Alternate Source Term Models for Yucca Mountain Performance Assessment Based on Natural Analog Data and Secondary Mineral Solubility

1999 ◽  
Vol 556 ◽  
Author(s):  
William M. Murphy ◽  
Richard B. Codell
Keyword(s):  
Performance Assessment ◽  
Release Rate ◽  
Source Term ◽  
Yucca Mountain ◽  
Solution Chemistry ◽  
Base Case ◽  
Total System ◽  
Spent Fuel ◽  
Natural Analog ◽  
Mineral Solubility

AbstractPerformance assessment calculations for the proposed high level radioactive waste repository at Yucca Mountain, Nevada, were conducted using the Nuclear Regulatory Commission Total-System Performance Assessment (TPA 3.2) code to test conceptual models and parameter values for the source term based on data from the Peña Blanca, Mexico, natural analog site and based on a model for coprecipitation and solubility of secondary schoepite. In previous studies the value for the maximum constant oxidative alteration rate of uraninite at the Nopal I uranium body at Peña Blanca was estimated. Scaling this rate to the mass of uranium for the proposed Yucca Mountain repository yields an oxidative alteration rate of 22 kg yr−1, which was assumed to be an upper limit on the release rate from the proposed repository. A second model was developed assuming releases of radionuclides are based on the solubility of secondary schoepite as a function of temperature and solution chemistry. Releases of uranium are given by the product of uranium concentrations at equilibrium with schoepite and the flow of water through the waste packages. For both models, radionuclides other than uranium and those in the cladding and gap fraction were modeled to be released at a rate proportional to the uranium release rate, with additional elemental solubility limits applied. Performance assessment results using the Peña Blanca oxidation rate and schoepite solubility models for Yucca Mountain were compared to the TPA 3.2 base case model, in which release was based on laboratory studies of spent fuel dissolution, cladding and gap release, and solubility limits. Doses calculated using the release rate based on natural analog data and the schoepite solubility models were smaller than doses generated using the base case model. These results provide a degree of confidence in safety predictions using the base case model and an indication of how conservatism in the base case model may be reduced in future analyses.

Effects of Uncertainty and Spatial Variability on Seepage Into Drifts in the Yucca Mountain Total System Performance Assessment Model

2001 ◽  
Author(s):  
Donald A. Kalinich ◽  
Michael L. Wilson
Keyword(s):  
Spatial Variability ◽  
Performance Assessment ◽  
System Performance ◽  
Seepage Flow ◽  
Yucca Mountain ◽  
Assessment Model ◽  
Base Case ◽  
Total System ◽  
Performance Uncertainty

Abstract Seepage into the repository drifts is an important factor in total-system performance. Uncertainty and spatial variability are considered in the seepage calculations. The base-case results show 13.6% of the waste packages (WPs) have seepage. For 5th percentile uncertainty, 4.5% of the WPs have seepage and the seepage flow decreased by a factor of 2. For 95th percentile uncertainty, 21.5% of the WPs have seepage and the seepage flow increased by a factor of 2. When seepage was forced on 100% of the WPs the seepage flow increased by a factor of 3.

Identification of Secondary Phases Formed During Unsaturated Reaction of UO2 with EJ-13 Water

1989 ◽  
Vol 176 ◽  
Author(s):  
J. K. Bates ◽  
B. S. Tani ◽  
E. Veleckis ◽  
O. J. Wronklewicz
Keyword(s):  
Phase Formation ◽  
Secondary Phase ◽  
Yucca Mountain ◽  
Solution Chemistry ◽  
Spent Fuel ◽  
Secondary Phases ◽  
Secondary Phase Formation

ABSTRACTA set of experiments, wherein UO2 has been contacted by dripping water, has been conducted over a period of 182.5 weeks. The experiments are being conducted to develop procedures to study spent fuel reaction under unsaturated conditions that are expected to exist over the lifetime of the proposed Yucca Mountain repository site. One half of the experiments have been terminated, while one half are ongoing. Analyses of solutions that have dripped from the reacted UO2 have been performed for all experiments, while reacted UO2 surfaces have been examined for the terminated experiments. A pulse of uranium release from the UO2 solid, combined with the formation of schoepite on the surface of the UO2, was observed between 39 and 96 weeks of reaction. Thereafter, the uranium release decreased and a second set of secondary phases was observed. The latter phases incorporated cations from the EJ-13 water and include boltwoodite, uranophane, sklodowskite, compreignacite, and schoepite. The experiments are continuing to monitor whether additional changes in solution chemistry or secondary phase formation occurs.

Proceeding Toward a License Application for U.S. Nuclear Waste Repository: Total System Performance Assessment Approach

2003 ◽  
Author(s):  
Jerry McNeish ◽  
Peter Swift ◽  
Rob Howard ◽  
David Sevougian ◽  
Donald Kalinich ◽  
...  
Keyword(s):  
Performance Assessment ◽  
System Performance ◽  
Nuclear Regulatory Commission ◽  
The United States ◽  
Yucca Mountain ◽  
Nuclear Waste Repository ◽  
Total System ◽  
License Application ◽  
Regulatory Commission ◽  
The U.S

The development of a deep geologic repository system in the United States has progressed to the preparation of an application for a license from the U.S. Nuclear Regulatory Commission. The project received site recommendation approval from the U.S. President in early 2002. The next phase of the project involves development of the license application (LA) utilizing the vast body of information accumulated in study of the site at Yucca Mountain, Nevada. Development of the license application involves analyses of the total system performance assessment (TSPA) of the repository, the TSPA-LA. The TSPA includes the available relevant information and model analyses from the various components of the system (e.g., unsaturated geologic zone, engineered system (waste packaging and drift design), and saturated geologic zone) (see Fig. 1 for nominal condition components), and unites that information into a single computer model used for evaluating the potential future performance or degradation of the repository system. The primary regulatory guidance for the repository system is found in 10 CFR 63, which indicates the acceptable risk to future populations from the repository system. The performance analysis must be traceable and transparent, with a defensible basis. The TSPA-LA is being developed utilizing state-of-the-art modeling software and visualization techniques, building on a decade of experience with such analyses. The documentation of the model and the analyses will be developed with transparency and traceability concepts to provide an integrated package for reviewers. The analysis relies on 1000’s of pages of supporting information, and multiple software and process model analyses. The computational environment represents the significant advances in the last 10 years in computer workstations. The overall approach will provide a thorough, transparent compliance analysis for consideration by the U.S. Nuclear Regulatory Commission in evaluating the Yucca Mountain repository.

scholarly journals Derivation of a Waste Package Source Term for NNWSI from the Results of Laboratory Experiments

1985 ◽  
Vol 50 ◽  
Author(s):  
Virginia M. Oversby ◽  
Charles N. Wilson
Keyword(s):  
Laboratory Experiments ◽  
Source Term ◽  
Yucca Mountain ◽  
Maximum Amount ◽  
Well Water ◽  
Pressurized Water Reactor ◽  
Spent Fuel ◽  
Pressurized Water ◽  
J 13 ◽  
Fractional Release

AbstractResults are presented for the dissolution of Turkey Point pressurized water reactor (PWR) spent fuel in J-13 well water at ambient hot cell temperatures. These results are compared with those previously obtained on Turkey Point fuel in deionized water, on H. B. Robinson PWR fuel in J-13 water, and by other workers using various fuels in dilute bicarbonate groundwaters. A model is presented that represents the conditions under which maximum dissolution of spent fuel could occur in a repository sited at Yucca Mountain, Nevada. Using an experimentally determined upper limit of 5 mg/l for uranium solubility in J-13 water, a fractional release rate of 6.4 × 10−8 per year is obtained by assuming that all water entering the repository carries away the maximum amount of uranium.

scholarly journals Total-System Performance Assessment for the Yucca Mountain Site

2002 ◽  
Vol 713 ◽  
Author(s):  
Michael L. Wilson ◽  
Peter N. Swift ◽  
Jerry A. McNeish ◽  
S. David Sevougian
Keyword(s):  
Performance Assessment ◽  
System Performance ◽  
Safety Assessment ◽  
Yucca Mountain ◽  
Total System ◽  
Package Design ◽  
Waste Package ◽  
Igneous Activity ◽  
Nominal Performance ◽  
High Level

ABSTRACTYucca Mountain, Nevada, is under consideration as a potential site for a repository for high-level radioactive waste. Total-system performance-assessment simulations are performed to evaluate the safety of the site. Features, events, and processes have been systematically evaluated to determine which ones are significant to the safety assessment. Computer models of the disposal system have been developed within a probabilistic framework, including both engineered and natural components. Selected results are presented for three different total-system simulations, and the behavior of the disposal system is discussed. The results show that risk is dominated by igneous activity at early times, because the robust waste-package design prevents significant nominal (non-disruptive) releases for tens of thousands of years or longer. The uncertainty in the nominal performance is dominated by uncertainties related to waste-package corrosion at early times and by uncertainties in the natural system, most significantly infiltration, at late times.

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