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ST 6.3 –
Protección radiológica del público y el ambiente
PROBABILISTIC APPROACH TO POST-CLOSURE SAFETY ASSESSMENT
IN NEAR SURFACE REPOSITORY
Aguiar, Laís
1
*; Damaso, Vinícius
2
1
Brazilian Nuclear Energy Commission, Waste Mamagement Board. Brazil.
2
Brazilian Army - Office of the Army Commander. Brazil.
* Responsible author, email: laguiar@cnen.gov.br
The management of radioactive material should implement measures to ensure the protection
of human health and the environment in line with international principles and requirements for
radioactive waste management and radiation protection. The management has to include all
phases of the repository lifecycle that may involve or result in radiation exposure. In the post-
closure phase, radiological safety criteria are established as dose criteria or risk criteria or both.
This paper aims at evaluating cancer fatality risks corresponding to release of effluents from
near surface radioactive repository during post closure phase. Wastes focused on this work are
low and medium radioactive wastes. Potential radiological impacts after the closure of the
repository may be consequence of gradual processes, such as degradation of barriers, or
discrete events that affect the waste isolation. The repository should be robust and able to
withstand the effects of several possible events and failures. Radionuclide release rate to
biosphere is computed based on a module failure probability density function. The annual dose
rate to the critical group is determined from the environmental concentration, considering the
pathways of human exposure to radiation: ingestion of contaminated marine products and
recreation in contaminated environments. Cancer fatality risk due to radionuclide effluents from
repository to biosphere is evaluated in accordance to four subsets of ages in the critical group
(infancy, childhood, adolescence and adult). ). As results, this paper presents the relation
between the thickness of the geosphere layer and the radionuclide release rate in terms of dose
rate. Such results represent useful information for choosing the repository sites in order to keep
the released activity in acceptable levels over time.