Diapositive 1

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EUROTRANS WP1.5 Technical MeetingTask 1.5.1
ETD Safety approach Safety approach for XT-ADS
Deliverable 1.20
Sophie EHSTER

• Lyon, October 10-11 2006

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Contents

• Progress in activities associated with task 1.5.1
  
• Main safety objectives
• Safety functions
• "Dealt with" events
• "Excluded" events
• Conclusion and discussion

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Progress in activities associated with task 1.5.1

• Task 1.5.1 Safety approach
• Coordination FANP (AREVA NP)
• Participants FZK, CEA, EA, SCK, KTH
• Deliverables
• D1.20 Report on the approach and acceptance
  criteria for safety design of XT-ADS
• Meeting in May with designers and June regarding
  safety analyses
• Issued in summer 2006
• D1.21 Report on the approach and acceptance
  criteria for safety design of EFIT
• First draft To be issued by the end of October
  2006
• Participation to the safety studies (definition,
  assessment of results Design check
  review/Safety)

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Main safety objectives

• Application of defense in depth principle
  prevention and mitigation of severe core damage
• Elimination of the necessity of off site
  emergency response (Generation IV objective)
• Probabilistic design targets
• Cumulative severe core damage frequency
• 10-5 per reactor year for is a minimum objective
  (due to lack of experience feedback)
• Enhancement of prevention assessed with ALARP
• Severe core damage is studied as a Design
  Extension Condition
• Severe core damage situations which cannot be
  mitigated
• they must result from a limited number of
  sequences for which a higher level of prevention
  is required.
• Their exclusion has to be justified they have to
  be "practically eliminated" (i.e. implementation
  of adequate prevention provisions)

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Safety functions

• Reactivity control function
• Definition of sub-criticality level (from WP1.2
  and checked further by WP1.5)
• Consideration of most defavorable core
  configuration (possible adaptation)
• Consideration of reactivity insertionKeff to be
  justified through reactivity insertion studies
• Consideration of hot to cold state transient
• Consideration of uncertainties
• Consideration of experimental devices
• XT-ADS assumption 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

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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 2 a LOD (seems achievable with 2
  independent and diverse IC)
• to prevent "excluded" situations, 2ab 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

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Safety functions

• Decay heat removal function
• Performed by
• SCS Primary Heat exchangers (PHX) forced and
  natural convection
• ECS Emergency Heat Exchangers (EHX) natural
  convection
• 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) to be prevented by design
• Definition of safe shutdown state/mission
  duration
• Emergency core unloading (yes independent core
  storage within the vessel)
• DHR function needs optimization
• Review of systems and architecture (ECS, RVACS,
  SCS)
• MYRRHA draft2 ECS trains unsufficient to reach
  reliability targets (EFR 3 trains with
  diversification, PDS-XADS LBE concept)
• need to be confirmed by a reliability study ?
• Feedback from transient studies Dhmini (2m),
  Dpmaxi (lt1 bar)
• Design optimization to meet performances underway

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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
• Generation of polonium 210 due to the activation
  of bismuth under irradiation
• gtIn the current Draft 2 design, the reactor hall
  is oxygen free and with a slight overpressure/
  atmospheric conditions to avoid oxygen intrusion.
  Within the primary system, the cover gas pressure
  is below the pressure hall to avoid contamination
  of the reactor hall area.
• gtIf all the reactor building is in overpressure,
  control of release to atmosphere will not be
  possible and a double shell building would be
  required. It therefore recommended to limit the
  overpressure zone to the above roof and
  components maintenance/storage area within an
  underpressure building.

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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. For core support line, favourable option
  taken for MYRRHA. Possibility of storage of a
  full core and removal of core support barrel for
  inspection outside the reactor. Case of vessel
  and internal storage damage?)
• Consideration of oxide formation (design,
  monitoring, mitigation provisions)

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"Dealt with" events

• "Dealt with" events their consequences are
  considered in the design
• Initiating faults list has been established and a
  preliminary categorisation has been provided
• Practical analysis rules have been proposed
• A preliminary list of sequences to be analysed
  have been proposed
• Radiological consequences use of national method
  (i.e. Belgium)
• Determination of barriers (e.g. fuel, cladding,
  structures) criteria qualitative criteria are
  defined. The definition of quantitative values is
  underway. They have to be confirmed by RD about
  the knowledge of material behaviour for higher
  temperatures.

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"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

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Conclusion and discussion

• For XT-ADS, safety objectives with regard to
  design and analyses are established in D1.20
• Feedback on their consideration in the design?
• Feedback on their consideration in the analyses?