Publications

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This document records the Proceedings of the 2017 gathering of salt repository nations. In a spirit of mutual support, technical issues are dissected, led capably by subject matter experts. As before, it is not possible to explore all contemporary issues regarding nuclear waste disposal in salt formations. Instead, the group focused on a few selected issues to be pursued in depth, while at the same time acknowledging and recording ancillary issues.

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The Waste Isolation Pilot Plant (WIPP) disposal operations currently employ two different disposal methods: one for Contact Handled (CH) waste and another for Remote Handled (RH) waste. CH waste is emplaced in a variety of payload container configurations on the floor of each disposal room. In contrast, RH waste is packaged into a single type of canister and emplaced in pre-drilled holes in the walls of disposal rooms. Emplacement of the RH waste in the walls must proceed in advance of CH waste emplacement and therefore poses logistical constraints, in addition to the loss of valuable disposal capacity. To improve operational efficiency and disposal capacity, the Department of Energy (DOE) has proposed a shielded container for certain RH waste streams. RH waste with relatively low gammaemitting activity would be packaged in lead-lined containers, shipped to WIPP in existing certified transportation packages for CH waste and emplaced in WIPP among the stacks of CH waste containers on the floor of a disposal room. RH waste with high gamma-emitting activity would continue to be emplaced in the boreholes along the walls. The new RH container is similar to the nominal 208-liter (55-gallon) drum, however it includes about 2.5 cm (1 in) of lead, sandwiched between thick steel sheets. Furthermore, the top and bottom are made of thick plate steel to strengthening the package to meet transportation requirements. This robust configuration provides an overpack for materials that otherwise would be RH waste. This paper describes the container and the regulatory approach used to meet the requirements imposed by regulations that apply to WIPP. This includes a Performance Assessment used to evaluate WIPP's long-term performance and the DOE's approach to gain approval for the transportation of shielded containers. This paper also describes estimates of the DOE's RH transuranic waste inventory that may be packaged and emplaced in shielded containers. Finally, the paper includes a discussion of how the DOE proposes to track the waste packaged into shielded containers against the RH waste inventory and how this will comply with the regulated volume.

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This LDRD project has produced a tool that makes probabilistic risk assessments (PRAs) of nuclear reactors - analyses which are very resource intensive - more efficient. PRAs of nuclear reactors are being increasingly relied on by the United States Nuclear Regulatory Commission (U.S.N.R.C.) for licensing decisions for current and advanced reactors. Yet, PRAs are produced much as they were 20 years ago. The work here applied a modern systems analysis technique to the accident progression analysis portion of the PRA; the technique was a system-independent multi-task computer driver routine. Initially, the objective of the work was to fuse the accident progression event tree (APET) portion of a PRA to the dynamic system doctor (DSD) created by Ohio State University. Instead, during the initial efforts, it was found that the DSD could be linked directly to a detailed accident progression phenomenological simulation code - the type on which APET construction and analysis relies, albeit indirectly - and thereby directly create and analyze the APET. The expanded DSD computational architecture and infrastructure that was created during this effort is called ADAPT (Analysis of Dynamic Accident Progression Trees). ADAPT is a system software infrastructure that supports execution and analysis of multiple dynamic event-tree simulations on distributed environments. A simulator abstraction layer was developed, and a generic driver was implemented for executing simulators on a distributed environment. As a demonstration of the use of the methodological tool, ADAPT was applied to quantify the likelihood of competing accident progression pathways occurring for a particular accident scenario in a particular reactor type using MELCOR, an integrated severe accident analysis code developed at Sandia. (ADAPT was intentionally created with flexibility, however, and is not limited to interacting with only one code. With minor coding changes to input files, ADAPT can be linked to other such codes.) The results of this demonstration indicate that the approach can significantly reduce the resources required for Level 2 PRAs. From the phenomenological viewpoint, ADAPT can also treat the associated epistemic and aleatory uncertainties. This methodology can also be used for analyses of other complex systems. Any complex system can be analyzed using ADAPT if the workings of that system can be displayed as an event tree, there is a computer code that simulates how those events could progress, and that simulator code has switches to turn on and off system events, phenomena, etc. Using and applying ADAPT to particular problems is not human independent. While the human resources for the creation and analysis of the accident progression are significantly decreased, knowledgeable analysts are still necessary for a given project to apply ADAPT successfully. This research and development effort has met its original goals and then exceeded them.

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