Transcript Diapositive 1 - Royal Institute of Technology

EUROTRANS WP1.5 Technical Meeting
Task 1.5.1 – ETD Safety approach
Safety approach for XT-ADS: Deliverable 1.20
Sophie EHSTER
Lyon, October 10-11 2006
AREVA NP
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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Task 1.5.1 Safety approach for XT-ADS – October 10-11 2006
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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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Task 1.5.1 Safety approach for XT-ADS – October 10-11 2006
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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:
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
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)
Task 1.5.1 Safety approach for XT-ADS – October 10-11 2006
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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 insertion:Keff 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

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To be performed before start-up with accelerator, target and
absorbers inserted
Task 1.5.1 Safety approach for XT-ADS – October 10-11 2006
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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
I&C)

to prevent "excluded" situations, 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
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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 ?
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
Feedback from transient studies: Dhmini (2m), Dpmaxi (<1 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
=>In 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.
=>If 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:
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
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 R&D 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?
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