Markov chain model for inadvertent human intrusion into geological repositories for high level wastes

• Published in: Nuclear engineering and design 2019-01, Vol.341, p.209-219
• Main Authors: Ju, Heejae, Choi, Sungyeol, Hwang, Il-Soon
• Format: Article
• Language: English
• Subjects: Boreholes; Drilling; Exploratory drilling; Geological repository; Geology; Human wastes; Inadvertent human intrusion; Independent variables; Intrusion; Low frequencies; Markov analysis; Markov chain; Markov chains; Mathematical models; Natural gas exploration; Nuclear engineering; Nuclear fuels; Oil and gas exploration; Oil exploration; Probabilistic risk assessments; Radioactive waste; Radioactive wastes; Reduction; Repositories; Resource exploration; Risk factors; Risk reduction; Time dependence
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2018.11.009

•Assess Frequency and risk of human intrusion into a geological repository.•Consider a time-dependent drilling probability in a new model for resource exploration.•Human intrusion becomes vigorous for demands of resource explorations in the long-term.•Human intrusion is mitigated by enforcement of regulation and continuous knowledge during early time.•Reduced average radiotoxicity is effective to diminish the risk than reduced volume. Inadvertent human intrusion into a geological repository for radioactive waste is an incident of low frequency but high consequence. Until now, many studies have considered the frequency of deep borehole drilling for resource explorations in the site of the repository as a time-independent variable. However, future activities and technology of the human race will not be the same as today. Therefore, this study develops a new Markov chain model to estimate the frequency of human intrusion using time-dependent drilling frequencies based on the statistics of oil and gas exploration worldwide. The results showed that the frequency of human intrusion during the early time period is substantially reduced. After a few hundred years, the frequency steadily increases and approaches the value of the time-independent model. The low frequency during the early time period is attributed to enforcement of regulation, continuous knowledge of repository, and low utility of repository area. As these effects disappear, the frequency rapidly increases due to the future demand of resource exploration, which is a significant factor in increasing the risk of human intrusion. In addition, the reduction of average radiotoxicity in final waste is effective in reducing the risk, while the reduction of waste volume is insignificant for the frequency of human intrusion in the long-term.