2023/10/24 Poster Session P2 #276

21th International Conference on Fusion
Reactor Materials(ICFRM-21)
in Palacio de Congresos, Granada, Spain.

Thermal Diffusivity of Electron
Irradiated Tungsten Small Disk
Masafumi Akiyoshi (Osaka Metropolitan Univ.),
Hsin Wang , Takaaki Koyanagi, Yutai Katoh (ORNL),
Kiyohiro Yabuuchi, Tatsuya Hinoki (Kyoto Univ)

Supported by
2019-2024 Japan-US
FRONTIER Project

Acknowledgement: Research sponsored by the Office of Fusion Energy Sciences,
U.S. Department of Energy, under contract DE-AC05-00OR22725 with UT-Battelle, LLC.
This work is also supported by the "Joint Usage/Research Program on Zero-Emission
Energy Research, Institute of Advanced Energy, Kyoto University (ZE2022C-01).

2

Thermal diffusivity / mm ・s

Thermal diffusivity in Metal / Ceramics-1

Thermal diffusivity in Tungsten materials

In ceramics, high temperature increase
phonon-phonon scattering and thermal
diffusivity α is described as α= a/Tn ,where unirradiated specimens shown = 1 and irradiated them show n < 1.
Unirradiated pure tungsten showed
n～0.4 with the same function.
Furthermore, fusion neutron inducestransmutation element such asRhenium or Osmium that reduce
thermal diffusivity drastically.

Pure Tungsten (D10T1 size)with graphene coat

α = k/T
k=677
n=0.405|r|=0.99967

70n60
504030300

400

500

600

700800900

Measurement temperature / K

Thermal Diffusivity / mm2・s-1

In Tungsten, heat is mainly carried byelectron like typical metals, but about
1/3 of heat is carried by phonon likeceramics (at room temperature).

80

60

Unirradiated
40% drop

Irradiated40
Almost Flat

Unirradiated D6T2 specimens
4003: Pure W thick plate(//)
500H: Pure W thick plate(⊥)

2003003% Re

9003: K-doped W-3%Re(//)
A00C: K-doped W-3%Re( ⊥)400

600

500

700

Measurement Temperature / K800

RB-19J Irradiation in PHENIX Project
In light water fission reactor, most neutrons
are moderated to thermal neutrons that gives
larger amount of transmutations than thefusion reactor at the same irradiationinduced damage.

W → Re, Os
Thermal diffusivity change;

In the PHENIX project, irradiation in HFIR have been
performed with the Gadolinium thermal neutron shield.
Compare with rapid irradiation
without Gd shield is important.

Location: RB-19J
Dose: 0.2~0.7 dpa, 4 cycles
4.7×1018 n/m2・s (E > 0.1 MeV) and9.5×1018 n/m2・s (E < 0.5 eV)→ Shielded to about 1/100

Temperature regions
550℃, 850℃, 1050℃

Separate effect oflattice defects fromtransmutations.
Electronconduction

Phononconduction

The Oscillation problem at hightemperature measurement with LFA-467

・The annealing at 800℃ showed norecovery on the specimens irradiatedat 548℃ or 660℃.

705001: Pure W(⊥) TIrr 548℃

・The measurement at 900℃ showed
cyclic noise on the IR signals, that issaid the Oscillation problem.

A000: K-doped W-3Re(⊥) TIrr 660℃

60

measurements up to 600, 700, 800, 900 ℃

Therefore, we stop the annealing
procedure on the irradiated specimens.

5076540

Response

Thermal Diffusivity / mm2・s-1

In order to evaluate the recovery behavior by annealing at high temperature, we attempted toevaluate isothermal annealing effect as well as isochronal annealing by repeating themeasurement every minute for one hour at the target temperature, then lowering thetemperature and evaluating the temperature dependence again.

4321300400600

800

1000

Measurement Temperature / K1200

Calculation range-1-50

050Time /ms

100

150200D3TH Miniature Specimen Holder

D10T1D3THThe Netzsch LFA-467/467HT isequipped with a zoom optics system, an
optical system for a sensor thatmeasures infrared radiation emitted fromthe back side of the specimen, allowing
measurement of small specimens.

In the measurement of D10T1 and D3TH Pure W samples at 900℃, oscillations occurred only in
the D3TH sample, even though the measurement range by zoom optics was the same φ2.8 mm.
This is thought to be because the sample holder used to measure the D3TH sample interferedwith the zoom optics optical system, limiting the amount of infrared light entering the sensor,
resulting in a lower signal-to-noise ratio that caused the oscillations to become apparent due tobackground noise.
InSb IR Detector

InSb IR Detector

Zoom optics
view area
Rear apertureInterfere

Radiated IR
φ3mm specimen

Specimen holder

Pre aperture
Buffer ring

Removebuffer ring andrear aperture

Radiated IRSpecimen holder

φ3mm specimenPre aperture

Flash Light

Flash Light

φ10 mm

φ10 mmFIX the oscillation problem
IR signals at 900℃ by LFA-467

D10T1

D3TH60
D10T1 W specimen
D3TH1 W specimen
with 5push graphene coating

2Thermal diffusivity / mm ・s-1

Pure W polished samples
were sparsely (5 push)graphene-sprayed andmeasured under rare gas
purification and ultra-highpurity Ar gas flow (200ml/min) conditions.

50

The D3TH sample did not show theoscillation up to 900℃, andshowed thermal diffusivity
measurements comparable tothose of the D10T1 sample.

40305001000Measurement temperture / K

1500

Thermal diffusivity /mm 2/s

Thermal diffusivity of electron
irradiated pure W
80
unirradiated Pure W
8MeV electron irradiated W upto 3 ×10-3dpa at 216℃

70
605040300

400500600
Temperature / K700

To clarify the lattice defect contribution, pureW specimens were irradiated by 8 MeV
electron beams using KURRI-LINAC at 216℃
to 3.8×1023 electrons/m2 that corresponding
to 2.8×10-3 dpa. At these condition, ceramics
material such as β-SiC showed obvious
change in thermal diffusivity, but thesespecimens did not show decrease.

800This result suggests that recovery afterstage III in W is quite limited because noI-loops are induced in this specimen andmost point defects have recovered
below 300 K [1979Ishino]. In the case ofpure Cu, stage III in electron irradiatedspecimen above 300 K is quite limited
compared with neutron irradiated ordeuterium irradiated specimens.

Recovery of electric resistivity in pure Cu irradiated bydifferent source (detail is not given) [1979Ishino].

Estimation of thermal conductivity
From the experimental and calculation results in this study, the phonon contribution inthermal diffusivity is about 15mm2/s at room temperature for pure W and also W-5%Re.
The thermal diffusivity α is obtained by α = vl / 3 (v : phonon velocity, l : phononmean free path) and v = sqrt(E /ρ) (E : Young's modulus, ρ: density), so using E =400 GPa and ρ = 19.25 g/cm3, v = 4.56×103 m/s and l is obtained as 9.87 nm (athigher temperature, this phonon mean free path is shorter).
It represent that large crystalline defect such as I-loops or grain boundary gives quite
small contribution to thermal diffusivity in phonon conduction. There is no electric
resistivity measurement at high temperature for neutron irradiated specimen, but
annealing measurement in this study indicates that the effect of crystalline defect toelectric resistivity seems to be limited too.

Then, only Re (and also Os) distribution (NOT only amount) is
important to estimate thermal diffusivity in irradiated W and W-Re
alloy.