74 Research focus and highlights – Nuclear energy and safety
PSI Scientific Highlights 2012
Non-destructive testing and proton distribution profile determination of the MEGAPIE target Yong Dai, Laboratory for Nuclear Materials (LNM); Michael Wohlmuther, High Intensity Proton Accelerators (ABE); Viktor Boutellier, Didier Gavillet, Sandro Hahl, Daniel Kuster, Hans-Peter Linder, Andreas Lagotzki, Rudolf Schwarz and Holger Wiese, Hot Laboratory Division (AHL); Kurt Geissmann, Knud Thomson and Werner Wagner, Spallation Neutron Source Division (ASQ); Patrick Suter, Rudolf Thermer and Charles Zumbach, Mechanical Engineering Sciences (AMI), all PSI
The MEGAPIE test, performed at the SINQ facility at PSI in 2006, was the first time a liquid lead-bismuth eutectic (LBE) spallation target had ever been operated in the 1 MW regime. The container window, through which the proton beam passed into the target, is now being visually inspected and non-destructively tested ultrasonically. No visible failure and no detectable change in thickness in the beam window area have been detected. Gamma mapping was also performed and the results were used to evaluate the accumulated proton fluence distribution profile – the input data for determining irradiation parameters. The results of these investigations will provide important information for the R&D of future accelerator-driven systems (ADS) for nuclear waste transmutation.
MEGAPIE [Link 1] was the unique experiment, performed at
material had been deposited on the beam window [1]. This was
the SINQ facility at PSI in 2006, in which a liquid lead-bismuth
sticking to the calotte and was difficult to remove. Figure 1a shows
eutectic (LBE) target was operated in the 1 MW regime. The
the appearance of the T91 calotte after irradiation and Figure 1b
post-irradiation examination (PIE) of the target components
its appearance after removal of the deposited material. Observa-
exposed to high fluxes of high-energy protons and spallation
tion using a high-resolution video camera installed in the hot-cell
neutrons in a flowing LBE environment is one of most impor-
showed no visible failure in the proton beam window area.
tant tasks of the MEGAPIE project. The PIE of MEGAPIE will
The LBE in the selected pieces was removed by melting in a
provide important information for the R&D of future acceler-
specially designed oven. This melting was performed in an
ator-driven systems (ADS) for nuclear waste transmutation.
argon atmosphere at below 180°C. After melting of the LBE,
Non-destructive testing (NDT), including visual inspection
the selected pieces were again inspected. Figure 2 shows the
and ultrasonic measurement, is an important part of the PIE,
appearance of the inner surface of the T91 calotte after LBE
and can detect relatively large failures and changes in the
removal. It can be seen that the inner surface of the calotte
proton beam window area of the so-called T91 calotte, the
was only partially covered with LBE. The same is true for the
most intensively irradiated part of the LBE container, made of
other pieces. This means that the surfaces of components
ferritic/martensitic T91 steel. Gamma mapping on the T91
were not well wetted by LBE during irradiation. Again, no evi-
calotte is necessary for evaluating the accumulated proton
dence of failure was found.
fluence distribution profile, which is needed for determining
The material deposited on the T91 calotte is black within its
the irradiation parameters of the target.
bulk, but with a thin white surface layer on some parts. Analysis using energy-dispersive X-ray spectroscopy (EDX)
Non-destructive testing on the T91 calotte
indicated that the black material contained mainly carbon (~80 at.%) and oxygen (~20 at.%), while the white material in the surface layer was mainly silicon oxide with some carbon
After operation, the MEGAPIE target cooled down without the
content. The deposited material was most likely produced
liquid LBE being removed. The target was sawed into large
from oil leaked out of the secondary oil-cooling loop.
pieces at ZWILAG (the interim storage facility for radioactive
Ultrasonic measurements were conducted on the proton beam
waste, adjacent to PSI [Link 2]), with solidified LBE inside it [1].
window of the T91 calotte before and after irradiation. Before
Visual inspection was performed on some selected pieces in
irradiation, the measurement was conducted before filling
PSI’s hot cells. It was observed at ZWILAG that some foreign
the calotte with LBE. After irradiation, the measurement was