data The base documents for the safety analysis are: • sadl.pdf • TBM DDDs In addition data necessary for the selected accidents are: • section of the pipe for the double ended break in the TBM cooling loop • melting temperature for the TBM wall towards plasma and/or embrittlement temperature for TBM box • Section of the break in TBM box towards plasma to simulate in-vessel LOVA for HCPB and in-vessel LOCA for HCLL • Be dust inventory to be mobilized in TBM box for HCPB

17. HCPB: section of the break ex-vessel At the inlet of the circulator a pipe DN 100 is designed. The section of the break is 8119.17 mm2

18. HCLL: section of the break ex-vessel Reference DDD: The number of the TBM pipes leaving the TBM from the rear has been fixed to four, two for the cooling helium (inlet pipe having ∅in = 60mm, outlet pipe having ∅in = 70 mm) It is not specified if the pipe at the compressor inlet has the same section.

19. Schedule C = coordinator, AA = Associations