Transcript OPTIMIZING THE OVERALL CONFIGURATION OF A HE- COOLED W-ALLOY DIVERTOR

OPTIMIZING THE OVERALL
CONFIGURATION OF A HECOOLED W-ALLOY DIVERTOR
FOR A POWER PLANT
A. R. Raffray, S. Malang and X. Wang
Mechanical and Aerospace Engineering Department and Center
for Energy Research, University of California,
San Diego, La Jolla, CA 92093-0417, USA
([email protected])
Presented at the 25th Symposium on Fusion Technology
Rostock, Germany
September 15-19, 2008
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He-cooled W-Alloy Divertor Concepts of Different Sizes
Have Been Proposed for MFE Power Plant Application
• Representative designs include:
- Plate configuration (characteristic dimension ~1 m) [1,2]
- ARIES-CS T-tube configuration (characteristic dimension ~10 cm) [3,4]
- FZK finger concept (characteristic dimension ~1.5 cm) [5,6]
• Use of smaller-scale units tends to minimize the thermal stress under a
given heat load; however, this results in an increase in the number of
units, with a corresponding impact on the reliability of the system.
- ~750 for the plate concept
- ~110,000 for the T-tube concept
- ~535,000 for the finger concept
• For all designs, W alloy development required to widen operating
temp. range and to develop reliable fabrication and joining processes.
- ~600-700°C (governed by W ductility considerations) to enable coupling to an
ODS ferritic steel manifold
- ~1300°C (governed by the W recrystallization limit) to provide desirable
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high- temperature capability
Plate-Type Concept [2]
• The He-cooled plate-type divertor
concept provides larger and fewer
units (which minimizes the length of
pressure joints) [1,2].
- Unit consists of a number of ~ 1-m long
poloidal channels with a 2.2 cm toroidal
pitch (typical toroidal dimension ~20 cm)
- The plate is made of W-alloy with a 5 mm
castellated W armor region
- The concept makes use of a jet flow similar
to the design of the finger and T-tube
concepts to cool the heated surface
• In order to minimize thermal stresses,
the unit was designed for uniform
temperature distribution for the given
heat flux and volumetric heat
generation and flow conditions.
- Tailored side and back wall thicknesses
- Stagnant He insulating gap
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Example Analysis Results for Plate Concept [2]
• Thermo-hydraulic and mechanical
analysis performed using CFX/ANSYS
- Surface heat flux = 10 MW/m2
- Vol. heat generation = 17.5 MW/m3
- He
inlet/outlet
temperatures
=
600/677°C
- He pressure =10 MPa
- P through jet region ~0.18 MPa
- Pumping power/thermal power <10%
Maximum W armor temp. =
1849°C
- Max. W structural alloy temp.= 1306°C
(recrystallization limit ~ 1300°C )
- Maximum thermal stress = 332 MPa
- Max. thermal+primary stress = 387 MPa
(assumed 3 Sm ~ 450 MPa)
• These results are encouraging; however,
concerns exist as to the dynamic stress
under heat flux transients or during
startup/shutdown because of the
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ARIES T-Tube Divertor Concept [3,4]
• T-tube: ~15 mm dia.
and ~100 mm long.
• Concept consists of
a W-alloy inner
cartridge and outer
tube with a
castellated W armor
layer on top.
• Both W alloy pieces are connected to a base ODS FS unit through a
graded transition to minimize thermal stresses.
• The He coolant is routed through the inner cartridge first and then
pushes through thin slots (~0.4 mm) for jet-cooling the heat-loaded
outer tube surface.
• The design provides some flexibility in accommodating the divertor
area since a variable number of such T-tubes can be connected to a5
Example Analysis Results for T-Tube Divertor Concept
• Thermo-hydraulic and mechanical
analysis performed using
CFX/ANSYS
- Surface heat flux = 10 MW/m2
- He inlet/outlet temp. = 570/700°C
- He flow rate ~6 kg/s per m2 of
surface area
- He pressure = 10 MPa
- P through jet region ~0.11 MPa
- Max. W alloy temp. <1300°C
(assumed recrystallization limit)
- Maximum thermal stress = 291 MPa
- Max. thermal+primary str.=372MPa
(assumed
3 Sm ~ 450
MPa)
• The
performance
of the
T-tube concept can be increased by scaling.
• Stress and temperature limits can be satisfied by reducing the
dimensions in the same proportion as the heat flux is increased.
• However, since the thicknesses are already small (e.g. the outer tube
thickness is 1 mm), there is limited margin to increase the T-tube
performance much beyond 10 MW/m2.
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EU FZK Finger Concept [5,6]
• Small modular units to
minimize thermal stresses
and allow for higher
q’’ accommodation.
• Small hexagonal W armor
tiles (5 mm thick) brazed
to a W-alloy thimble (~15 x
1 mm), forming a cooling
finger.
• Different flow
configurations have been
investigated, including:
- HEMJ (with jet cooling)
- HEMS(with slot array)
• The cooling finger is fixed to the front plate of the supporting structure
made of oxide dispersion-strengthened (ODS) steel with a Cu casting
transition piece to compensate for the large mismatch in the thermal
expansion coefficients of W and steel.
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Example Analysis Results for FZK Finger Concept [5,6]
• CFD Simulation with
FLUENT
- Surface heat flux = 10 MW/m2
- He inlet/outlet
temp.=600/700°C
- He flow rate ~6.8 g/s per finger
- He pressure = 10 MPa
- P through jet region ~0.12 MPa
- Max. W alloy temp. 1170°C
(<1300°C, assumed
recrystallization limit)
- Maximum armor temp.=1710°C
• The concept is designed to
accommodate an incident
heat flux of at least 10
MW/m2 and probably higher
based on recent mock-up
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Heat Flux on Divertor Target
• The heat flux on the divertor target plates is governed by a number of
parameters including the fusion power, core and edge radiation fractions
and peaking factor.
• The resulting heat flux footprint on the divertor usually follows a
Gaussian-like distribution (sometime skewed).
• Clearly, only a fraction of the divertor would see very high heat fluxes
- For example case, about
25% of the footprint
results in a heat flux >6
MW/m2 (zone 2).
- Zones 1 and 3 see a much
lower heat flux.
• Sometime, the
distribution is skewed in
one direction with
effectively two zones: the
high heat flux zone and a
longer low heat flux zone
next to it.
Example Symmetric Gaussian Profile with
Average/Maximum Heat Fluxes of 3/10 MW/m2 over a 9
Poloidal Distance of 1 m [5]
Combined Divertor Configuration
• The divertor heat flux profile brings up the possibility of
optimizing the heat flux accommodation and reliability measure
(based on number of pressure joints or units) by utilizing the
smaller-scale designs for the high heat flux region and the larger
scale design (plate) for the lower heat flux region.
• Two possible combined configurations:
- Separate design with smaller units in the high heat flux region and the plate
design in the lower flux region and routing the coolant so as to cooled these
regions in parallel.
- Integrating the smaller scale unit within the plate design and routing the
coolant through the integrated unit.
Key Features of the Typical He-Cooled Divertor Concepts for
an Assumed Divertor Area of ~150 m2
Divertor
Unit
Number of Units
Allowable
Concept
Characteristic
for a Typical
Incident Heat
Dimensions
Tokamak
Flux (MW/m2)
Finger
1.5 cm dia
~535,000
>12
T-Tube
10 cm x 1.5 cm ~110,000
~10-12
Plate
100 cm x 20 cm ~750
~8-10
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Example Combination of Separate T-Tube and Plate
Configurations for Two Heat Flux Zones
• T-tube plate unit covers the high heat
flux zone (of poloidal length ~~25-30
cm).
• Plate design covers the adjacent lower
heat flux zone (of poloidal length ~7075 cm).
• Each zone is cooled in parallel, the flow
and design parameters for each unit
being similar to those previously
described for the individual concepts.
• This would reduce the number of units
to as low as ~27,500 T-tube units and
562 plate units.
Divertor T-tube Unit Over High Heat Flux Zone
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Example Integrated Plate/Finger Concept
• An integrated configuration
combines the high q’’ unit
with the lower q’’ unit in one
design and provides the
flexibility of including the high
q’’ region at any poloidal
location along the design.
- Design based on plate concept but
with an integrated number of
finger units in the high q’’ zone
• For a high q’’ zone of 25 cm,
the no. of finger units within
the ~750 integrated plate
components is ~ 87,820
(compared with the 535,000 finger units required for full
target plate coverage)
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Integrated Plate/Finger Concept Includes:
• A front plate with
castellation in the low q’’
zone, grooves for brazing
the side walls, and
machined holes for
inserting the modular
tiles and caps in the
high q’’ zone
• A back plate with
grooves for brazing in the
side walls of the large He
channels
• Side walls
• Hexagonal tiles and small
caps, brazed together and
inserted in the front plate
in the high q’’ zone.
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Assembly Process
• The small finger modules are brazed into the front plate (an
improved characteristic of this design is that this braze is made
between two W alloy parts; in the original finger design, the Walloy front part is brazed to an ODS-FS back part requiring a
technique to compensate for differential thermal expansion
between the two materials);
• The front plate, the back plate and all the side plates are then
brazed together as one unit;
• The manifold for the small modules are inserted into the plate unit
and aligned with the front plate;
• The inlet manifold for the low heat flux zone is inserted from the
end of the low heat flux zone and aligned with the front plate;
• Finally, the outlet manifold for the low heat flux zone is inserted
from the end of the low heat flux zone.
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CFD Analysis of the Integrated Plate/Finger Concept
• Parameters and results from thermo-fluid analysis (using CFX) for integrated
concept with poloidal flow routing from the entry manifold at one end of the
plate to the exit manifold at the other end, and parallel cooling of the fingers .
- He inlet/outlet temperatures = 600/700°C; He inlet pressure = 10 MPa
- Incident q’’ = 10 MW/m2 and neutron volumetric heat generation = 17.5MW/m3
- Maximum jet velocity = ~ 250 m/s; maximum h ~5.84x104 W/m2-K
Velocity distribution in the
- Ppumping /Pthermal ~7.5%
integrated finger
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Temperature Distribution in Finger from ANSYS
Thermo-Mechanical Analysis
•
•
Max. temp. of the W armor = 2121 K (1848°C)
Max. temp. of the thimble (structural component under the armor) = 1514 K
(1241°C) ( within the 1300°C recrystallization limit assumed for W alloy)
Temperature
distribution in
finger
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Combined Stress Distribution in Finger from
ANSYS Thermo-Mechanical Analysis
• Analysis performed under
conservative assumption of no
castellation in the cap.
• Max. combined stress = 435
MPa (within the assumed 3Sm
limit of 450 MPa) .
• Maximum pressure stress (not
shown) = 110 MPa (within the
assumed Sm limit of 150 MPa).
• If required, this stress could be
reduced by reducing the
thimble diameter from the 18
mm assumed here closer to the
15 mm of the original finger
design.
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Summary
• A number of He-cooled W-alloy divertor concepts have been developed over the
last decade, covering a range of unit sizes, such as the FZK finger concept (~1.5
cm), the ARIES T-tube concept (~10 cm) and the plate concept (~ 1m).
• Typically, the smaller dimension concepts tend to accommodate higher heat
fluxes but at the price of having a large number of units and associated pressure
joints, which tend to negatively affect reliability.
• A possibility of optimizing the design is to combine different configurations in an
integrated design based on the anticipated divertor heat flux profile.
• An example of such an integrated design has been proposed, consisting of small
finger units in the high heat flux region integrated in a larger plate design.
• Its performance in term of accommodating the incident heat flux within the
material stress and temperature limits is comparable with the original finger
unit but is achieved with much fewer units and pressure joints.
• These initial results are encouraging in assessing the potential of such a concept,
but further work is needed for a more complete assessment, including more
design details on the fabrication and assembly procedures and analyses of
transient events.
Acknowledgement: This work was supported under U.S. Department of Energy Grant number
DE-FG02-04ER54757.
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References
[1] S. Hermsmeyer and S. Malang, "Gas-Cooled High Performance Divertor
for a Power Plant, Fusion Engineering and Design, 61-62 (2002) 197-202.
[2] X. Wang, S. Malang, A. R. Raffray and the ARIES Team, "Design
Optimization of High-Performance Helium-Cooled Divertor Plate Concept,"
accepted for presentation at the 18th ANS TOFE, September 2008.
[3] T. Ihli, A. R. Raffray, S. Abdel-Khalik, M. Shin and the ARIES Team,
"Design and Performance Study of the Helium-Cooled T-Tube Divertor
Concept," Fusion Engineering & Design, 82 (2007) 249-264 .
[4] A. R. Raffray, L. El-Guebaly, T. Ihli, S. Malang, X. Wang, and the ARIESCS Team, "Engineering Design and Analysis of the ARIES-CS Power
Plant," Fusion Science & Technology, 54 (3) (October 2008) 725-746.
[5] T. Ihli, R. Kruessmann, I. Ovchinnikov, P. Norajitra, V. Kuznetsov and R.
Giniyatulin, "An Advanced He-Cooled Divertor Concept: Design, Cooling
Technology, and Thermohydraulic Analyses with CFD," Fusion Engineering
and Design, 75-79 (November 2005) 371-375.
[6] P. Norajitra, S. Abdel-Khalik, L. M. Giancarli, T. Ihli, G. Janeschitz, S.
Malang, I. V. Mazul and P. Sardain, "Divertor Conceptual Designs for a
Fusion Power Plant," Fusion Engineering & Design, in press.
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