Geochemistry Model Validation Report: External Accumulation Model

Technical Report · Thu Sep 27 04:00:00 EDT 2001

DOI:https://doi.org/10.2172/837044· OSTI ID:837044

Zarrabi, Kaveh ^[1]; Nicot, Jean-Philippe ^[1]; Stockman, Harlan ^[1]; LeStrange, Susan ^[1]

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1. Yucca Mountain Project, Las Vegas, NV (United States)

The purpose of this Analysis and Modeling Report (AMR) is to validate the External Accumulation Model that predicts accumulation of fissile materials in fractures and lithophysae in the rock beneath a degrading waste package (WP) in the potential monitored geologic repository at Yucca Mountain. (Lithophysae are voids in the rock having concentric shells of finely crystalline alkali feldspar, quartz, and other materials that were formed due to entrapped gas that later escaped, DOE 1998, p. A-25.) The intended use of this model is to estimate the quantities of external accumulation of fissile material for use in external criticality risk assessments for different types of degrading WPs: U.S. Department of Energy (DOE) Spent Nuclear Fuel (SNF) codisposed with High Level Waste (HLW) glass, commercial SNF, and Immobilized Plutonium Ceramic (Pu-ceramic) codisposed with HLW glass. The scope of the model validation is to (1) describe the model and the parameters used to develop the model, (2) provide rationale for selection of the parameters by comparisons with measured values, and (3) demonstrate that the parameters chosen are the most conservative selection for external criticality risk calculations. To demonstrate the applicability of the model, a Pu-ceramic WP is used as an example. The model begins with a source term from separately documented EQ6 calculations; where the source term is defined as the composition versus time of the water flowing out of a breached waste package (WP). Next, PHREEQC, is used to simulate the transport and interaction of the source term with the resident water and fractured tuff below the repository. In these simulations the primary mechanism for accumulation is mixing of the high pH, actinide-laden source term with resident water; thus lowering the pH values sufficiently for fissile minerals to become insoluble and precipitate. In the final section of the model, the outputs from PHREEQC, are processed to produce mass of accumulation, density of accumulation, and the geometry of the accumulation zone. The density of accumulation and the geometry of the accumulation zone are calculated using a characterization of the fracture system based on field measurements made in the proposed repository (BSC 2001k). The model predicts that accumulation would spread out in a conical accumulation volume. The accumulation volume is represented with layers as shown in Figure 1. This model does not directly feed the assessment of system performance. The output from this model is used by several other models, such as the configuration generator, criticality, and criticality consequence models, prior to the evaluation of system performance.

• Research Organization: Yucca Mountain Project, Las Vegas, NV (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
• OSTI ID: 837044
• Report Number(s): ANL-EBS-GS-000002-Rev.00; MOL.20011008.0005, DC 28775
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
CERAMICS
CRITICALITY
Computer Software
DATA
FISSILE MATERIALS
Fractures
GEOCHEMISTRY
Geometric Characteristics
HYDROXIDES
NUCLEAR FUELS
Nuclear Criticality Safety Program (NCSP)
PH VALUE
PHREEQC
PLUTONIUM
Quality Assurance
RISK ASSESSMENT
SOURCE TERMS
VALIDATION
YUCCA MOUNTAIN