BEHAVIOR OF C-14 IN WASTE PACKAGES FOR SPENT FUEL IN A TUFF REPOSITORY

Light water reactor spent fuel in the U.S. contains only about 37 MBq of carbon-14 per kg U (1 curie per metric tonne of initial uranium); however, the potential U.S. repository at Yucca Mountain would be located above the water table, where air is present. Temperatures might be intentionally elevated by design in order to drive away water. If waste package containment is breached prior to depletion by radioactive decay, C-14 could be released as (CO2)-C-14 and transported in the gas phase. Since it appears that transport would be rapid relative to radioactive decay, release to the accessible environment would be possible. This paper reviews the evaluation of the inventory of C-14 and what can be projected about its likely behavior. Uncertainties in the containment lifetimes of waste packages, and costs involved in attempting to assure long-term containment, are discussed. Consequences of total release are placed in perspective. An opinion is offered that these consequences are too small to justify the costs of trying to assure that releases would be below the previously prevailing U.S. regulatory limits. The regulations are currently being reconsidered by a committee of the National Academy of Sciences.