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MYRRHAPrimary Heat Exchanger design status
Diego CastellitiSCK•CEN
IAEA, Vienna, 21-22 December 2011Copyright © 2011 SCK•CEN
2
Introduction
� MYRRHA project:� Targets� Characteristics� Design status
� MYRRHA Primary Heat Exchanger design� Current layout� T/H parameters� Design choices� Control strategy
3
MYRRHA project [1/5]
� MYRRHA: Multi-purpose hYbrid Research Reactor for High-tech Applications
� MYRRHA facility main targets� Flexible irradiation facility� Minor Actinides (MAs) transmutation aiming at "closed cycle“
(Generation IV requirement)� Accelerator-driven system (ADS) demonstrator� Lead Fast Reactor demonstrator� (Pre-) Gen IV plant
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MYRRHA project [2/5]
� MYRRHA facility main characteristics� ADS reactor operating in sub-critical mode with ability to operate in
critical mode as well� Fast neutron flux� No electrical power generation� Material testing and isotope production facility � flux performance
maximized in the In-Pile Sections (IPS)� Primary coolant: Lead-Bismuth Eutectic (LBE)� Pool-type reactor� 4 Primary Heat Exchangers (PHXs)� 2 Primary Pumps (PPs)� Secondary coolant: 2-phase water� Tertiary coolant (heat sink): air
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MYRRHA project [3/5]
� MYRRHA main plant parameters
General design parameters Unit MYRRHA ValueMaximum core power MW 100
Reactor power MW 110Primary System Temperatures
Cold shutdown state °C 200Maximum core inlet temperature °C 270
Average core ∆T °C 140Average core outlet temperature °C 410
Maximum hot plenum temperature °C 350
Secondary System Temperatures2-phase water temperature °C 200
2-phase water pressure bar 16Fuel Pin
Fuel type MOX, max. 35wt.% PuO2 from spent fuel, the balance is natural UO2
Pellet type Solid pellet
Fuel element length mm 1400
Fuel active height mm 600
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MYRRHA project [4/5]
� MYRRHA main plant parameters (continued)
Fuel assembly
Assembly type Hexagonal fuel bundle with wrapper
Number of pins - 127
Spacer type Wire spacer
Assembly length mm 2000
Maximum LBE bulk velocity m/s 2
Core
Number of positions 151
Core diameter mm 1450
Maximum core pressure drop bar 2.5
Reactor vessel
Internal diameter mm ~7600
Length mm ~11000
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MYRRHA current PHX layout [1/2]
Shell and tubes counter-current PHX (water flowing in tubes)
Lower HX zone (Water tubes, tube plates and lower plenum)
HX shroud and feed-water tube double-walled against SG rupture accident
Upper HX zone (Feed-water inlet and 2φoutlet)
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MYRRHA current PHX functional requirements
� Normal operation: reactor core power (and all other heat sources) removal � PHX operating in forced circulation regimes on both sides
� Decay Heat Removal (DHR) condition: accidental situation �reactor must be able to operate in passive conditions (natural circulation) to guarantee the DHR function (conservatively estimated at ~7% of the total core power)
� Safe Shutdown condition: during shutdown periods (decay heat power low enough to be compensated by thermal heat losses) � PHX to provide power to the primary LBE in order to prevent freezing (Safe Shutdown Temperature: 200 °C) operat ing in"reverse" mode
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MYRRHA current PHX design choices
� Possible advantages:� No change in flow area � no phase separation, TH conditions preserved for the
whole tube length� Pressure drop � reduced need to orifice the water tubes for tube bundle flow
stabilization� Aspect ratio comparable to past LMFBRs � counter-current flow development
through the bundle� Possibility to adopt a wide inlet for LBE � full flow area for full power and partial
flow area (hot free surface at LBE inlet level) for DHR conditions� No need to adopt a double-walled structure for the upper part of the PHX shroud� Only one tube plate (� set of weldings) under LBE (upper tube plate above hot
free surface)� Relatively easy inspection and repair
� Possible disadvantages:� Tube length � stresses (weight, thermal-induced) in the tube plates� Upper fraction of tube bundle not in contact with LBE � free surface zone with
possible problems due to differential thermal expansion and level fluctuation (�thermal fatigue)
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MYRRHA PHX calculation and verification
� Heat Treansfer Coefficient (HTC) and material properties correlations used for design:� For LBE properties and HTC correlation: LBE handbook (2007)� For steel properties: RCC-MRx (2010)
� PHX T/H performances verified with RELAP5 and TRACE system codes
� High level of agreement has been found between design and system code verification
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MYRRHA current PHX control strategy [1/3]
� MYRRHA � research, experimental and material testing reactor
� Need to operate at different power levels when possible (in compatibility with performances required)
� Control issues arising when departing from T/H full power conditions:� Core parameters: Tin, Tout, ∆T, mass flow rate� Secondary side parameters: pw (and Tw), mass flow rate, exit quality
� Basing on the strategies comparison and taking into account the purpose and the needs of MYRRHA/FASTEF, it appears that the control solution involving a constant secondary loop conditions is preferable
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MYRRHA current PHX control strategy [2/3]
� Advantages in keeping primary conditions constant:� Unchanged stresses for primary structural materials� Control rods operation not required to compensate temperature
feedbacks
� Advantages in keeping secondary conditions constant:� No pressure variations in secondary side � no need to design the
loop for pressure > 16 bar� SGTR accident condition mitigation � more margins for vessel
design, safety valves, rupture disks, etc…
� IPS thermally decoupled from primary system � No real need (differently than power reactors!) to keep constant primary system conditions
� Power level varied only between irradiation cycles (in function of IPS requirements) � no drawbacks!
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MYRRHA current PHX control strategy [3/3]
� Control strategy proposed for PHX operation:� Constant secondary system condition� Primary system following load changes� Constant mass flow rate in both primary and secondary systems
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150
200
250
300
350
400
450
0 10 20 30 40 50 60 70 80 90 100
Te
mp
era
ture
(°C
)
Power (MW)
PHX EoL operating temperatures at different power levels
EoL lower plenum temperature
EoL upper plenum temeprature
Core average exit temeprature
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MYRRHA current PHXinspection and tube plugging
� Need to identify, inspect and plug failed PHX tubes
� Current available solution (Phénix experience):� PHX extraction� Lower plenum cut in the reactor hall (by remote
handling)� Tube plug� Re-weld� PHX insertion
� Inspection and plugging in-situ are considered
� Mechanical assessment of plugged pipe could show higher stresses than normal conditions
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MYRRHA current PHXHTC and tubes thermal stresses
� Very preliminary mechanical assessment performed on the tangential stress in water tubes
� According to the HTC values evaluated, top wall temperatures are the following:� LBE side: 281 °C (292 °C at EoL)� Water side: 221 °C
� Thermal stresses intensity (~174 MPa in EoL conditions) is well below the 3Sm for AISI 316L (342 MPa)
� Use of different steel (2Cr 1Mo) with lower thermal deformation and higher Sm could represent an improvement
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Flow instability problem
� Two kinds of instabilities can be found in a boiling (2φ) tube bundle of an HX:� Static instability� Dynamic instability
� Static instability (boiling channel problem): different pressure drop between liquid phase and vapor phase (assuming constant mass flow rate) � instability range in certain 2φ flow conditions (function of power, pressure, mass flow rate, quality, void fraction…) may appear in the heated channel
� Dynamic instability (tubes connected to plena problem): differences in mass flow rate distribution may appear among tubes � different flow regimes, obscillations, possible thermal fatigue, flow inversion, etc…
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MYRRHA PHX static instability [2/3]
� Static instability:� Does not require time-dependent
approaches � can be evaluated with “steady-state" models without solving PDE systems
� Different approaches available, with different complexity
� Approach used: full non-equilibrium model
� Heated tube generally divided in 4 regions:� Single phase liquid� Subcooled nucleate boiling� Bulk boiling� Single phase vapor
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MYRRHA PHX static instability [3/3]
� In nominal operation conditions, 99% of the heated length is in the Bulk boiling region
� At 7% of power (start DHR), about 85% of the heated length is in the Bulk boiling region
� Results to be confirmed with system code (RELAP5) model
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MYRRHA PHXStatic instability – Results [1/3]
� In nominal conditions (full power, full mass flow rate), the working point of the system falls in a perfectly stable range
∆p = 1.15 bar
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MYRRHA PHXStatic instability – Results [2/3]
� Also in DHR conditions (7% power, full mass flow rate), the working point falls in a stable range: less power �higher stability (saturated steam production very unlikely)
� For lower mass flow rates (to be expected in NC), the working point is also stable
∆p = 0.44 bar
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MYRRHA PHXStatic instability – Results [3/3]
� Interesting behavior at very low power (with nominal mass flow rate): at very low void fractions, gravity pressure drops > friction pressure drops � overall pressure drop increase
0.0E+00
2.0E+04
4.0E+04
6.0E+04
8.0E+04
1.0E+05
1.2E+05
1.4E+05
0 10 20 30 40 50 60 70 80 90 100
Pre
ssur
e d
rops
(P
a)
Power (MW)
PHX pressure drops vs. reactor power
Pressure losses
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Dynamic instability
� Dynamic instability evaluation � time-dependent problem� A perturbation of any kind (power peak, mass flow rate
maldistribution, etc…) can change conditions in one pipe �consequences will be felt in other pipes
� Need to consider thermal inertiae of pipe walls for accurate thermal perturbation propagation
� Solution requiring time-space PDE coupled system � use of system codes (RELAP5) could be adviced
� Instability analysis methods could provide results about bundle stability without fully PDE system solution
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Conclusions
� Further developements:� PHX inspection and tube plugging� PHX inlet – outlet thermal-hydraulic behaviour analysis and
design� Tube bundle spacer grids and their influence on the LBE flow� Complete mechanical assessment: water tubes, feed-water
inlet tube, upper and lower tube plates� Dynamic instability assessment� Cover and secondary system interfaces design
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