Statement of Problem: The
Japanese High-Level Radioactive Waste Disposal program is presently
evaluating several sites for a potential deep geologic repository.
Performance assessments are used to support feasibility analyses. CNWRA®
has been conducting a research and development program for IHI to
support technology transfer in performance and risk assessment. The
overall goal is to assist IHI to become a contending organization in
areas related to repository construction and operation in Japan.
Approach and Accomplishments:
A model for diffusive transport in buffer material was developed to
evaluate the relevance of processes such as retardation and
precipitation to delay radionuclide release to the geosphere. A clay
material that expands when wet, bentonite, may be used as buffer
material to enclose waste packages, drive the system towards anoxic
conditions, and delay the release of radionuclides to the geosphere in
case of waste package failure. The buffer material could delay release
of radioactive contaminants by thousands of years.
CNWRA® developed performance assessment
models of a hypothetical repository concept to estimate dose
consequences to a critical group. The models account for source terms,
diffusive transport of radionuclides in buffer material, and advective-dispersive transport in the geosphere. An exposure model was
developed considering diverse pathways (e.g., ingestion, inhalation,
direct exposure) to estimate doses resulting from release of radioactive
material into surface waters. The models considered transport models
developed for the potential repository at Yucca Mountain. A stochastic
performance assessment model was constructed in GoldSim® (commercial
software for stochastic and dynamic modeling) to account for uncertainty
and variability in the contaminant release and transport processes. The GoldSim performance assessment model was presented at an international
conference on the nuclear fuel cycle in Japan.
Client Benefits: CNWRA® has
promoted transfer of corporate expertise in the development and
interpretation of complex stochastic performance assessment models to
support client interest in active involvement in development of a
repository system in Japan.
Hypothetical Repository Concept