This analysis is prepared by the Mined Geologic Disposal System (MGDS) Waste Package Development (WPD) department to provide a probabilistic evaluation of the potential for criticality of fissile material which has been transported from a geologic repository containing breached waste packages of commercial spent nuclear fuel (SNF). This analysis is part of a continuing investigation of the probability of criticality resulting from the emplacement of spent nuclear fuel in a geologic repository.

The purpose of this study is to evaluate dissolved concentration limits (also referred to as solubility limits) of elements with radioactive isotopes under probable repository conditions, based on geochemical modeling calculations using geochemical modeling tools, thermodynamic databases, field measurements, and laboratory experiments.

The Monitored Geologic Repository Waste Package Operations of the Civilian Radioactive Waste Management System Management & Operating Contractor (CRWMS M&O) performed calculations to provide input for disposal of spent nuclear fuel (SNF) from the Navy (Refs. 1 and , 2). The Navy SNF has been considered for disposal at the potential Yucca Mountain site. For some waste packages, the containment may breach (Ref. 3), allowing the influx of water. Water in the waste package may moderate neutrons, increasing the likelihood of a criticality event within the waste package.

The Monitored Geologic Repository (MGR) Waste Package Operations (WPO) of the Civilian Radioactive Waste Management System Management & Operating Contractor (CRWMS M&O) performed calculations to provide input for disposal of spent nuclear fuel (SNF) from the Emico Fermi Atomic Power Plant (Ref. 1). The Fermi fuel has been considered for disposal at the potential Yucca Mountain site.

The purpose of this report is to document and validate the external accumulation model that predicts accumulation of fissile materials in the invert, fractures and lithophysae in the rock beneath a degrading waste package containing spent nuclear fuel (SNF) in the monitored geologic repository at Yucca Mountain. (Lithophysae are hollow, bubblelike structures in the rock composed of concentric shells of finely crystalline alkali feldspar, quartz, and other materials (Bates and Jackson 1984 [DIRS 128109], p.

In this study, the long-term geochemical behavior of waste package (WP), containing Pu-ceramic, was modeled. The ceramic under consideration contains Ti, U, Pu, Gd and Hf in a pyrochlore structure; the Gd and Hf stabilize the mineral structure, but are also intended to provide criticality control. The specific study objectives were to determine:
1) the extent to which criticality control material, suggested for this WP design, will remain in the WP after corrosion/dissolution of the initial package configuration (such that it can be effective in preventing criticality), and

Fuel from the Fast Flux Test Facility ' (FFTF) has been considered for disposal at the proposed

The Disposal Criticality Analysis Methodology Topical Report (Reference 1) states that the accuracy of the criticality analysis methodology (MCNP Monte Carlo code and cross-section data) designated to assess the potential for criticality of various configurations in the Yucca Mountain proposed repository is established by evaluating appropriately selected benchmark critical experiments.

This study is prepared by the Mined Geologic Disposal System (MODS) Waste Package Development Department (WPDD) to provide input to a separate evaluation on the probablility of criticality in the far- field environment. These calculations are performed in sufficient detail to provide conservatively bounding configurations to support separate probabilistic analyses.

The Monitored Geologic Repository Waste Package Operations of the Civilian Radioactive Waste Management System Management & Operating Contractor (CRWMS M&O) performed calculations to provide input for disposal of spent nuclear fuel (SNF) from the Training, Research, Isotopes, General Atomics (TRIGA) reactor (Ref. 1). The TRIGA SNF has been considered for disposal at the potential Yucca Mountain site.

The Monitored Geologic Repository (MGR) Waste Package Department of the Civilian Radioactive Waste Management System Management & Operating contractor (CRWMS M&O) performed calculations to provide input for disposal of spent nuclear fuel (SNF) from the Shippingport Light Water Breeder Reactor (LWBR) (Ref. 1). The Shippingport LWBR SNF has been considered for disposal at the potential Yucca Mountain site.

This report presents a two-phased approach to develop and analyze a “thermal envelope” to represent the postclosure response of the repository to the anticipated range of repository design thermal loadings. In Phase 1 an estimated limiting waste stream (ELWS) is identified and analyzed to determine the extremes of average and local thermal loading conditions. The coldest thermal loading condition is represented by an emplacement drift loaded exclusively with high-level radioactive waste (HLW) and/or defense spent nuclear fuel (DSNF).

This report is developed from Technical Work Plan for: Thermodynamic Databases for Chemical Modeling (BSC 2006 [DIRS 177885]). The purpose of this analysis report is to update the thermochemical database data0.ymp.R4 (Output DTN: SN0410T0510404.002). Various data have been added, corrected, or corroborated, partly in response to four Condition Reports (CRs): CR 6489, CR 6731, CR 7542, and CR 7756. The most notable changes are a general revision of phosphate data to achieve consistency with the recommendations from the Committee on Data for Science and Technology (CODATA) (Cox. et al.

This report documents the development and validation of the in-drift precipitates/salts (IDPS) process model. The IDPS process model is a geochemical model designed to predict the postclosure effects of evaporation and deliquescence on the chemical composition of water within the Engineered Barrier System (EBS) in support of the total system performance assessment (TSPA). Application of the model in support of TSPA is documented in Engineered Barrier System: Physical and Chemical Environment (BSC 2005 [DIRS 175083]).

The purpose of this model report is to describe the evolution of the physical and chemical environmental conditions within the waste emplacement drifts of the repository, including the drip shield and waste package surfaces. This report documents the development of a new process-level model, the near-field chemistry (NFC) model, and develops two abstraction models.

This report presents the analyses and results for the potential occurrence of external criticality events which could result from plutonium waste forms emplaced in a geologic repository similar to the one being developed at Yucca Mountain. The analyses evaluate both the MOX spent fuel and the immobilized plutonium waste forms in a repository if the waste package has degraded and if the fissile material has migrated to the invert and out into the far-field.