Diapositiva 1

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6th FRAMEWORK PROGRAM EURATOM Management of
Radioactive Waste
EUROTRANS - DM1 WP 1.5 Meeting
Forschungszentrum Karlsruhe, 27-28 November, 2008
Analysis of EFIT Protected and Unprotected
Accidental Transients with PARCS/RELAP5 Coupled
Code
Massimiliano Polidori, Giacomino Bandini, Paride
Meloni
Italian National Agency for New Technologies,
Energy and Environment Advanced Physics
Technology Division Via Martiri di Monte Sole 4,
40129 Bologna, Italy
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Outline

• Description of the Codes
• The RELAP5 Model of EFIT
• The PARCS Model and Assumption of EFIT
• Analysis of Protected Transients
• Spurious Beam Trip 1 sec
• Analysis of Unprotected Transients
• Loss of Flow (ULOF)
• Loss of Heat Sink (ULOH)
• ULOF ULOH
• Beam Overpower from Hot Full Power (HFP)
• Beam Overpower from Hot Zero Power (HZP)
• Conclusions

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PARCS/RELAP Coupled Code
Our State-of-the-Art code to simulate the
Neutronic-T/H coupled phenomena for safety
purpose is
PARCS v1.01 3D Neutronic coarse mesh code that
solves the 2-group diffusion equation in
cartesian geometry, modified to treat fast
spectrum and external neutron source. RELAP5 mod
3.2.2b Thermal-Hydraulic 1D code modified to
treat heavy liquid metal (lead, LBE)
Fuel/Coolant Temperature and Density, Void
Fraction, ..
D Cross Section Neutron Flux Reactor Power
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The RELAP5 Model of EFIT

• Primary system layout by D1.26 of ANSALDO
  (November 2007)
• Gagging at core inlet according to SIM-ADS
• Active Core Region is represented by rings in
  according with the designed layout.
• Ring 1 18 FA (Inner Zone)
• Ring 2 24 FA (Inner Zone)
• Ring 3 30 FA (Interm Zone)
• Ring 4 36 FA (Interm Zone)
• Ring 5 42 FA (Outer Zone)
• Ring 6 30 FA (Outer Zone)
• GAP behavior at BOC according to FZK-SIMADS
  analysis (114 µm).
• It is considered also the target and bypass
  (reflector) regions with their own thermal power
  deposition.

RELAP5 Noding Scheme
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The PARCS Model and Assumption of EFIT
PARCS Mesh Dimension
At Cold (20C) Conditions Width 8.27 cm Height
9.55 cm
EFIT Core Layout
At Nominal Power Width 8.33 cm Height 9.62 cm
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The PARCS Model and Assumption of EFIT
Axial View of EFIT Core Layout
Axial Nodal Correspondance
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The PARCS Model and Assumption of EFIT - XSEC
XSEC Formalism in PARCS
XSEC Data Set to Find the Derivative Cross
Sections at BOC Conditions

• Omogenized
• Collapsed in 2 groups
• (0.079 MeV Cutting Energy)

keff ? 0. 960778
at nominal power condition
Normalization of kSf to achieve the desired
Power in each Zone (not each Ring)
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Steady-State Nominal Power Conditions
() The temperature of RELAP S.A. refers to the
Average Pin of Hot FA.

• It doesn't make sense a direct comparison between
  the two model due to the different hypothesis
  unless to consider that RELAP5 stand-alone refers
  to 1 HOT FA instead of those could be considered
  the "HOT FAs" in RELAP5/PARCS, i.e.
  18(CZ1-RING1), 30(CZ2-RING3), 42(CZ3-RING5).
• Weighting the lead outlet temperatures of each
  ring for the numbers of relative FAs, we obtain
  the same outlet average temperatures in each core
  zone obtained by RELAP5 stand-alone 482C (same
  mass flowrates).

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T/H-Neutronic Coupled Simulations
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Spurious beam trip of 1 sec
Fission and Total Exchanged Power
Reactivity
Switch-off and switch-on in 1ms

• the prompt and strong power drop following the
  source switch-off agrees with what is expected
  for a sub-critical reactor dominated by the
  prompt neutrons of source
• this transients is too fast to appreciate a
  change in SGs thermal power exchange
• thermal feedback, due to the fast cooling of the
  fuel, is responsible for a slight increase of the
  reactivity and a consequent peak of the fission
  power at the accelerator restart

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Spurious beam trip of 1 sec
Lower and Upper Plenum Temperature
Fuel, Clad and Lead Max Temperature
RING - 3

• -4C in the Upper Plenum after about 10s
• No variation of Inlet Core temperature also after
  600s of transients
• Jump of fuel max temperature of 164C
• Jump of clad and outlet lead temperature of 16C

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Unprotected Loss of Flow
Fission and Total Exchanged Power
Reactivity

• All the primary pumps stop at 100 s, the
  accelerator remain at the same flux level
• Small peak of power of 11 MWth after which return
  at the same initial level 376 MWth
• SGs reduced their exchange capability for 25s,
  until the natural circulation is started
• Core mass flowrate undershoot to the 30
• Peak of reactivity of 130 pcm due mainly to the
  positive effect of coolant temperature

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Unprotected Loss of Flow
Lower and Upper Plenum Temperature
Fuel, Clad and Lead Max Temperature
RING - 3

• Outlet plenum temperature maximum value of 631C,
  stable at 621C
• Inlet core temperature overcooling at 359C
• Fuel temperature peak to 1390C with a jump of
  177C
• Clad temperature peak up to 790C

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Unprotected Loss of Heat Sink
Fission and Total Exchanged Power
Reactivity

• All the secondary pumps stops at 100 s, the
  accelerator remain at the same flux level
• The power level remain the same, Core mass
  flowrate slightly decrease
• DHR system (3 out of 4 units) reaches full
  operation (21 MW) after 280s
• Coolant temperature positive effect and Fuel
  temperature negative effect

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Unprotected Loss of Heat Sink
Lower and Upper Plenum Temperature
Fuel, Clad and Lead Max Temperature
RING - 3
DHR Temperature and Mass Flowrate

• All the temperature increase and they can go on
  if nothing happen
• DHR mass flowrate increase just after the pumps
  trip
• Delta Temperature over the DHR 20C

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ULOF ULOH
Fission and Total Exchanged Power
Reactivity

• The superposition of the effects come true!
• Seems that the reactivity inserted could reach
  the 0 or a negative value.

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ULOF ULOH
Lower and Upper Plenum Temperature
Fuel, Clad and Lead Max Temperature
RING - 3

• Fuel temperature peak 1410C than 1930 after
  2000s of transient
• Lead temperature at outer ring 3 reach 1510C
• The transient is ended by time step card, but
  seems that should crash in few more seconds

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Beam Overpower to 120 from HFP
Power Evolution
Reactivity

• Source overpower of 20 at 100 s without
  recovery action
• Peak of power of 75 MWth (20) after which the
  core power have no variation
• SGs increase their performances and DHR start to
  work after 600s of transient
• As expected it is the fuel reactivity that have
  the major worth with a peak of 30 pcm

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Beam Overpower to 120 from HFP
Fuel, Clad and Lead Temperature
Lower and Upper Plenum Temperature
RING - 3

• Fuel temperature peak 1375C than 1410 at the
  end of transient
• Clad temperature 565C
• Lead temperature at outer ring 3 reach 539C

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Beam Overpower to 120 from HZP
Power Evolution
Reactivity

• Source overpower from 0 level to 120 at 0s
  without recovery action
• Instantaneous jump of power at about 450 MWth
• SGs increase their performances and DHR start to
  work after 600s of transient
• Overpower at HFP vs HZP without difference
  regarding the reactivity inserted

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Beam Overpower to 120 from HZP
Fuel, Clad and Lead Max Temperature
Lower and Upper Plenum Temperature
RING - 3

• Fuel temperature peak 1375C than 1410 at the
  end of transient
• Clad temperature 570C after 1500s
• Lead temperature at outer ring 3 reach 544C
  after 1500s

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Conclusions

• The analyses of the thermalhydraulics-neutronics
  behavior of the EFIT reactor have been conducted
  with the coupled code RELAP5/PARCS.
• Nominal steady state conditions achieved with the
  coupled model are in line with those calculated
  by RELAP5 stand-alone, taking into account the
  large modelling differences over the core.
• In the transients analyzed the feedback effects
  are quite negligible as expected unless we
  consider an accident that take into account a
  partial or total coolant voiding.
• All the unprotected transient analyzed shows that
  no major challenging situation are expected for
  the materials in accidental conditions and that
  there is a lot of time to recover those
  situations.