AREVA NP EUROTRANS WP1.5 Technical Meeting Task – ETD Safety approach Safety approach for EFIT: Deliverable 1.21 Lyon, October Sophie EHSTER

Task D1.21 Safety approach for EFIT – October AREVA NP Contents  Main safety objectives  Safety functions  "Dealt with" events  "Excluded" events  Conclusions

Task D1.21 Safety approach for EFIT – October AREVA NP 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: 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)

Task D1.21 Safety approach for EFIT – October AREVA NP 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 performed before start-up with accelerator, target and absorbers inserted

Task D1.21 Safety approach for EFIT – October AREVA NP 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

Task D1.21 Safety approach for EFIT – October AREVA NP 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: 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

Task D1.21 Safety approach for EFIT – October AREVA NP 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

Task D1.21 Safety approach for EFIT – October AREVA NP 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)

Task D1.21 Safety approach for EFIT – October AREVA NP "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

Task D1.21 Safety approach for EFIT – October AREVA NP "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)

Task D1.21 Safety approach for EFIT – October AREVA NP "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)

Task D1.21 Safety approach for EFIT – October AREVA NP "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

Task D1.21 Safety approach for EFIT – October AREVA NP 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