Modeling and simulation of disused radioactive sources’ dose distribution in a proposed centralized waste management facility and dose optimization using the Monte Carlo transport code (MCNP)

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Résumé

Radioactive sources are extensively utilized in research, medical (non-invasive diagnosis, radiotherapy, etc),
industry (radiography, well logging, industrial gauge, etc.), and agricultural applications like pest control, food
preservation (irradiation), etc. However, once the intended purpose of its design is no longer required (i.e., the
so-called disused sealed radioactive sources-DSRS), their management as radioactive waste poses significant
challenges, particularly in developing countries.
This study examined the accounting process for DSRS in Burkina Faso and proposed a centralized facility
model for their storage. This paper provides comprehensive simulations of spatial radiation dose distributions
using the Monte Carlo Transport code (MCNP). The source term was obtained from Burkina Faso’s national
inventory of sealed radioactive sources (SRS). The inventory includes, 60Co, 137Cs, 192Ir, 90Sr, and 241Am/9Be
sources, with a total activity of 1.167 ×1015 gigabecquerels. 95 % of the sources belong to Categories IV and V,
which are considered least dangerous according to the IAEA sources categorization scheme. Category III accounts
for 1 %, while Category I represent 4 % of the total inventory.
A preliminary simulation results identified areas of possible high radiation doses ranging from 9.78 ×10 2
mSv/h to 23.4 mSv/h. For example, in a designated public area, the dose (9.78 ×10 2 mSv/h) obtained was
more than 100 times the public exposure limits (5 ×10 4 mSv/h), while in designated room, the obtained dose
(1.02 mSv/h) was also 100 times the regulatory limit for workers (10 2 mSv/h).
The designated high dose areas were addressed throughout facility redesign and optimization, i.e., increased
wall-thickness, incorporating lead into wall materials and storage compartments. The results provide a pre
liminary roadmap for effective source accounting, DSRS facility design optimization, and provide data to sup
ports effective management of DSRS in storage

Mots-clés

Monte Carlo simulation, MCNP, Disused sealed radioactive sources, Ambient dose, Radioactive waste storage facility