THE IMPACT OF MATERIALS R&D ON THE OPERATION OF A WATER-COOLED DEMO DIVERTOR …
M. Rieth, S. Antusch, J. Hoffmann, M. Klimenkov, J. Reiser, S. Brezinsek, W. Biel, J. Coenen, J. Linke, Ch. Linsmeier, A. Litnovsky, Th. Loewenhoff, G. Pintsuk,
B. Unterberg, M. Wirtz, H. Greuner, A. Kallenbach, R. Neu, J. Riesch, J.H. You,
T. Barrett, F. Domptail, S. Dudarev, M. Fursdon, M. Gilbert, A. Galatanu, W. Pantelon,
L.M. Garrison, Y. Katoh, L.L. Snead, D. Armstrong, S. Roberts, and the WPMAT-HHFM team
AND VICE VERSA
Outline
Normal and Off-Normal loads in a plasma facing unit (PFU)
Basic thermo-mechanic analysis on the example of ITER
Identification of failure mechanisms and related material properties
The situation for a DEMO PFU
Simple Load Studies
Thermal off-normal 20 MW/m
2#1 #2 #10000
2 fpy
normal 10 MW/m
2t
HF 0.2-1 GW/m
2ELM
15 MW/m 2 (30s), small monoblock 23 mm x 22 mm x 4 mm, D15 mm
water cooling, 200 °C M. Li, IPP
10 MW/m 2 + 0.4 GW/m 2 (1ms on, 50ms off) ITER type monoblock
28 mm x 28 mm x 12 mm, D17 mm
Load Analysis, Elastic
Mechanical, elastic
normal
t HF
10 MW/m
210s
pat h
-1200 +1200
path (mm) Temperature (°C)
Stress (MPa)
Yield Limit (MPa)
Sxx plastic deformation
under compression
+740 MPa
-670 MPa
Stress
Load Analysis, Plastic Deformation
Mechanical, plastic normal
t HF
10 MW/m
210s 20s
Plastic Deformation (10 s)
0.3 %
0 % Pl. Strain
0.1 % 0.2 %
Secondary Stresses (20 s)
365 MPa
-110 MPa Stress
0
200 MPa
7 mm
Failure Analysis
Mechanical, plastic normal
t HF
10 MW/m
210s 20s
Max. Stress during cooling
• Strain rate: 10 -3 /s – 10 -2 /s
• 150 °C < DBTT <250 °C
• T > 300 °C
ductile regime
no brittle fratcure
Mechanical, dynamic
properties depend strongly on specific material
Basic Properties
Rxx
DBTT
• brittle fracture
• no plastic deformation
• no yield limit
Microstructure, Grain Size, Rxx
as received 7 h, 1200 °C
25 h, 1200 °C
GS 150 µm x 50 µm GS 300 µm x 70 µm
GS 300 µm x 300 µm
4 mm W plate
PIM W, 2400 °C
GS 100 µm x 100 µm
Failure under Off-Normal Load
Thermal: T surf = 1800-2100 °C
Recrystallisation (Rxx) off-normal
t HF
20 MW/m
210s 20s
Dynamical: DBTT 250-350 °C (W-Rxx)
ductile-brittle regime
Fracture Mechanics
o K Ic = 5-8 MPa m 1/2 (W-Rxx)
o critical crack length = 16-40 µm
o grain size: min. 50 µm, max. >300 µm
ductile/brittle crack formation likely
Mechanical
o plastic surface deformation > 1%
during heating
o secondary surface tensile stresses after cooling down: > 710 MPa
710 MPa
-973 MPa Stress
-500 MPa
0
Relevant Material Properties
Comparison with experiment: ITER mockup, 300 x 20 MW/m 2 pulses
ductile or brittle crack depend on geometry and load history
relevant material properties for this particulare case:
o Recrystallisation Temperature o Toughness, static DBTT
o Crack formation strength & plasticity
6- 7.5 mm
Critical operating point for cracking
>1700°C
t Surface Temperature
20 MW/m
2compression
10s 20s
<100°C DBTT
0 MW/m
2tensile stress
Additional Load Conditions
Fatigue
#1 #2 #10000
2 fpy
normal 10 MW/m
2t
HF 0.2-1 GW/m
2ELM
0
t
stress t
T
o ELM discharges correspond to high strain rate, high temperature, High Cycle Thermal (Shock) Fatigue
this is not covered by usual material tests (LCF, LCTF, HCF, etc.)
specific requirements for thermal shock tests
possible surface modification, roughnening, crack initiation
Changing Conditions During DEMO Operation
Microstructure o Recrystallisation
o Cyclic plastic deformation
Strength, DBTT, toughness, ductility will vary during operation
Geometry o Erosion of armour surface due to PSI (max.
2-3 mm/fpy ?, depending on T ?)
Temperature and load will vary with time
Irradiation o Continuous increase of damage (2 dpa/fpy in striking point, 4 dpa/fpy elsewhere)
o Damage strongly depends on temperature
Inhomogeneous variation of material properties
Strength, DBTT, toughness, ductility, thermal
conductivity, fatigue properties, microstructure,
density (swelling), erosion rate?, others?
Irradiation Defects
Void Formation (Swelling) Transmutation to about 2% Rhenium
HFR irradiation, 900 °C, 4 dpa
o DEMO: about 0.5-1% Rhenium/fpy
Hardening, embrittlement, loss of conductivity, …
Exact extend unknown (lack of data)!!!
o Max. at 600-900°C
Embrittlement, …
DBTT shift due to n-irradiation
V. Barabash et al. / Journal of Nuclear Materials 283-287 (2000) 138-146
3-PB Tests
80 0 K sh ift
Situation with n-Irradiation Damage + ELMs
significant DBTT shift
possible surface roughening or microcracks
critical fracture limits (K c, J c, a c ) decrease
cracking very likely
6- 7.5 mm
>1700°C
t Surface Temperature
10s 20s
<100°C DBTT
0 MW/m
2tensile stress 10 MW/m
2+ ELMs
compression
Impact on DEMO Divertor Operation The “ITER limit”
o normal operation 10 MW/m 2 o target tilt and monoblock
shaping (edge shadowing) will lead to 15 MW/m 2
o off-normal transients up to 20 MW/m 2 possible for a limited period
The “DEMO limit”
1. If we use the same design, the requirements must be reduced.
2. If we want to meet the ITER
requirements, we have to change the design and/or concept.
Open question: What is the true minimum required ELM energy density for divertor lifetime?
R. Pitts, ITER
Impact on Armor Materials R&D
Mitigation by improved materials (topics in WPMAT)
W alloys (increased strength, higher Rxx) S. Antusch
W(fiber)-W composites J. Riesch, J.-H. You, J.W. Coenen
Mitigation by design (the ITER monoblock design seems not to be optimal for DEMO conditions)
Various concepts are under examination J.-H. You (WPDIV)
Close collaboration between DIV and MAT projects
Mitigation by experiment (increase knowledge)
Neutron irradiation campaigns will be launched in WPMAT
brief overview in WGIFT satellite meeting
Tailored High Heat Flux Tests
G. Pintsuk (WPMAT-HHFM programme)
Thank you !
Partners:
and joined universities
Disclaimer: „This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed therein do not necessarily reflect those of the European
