Integrated waste management system and tools for SNF management

Commercial SNF at reactor sites and independent spent fuel storage installations amounted to approximately 91,000 metric tons of heavy metal as of the end of 2022. The U.S. Department of Energy is responsible for siting, building, and operating a deep geological repository for the ultimate disposal of SNF and the high-level waste (HLW) generated from reprocessing some of that SNF. The Office of Spent Fuel and High-Level Waste Disposition within DOE’s Office of Nuclear Energy, which is tasked with fulfilling this mission, is planning for the transportation, interim storage, and ultimate disposal of SNF and HLW.

Fig. 1. The systems that make up the IWMS and their interdependencies.

These three broad pillars—transportation, storage, and disposal—and their interdependencies are collectively referred to as the Integrated Waste Management System (IWMS). Each pillar has its own processes and steps that together work toward the common goal of managing SNF. The IWMS can be thought of as a collection of systems; it includes reactor site storage systems (wet and dry storage) in terms of modeling, transportation systems (rail, barge, and heavy-haul trucks), federal consolidated interim storage facilities (CISFs), and the disposal system (see Fig. 1).

To inform decision makers tasked with evaluating the IWMS, the DOE’s Office of Storage and Transportation (within the Office of Spent Fuel and High-Level Waste Disposition) is developing several SNF management tools, including the Stakeholder Tool for Assessing Radioactive Transportation (START), the Unified Database (UDB), the Next Generation System Analysis Model (NGSAM), and STANDARDS (formerly known as UNF-ST&DARDS), among other tools. The tools broadly cover spent fuel transportation; back-end systems engineering; data storage and management; and SNF analysis from dose, thermal, and criticality standpoints. These tools represent a national capability for the successful long-term management of SNF in the United States. Development efforts for these tools are supported by several national labs, including Argonne, Idaho, Oak Ridge, Pacific Northwest, Sandia, and Savannah River National Laboratories.

Stakeholder tool

START is a web-based geospatial decision-support tool that uses the ArcGIS server to create routes between origin and destination sites. Development for the START tool is being led by PNNL and is supported by 3 Sigma Consulting LLC. The process starts by the user selecting an origin site, which can include facilities like nuclear reactors, research reactors at universities, and DOE installations. The destination can include any of these facilities, as well as other user-defined points on the map (provided a transportation route exists to that point). This tool is akin to Google or Apple maps and is fine-tuned to address SNF routing and transportation needs. The user defines the preferred mode of transportation—rail, barge, heavy-haul trucks, or a combination thereof—then selects the routing criteria, including factors such as minimum distance, minimum time, or minimum population. Users can also define a weighted routing logic using the three criteria. A buffer distance of either 800 or 2,500 meters is then selected. Buffer distance is subtended around a START-generated route. The user can then choose to enter preferred and prohibited carriers, identify additional stops along the routes, and define barriers to prevent routes from being created in specific locations.

Fig. 2. Sample START routes from various origin sites (green balloons) to a hypothetical destination site (red balloon) at the geographical center of the United States. Note: Routes are for illustrative purposes only and do not represent planned SNF/HLW transport routes.

START initially provides the user with a preliminary set of results that include distance, travel time, number of railroad intersections, tunnel crossings, and incident-free dose along the route. The tool also provides additional results, such as population, population density, tribal lands, environmentally sensitive areas, number of local law enforcement agencies, fire stations, educational institutes, correctional facilities, and hospitals along the route buffer zone (see Fig. 2).

The START team periodically releases new versions of the tool with enhanced performance and new features. A verification and validation process ensures the new releases produce expected results and that the tool functions as intended.

Unified database

The UDB, which is maintained by PNNL, stores the necessary information required for SNF analyses. It serves as a robust and streamlined tool for integration with other safety or systems analysis tools (such as STANDARDS and NGSAM). In addition to data, references are stored for each value in the UDB, making it easy to find the documents containing the original values.

A large portion of UDB data comes from the Nuclear Fuel Data Survey (Form GC-859), which utilities use to report assembly-level SNF data to the DOE’s Office of Standard Contract Management. This data is then curated and imported into the UDB. To improve efficiency and to streamline the process, utilities can directly upload their GC-859 data using a web-based application. Any errors in data uploaded by the utilities are flagged in real time and can be corrected before the data is exported to the UDB.

The data stored in the UDB consists of eight attributes: dry cask, assembly, economic, transportation infrastructure, facility features, federal government, site, and calculated attributes. Each contains additional data, such as cask dimensions, average assembly discharge burnup, mode of transportation at each facility, and so forth. In essence, the UDB acts like a central data lake of all information needed to perform various types of SNF analyses.

Next generation model

Fig. 3. Landing page of the NGSAM tool site.

NGSAM is an agent-based simulation toolkit used to study “what if” scenarios in the back end of the nuclear fuel cycle. This tool can analyze several SNF and HLW management scenarios at a system level, covering the entire U.S. nuclear fleet. Argonne leads the NGSAM development efforts. NGSAM is based on the process analysis tool used by the Department of Defense and the Federal Emergency Management Agency for system-level logistical modeling (Fig. 3).

Analysts use NGSAM to accomplish tasks such as gathering cost and timeline information for a scenario and studying the impacts of various waste management options. On the back end of the fuel cycle, the analyst can modify multiple options, including the number of casks shipped per year, shipping sequence logic, shipping start year, number of CISFs, operational hours per day at a facility, transportation infrastructure availability (casks, railcars), emplacement capacity at a deep geological repository, and so forth.

This flexibility gives the analyst freedom to model different IWMS architectures and scenarios and understand their implications. NGSAM uses several data sources: cask and fuel-related information imported from the UDB, START-generated transportation routing information, and scenario-specific information provided by the analyst. Systems analysts can run the NGSAM tool on their personal desktop computer or on Argonne’s server, which has 14 nodes and allows for 14 NGSAM scenarios to be run simultaneously.

NGSAM can model SNF at an assembly level for reactor sites in the United States. It tracks assemblies between their discharge from a reactor site to their placement in a repository. It also models intermediate steps, including storage (wet and dry), transportation and repackaging (if required by the scenario). NGSAM makes assembly level data—including storage of assemblies in an SFP, transfer of assemblies from an SFP to a storage cask, and transportation of the cask on a railcar—available to analysts as they move through the IWMS. Information of interest could include total metric tons of heavy metal or number of assemblies stored in dry storage per year, thermal heat limit of casks, CISF inventory, railcar miles per campaign, and more.

STANDARDS

STANDARDS is an integrated SNF analysis tool with a scope that goes from SNF discharge in a reactor to ultimate SNF disposition, providing an end-to-end solution for SNF analysis. The tool allows analysts to support design-, safety-, and licensing-related activities of spent fuel systems and facilities. ORNL and PNNL are involved in STANDARDS development efforts. STANDARDS includes automation that enables the temporal characterization of discharge inventory from a criticality, thermal, and dose standpoint. These capabilities extend to cask-specific, as-loaded safety analysis and results visualization. The tool can also incorporate user-specific data, giving the analyst additional flexibility. STANDARDS integrates with the UDB for its data needs and with the SCALE code suite for performing calculations.

Some of the nuclear safety analyses provided by STANDARDS include depletion and decay heat calculations, criticality estimations, cladding and surface temperature calculations of as-loaded casks, and radiation dose maps outside the as-loaded casks. These calculations are performed by various SCALE modules, and when basic information about the SNF and cask types is made available, it generates input files, eliminating the need for the analyst to individually develop them.

Potential applications of STANDARDS include the following:

Decay heat management in an SFP.

Identifying assemblies in an SFP for cask loading (dry storage).

Informing an aging management plan.

Source term calculations and dose estimations.

Designing and licensing a federal CISF.

Transportation and final disposition planning.

SNF management tools

START and the UDB provide critical information to analysis tools like STANDARDS and NGSAM, which are used to gain an in-depth understanding of the IWMS in support of the DOE’s SNF disposition strategy. One of the program’s key priorities is the siting, construction, and operation of one or more federal CISFs using a consent-based siting process. The federal CISF project aims to consolidate commercial SNF from reactor sites across the nation to a central location. In May 2024, the DOE approved the mission need statement (Critical Decision 0, or CD-0) for a federal CISF. The next stage is the approval of alternative selection and cost range, sometimes referred to as Critical Decision-1 (CD-1), which requires several technical assessments. Potential analyses using these IWMS tools in support of CD-1 and other future needs could include the following:

Estimating the size of a CISF to meet U.S. Nuclear Regulatory Commission annual dose limits (10 CFR 72.104).

Calculating the cost and time profiles to clear reactor sites.

Estimating the rail infrastructure required to complete a transportation campaign.

Exploring the feasibility of casks and loading profiles from a transportation standpoint.

Developing environmental impact statements.

Planning for transportation campaign and stakeholder engagement.

The IWMS assessment tools discussed above are a crucial component for SNF analysis and management. The tools are constantly updated via new data, integration, improved user experience, and new functionalities to meet stakeholders’ and the program’s evolving needs. They represent a national capability with long-term significance for SNF inventory management. Given that demand for electricity generated by nuclear power is expected to increase in coming decades, maintaining and improving SNF management tools will be a key component of safely leveraging nuclear power’s potential.

Harish Gadey, Robert Joseph, and Gordon Petersen work in spent fuel analysis at Idaho National Laboratory.

Authors’ note
This is a technical paper that does not take into account contractual limitations or obligations under the Standard Contract for Disposal of Spent Nuclear Fuel and/or High-Level Radioactive Waste (Standard Contract) (10 CFR Part 961). To the extent discussions or recommendations in this presentation conflict with the provisions of the Standard Contract, the Standard Contract governs the obligations of the parties, and this paper in no manner supersedes, overrides, or amends the Standard Contract. This paper reflects technical work which could support future decision making by the Department of Energy. No inferences should be drawn from this paper regarding future actions by the DOE, which are limited both by the terms of the Standard Contract and congressional appropriations for the Department to fulfill its obligations under the Nuclear Waste Policy Act, including licensing and construction of a spent nuclear fuel repository.

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