Criticality Control During the Dismantling of a Uranium Conversion Plant Page: 3 of 8
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
WM'03 Conference, February 23-27, 2003, Tucson, AZ
3/8
chemical reactants, the mapping of the contamination, and the securing of the electrical
circuits.
To the Final Shut Down phase was added a Clean Up consisting of the removal of the
peripheral equipment (such as reactant and gas circuits, insulation materials and electrical
circuits) and the removal of the part of the process equipment requiring no special heavy
dismantling technologies (the pipes under a diameter of 80 mm, the valves and other small
elements). An important goal is to decrease the quantity of fissile material still present in the
equipment.
This Clean Up, which began in 2001, was performed under clearance of the French Nuclear
Safety Authority.
The decree allowing the dismantling of the whole plant is expected in 2003, and the final
decommissioning in four phases will be finished in 2007.
The first phase is the dismantling of the remaining process equipment, their framework, and
the effluents pipes and tanks.
Ventilation and electrical circuits will be dismantled during the second phase, replaced
meanwhile by site devices.
Final clean up of the empty buildings, by concrete scrapping, and examination of the
radiological mapping will be done within the two last phases, followed by a final report.
CRITICALITY CONTROL
During the production period the uranium conversion processes were either geometrical safe,
or were operated under strong administrative control to prevent any criticality accident. The
ATUE facility was and is still equipped with a Criticality Accident Detection Device, which
covered mainly the wet process area and the radioactive effluents circuits.
Dismantling operations will modify the global geometry, so it is necessary to control the
criticality risk by a specific 235U mass management.
The evaluation of 235U quantities involved in the dismantling operations has been carried out
for the whole facility inventory. It is mainly based on in site gamma spectrometry
measurements, modeling, and radiation flow rate measurements associated to transfer
functions.
In site gamma spectrometry
Gamma spectrometry enables to identify radio isotopes present in the facility by their gamma
ray emission characteristics and to quantify their activity.
The activity and the fissile material mass are checked out by means of measurements and
modeling.
The activity of a simple shaped piece (cylindrical column, flat filter,...) with an
homogeneous contamination, is determinated with the following procedure:
- gauge the spectrometry measurement system with a perfectly known point source at a
distance "d",
- measure the radioactive piece to be analyzed at the same distance "d",
- compute the "equivalent activity" which is the activity value of a point source that would
give the same measurement value,
- compute the "measurement sensitivity" for a point source at a distance "d" and for the
piece geometry at the same distance,
- transform the equivalent activity in real activity with: Areal = Aeq * Sref /Sgeom
- Areal : contaminated piece activity
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Ladurelle, Laurent & Lisbonne, Pierre. Criticality Control During the Dismantling of a Uranium Conversion Plant, article, February 27, 2003; Tucson, Arizona. (https://digital.library.unt.edu/ark:/67531/metadc779204/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.