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Master's Dissertation
DOI
https://doi.org/10.11606/D.85.2020.tde-18092020-162836
Document
Author
Full name
Natalie Costa Rolindo
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2020
Supervisor
Committee
Vicente, Roberto (President)
Freire, Carolina Braccini
Mourão, Rogério Pimenta
Title in Portuguese
Determinação da atividade de fontes radioativas seladas de irídio-192 em desuso
Keywords in Portuguese
caracterização de rejeito radioativo
fontes radioativas seladas em desuso
irídio-192
método dose-para-atividade
Abstract in Portuguese
Fontes radioativas seladas de 192Ir são amplamente utilizadas em gamagrafia pela indústria em testes não destrutivos. Estas fontes são obtidas em um reator nuclear por meio da reação nêutron-gama com o radioisótopo natural do irídio e após uma vida útil de cerca de um ano, tornam-se "fontes radioativas seladas em desuso" (FRSD). Considerando a meia-vida de 73,8 dias e as atividades iniciais típicas do 192Ir disponíveis comercialmente, a atividade destas fontes deveria cair abaixo do nível de dispensa em um período de 5 a 6 anos, quando poderiam ser liberadas do controle regulatório. No entanto, após o decaimento, estas fontes ainda apresentam taxas de dose mensuráveis e atividade acima dos níveis de dispensa. Uma investigação sobre as causas indicou que as fontes apresentam radioatividade residual devido à presença de 60Co (T1/2 de 5,3 anos) e do segundo estado metaestável 192m2Ir (T1/2 de 241 anos). Portanto, essas se qualificam para deposição em repositório para fontes seladas de meia-vida longa. O objetivo deste trabalho foi o desenvolvimento de um método para determinar a atividade de, pelo menos, 6 mil fontes de 192Ir armazenadas no Serviço de Gerenciamento de Rejeitos Radioativos do IPEN. Espectrometria gama, medida da taxa de dose realizadas com um detector CZT portátil e simulação com o software Microshield® foram usados no método dose-para-atividade para determinar as atividades.
Title in English
Determination of the activity of disused sealed radioactive sources of iridium-192
Keywords in English
disused sealed radioactive sources
dose-to-activity method
iridium-192
radioactive waste characterization
Abstract in English
192Ir sealed radioactive sources (SRS) are widely used in gammagraphy for non-destructive testing in the industry. These sources are obtained by irradiating natural iridium in a nuclear reactor by neutron-gamma reaction, after a service life of about one year, these sources become disused sealed radioactive sources (DSRS). Considering the half-life of 73.8 days and the typical initial activity of the commercially available sources, the activity of 192Ir DSRS should decay to below the waste clearance level in about 5 to 6 years, when they could be released from the regulatory control. However, after decaying these sources still present measurable dose rates and activity above clearance levels. An investigation on the causes indicated the presence of 60Co (T1/2 5.3-year) and the second metastable state of 192m2Ir (T1/2 241-year). Consequently, these sources qualify for disposal in a repository for long-lived DSRS. The objective of this work was to develop a method to determine the activity of about 6.000 192Ir DSRS stored at the Radioactive Waste Management Service at IPEN. Gamma spectrometry, dose rates measurements with a handheld CZT detector and modelling with the Microshield® software were used in the dose-to-activity method to determine source activities.
 
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Publishing Date
2020-09-22
 
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