The High-Temperature HTV Graphite Irradiation Capsule for the High Flux Isotope Reactor at Oak Ridge National Laboratory
J.L. McDuffee, T.D. Burchell, K.R. ThomsSeptember 18, 2013
2 2013 INGSM
Purpose
• The key data to be obtained from the graphite specimens are– Dimensions, volume– Mass, density
• Data are critical to the design of the NGNP and the high-temperature graphite irradiation creep capsule (AGC-5) planned for irradiation in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL)
• Supports ongoing work in the area of model development; e.g., irradiation effects models such as dimensional change, structural modeling, and fracture modeling
• Used to underpin the American Society of Mechanical Engineers (ASME) design code currently being prepared for graphite core components.
3 2013 INGSM
Specimens
5.33 cm(0.210 in)
7.62, 8.89, 10.16 mm(0.300, 0.350, 0.400 in)
2.1 mm(0.082 in)
4 2013 INGSM
Specimens• PCEA (15 samples)
– Supplied by Graftech International– Country of origin: Germany/France– Petroleum coke, extruded, medium grain e
• NBG-18 (14 samples)– Supplied by SGL Carbon– Country of origin: Germany/France– Pitch coke, vibrationally molded, medium grain
• IG-110 (14 samples)– Supplied by Toyo Tanso– Country of origin: Japan– Petroleum coke, isostatically molded, fine grain
5 2013 INGSM
Specimens• NBG-17 (9 samples)
– Supplied by SGL Carbon– Country of origin: Germany/France– Pitch coke, vibrationally molded, medium grain
• Grade 2114 (13 samples)– Supplied by Mercen– Country of origin: USA– Nonpetroleum coke, isostatically molded, super fine grain
• H-451 (7 samples)– Supplied by SGL Carbon– Country of origin: USA– Petroleum coke, extruded, medium grain, no longer in production
6 2013 INGSM
Overall Design• 1 capsules with 8 subcapsules
– Each subcapsule has one design temperature– 9 specimens per subcapsule– 64 specimens total
• HTV capsule will be irradiated for 2 cycles (3.2 dpa)
• Design goal is to distribute specimens as evenly as possible across fluence and temperature
7 2013 INGSM
Graphite Specimen Distribution in the HTV Capsule
8 2013 INGSM
The High Flux Isotope Reactor• Pressurized, light-water-cooled and –
moderated, flux-trap-type reactor
• HEU fuel — U3O8 dispersed in aluminum
• Two annular fuel elements
• Center cylindrical flux trap, 12.70 cm diameter
• Nominally 6 cycles/year, with a 25 day cycle length
9 2013 INGSM
Irradiation Capsule Design
10 2013 INGSM
Irradiation Subcapsule Design
Centering thimble
Specimen
POCO graphite sleeve
Thermometry (SiC or Graphite
Nb1Zr holder
11 2013 INGSM
Irradiation Capsule Design• Subcapsule separators
– Stack of grafoil wafers held together with a molybdenum tube & washer
– Dosimetry is located in cutouts in separators– Grafoil provides axial insulation between
subcapsules
• Nb1Zr centering thimble– Contains specimens inside holder– Radial prongs center holder inside outer housing– Small contact surface area minimizes heat loss
• Critical for 1500 ºC capsules
12 2013 INGSM
Irradiation Capsule Design
• Subcapsule holder– Nb1Zr holder is tapered from the
middle to each end to compensate for axial heat losses
– POCO graphite liners (~0.5 mm thick) prevent potential sticking between the specimens and the Nb1Zr due to prolonged exposure at high temperature
13 2013 INGSM
Relative Importance of Modeling InputsInitial gas gap sizeHeat generation rateThermophysical properties
· Modeling approach is also a significant contributor
14 2013 INGSM
Heat Generation Rate in Materials
2013 — Design for Irradiation Experiments
fission neutrons
fission photons
fission product photons
n, reactions
decay
Nb1Zr Graphite
Core fission neutrons <1% 11%
Core fission photons 64% 57%
Core fission product photons 36% 31%
Local decay — —
Relative Contributions to the Total Heat Generation Rate
16 2013 INGSM
Heat Generation Rate in HFIR• Axial profile is strong, but relatively
independent of material
• Radial profile in the flux trap is weaker, but material dependent
• Radial profile in the reflector can be large
2013 — Design for Irradiation Experiments
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
-25 -20 -15 -10 -5 0 5 10 15 20 25
Peak
ing
Fact
or
Location from Horizontal Midplane (cm)
EOC-TRRH-Water
EOC-TRRH-Steel
EOC-TRRH-V4Cr4Ti
EOC-TRRH-Al6061
EOC-PTP-Water
EOC-PTP-Steel
EOC-PTP-V4Cr4Ti
EOC-PTP-Al6061
EOC-HT-Water
EOC-HT-Steel
EOC-HT-V4Cr4Ti
EOC-HT-Al6061
EOC correlation
s+ = 31.9 cms- = 31.8 cm
Axial Peaking Factor
Radial Heat Generation Factor
17 2013 INGSM 2013 — Design for Irradiation Experiments
Thermal Modeling• Temperature is controlled by the size and composition of the fill gas
– Inert gases are most common: helium, neon, and argon
Temperature is controlled by the outer gas gap
0.00000.00050.00100.00150.00200.00250.00300.00350.00400.00450.0050
300 500 700 900 1,100 1,300 1,500Temperature (°K)
Ther
mal
con
duct
ivity
(W/c
m-°
K)
Helium
Neon CO2
Argon
18 2013 INGSM
Thermal Modeling With Finite Elements• Small gap modeling
2013 — Design for Irradiation Experiments
Specimen/holder region
Gas gap
Housing1100°C over 0.33 mm = 3-4°C/µmThermal expansion ≈ 35 µm
19 2013 INGSM
Conduction Through a Small Gas Gap• Thermal jump condition
– Important at small gap sizes typical in irradiation experiments
– Accounts for inefficiency in energy transfer between the gas molecules and the solid surface• especially important when
MWgas ≠ MWwall
– Modifies Fourier’s Law by adding a small extra conduction length on each side
2013 — Design for Irradiation Experiments
gs2
gs1
20 2013 INGSM
Conductance Between Parts in Contact
• In real contact, two surfaces never truly conform at the microscopic level
• To simplify analysis, the effective heat transfer coefficient is divided into two parts:– Solid spot conductance, hs
• Represents conductance at the solid-solid interface points
– Gap conductance, h
• Represents conductance through the interstitial gap
21 2013 INGSM
Preliminary Temperature Modeling
22 2013 INGSM
Summary• Objective is to provide design data for NGNP relevant graphites
– Neutron dose range of 1.5 to 3.2 dpa– Irradiation temperatures of 900°C, 1200°C, and 1500°C
• Specimens are PCEA, NBG-17, NBG-18, IG-110, 2114, and H-451 (for reference)
• High temperatures are achieved through thermal barriers between subsections and profiled gas gaps
23 2013 INGSM
Questions?