Reset of U.S. Nuclear Waste Management Strategy and Policy
Meeting #4: Integration of Storage, Transportation and Disposal of
Commercial Spent Nuclear Fuel
May 17-18, 2016, George Washington University, Washington, DC
Spent nuclear fuel must be managed from the time it is removed from the reactor to its eventual reprocessing or permanent disposal in a geologic repository. The present management strategy for commercial spent fuel in the United States is not what was originally envisioned, even as recently as a decade ago.
The inventory of commercial spent nuclear fuel in in the U.S. is growing at a rate of ~2,000 metric tons per year, and is projected to be ~140,000 metric tons by mid-century, which is the earliest time that current Administration policy projects the availability of a permanent geologic repository. Without options for off-site storage or disposal and with no prospects for reprocessing, utilities have expanded their capacity to store the growing spent fuel inventory at existing reactor sites, choosing without exception to rely on large dry-storage casks. These casks are characterized as “dual purpose” systems, in that the sealed canisters are designed for both extended on-site storage and, with appropriate over-packs, subsequent transportation. The dual-purpose canisters are not, however, designed for disposal, and they are significantly larger than the disposal canisters planned for all repository concepts currently proposed world-wide.
Current Practice and Technical, Operational, and Institutional Concerns
The current practice of loading commercial spent fuel into dry storage systems carries with it an unavoidable commitment to one of three future alternatives:
a) all spent fuel placed in large dual-purpose canisters will eventually need to be repackaged into purpose-built casks for disposal,
b) the nation will need to construct one or more repositories that can directly accommodate large dual-purpose canisters for disposal, or
c) spent fuel will remain indefinitely at interim storage facilities and be repackaged as needed, perhaps every century.
Suboptimal alternatives will lead to increased uncertainties.
All of these options are technically feasible, but none are what was originally planned, and all introduce major new uncertainties regarding the design and operation of future storage and disposal facilities. These uncertainties will impact already large and uncertain future costs: for example, as part of its 2013 assessment of the adequacy of the Nuclear Waste Fee to meet total disposal costs, the DOE estimated a range for $24 billion to $81 billion (2012 dollars) for future repository costs, not including costs associated with repackaging spent fuel.
Industry continues to load larger and heavier canisters, which pose logistical challenges.
The dual purpose storage canisters themselves are large: up to 2 meters in diameter and 5 meters in length, and the largest currently in use accommodate up to 37 intact fuel assemblies from pressurized water reactors, which account for about two thirds of the U.S. reactor fleet. A loaded canister may weigh on the order of 70 metric tons, and transportation shielding may increase the weight to 150 metric tons. Because it is economically advantageous for nuclear power plants to load larger canisters, the canister size exceeds sizes and weights that may be optimal for transportation and subsequent disposal. Engineering solutions for hoist, ramp, and transporter operations appear to be feasible, but need to be accounted for in planning.
Larger canisters will be hotter for longer and therefore may require a longer time to cool before transportation and subsequent disposal.
Although dual purpose canisters are certified by the Nuclear Regulatory Commission for both storage and subsequent transportation, the certificates of compliance set different temperature limits for storage versus transportation. This results in a situation where some canisters may need to cool before they can be transported. This delay may be on the order of decades for some canister designs, and in particular for higher-burnup fuels that generate more heat.
With respect to disposal, different geologies impose different temperature constraints on the underground environment. For example, some repository designs have assumed that the maximum temperature in clay backfill must remain below 100˚C, while salt may accommodate temperatures up to 200 to 250˚C. High thermal loads may be accommodated by cooling canisters above ground for many years, ventilating the repository for many years after waste emplacement, or increasing the spacing between canisters. These choices will affect repository costs.
Consolidated Interim Storage is an option.
Constructing consolidated interim storage facilities has the potential to alleviate storage concerns at reactor sites and may provide a path to resolution of legal issues associated with federal responsibility for spent fuel management. Consolidated storage facilities could also be used to provide flexibility in repackaging options for ultimate disposal. Consolidated storage facilities will introduce additional cost and siting concerns, and technical issues associated with the mechanical effects of repeated transportation and storage will need to be addressed.
Legislative and regulatory issues must be addressed.
All options for the management and disposal of commercial spent nuclear fuel currently under consideration in the U.S. will require legislative and regulatory actions.
Questions to be addressed:
- What might a better-integrated spent fuel management system for the United States look like?
- What metrics (e.g., cost, safety, and security) should be used to judge the optimization of the spent fuel management system?
- What are the barriers to achieving the integration of the spent fuel management system?
- What are the potential benefits of an integrated spent fuel management system?
- What actions could be taken now that would have an impact on future spent nuclear fuel management practice?
- What are the implications of taking no action?
Reset Conference Documents for meeting no. 4 can be accessed through this link.
For information related to the first meeting in this series, and relevant materials, please click here.
For information related to the second meeting in this series, and relevant materials, please click here.
For information related to the third meeting in this series, and relevant materials, please click here.