Transcript Diapositive 1 - Royal Institute of Technology

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
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Contents
 Main safety objectives
 Safety functions
 "Dealt with" events
 "Excluded" events
 Conclusions
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Task 1.5.1 D1.21 Safety approach for EFIT – October 10-11 2006
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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)
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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

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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 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

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
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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

No generation of polonium 210
 Control of radiological releases to the atmosphere has to
be performed
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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 (e.g. core
support inspection inside or outside the reactor vessel?)

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
 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
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"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)
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"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)
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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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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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