Publications

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For the U.S. Nuclear Regulatory Commission (NRC) Extremely Low Probability of Rupture (xLPR) pilot study, Sandia National Laboratories (SNL) was tasked to develop and evaluate a probabilistic framework using a commercial software package for Version 1.0 of the xLPR Code. Version 1.0 of the xLPR code is focused assessing the probability of rupture due to primary water stress corrosion cracking in dissimilar metal welds in pressurizer surge nozzles. Future versions of this framework will expand the capabilities to other cracking mechanisms, and other piping systems for both pressurized water reactors and boiling water reactors. The goal of the pilot study project is to plan the xLPR framework transition from Version 1.0 to Version 2.0; hence the initial Version 1.0 framework and code development will be used to define the requirements for Version 2.0. The software documented in this report has been developed and tested solely for this purpose. This framework and demonstration problem will be used to evaluate the commercial software's capabilities and applicability for use in creating the final version of the xLPR framework. This report details the design, system requirements, and the steps necessary to use the commercial-code based xLPR framework developed by SNL.

Sandia National Laboratories (SNL) participated in a Pilot Study to examine the process and requirements to create a software system to assess the extremely low probability of pipe rupture (xLPR) in nuclear power plants. This project was tasked to develop a prototype xLPR model leveraging existing fracture mechanics models and codes coupled with a commercial software framework to determine the framework, model, and architecture requirements appropriate for building a modular-based code. The xLPR pilot study was conducted to demonstrate the feasibility of the proposed developmental process and framework for a probabilistic code to address degradation mechanisms in piping system safety assessments. The pilot study includes a demonstration problem to assess the probability of rupture of DM pressurizer surge nozzle welds degraded by primary water stress-corrosion cracking (PWSCC). The pilot study was designed to define and develop the framework and model; then construct a prototype software system based on the proposed model. The second phase of the project will be a longer term program and code development effort focusing on the generic, primary piping integrity issues (xLPR code). The results and recommendations presented in this report will be used to help the U.S. Nuclear Regulatory Commission (NRC) define the requirements for the longer term program.

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We present a model to evaluate the water mass balance inside a breached waste package in Yucca Mountain (YM) repository environments. The amount of water as liquid or vapor that can accumulate inside or percolate through the package in the emplacement drift is modeled as a function of the temperature and relative humidity (RH) near the waste package, the dripping rate of water from seepage, the area of failure patches on the waste package, and the extent of waste degradation. The water activity inside the waste package is assumed to be determined by both matric and osmotic potentials in the porous waste degradation products that also includes hygroscopic salts. We implemented the model and conducted a set of Monte Carlo simulations to gain insight into the variability and uncertainty associated with model predictions. The model shows that water vapor diffusion can be as important as the advective seepage flow. In addition, chemical reactions during waste degradation can consume a significant fraction of water accumulated in the waste package.

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A total system performance assessment (TSPA) model has been developed to analyze the ability of the natural and engineered barriers of the Yucca Mountain repository to isolate nuclear waste over the period following repository closure. The principal features of the engineered barrier system are emplacement tunnels (or "drifts") containing a two-layer waste package (WP) for waste containment and a titanium drip shield to protect the WP from seeping water and falling rock. The 25-mm-thick outer shell of the WP is composed of Alloy 22, a highly corrosion-resistant nickel-based alloy. There are five nominal degradation modes of the Alloy 22: general corrosion, microbially influenced corrosion, stress corrosion cracking, early failure due to manufacturing defects, and localized corrosion (LC). This paper specifically examines the incorporation of the Alloy 22 LC model into the Yucca Mountain TSPA model, particularly the abstraction and modeling methodology, as well as issues dealing with scaling, spatial variability, uncertainty, and coupling to other submodels that are part of the total system model, such as the submodel for seepage water chemistry.

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Sandia National Laboratories (Sandia), a U.S. Department of Energy National Laboratory, has over 30 years experience in the assessment of radioactive waste disposal and at the time of this publication is providing assistance internationally in a number of areas relevant to the safety assessment of radioactive waste disposal systems. In cooperation with the Republic of Taiwan's Institute of Nuclear Engineering and Research (INER), Sandia National Laboratories (SNL) has developed software that provides an interface between a deterministic far field mass transport code and GoldSim (a commercial software used to conduct Monte Carlo analyses). The SNL developed software enables INER to perform probabilistic simulations for safety analysis and performance assessment of geologic disposal of commercial spent nuclear fuel. The following report details the software design, the steps necessary to use the software, and presents an example application of the paradigm of coupling deterministic codes to a contemporary probabilistic software application.

Sandia National Laboratories (Sandia), a U.S. Department of Energy National Laboratory, has over 30 years experience in the assessment of radioactive waste disposal, and at the time of this publication is providing assistance internationally in a number of areas relevant to the safety assessment of radioactive waste disposal systems. In cooperation with the Republic of Taiwan’s Institute of Nuclear Engineering and Research (INER), Sandia National Laboratories (SNL) has developed software that provides an interface between a deterministic mass transport code and GoldSim™ (a commercial software used to conduct Monte Carlo analyses). The SNL-developed software enables INER to perform probabilistic simulations for safety analysis and performance assessment of geologic disposal of commercial spent nuclear fuel. This report details the software design, the steps necessary to use the software, and presents an example application of the paradigm of coupling deterministic codes to a contemporary probabilistic software application.