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Lyon, October 10-11 2006

EUROTRANS WP1.5 Technical Meeting Task 1.5.1 – ETD Safety approach Safety approach for EFIT: Deliverable 1.21. Sophie EHSTER. Lyon, October 10-11 2006. Contents. Main safety objectives Safety functions "Dealt with" events "Excluded" events Conclusions. Main safety objectives.

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Lyon, October 10-11 2006

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  1. EUROTRANS WP1.5 Technical MeetingTask 1.5.1 – ETD Safety approach Safety approach for EFIT: Deliverable 1.21 Sophie EHSTER Lyon, October 10-11 2006

  2. Contents • Main safety objectives • Safety functions • "Dealt with" events • "Excluded" events • Conclusions

  3. Main safety objectives • Application of defense in depth principle: prevention and mitigation of severe core damage are considered • Elimination of the necessity of off site emergency response (Generation IV objective) • Probabilistic design targets: • Higher level of prevention than XT-ADS is aimed at since the core is loaded with a high content of minor actinides (low fraction of delayed neutons, low Doppler effect). Cumulative severe core damage frequency: • 10-6 per reactor year • If LOD approach is used: 2a + b per sequence • At the pre-conceptual design phase (EUROTRANS), severe core damage consequences are assessed in order to determine the main phomena, associated risks and possible design provisions (core and mitigating systems)

  4. Safety functions • Reactivity control function: • Definition of sub-criticality level (dealt with by WP1.2, checked further by WP1.5): • Consideration of most defavorable core configuration (possible adaptation) • Consideration of reactivity insertion: Keff to be justified through reactivity insertion studies • Consideration of hot to cold state transient • Consideration of uncertainties • Consideration of experimental devices • Use of aborber rods (design in WP1.2): • during shutdown conditions to be moved preferentially by dedicated mechanisms • (in case of critical core configuration) • Measurement of sub-criticality level • To be performedbefore start-up with accelerator, target and absorbers inserted

  5. Safety functions • Power control function: • Power control by the accelerator • Proton beam must be shut down in case of abnormal variation of core parameters, in particular in case of failure of heat removal means • High reliable proton beam trip is requested: • at least 2a+b LOD are requested: b must be diversified (passive devices (target coupling) and operator action (large grace time needed)) • Implementation of core instrumentation: • Neutron flux • Temperature at core outlet (each fuel assembly if efficient for flow blockage) • DND (very efficient in the detection of local accidents for SFR) • Flowrate • Implementation of target instrumentation

  6. Safety functions • Decay heat removal function: • Performed by • Forced convection: 4x (1primary pump + 2 Steam Generators) provided for power conditions. Use to reach "cold" shutdown state? • Natural convection: 3 + 1 safety trains (redundancy) cooled by two-phase oil system • Reactor Cavity Cooling System would not be capable to remove decay heat at short term • A high reliability of the function is requested • e.g. number of systems, redundancy, diversity, duty of the cavity walls cooling system • Consideration of common modes (e.g. freezing, corrosion, oil induced damage) to be prevented by design • Definition of safe shutdown state/mission duration • EFR background: 3 trains 100% or 6 trains 50% and diversification • Need for a reliability study? • Emergency core unloading

  7. Safety functions • Confinement function: • Performed by three barriers • Fuel cladding • Reactor vessel and reactor roof • Reactor building • Design must accommodate • The radiological releases • The pressure if any (cooling system lekage) • Specific issues: • Coupling of the reactor, spallation target and the accelerator needs to be assessed • No generation of polonium 210 • Control of radiological releases to the atmosphere has to be performed

  8. Safety functions • Core support function: • Performed by • The reactor internals • The reactor vessel and its supports • Exclusion of large failure? • Is the demonstration credible? • Checking of the capability of severe core damage mitigation provisions on this scenario • Specific issues: • ISIR of in-vessel structures under a metal coolant (e.g. core support inspection inside or outside the reactor vessel?) • Consideration of oxide formation (design, monitoring, mitigation provisions)

  9. "Dealt with" events • "Dealt with" events: their consequences are considered in the design • Determination of the "dealt with" initiating faults list and associated sequences: • assessment of XT-ADS list and consideration of EFITdesign features ANSALDO task: to confirm the list of initiating faults • sequences (success/failure of mitigating means) will be determined in accordance with the main safety objectives • Same practical analysis rules as XT-ADS ones • Consideration of EFIT specific features: increase of the core power density, consideration of core loaded with a high content of minor actinides, risk of water/steam ingress (Steam Generator), much higher risk of freezing (327°C) • Radiological consequences: use of method? • Determination of barriers (e.g. fuel, cladding, structures) criteria: to be preliminary defined and confirmed by R&D about the knowledge of material behaviour for higher temperatures

  10. "Dealt with" events/ Consequences of implementation of a steam cycle • Additional initiators (in accordance with the European background) : • Steam Generator leakage: DBC2 • Steam Generator Tube Rupture: DBC3 • Several SGTR has to be considered at least as a limiting event (assessment of the phenomenology e.g. combination of corrosion and loading due to DBC) • DHR HX leak (two phase oil): DBC2 (1 tube) or DBC3 (multiple tube rupture) • Feedwater system malfunction: DBC2 • Secondary steam system malfunction: DBC2 • DHR cooling system malfunction: DBC2 • Feedwater leakage/line break: DBC3 or DBC4 depending on the size of the leak • Secondary steam leakage: DBC3 or DBC4 depending on the size of the leak • DHR cooling system leakage: DBC2 or DBC3 depending on the size of the leak • Combination of SGTR and steam line break has to be considered as a limiting event (DEC)

  11. "Dealt with" events/ Consequences of implementation of a steam cycle • Associated risks: • Reactivity insertion: moderator effect, void effect, core compaction • Mechanical transient due to the depressurisation into the reactor vessel • Steam explosion • Draining of the primary coolant outside the reactor vessel • Pressurisation of the reactor buiding • Overcooling and subsequent freezing (SG overflow)

  12. "Excluded" events • "Excluded" events: their consequences are not considered in the design • Their non consideration had to be justified • Preliminary list: • Large reactivity insertions • Core support failure • Complete loss of proton beam trip function • Complete loss of decay heat removal function

  13. Conclusions • D1.21: • First draft to be issued at the end of October 2006 (FANP) • To be reviewed by ANSALDO (design) and partners involved in the safety analyses

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