Thermal fatigue testing of a diffusion-bonded beryllium divertor mock-up under ITER relevant conditions Page: 4 of 6
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bonded beryllium as an actively cooled PFC
under ITER relevant conditions. High heat
flux testing of a flat tile beryllium divertor
mock-up was performed using the 30 kW
Electron Beam Test System (EBTS) at
Sandia National Laboratories [5]. The flat
tile mock-up was provided by the D.V.
Efremov Scientific Institute in the Russian
Federation as part of a US/RF
ITERcollaboration.
2. EXPERIMENT
The mock-up consisted of four 5 mm thick
and four 10 mm thick Be tiles, 1 cm x 2 cm in
area. Only the 5 mm thick tiles were tested.
To fabricate the mock-up, a block of TGP-
56 isotropic Be was made from hot
isostatically pressed Be powder. The mating
surfaces between the Be and Cu saddleblock
were electrochemically polished. The Be
block and Cu saddle were then mechanically
clamped under 30-50 MPa of applied
pressure and placed in a vacuum furnace.
The diffusion bonding occurred at 840 0C in a
background pressure of 7X10.3 Pa.
The Be tiles were then wire cut from the
attached Be block. Each tile had two holes,
1.05 mm in DIA, drilled laterally to a depth
of 5 mm to accommodate 1.02 mm DIA,-
sheathed, type K thermocouples. The top
thermocouple was located 1.7 mm from the
surface; whereas, the bottom thermocouple
was 3.4 mm from the surface. The OFHC
saddleblock was also diffusion bonded onto a
DSCu (MAGT) tube measuring 1.3 cm in ID
and 1.6 cm in OD. Figure 1 is a picture of
this mock-up prior to testing.
Be 5 mm
Cu 1 mm
Figure 1. Flat tile beryllium mock-up
The inside of the MAGT tube contained a
porous coating consisting of 100-150 gm
spherical copper pellets which were bonded
to the inside of the tube. The purpose of theporous coating is to provide more margin for
critical heat flux and enhance the heat
transfer at the wall.
During the thermal response tests, the
electron beam was rastered over all four
tiles, A-D. They showed similar behavior to
increasing absorbed heat fluxes up to 5
MW/m2 producing surface temperatures as
high as 300 'C. Coolant water was supplied
to the mock-up at a water inlet temperature
of 8-15 0C, pressure of 1.4 MPa and flow
velocity of 5 m/s. The low inlet temperature
was chosen to avoid the safety hazards
associated with hot water-beryllium aerosols.
An IR camera was used to monitor the
temperature distribution across the entire
mock-up.
During routine beam alignment, tile B
unexpectedly debonded after only 25-30
cycles at less than 0.5 MW/m2. Tile A was
subjected to a thermal response test up to 10
MW/m2. The electron beam was rastered
over the 1 cm x 2 cm surface area of the tile
using shot durations of 60 s to ensure steady
state conditions in the water. A one-color,
spot pyrometer was used to measure the
surface temperature at the center of tile A.
Thermal fatigue testing was performed on
tiles C and D using an absorbed heat flux of
5 MW/m2. Flow conditions consisted of a
water inlet temperture of 12 0C, flow velocity
of 5 m/s and pressure of 1.4 MPa. The low
inlet temperature also allows the beryllium
to be cycled below its ductile-to-brittle
transition temperature. Heat flux cycle times
of 15 s on and 15 s off were used. Steady
state temperatures were reached in the bulk
thermocouples in 10 to 12 s for all shots.
3. THERMAL RESPONSE
Figure 2 shows the temperature response
of tile A measured by the pyrometer and the
top thermocouple vs absorbed heat flux. The
surface temperature of tile A increased
throughout this series, eventually reaching
690 'C at 9.5 MW/M2. At 10 MW/m2, the tile
completely detached from the copper
substrate.v
P
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Youchison, D. L.; Guiniiatouline, R. & Watson, R. D. Thermal fatigue testing of a diffusion-bonded beryllium divertor mock-up under ITER relevant conditions, article, December 31, 1994; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc627269/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.