Probabilistic assessment of volcanic hazard to radioactive waste repositories in Japan: Intersection by a dike from a nearby composite volcano

Geologic hazards such as volcanism must be assessed when evaluating potenti al sites for the geologic disposal of high-level radioactive waste. The Jap anese islands comprise one of the more volcanically active regions on Earth and the risk of volcanism to a geologic repository is being evaluated as p art of the Japanese high-level radioactive waste-disposal program, One haza rd that is being evaluated as part of volcanic risk assessment is the possi ble intersection of a repository by a dike, if a composite volcano were to form near a repository during the long (100 k.y.) performance period of the repository. In this paper we use the characteristics of a well-exposed rad ial dike system at the Summer Goon volcano in Colorado to define Monte Carl o simulations that estimate the probability of a dike intersection of a rep ository as a function of volcano distance, dike length and density, and rep ository area. The models indicate that the probability of intersection decl ines rapidly as a function of distance from a volcano, as dike density decr eases due to the radial dike geometry. The probability of intersection for a mafic dike set with shorter average length declines more rapidly than tha t of a silicic dike set with longer average length. However, mafic dikes ha ve a higher probability of intersecting a repository close to a volcano (<5 -6 km) because they are more numerous than longer silicic dikes. The probab ility of a silicic dike intersecting a repository is <less than or equal to >10(-2) at distances greater than 15 km from the volcano, decreasing to les s than or equal to 10(-4) at distances greater than 30 km.