Sampling and evaluation of in-situ studies for 60Co diffusion in bentonite
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Typ
Examensarbete för masterexamen
Program
Publicerad
2020
Författare
Beckius, Mikael
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
This study focuses on evaluating the diffusion of 60Co in bentonite clay as part of an
in-situ experiment made by SKB at Äspö. This experiment has been running for 20
years, and its purpose is to evaluate the potential of using bentonite clay as backfill
material in a final repository for used nuclear fuel. Evaluating the diffusivity is one
method of assessing the long-term structural integrity of the bentonite clay. This is
done by using 60Co as a radioactive tracer placed in a block of bentonite inside a test
parcel designed to mimic the proposed setup of the Swedish KBS-3 final repository
model. This specific setup is under adverse conditions where the temperature is
higher than the estimated temperature in the final repository. This is done to obtain
a comparison with previous studies done under normal conditions. The bentonite
around the radioactive source is sampled and crushed before the radioactivity is
measured using an HPGe detector with sample changer. The calculated diffusivity
is used to evaluate whether the diffusion model used in earlier studies is applicable
on this test parcel as well.
The results obtained in this study, shown in Table 0.1, supports earlier studies, as
the calculated diffusivity fits well into the diffusion model and yields a diffusivity
within an order of magnitude from the results obtained in earlier studies for the fast
profiles, and in line with earlier results for the slow profiles. Combining this result
with the previous studies on the subject show that the bentonite structure appears
to be intact, which further supports the idea that bentonite clay is a very promising
material for use as backfill material in a final repository.
Beskrivning
Ämne/nyckelord
bentonite , diffusion , cobalt , nuclear fuel , final repository , SKB