International Collaboration with the Shutdown of the BN-350 Reactor Page: 4 of 7
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II B. Primary Sodium Decontamination
After shutdown of the BN-350 reactor, the
primary sodium coolant contained high levels of
cesium-137. This fission product was released to
the sodium coolant during in-core fuel failures,
and was the primary source of radiation in the
primary system. In order to make handling of the
sodium safer during draining and processing
operations, an ISTC project, funded by the U.S.,
was established to "trap" the cesium from the
sodium using the technology used at the
Experimental Breeder Reactor - II (EBR-II) at the
Idaho National Laboratory (INL, formerly
Argonne National Laboratory - West).
This process involved fabricating a series of
seven traps containing reticulated vitreous carbon
(RVC). This RVC is proven to be effective in the
adsorption of cesium.
Using the INL design as a basis, RK scientists
and engineers designed the traps and system to
decrease the cesium concentration in the primary
sodium. A total of seven traps were fabricated
and used for this process. This project was
successful in that the concentration of cesium in
the primary sodium was decreased by a factor of
>800. [1]
Operation of the cesium traps was an essential
pre-requisite for draining and processing primary
sodium. However, it was also recognized that the
high radioactivity content and the high chemical
reactivity within the traps represents a continuing
hazard during their secure storage at the reactor.
Heightened awareness of the possibility of the
traps becoming a future terrorist target has also
been a factor in the desire to seek a longer term
solution for the traps, consistent with their
eventual consignment to a disposal facility.
Accordingly, the ISTC project has been extended
to study the options for safe disposal, provide for
any necessary testing, and determination of the
ultimate disposition of the traps.The UK and U.S. are collaborating on the
disposition of these traps. The process of
"optioneering", fairly common in the UK but not
widely used in the U.S., was proposed by the UK
contingent to determine the most reasonable
options for cesium trap disposition. Two
optioneering sessions were facilitated by RWE
NUKEM to clarify the path forward for this
ultimate disposition. These sessions, one in the
UK and the other in Kazakhstan, were attended by
experts from all three involved nations. The
sessions were designed to identify the options for
disposal, and to narrow the list of options to those
that would be evaluated in the extension to the
ISTC contract. This contract extension has been
funded by the U.S. and the UK and is currently
underway.
The next phase of cesium trap disposition,
forecast to be funded by the UK, will do any
necessary testing to substantiate the results of the
study. Finally, the cesium traps will be
dispositioned as the last phase of the ISTC
program.
I C. Geocement Stone
The EBR-II sodium was processed into a 70
wt % sodium hydroxide solution. This solution is
a solid at room temperature, and is an acceptable
waste form for disposal in the State of Idaho. In
Kazakhstan, further processing is necessary to
satisfy the waste disposal requirements.
Kazakhstan has proposed producing a
geocement stone using the sodium hydroxide
from the sodium processing and mixing it with
materials such as slag, clay, and Portland cement.
This geocement stone would be an acceptable
waste form for disposal in Kazakhstan.
An ISTC project was formed to evaluate this
proposal. This project was initiated using U.S.
funds, and was scoped with the study of material
availability, determination of the "recipe" for the
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Michelbacher, J. A.; Wells, P. B.; Organ, N. & Wells, D. International Collaboration with the Shutdown of the BN-350 Reactor, article, August 1, 2005; [Idaho Falls, Idaho]. (https://digital.library.unt.edu/ark:/67531/metadc889165/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.