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Integrated Radionuclide Transport Model for a High-Level Waste Repository in Water-Saturated Geologic Formations

Joonhong Ahn

Nuclear Technology / Volume 121 / Number 1 / January 1998 / Pages 24-39

Technical Paper / Kiyose Birthday Anniversary /

Presented are results of a mathematical analysis on radionuclide transport in parallel planar fractures in water-saturated geologic formations integrated with the source term model, where precipitation of hardly soluble species at the waste-form alteration location and subsequent radionuclide transport in the engineered barriers are considered. Radioactive decay chains of an arbitrary length are considered. A computer code has been developed based on the analytical solutions.

The major hazard contributors are 241Am and 243Am in the waste form; 239Pu, 229Th, and 243Am at the surface of the engineered barriers; 223Ra, 231Pa, and 227Ac at a 10-m location from the engineered barriers; and 99Tc, 223Ra, and 225Ra at a 100-m location. With a transport distance of 100 m through the natural barrier, a four-orders-of-magnitude reduction in the total hazard is observed.

Thus, the importance of the region in the vicinity of the engineered barriers in the context of the safety assessment can be pointed out. Because the region is disturbed by repository construction, further analysis must be performed by taking into account differing geochemical, hydrological, and mechanical properties from those in the undisturbed host rock.

Because the major contributors in the host rock are the decay daughters of minor actinides, recovery of minor actinides reduces the total hazard evaluated at the exit of the geosphere. However, the radiological hazard would be reduced much more effectively by the 100-m-thick geologic formation around the repository than by even a 99% recovery of the actinides.

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