QA: NA 
November 2003 
Technical Basis Document No. 13: 
Volcanic Events 
Revision 2 
William R. Hackett and David C. Dobson 
Prepared for: 
U.S. Department of Energy 
Office of Civilian Radioactive Waste Management 
Office of Repository Development 
1551 Hillshire Drive 
Las Vegas, Nevada 89134-6321 
Prepared by: 
Bechtel SAIC Company, LLC 
1180 Town Center Drive 
Las Vegas, Nevada 89144 
Under Contract Number 
DE-AC28-01RW12101
Revision 2 
November 2003 No. 13: Volcanic Events
Revision 2 
EXECUTIVE SUMMARY 
The possibility that volcanic activity could affect a repository at Yucca Mountain has been 
recognized since the site was identified in the late 1970s. The geologic and hydrologic setting of 
the southern Great Basin, which has many features that are favorable for waste isolation, is also 
characterized by ongoing low levels of seismic activity and geologically recent volcanic activity. 
Volcanic activity in the Yucca Mountain region peaked between about 13 and 11 million years 
ago with the eruption and deposition of the silicic volcanic tuffs that form Yucca Mountain from 
caldera complexes in and near Timber Mountain. Since then, volcanic activity has declined to 
very low levels, with the last event occurring approximately 80,000 years ago at the Lathrop 
Wells Cone 18 km south of Yucca Mountain. The potential for future igneous intrusion or 
volcanic activity has been evaluated through an integrated approach utilizing information from 
geological, geophysical and geochemical investigations, and an expert elicitation and peer 
review. The mean probability of a future volcanic event intersecting a repository has been 
estimated to be on the order of 1.7  10-8 per year, or approximately one chance in 6,000 of 
occurring over the next 10,000 years. The sensitivity of the probability estimate has been tested 
through the consideration of a variety of alternative models and multiple lines of evidence. The 
probability estimate has been found to be robust. That is, it is unlikely that new information will 
lead to a substantive revision of the estimate, because uncertainties associated with the available 
information and models used to calculate the probability have been incorporated into the 
analysis. 
The potential consequences of volcanic activity have also been evaluated. Although the likely 
styles of volcanic activity that could occur at Yucca Mountain are small in scale compared to the 
style and magnitude of events associated with large volcanoes such as Mount St. Helens or 
Mount Pinatubo, repository performance could be affected if volcanic activity intersected a 
repository. The physical processes and conditions associated with basaltic volcanism, and the 
potential effects of such activity on the integrity of the repository, have been evaluated. If 
basaltic magma intrudes into emplacement drifts, possible consequences could include damage 
to waste packages leading to eventual release of radionuclides to groundwater. An eruptive 
event through a repository could incorporate spent nuclear fuel or high-level radioactive waste 
into the volcanic ash ejected into the atmosphere. These possibilities have been incorporated 
into total system performance assessment calculations. Analyses to date have indicated that 
potential releases associated with these disruptive events are not likely to affect the 
repositorys ability to comply with the performance requirements specified in applicable 
regulations (40 CFR Part 197; 10 CFR Part 63). 
November 2003 iii No. 13: Volcanic Events
 
1. INTRODUCTION 
Volcanism studies for the U.S. Department of Energy (DOE) Yucca Mountain Project began in 
1979, and researchers from many organizations and universities, particularly Los Alamos 
National Laboratory, have conducted investigations in the Yucca Mountain region. 
DOE-sponsored investigations of volcanism in the Yucca Mountain region include: geological 
mapping; geophysical investigations; physical, petrological, geochemical, and geochronological 
investigations of the erupted materials; and numerical modeling of magma ascent through dikes 
and conduits and its eruption onto the surface as pyroclastic material and lava flows. The 
principal references describing this work are: 
 Yucca Mountain Site Description (CRWMS M&O 2000a) 
 Probabilistic Volcanic Hazard Analysis for Yucca Mountain, Nevada (CRWMS 
M&O 1996) 
 Dike/Drift Interactions (BSC 2003a) 
 Characterize Eruptive Processes at Yucca Mountain, Nevada (BSC 2003b) 
 Synthesis of Volcanism Studies for the Yucca Mountain Site Characterization Project 
(CRWMS M&O 1998a) 
 Number of Waste Packages Hit by Igneous Intrusion (BSC 2003c) 
 Igneous Intrusion Impacts on Waste Packages and Waste Forms (BSC 2003d) 
 Characterize Framework for Igneous Activity at Yucca Mountain, Nevada (CRWMS 
M&O 2000b; BSC 2003e). 
The purpose of this technical basis document is to review what is known about volcanism in the 
Yucca Mountain region, and to show how this information has been used in probabilistic 
volcanic hazard analysis of disruption of the repository by a basaltic volcanic event. Risk is the 
product of hazard times consequence. Accordingly, the hazard and consequence analyses are 
used to evaluate the risk of volcanic disruption of the repository. 
Note Regarding the Status of Supporting Technical InformationThis document was 
prepared using the most current information available at the time of its development. This 
technical basis document and its appendices providing Key Technical Issue agreement responses 
were prepared using preliminary or draft information that reflect the status of the Yucca 
Mountain Projects scientific and design bases at the time of submittal. In some cases, this 
involved the use of draft analysis and model reports and other draft references whose contents 
may change with time. Information that evolves through subsequent revisions of the analysis 
model reports and other references will be reflected in the license application (LA) as the 
approved analyses of record at the time of LA submittal. Consequently, the Project will not 
routinely update either this technical basis document or its Key Technical Issue agreement 
appendices to reflect changes in the supporting references prior to submittal of the LA. 
November 2003 1-1 No. 13: Volcanic Events
INTENTIONALLY LEFT BLANK 
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2. OVERVIEW OF VOLCANISM IN THE YUCCA MOUNTAIN REGION 
Two major types of volcanism, explosive silicic volcanism followed by basaltic volcanism, have 
occurred in the Yucca Mountain region. The early period of Miocene silicic volcanism in the 
southwestern Nevada volcanic field culminated between 11.8 and 12.4 Ma with the eruption of 
four voluminous ash-flow tuffs of about 1,000 km3 each (Sawyer et al. 1994). One of the silicic 
ash-flow tuffs that erupted from the Timber Mountain caldera complex (Figure 2-1) is the 
Topopah Spring Tuff, which forms the rock unit that will be used for waste emplacement. Yucca 
Mountain is a structurally uplifted, erosional remnant of these voluminous ash-flow tuff deposits. 
The hazards of silicic volcanism are considered to be negligible because of the absence of silicic 
activity in the Yucca Mountain region during the past 6 to 8 Ma (Crowe, Self et al. 1983, p. 261). 
The early caldera-forming, silicic volcanism was approximately coincident with a major period 
of crustal extension, which occurred primarily between 13 and 9 Ma (Sawyer et al. 1994). The 
onset of basaltic volcanism in the Yucca Mountain region occurred during the latter part of the 
caldera-forming period of silicic volcanism, as extension rates waned, and small-volume basaltic 
volcanism continued into the Quaternary. In terms of eruption volume, the 15-million-year 
history of volcanism in the Yucca Mountain region is viewed as a magmatic system that peaked 
between 13 and 11 Ma, with the eruption of over 5,000 km3 of ash-flow tuffs, and has been in 
decline since, with relatively minor volumes of basalt erupted since 11 Ma (CRWMS M&O 
1998b, Figure 3.9-2). Approximately 99.9 percent of the volume of the southwestern Nevada 
volcanic field erupted by about 7.5 Ma with the eruption of tuffs from the Stonewall Mountain 
volcanic center, which is the last active caldera system of the southwestern Nevada volcanic 
field. The last 0.1 percent of eruptive volume of the volcanic field consists of basalt erupted 
since 7.5 Ma (CRWMS M&O 1998b, Figure 3.9-5). Considered in terms of total eruption 
volume and frequency of eruptions, basaltic volcanic activity in the Yucca Mountain region 
defines one of the least active basaltic volcanic fields in the western United States (e.g., CRWMS 
M&O 1998a, Chapter 4, Figure 4-2, for postMiocene basalts of Crater Flat). 
The earliest episode of basaltic volcanism in the Yucca Mountain region occurred between 
approximately 9 and 11 Ma and was closely associated with the waning of silicic, 
caldera-forming volcanism. Postcaldera basalts in the Yucca Mountain region can be divided 
into two episodes: Miocene (eruptions between approximately 9 and 7.3 Ma) and postMiocene 
(eruptions between approximately 4.8 and 0.08 Ma). The time interval of about 2.5 million years 
between these episodes is the longest eruptive hiatus of basalt in the Yucca Mountain region 
during the last 9 million years (CRWMS M&O 1998a, Chapter 3, Table 3.1). This eruptive 
hiatus also marks a distinct shift in the locus of postcaldera basaltic volcanism in the Yucca 
Mountain region to the southwest (CRWMS M&O 1998b, Figure 3.9-6). The Miocene basalts 
and postMiocene basalts are both temporally and spatially distinct. For assessing the future 
potential for volcanism, the past 5 million years (and especially the last 1 million years) are most 
relevant to hazard assessment at Yucca Mountain (CRWMS M&O 1996, Figure 3-62). 
November 2003 2-1 No. 13: Volcanic Events
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MO0003YMP98126.001 (both are used for reference only). 
Source: CRWMS M&O 1998a, Chapter 2, Tables 2.B and 2.C; DTNs: LAFP831811AQ97.001; 
Figure 2-1. Locations and Ages of PostMiocene (Less than 5.3 Ma) Volcanoes (or Clusters Where 
Multiple Volcanoes Have Indistinguishable Ages) in the Yucca Mountain Region 
November 2003 2-2 No. 13: Volcanic Events
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PostMiocene basalts have erupted at several locations within 50 km of the repository 
(Figure 2-1). In order of decreasing age, these are the (1) basalt of Thirsty Mesa, (2) Pliocene 
Crater Flat and Amargosa Valley, (3) Buckboard Mesa, (4) Quaternary Crater Flat (i.e., Makani 
Cone, Black Cone, Red Cone and Little Cones), (5) Hidden Cone and Little Black Peak (the 
Sleeping Butte centers), and (6) Lathrop Wells. Three of these basaltic-vent groups are in or 
near the Crater Flat topographic basin, within 20 km of Yucca Mountain. 
Several aeromagnetic anomalies in the Amargosa Valley south of Yucca Mountain have 
characteristics that indicate buried basaltic volcanic centers (Langenheim et al. 1993, p. 1,840). 
One of these anomalies (anomaly B of Langenheim et al. 1993) was drilled and basalt cuttings 
dated at 3.85 Ma using the 40Ar/39Ar method (CRWMS M&O 1998a, Chapter 2, Table 2.B). 
Because of the similarity in age to the 3.75 Ma Pliocene Crater Flat episode, the buried basalts of 
Amargosa Valley are considered likely to be part of the same episode. 
The total eruption volume of the postMiocene basalts is about 6 km3. The volume of individual 
episodes has decreased progressively through time, with the three Pliocene episodes having 
volumes of approximately 1 to 3 km3 each and the three Quaternary episodes having a total 
volume of only approximately 0.5 km3 (CRWMS M&O 1998b, Figure 3.9-2; Table 3). The 
Quaternary volcanoes are similar in that they are of small volume (approximately 0.1 km3 or less, 
Table 2-1) and typically consist of a single main scoria cone surrounded by a small field of aa 
basalt flows, which commonly extend approximately 1 km from the scoria cone. 
The seven Quaternary volcanoes in the Yucca Mountain region (if Little Cones is counted as one 
volcano) occur to the south, west, and northwest of Yucca Mountain in a roughly linear zone 
defined as the Crater Flat Volcanic Zone (Crowe and Perry 1990, p. 328). Five of seven 
Quaternary volcanoes are in or near Crater Flat and lie within 20 km of the Yucca Mountain site 
(Figure 2-1). Models that attempt to relate volcanism and structural features in the Yucca 
Mountain region have emphasized the Crater Flat basin because of the volcanic centers within 
Crater Flat and its proximity to the repository (e.g., Smith, Feuerbach et al. 1990, p. 84; Connor 
and Hill 1995, p. 10,122). 
2.1 STRUCTURAL CONTROLS ON BASALTIC IGNEOUS ACTIVITY 
Evaluation of the likelihood of future igneous intrusion or volcanism at a specific location such 
as the repository requires knowledge of both the timing and the likely locations of potential 
activity. Basaltic centers in tectonic settings such as the southern Great Basin are fed by dikes 
that ascend from source regions in the subcontinental lithospheric upper mantle (Crowe, Self 
et al. 1983, p. 262). As they approach the surface, the dikes are typically 1 to 5 km in length. 
The location, length, and orientation of the dikes will directly affect the potential that they could 
intersect a repository. 
2.1.1 Influence of the Crater Flat Structural Domain 
PostMiocene volcanoes in the Yucca Mountain region are spatially clustered (Crowe, Perry, 
Geissman et al. 1995, Chapter 3; Connor and Hill 1995, Figure 2). For probability models that 
incorporate clustering of volcanoes (Connor and Hill 1995) or specify volcanic source zones 
based primarily on the location or clustering of volcano centers (CRWMS M&O 1996), 
November 2003 2-3 No. 13: Volcanic Events
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estimation of the hazard to Yucca Mountain is often dominated by the presence of the Crater Flat 
cluster. This is due to the relatively high frequency and Quaternary age of volcanoes in the 
Crater Flat structural domain (including Lathrop Wells volcano, which lies within the domain 
and is the youngest volcano in the Yucca Mountain region) and the proximity of Crater Flat 
volcanoes to Yucca Mountain, compared to other volcano clusters in the Yucca Mountain region 
(Figure 2-1). 
Region 
Volcano 
Table 2-1. Estimated Volumes and 40Ar/39Ar Ages of Quaternary Volcanoes in the Yucca Mountain 
Volume (km3)b 
0.07 
>0.01c 
Age (m.y.)d 
1.16-1.17 
0.94-1.10 
0.92-1.08 
0.77-1.02 
0.32-0.56 
0.36-0.39 
0.074-0.084 
Volume (km3)a 
0.006 
0.105 
0.105 
0.002 
0.03 
0.03 
0.086 
NOTES: 
Makani Cone 
Black Cone 
Red Cone 
Little Cones 
Hidden Cone 
Little Black Peak 
Lathrop Wells Cone 
DTNs: LA0004FP831811.002; LAFP831811AQ97.001 (both are used for reference only). 
c
aCRWMS M&O 1998a, Chapter 3, Table 3.1, DTN: LA0004FP831811.002, except for Lathrop 
Wells Cone, from BSC 2003b, Table 9. 
b Stamatakos et al. 1997, p. 327. 
Accounts for volume of buried flows detected by ground magnetic surveys. 
dRange of ages from CRWMS M&O 1998a, Chapter 2, Table 2.B. Lathrop Wells ages (Heizler 
et al. 1999, Table 3) represent the range of plateau ages measured, except for sample LW157, 
a statistical outlier (DTN: LAFP831811AQ97.001). 
40Ar/39Ar dates provide the most complete and self-consistent chronology data set for Quaternary 
volcanoes of the Yucca Mountain region. A full discussion of other chronology methods used to 
date basaltic rocks in the Yucca Mountain region can be found in Synthesis of Volcanism 
Studies for the Yucca Mountain Site Characterization Project (CRWMS M&O 1998a, Chapter 2). 
Other chronology methods may not provide consistent or accurate estimates of the time of 
eruption. 
2.1.2 Influence of Regional Stress on Dike Orientation 
Together with faulting, magma intrusion is an important component of worldwide crustal 
extension (Parsons and Thompson 1991). Yucca Mountain lies within the southern Great Basin 
in the Basin and Range province, which is undergoing active ESEWNW extension (Zoback and 
Zoback 1989). The state of stress in the Yucca Mountain region has been investigated using 
hydraulic-fracturing stress measurements, borehole breakouts, drilling-induced fractures, 
earthquake focal mechanisms and fault-slip orientations. A review of these data is given by 
Stock and Healy (1988). 
Magma-filled fractures (dikes) will tend to strike orthogonal to the direction of the least 
compressive horizontal stress, and parallel to the direction of the greatest compressive horizontal 
stress (Pollard 1987). Most investigations give the orientation of the greatest compressive 
horizontal stress in the Yucca Mountain region as N30E 15 degrees. Uncertainty in this 
orientation results from both inaccuracies in measurement and real variations in stress with depth 
and location, as observed, in breakout and drilling-induced fracture orientations, which vary by 
up to 40 in Yucca Mountain boreholes (Stock et al. 1985). By comparison, probabilistic 
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volcanic hazard analysis (CRWMS M&O 2000b, p. 102; BSC 2003e) suggests that the dike that 
intersects the repository will be oriented between N35E  25, within the 90 percent confidence 
interval (between the 5th and 95th percentiles). This range is reasonable given the state of stress 
at Yucca Mountain and the uncertainty associated with it. 
The Crater Flat structural domain as defined by Fridrich (1999, pp. 170 to 178) is a structural 
basin or graben. It is bounded on the west by the Bare Mountain fault and on the east by 
structures buried beneath Jackass Flats (Figure 2-2). Seismic reflection surveys show that the 
Crater Flat basin is deepest to the west (Brocher et al. 1998). It includes the Crater Flat 
topographic basin on the west and Yucca Mountain near the center of the structural domain 
(Figure 2-2). Because the repository lies within the Crater Flat structural basin, the structural 
and geophysical features of the domain, and the degree to which they influence the location of 
volcanism within the domain, have been key factors in conceptual models of volcanism for 
assessing hazards to the repository. 
The following sections briefly describe the internal structure of the Crater Flat basin, as well as 
how the probabilistic volcanic hazards assessment (CRWMS M&O 1996) interpreted the 
influence of structural characteristics of the basin in estimating the locations of future volcanic 
events. Based largely on work published since 1996, the evidence that the northeastern and 
southwestern portions of the basin have different extensional histories that may have influenced 
the location of basaltic volcanism within the basin is summarized below. 
2.1.3 Internal Structure and Boundaries of the Crater Flat Structural Domain 
The Crater Flat structural domain includes the Crater Flat topographic basin (west of Yucca 
Mountain), Yucca Mountain, and the western part of Jackass Flats (Fridrich 1999, p. 174). 
Based on geologic mapping and interpretation of subsurface structures from geophysical surveys, 
the Crater Flat structural domain appears to be a single, westward-sloping, faulted basin 
(Figure 2-3). The western boundary of the Crater Flat basin and structural domain coincides 
with the Bare Mountain fault and its northward extension, which dips steeply (64 near the 
southern end) and can be imaged by seismic reflection to depths up to 6 km (Brocher et al. 
1998). This major fault probably extends to the brittle-ductile transition in the middle crust. The 
northern boundary consists of a gradational termination of intrabasin structure at the perimeter of 
the Timber Mountain caldera complex (Fridrich 1999, p. 174). 
The eastern and southern margins of the domain are not physiographically distinct but, rather, 
merge with adjacent portions of the Basin and Range. The eastern margin of the Crater Flat 
structural domain is probably a buried, down-to-the-west fault known as the Gravity fault 
(Fridrich 1999). The southern margin is inferred from gravity and magnetic data and from 
discontinuous outcrops to be a fault structure buried beneath young alluvium. It is typically 
drawn in a northwestern direction along the Amargosa Valley (Fridrich 1999, p. 176). 
Fundamental changes in the style, timing, magnitude of extension, and other deformation occur 
across all of the boundaries of the Crater Flat structural domain. 
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NOTE: Basalts of different ages are shown in relation to basin structure (modified from Fridrich et al. 1999, 
Figure 1). The 80-ka age of the Lathrop Wells volcano is from Heizler et al. (1999). MC = Makani Cone; 
BC = Black Cone; RC = Red Cone; LC = Little Cones; LW = Lathrop Wells volcano; PCF = Pliocene 
Crater Flat. 
Figure 2-2. Local Structural Domains and Domain Boundaries of the Yucca Mountain Region and 
Internal Structures of the Crater Flat Basin and Selected Parts of Adjacent Domains 
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NOTE: Location of cross section is indicated in Figure 2-2. 
Source: Modified from Brocher et al. 1998. 
Figure 2-3. Schematic Cross Section of the Crater Flat Basin, from Seismic Reflection, Surficial 
November 2003 2-7 
Geology, and Borehole Information 
2.1.4 Extensional History of the Crater Flat Structural Domain 
Based on the strike directions of faults within the Crater Flat structural domain, a 
northwest-trending hinge line can be defined (Fridrich et al. 1999, p. 208) that separates an 
area of predominantly north-striking faults on the northeast from an area of predominantly 
northeast-striking faults on the southwest (Figure 2-2). The hinge line marks the approximate 
location of (1) the 20 contour of clockwise rotation of the Tiva Canyon Tuff, (2) a subtle yet 
abrupt decline in elevation to the southwest, and (3) an increase in Quaternary displacement for 
faults southwest of the hinge line (Fridrich et al. 1999, p. 208; Stamatakos et al. 1997, p. 327). 
These observations are consistent with a division of the Crater Flat structural domain into two 
parts, separated at the approximate position of the hinge line (Figure 2-2): (1) a northeastern, 
less extended part, and (2) a southwestern, more extended part (Fridrich et al. 1999, p. 208; 
Stamatakos et al. 1997, pp. 327 to 328). 
2.1.5 Correlation with Volcanism 
Basalts of the past 11 Ma in the Crater Flat basin have erupted in four episodes that together 
define a trend of progressively declining volume of magma erupted (Fridrich et al. 1999) 
(Figure 2-4). 
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Source: Fridrich et al. 1999. 
Figure 2-4. Estimated Extension Rates in Crater Flat Basin as a Function of Time and Magma Volume 
November 2003 2-8 
Erupted as a Function of Time 
Vents for these eruptions form a northwest-trending belt across the southwest part of the basin, 
coincident with the strongest transtensional (lateral and extensional) deformation in the basin, 
suggesting that ascent of basalt through the crust is structurally controlled. The rates of 
extension and volcanism in the Crater Flat basin include initial peaks in the Miocene, followed 
by strongly declining patterns to the present. The similarity and approximate synchroneity of 
these trends suggest that they are reflections of a single phenomenona tectonic system that, at 
its peak, must have been among the most active zones of tectonism in the Great Basin, 
comparable to Death Valley today. The Crater Flat basin remains tectonically active, but is now 
in an advanced stage of decline. Existing data suggest that, within the overall declining pattern, 
extensional faulting has been cyclical, and that it has varied partly in concert with episodic 
volcanism in the Crater Flat basin (Fridrich et al. 1999). 
The youngest volcano in the Crater Flat basin, the 80-ka Lathrop Wells volcano, lies between the 
southern ends of the Windy Wash and Stagecoach Road faults, the most active site of late 
Quaternary faulting in the Crater Flat basin (Fridrich et al. 1999, p. 211). There is a close spatial 
and temporal relationship between sites of extension and volcanism throughout the Crater Flat 
basin (Fridrich et al. 1999, p. 211). The occurrence of the three episodes of postMiocene 
volcanism in the more extended, southwestern part of the Crater Flat basin suggests that 
volcanism is less likely to occur at Yucca Mountain, which lies outside of the transtensional 
zone, in an area where no post-Miocene volcanism has occurred (Fridrich et al. 1999). Other 
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geologic and geophysical studies provide corroborative evidence that areas of maximum 
extension in the southwestern Crater Flat basin correspond closely to volcanic source zones 
(CRWMS M&O 1996; Stamatakos et al. 1997; Brocher et al. 1998; Fridrich et al. 1999). 
2.1.6 Relationship of Volcanic Source Zones to Crater Flat Structural Features and the 
Probability of Dike Intersection 
The correlation between the structurally active part of the Crater Flat structural domain and sites 
of volcanism within the active part of the domain indicate that Yucca Mountain is near, but not 
within, a local volcanic zone that may produce small volumes of basaltic magma in the future 
(CRWMS M&O 1996, Appendix E, expert zone maps). Although the PVHA experts 
(Section 2.2) chose local volcanic source zones (Figure 2-5) based largely on the location of past 
volcanic events (CRWMS M&O 1996), the zones also correspond to the areas of highest 
cumulative extension and most active faulting in the Crater Flat basin (Fridrich et al. 1999). This 
association was recognized by several of the PVHA experts (CRWMS M&O 1996, pp. RC-5, 
BC-12, AM-3-5, GT-2). In the cases in which local zones were defined, they were limited to the 
southwestern portion of the Crater Flat basin, or were elongated, northwest-trending belts that 
included the southwestern portion. The local volcanic source zones excluded the northeastern 
portion of the Crater Flat basin, in which the repository is located. Given the close association of 
volcanism and extension, the eastern boundaries of local volcanic source zones separate more 
tectonically active and less tectonically active portions of the Crater Flat structural domain and 
are, therefore, reasonable predictors of the eastern extent of volcanism expected in the future. 
In summary, the areas of greatest likelihood for future volcanic activity in the region are those 
where previous volcanism has occurred, and where extensional deformation has been and 
continues to be greatest, (i.e., the southwestern part of the Crater Flat structural domain) 
(Figure 2-5) (CRWMS M&O 1996, pp. RC-5, BC-12, AM-5, MS-2, GT-2, and expert zone 
maps). Analysis by the U.S. Nuclear Regulatory Commission (NRC) also indicates that the 
highest likelihood of future volcanic activity is in southwestern Crater Flat (Reamer 1999, 
Sections 4.1.5.4 and 4.1.6.3.3; Figure 28). The southern and southwestern part of the Crater Flat 
basin is the most extended (Ferrill et al. 1996; Stamatakos et al. 1997; Fridrich et al. 1999) and is 
the locus of post-Miocene volcanism (Fridrich et al. 1999; Reamer 1999, p. 47). Therefore, the 
volcanic source zones defined in the PVHA (CRWMS M&O 1996) (Figure 2-5) are consistent 
with the tectonic history and structural features of the Crater Flat structural domain.
November 2003 2-9 No. 13: Volcanic Events
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Source: DTN: MO0002PVHA0082.000 (for zone boundaries only). 
NOTE: Superimposed on the Fridrich et al. (1999, Figure 1) map are boundaries of selected volcanic source zones 
(locally homogeneous spatial and temporal model, CRWMS M&O 1996, Section 3.13) that lie within the 
Crater Flat basin as defined by the PVHA experts (CRWMS M&O 1996, Appendix E). Other experts (not 
shown for clarity) used similar source-zone boundaries. MC = Makani Cone; BC = Black Cone; RC = Red 
Cone; LC = Little Cones; LW = Lathrop Wells volcano; PCF = Pliocene Crater Flat. 
Figure 2-5. Local Structural Domains and Volcanic Source Zones of the Yucca Mountain Region 
November 2003 2-10 No. 13: Volcanic Events
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2.2 PROBABILISTIC VOLCANIC HAZARD ASSESSMENT 
Volcanic hazard analyses have been conducted throughout the Yucca Mountain Project 
volcanism data-collection process (Crowe, Perry, Geissman et al. 1995; Crowe, Johnson 
et al. 1982; CRWMS M&O 1996). Results described in the volcanism synthesis report 
(CRWMS M&O 1998a, p. 6-14) show that 75 percent of Pliocene and Quaternary volcanic 
centers in the Yucca Mountain region occur in alluvial basins, 12.5 percent occur along range 
fronts, and 12.5 percent occur in range interiors (CRWMS M&O 1998a, Table 6.3). The 
distribution of past events indicates that a future volcanic event in the Yucca Mountain region is 
about six times more likely to occur in an alluvial valley or along a range edge than in a range 
interior such as the repository location in Yucca Mountain. Early analyses were preliminary 
assessments of disruption probabilities for the repository, and they also served to focus 
subsequent data collection toward information with greatest importance to the hazard 
assessment. The volcanic hazard assessment of Crowe, Perry, Geissman et al. (1995) provided a 
systematic, comparative analysis of published hazard models and methodologies; presented a 
range of possible results based on current knowledge and methods; and provided valuable 
insights into the sensitivities that the various approaches, models, and input parameters would 
have in the calculated results. 
In 1995 and 1996, the DOE sponsored a probabilistic volcanic hazard analysis to assess the 
probability of a future volcanic event intersecting the repository at Yucca Mountain, and to 
explicitly characterize the uncertainties in the hazard analysis (CRWMS M&O 1996). This 
specific probabilistic volcanic hazard analysis is known as the PVHA. The analysis considered 
the data and insights from previous hazard assessments. To ensure that a wide range of 
approaches was considered in the analysis, 10 experts were selected. The use of multiple experts 
was part of an attempt to fully characterize uncertainties. Each expert played the role of an 
informed technical evaluator of data, rather than a proponent of a particular interpretation. On 
occasion, however, some experts were asked to present particular interpretations to facilitate 
discussion and the consideration of alternative interpretations. During the PVHA process, it was 
made clear that the purpose of the PVHA was to identify and understand uncertainty, not to 
eliminate it. It was also emphasized that the purpose was not necessarily to achieve consensus. 
Instead, disagreement was expected and accepted. The experts provided weighted alternative 
models and parameters, expressing their degree of belief that these were appropriate models and 
values. The panel included individuals with expertise in geology, geochemistry, and geophysics, 
and representing government agencies, universities and private industry. Following a series of 
workshops, field excursions, and other structured interactions between February and 
December 1995, the experts evaluations were gathered in a deliberate elicitation process. Their 
evaluations were then combined to produce an integrated assessment of the volcanic hazard, an 
assessment representing the range of alternative scientific interpretations and uncertainties from 
the informed scientific community. The analysis expressed the volcanic hazard as the annual 
probability of intersection of the repository by a basaltic dike. This result, in turn, provides input 
to the assessment of volcanic risk, which is the product of hazard and consequence. 
2.2.1 The Fundamental Basis of Volcanic Hazard Assessment 
A principal assumption in the volcanic hazards analyses sponsored by DOE, including the 1996 
PVHA, is that the recent geologic past is the key to the future (CRWMS M&O 1996). This 
November 2003 2-11 No. 13: Volcanic Events
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means that the record of volcanism, as revealed by geological and geophysical data from the area 
of interest and the geologic time period of interest, is the basis for assessing the probability of 
future volcanism. A validation of this paradigm was provided in the Final Report of the Igneous 
Consequences Peer Review Panel (Detournay et al. 2003, p. 10). 
2.2.2 Temporal and Spatial Aspects of Probability Models 
The uncertainty in modeling the spatial and temporal distribution of future volcanic events in the 
region surrounding Yucca Mountain was incorporated in the probabilistic volcanic hazards 
analysis using a logic tree methodology. Temporal models describe the frequency of occurrence 
of volcanic activity and include homogeneous and nonhomogeneous models. Many of the 
PVHA experts used homogeneous Poisson models to define the temporal occurrence of volcanic 
events, which assumes a uniform rate of volcanism based on the number of volcanic events that 
occurred during various periods in the past. Nonhomogeneous models were used by some 
experts to consider the possibility that volcanic events are clustered in time or to describe the 
possible waning or waxing of volcanic activity in the region during the period of time the experts 
considered to be relevant to hazard analysis. 
Spatial models describe the spatial distribution (location) of future volcanic activity. The models 
most commonly used by the PVHA experts considered the future occurrence of volcanoes to be 
homogeneous within particular defined regions or source zones (CRWMS M&O 1996, 
Figure 3-62). Source zones were defined based on several criteria: the spatial distribution of 
observed volcanoes, especially post5 Ma volcanoes; structurally controlled regions; and regions 
defined based on geochemical affinities, tectonic provinces, and other criteria. 
Nonhomogeneous parametric spatial distributions of future volcano occurrences were also 
modeled, (e.g., that the location of future volcanoes will follow a bivariate Gaussian distribution 
based on the location of volcanoes in Crater Flat). Finally, nonhomogeneous, nonparametric 
spatial-density models were used by some experts to assess the spatial distribution of future 
volcanoes. These models make use of a kernel density function and smoothing parameter based 
on locations of existing centers to obtain the spatial distribution for location of future volcanoes. 
2.2.3 Probabilistic Volcanic Hazards Analysis Results and Uncertainty 
The product of the PVHA was a quantitative assessment of the probability of a volcanic event 
intersecting the repository and the uncertainty associated with the assessment (CRWMS 
M&O 1996, Figure 4-32). Specifically, a probability distribution of the annual frequency of 
intersection of a basaltic dike with the repository footprint was defined. The contributions to 
uncertainty from each of the probabilistic volcanic hazards analysis components are described in 
the PVHA (CRWMS M&O 1996) and are shown in Figure 2-6. The analysis results indicated 
that the statistical uncertainty in estimating the event rate was the largest component of 
intra-expert uncertainty. The next largest uncertainty was uncertainty in the appropriate spatial 
model. Another important spatial uncertainty was the spatial smoothing distance. The temporal 
issues of importance included the time period of interest, event counts for Crater Flat, and the 
frequency of hidden events (buried volcanic events, or intrusive events that never reached the 
surface). Additional discussion of the potential effects of buried or hidden events is presented in 
Section 2.3.11.3. The variance for frequency of intersection defined by the composite 
distribution was disaggregated to identify the contributions from each of the sources of 
November 2003 2-12 No. 13: Volcanic Events
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uncertainty, including variability between the experts interpretations (Figure 2-6). Most of the 
uncertainty in characterizing the hazard arose from uncertainty in an individual experts 
assessment of the hazard (e.g., the likelihood that an event could occur at a given location or 
time), rather than differences in scientific interpretation between the experts (CRWMS 
M&O 1996). 
Source: CRWMS M&O 1996, Figure 4-33. 
NOTE: (a) Comparison of inter-expert and intra-expert components, and (b) breakdown of intra-expert components 
of variance. LW = Lathrop Wells; NWCF = Northwest Crater Flat; SECF = Southeast Crater Flat; 
AV = Amargosa Valley; SB = Sleeping Buttes; TM = Timber Mountain; BM = Buckboard Mesa. 
Figure 2-6. Relative Contribution of Uncertainty in Various Components of the Aggregate Probabilistic 
Volcanic Hazards Analysis Model to the Total Variance in Annual Frequency of Intersection 
November 2003 2-13 No. 13: Volcanic Events
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For the annual frequency of intersection of the repository footprint by a dike, each of the 
10 experts independently arrived at a probability distribution that typically spanned 
approximately 2 orders of magnitude (CRWMS M&O 1996, Figure 4-31). From these 
individual probability distributions, an aggregate probability distribution for the annual 
frequency of intersection of the repository footprint by a dike was computed, reflecting the 
uncertainty across the entire expert panel. The individual experts distributions were combined 
using equal weights to obtain the aggregate probability distribution (Figure 2-7). 
The computed mean annual frequency of intersection of the repository footprint by a dike is 
1.7  10-8 for the LA footprint as compared to 1.5  10-8 obtained in the PVHA (CRWMS 
M&O 1996, p. 4-10). The change is due to the revised size and configuration of the repository. 
The computed 5th and 95th percentiles of the uncertainty distribution for frequency of 
intersection are 7.4  10-10 to 5.5  10-8 (BSC 2003e, Section 6.5.3.1), respectively, as compared 
to 5.4  10-10 and 4.9  10-8 obtained in the PVHA (CRWMS M&O 1996, p. 4-10). The 
composite distribution spanned about three orders of magnitude for intersection frequency. The 
range in the mean frequencies of intersection for the individual experts interpretations spanned 
about one order of magnitude (CRWMS M&O 1996). 
The probability distribution arrived at in the PVHA accounted for hidden events by using a 
hidden-event factor ranging from 1 to 5 times the number of observed events, with most 
estimates in the range of 1.1 to 1.5 (CRWMS M&O 1996, Figure 3-62). 
2.2.4 Consideration of Alternative Conceptual Models 
The PVHA was an exercise in combining multiple alternative conceptual models into a single 
distribution, and expressed the uncertainty in the experts conceptual models of volcanism in the 
Yucca Mountain region. The PVHA experts were also informed of alternative conceptual 
models during workshops and other structured interactions, and these were considered by the 
experts in formulating their own temporal and spatial models of volcanism. No single, principal 
conceptual model is appropriate in the area of volcanism, because the interplay of physical 
processes that control the precise timing and location of volcanic events within a particular 
region is not well constrained. The complexity of the processes and features that can influence 
volcanic events, and the relatively small number of events available for study, make 
characterization of the future hazard intrinsically uncertain. 
Several alternative models not considered in the PVHA have emerged since the analysis was 
completed in 1996. These models are listed in Table 2-2 and their key assumptions and 
assessments of their impact on the results of the analysis are described. None of the alternative 
conceptual models identified would result in significant change in the PVHA results.
November 2003 2-14 No. 13: Volcanic Events
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Source: CRWMS M&O 1996, Figure 4-32. 
NOTE: (a) Aggregate distribution for frequency of intersection. (b) Individual and aggregate means, medians, and 
90-percent confidence intervals (horizontal bars). 
Figure 2-7. Aggregate Results for Frequency of Intersecting the Repository Footprint by a Volcanic 
Event 
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Table 2-2. Alternative Conceptual Models Not Considered in the Probabilistic Volcanic Hazards Analysis 
Alternative Models 
Anomalous strain rate in 
the Yucca Mountain region 
(Wernicke et al. 1998) 
Mantle hotspot beneath the 
Yucca Mountain region 
(Smith, Keenan et al. 2002) 
Tectonically weighted 
probability models (Connor, 
Stamatakos, Ferrill, Hill, 
Ofoegbu et al. 2000, 
p. 427) 
Significant number of 
buried or undetected 
volcanic centers in the 
Yucca Mountain region (Hill 
and Stamatakos 2002) 
NOTE: See BSC 2003e for detailed discussion of assessments. 
2.2.5 Significance of Buried Volcanic Centers on Probabilistic Volcanic Hazards 
Analysis Results 
The event or recurrence rate is one of the fundamental parameters needed to estimate the 
volcanic hazard or the frequency of intersection of the repository by a future volcanic event. 
A key parameter for estimating event rates is an estimate of the number of volcanic events that 
have occurred in the Yucca Mountain region, particularly since the Miocene. The uncertainty in 
the event rate accounted for about 40 percent of the total intra-expert uncertainty (Figure 2-6) 
(CRWMS M&O 1996, Figure 4-33). The event rate depends on the number of events estimated 
for a particular time period and for a particular source zone, and can be expressed as events per 
year per square kilometer (CRWMS M&O 1996, p. 3-2). Since all postMiocene volcanic 
centers having surface expression in the Yucca Mountain region have been identified, the only 
factor that could significantly change analysis results would be evidence not considered by the 
PVHA expert-panel members of a significant number of previously unidentified buried volcanic 
centers or intrusions. The significance of such buried volcanic centers on the probability of 
repository intersection by a basaltic dike would depend, in turn, upon (1) the geologic age of the 
buried event, because different weights are assigned to different time periods with more recent 
events being more heavily weighted; and (2) the distance and location relative to the repository, 
because basaltic dikes are assigned weighted lengths and azimuths and not all dikes will reach 
the repository. 
Langenheim et al. (1993) presented data for aeromagnetic anomalies in Amargosa Valley and 
interpreted them as shallowly buried basaltic volcanic centers. Anomaly B was drilled, basalt 
was found in the drill cuttings, and the cuttings were dated at about 3.85 Ma (CRWMS 
No. 13: Volcanic Events 
Key Assumptions 
Anomalously high current strain rate 
based on GPS measurements 
indicates volcanic event rate may be 
underestimated by factor of 10. 
Anomalously high mantle basalt 
source temperatures lead to 
underestimation of future volcanic 
event rate. 
Weighting of certain tectonic 
elements in probability models lead 
to probability estimates as high as 
10-7. 
Aeromagnetic anomalies suggest 
that significant number of volcanic 
events were unaccounted for in the 
probabilistic volcanic hazards 
analysis, underestimating the 
volcanic hazard. 
2-16 
Revision 2 
Assessment 
Not considered plausible based on later 
measurements from Savage et al. (1999) 
that show low strain rate as well as 
questionable assumptions about links 
between strain rate and volcanic event rate. 
Not considered plausible based on weight of 
documented scientific opinion showing that 
a mantle hotspot is not present beneath 
Yucca Mountain region; not consistent with 
waning Yucca Mountain region volcanism. 
Not considered plausible based on 
observation that tectonically weighted 
probability models are poor predictors of 
location of volcanism in Yucca Mountain 
region. 
Sensitivity studies documented in this report 
(see Section 2.2.5) show that the most 
conservative assumptions about event 
counts produce only a 40% increase in the 
mean annual frequency of intersection. 
November 2003
Revision 2 
M&O 1998a, Table 2.1, sample well 25-1-BMC, and pp. 2-22 to 2-23). These data and 
interpretations were used by the PVHA experts (CRWMS M&O 1996, p. B-4). 
The most common assessment among the PVHA experts of the number of volcanic events 
represented by the aeromagnetic anomalies in Amargosa Valley was 5, with slightly less weight 
assigned to 3, 4, and 6 events (CRWMS M&O 1996, Figure 3-63). The experts also applied a 
hidden-event multiplier, typically 1.1 to 1.5 times the number of volcanic events, to incorporate 
the possibility of undetected events; i.e., events not accounted for in the aeromagnetic data and 
the surface geology. The hidden-event multiplier typically resulted in an increase of 10 to 
50 percent in the number of volcanic events over that computed from the observed or inferred 
volcanoes. This information is incorporated in the mean annual frequency of intersection 
obtained in the PVHA. 
New data that could potentially change the assessment of the number of volcanic events in the 
analysis include ground magnetic surveys of aeromagnetic anomalies (Connor, Stamatakos, 
Ferrill, Hill, Magsino et al. 1996; Magsino et al. 1998). These magnetic data include surveys of 
14 selected aeromagnetic anomalies located in the vicinity of the repository site (Magsino 
et al. 1998, Figure 1-1). Collectively, these surveys are a comprehensive assessment of 
aeromagnetic anomalies nearest the repository site and lend confidence that the geologic record 
of basaltic volcanism near Yucca Mountain is adequately understood. Of the 14 surveys, seven 
provide no evidence of buried basalt and three were conducted over areas with known surface 
exposures of basalt and partly to enhance understanding of the relationship between volcanism 
and geologic structure (Magsino et al. 1998, Section 4). Four of the 14 surveys provide evidence 
of buried volcanic centers. Two of these anomalies were known to the PVHA experts as 
possible buried basaltic volcanic centers (from the data of Langenheim et al. 1993; and Crowe, 
Perry, Geissman et al. 1995), but the data presented by Connor, Stamatakos, Ferrill, Hill, 
Magsino et al. (1996) and Magsino et al. (1998) provide increased detail and confidence in their 
volcanic origin. Of the two remaining surveys, anomalies in the Steves Pass area on the 
southwest margin of Crater Flat are interpreted as buried basalt. Interpretation of a buried, 
reversely magnetized body of rock southwest of Northern (or Makani) Cone is less certain and 
may be either a basalt body or Miocene-age tuff (Magsino et al. 1998). Each of the four 
anomalies representing probable buried volcanic centers occur within volcanic source zones 
previously specified in the PVHA (CRWMS M&O 1996, Appendix E), except for the anomalies 
in the Steves Pass area, which lie to the southwest of most volcanic source zones in a direction 
away from Yucca Mountain. 
On the basis of evidence for buried volcanic centers presented by Connor, Stamatakos, Ferrill, 
Hill, Magsino et al. (1996), Brocoum (1997) described sensitivity analyses to assess the potential 
impact on the analysis results of increased event counts in Amargosa Valley and Crater Flat. 
Considering the PVHA method for assessment of event counts, particularly for northeast 
alignments of vents (as in the case of Amargosa anomaly F/G), the mean value for the number of 
buried volcanic centers was increased from the original PVHA value of 4.7 events to 6.1 events 
(Brocoum 1997). The mean annual frequency of intersection of a dike with the repository 
footprint was recalculated using the revised event count distributions, resulting in an increase in 
the mean annual frequency of intersection of 4 percent (Brocoum 1997). Given the uncertainty 
factored into the PVHA by assessment of alternative event counts and hidden-event factors, 
small changes in the event counts have an insignificant impact on the annual frequency of 
November 2003 2-17 No. 13: Volcanic Events
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intersection distribution derived from the analysis. A later sensitivity analysis (CRWMS 
M&O 1998a, Chapter 6, pp. 6-83 and 6-84) conservatively assumed that all known aeromagnetic 
anomalies in Crater Flat and Amargosa Valley were of Quaternary age (less than or equal to 
1.8 Ma), rather than Pliocene. Using this assumption, the most likely number of Quaternary 
volcanic events near Yucca Mountain based on event counts was increased from 3.8 to 8 events. 
This increase in the Quaternary event count resulted in a disruption probability of approximately 
2.5  10-8 per year (CRWMS M&O 1998a, Chapter 6, p. 6-84), a result not significantly 
different from the mean PVHA result of 1.5  10-8 per year (CRWMS M&O 1996, pp. 4-10, 
4-14). 
Four anomalies east of Yucca Mountain (Magsino et al. 1998, Figure 1-1) show no evidence of 
buried volcanic centers. This provides corroborative evidence that the volcanic source zones 
specified by the experts to the south and west of Yucca Mountain are a valid representation of 
the spatial distribution of postMiocene volcanism in the Yucca Mountain region. 
In 1999, the U.S. Geological Survey conducted a regional aeromagnetic survey for the purpose 
of assessing potential hydrologic pathways in the Yucca Mountain/Death Valley region (Blakely 
et al. 2000). Subsequent interpretation of these data indicated that as many as 20 to 
24 aeromagnetic anomalies present to the west and south of Yucca Mountain could potentially 
represent buried basalt (OLeary et al. 2002; Hill and Stamatakos 2002). Eight of these 
anomalies were recognized at the time of the PVHA (CRWMS M&O 1996). The effect of these 
potential buried volcanic centers on the results of the analysis was assessed and is described in 
Section 2.2.6. 
2.2.6 Impact of 1999 Aeromagnetic Data on Frequency of Intersection 
Anomalies observed in aeromagnetic and ground magnetic data gathered by the U.S. Geological 
Survey and the Center for Nuclear Waste Regulatory Analyses, respectively, since completion of 
the PVHA suggest that a number of basaltic volcanic centers could be buried beneath alluvium in 
Crater Flat and the northern Amargosa Desert (Blakely et al. 2000; OLeary et al. 2002; Hill and 
Stamatakos 2002). Interpretation of these data indicates that 20 to 24 magnetic anomalies occur 
within Crater Flat and the northern Amargosa Desert that could represent buried basaltic 
volcanoes (OLeary et al. 2002; Hill and Stamatakos 2002). Of these anomalies, eight were 
known at the time of the PVHA (CRWMS M&O 1996) from previous surveys and were 
considered as possible volcanic events as part of the analysis (Figure 2-8). 
The effect of potential buried volcanic centers on the results of the analysis was evaluated using 
estimates of the ages of possible buried centers and an assessment of the likelihood that 
anomalies or groups of anomalies represent buried basaltic volcanic centers (BSC 2003e, pp. 113 
to 118). The probable age range of potential buried volcanic centers was estimated using a range 
of calculated sedimentation rates in Crater Flat and the Amargosa Valley and the modeled depth 
of anomalies from OLeary et al. (2002). Consideration of magnetic-polarity data adds another 
constraint. This approach leads to probable ages for the anomalies that range from 2.6 to 6.3 Ma 
(BSC 2003e, p. 114). All age ranges represent minimum ages and are therefore conservative for 
the purposes of volcanic hazard assessment. 
November 2003 2-18 No. 13: Volcanic Events
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Source: BSC 2003e, Figure 24; coordinates from Hill and Stamatakos 2002. 
NOTE: MC: Makani Cone, BC: Black Cone, RC: Red Cone, LC: Little Cones, LW: Lathrop Wells volcano. PCF: 
Pliocene Crater Flat. Magnetic Anomaly designations are from Hill and Stamatakos 2002 
Figure 2-8. Locations of Potential Buried Basalt Inferred from Aeromagnetic Data 
The potential impact of the aeromagnetic and ground magnetic data on the probability of igneous 
disruption of the repository was assessed by developing distributions for the number of volcanic 
events represented by the anomalies, assigning these events to the Crater Flat and Amargosa 
Valley volcanic source zones defined in the 1996 PVHA, assigning ages to the events, and 
calculating the annual frequency of intersection of the repository footprint (BSC 2003e, pp. 115 
to 119). The distributions for the number of volcanic events were developed using the tendency 
of each expert to group aligned anomalies into single or multiple volcanic events. Two cases 
were developed. Case 1 is consistent with the PVHA approach, and factors the likelihood that 
the anomalies represent buried volcanic centers into the assessment of the number of volcanic 
events that have occurred. The distributions for the number of volcanic events represented by 
the magnetic anomalies for Case 1 were developed using the qualitative likelihoods that the 
anomalies represent buried volcanic centers and using each experts tendency for including 
November 2003 2-19 No. 13: Volcanic Events
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anomalies with various levels of confidence into their distributions for volcanic events. In 
Case 2, all anomalies were assumed to be buried volcanic centers, and the distributions for the 
number of volcanic events were developed on the basis of each experts tendency for grouping 
aligned volcanic centers into events. 
In Table 2-3, the volcanic-event-count distributions developed for sensitivity Case 1 result in a 
22 percent increase in the mean annual frequency of intersection, and those for sensitivity Case 2 
result in a 40 percent increase. The increase in the frequency of intersection is less than the 
increase in the mean number of volcanic events because the additional events are located in the 
volcanic source zone to the west of the site. 
1996 Probabilistic 
Volcanic Hazards 
Analysis 
Sensitivity Case 1 
Table 2-3. Summary of Computed Frequency of Intersection from Sensitivity Cases 1 and 2 for 70,000- 
Annual Frequency of Intersection 
Mean 
1.6  10-8 
1.9  10-8 
2.2  10-8 
95th percentile 
5.2  10-8 
6.5  10-8 
7.6  10-8 
50th percentile 
9.8  10-9 
1.0  10-8 
1.1  10-8 
MTU No-Backfill Repository Layout 
Input Parameters 
5th percentile 
7.9  10-10 
7.8  10-10 
7.9  10-10 Sensitivity Case 2 
Source: BSC 2003e, Table 21. 
NOTE: The repository layout used in this calculation includes both primary and contingency blocks of 
a preliminary design different from the LA footprint used in calculation presented in Table 2-5. 
2.2.7 Alternative Estimates of the Intersection Probability 
Several alternative estimates of the intersection probability (the annual probability of a volcanic 
event intersecting the repository footprint) were presented between 1982 and 1998 (Table 2-4). 
Volcanic events in hazard calculations have been represented as both points and lines. For point 
events, volcanic source zone areas or the repository area have generally been increased to 
account for the fact that volcanic events have dimension due to the length of associated dikes. 
Calculations that incorporate dike length become more comparable to calculations representing 
volcanic events as points, as dike lengths decrease. Intersection probabilities near 
10-7 intersections per year (Ho and Smith 1998, pp. 507 to 508; Reamer 1999, p. 61) reflect 
unusually small volcanic source zone areas or unusually long event lengths. 
Most of the published intersection probabilities, including the mean intersection probability 
estimated in the PVHA (CRWMS M&O 1996), cluster at values slightly greater than 10-8 per 
year, indicating that this probability estimate is robust, given the range of alternative temporal 
and spatial models and event geometries considered in the probability calculations. 
November 2003 2-20 No. 13: Volcanic Events
Crowe, Johnson et al. 
1982, pp. 184 to 185 
Crowe, Perry, Valentine 
et al. 1993, p. 188 
Connor and Hill 1995, 
pp. 10, 121 
Crowe, Perry, Geissman 
et al. 1995, Table 7.22 
Ho and Smith 1998, 
pp. 507 to 508
a Volcanic Event
Intersection 
Probability (per year) Reference 
(1) 1.5  10-8, 
(2) 1.09  10-8, 
2.83  10-8, 
(3) 3.14  10-7 
CRWMS M&O 1998a, 
Chapter 6, p. 6-84 
Connor, Stamatakos, 
Ferrill, Hill, Ofoegbu 
et al. 2000, p. 427 
Table 2-4. Published Estimates of the Probability of Intersection of the Repository at Yucca Mountain by 
3.3  10-10 to 
4.7  10-8 
2.6  10-8 
15  10-8 
1.8  10-8 
2.5  10-8 
10-8 to 10-7 
Comment 
Range of alternative probability 
calculations 
Median value of probability distribution 
Range of 3 alternative models 
Median value of 22 alternative probability 
models 
3 alternative models; 3rd model assumes 
a spatial intersection ratio (using a 
Bayesian prior) of 8/75 or 0.11, 
approximately one order of magnitude 
higher than other published estimates, 
because volcanic events are forced to 
occur within a small zone enclosing 
Yucca Mountain 
Sensitivity analysis that conservatively 
assumes all aeromagnetic anomalies in 
Amargosa Valley are Quaternary age 
Value of 10-7 assumes maximum event 
length of 20 km, regional recurrence rates 
of 5 events/m.y., and that crustal density 
variations contribute to event location. 
2-21 
Event 
Representation 
point 
point 
point 
point 
point 
point 
line 
November 2003 
Source: BSC 2003e, Table 13. 
2.2.8 Definitions and Parameters of a Volcanic Event and Implications for Probability 
Calculations 
An important issue in the PVHA and in alternative volcanic hazard assessments of the repository 
is the definition of a volcanic event. The definition of a volcanic event can affect the outcome 
of probability calculations and must be clearly understood to meaningfully compare the results of 
alternative probability calculations. The PVHA experts defined a volcanic event to be a spatially 
and temporally distinct batch of magma ascending from the mantle through the crust as a dike or 
system of dikes (CRWMS M&O 1996, Appendix E). The physical manifestation of a volcanic 
event includes the dike or dike system, and any surface eruption deposits. For the purposes of 
probability models here, a volcanic event is defined as a point in space representing the expected 
midpoint of the dike system involved in the magma ascent. The dike system associated with the 
volcanic event is represented in the probability model by a line element defined in terms of a 
length, azimuth and location relative to the point event (Figure 2-9). The term dike length used 
in the PVHA and in this report when discussing volcanic events refers to the total length of the 
dike system associated with the volcanic event. The phrase intersection of the repository 
footprint by a dike refers to intersection of the emplacement area of the repository by the line 
element representing the dike system associated with the volcanic event. The possibility that a 
dike system has width or consists of multiple parallel dikes does not significantly affect the 
intersection probability and is not part of the hazard calculations. The width of the dikes and the 
number of parallel dikes does affect the consequences of an intersection, is incorporated into the 
igneous intrusion scenario presented in Number of Waste Packages Hit by Igneous Intrusion 
No. 13: Volcanic Events 
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Revision 2 
(BSC 2003c), and is discussed in Sections 5.2 through 5.4. Although the PVHA analysis 
considered volcanic events to have both an extrusive and intrusive component (volcano and 
dike), the output of the PVHA was the annual frequency of intersection of the repository by an 
intrusive basaltic dike (CRWMS M&O 1996). The PVHA analysis did not calculate the 
conditional probability that a dike intersecting the repository would result in an extrusive 
volcanic eruption through the repository. 
Source: BSC 2003e, Figure 12. 
NOTE: L is dike length, LI and  are the length and azimuth, respectively, for that portion of an intersecting dike 
within the repository footprint; Li
m and n are specific bins of intersection length and azimuth; 1 and 2 
define the range of azimuths over which a dike extending distance d from a volcanic event at (x,y) will 
intersect the repository footprint 
Figure 2-9. Definition of Parameters Used to Compute the Probability of Intersection of the Repository 
Footprint by a Volcanic Event 
November 2003 2-22 No. 13: Volcanic Events
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The PVHA represented volcanic events as having both length and orientation. Typical dike 
dimensions assigned by the experts were a dike width of 1 m and a dike length (the total length 
of the dike system associated with a volcanic event) of 1 to 5 km (CRWMS M&O 1996, 
Appendix E, Figure 4). The most likely values for maximum dike lengths were estimated to be 
in the range of 17 to 22 km (CRWMS M&O 1996, Figure 3-62). The values of maximum dike 
length represent tails of distributions that have a small impact on the probability of dike 
intersection. The aggregate dike-length distribution derived from the PVHA has 5th-percentile, 
mean, and 95th-percentile values of 0.6, 4.0, and 10.1 km, respectively (Figure 2-10). The most 
commonly assigned dike orientation centers around N30E (CRWMS M&O 1996, Figure 3-62). 
Source: CRWMS M&O 1996; DTN: LA0009FP831811.001. 
NOTE: The 5th-percentile, mean, and 95th-percentile values are 0.6, 4.0, and 10.1 km, respectively. The 
distribution contains a very long upper tail extending to 86 km. The irregular shape of the probability mass 
function in the lower plot reflects the variation in the distributions defined by the individual experts. 
Figure 2-10. Composite Distribution for Dike Length Averaged across All Ten Probabilistic Volcanic 
Hazards Analysis Experts 
November 2003 2-23 No. 13: Volcanic Events
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2.2.9 Intrusive Versus Extrusive Events: Evidence from the Yucca Mountain Region 
and Analog Sites 
In the PVHA (CRWMS M&O 1996) definition of a volcanic event, the definition requires an 
intrusive event and allows an extrusive event. A volcanic event is a dike or dike system, together 
with its associated eruptive products. Dikes that ascend to depths of less than about a kilometer 
are thought to erupt at some point along the length of the dike, mainly because of volatile 
exsolution from basaltic magma. 
An appropriate analog in the Yucca Mountain region for understanding the relationship between 
intrusive and extrusive components of a volcanic event is the Paiute Ridge intrusive/extrusive 
center (Byers and Barnes 1967) on the northeastern margin of the Nevada Test Site. Paiute 
Ridge is a small-volume Miocene volcanic center comparable in volume and composition to 
Quaternary volcanoes near Yucca Mountain (CRWMS M&O 1998a, Chapter 5, p. 5-29). 
Paleomagnetic, geochronologic, and geochemical data indicate that the entire intrusive/extrusive 
complex formed during a brief magmatic pulse and, thus, represents a single volcanic event 
(Ratcliff et al. 1994; CRWMS M&O 1998a, p. 5-29). The vents and associated dike system 
formed within an NNW-trending extensional graben, and excellent exposures of the system 
include remnants of surface lava flows, volcanic conduits, and dikes and sills intruded into tuff 
country rock at depths up to 300 m (CRWMS M&O 1998a, p. 5-27 through 5-41). There is 
evidence of shallow structural control of dike emplacement at Paiute Ridge, including dike 
emplacement along fault planes (Byers and Barnes 1967; CRWMS M&O 1998a, Chapter 5, 
pp. 5-27 through 5-28). Dike lengths at Paiute Ridge range from less than 1 to 5 km (CRWMS 
M&O 1998a, Chapter 5, p. 5-31), comparable to the range estimated for postMiocene 
volcanism near Yucca Mountain (Figure 2-10). Field observations at Paiute Ridge clearly show 
that, while some parts of individual dikes stagnated within about 100 m of the surface without 
erupting, other parts of the same dike did erupt, as evidenced by associated lava flows and 
volcanic conduits (Byers and Barnes 1967; CRWMS M&O 1998a, p. 5-29 to 5-33). 
In the San Rafael dike swarm on the western Colorado Plateau, Delaney and Gartner (1997, 
p. 1180) estimate that 174 dikes are represented where an extensive system of shallowly intruded 
dikes is well exposed. Breccias are present along portions of 45 of these dikes, which are 
interpreted to represent the subsurface beneath eruptive centers (Delaney and Gartner 1997). No 
attempt is made by Delaney and Gartner (1997) to estimate the frequency of temporally discrete 
intrusive versus eruptive events. They suggest only that at least 45 dikes show evidence of 
eruption along some segment of a dike; other parts of the same dike, or other parts of the same 
dike system, may have erupted, as is observed at Paiute Ridge. Given the Paiute Ridge analogy 
and the Delaney and Gartner (1997) interpretation that the San Rafael swarm likely represents 
the subsurface beneath a large volcanic field that was active for about a million years, it is likely 
that many individual intrusive/extrusive events are represented at San Rafael, with some part of a 
dike system erupting during each event, and other parts of the same dike system not erupting. 
The ratio of intrusive to extrusive events is close to 1, an interpretation that is consistent with the 
Paiute Ridge analog site and the results of the PVHA (CRWMS M&O 1996). 
November 2003 2-24 No. 13: Volcanic Events
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2.2.10 Event Lengths: Evidence from the Yucca Mountain Region and Analog Sites 
The length of dikes or vent alignments can significantly affect intersection probabilities, because 
volcanic events occurring at some distance from the repository must have sufficient length to 
intersect the repository, and longer event lengths will result in higher intersection probabilities. 
Nearer to the repository, volcanic events with shorter lengths are able to intersect the repository 
with higher frequency. 
The mean dike length associated with a volcanic event in the Yucca Mountain region is 4 km, 
and 95 percent of dikes are shorter than 10.1 km (Figure 2-10). These values are consistent with 
observed volcanic features in the Yucca Mountain region. For instance, the maximum 
aligned-vent spacing in the Yucca Mountain region is 5.4 km between Black and Makani Cones, 
and volcanic-vent alignment lengths are typically in the range of 2 to 5 km (e.g., Hidden 
Cone-Little Black Peak, Amargosa Aeromagnetic Anomaly A, Red Cone-Black Cone). The 
longest proposed vent alignment in the Yucca Mountain region, assuming it represents one 
volcanic event, is the Quaternary Crater Flat alignment with a length of about 11 km 
(Figure 2-1). Dikes, such as those at Paiute Ridge, range in length from less than 1 to 5 km. 
Dike and vent alignments of the 3.7 Ma basalts in southeast Crater Flat are no more than 4 km in 
length (see Figure 2-11). 
November 2003 2-25 No. 13: Volcanic Events
Source: Vaniman and Crowe 1981, Figures 4, 6, 8; CRWMS M&O 1998a, Figure 2.7; Perry et al. 1998. 
Figure 2-11. 
No. 13: Volcanic Events 
Revision 2 
Geologic Map of the Pliocene Basalt of Crater Flat 
November 2003 2-26
Revision 2 
About 97 percent of the 174 dike lengths measured in the San Rafael volcanic field (discussed 
above) have total lengths less than 5 km (Delaney and Gartner 1997, Figure 4). The median of 
the length distribution at San Rafael is approximately 1.1 km, and the maximum dike length is 8 
to 9 km (Delaney and Gartner 1997, Figure 4), a distribution similar to that used in the PVHA 
(Figure 2-10). 
A measure comparable to dike half-length, the distance from the end of the dike nearest the 
repository to the point of origin (the midpoint) of the volcanic event, can be derived from 
information elicited in the PVHA. This distribution has 5th-percentile, mean, and 
95th-percentile values of 0.2, 2, and 5.6 km, which, given the previous discussions of observed 
dike lengths, vent spacings, and maximum observed half-length vent alignment of 5.6 km, is in 
excellent agreement with observed volcanic-event features in the Yucca Mountain region. 
2.2.11 Conceptual Models of Volcanism and Formulation of Probability Models 
In the analysis of volcanic hazard for the repository, the conceptual model of volcanismhow 
and where magmas form and what processes control the timing and location of magma ascent 
through the crust to form volcanoeshas a fundamental impact on how probability models are 
formulated and the consequent results of probability models (e.g., Smith, Feuerbach et al. 1990; 
CRWMS M&O 1996; Reamer 1999). 
The PVHA experts viewed the Yucca Mountain region as part of the same extensional tectonic 
and volcanic regime as the rest of the southern Great Basin portion of the Basin and Range 
province, and several members of the panel noted the possible additional influence on volcanism 
of the Walker-Lane structural zone (CRWMS M&O 1996, Appendix E, e.g., pp. WD-1, WH-1). 
The Walker Lane Fault Zone is a major tectonic system located at the boundary of the Sierra 
Nevada and the Basin and Range, that includes several major fault systems. The Walker Lane 
region, which extends from near Las Vegas to south-central Oregon, is being deformed by both 
extensional and lateral fault movement. The smaller volumes of basalt erupted in the Yucca 
Mountain region since the Miocene reflects waning of both tectonism and magmatism in this part 
of the Basin and Range Province (CRWMS M&O 1996, Appendix E, e.g., pp. RC-1, BC-3, 
WD-2, RF-3, WH-1, MK-1, AM-3). 
Some experts distinguished between deep (mantle source) and shallow (upper crustal structure 
and stress field) processes when considering different scales (regional and local) of spatial 
control on volcanism (CRWMS M&O 1996, Appendix E, e.g., pp. MK-2, AM-1). In the PVHA, 
volcanism in the Yucca Mountain region was viewed as a regional-scale phenomenon, involving 
melting processes in the upper lithospheric mantle that produce small volumes of alkali basalt, 
which is a basalt type generated by relatively small percentages of mantle melting compared to 
other basalt types (CRWMS M&O 1998a, Chapter 4, p. 4-4). The exact mechanism of mantle 
melting in the Yucca Mountain region is poorly understood but may be controlled by a 
combination of processes. These include the effect of residual heat in the lithospheric mantle 
from previous episodes of volcanism and the presence of a former plate-subduction system, local 
variations in volatile (water) content, variations in mantle mineralogy and chemistry, and the 
effect of regional lithospheric extension (CRWMS M&O 1996, Appendix E). Researchers who 
have analyzed magmatic processes in the Yucca Mountain region generally agree that the 
magnitude of mantle melting has decreased greatly since the middle Miocene and that all melts 
November 2003 2-27 No. 13: Volcanic Events
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in the past few million years have been generated within relatively cool (compared to 
asthenospheric mantle) ancient lithospheric mantle, a factor that may contribute to the relatively 
small and decreasing volume of basaltic melt erupted in the Yucca Mountain region since the 
Miocene (Farmer et al. 1989; Yogodzinski and Smith 1995; CRWMS M&O 1996, Appendix E; 
Reamer 1999, pp. 17 and 47). 
2.2.12 Current Volcanic Hazard Estimate 
In terms of probability calculations, the volcanic source zones defined in the PVHA represent 
local regions of higher event frequency (southwestern part of the Crater Flat structural domain), 
whereas the northeastern part of the Crater Flat structural domain (including Yucca Mountain) 
falls within a regional background source zone of lower event frequency (BSC 2003e, p. 63, 
Figure 17a). According to the intersection probability models used, two mechanisms could 
generate a disruptive event at Yucca Mountain. Either a volcanic event is generated within a 
local source zone (higher probability event) to the west of Yucca Mountain and has the 
appropriate location and dike characteristics (length and azimuth) to intersect the repository, or a 
volcanic event is generated with a regional background zone (lower probability event) and 
intersects the repository. Because the total probability of intersection of a volcanic event with 
the repository includes components of both mechanisms, the intersection probability estimated 
for the repository should reflect spatial event frequencies that lie between local source zone 
values and regional background values. This is consistent with the results of the PVHA, and is 
appropriate for a site that lies outside of a local volcanic source zone but near enough to possibly 
be affected by dikes generated within that source zone. To compute the consequences of an 
intersection, information is also needed on the length and orientation of the intersecting dike and 
the probability that an eruptive center (a surface vent fed by the dike) may form within the 
footprint. The result of the PVHA (CRWMS M&O 1996) has been recalculated to account for 
the repository footprint and extended to include the probability of an eruption within the 
repository footprint, conditional on a dike intersection (Table 2-5). The annual frequency of 
intersection of the repository footprint by a dike or dike system associated with a volcanic event, 
and the annual frequency of a volcanic event producing one or more eruptive centers within the 
repository have been recalculated, based on the current repository footprint. These results are 
summarized below and shown in Table 2-5. 
The volcanic hazard recalculated using the LA footprint (BSC 2003c, Section 4.1) is not 
significantly different from the PVHA estimate. These updated analyses will be used as the 
technical basis for probability weighted dose calculations in the LA. The studies of the 
sensitivity of the PVHA hazard estimate were consistent with NRC guidance on the use of expert 
elicitation (NUREG-1563, Kotra et al. 1996). 
November 2003 2-28 No. 13: Volcanic Events
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Table 2-5. Summary Frequencies of Disruptive Volcanic Events for the License Application 
Repository Footprint 
Annual Frequency of 
Occurrence of One or 
More Eruptive Centers 
within Repository 
Annual Frequency of 
Intersection of Repository by a 
Volcanic Event 
5.6  10-10 
1.3  10-8 
4.3  10-8 
Composite 
Conditional 
Probability of At 
Least One 
Eruptive Center 
0.75 
0.78 
0.77 
7.4  10-10 (5th percentile) 
1.7  10-8 (mean) 
5.5  10-8 (95th percentile) 
Source: DTN: LA0307BY831811.001. 
November 2003 
NOTE: Results presented in this table were rounded to two significant digits after 
calculation. 
2.2.12.1 Length and Azimuth of an Intersecting Dike 
The hazard computation gives the overall frequency of a dike intersecting a repository. 
However, to compute the consequences of an intersection, the distribution for length and 
orientation of the intersecting dikes is needed. This distribution is developed by breaking down 
(disaggregating) the total frequency into frequencies for specific values of intersecting dike 
length and dike azimuth (BSC 2003e, Section 6.5.1.2, paragraph 1, p. 72). The process involves 
computing the spatial disaggregation of the frequency of intersection into the contributions from 
each location (xi,yj) in the spatial grid around the repository. At each point, the conditional 
probability of intersection is the probability that dikes of all lengths and azimuths will intersect 
the repository. The conditional probability of intersection is divided into probabilities for 
intersection from dikes with specific lengths and azimuths. As a result, the frequency of 
intersection from volcanic events at point (xi,yj) is divided into the frequency of intersection from 
volcanic events at point (xi,yj) that produce specific values of length and azimuth within the 
repository footprint. Summing these frequencies over all locations gives the frequency of 
intersection with a specific value of length and azimuth from all volcanic events. Dividing this 
frequency by the total frequency of intersection gives the conditional probability that an 
intersecting dike will produce a specific value of length and azimuth within the repository. 
2.2.12.2 Conditional Distributions for the Number of Eruptive Centers within the 
Repository Footprint 
The mathematical formulation for assessing the conditional distribution for the number of 
eruptive centers within the footprint of the repository is based on the concept that eruptive 
centers will occur at uncertain locations along the length of the dike associated with a volcanic 
event (BSC 2003e, Section 6.5.1.3, paragraph 1, p. 77). The length of intersection within the 
repository footprint compared to the total length of the dike, the number of eruptive centers per 
volcanic event, and the spatial distribution of eruptive centers along the length of the dike 
provide the bases for assessing the likelihood that one or more eruptive centers will occur within 
the repository footprint. The total length of the dike and the length of intersection within the 
repository are completely defined by the PVHA experts interpretations (BSC 2003e, 
Section 6.5.1.3, paragraph 1, p. 77). The number of eruptive centers per volcanic event and the 
spatial distribution of eruptive centers along the length of a dike were not defined as part of the 
2-29 No. 13: Volcanic Events
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expert elicitation. However, with a limited set of assumptions (described in the next paragraph), 
these can be derived from the experts interpretations. There are alternative ways that these 
assumptions can be applied. In keeping with the concept of uncertainty characterization 
employed in the probabilistic volcanic hazards analysis, alternative assessments were developed 
of the conditional distribution for the number of eruptive centers within the repository footprint. 
To produce a composite distribution, these assessments were then combined using the relative 
weights assigned to each alternative assessment. 
Two approaches for assessing the number of eruptive centers per volcanic event are considered. 
The first uses the number of mapped volcanoes in the Yucca Mountain region to derive empirical 
distributions for the number of eruptive centers per volcanic event independent of any 
assessment of the length of the dike associated with the volcanic event. In this approach, 
volcanic events can have from 1 to 5 eruptive centers, the range of individual volcanoes that was 
associated with a single volcanic event by the PVHA experts. The second approach uses the 
number and location of the mapped volcanoes to derive empirical distributions for the average 
spacing between eruptive centers. This distribution, together with the length of the dike 
associated with a volcanic event, determines the number of eruptive centers for a given volcanic 
event (BSC 2003e, Section 6.5.1.3, paragraph 2, p. 77). 
November 2003 2-30 No. 13: Volcanic Events
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3. ERUPTIVE PROCESSES AND CHARACTERISTICS OF BASALTIC MAGMA 
The behavior of basaltic magmas that could intrude or erupt through a repository provides 
important constraints on the consequences associated with igneous or volcanic activity. This 
section describes the properties of basaltic magmas and the mechanisms that determine the style 
and energy of intrusive or extrusive events. It provides a physical and technical basis for the 
consequence analysis presented in Section 5. 
3.1 GENERAL CONCEPTUAL MODEL OF BASALTIC VOLCANISM IN THE 
YUCCA MOUNTAIN REGION 
The general conceptual model is shown in Figure 3-1. It depicts the key features and processes 
involved in the formation and construction of the small volcanic centers typical of the Yucca 
Mountain region. It shows the dikes that feed lava flows and Strombolian eruptions, as well as 
the ash clouds that deposit air-fall ash (tephra) downwind of the cone. 
Figure 3-1. General Conceptual Model of Basaltic Volcanism in the Yucca Mountain Region 
Alkali-basaltic magma is generated by partial melting of ancient lithospheric mantle beneath the 
Yucca Mountain region. Driven by buoyancy, the magma ascends through the lithosphere and 
continental crust of the southern Great Basin. In the brittle crust above approximately 15 km 
depth, batches of melt ascend as magma-filled cracks or dikes. The dikes are intruded with 
November 2003 3-1 No. 13: Volcanic Events
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azimuths approximately N30E, a direction that is perpendicular to the direction of least 
compressive stress in the upper crust of the Yucca Mountain region. Within a few hundred 
meters of the surface, dikes in the Yucca Mountain region are generally 1 to 2 m thick, average 
4 km in length, and nearly always erupt to form basaltic volcanoes. As dikes reach the surface, 
fissure eruptions are focused into central vents within hours or days. The conduits feeding such 
vents are estimated to be tens of meters in diameter. Conduits may shift in location and change 
in their subsurface configuration, vent locations may correspondingly change during the course 
of an eruption, multiple vents may be simultaneously active, and single vents may 
simultaneously produce lava and tephra. 
The petrographic features of the erupted lava and experimental data on similar magma 
compositions indicate eruption temperatures near 1,170C, the presence of 2 to 4 weight percent 
water as the dominant volatile constituent and viscosity of approximately 102 poise. 
Experimental and theoretical data indicate that alkali basaltic magma of the Yucca Mountain 
region will begin to exsolve gas at about 6 to 7 km depth. Volatile exsolution is a continuous 
process during the ascent of magma through the upper crust. The resulting volume expansion is 
a significant factor in driving the basaltic dikes upward through the final kilometer or so of 
brittle, fractured rock. The inception of basaltic volcanism is typically characterized by 
pyroclastic eruptions of gas-rich magma. 
Based on geologic observations in the Yucca Mountain region, future volcanism in the Yucca 
Mountain region is expected to produce small, monogenetic basaltic centers, each with a total 
erupted volume of 0.01 to 0.1 km3. The dominant style of volcanism is Strombolian, involving 
the construction of basaltic scoria cones and the effusion of lava flows. Violent Strombolian 
eruptions may also occur, involving sustained, vertical eruption columns that eject volcanic ash 
to heights of 3 to 5 km above the scoria cone. Subsequent wind-borne dispersal of the fine 
tephra may form ash sheets up to approximately 15 km from the vents. The volumes of the ash 
sheets are estimated to be two to four times the volumes of the associated scoria cones. 
The unsaturated zone beneath Yucca Mountain is approximately 550 m deep. Together with 
magma properties, the high permeability and unsaturated condition of the tuffaceous host rocks 
of the repository play a major role in determining the style and dynamics of volcanic eruptions 
and the nature of potential interaction between basaltic magma and the repository drifts. 
Hydrovolcanism is uncommon in the Yucca Mountain region geologic record due to the deep 
water table and paucity of surface or perched water. Future hydrovolcanism is unlikely at Yucca 
Mountain because of the elevated terrain, the great depth of the water table, and the high 
permeability and low porosity of the unsaturated host tuffs. 
Based on historical observations of similar eruptions in analog regions, the duration of single 
igneous events in the Yucca Mountain region is estimated to have been weeks, months, or 
perhaps a few years. The estimated durations and volumes of the small basalt volcanic centers in 
the Yucca Mountain region suggest peak Strombolian mass-eruption rates of 104 to 105 kg/s, 
with average rates of approximately 103 kg/s. Maximum rates of approximately 106 kg/s are 
possible during violent Strombolian phases of basaltic volcanism in the Yucca Mountain region. 
Crustal extension in the Yucca Mountain region is accommodated through a combination of 
faulting and magma intrusion. There is a strong tendency for basaltic dikes of the Yucca 
November 2003 3-2 No. 13: Volcanic Events
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Mountain region to preferentially ascend and erupt through upper crust that is undergoing 
extension. The southwestern part of the Crater Flat structural domain, which closely corresponds 
to Crater Flat, a topographic basin to the west and southwest of Yucca Mountain, is an area of 
Quaternary faulting and basaltic volcanism in the Yucca Mountain region. Crater Flat is the 
location of most of the Quaternary volcanoes in the Yucca Mountain region and is identified as 
the major volcanic source zone that may impact the repository. The most probable scenario for 
disruption of the repository is the intersection of repository drifts by a basaltic dike, associated 
with a volcanic event in Crater Flat. If a dike intersects the repository drifts, magma will flow 
into them as pyroclastic material or gas-poor lava. 
3.2 COMPOSITION AND PROPERTIES OF BASALTIC MAGMA IN THE YUCCA 
MOUNTAIN REGION 
Magma is a mixture of silicate melt, crystals (phenocrysts and xenocrysts), and volatiles (present 
as dissolved constituents in the melt or as exsolved vapor bubbles in the melt). In magmatic 
systems where explosive interaction with external groundwater or surface water (hydrovolcanism 
or phreatomagmatic volcanism) plays no role, the viscosity and volatile content of the melt play 
a fundamental role in the eruption energetics, expressed as volcanic style. Magma viscosity is 
primarily influenced by melt composition and temperature. In comparison with other types of 
magma, basaltic magma is relatively fluid and is poor in dissolved gas. Eruptions from basaltic 
volcanoes, therefore, tend to be less explosive than eruptions of silicic magma. 
General information on basaltic magma composition and properties in the Yucca Mountain 
region is given here, based on the more detailed data, calculations and tables of magma 
properties found in Characterize Eruptive Processes at Yucca Mountain, Nevada (BSC 2001; 
BSC 2003b) and Final Report of the Igneous Consequences Peer Review Panel (Detournay 
et al. 2003). 
3.2.1 Magma Composition 
Magma-chemistry data are used to determine parameters for important variables such as magma 
viscosity, temperature, and density. The magma composition of the Lathrop Wells volcano is 
adopted to represent the composition of future Yucca Mountain region volcanoes. The Lathrop 
Wells composition is selected because it represents the most recent eruption in the Yucca 
Mountain region, and emphasizes the composition that produced more violent explosive 
eruptions compared to other Yucca Mountain region volcanoes (as inferred from Perry 
et al. 1998, Chapter 2). The major-element composition for Lathrop Wells is based upon 
45 chemical analyses (DTN: LA000000000099.002). Mean values for selected major-element 
constituents are (weight percent) SiO2 = 48.50; TiO2 = 1.93; Al2O3 = 16.74; Fe2O3T = 11.63, 
MgO = 5.83; CaO = 8.60; Na2O = 3.53; K2O = 1.84; P2O5 = 1.22. These values indicate that the 
magma is a variety of alkali basalt. 
3.2.2 Water Content of Primary Basaltic Magma 
Eruptive styles in the Yucca Mountain region are inferred to have ranged from violent 
Strombolian on one end of the spectrum to quiescent aa lava on the other (Perry et al. 1998, 
Chapter 2). Eruption style was primarily controlled by volatile content (which is dominated by 
November 2003 3-3 No. 13: Volcanic Events
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water with subordinate CO2) and the rate at which volatiles were exsolved from the magma. The 
eruptive products of the Crater Flat and Lathrop Wells volcanoes indicate a large range in 
volatile contents and, hence, water content of Yucca Mountain region magmas. 
Mineralogical and geochemical data indicate that primary magmatic water contents ranged up to 
as much as 4 weight percent. Amphibole, possibly of magmatic origin, is found as a rare and 
sparse phase in some Quaternary Crater Flat basalts. Knutson and Green (1975, Figure 1, 
p. 126), performing experiments on material similar in composition to Yucca Mountain region 
basalts, observed that magmatic amphibole was stabilized at water contents of between 2 and 
5 weight percent. Baker and Eggler (1983, p. 387) showed that at 2 kbar pressure, water content 
in excess of 4.5 weight percent is required to stabilize amphibole in high-alumina basalt similar 
to Yucca Mountain region basalts. Sisson and Grove (1993, p. 167) note that low-Mg basalts 
with high alumina content cannot erupt as liquids with water content in excess of 4 weight 
percent because they will exsolve liquid and rapidly crystallize to form phenocryst-rich magmas 
as they approach the surface. Based on mineralogical and petrologic arguments (BSC 2003b, 
Section 6.3.2), 4 weight percent water is used as an upper bound on initial dissolved-water 
content, and zero percent magmatic water has a zero probability of occurrence. The most likely 
range of water contents for alkali-basaltic magma in the Yucca Mountain region is 1 to 3 weight 
percent. Direct measurements of water in mafic (low silica) magmas or magmatic products from 
a range of tectonic settings also support these recommended values (BSC 2001). 
3.2.3 Mole Percent of Constituents in Volcanic Gas 
Because there is no ongoing volcanism in the Yucca Mountain region, gas composition cannot 
be directly observed. Therefore, a survey of data from the literature, including volcanoes from 
various tectonic settings, has been used to constrain the relative proportions of major gas 
constituents in Yucca Mountain region basalts. Three types of data exist in the literature: 
(1) measurements of emitted volcanic gases, (2) measurements of gases trapped in volcanic glass 
or melt inclusions, and (3) experiments on gas solubilities in silicate melts. The values used for 
gas constituents in Yucca Mountain region mafic magmas are (mol percent): H2O = 75, 
CO2 = 15, SO2 = 9, H2 = 1 (BSC 2001, simplified from Table 7). 
3.2.4 Magmatic Temperatures, Viscosities, and Densities 
Experimental results are used to constrain magmatic temperatures for magmas with elevated 
water content. Table 3-1 gives several properties calculated for Lathrop Wells magma (see 
BSC 2001, pp. 63 to 65 for details of the calculations). Yucca Mountain region basaltic lavas are 
generally aphyric to sparsely porphyritic (Perry and Straub 1996, p. 6), which indicates that they 
erupted at near-liquidus or superliquidus temperatures (liquidus temperature is the temperature at 
which crystallization begins). 
November 2003 3-4 No. 13: Volcanic Events
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0 
0.5 
Function of Water Content for Lathrop Wells Basaltic Magma 
Viscosity 
(log poise) 
Water Content 
(wt%) 
2.678 
2.572 
2.472 
2.284 
2.112 
1.957 
Saturation Pressure 
(Pa) 
1  105 
9.0  106 
2.4  107 
6.5  107 
1.2  108 
1.7  108 
Liquidus 
Temperature (C) 
1169 
1153 
1137 
1106 
1076 
1046 
1
2
3
4 
Table 3-1. Calculated Saturation Pressures, Liquidus Temperatures, Viscosities, and Densities as a 
Density 
(kg/m3) 
2663 
2633 
2605 
2556 
2512 
2474 
November 2003 
NOTE: Derived using mean Lathrop Wells compositions. 
A review of relevant experimental data reveals that these values are reasonable. The liquidus 
temperature for a mildly alkalic basalt similar in composition to the mean Lathrop Wells lava 
composition is between 1,174 and 1,188C (Mahood and Baker 1986). The Mahood and Baker 
(1986) temperature calculations are close to temperatures reported by Knutson and Green (1975, 
Figure 1) for a hawaiite that is also similar in composition to Lathrop Wells basalt. Yoder and 
Tilley (1962, Figure 28) published results on the water-saturated liquidus for a high-alumina 
basalt. At 1.75  108 Pa water pressure, the liquidus was more than 100C cooler than the 105 Pa 
liquidus temperature. Thus, the calculated parameter values are consistent with a 
well-established body of experimental data. 
3.3 PHYSICAL VOLCANOLOGY OF BASALT VOLCANOES IN THE YUCCA 
MOUNTAIN REGION 
Figures 2-11 and 3-2 show geologic maps of selected Quaternary and Pliocene volcanoes near 
Yucca Mountain (Vaniman and Crowe 1981; CRWMS M&O 1998a; Perry et al. 1998). The 
deposits consist of scoriaceous tephra cones, with associated aa lava flows. Exposed deposits at 
most of the centers cover less than 2 square km. The cones are typical scoria cones of 300 to 
700 m basal diameter and up to 220 m but generally less than 100 m in height, composed 
predominantly of frothy bombs and lapilli that were produced during Strombolian eruptions. For 
a number of the centers, several conduits were apparently active along a fissure or set of eruptive 
fissures, as at Red Cone. Most of the cones produced aa lava flows from their flanks or bases. 
The eruptive products of the 1-Ma Crater Flat volcanoes are deeply eroded and are in places 
covered by alluvial and eolian deposits, particularly the lava flows, but the proportion of lava to 
cone tephra deduced from mapping and interpretation of associated aeromagnetic anomalies 
appears to be generally greater than 1. The tephra-fall deposits from these eruptive centers have 
been largely removed by erosion or buried by younger sediments and are therefore unmappable. 
Even at the 80-ka Lathrop Wells volcano, primary tephra-fall deposits are not found at distances 
greater than about 2.5 km from the vent (BSC 2003b, p. 120). 
3-5 No. 13: Volcanic Events
Source: Perry et al. 1998.
Figure 3-2. 
No. 13: Volcanic Events 
Revision 2 
Geologic Map of Little Cones in Crater Flat 
November 2003 3-6
Revision 2 
More than half of the ejecta during Strombolian eruptions fall within 500 m of the vent, and 
cones are usually built rapidly during initial high rates of eruption. During such eruptions, the 
rapid expansion of dissolved gas leads to the formation of bubbly clots. The largest clots and 
those rising in the core of the fountain remain fluid during their brief flight and coalesce near the 
vent into rootless lava flows or lava ponds. Others are quenched by entrained air and are 
deposited as chilled, individual clasts on the cone flanks or within the summit crater. Dilute 
convective plumes of volcanic gas, aerosols and ash are inferred to have formed above the Crater 
Flat vents, although the tephra-fall deposits of such plumes are not well preserved, having been 
removed by erosion or covered by surficial deposits (BSC 2003b, Section 6.4.2). Observations 
of historical Strombolian and Hawaiian eruptions indicate that these plumes contain less than 
0.17 percent of the total mass fraction of lava erupted and rarely penetrate the tropopause 
(Vergniolle and Mangan 2000, p. 452), or upper atmosphere. 
At the location of the Pliocene basaltic centers of southeastern Crater Flat (Figure 2-11), most of 
the cone-building scoria deposits have been eroded, exposing the shallow feeder systems of these 
volcanic centers. Sinuous dike segments of 50 to 300 m length occur in close association with 
remnants of welded scoria or as rootless lava ponds or intrusions into alluvial deposits. Dike 
widths are generally less than 2 m but in places the dikes swell into pluglike lava masses of 
approximately 5 m width. 
3.4 PHYSICAL VOLCANOLOGY OF THE LATHROP WELLS CONE 
Because of its relative youth, exposure, composition, and position in the sequence of basaltic 
eruptive events in the Yucca Mountain region, the Quaternary Lathrop Wells volcano is an 
appropriate example of the type of eruptive event that could disrupt the repository (Figures 3-3 
and 3-4). An exception to this generalization is the occurrence of hydrovolcanic tephra deposits 
from the early and late stages of eruption at Lathrop Wells volcano, reflecting the interaction of 
basaltic magma with shallow groundwater, perhaps contained in near-surface alluvial deposits. 
Such magma-water interaction would not be expected during a future eruption through the 
repository, because the repository is located in the unsaturated zone, the saturated zone is located 
several hundred meters beneath the repository, and the low porosity and unsaturated condition of 
the repository tuff would not permit the water inflow needed to maintain continuous 
hydrovolcanism (Crowe, Self et al. 1983, p. 268). 
The Lathrop Wells lava flows have an eruption age of approximately 77.3  6.0 ka, based on 
seventeen 40Ar/39Ar ages on the stratigraphically oldest lava flow. An age of 80,000 years is 
used, based on the discussion of Perry et al. (1998) and the detailed geochronology studies of 
Heizler et al. (1999). The most probable interpretation for the Lathrop Wells eruptive center is 
that of a complex monogenetic volcanic center producing a cone, lava flows, and tephra-fall 
deposit erupted within a span of a few months or years, but the center also exhibits some features 
that support other interpretations of age and eruptive history (Perry et al. 1998). 
The Lathrop Wells volcano consists of lava flows with an estimated volume of 0.029 km3, a 
scoria cone of 0.018 km3, and a tephra-fall deposit of 0.039 km3, for a total erupted volume 
of 0.086 km3 (BSC 2003b). 
November 2003 3-7 No. 13: Volcanic Events
Source: Perry et al. 1998. 
NOTE: The alphanumeric designations (e.g., Ql1a, b, and c) refer to subunits (lava flow and scoria) of 
chronostratigraphic units Q1, Q2, Q3, and Q4. 
Figure 3-3. 
No. 13: Volcanic Events 
Geologic Map of the Lathrop Wells Volcanic Center 
3-8 
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November 2003
Revision 2 
3.4.1 Scoria Cone 
The Lathrop Wells scoria cone (Figure 3-4) is approximately 140 m high and oval, with its long 
axis oriented NNW-SSE. The cone measures 875 m by 525 m at its base and is capped by a 
similarly elongate, 190-m by 145-m crater that is about 20 m deep. The outer slopes of the cone 
range from 28 to 32 and consist of mostly loose scoria lapilli. The cone shape has been 
somewhat modified by erosion and is rapidly changing because of active quarrying along the 
south margins. Quarrying is revealing the three-dimensional structure of the cone, currently 
exposing approximately one-quarter of the cones interior. Figure 3-5 is a digital elevation 
model portraying the relief of the cone and surrounding area as if illuminated from the northwest. 
It shows the locations of samples used to investigate the physical volcanology of the volcano, 
details of which are given in Characterize Eruptive Processes at Yucca Mountain, Nevada 
(BSC 2001; BSC 2003b). 
Source: BSC 2003b, Figure 16. 
Figure 3-4. Lathrop Wells Scoria Cone and Adjacent Lava Flows (Capped by Beige Eolian Sand) 
November 2003 3-9 
Viewed from the North 
No. 13: Volcanic Events
Revision 2 
Source: BSC 2003b, Figure 17. 
NOTE: The Lathrop Wells Cone occupies the lower center of the map. The dots show locations of samples; grid 
is NAD 1927 UTM, Zone 11 North, in meters. Contour interval is 20 feet. 
Topographic Map and Tephra Sample Locations for Lathrop Wells Cone Area Figure 3-5. 
November 2003 3-10 No. 13: Volcanic Events
Revision 2 
Most cone deposits exposed in the quarry dip concentrically outward from the cone (Figure 3-6), 
and the lowest deposits exposed in the quarry are irregular masses of welded scoriaceous bombs 
and lapilli. Some of these agglutinate masses dip inward approximately 10 toward the 
presumed location of the vent. 
Source: BSC 2003b, Figure 18. 
NOTE: Left photo: Exposures of cone interior showing sharp transition from nonwelded, massive or poorly 
bedded, lapilli- and bomb-size ballistic ejecta to overlying moderately bedded avalanche deposits of ash 
and lapilli (more than 50 percent ash); most clasts are deposited at angle of repose as ballistic ejecta. 
Height of the lower coarse beds is about 2.5 m. Right photo: Close-up of ejecta (at base of left image), 
mostly broken scoria bombs and lapilli. The scale is 10 cm. 
Lathrop Wells Cone Interior Showing Scoria and Close-Up of Ejecta 
3.4.2 Lithic Clasts in the Lathrop Wells Cone Deposits 
Estimates of the volume and types of lithic clasts are important to repository risk assessment 
because the same processes that erode dike and conduit wall rock could influence the volume of 
waste reaching the surface (e.g., Crowe, Self et al. 1983, p. 270 to 271). 
Larger and more interior quarried exposures provide a better opportunity to measure lithic clast 
abundances within the Lathrop Wells Cone now than in the past. Results from Crowe, Wohletz 
et al. (1986), based on only four nonhydrovolcanic samples of the cone, ranged from 0.3 to 
2.4 vol% in the less than 0.707-mm size fraction. Table 3-2 lists results of counts of 18 1-m2 
areas located at several elevations in the cone. Access to outcrops in quarry walls and road cuts 
means that the elevations recorded with each measurement accurately reflect relative 
stratigraphic position. Measurements of lithic clasts greater than 1 mm were made in nonwelded 
deposits of coarse ash, lapilli, and larger material; they are not representative of the 
November 2003 3-11 
Figure 3-6. 
No. 13: Volcanic Events
stratigraphically lower, short pulse of hydrovolcanic activity recorded in deposits outside the 
cone (BSC 2003b, Section 6.4.2.3, Figure 26; Wohletz 1986, p. 258). 
NOTE: 
Table 3-2. Lithic Clast Measurements in the Lathrop Wells Scoria Cone 
Source: BSC 2003b, Table 18, p. 94; DTN: LA0302GH831811.003. 
Lithic clast measurements were done in eighteen 1-m2 areas in Lathrop Wells Cone 
outcrops. Elevations reflect relative stratigraphic position (early to late cone activity), as 
explained in the text. Multiply volume fraction by 100 to obtain percent. 
Mean lithic-clast abundances range from 0.29 vol% to less than 0.002 vol% (maximum value 
noted here is the mean of patches 1 through 6 measured within the same unit; maximum single 
measured value is 0.9 vol%) (BSC 2003b, p. 18). The volume data indicate that lithic clasts 
abundance is greatest within the measured lower stratigraphic levels in the scoria cone and 
decreases one to two orders of magnitude upward in younger scoria intervals. Not surprisingly, 
the lithic clast production during eruption was not uniform throughout the cone construction 
period, and the variation suggests less vigorous conduit enlargement with time. This observation 
is tempered with the recognition that much of the scoria (and included lithic clasts) within 
volcanic cones is subject to avalanching, slumping, and redeposition during construction 
(McGetchin et al. 1974, p. 3268). 
Lathrop Wells Cone lithic clast abundances are not unusually high. Within the studied 
exposures, which represent a substantial vertical section through the cone, no lithic clast 
abundances were encountered that are indicative of significant conduit-clearing activity at the 
cone (BSC 2003b, Section 6.4.2.1, p. 95). 
There is a common occurrence of secondary mineralization by silica and/or carbonate that coats 
many lapilli and larger grain surfaces that may be the cause of the elevated volume of lithic 
Volume Fraction 
0.000140 
0.000200 
0.000160 
0.000029 
0.000083 
0.000940 
0.000290 
0.000039 
0.006700 
0.000940 
0.008700 
0.003600 
0.009100 
0.005800 
0.000075 
0.001300 
0.001100 
0.000018 
3-12 
Patch 
17 
15 
12 
14 
13 
18 
16 
11 
7
8
9 
10 
1
2
3
4
5
6 
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Elevation (ft) 
3146 
3136 
3119 
3106 
3079 
3074 
3056 
2940 
2926 
2926 
2926 
2924 
2886 
2886 
2886 
2886 
2886 
2886 
0.004985 
Mean (710) 
0.002899 
Mean (16) 
Revision 2 
November 2003
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clasts obtained using computer-assisted image analysis (0.9 vol%; Doubik and Hill 1999, p. 60). 
Using this approach (digital images and image analysis) will result in a high estimate of lithic 
clasts. 
3.4.3 Eruption Mechanisms and History for the Lathrop Wells Cone and Tephra Fall 
The history of eruption phenomena that built the Lathrop Wells volcano is contained in the 
tephra cone and fall deposits, as described in Characterize Eruptive Processes at Yucca 
Mountain, Nevada (BSC 2003b) and by Crowe, Perry, Geissman et al. (1995) and Perry et al. 
(1998). Evolution of the Lathrop Wells volcano is tied to a general model of scoria cone 
formation proposed by McGetchin et al. (1974) and shown in Figure 3-7. 
1. Within 1 km of the vent, the earliest eruption deposited moderately sorted coarse ash 
with up to 52 percent vesicular sideromelane droplets. These are similar in shape and 
composition to glassy droplets produced in fire (lava) fountains. The fire fountaining 
could have been from a north-south-trending fissure (parallel to the long axis of the 
oval-shaped Lathrop Wells Cone and equivalent to stages 1 and 2 in Figure 3-7). The 
predominantly glassy droplets imply a largely unimpeded spray of melt from a vent or 
fissure. Some conduit opening is implied from the 7.6 percent tuff lithic clasts in the 
ash. Closer to the vent, a greater proportion of tachylite and glassy tachylite than 
sideromelane is present, indicating that some quench-crystallization was occurring 
within the rising magma, possibly due to avalanching of scoria and ash back down the 
incipient crater slopes to intermittently block the vent. There are four or five repeating, 
upward-coarsening tephra sequences in the lowest 125 cm of the observed section, with 
no recognized unconformities. This can be interpreted either as a continuous pulsing 
eruption or the result of varying wind directions during this part of the eruption. 
2. The tephra deposits immediately northwest of the Lathrop Wells Cone are 
representative of the hydrovolcanic phase of the eruption (Vaniman and Crowe 1981; 
Wohletz 1986). Hydrovolcanic activity can occur when rising magma comes into 
contact with water in an aquifer(s) or a shallow-water body at the ground surface 
(Fisher and Schmincke 1984; Wohletz and Heiken 1992). The resulting steam 
explosions fragment the magma into predominantly ash- and lapilli-sized particles and 
produce large amounts of kinetic energy. When these explosions occur below the 
ground surface, the host rocks are highly fractured and the eruption products contain 
abundant lithic clasts. Hydrovolcanic deposits consist mostly of ash deposited in 
density currents (surges), leaving distinctive thin planar beds and cross-beds, which are 
typical of the sequence immediately northwest of Lathrop Wells Cone. Most basaltic 
hydrovolcanic pyroclasts in hydrovolcanic deposits are glassy and have low 
vesicularity and blocky shapes (Heiken and Wohletz 1985). However, in many 
examples, there is some rounding, perhaps by grain-to-grain interactions in surges. 
Pyroclasts in hydrovolcanic surge deposits of the Lathrop Wells volcano are 
characterized by considerable edge modification (rounding). The fragmentation 
process produces consistently fine-grained tephra, at the Lathrop Wells Cone, median 
grain sizes for this tephra range from 0.15 mm to 0.5 mm. Volume fractions of lithic 
clasts in the fine-grained ash deposits range from 0.003 to 0.036 and consist mostly of 
white tuff and rounded quartz and feldspar sand grains. The presence of rounded 
November 2003 3-13 No. 13: Volcanic Events
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quartz and feldspar grains and tuff xenoliths in the hydrovolcanic deposits suggest the 
water-magma encounter may have occurred in the shallow surficial deposits upon 
which the cone was built. Crowe, Wohletz et al. (1986, p. 38) ascribe the dominant tuff 
xenoliths to the Tiva Canyon Tuff, which forms most of the surface outcrops in the area 
and is also a major constituent of the surficial colluvium. This hydrovolcanic event 
occurred during the early phases of the eruption. 
3. Later cone-forming activity deposited moderately sorted lapilli with 81 percent to 
92 percent tachylite and glassy tachylite pyroclasts. These are similar to ash and lapilli 
formed during later stages of scoria cone construction (Figure 3-7, stages 3 and 4; 
Heiken and Wohletz 1985). During later stages of cone formation, avalanching of 
scoria and ash down crater slopes blocked the vent, allowing degassing of magma and 
quench-crystal growth to occur (in contrast with the glass droplets formed during lava 
fountaining). Sporadic blasts carried out a mixture of scoria bombs, comminuted 
fragments of partly crystalline, quenched melt and recycled scoria bombs, lapilli, and 
ash that slumped into the crater. Lithic clast concentrations are low in these tephra-fall 
deposits. 
Exposed within the lower quarry wall is an abrupt transition from coarse Strombolian 
scoria lapilli to overlying fine lapilli and ash (Figure 3-6). This transition is inferred to 
mark an increase in eruption energy from Strombolian to violent Strombolian. Lapilli 
and ash fallout from a violent Strombolian eruption column were deposited on the 
upper slopes of the cone, became oversteepened, and avalanched downslope to be 
deposited as grain-flow material together with primary air-fall material raining down 
from the eruption column. These upper deposits are estimated to compose about twothirds 
of the cone volume. The ash fall that is mapped beyond the scoria cone 
(Figure 3-8) is inferred to be related to this phase of the eruption. 
4. Quarry exposures of the cone suggest cone building continued largely unabated. An 
event toward the end of the eruption deposited nearly 0.5 m of inward dipping, thin 
planar ash beds and cross beds, interpreted as hydrovolcanic in origin. Rounded 
quartz grains, although not numerous in the deposit, suggest this event may have 
occurred, once again, at shallow depth in or near the elevation of prevolcanic surficial 
deposits. Shallow groundwater in alluvium or sand-ramp deposits is inferred to have 
reached the near-surface conduit system, fueling a steam explosion. Above these 
fine-grained beds, coarse scoria deposits indicate a return to the less violent eruptions 
that preceded this brief hydrovolcanic event. These scoria deposits are some of the 
last observed units that were deposited on the cone. 
November 2003 3-14 No. 13: Volcanic Events
Revision 2 
Source: McGetchin et al. 1974, p. 3,268. 
NOTE: In stages 1 and 2, nearly all tephra are deposited ballistically (with the exception of finer material carried 
away by the wind). Much of this activity could be characterized as lava fountaining. At the Lathrop Wells 
Cone, this sequence would include hydrovolcanic activity that formed hydrovolcanic beds outside the 
low-rimmed scoria ring. Early activity could have consisted of fountaining along a fissure, accounting for 
the N-S elongation of the cone. 
In stages 3 and 4, cone growth occurs during Strombolian and violent Strombolian activity. Early 
Strombolian activity consists of bursting gas bubbles in ponded lava; blockage of the vent by slumping of 
unconsolidated ejecta leads to intermittent Strombolian blasts. Later violent Strombolian activity involves 
fallout of lapilli and ash from sustained eruption column(s), adding to the cone volume and depositing a 
tephra blanket beyond the cone flanks. Occasional interbeds of hydrovolcanic tephra reflect intermittent 
interaction with groundwater. 
Stages of Scoria Cone Formation Figure 3-7. 
November 2003 3-15 No. 13: Volcanic Events
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3.4.4 Tephra Distribution and Description 
The tephra deposits beyond the Lathrop Wells Cone flanks provide important information about 
the character of eruptive processes that could result in the dispersal of waste-contaminated 
material in the event that a similar volcano erupted through the repository. 
Figure 3-8 shows estimated isopachs for the thickness of tephra from violent Strombolian 
eruptions of the Lathrop Wells volcano. The isopachs are drawn based on a visual fit to the data 
collected from both hand-dug pits and natural exposures. The tephra thicknesses in most 
instances represent minima because of erosion of the tops of the sections of tephra. The 
maximum thickness of the tephra-fall deposits is 2.5 to 3 m in exposures near the base of the 
scoria cone, and the approximate area enclosed by the 1-cm isopach is 300 km2. The northern 
1-cm isopach is chosen to be near the location of Solitario Canyon fault trench T8, where 
U.S. Geological Survey workers exposed Lathrop Wells ash within deposits in the fault plane 
(Perry et al. 1998, p. 425). The amount and condition of ash particles suggest they represent ash 
runoff from the surrounding slopes and deposition in the fault plane when it was open during or 
soon after the earthquake that exposed the fault plane. Scattered basaltic ash on the west side of 
Busted Butte (Crowe 1996, p. 54) suggests that some Lathrop Wells ash was also deposited 
there. Although no primary ash deposits are preserved at these two distal exposures, the original 
thickness of ash deposited was probably about 1 cm. 
The known tephra distribution around the Lathrop Wells Cone suggests that during eruption the 
lofted basaltic ash column was dispersed northward by prevailing winds, with minimal ash 
deposition south of the cone. 
November 2003 3-16 No. 13: Volcanic Events
Source: Krier and Harrington 2003, p. 153. 
NOTE: 
No. 13: Volcanic Events 
Revision 2 
The triangle marks the volcano summit; the numbers are thicknesses, in centimeters, in dug pits or natural 
exposures. Approximate limit of the ash deposit is indicated by the 1 cm isopach. 
Figure 3-8. Isopach Map (Estimated) of Tephra Fall from the Lathrop Wells Volcano 
November 2003 3-17
Revision 2 
3.4.5 Magma Eruption Rates and Duration 
The duration and magma-eruption rates of Yucca Mountain basaltic volcanism can be estimated 
by using information from the observed eruptions of analog volcanoes. No single analog 
volcanic system makes a perfect fit for the monogenetic, alkali-basalt scoria cone in a continental 
setting with eruptive volume in the range of 0.01 to 1 km3, because volcanic eruptions are unique 
events. Detournay et al. (2003, p. 17-19, Appendix 2) surveyed and discussed eruption 
narratives from Strombolian and violent Strombolian eruptions to show the variability of such 
eruptions and their relevance to Pliocene-Quaternary and possible future volcanism at Yucca 
Mountain. 
The duration of short-lived basaltic eruptions ranges from less than a day to tens of months. 
During violent Strombolian eruptions, peak mass eruption rates of approximately 106 kg/s are 
possible, and a sustained violent Strombolian eruption could produce 0.1 km3 (the total Lathrop 
Wells volume) in about one day. This is extreme behavior, and for the more typical Strombolian 
eruption rates of approximately 104 to 105 kg/s, eruption durations are on the order of months to 
years. Eruptions that produce 0.1 to 1 km3 typically last one to several years (Detournay et al. 
2003, Appendix 2, Section A2.5.2 and Table 2D). The erupted volumes of Pliocene-Quaternary 
Crater Flat volcanic centers are between about 0.01 and 0.1 km3 (Table 2-1). These volumes 
suggest eruptive durations in the range of weeks to months, assuming an average Strombolian 
rate of 104 kg/s over the course of the eruptions. At such a rate, the Lathrop Wells volcano 
would have formed in about 5 months. The rates cited above are peak rates. If periods of 
normal and violent Strombolian activity are interspersed with the effusion of lavas, then average 
mass-flow rates of approximately 103 kg/s are more representative, and the Lathrop Wells 
eruption may have continued for several years. 
November 2003 3-18 No. 13: Volcanic Events
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4. CHARACTERISTICS OF DIKE WIDTHS, DIKE SWARMS, 
AND ERUPTIVE CONDUITS 
4.1 DIKE WIDTHS 
Crowe, Self et al. (1983, p. 266) measured basaltic dikes intruded into tuff at eroded volcanic 
centers of the Yucca Mountain region, and observed dike widths ranging from 0.3 m to 4 m, with 
most dikes between 1 and 2 m wide. The typical dike-width dimension assigned by the PVHA 
experts was 1 m (CRWMS M&O 1996, Appendix E). 
4.2 DIKE SWARMS 
Most basaltic volcanoes in the Yucca Mountain region are small in volume and fed by one main 
dike, along which a central and subsidiary vents formed, but sets of dikes are also present. The 
Lathrop Wells volcano is probably underlain by three dikes (inferred from Perry et al. 1998, 
Figure 2.10): (1) the dike that fed the main cone and small spatter vents in a chain to the north 
and south of the cone, (2) a dike that fed spatter and scoria mounds in a parallel chain just to the 
east of the main dike, and (3) a possible dike that fed scoria vents near the northern edge of the 
volcano, although these could be an extension of (2) above. Although not exposed by erosion or 
quarrying, there are also likely to be small dikes that radiate outward from the conduit of the 
main cone. This is suggested by the short (within a few hundred meters of the central vent), 
crudely radiating dikes that are enclosed in near-vent scoria at the eroded Pliocene basalt centers 
of Crater Flat (Vaniman and Crowe 1981) (Figure 2-11). The Paiute Ridge intrusive complex, 
approximately 55 km NE of Yucca Mountain, which appears to have fed at least one volcanic 
vent (evidenced by the presence of lava-flow remnants and a plug-like body), may have as many 
as 10 dikes, in addition to sill-like bodies (as inferred from examination of Perry et al. 1998, 
Figures 5.15 and 5.16). 
Analyses of a variety of basaltic volcanic fields indicates that the spacing between multiple dikes 
can vary from about 100 m to approximately 1 km. Based upon field observation and map 
measurement, the estimated dike spacing at Lathrop Wells volcano is approximately 320 m 
between the two inferred NW-trending dikes that fed the cone and the linear set of scoria mounds 
(vents) immediately east of the cone. Spacing is approximately 700 m between the mounds and 
an inferred third dike related to scoria mounds on the eastern lava flows. For the Paiute Ridge, 
intrusion, measurements from the geologic map of Byers and Barnes (1967) show that the mean 
dike spacing for dikes greater than 1 km long is approximately 995 m (maximum 1,440 m; 
minimum 250 m) (Perry et al. 1998, Figure 5-15). For the 3.7-Ma-old Crater Flat basalts, dike 
spacing is approximately 385 m (Perry et al. 1998, Appendix 2-M1). Map measurements from 
the Rim Rock, Texas dike swarm (1823 Ma; Dasch et al. 1969), taken from a population of 
about 100 dikes, gives an average of 410 m (standard deviation equal to 430 m) for a N-trending 
dike set and 690 m (standard deviation equal to 482 m) for a NW-trending dike set. Dike 
spacing in the Yucca Mountain region generally ranges from about 100 m to 690 m (BSC 2003b, 
Table 37). 
November 2003 4-1 No. 13: Volcanic Events
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4.3 ERUPTIVE CONDUITS 
Most observed basaltic eruptions begin as fissure eruptions, discharging magma where a dike 
intersects the Earths surface, and soon focus into roughly cylindrical conduit eruptions. The 
best data to constrain conduit diameters and depths to which conduits extend would come from 
basaltic volcanic necks exposed by erosion, where direct measurements could be made of 
conduit diameter and variation with depth. Although many volcanic necks have been mapped as 
part of regional studies, few have been measured in detail, at least for the basaltic compositions 
of interest in the Yucca Mountain region. Without direct measurements of conduit diameter in 
the Yucca Mountain region, estimates are based on analog volcanoes. 
The transition from magma flow in a subplanar dike to flow in a cylindrical plug has been 
inferred at many field locations (e.g., Delaney and Pollard 1978, p. 1212; Hallett 1992a, p. 140). 
From a continuum-mechanics view, a planar dike is the preferred form for propagation of 
magma through brittle and elastic host rock, whereas a cylindrical conduit is the preferred form 
for magma flow and delivery to the surface (Delaney and Pollard 1981, p. 1). Several processes 
have been put forward to explain this transition, including (1) magma viscosity variations 
induced by the solidification of magma at dike margins (Wylie et al. 1999); (2) brecciation and 
erosion of the dike wall rocks, as in the Shiprock NE dike (Delaney and Pollard 1978; Delaney 
and Pollard 1981) and the San Rafael dikes (Delaney and Gartner 1997); and (3) progressive 
melting of the host rocks, enhancing localized flow (Quareni et al. 2001). 
Once a zone of widening and flow focusing has initiated, the evolving conduit may continue to 
widen. Several hypothetical processes, similar to those for the initial dike enlargement, have 
been described to explain this: (1) erosion from shear stress of flowing magma below the 
fragmentation level (Dobran 2001, p. 481), (2) thermoelastic stressing of wall rock 
(McBirney 1959, p. 443; Valentine and Groves 1996, p. 85), (3) erosion from particle collision 
above the fragmentation level (Valentine and Groves 1996, p. 85; Dobran 2001, p. 481), 
(4) conduit-wall collapse due to variations in magma pressure or shock/rarefaction waves) 
(Dobran 2001, pp. 480 to 484), (5) hydromagmatic processes involving the interaction of magma 
with groundwater or saturated sediment (McBirney 1959, pp. 443 to 445; Valentine and 
Groves 1996, p. 85), (6) conduit-wall collapse due to offshoot dikes (Valentine and 
Groves 1996), and (7) pore-pressure buildup (Delaney 1982, Valentine and Groves 1996, p. 85; 
McBirney 1959, p. 443). 
Volcanic conduits are features that integrate magma paths over the duration of a volcanic 
eruption. Although a conduit may be large, only a fraction of it might be active at any given 
time during an eruption: the entire cross-sectional area of a conduit may transfer magma to the 
vent (e.g., Keating and Valentine 1998; WoldeGabriel et al. 1999), or to only a fraction of its 
cross-sectional area within a localized flow annulus, due to variations in flow velocity or 
viscosity (Hallett 1992b; Detournay et al. 2003). 
Basaltic conduits vary greatly in diameter, depth and geometry. Valentine and Groves (1996) 
used the well-established sedimentary stratigraphy beneath the tephra deposits of Alkali Buttes, 
Lucero Volcanic field, New Mexico, to evaluate the variations in conduit size beneath a 
monogenetic alkali-basalt center. Based on xenolith data and assuming a 1.5-m-thick feeder 
dike, the conduit that formed in the sedimentary country rock is calculated to range in diameter 
November 2003 4-2 No. 13: Volcanic Events
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from 3.5 to 10 m. The upper 500 m of country rock at Alkali Buttes consists of mudstones and 
shales that provided a wet host rock, as indicated by lithic-rich hydromagmatic deposits. 
Conduit-size calculations, based on the proportion of lithics in these hydromagmatic deposits, 
indicate that a cylindrical conduit up to 40 m wide may have formed in the uppermost strata. A 
flared conduit could also have developed, varying in size from 6 m at depth to 300 m at the 
surface, which is a diameter equivalent to the mapped extent of the hydromagmatic deposits 
(Valentine and Groves 1996, p. 75). 
In a similar investigation, Mastin (1991) calculated the size of a rhyolite conduit, using both the 
proportion of lithics in the eruption deposits and the results from a drillcore through the conduit 
(Eichelberger et al. 1988, p. 13,208). About 1 km3 of tephra was erupted, and the dominant 
eruption mechanism was hydromagmatic, with less than 10 percent juvenile material. At 300 to 
600 m beneath the vent, the conduit was estimated to be on the order of 20 to 30 m in diameter 
(Mastin 1991, p. 590). 
An upper bound for basaltic conduit diameter in the Yucca Mountain region is 150 m, which is 
the diameter of the Grants Ridge conduit in New Mexico (Keating and Valentine 1998, p. 41; 
WoldeGabriel et al. 1999, p. 392). A conduit diameter of this size is expected to be a 
conservative upper bound for Yucca Mountain, because the Grants Ridge plug formed during an 
eruption of several cubic kilometers of alkali basalt (compared, for example, to the much smaller 
Lathrop Wells volcano with its approximate total volume of 0.086 km3). Based on data from the 
Yucca Mountain region and selected analog regions, the conduit diameter for a future basalt 
volcano is, therefore, constrained at its lower bound by 1- to 2-m-wide dikes, and at its upper 
bound by the 150-m Grants Ridge plug. 
Doubik and Hill (1999, p. 59) used a process that may overestimate the volume fraction of tuff 
xenoliths (see Section 3.4.2) to estimate a 50-m conduit diameter for the Lathrop Wells scoria 
cone. Thick Miocene volcanic units beneath the Lathrop Wells volcano are lithologically 
similar, making it difficult to assign relative proportions of those units represented by lithics. 
Given the limitations on specific data to test the assumptions made by Doubik and Hill (1999, 
p. 59), their estimate of a 50-m conduit diameter for the Lathrop Wells Cone is used as a mode or 
most likely value for conduit diameter at depth for potential eruptions at Yucca Mountain. 
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5. SUMMARY OF THE VOLCANIC CONSEQUENCES ANALYSIS 
Because the probability that volcanic events could intersect a repository at Yucca Mountain has 
been estimated to be slightly greater than one chance in 10,000 over 10,000 years (a mean value 
of 1.7  10-8 per year), DOE has evaluated the potential consequences of such activity. Based on 
the geologic and volcanic history of the Yucca Mountain region, it is expected that any future 
igneous or volcanic activity would be similar to the basaltic activity that formed the small scoria 
cones in southern Crater Flat. The Lathrop Wells Cone is the largest of these. These small 
volcanic systems are fed by narrow basaltic dikes that ascend from depths of 40 km or more, and 
are typically a few kilometers in length and 1 to 2 m in width (BSC 2003b, Section 7). The 
intersection of such a dike with the repository could impact repository performance by thermally 
or mechanically damaging waste packages inside emplacement drifts, or by affecting the 
geochemical environment and hydrologic conditions within the repository (BSC 2002, 
Section 4.2, paragraph 3). Damaged or breached waste packages would be susceptible to 
percolating water that could contact, dissolve and transport radionuclides away from the 
repository. This is known as the igneous intrusion groundwater transport scenario. 
If the dike continued ascending to the surface and fed a volcanic eruption, it could damage or 
destroy packages within the eruptive conduit and entrain package materials and spent nuclear 
fuel or high-level radioactive waste within the volcanic ejecta (BSC 2002, Section 4.2, 
paragraph 2). This volcanic eruption scenario is important because it could lead to the 
airborne transport of radionuclides and direct exposure to the environment. 
Figure 5-1 is a schematic depiction of a dike intersecting a repository: the first panel (upper left) 
shows the dike approaching an emplacement drift; the second panel (upper right) shows the dike 
intruding magma into the repository and continuing to ascend toward the surface; the third panel 
(lower left) shows the dike erupting at the surface, and the fourth panel (lower right) shows the 
dike cooling and degassing in place. The extent of consequences of a dike intersection and/or 
volcanic eruption would depend on the characteristics of the basaltic magma, the geologic and 
hydrologic conditions in the repository, and the configuration and design of the repository and its 
engineered barrier systems. 
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Source: BSC 2003a, Figure 1. 
Figure 5-1. Schematic Drawing of the Processes Associated with a Dike Intrusion into or Eruption 
through a Repository 
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The analyses presented in the following sections describe the processes that could lead to 
radionuclide releases from a repository. The consequences associated with igneous intrusion are 
summarized separately from those associated with a volcanic eruption through a repository. 
Both of the analyses depend on the probability estimates summarized in Section 2. 
Section 5 is organized as follows: 
 Section 5.1 describes a model developed to analyze the interaction of ascending basaltic 
dikes with the drifts containing waste in the repository. These processes determine the 
number of waste packages that could be affected, as well as the extent of potential 
damage to the packages. 
 Section 5.2 describes analyses of how many drifts and waste packages would be affected 
by a dike intrusion into the repository. It discusses the length, width and orientation of 
dikes that could intersect the repository, the geometry of the repository emplacement 
drifts, and the number of packages that could be exposed to magma intrusion. 
 Section 5.3 describes the effects that an intruding magma could have on the integrity of 
drip shields and waste packages, from the thermal and mechanical effects associated 
with an intrusion, and from geochemical changes to the underground environment 
caused by the exsolution of magmatic gas. 
 Section 5.4 evaluates the consequences associated with a volcanic eruption through the 
repository. It describes the size, number and characteristics of eruptive conduits that 
could intersect the repository, and the number of waste packages that would be involved. 
It summarizes an analysis of the effect of erupting magma on waste packages and the 
waste form, including and the potential for packages to be destroyed and waste entrained 
in volcanic ash. 
 Section 5.5 describes the areal distribution of volcanic ash and entrained waste that 
could be ejected in plumes during volcanic eruptions. 
 Section 5.6 describes the redistribution of ash and radionuclides by surficial processes. 
The models describing analyses of igneous and volcanic consequences are summarized in a 
series of analysis and model reports shown on Figure 5-2. The key references are Characterize 
Eruptive Processes at Yucca Mountain, Nevada (BSC 2003b); Dike/Drift Interactions 
(BSC 2003a); Characterize Framework for Igneous Activity at Yucca Mountain, Nevada 
(BSC 2003e); Number of Waste Packages Hit by Igneous Intrusion (BSC 2003c); and 
Atmospheric Dispersal and Deposition of Tephra from a Potential Volcanic Eruption at Yucca 
Mountain, Nevada (BSC 2003f). In addition, potential damage to waste packages during an 
intrusion is evaluated in Igneous Intrusion Impacts on Waste Packages and Waste Forms 
(BSC 2003d). 
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the Evaluation of Igneous and Volcanic Consequences 
Figure 5-2. Model/Document Hierarchy Depicting the Relationship of Analyses and Models Supporting 
5.1 DIKE DRIFT INTERACTION MODEL SUMMARY 
5.1.1 Model Description 
The dike/drift interaction model was developed to analyze the behavior of magma and gases in 
ascending dikes that could intersect a repository. The model consists of two main components, a 
dike propagation model and a model of magma flow to the surface (BSC 2003a). Post 
emplacement effects (gas flow from the cooling magma and magma cooling) are also analyzed 
and discussed. These models describe processes ranging from initial propagation of the dike 
from depth, how the repository structure itself modifies that propagation, magma breakout to the 
surface, and effects such as cooling and gas transport. The key parts of the models, and the 
software codes used for the simulations, are shown on Table 5-1. Several alternative models of 
dike/drift interaction are also described and evaluated. One of these models (Woods et al. 2002) 
proposed that dikes intruding a repository could result in highly energetic pyroclastic eruptions 
accompanied by shock waves that travel the length of repository drifts. In this scenario, waste 
packages and other materials could be damaged and ejected from the repository through other 
repository openings such as ventilation shafts or through a new dike initiating at another point 
down the drift resulting in a dog-leg. 
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Used for the Analysis 
Dike/Drift Interactions Model Components 
Dike Propagation Model 
Model For Magma Flow 
Flow Through Mined Openings 
Crack Opening Rates 
Stress-Related Effects 
Fracture Criteria 
Magma Cooling Rates 
Synthesis for Dog-Leg 
Postemplacement Effects 
Gas Flow Between Drifts 
Table 5-1. Table Outlining the Components of the Dike/Drift Interactions Model and the Software Codes 
Software Code 
NPHF2D 
FLAC3D 
FLAC3D, spreadsheet 
NPHF2D, FLAC3D, spreadsheet 
FLAC3D 
UDEC, FLAC3D 
spreadsheet 
N/A 
spreadsheet 
N/A 
TOUGHREACT 
spreadsheet 
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Propagation From Depth 
Effect of Natural Stresses on Dike Propagation 
Effect of Repository Structure on Dike Propagation 
Diversion of Magma Into a Drift 
5-5 
Magma Cooling and Solidification 
The conceptual model for dike propagation considers a dike to be a pressurized fracture, much 
like a hydraulic fracture created in an oil or gas well, which is fed by a high-pressure source of 
magma deep in the earth. Figure 5-3 schematically depicts the key features, processes, and 
properties that control the ascent of magma in dikes through the shallow crust. The 
hydraulic-fracture model includes a sink point or drain to model loss of magma flowing into a 
repository. 
The pressure of the magma in the dike pushes aside the surrounding rock, creating dike widths 
up to several meters. The restricted width of the dike induces frictional losses in the magma that 
result in a pressure drop along the length of the dike. Thus, the overall dike-propagation model 
is constrained by a balance between the pressure necessary to keep the dike open at a given 
width and the appropriate restriction (width) necessary to keep the pressure at the required level 
through viscous losses (energy dissipation). 
Although liquid or vapor such as water can move from the magma into the wall rock surrounding 
the ascending dike, the magma viscosity is too high for it to leak into the host rock. The model 
simulates the propagation of the crack tip ahead of the ascending magma and includes a free 
surface, so that effects near the earths surface, such as unstable growth and an altered width 
distribution, can be evaluated. 
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Source: Modified from Detournay et al. 2003, Figure 3-1. 
Figure 5-3. Schematic Depicting a Magma-Filled Dike Ascending through the Crust, Showing 
Magma, Rock Properties, and Physical Conditions that Affect the Rate of Ascent 
Most dikes have a limited strike length (approximately 1 to 5 km) compared to their depth of 
origin. Thus, although they are clearly three-dimensional features, it is reasonable in 
near-surface environments such as the repository to use a two-dimensional approximation of dike 
propagation for calculating dike parameters. The basic components of the dike model include 
(1) the elastic deformation of a crack due to the internal pressure of the fluid, (2) the viscous 
losses of the moving magma within the fracture, (3) fluid losses into the surrounding medium, 
and (4) a crack propagation criterion that accounts for the resistance of the rock to fracture. 
These components must be calculated interactively to assure proper coupling of the various 
mechanisms. A detailed description of the mathematical formulation of the dike-propagation 
model, including the simplifying assumptions and limitations, is presented in Dike/Drift 
Interactions (BSC 2003a). 
The input data for the dike propagation model consist of formation (rock) properties, magma 
properties, boundary stresses, and dike parameters. The inputs are summarized in Dike/Drift 
Interactions (BSC 2003a, Section 6.3.4.2). There are uncertainties in these parameters because 
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of the scale of the calculations (dike length of several kilometers) and the possible changes in 
properties over such distances. The formation properties (those of the repository country rock) 
include Youngs modulus, Poissons ratio, and density and fracture toughness. Fracture 
toughness has not been specifically measured for the repository, but the results of the analysis are 
not sensitive at this scale. 
Rock properties representative of units that host the repository were used for the model 
(BSC 2003g, Attachment V, Table V-5). Magma properties were derived from a survey of 
relevant literature, as described in Characterize Eruptive Processes at Yucca Mountain, Nevada 
(BSC 2001). Various dike velocity and width distributions were used to obtain the flow rate for 
the dike propagation. A range of magma densities between 751 and 2282 kg/m3 
was considered 
to allow for volatile exsolution. Viscosities between 10 and 40 Pas were used in the analysis. 
Most results are for a viscosity of 10 Pas, which is conservative because lower viscosities 
enhance dike/drift interaction by maximizing magma flow in drifts. The boundary stresses 
include the overburden stress and the distribution of the minimum principal horizontal in situ 
stress (against which the crack must open). The distribution of the minimum principal horizontal 
in situ stress is taken from either (1) stress measurements at Yucca Mountain for in situ 
conditions or (2) thermal-mechanical modeling of the repository due to heating. Both cases are 
considered in the calculations and serve as the two logical end points of possible stress 
distributions. The density of the rock mass was used to establish a value for magma buoyancy 
and to fix the magnitude of overburden stresses in the dike propagation model. 
The rock mass, which in reality is a heterogeneous, layered medium, is modeled as homogeneous 
and isotropic, and ground surface is assumed to be planar. A uniform depth of the repository 
(300 m) was used as an input for the analysis. 
Dike widths and dike propagation rates depend on rock mass density, the coefficient of 
horizontal stress, and magma density. In the model, these three parameters are combined in a 
dimensionless group called relative density. Conditions of dike ascent are controlled by value of 
relative density. A wide range of relative density between 2.67 and 20.28 has been investigated. 
Boundary conditions for the model can be specified to be either the magma injection rate at the 
source depth or the far-field magma velocity and dike width. Because conditions of dike 
propagation are usually specified in terms of far-field velocity and width, these parameters were 
used as boundary conditions. Magma velocities between 1 and 15 m/s, and dike openings 
between 0.12 and 3.49 m were analyzed. 
The inputs for the magma flow into drifts analysis are the diameter (5.5 m) and spacing of drifts 
(assumed to be 80 m), the diameter of waste packages (assumed to be 1 m), the density 
(2000 kg/m3) and viscosity of the magma (1 to 10 Pas), the velocity of the magma front 
approaching the drift level (1 to 10 m/s), and the width of a dike at drift level (1 m). The waste 
package diameter was varied to illustrate how its presence would affect the flow of magma. The 
effect of reduced flow due to obstructions such as waste packages is greater than just that of a 
reduced open cross-section of a drift, because of increased viscous drag. This combined effect is 
included in the equations to be solved as the hydraulic radius (Rh) defined as the open 
cross-sectional area divided by the wetted perimeter of the flow. 
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The magma density is a nominal value that is more than the fully expanded density that would be 
found in a pyroclastic flow but less than the fully condensed value provided in Characterize 
Eruptive Processes at Yucca Mountain, Nevada (BSC 2001). It is intended to represent a magma 
which is partially degassed enough to flow into the drift effusively. The results of the analysis 
are affected only for the case of flow from a dike into a pipe, which is the controlling mode of 
flow when the magma supply rate and magma viscosity are high, and then only late in the short 
history of filling a drift. The magma viscosity and magma supply velocity are chosen to 
represent the lower and upper ends of the ranges described in Characterize Eruptive Processes at 
Yucca Mountain, Nevada (BSC 2001). Use of bounding values allows illustration of the effects 
of these variables on the solution. 
5.1.2 Summary of Model Results 
Although an ascending dike could theoretically be deflected around a repository by topographic 
and/or thermal-mechanical stress, the modeling described here makes the assumption that the 
dike will propagate through the repository. As the dike approaches the level of the drifts, the 
crack tip advances ahead of the magma front. This separation results in a vapor-filled cavity, 
which is the first part of the propagating dike that encounters the drift. A significant difference 
between the present model and previous analyses (see CRWMS M&O 2000c), is that the cavity 
pressure is taken to be negligible in the present model because of the very high gas permeability 
of the tuff (Detournay et al. 2003, p. 50). As the magma rises in the dike, the flow will be 
concentrated toward the center of the dike. There are two possibilities for the state of the magma 
as it moves upward into the cavity. One is that it steadily releases gas as it approaches the 
cavity. The other involves catastrophic gas release. Analysis using Stokes law indicates that gas 
bubbles formed as the magma ascends will rise faster than the liquid magma, so that the liquid at 
the magma front will have lost much of its volatile content. If this occurs, the magma will not be 
likely to produce violent explosive behavior when it encounters the repository, and it will flow 
effusively into the drifts. The results of a model of effusive flow into drifts are presented below. 
Alternative scenarios (in which gas explosively exsolves, and the magma flows into drifts as a 
fully or partially coupled two-phase gas-magma flow) are discussed in Section 5.1.3. 
When the dike reaches the level of the repository, magma will be available to flow into drifts, 
like a fluid flowing into a pipe or over a weir in a channel. Figure 5-4 is a schematic drawing 
that depicts the hydraulic features of the flow model. The rate at which drifts are filled with 
magma will depend on the magma flow rate, as determined by the hydraulic properties 
(particularly viscosity) of the magma. The model used to calculate flow into the drifts is 
simplified, ignoring frictional losses at the dike/drift interface, and ignoring the hydraulic 
impedance of waste packages and drip shields within the drifts. Limited sensitivity studies have 
been performed to assess how restricted openings caused by obstructions could affect flow 
(BSC 2003a, Section 6.3.9.2.3.1.2). These analyses indicate that, for the range of magma supply 
rates and viscosities considered in the model, the rate at which magma would flow into drifts 
would not be significantly affected. Given the assumptions summarized above, magma 
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NOTE: The figure represents flow of magma for two distinct situations. In the lower drawing, the magma has not 
risen to the top of the drift, and a weir equation is used. In the upper drawing, viscous drag in either the dike 
or the drift limits flow and is appropriate. 
Figure 5-4. Schematic Depicting Magma Flow from a Dike into a Repository Emplacement Drift 
ascending at 1 m/s and with viscosity between 10 Pas and 100 Pas would flood the drifts in 
about 5 minutes. The magma front would not rise much above the drift level until the drifts were 
essentially filled. Magma rising at 10 m/s would fill the drifts in less than 1 minute. In this case, 
magma would continue rising in the dike, but its rate of advance would be slower as the magma 
drained into drifts. Drainage of magma into drifts would reduce magma front velocities from 
5 m/s to 0.1 to 0.3 m/s for lower-viscosity (10 Pas) magma and to about 2 m/s for the 
higher-viscosity (100 Pas) magma (BSC 2003a, Sections 8.1 and 6.3.9.2.3.2). As the dike 
approaches the free surface, the crack tip accelerates, although the speed of the magma front is 
little changed. As a result, the vapor-filled cavity between the tip and the magma will lengthen. 
For a dike with the properties postulated, this process will already be underway when the tip 
reaches repository level. In the absence of any drifts, the crack would take about 100 s to grow 
from repository depth to breakout at the surface. This conclusion is based on treating the magma 
as an incompressible fluid. 
Although loss of magma into drifts may slow the progress of the magma front to the surface, it 
will have little effect on the tip of the dike cavity, which will already have begun accelerating in 
response to the presence of the free surface and will reach it only seconds after passing the drift 
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horizon. Three-dimensional simulation of the diversion of magma from a dike to a drift 
(BSC 2003a, Section 6.3.9.2.3.3 and 6.3.9.2.3.4) has demonstrated that the diversion will cause 
both the height of magma in the dike and the pressure in the magma to be depressed directly 
above the drift, compared to portions of the dike that are between drifts. However, the delay in 
magma ascent will be short-lived, as the drifts would be filled with magma within a few minutes. 
5.1.3 Alternative Conceptual Models 
A variety of alternative conceptual models have also been considered in connection with the 
analysis of dike propagation and magma flow. Examples include analytic solutions of the 
fracture propagation problem, as well as a number of commercially available hydraulic-fracture 
models that are used in geothermal and waste injection applications. 
Analytic conceptual models are useful for parameter estimation and have been used as a check 
on the models that predict the length, width, and pressure conditions in fractures of a given 
height. However, these models have limited applicability to the dike propagation and magma 
flow problem because they do not permit analysis of the effects of a free surface, and they do not 
include a sink point at a specific location that would enable the modeling of magma flow out of 
the dike and into a repository (BSC 2003a, Section 6.3.3). 
Industrial hydraulic-fracture models are based on the same concepts as the analytic solutions, but 
numerical solutions allow additional flexibility in defining the problems modeled, especially 
with respect to the evolution of the height and length of fractures. As proprietary models, 
however, no detailed accounting of the equations, algorithms, or applications is available. 
Review papers indicate that various models yield widely different fracture geometries and 
pressures for the same input parameters. In addition, these models are primarily appropriate for 
fracturing at distances far from the free surface in layered media, not in near-surface situations. 
Due to these limitations, industrial models have not been used for simulating dike/drift 
interactions in a repository. 
Several models of dike propagation using hydraulic-fracture principles with the addition of 
buoyancy effects were also evaluated. Although buoyancy may be important to the upward 
growth of a dike, and to magma density, none of the available models can accommodate a free 
surface or a leak-off point that would allow simulation of magma flow out of the dike. Thus, 
models considering buoyancy effects have not been used in the dike/drift interaction analysis 
(BSC 2003a, Section 6.3.3). 
The Alternative Models of Woods et al. (2002)The models described in Section 5.1.2 
consider the effusive flow of low viscosity magma upward in dikes and laterally into repository 
drifts. An alternative model of dike/drift interaction at a repository was proposed by Woods 
et al. (2002). In this conceptual model, a dike intersecting a drift was hypothesized to cause the 
drift to fill with magma, after which the pressure would rebuild to generate a new crack opening 
some distance downdrift. This new opening would propagate to the surface (a dog-leg 
scenario) and become the main surface opening of the system. This model has been analyzed in 
detail in Dike/Drift Interactions (BSC 2003a, Section 6.4.11). The analysis considered the 
propagation of pressure and stress through the dike system, and the effect of cooling on magma 
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properties, and concluded that a secondary dog-leg dike could not propagate more than a few 
meters from the drift (BSC 2003a, Section 6.4.11.5). 
Woods et al. (2002) presented another alternative model for flow of magma from a dike to a 
drift. Unlike the analysis described in Section 5.1.2, which simulates effusive flow into the drift, 
this model proposed rapid, explosive decompression, such that the bubbles formed would not be 
able to coalesce. In this case, the magma would rapidly expand as a two-phase mixture (a 
pyroclastic mixture of magma and gas), would accelerate upward (the only direction in which it 
is unconstrained) until reaching the drifts, and would then expand both into the drift and upward 
into the crack tip. 
This explosive model assumes that the magma consists of liquid and vapor fractions that are 
fully coupled, meaning that they are constrained to move at exactly the same velocities and that 
they are at the same pressures and temperature. Vapor is also always assumed to be at 
equilibrium with the liquidthat is, that vapor exsolves (or dissolves) from the liquid 
instantaneously in response to pressure changes. Given these limiting assumptions, Woods 
et al. (2002) solved the hydrodynamic equations in a quasi-one-dimensional form in which the 
flow in both the dike and the drift is treated as being in the same direction. The equations used 
do not solve for any motions transverse to the direction of flow, and as such, the model is not 
two-dimensional. The boundaries of the drift and dike are treated as impermeable and rigid, 
much like a shock tube. The initial condition is that magma at high pressure fills the dike portion 
of the model and air at atmospheric pressure fills the remainder of the computational volume. 
The Woods et al. (2002, pp. 19-2 to 19-3) model predicts a wall of magma accelerating into the 
drift at speeds reaching: 
tens to hundreds of meters per second, with the density decreasing as the 
pressure falls. Air is displaced and compressed ahead of the magma-volatile 
mixture and, as a result, a shock forms in the air and moves down the drift at 
speeds of several hundred meters per second. on reaching the end of the drift, 
the shock is reflected and its amplitude increases by an order of magnitude. The 
shock then propagates back upstream, moving into the magma-volatile mixture 
and back towards the dike at speeds of 2030 m/s. As the shock moves through 
the magma-volatile mixture, the mixture is recompressed. A region of higher 
pressure, of order several MPa, and hence higher density, develops between the 
end of the drift and the shock The calculations suggest that, if the dike 
intersects the drift 200300 m from the end of a closed drift, then the pressure 
within this drift will build up to about the initial level in the dike in a time of order 
10 s. 
The Woods et al. (2002) model represents a valuable first step toward developing a valid model 
of the flow of magma from a dike into a drift. However, the initial and boundary conditions in 
the Woods et al. (2002) model are unrealistic (Detournay et al. 2003, p. 51). In particular, the 
initial condition is not physically realizable and leads to results that are not achievable in nature. 
As described in Dike/Drift Interactions (BSC 2003a, Section 6.3.8.2), magma does not fill the 
propagating crack completely, nor does the crack reach its full width immediately after opening. 
Rather, there will be a vapor-filled tip, which is expected to be on the order of tens to hundreds 
of meters long. Near the tip, this crack will be only millimeters wide. Even if the magma were 
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to fill the crack nearly to the tip, the cross-sectional area of the intersection would be only a 
fraction of a square meter in this early phase, rather than the approximately 5.5 m2 
assumed by 
the Woods et al. (2002) model. This cross section would gradually increase as the crack 
propagated beyond the repository, a process that could take seconds to minutes (BSC 2003a, 
Section 6.3.9.2.3.1). At the rates of flow associated with effusive magmas (e.g., 5 m/s), shock 
waves would be unlikely to form in the drift. Specific analysis of the potential effects of a 
pyroclastic flow rising at a rate on the order of 100 m/s have not been performed, but may 
require further investigation. 
The assumption of rigid, impermeable boundaries in the Woods et al. (2002) model adds to the 
severity of the consequences of magma interaction with drifts. Air, pressurized by the shock 
they describe, would seep into the walls of the drift, reducing the pressure behind the shock and 
decreasing its amplitude as it propagated. An even larger effect is to be expected at the blocked 
end of the drift, where the shock will encounter backfill. The backfill is quite compressible and 
will not reflect an incident shock wave nearly as efficiently as the rigid wall assumed in the 
calculation. In addition, the edge of the backfill will not be a vertical wall, as required by the 
one-dimensional numerical model of Woods et al. (2002), but will lie at the angle of repose. The 
net result of these real-world situations will be to greatly reduce the amplitude of reflection of 
any shock that might develop. 
In addition, the Woods et al. (2002) model ignores phase separation between the silicate liquid 
and the volatiles. Although this assumption may provide an adequate estimate of steady flow in 
such a mixture, it is precisely the response to dynamic events such as shocks and rapid 
decompression that is not well treated with this assumption. In situations with such high 
accelerations, the differences in density between the vapor and the silicate magma become 
important, and the magma and vapor will move at different speeds. Only later, as viscous forces 
have had a chance to act, will the velocities approach each other. If these effects were included 
in the model, the result would be to reduce the sharpness of both compression and 
decompression waves and to increase dissipation of kinetic energy. Shock waves would be 
considerably dampened when propagating through such mixtures. Woods et al. (2002, p. 19-2) 
state that the drift is assumed to be empty, and since the drift cross-sectional area is much larger 
than that of a 1.8-m-diameter canister, A(x) is taken to be the total drift cross-sectional area. 
Although it is true that the ratio of area of the drift (approximately 23.8 m2) to that of a canister 
(approximately 2.5 m2) is large, a more important comparison would be that of hydraulic radii, 
Rh, equal to A/P, where A is the cross-sectional area and P is the perimeter (both exterior and 
interior) of the flow. The ratio of hydraulic radii is about 0.67, whereas the ratio of open areas is 
about 0.89. The smaller value will result in more drag and loss of energy in the flows than in the 
Woods et al. (2002) model. By not considering waste canisters, the Woods et al. (2002) model 
eliminates another mechanism for energy dissipation in the shock wave that their model 
produces. 
In summary, the Woods et al. (2002) model of magma expansion into a drift overestimates the 
violence of the encounter. Realistic boundary conditions including compressible walls and 
backfill, permeable country rock and backfill, phase separation in the magma-volatile mixture, 
partial blockage of the drift by waste canisters and other engineering features, and the axial 
spacing of the canisters would combine to greatly reduce the amplitude of any shock wave that 
might form in the initial encounter. More importantly, use of realistic initial conditions such as a 
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dike tip would preclude the formation of a shock wave for all but the most rapid magma ascent 
rates. 
Partially Coupled Liquid and Vapor Phase (Pyroclastic) Alternative ModelA third model 
for magma and gas flow in drifts is a partially coupled model in which the vapor phase and the 
condensed-liquid phase are free to move at different velocities subject to viscous drag of the 
continuous phase on the discontinuous one. Detournay et al. (2003, Section 3.3.3.2) postulated 
that magmatic material would be likely to first enter drifts as a pyroclastic flow resulting from 
gas exsolution and expansion of the magmagas mixture. Although the fully coupled highly 
explosive scenarios considered by Woods et al. (2002) have been discounted, a model 
incorporating partially coupled magma and gas flow is probably the most realistic of the models 
considered. This model could also be used to simulate the potential for a pyroclastic dog-leg 
scenario, in which the magmagas mixture would open and sustain a crack downdrift from the 
intruding dike and then flow upward to the surface. It is also the most complicated and difficult 
to simulate numerically. 
If the discontinuous phase is vapor, then the fluid is magma with bubbles which may rise faster 
than the silicate liquid. Two-phase flow in which the continuous phase is the silicate liquid is not 
expected to be much different from the effusive case of the magma flow model (Section 5.1.2) 
because the liquid properties will dominate the flow. If the continuous phase is the vapor, then 
the rising magma will consist of droplets of magma suspended in vapor streaming past them. 
This latter case can be termed pyroclastic and, because of the large velocities that may result, is 
of concern. Such vapor-dominated flow can arise by decompression of a magma with dissolved 
gases, or by mixing of magma with water as the magma penetrates the environment. This latter 
mechanism would be termed hydrovolcanic. 
Four preliminary single-phase simulations have been conducted of the flow of a pyroclastic 
magma into a preexisting crack (initially 1 mm thick) using material properties representative of 
those derived by Heiken et al. (1988) in order to determine the feasibility of a similar 
phenomenon occurring at Yucca Mountain (BSC 2003h, Section 6.3.3.5). Details of the method 
are described in Dike/Drift Interactions (BSC 2003h, Section 6.4.10.2.1), where the model is 
applied to effusive flow. The calculation used the following properties: 
 Overburden300 m at density 2,400 kg/m3 
 Overburden Stress (Horizontal)3.6 MPa (lateral stress coefficient of 0.5) 
 Crack OrientationVertical along axis of drift 
 Country Rock Youngs Modulus15 GPa 
 Magma Pressure12.6 MPa (9 MPa above overburden) 
 Magma Viscosity0.5 Pas. 
In addition to these values, the bulk modulus of the pyroclastic magma was set at 50 MPa 
according to the following rationale. The bulk modulus of an ideal gas is equal to its pressure; 
however, with density near 1.0 due to mass loading by magmatic liquid and (perhaps) 
comminuted country rock, much of the volume will not be available to the gas component, so the 
mixture will be stiffer than an ideal gas, just as in a van der Waals gas. Thus, a value about four 
times the ideal gas value was selected for the simulation. 
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Four calculations of crack growth and magma flow were carried out at various scales: one with a 
zone size of 1 m extending to a height of 100 m above the drift, one with 2.7-m zones extending 
to 150 m above the drift, and two with 10-m and 20-m zones extending 300 m to the surface. 
Boundary conditions were varied to simulate an infinitely long dike in the strike direction and a 
dike of smaller strike length. The drift was explicitly represented in the small- and intermediatescale 
calculations. In the large-scale calculations, a point source with prescribed magma 
pressure was assigned to the location of the drift. The small and intermediate calculations 
provide detail on the crack growth near the drift but do not extend to late enough times or large 
enough ranges to illuminate crack propagation to the surface. On the other hand, the large-scale 
calculations can follow the crack to the surface but will miss fine details. 
The results of these calculations include the crack-width history at selected locations, the 
location of the magma front in the opening crack, and the velocity of the magma front. In the 
fine-scale calculation, the maximum crack width is about 27 mm. By 1.65 s, the magma has 
almost reached 32 m above the drift, where the crack width has opened to about 8 mm. The 
maximum crack opening for the large-scale simulations is about 170 mm at about 110 m from 
the dike; the opening at the surface is about 100 mm. 
The two large-scale calculations indicate that the pyroclastic dike will reach the surface in 6 to 
10 s. Linear extrapolation of the intermediate-scale calculations supports the conclusion, 
although the calculated time to breakout would be about twice as long (18 s). 
The velocities of the propagating-magma front range from about 5 m/s to more than 75 m/s. 
Because the calculation models the magma as a single phase and the bulk modulus is at least four 
times the pressure, the velocity of the front will be close to the magma flow velocity. These 
results are consistent with the findings of Heiken et al. (1988), which were obtained with 
analytical forms, thus increasing confidence in the results. 
Based on the results of these preliminary calculations, it appears that a pyroclastic dike as a 
dog-leg could reach the surface, if certain conditions were met. First, as noted above, the 
eruptive energy associated with a dike intrusion depends in part on the availability of water. 
Given a width of 0.2 m, an average velocity of 50 m/s, and a strike length of 10 m, the total 
volume flow rate would be 100 m3/s, corresponding to a total mass (given the assumed density of 
the pyroclastic flow) of about 1,000 MT over 10 s. For a hydrovolcanic source, such flow rates 
may be reasonable, as sufficient water volumes could be present at the water table or in a 
perched water body. However, because of the very dry nature of the Yucca Mountain site, 
hydrovolcanic activity is thought to be unlikely (Crowe, Self et al. 1983). 
A second assumption not addressed by these preliminary calculations is whether pressure in the 
propagating crack and dike of 9 MPa above overburden can be maintained for the 6 to 10 s 
needed for a pyroclastic dike to reach the surface. Detournay et al. (2003, Section 3.2.2.3) 
suggested that the large intrinsic permeability of the fractured tuffs that would host the repository 
was too high to maintain pressures approaching 10 MPa. For a nonhydrovolcanic source, where 
the pressure would derive from the kinetic energy of a pyroclastic flow down a drift, velocities in 
excess of 300 m/s would be needed with a flow density of 100 kg/m3; this is not a likely flow 
environment (see BSC 2003h, Section 6.3.3.4) and would be unlikely to generate sustained 
pressures. This approximation also indicates that insufficient pressure to sustain a pyroclastic 
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dog-leg would accompany dike intrusion unless the magma came in contact with a substantial 
source of groundwater. 
In summary, for a variety of reasons, Detournay et al. (2003, Section 3.4.8) considered the 
propagation of either a magmatic or pyroclastic dog-leg scenario to be quite improbable. The 
calculations summarized in Section 5.1.2 have confirmed this assessment for the magmatic 
(effusive) scenario. Analyses presented in this section indicate that the fully coupled and highly 
explosive pyroclastic flow scenario postulated by Woods et al. (2002) is inconsistent with the 
volcanic processes that would operate and conditions that would exist if a dike intersected the 
repository. However, Detournay et al. (2003, Section 3.5) also recommended further analyses to 
assess the impacts of a partially coupled pyroclastic flow scenario on repository performance. 
Preliminary analyses have been performed to identify under what conditions pyroclastic flows 
could occur and to assess their behavior during dike/drift interactions. 
Further analyses to refine the partially coupled pyroclastic flow model are underway. These 
analyses will address several of the key assumptions and uncertainties that have not been 
addressed to date. A partial list of additional features that may be incorporated in the model 
includes accounting for cavity pressures in the propagating crack that are less than the magma 
vapor pressure, as well as other aspects of the coupling between vapor and condensed phases, 
variable material properties (e.g., temperature, composition, viscosity), and the dimensionality of 
the analysis (three-dimensional versus two-dimensional). 
5.1.4 Uncertainties, Assumptions, and Limitations 
The dike propagation and magma flow problem is relatively complex, and numerical modeling 
entails uncertainties, including the complexities introduced by the three-dimensional nature of 
the problem uncertainties with regard to fluid and rock properties, and the model assumption that 
the fluid is incompressible and has constant properties. The large range of possible magma 
properties (e.g., viscosity, density, temperature) has been dealt with through the evaluation of a 
range of conditions in an attempt to bound the problem. The boundary-element approach also 
requires homogeneous material properties for the host rock, and stratigraphic variability is 
therefore not accounted for. 
Some of the key assumptions and limitations of the numerical models are summarized below 
(BSC 2003a, Section 6.3.5 and 6.4.6). Additional analysis of the effects of these uncertainties is 
planned to assess their effects on conclusions about the behavior of basaltic magma interacting 
with drifts. However, the bounding analyses and sensitivity studies completed to date indicate 
that the basic conclusions about magma flow are unlikely to change. 
 Magma compressibility: The analysis of dike propagation assumes that the magma is 
incompressible, whereas basaltic magma within several hundred meters of the surface is 
a mixture of liquid and exsolved gas (with or without crystalline solids) that can be 
highly compressible (BSC 2001). 
 Two-dimensional calculation: Although the problem of a dike propagating away from a 
deep magma source clearly is a three-dimensional problem, the behavior as the dike 
approaches the surface is considerably more constrained. First, the extent of the dike 
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along strike is generally much less than the length of the dike from source to tip. 
Second, the effect of the free surface will attract the dike as it approaches, thus limiting 
further breadth. As a result, the dike propagating upward near the surface takes on 
two-dimensional characteristics that are much more amenable to modeling. 
 Elastic behavior: Elastic behavior is a reasonable assumption for small-scale pressurized 
fractures in the Earth but may be questionable for a dike-scale event within 1 km of the 
earths surface where rocks are fractured. A dike would cross many discontinuities in 
the rock and would generate small earthquakes as slippage occurs in response to the 
changes in stress generated by the propagating dike. However, inelastic effects will 
serve to increase the width of the dike and decrease the pressure. These are competing 
effects. Because the pressure is the main factor for the subsequent calculation, using 
elastic behavior is a conservative assumption because it serves to generate the highest 
pressures. 
 Linear-elastic properties: Most rocks have nonlinear behavior with lower moduli (a) at 
low stress and (b) at shallow depths in the presence of joints and bedding planes. 
Linear-elastic behavior produces the greatest possible pressure and is, thus, a 
conservative assumption. 
 Homogeneous, isotropic material: Rocks are typically jointed, faulted and 
stratigraphically heterogeneous. Also, characteristics of the strata, joints and faults deep 
in the Earth are not known. Dike behavior near the repository has been modeled by 
using the rock properties measured at the repository. This assumption results in 
tractable models and a complete set of input parameters but is not necessarily 
conservative. 
 Single fracture: Although many hydraulic fractures and dikes are known to exhibit 
multiple fracture strands and en chelon behavior, the overall impact of dike 
intersections with drifts is reasonably modeled with a single fracture. The high viscosity 
of the magma does not allow easy penetration of the fluid into joints or faults, and thus, 
secondary fracture strands are not easily initiated. Most volcanic systems are fed by 
one, or a small number of dikes. 
 Laminar flow: Laminar flow of the magma in the dike is essential for pressure drop 
calculations under the Poiseuille formulation. Laminar flow is expected to occur for 
Reynolds numbers less than 2,000. Although Reynolds numbers do approach and may 
exceed 2,000 for some combinations of conditions, fully turbulent flow is unlikely for 
any possible set of conditions. Thus, it seems reasonable to assume laminar-flow 
behavior under all circumstances. 
 Lubrication approximation: The lubrication approximation is appropriate (and exact) for 
slow motion of viscous fluids so that the viscous forces are considerably greater than the 
inertial forces, thus allowing the inertial forces to be neglected. The approximation 
appears to be appropriate for flow in a long two-dimensional fracture (parallel flow) 
and has been used for 40 years in hydraulic fracturing with good success and no 
apparent discrepancies. Thus, this approximation appears reasonable and appropriate 
here. 
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 Newtonian fluid: A Newtonian fluid is one for which the relationship between stress 
and rate of strain is linear. This formulation simplifies calculations of fluid resistance 
and is known to apply to many common fluid systems. Although a more complex fluid 
rheology could be used (e.g., with yield stress and power-law behavior), little is known 
about magmas, and the additional parameters in such models would be highly uncertain. 
It seems more appropriate to assume Newtonian rheology and to vary the viscosity in 
accord with temperature and pressure changes. 
 Stress-intensity factor governs tip behavior: The applicability of linear-elastic fracture 
mechanics has been questioned for large-scale fractures propagating under internal 
pressure. The dike-propagation problem is concerned with an even larger-scale feature 
and undoubtedly involves anelastic behavior in the surrounding rock. Thus, 
linear-elastic fracture mechanics may not be strictly appropriate for this application. 
However, the linear-elastic fracture mechanics formulation allows the fracture toughness 
to be used as a parameter that is indicative of the resistance of the rock to fracture, 
whatever the actual mechanism. Treated as a parameter, fracture toughness can be used 
to investigate the effect of any mechanism that resists fracture growth and thus increases 
the pressure. 
 Horizontal free surface: The surface relief at Yucca Mountain is relatively severe, but 
the dike propagation model treats it as a horizontal surface. This approach is a 
conservative assumption because the additional load of the mountain would serve to 
deflect any dike away from the mountain (e.g., into the basins). However, analysis 
indicates that topography probably has a negligible effect on the dike path. 
5.2 NUMBER OF REPOSITORY DRIFTS AND WASTE PACKAGES INTERSECTED 
BY IGNEOUS INTRUSION 
The number of emplacement drifts that would be directly affected by igneous activity depends on 
the number, length, and orientation of the basaltic dike(s) intruding the repository, as well as the 
configuration of the drifts containing waste packages. Figure 5-5 depicts a dike approximately 
4 km in length that would intersect 46 emplacement drifts along the north-south extent of the 
repository. This is the maximum number of drifts (spaced 81 m apart) that could be encountered 
by a single planar dike. 
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Source: BSC 2003c, Figure 2. 
NOTE: For illustration purposes only. Dike width is exaggerated for clarity. The dike length in this example is 
approximately 4 km, which would encompass the entire length of the repository. The anchor point (shown 
as a blue dot) marks the point where the dike enters the repository. 
Figure 5-5. Example of a Single Dike Intruding the Repository at Zero-Degree Azimuth 
As described previously, typical lengths for individual dikes in the Yucca Mountain region range 
from about 1 to 5 km, and the range of maximum dike lengths has been estimated at 17 to 22 km 
(see Figure 2-10). Volcanic centers may be fed by a single dike, but systems with multiple dikes 
(known as dike swarms) also occur. For example, at the Lathrop Wells Cone, three dikes have 
been inferred. In determining the number of drifts intersected by a volcanic event, the number of 
dikes per event has been represented as a lognormal distribution with 3 as the mode, 1 as the 
minimum, and 6 as the 95th percentile. The distance between dikes (dike spacing) associated 
with single basaltic systems in the Yucca Mountain region is typically on the order of hundreds 
of meters (see Section 4.2). For the calculations described below, the distance between dikes is 
based on observations in the Yucca Mountain region and is specified as a uniform distribution 
ranging from 100 to 690 m. 
The expected orientation of dikes that could intrude the repository has also been analyzed, and 
the effect of orientation on the probability of drift intersection has been characterized. Dikes 
tend to orient perpendicular to the least compressive horizontal stress (i.e., the direction of 
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extension), which in the Yucca Mountain region is oriented about N60W. Therefore, vertical 
dikes are expected to propagate within a range of azimuths but will favor an orientation of about 
N30E (see Section 2.1.2). Figure 5-6 shows the expected orientation of potential dikes. Because 
the emplacement drifts at Yucca Mountain trend at about N70E, dikes would most likely 
intersect the drifts at an angle of approximately 40. The number of intersections would decline 
as the angle between dikes and drifts decreased. Dikes striking approximately N70E would 
intersect the fewest drifts, since dikes with that orientation would be parallel to the drifts. 
Source: BSC 2003e, Figure 22. 
Mountain region. 
NOTE: The mean dike azimuth is about 30 (N30E), perpendicular to the least principal stress in the Yucca 
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Figure 5-6. Likely Orientation of Dikes Intruding the Repository 
To calculate the potential number of dikedrift intersections associated with igneous or volcanic 
activity within the repository footprint, the ranges and distributions of the length, number, 
spacing (in the case of dike swarms), entry points (also called anchor points), and orientations of 
possible dikes have been probabilistically combined. The results of this analysis are documented 
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in Number of Waste Packages Hit by Igneous Intrusion (BSC 2003c; DTN: 
SN0311T0503303.003). 
Figure 5-7 depicts several of the key parameters used to estimate the number of potential dike 
intersections with the repository if an igneous event occurred. A dike swarm is associated with a 
specific geographic location referred to as an anchor point and shown in blue in Figure 5-7. 
This point represents the entry point for the central dike of a swarm into the repository. The 
spacing between dikes can vary from 100 to 690 m. The dike lengths are constrained by the 
variability of the dike-length parameter. All dikes in a swarm are assumed to be parallel, but the 
azimuth angle is constrained by the sampled azimuth angle parameter. 
Source: DTN: SN0311T0503303.003. 
NOTE: For illustration purposes only. Dikes shown in red are not to scale; dike widths are exaggerated for clarity. 
Drifts highlighted in red are those intersected by dikes. The anchor point is shown as a blue dot. The figure 
shows the parameters sampled by the model, including the number of dikes and dike orientation, spacing, 
November 2003 
and dike length within the repository. 
No. 13: Volcanic Events 
Figure 5-7. Illustration of Dike-Swarm Implementation 
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The number of waste packages that would be contacted by magma intruding a repository 
depends on the number of drifts encountered and on the extent of downdrift flow of magma. As 
described in the previous section, the results of the dikedrift interactions model (BSC 2003a, 
Section 6.3.9.2.3.1.6) indicate that magmas may behave as low-viscosity fluids or as pyroclastic 
mixtures of magma and gas that could completely fill emplacement drifts, covering or engulfing 
all of the drip shields and waste packages contained in each intersected drift. Thus, the number 
of waste packages hit can be directly estimated from geometric analysis. The combined length 
of an average waste package plus the spacing between packages is 5.2 m (BSC 2003c, Section 
4.1). For each drift that is intersected by a dike, the emplacement drift length is simply divided 
by 5.2 m. The average length of an emplacement drift is approximately 600 m, and, therefore, 
the average estimated number of waste packages per drift is approximately 115. 
Each of the stochastic parameters is sampled to calculate the range and probability of the number 
of dikedrift intersections. In conjunction with that sampling, each intersection between the 
resulting configuration of dikes and drifts is calculated. The drifts that are intersected are used to 
calculate the number of waste packages hit, and the number of waste package hit is tallied for 
each case. The results are then averaged to generate a single composite cumulative distribution 
function, which is shown as Figure 5-8. 
Figure 5-8 is a graph of the composite cumulative distribution function for the number of waste 
packages hit by a swarm of dikes intruding the repository. A wide range of possibilities is 
displayed, from virtually no waste packages hit to the entire inventory of more than 11,000 waste 
packages hit. The 50th percentile (median) shows approximately 1,610 waste packages hit. 
Source: DTN: SN0311T0503303.003. 
NOTE: CDF = cumulative distribution function. 
Figure 5-8. Cumulative Distribution Function of Number of Waste Packages Hit: Igneous Intrusion 
November 2003 5-21 
Scenario 
As described in Number of Waste Packages Hit by Igneous Intrusion (BSC 2003c, Sections 5 
and 6.3; DTN: SN0311T0503303.003), the assumptions used in this analysis are based on 
geologic observations (e.g., dike length, orientation, and number) of the characteristics of 
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volcanic events in the Yucca Mountain region. The parameter distributions used are considered 
to be representative of the potential future events. The analysis does, however, include some 
conservative elements. For example, it was assumed that all waste packages in each intersected 
drift would be damaged (BSC 2003c. Section 5.2). 
5.3 DAMAGE TO ENGINEERED BARRIERS ASSOCIATED WITH IGNEOUS 
INTRUSION 
The analysis of consequences to engineered barriers associated with igneous intrusion processes 
is built on the conceptual model of dike-drift interaction, which indicates that intruding magmas 
could, under certain conditions, flow down the length of repository emplacement drifts. In this 
case, all of the drip shields and waste packages in the affected drifts would be directly contacted 
and affected by the magma (this area within the repository is referred to as Zone 1). In adjacent 
drifts (referred to as Zone 2), the potential for damage to drip shields and waste packages due to 
deleterious geochemical conditions caused by heat and volatiles from the intruding magmas has 
also been evaluated. 
During an igneous intrusion, drip shields, waste packages, and the other engineered features 
within the drift would be engulfed by magma. Depending on the magma characteristics and the 
energy associated with the intrusion, this would result in varying degrees of mechanical damage 
to the drip shields and waste packages and would expose them to thermal and geochemical 
conditions that would likely affect their integrity. 
Although no direct testing or evidence has been identified to constrain the extent of damage that 
could occur in an intrusive event, several observations and related analogs have been considered 
in developing the consequence models. These are summarized below. 
The temperature of intruding magma is estimated to range from 1,046 to 1,169C (BSC 2003b, 
Table 37). The melting temperatures of the drip shield (Titanium Grade 7: 1,660C), and the 
waste package materials (Alloy 22: 1,357C; structural Stainless Steel Type 316NG: 1,375C) 
(CRWMS M&O 1999, Section 5.1) are well above the magma temperature, but the strength of 
the metals would certainly decrease at magmatic temperatures. 
Waste Package Behavior in Magma (CRWMS M&O 1999) provides calculations of the pressure 
that would develop within waste packages as the result of gas expansion at high temperatures. It 
concludes that as temperatures approach 1,200C the resulting stresses on the packages would 
reach the tensile strength of the package materials. If a package was weakened by corrosion or 
other factors, its tensile strength could be exceeded by the internal pressure at temperatures lower 
than 1,200C. Thus, thermal stresses provide a possible mechanism for package breaching. 
A literature review on the performance of waste package and drip shield materials, documented 
by Structural Integrity Associates (Gordon 2003), suggested that the structural integrity of these 
materials would be compromised by exposure to magmatic environments. For example, 
Types 310 and 446 stainless steels, exposed to Hawaiian basaltic lava at 1,300C for 100 hours, 
were extensively reacted and damaged, while alloy 718 suffered a loss of structural integrity 
(Gordon 2003). 
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Testing of transportation containers also provides anecdotal evidence that high energy impacts 
and high temperatures can damage metal containers. These tests considered 120 miles per hour 
truck impact accidents (with linear forces of up to 100,000 pounds/ft), variable energy shocks 
and vibrations, engulfing fire at 800C temperature, and high energy explosions (Sanders 
et al. 1992, Appendix III; Fischer et al. 1987, Section 6.0; Sandoval et al. 1983). The containers 
were damaged to varying degrees during these tests, although the direct relevance to the igneous 
intrusion scenario is uncertain because the energy associated with the impacts and explosions 
probably greatly exceeds what would be expected during an igneous intrusion into a drift. 
If magma intrudes the repository, waste packages and other engineered materials may be subject 
to enhanced corrosion, the degree of which will depend on material and magma composition, the 
temperature on contact and during cooling, and the in situ geochemical environment. The 
geochemical environment in the drift will be affected by the composition and volume of 
exsolving volatile gases, such as H2O, H2, CO2, CO, SO2, S2, HCl, HF, and H2S. 
A variety of literature studies regarding the potential for enhanced corrosion in magmatic 
environments are summarized in Igneous Intrusion Impacts on Waste Packages and Waste 
Forms (BSC 2003d). These studies, which include tests and observations conducted over 
periods of time ranging from minutes to weeks, indicate that high temperatures and corrosive 
geochemical environments can measurably increase the corrosion rates of steel and other metal 
alloys. 
Although none of the analyses described above indicate that the metallic engineered barriers 
would be destroyed or fail instantaneously, it appears that the effects would be rapid compared to 
the 10,000-year regulatory period for the repository. Therefore, because of the uncertainty 
associated with analyzing the effects of enhanced corrosion rates, performance assessment 
analyses for Yucca Mountain conservatively assume that any engineered materials contacted by 
magmas (e.g., drip shields, waste packages, cladding) during an intrusion will no longer provide 
any waste isolation function. Specifically, this assumption means that none of the engineered 
barriers in Zone 1 (within the drifts intersected by magma) would impede the movement of water 
to and through the waste package or the contact of water with the waste forms. The magmas that 
encase the waste packages are further assumed to have hydrologic properties similar to the 
fractured tuff in the drift wall, so that the magma filling the drifts also provides no barrier to the 
movement of water or to the contact of water and the waste form. The analyses do assume that 
the geochemistry of the water inside the drifts would be controlled by the contact of water with 
basaltic igneous rock. 
An analysis of the effects on engineered barrier integrity was also performed for the drip shields 
and waste packages in emplacement drifts that were not intersected by magmatic intrusions 
(Zone 2 of the repository). This analysis included evaluation of the thermal impacts of dike 
intrusion in adjacent drifts and a gas-flow analysis, which describes the movement of potentially 
corrosive magmatic vapors through the rock and backfilled drifts separating the Zone 2 drifts 
from the magma filled drifts (BSC 2003a, Section 6.5.1 and 6.5.2; BSC 2003d, Section 6.5.1). 
Predicting the possible impacts of an igneous dike-intrusion event on the waste packages and 
waste forms in potentially affected Zone 2 emplacement drifts requires several simplifying 
assumptions to determine the amount and composition of volcanic gases that could be released 
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from the cooling magma. The volume of the magma is assumed to be equal to the total volume 
of the emplacement drift minus the volume of waste packages. This assumption yields a 
conservatively large estimate of the volume (and mass) of magma in Zone 1 drifts, and it is, 
therefore, conservative for calculating the molar volumes of emanating gases and modeling the 
gas diffusion and heat conduction between Zones 1 and 2 emplacement drifts. 
After intrusion, it is assumed that an average 3.5 weight percent out of 4.0 weight percent 
dissolved water will be released as volatile water containing corrosive gases and will diffuse 
away from the intrusive body. The data on water contents of postMiocene basaltic magma in 
the Yucca Mountain region is sparse, but based on the considerations summarized in Section 3.3, 
the selected values are considered to be conservative. 
The advective flow of water vapor and other volatiles from the magma in the emplacement drifts 
is two dimensional from the magma filled drift to the adjacent emplacement drifts on both sides. 
The analyses were performed assuming linear flow with the initial moles and volume halved. 
This linear flow assumption is conservative because it ignores radial movement that would not 
reach the Zone 2 drifts and allows volatile components to move down a pressure gradient from 
the higher temperature, higher-pressure magma filled drifts to a lower-pressure-and-temperature 
state. The model of gas migration assumes that the ideal gas law is applicable over 
Van der Waals Equation. Analysis of this assumption indicates that the ideal gas law can be 
used for pressures less than 7.5 atm (110 psi). The gas in the magma is assumed to be in 
pressure communication throughout. This assumption is conservative and will ensure the full 
volume of gas will be available for flow into the backfill and rock matrix. The initial pressure is 
represented by the pressure resulting from the elevated gas temperature associated with the 
magma intrusion, not by pressure conditions within the magma. The initial gas pressure was 
calculated as 2.35 atm. The full volume of volatile gases will not be immediately available for 
movement after the intrusion but will evolve slower than the magma movement. 
The migration of volcanic gas associated with a magma-filled drift into a neighboring drift was 
analyzed using reaction-transport modeling that couples thermal, hydrological, and chemical 
processes for a multiphase, multicomponent, multimineralic system. Simulation results were 
obtained for the migration of volcanic gas out of a waste-emplacement drift through the fractured 
tuff repository rock and, alternatively, through a backfilled access drift (BSC 2003a, 
Section 6.5.1). Figure 5-9 is a schematic drawing showing the configuration of Zone 1 and 
Zone 2 drifts simulated by the model. 
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Source: BSC 2003a, Figure 144. 
NOTE: The drawing is not to scale. Dikes would typically be 1 to 2 m in width. Drifts are 5.5 m in diameter and are 
spaced 81 m apart. 
Figure 5-9. Schematic View of the Configuration of Zone 1 and Zone 2 Drifts Simulated in the Reactive 
2 (BSC 2003a, Section 6.5.1.1). 
November 2003 5-25 
Gas Transport Model 
Several simulations were performed to bound the potential rate of advance of the gas and to 
examine the controls on the migration of soluble gas species. Diffusive and advective gas phase 
transport of air, H2O, CO2, and SO2 were modeled along with the appropriate equilibrium 
gas-water solubility relations. Calculations of gas density and pressure considered only water 
vapor and air. The model of the geochemical system includes the major aqueous species, 
minerals, and gaseous components in the unsaturated zone. Additionally, minor species such as 
F-, are included for their relevance to waste package corrosion. The geochemical model consists 
of the following primary aqueous species: H+, Na+, K+, Ca2+, Mg2+, AlO2
-, NO3
2-, SO4
2-, 
SO2(aq), F-, Cl-, HCO3
-, SiO2(aq), and HFeO2(aq). Gaseous components include air, H2O, CO2, 
and SO2. Oxidation-reduction reactions were not treated; however, reactions involving sulfur 
oxidation would result in stronger retardation of SO 
The initial mineralogy of the tuff matrix and fracture coatings is represented by the following 
assemblage (some as end members of an ideal solid-solution phase): -cristobalite, opal, 
tridymite, quartz, K-feldspar, albite, anorthite, Ca-smectite, Na-smectite, Mg-smectite, illite, 
calcite, fluorite, rhyolitic glass, hematite, stellerite, clinoptilolite, mordenite, and heulandite. 
Several other potential secondary phases are considered (e.g., amorphous silica, kaolinite, 
sepiolite, gypsum) as well as various salt phases, such as halite and sylvite, which precipitate 
only under conditions of complete evaporation (BSC 2003a, Section 6.5.1.1). 
The high solubility in water of SO2 and to a lesser extent CO2, along with the development of a 
boiling zone around a drift where magma has been emplaced, would limit the migration of these 
gases through the repository host rock. Preliminary model results, under ambient pressure 
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conditions, indicate that these gases would not migrate to adjacent drifts through the rock in less 
than 10 years. This period of time is significantly longer than the period over which volcanic gas 
from a single intrusion would be present in significant volume (BSC 2003a, Section 6.5.1.6.6). 
Under prolonged elevated pressure conditions (2 bars for 1 day or more), gas transport through 
the relatively dry high-permeability fractured tuff is rapid. However, the volume of the gas 
would be relatively small because it is moving through fractures that make up less than 1 percent 
of the total rock volume. After the pressure subsides back to ambient values, the CO2 and SO2 in 
the fractures diffuse into the rock matrix where they dissolve readily and are immobilized 
(BSC 2003a, Section 6.5.1.6.6). 
Gas migration may also be relatively rapid through a tunnel filled with coarse crushed tuff, such 
as the repository main drifts that connect emplacement drifts. In this case, an adjacent drift could 
be affected by migrating volcanic gas within a year or less without any strong advective flow due 
to large pressure differences. Depending on the volume of gas emplaced, though, the gas could 
be strongly diluted by air as it migrates through the connecting drifts (BSC 2003a, 
Section 6.5.1.6.6). Therefore, the impact of volcanic gases on geochemical conditions would be 
limited. 
Additional thermal and geochemical simulations of the effects on Zone 2 drifts are reported in 
Igneous Intrusion Impacts on Waste Packages and Waste Forms (BSC 2003d, Sections 6.5.2.1.1 
and 6.5.2.2.3). Maximum temperature increases in drifts adjacent to magma filled drifts are 
small (less than 10C), as the rock provides effective thermal insulation. Therefore, waste 
packages in Zone 2 emplacement drifts would not be affected by the heat from magma intruded 
into adjacent drifts. See additional discussion in Appendix C. 
Geochemical analyses, using the EQ3/6 geochemical code, similarly showed that gas movement 
associated with magmatic intrusions would be very short lived and minimal in volume. The 
model predicts that the gas front would extend only about 3.6 m into the host rock adjacent to 
intruded drifts, and about 1.4 m into backfilled drifts adjacent to the emplacement drifts. In 
summary, multiple analyses indicate that the thermal and geochemical effects of magma 
intrusion on Zone 2 drifts would be negligible. 
5.4 NUMBER OF WASTE PACKAGES HIT BY ERUPTIVE CONDUITS 
INTERSECTING THE REPOSITORY 
If a volcano erupted through the repository, the consequences (in terms of radionuclide releases) 
would depend on the style and energy associated with the eruption. Section 3 described the 
eruptive styles typical of the small basaltic scoria cones that occur in the Crater Flat Volcanic 
Zone. As the basaltic dikes that feed eruptive centers ascend to the surface, the flow of magma 
becomes concentrated in conduits in which the magma fragments as volatiles exsolve. 
The size (width and depth) of the conduits feeding eruptions is important to repository 
performance analyses because it directly influences the potential for waste materials to be 
incorporated in the eruption. In general, considerations described in Characterize Eruptive 
Processes at Yucca Mountain, Nevada (BSC 2003b), indicate that conduits feeding small 
volcanoes like the Lathrop Wells Cone will likely range from 0 to about 900 m in depth. If the 
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conduit formed at a depth of less than 300 m, then its only expression at the depth of the 
repository would be the dike(s) feeding it, which are typically 1 to 2 m wide. If the conduit 
extends to depths greater than 300 m, then its dimensions at the level of the repository would 
depend on its shape and volume. 
Evidence summarized in Characterize Eruptive Processes at Yucca Mountain, Nevada 
(BSC 2003b, Section 6.3.1) from several volcanoes that are analogous (to varying degrees) to the 
basaltic systems in Crater Flat indicates that the width of potential conduits could range from a 
few meters to as much as 150 m (Section 4.3). 
Total system performance analyses have conservatively adopted 50 m as the median conduit size 
for an eruption through a repository. The minimum conduit diameter used for the calculation is 
5 m. The minimum conduit diameter is constrained by the dike width parameter, and the 
95th percentile of dike width cumulative distribution function is 4.5 m. The slightly more 
conservative value of 5 m has been selected as minimum conduit diameter (BSC 2003c, 
Section 5.4). Based on observations at another potential analog volcano (Grants Ridge in 
New Mexico), the maximum size of the potential conduit has been chosen as 150 m. This value 
is believed to bound the range of conduit sizes for a potential Yucca Mountain volcanic event, 
given that the Lathrop Wells Cone (which is the largest of the Crater Flat volcanic centers) has a 
basal diameter of about 700 m and a height of 140 m. 
The entire width of a conduit is not necessarily actively transferring magma to the vent at all 
times during an eruption. Due to variations in local flow geometry, magma velocity and 
viscosity and other factors, the eruption may use only a small fraction of the conduit at any one 
time. Using conduit width estimates based on analog observations provides a conservative 
estimate of the total volume of rock (and the total area of a repository) that could be affected 
during a single event. 
The number of waste packages destroyed by a system of eruptive conduits is treated as a joint 
probability, dependent on both the number of conduits and the diameter of the conduits. The 
distributions for the number of conduits associated with a dike intersecting the repository has 
14 bins, ranging from 0 conduits to 13, with a maximum probability of 1 conduit. 
For any particular realization in the performance assessment analysis, it is assumed that all 
conduits have the same diameter. This is a simplifying assumption, but the analysis does sample 
a distribution of conduit diameters (BSC 2003c, Section 5.5) when all realizations are 
considered. 
The analysis of the number of waste packages intersected by conduits is facilitated by an 
abstraction in which the number of waste packages within a conduit is simply a function of 
conduit area and the average waste package density within the repository. This geometric 
simplification does not affect the mean number of packages hit by any individual conduit, but it 
does affect the range of packages incorporated in each conduit. Ignoring the actual location of 
waste packages in linear emplacement drifts will decrease the number of conduits that see no 
waste packages (i.e., that erupt entirely through the pillars in the repository), but may also 
decrease the maximum number of packages in a conduit that erupts through a drift. No attempt 
is made to specifically determine or assign where in the repository a conduit occurs. Although 
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magma associated with an eruption may contact other packages along the drift, the magma 
moving with sufficient velocity to entrain waste in an eruption is assumed to be located only 
within the conduit (BSC 2003c, Section 5.6). 
The result of the calculation of the number of waste packages hit by volcanic conduits is shown 
on Figure 5-10. The number of packages intersected by conduits during an eruption varies from 
zero to about 40 (at the 95th percentile of the cumulative distribution function). The mean 
number of packages hit by conduits is about six. 
The Effect of Volcanic Eruptions on Waste Packages and the Waste FormAs noted in 
Section 5.3, no known analog observations, tests, or experiments provide evidence that would 
enable analysts to constrain how completely waste packages would be damaged or destroyed and 
the waste forms inside the packages fragmented in the event of a volcanic eruption. For this 
reason, performance assessment analyses of the effects of volcanic eruptions have conservatively 
assumed that the waste packages would be completely destroyed, and the waste form pulverized 
such that particle sizes range from 0.0001 to 0.05 cm, with a mode of 0.002 cm (CRWMS 
M&O 2001). This size distribution makes virtually the entire waste inventory of the intersected 
waste packages available for airborne transport along with the volcanic ash associated with the 
eruption. It is also conservatively assumed that the waste is entirely composed of spent nuclear 
fuel which has higher concentrations of radionuclides than the high-level radioactive waste glass 
also disposed in the repository. 
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Source: BSC 2003c, Figure 12. 
Figure 5-10. Composite Cumulative Distribution Function for Number of Waste Packages Hit by 
November 2003 5-29 
Conduits 
5.5 THE AREAL DISTRIBUTION OF ENTRAINED WASTE IN PLUMES OF 
VOLCANIC ASH 
The potential distribution of volcanic ash and radioactive waste during and after a volcanic 
eruption is described in Atmospheric Dispersal and Deposition of Tephra from a Potential 
Volcanic Eruption at Yucca Mountain, Nevada (BSC 2003f). A conceptual and mathematical 
model has been developed for atmospheric dispersion and subsequent deposition on the land 
surface of tephra from a potential eruption at Yucca Mountain, Nevada. The model is 
implemented in a computer code known as ASHPLUME. Figure 5-11 is a schematic 
representation of an eruption, showing the transport of volcanic ash and waste in an ash plume. 
The conceptual model accounts for the entrainment of spent nuclear fuel particles within the gas 
and ash ejected during a hypothetical eruption through the repository and describes the factors 
controlling downwind transport of contaminated tephra. The mathematical model describes the 
conceptual model in mathematical terms to allow for prediction of radioactive waste/ash 
deposition on the ground surface given that the hypothetical eruptive event occurs. The 
distribution and amounts of ash and waste predicted by ASHPLUME are used to calculate the 
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dose resulting from exposure to waste-contaminated ash and redistributed contaminated soils at 
the location of the receptor (known as the reasonably maximally exposed individual, or RMEI). 
The ASHPLUME numerical model and computer code are a component of the total system 
performance assessment (TSPA) model of Yucca Mountain. 
Figure 5-11. Schematic Representation of a Volcanic Eruption at Yucca Mountain, Showing Transport of 
Radioactive Waste in an Ash Plume 
Section 5.4 described the number of packages encountered within eruptive conduits, and 
explained the conservative assumption that all waste contained in waste packages within the 
conduit would be pulverized to a fine grain size that could be entrained in the erupting magma. 
This section discusses the postentrainment and atmospheric transport portions of the eruptive 
conceptual model, specifically the following topics: 
 Eruptive styles associated with atmospheric transport of ash 
 Entrainment of waste in an ash plume in the atmosphere 
 Atmospheric transport of waste in the ash plume 
 Deposition of waste and ash. 
Conceptual and Mathematical ModelThe ASHPLUME mathematical model is based on a 
two-dimensional diffusion model in which only horizontal turbulent diffusion is considered. The 
movement of air in the atmosphere is random due to the many eddy currents that exist 
(Suzuki 1983). The movement of particles within the air mass is also random for the same 
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reason. Particles diffuse in the atmosphere in both vertical and horizontal directions, but because 
the scale of horizontal turbulence is much greater than the scale of the vertical turbulence 
(Suzuki 1983), horizontal diffusion is the dominant factor in determining the width of a plume as 
it moves downwind. Therefore, the ASHPLUME model is based on a two-dimensional diffusion 
equation in which only horizontal turbulent diffusivity is considered. 
The ASHPLUME conceptual model for the atmospheric dispersal and deposition of 
contaminated tephra begins with a magmatic dike rising through the Earths crust and 
intersecting the repository at Yucca Mountain (Figure 5-1). An eruptive conduit, or conduits, 
can form when a portion of the dike begins to widen and forms a preferential pathway to focus 
an eruption that penetrates the Earths surface. If the conduit intersects the repository, the 
assumption is made that all canisters located partially or entirely within the conduit provide no 
further protection to the waste, which will become entrained within the rising magma. 
Typical eruptions from the types of scoria cones characteristic of the Yucca Mountain region are 
known as Strombolian eruptions. Strombolian eruptions are characterized by the explosive 
ejection of a high-speed column of a gaspyroclast mixture. The column consists of two regions. 
The lower region directly above the vent is called the gas-thrust region, and it behaves as a 
ballistic fountain of tephra moving under the influence of its eruption momentum. The upper 
region of the column is called the convective-thrust region, in which tephra rise by buoyant 
convective currents. Strombolian eruptions typically vary in eruptive intensity as measured by 
the degree of magma fragmentation and eruptive velocity. A violent Strombolian eruption is one 
that is dominated by an energetic upper column, with atmospheric transport of the fragmented 
magma and gas mixture that approximates a thermally buoyant plume. Eruptive sequences at a 
representative volcano, such as the Lathrop Wells scoria cone, might include intermittent and 
sporadic periods of lava fountaining, Strombolian blasts, and periods of violent Strombolian 
eruptions that may last for a few days (BSC 2003b, Section 6.3.5.1). The ASHPLUME model 
specifically simulates the atmospheric transport of ash (and waste particles) associated with 
violent Strombolian eruptions. 
As the eruptive mixture rises in the plume of a violent Strombolian eruption, it entrains and heats 
air, which, in turn, reduces the bulk density of the mixture, and the plume becomes buoyant and 
continues to rise (BSC 2003f, Section 6.3). The plume rises to an altitude of neutral buoyancy 
compared to the surrounding atmosphere, in which it then spreads laterally as an anvil cloud and 
is transported down wind. Tephra particles fall out from both the vertical eruption column and 
from the anvil cloud according to their settling velocities. Such eruptions produce a fallout sheet 
of varying thickness extending from the volcanic vent. The thickness of the deposit depends on 
factors such as particle density, eruptive parameters, wind speed and direction, and distance from 
the vent. 
Wind speed and direction vary with altitude, so the model incorporates wind data that are 
consistent with observations for the Yucca Mountain region. Meteorological data characterizing 
the variability in wind speed and wind direction in the Yucca Mountain region under present 
climatic conditions are described by Quiring (1968, pp. VI-1VI-21) and have been augmented 
by more recent data from the Desert Rock airport near Mercury, Nevada (NOAA n.d.). The 
Desert Rock data have been used to calculate variability in both wind speed and direction as a 
function of altitude up to 13 km (BSC 2003f, Appendix 3). 
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Modeling studies of past climatic conditions provide insight into projections of future climatic 
conditions at Yucca Mountain. Kutzbach et al. (1993, p. 60) have modeled global climates at 
3,000-year intervals during the last 18,000 years using general circulation models with available 
paleoclimatic information used to define boundary conditions. Resolution of the model is very 
coarse (grid blocks are 4.4 latitude by 7.5 longitude (Kutzbach et al. 1993, p. 60), and results 
are, therefore, not intended to be interpreted at local scales. However, at a regional scale, the 
model provides qualitative information about modeled wind speeds and directions throughout the 
southwestern United States. Model results are provided for 18,000 years ago, at the end of the 
last major glaciation of northern North America; at 12,000, 9,000, and 6,000 years ago; and also 
for present conditions. Climatic conditions over this time interval span the range of conditions 
that might reasonably occur during a glacial transition in the next 10,000 years. 
The wind speeds and directions modeled by Kutzbach et al. (1993) for the transition from glacial 
to interglacial climates in the southwestern United States are not significantly different from 
modern conditions. The largest changes, occurring during full glacial conditions 18,000 years 
ago, appear qualitatively to correspond to a decrease in the relative frequency of winds blowing 
toward the RMEI location south of Yucca Mountain. Therefore, these changes are reasonably 
and conservatively neglected, and the significant variability in present wind conditions is 
assumed to adequately represent variability in future conditions. 
ASHPLUME models eruption behavior as a thermally buoyant plume, calculating the 
atmospheric dispersion of tephra and its deposition on the ground. The total mass of waste 
materials that can potentially be entrained in an eruption is determined by the number of 
packages hit by the volcanic conduits. The waste is assumed to have been finely fragmented by 
the force of the eruption, and waste particles are assumed to combine with larger ash particles for 
airborne transport. ASHPLUME defines an incorporation ratio, which relates the minimum 
ash particle size needed to carry a given waste particle size in the plume, to calculate the fraction 
of waste entrained in the erupted plume (Jarzemba et al. 1997; BSC 2003f, Section 6.5.1). By 
doing so, the fallout of tephra carries contamination to where it is deposited on the ground, 
forming a contaminated fallout deposit. The contaminated fallout has the potential to affect the 
food and water supplies of the RMEI by direct contamination or by later surface redistribution of 
fallout deposits, which could be caused by a number of mechanisms (BSC 2003i, Sections 5.6 
and 6.6.1). The outputs of the ASHPLUME model include the distribution and surface area 
density (g/cm2) of volcanic ash and associated concentrations of waste, which is specified to be 
spent nuclear fuel. These outputs are then input into biosphere models that predict dose. 
The ASHPLUME model has been tested by comparison to several analog sites, including the 
Lathrop Wells Cone, Cerro Negro volcano in Nicaragua, and a Holocene cinder cone in Lassen 
Volcanic National Park in California. In each case, the ash distribution patterns, and depths 
predicted by ASHPLUME were consistent with observations from known eruptions. 
5.6 ASH REDISTRIBUTION MODEL 
If an eruption were to occur through the repository at Yucca Mountain, radioactive waste 
particulates could be ejected along with the volcanic ash as attached and individual particles. 
The result would be a tephra sheet containing radioactive waste. Shortly after deposition of the 
tephra sheet, normal sedimentary processes (Folk 1980) would begin redistributing the ash. 
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Wind and water would begin eroding, transporting, sorting, and depositing the unconsolidated 
ash in greater or lesser concentrations of waste, depending on the mixing processes. The RMEI 
could then be exposed to the radionuclides contained within the redistributed deposits. For this 
reason, surface redistribution of contaminated tephra deposits has been evaluated for inclusion in 
TSPA (BSC 2003f, Sections 6.6 and 6.7). 
The transport of tephra occurs by both wind and water action; however, while water can 
transport large amounts and much larger sizes of material in a short period of time (flooding 
event), wind is a continuous source of transport. Transport of tephra by water begins with 
hillslope erosion processes, continues as sediment moves into drainages and is transported in the 
beds of drainages that coalesce into larger and larger channels. At all scales within drainage 
systems, water and sediment from different channels begin a process of mixing that ultimately 
leads to a homogeneous sediment containing elements derived from all drainages in the basin 
(Folk 1980, pp. 14 to 15). This mixing of sediments occurs in all environments where sediment 
is transported by water, including intermittent and perennial stream systems, and occurs at higher 
rates and is able to carry larger clast sizes in larger drainages than smaller ones and on steeper 
hillslopes than on low-gradient landscape surfaces. Sediment mixing also occurs from wind 
action by transporting sediment across the landscape. Drainage channels that form and flow 
across newly deposited tephra sheets exhibit the same processes as observed in streams, and, 
after small transport distances, have well-mixed sediment loads. 
Sedimentary depositional systems at the Lathrop Wells volcanic cone near Yucca Mountain and 
at Sunset Crater in the San Francisco volcanic field near Flagstaff, Arizona (Harrington 2003, pp. 
14 to 16) have been studied to evaluate the potential redistribution of tephra and radioactive 
waste after a possible volcanic eruption through Yucca Mountain. Both areas have tephradraped 
slopes of 5 to 10. Drainage systems that have formed on the slopes at both locations 
show a similar pattern of development from normal sedimentary processes (BSC 2003f, 
Section 6.6). 
In small channels, material is moved downslope by incorporating ash and sand in mixtures with 
water until the channel is choked, thereby causing the material to overflow out of the channel 
sides and move downslope as small debris flows. Depending on the slope angle, the transport of 
the tephra could begin with small debris flows. Thus, tephra moves downslope progressively, 
until it reaches the base of the tephra sheet or, more commonly, until it reaches a channel at the 
base of the slope. In these channels, which are part of a larger drainage system, the tephra is 
mixed with the sediment load from upstream. Depending on the size of the drainage system and 
the area of the tephra deposit, the majority of sediment in the larger channels is likely to be 
composed of materials other than fresh tephra (Harrington 2003, pp. 14 to 16). 
In the Yucca Mountain area, sediments in drainage channels are commonly clasts of siliceous 
welded tuff and eolian quartz sand, which are more durable than the basaltic tephra. Mixing of 
the sediments occurs very rapidly, and welded tuff clasts and quartz sand/silt deposits are more 
abundant in the larger channels, so that the Lathrop Wells ash component has been progressively 
diluted during transport relative to the total sediment volume. Eolian processes also contribute to 
the mixing of sand and silt with the fluvially transported ash and other channel material. On the 
tephra sheet, sand and silt is trapped in the ash interstices. As this ash-dominant material moves 
downslope, more and more nonash and noneolian material is incorporated at channel 
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confluences. Thus, the quantity of basaltic ash (ratio of ash to nonash) continues to decrease 
(BSC 2003f, Section 6.6). 
Studies of ash redistribution near Lathrop Wells have been performed to evaluate the fraction of 
basaltic ash components as a function of transport distance from the tephra sheet. These data 
indicate that the concentration of basaltic ash in sediments decreases to about 50 percent within 
1 km of the head of the tephra sheet drainage on the eastern side, whereas the channel on the 
west side has less than 40 percent basaltic ash after 1 km of transport. These results indicate a 
dilution factor of 50 to 60 percent per kilometer. 
Fortymile Wash is a major 800-km2 drainage basin that includes the entire eastern slope of 
Yucca Mountain and the Fortymile Wash alluvial fan; therefore, understanding the redistribution 
processes along Fortymile Wash is important to volcanic-eruption consequence scenarios. The 
fan spreads out into the Amargosa Valley from the mouth of Fortymile Wash. In the upper or 
northern half of the fan, the channels are well defined and widely spaced, with sizable 
interstream area between all pairs of channels. These interstream divide tracts are more 
prominent on the upper fan. On the lower fan they are neither as topographically prominent nor 
as wide because the distributary channels become progressively closer on the lower fan. 
From the mid-1950s through the mid-1960s, worldwide aboveground nuclear tests introduced 
radioactive 137Cs into the atmosphere (Ely et al. 1992, p. 196). 137Cs forms a time-stratigraphic 
marker in alluvial or eolian deposits and can be used to assess the extent of local erosion and 
deposition. Also, the depth to which 137Cs infiltrates into the soil can be used as a general proxy 
for the depth to which sorbing radionuclides may infiltrate after deposition with volcanic ash 
(BSC 2003f, Section 6.7.2.1). 
To evaluate erosion rates on the upper Fortymile Wash fan, soil samples were taken for analysis 
of 137Cs concentrations (BSC 2003b). The analyses indicate that the upper-fan interstreamdivide 
areas have been eroding over the last 50+ years and have lost 1 to 2 cm of the upper soil 
horizon. This stripping of the upper centimeter has most likely occurred as a result of wind 
erosion, rather than from removal by fluvial processes (BSC 2003b). 
Although wind erosion can be inferred from the 137Cs data, there is also evidence of some eolian 
deposition on these same surfaces. The evidence includes stratified eolian horizons of fine sand 
and silt, marked by the presence of gas bubble vesicles (Av horizons). Such soil horizons are 
found on most geomorphic surfaces that have been stable for several hundred years (YMP 1993, 
pp. 24 to 25). The presence of Big Dune in proximity to the Fortymile Wash fan, from which 
material is being removed and deposited almost continuously, clearly demonstrates that eolian 
processes play an important role in landscape modification. 
Ash Redistribution Model ResultsThe upper half of the Fortymile Wash alluvial fan consists 
primarily of an interstream divide area (82 percent); secondarily of distributary channels 
(17 percent); and the balance (1 percent) of minor areas of overbank deposits, sand dunes 
(coppice), and sand areas. Thus, the majority of the fan surface is interstream divide area, from 
which 1 to 2 cm of material, on average, has been removed during the last 50 years. 
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When large flood events occur, the flood waters can carry large quantities of sediment rapidly 
southward across the fan to the Amargosa River and may overflow channel banks to form small 
patches of overbank deposits. As flood levels subside, the suspended and bedload materials in 
the channel flow are deposited within the channel. The resulting deposits are stored in the 
channel until the next flood occurs. This may be a considerable time (more than 50 years) (BSC 
2003b). Although water erosion can be significant, wind erosion appears to be continuous. The 
50-year 137Cs record suggests that eolian removal of material has been the major process causing 
erosion (BSC 2003f, Section 6.7). 
Different processes of erosion and sedimentation will result in differing concentrations of 
contaminated ash and radionuclides on each of the major landforms. Therefore, the TSPA model 
calculates dose estimates separately for each region (interstream divide areas and distributary 
channels) and combines them, weighted by their areal frequency (0.82 and 0.18, respectively). 
The overbank deposits, dunes, and sand areas are combined with the distributary channel areas 
because their fractional area is small and their sediment composition is largely derived directly 
from the channel deposits (BSC 2003f, Section 6.7). 
Several important factors control the contribution to dose to the RMEI, including the amount of 
soil removal, the extent and amount of tephra deposits at the location of the RMEI, and the 
contamination of residual ash after erosion of the tephra sheet. 
In the interstream divide areas, erosion removes sediment at a relatively rapid rate (1 to 2 cm per 
50 years, as noted above). Therefore, the TSPA model will calculate doses using the initial ashlayer 
thicknesses and radionuclide concentrations from ASHPLUME, modified by a time 
dependent soil removal factor, estimated to range from 0.02 to 0.04 cm/yr. Given these erosion 
rates, the ash layers will be removed within a few centuries, depending on initial thickness. 
Based on field observations, it is likely some fine-grained ash and radionuclides will persist in 
the soil below the initial ash layer, and some additional radionuclides may be brought into the 
interstream divide areas by infrequent flooding events that cover the entire fan. Based on 137Cs 
data, it is estimated that residual contamination after erosion removal of the tephra deposits will 
be on the order of 0.01 of the initial ASHPLUME radionuclide concentration (BSC 2003f, 
Section 6.7). 
In contrast to the interstream divide areas, the amount of sediment deposited in channels varies 
greatly from location to location, and it is not feasible to provide a single realistic estimate for 
the thickness of a potentially contaminated layer of redistributed tephra. For the purposes of 
TSPA, distributary channel areas will be modeled as having a layer of contaminated ash of 
uncertain thickness that appears immediately following the eruption. This layer will be of 
variable thickness, ranging from zero to perhaps several tens of centimeters (represented by a 
uniform distribution from 0 to 15 cm). Although sediment thickness may exceed 15 cm, it is 
likely that contributions to dose from radionuclides at greater depths will be negligible. 
Observations of 137Cs content also indicate that radionuclides are unlikely to migrate more than 
9 cm into sediment below the ash layer due to the widespread presence of carbonate layers in soil 
(Harrington 2003, pp. 28 to 53). 
Conceptually, the contaminated layer in the channel areas represents a reasonable approximation 
of the amount of contaminated ash that might be present in transient storage in a channel at any 
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time following a volcanic eruption. Within any portion of the fan, such as the location of the 
RMEI, contaminated ash will be both removed and deposited continuously, and the appropriate 
layer thickness to consider in the TSPA model is an average value for the amount present at any 
one time. Incorporating uncertainty in the layer thickness into a single sampled parameter that 
characterizes the entire region, rather than attempting to capture local variability explicitly, is 
reasonable because exposures to the RMEI will be derived from a spatially heterogeneous area. 
Although dilution of radionuclides in tephra is certain to occur during transport in distributary 
channels, as discussed earlier in this section, field data are insufficient to quantify this reduction 
in concentrations for the Fortymile Wash drainage and fan. Therefore, the TSPA will 
conservatively assume that the concentration of radionuclides in the contaminated sediment in 
the channel areas is the same as that derived from ASHPLUME for the mid-line of a plume 
about 18 km from the vent. The extent to which this assumption overestimates concentrations is 
not well known but may be large, especially for eruptive events in which the wind is blowing 
from the west or southwest and the ash deposition occurs upstream from the location of the 
RMEI. The use of a single concentration to represent a spatially variable parameter is believed 
to be reasonable because exposures would be integrated over a region that is relatively large 
compared to the scale of local variability (BSC 2003f, Section 6.7). 
Observations from the Lathrop Wells Cone indicate that ash will not remain indefinitely in the 
channel area. The time scale over which most tephra is removed from the drainage is unknown 
but is substantially less than the age of the Lathrop Wells Cone. Given the limited presence of 
ash observed at all locations, except those immediately adjacent to intact tephra deposits, the 
time required to remove most ash from the distributary channels may be very short, perhaps on 
the scale of centuries. Therefore, the TSPA model applies a uniform removal rate to channel 
deposits such that the initial layer is removed fully within an uncertain period of time that is 
sampled uniformly between 100 and 1,000 years. Consistent with the approach taken above for 
the interstream-divide areas, some residual contamination will likely remain after the tephra 
deposits are eroded. This contamination is presumed to persist indefinitely (BSC 2003f, Section 
6.7). 
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date: 04/14/2000. 
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LA0009FP831811.001. Compilation and Summaries of Data Supporting Computation of 
Volcanic Event Intersection Frequencies. Submittal date: 09/01/2000. 
LA0302GH831811.003. Lithic Clasts Measured at Lathrop Wells Cone, Nevada. Submittal 
date: 02/25/2003. 
LA0307BY831811.001. Characterize Igneous Framework Additional Output. Submittal date: 
06/29/2003. 
LAFP831811AQ97.001. Chemical and Geochronology Data for the Revision and Final 
Publication of the Volcanism Synthesis Report. Submittal date: 08/29/1997. 
MO0002PVHA0082.000. Probabilistic Volcanic Hazard Analysis for Yucca Mountain, Nevada. 
Submittal date: 02/17/2000. 
MO0003YMP98126.001. Quaternary and Pliocene Basalt. Submittal date: 03/02/2000. 
SN0311T0503303.003. Updated Number of Waste Packages Hit by Igneous Intrusion. 
Submittal date: 11/06/2003. 
6.3 CODES, STANDARDS, AND REGULATIONS 
10 CFR Part 63. Energy: Disposal of High-Level Radioactive Wastes in a Geologic Repository 
at Yucca Mountain, Nevada. Readily available. 
40 CFR Part 197. Protection of Environment: Public Health and Environmental Radiation 
Protection Standards for Yucca Mountain, Nevada. Readily available. 
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APPENDIX A 
LIKELY RANGE OF TEPHRA VOLUMES 
(RESPONSE TO IA 2.03 AIN-1) 
November 2003 No. 13: Volcanic Events
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Note Regarding the Status of Supporting Technical Information 
This document was prepared using the most current information available at the time of its development. This 
Technical Basis Document and its appendices providing Key Technical Issue Agreement responses that were 
prepared using preliminary or draft information reflect the status of the Yucca Mountain Projects scientific 
and design bases at the time of submittal. In some cases this involved the use of draft Analysis and Model 
Reports (AMRs) and other draft references whose contents may change with time. Information that evolves 
through subsequent revisions of the AMRs and other references will be reflected in the License Application 
(LA) as the approved analyses of record at the time of LA submittal. Consequently, the Project will not 
routinely update either this Technical Basis Document or its Key Technical Issue Agreement appendices to 
reflect changes in the supporting references prior to submittal of the LA. 
No. 13: Volcanic Events November 2003
Revision 2 
APPENDIX A 
LIKELY RANGE OF TEPHRA VOLUMES 
(RESPONSE TO IA 2.03 AIN-1) 
This appendix provides a response to Key Technical Issue (KTI) agreement Igneous Activity 
(IA) 2.03 additional information needed (AIN-1). This KTI agreement relates to the likely range 
of tephra volumes from Yucca Mountain region volcanoes and is related to U.S. Nuclear 
Regulatory Commission (NRC) concerns with the Projects use of ASHPLUME V1.4LV-dll 
(ASHPLUME V1.4LV-dll, STN: 10022-1.4LV-dll-00). 
A.1 KEY TECHNICAL ISSUE AGREEMENTS 
A.1.1 IA 2.03 AIN-1 
Agreement IA 2.03 was reached during the NRC/U.S. Department of Energy (DOE) Technical 
Exchange and Management Meeting on Igneous Activity held August 29 to 31, 2000, in 
Las Vegas, Nevada (Reamer and Williams 2000). This agreement was later revised during the 
NRC/DOE Technical Exchange and Management Meeting on Igneous Activity held June 21 to 
22, 2001 (Reamer 2001). 
The wording of the revised agreement is as follows: 
IA 2.03
Document how the tephra volumes from analog volcanoes represent the likely 
range of tephra volumes from Yucca Mountain Region (YMR) volcanoes. DOE 
agreed and will document the basis for determining the range of tephra volumes 
that is likely from possible future volcanoes in the YMR in the Eruptive Processes 
AMR (ANL-MGR-GS-000002). This will be available to the NRC in FY 2002. 
For the total system performance assessment for the site recommendation, ASHPLUME 
V1.4LV-dll was used to model the direct release of radionuclides that could result from a 
volcanic eruption through the repository. ASHPLUME V1.4LV.dll used erupted volume as a 
proxy for eruptive power to calculate plume height. The range of erupted volume based on 
analogs in the Yucca Mountain Region was documented in Characterize Framework for Igneous 
Activity at Yucca Mountain, Nevada (CRWMS M&O 2000a, Table 4). The range of volumes 
used in the total system performance assessment for the site recommendation was documented in 
Igneous Consequence Modeling for the TSPA-SR (BSC 2001a). 
Agreement IA 2.03 was addressed in a letter report (Ziegler 2002) by describing the range of 
erupted volumes that had been documented in Characterize Framework for Igneous Activity at 
Yucca Mountain, Nevada (CRWMS M&O 2000a, Table 4) and Igneous Consequence Modeling 
for the TSPA-SR (BSC 2001a). In addition, the letter report described the sensitivity of mean 
annual eruptive dose rate to variations in the volume of erupted material, as documented in Total 
System Performance Assessment for the Site Recommendation (CRWMS M&O 2000b, 
Section 5.2.9.5). Results of the analysis showed that the total mean annual igneous dose rate was 
insensitive to the range of values selected for erupted volume. The letter report also noted that 
November 2003 A-1 No. 13: Volcanic Events
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the DOE intended to document the range of tephra volumes and the basis for the range used to 
support total system performance assessment for the license application (TSPA-LA) calculations 
in an update of Characterize Eruptive Processes at Yucca Mountain, Nevada (BSC 2001b). 
The ASHPLUME code (ASHPLUME V1.4LV-dll, STN: 10022-1.4LV-dll-00) utilized in the 
Total System Performance Assessment for the Site Recommendation (CRWMS-M&O 2000b) 
used erupted volume as a proxy for eruptive power in the computation of plume height estimates. 
Consistent with their concerns about this code, the NRC issued an additional information need 
(IA 2.03 AIN-1) (Schlueter 2002) based on the review of the DOE letter report (Ziegler 2002). 
Completion of the model report Atmospheric Dispersal and Deposition of Tephra from a 
Potential Volcanic Eruption at Yucca Mountain, Nevada (BSC 2003a) provides the NRC with 
the information needed to close IA 2.03 AIN-1. 
The wording of the additional information need is as follows: 
IA 2.03 AIN-1 
DOE needs to: (a) Provide a technical basis for demonstrating how tephra 
volumes have been calculated based on eroded deposits in the YMR, (b) Provide a 
technical basis for the inclusion of analog information, and (c) Demonstrate how 
buried deposits, such as the flows from Little Cones, has been incorporated into 
the calculation of tephra volumes. In addition, the apparent lack of sensitivity of 
tephra volume in performance assessment calculations should be demonstrated 
under appropriate wind conditions. The staff notes that in the letter report Range 
of Tephra Volumes, the DOE stated that DOE intends to document the range of 
tephra volumes and the basis for the range used to support TSPA-License 
Application (LA) in an update of the AMR, Characterize Eruptive Processes at 
Yucca Mountain, Nevada [ANL-MGR-GS-000002]. Completion of this report 
should provide the NRC with the information needed to close this open item. 
A.1.2 Related Key Technical Issue Agreements 
None. 
A.2 RELEVANCE TO REPOSITORY PERFORMANCE 
Tephra (volcanic fallout) deposits represent a potential dispersal mechanism for small particles 
of radioactive material that could be produced if an eruption through the repository disrupted 
waste packages. Volcanism during the postclosure period is unlikely, but in the types of basaltic 
eruptions considered to be representative of possible future volcanoes in the Yucca Mountain 
region, small particles are produced during moderately energetic explosions at the vent 
(Strombolian eruptions) ranging up to more violent and sustained jets of particles and gas from 
the vent, which can support an eruption column up to several kilometers in height (violent 
Strombolian). Analyses based on the geologic evidence of regional volcanism over the past 
5 m.y. indicate that a small volume, basaltic eruption exhibiting Strombolian to violent 
Strombolian activity is the form of possible volcanism in the Yucca Mountain region that is most 
credible within the postclosure performance period of 10,000 years. 
November 2003 A-2 No. 13: Volcanic Events
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The dispersal of ash and lapilli, mostly by winds active during eruption, serves as a first-order 
proxy for waste particle dispersal. The volume of tephra from a future Yucca Mountain region 
volcano is important to modeling of the downwind dispersal of ash + waste and in calculating the 
potential exposure to a reasonably maximally exposed individual at a specified distance from the 
eruption site. Tephra volume is difficult to determine because most basaltic volcanoes in the 
Yucca Mountain region are eroded remnants of former scoria cones and their associated tephra 
sheets and provide only a partial picture of eruption history. The exception is the Lathrop Wells 
volcano. The approximately 80,000-year-old Lathrop Wells Cone and tephra sheet are the 
youngest and best preserved in the Yucca Mountain region and currently serve as the principal 
basis for evaluating future eruption scenarios. 
NRC concerns about the range of tephra volumes and the representativeness of that range are 
related to the use of ASHPLUME V1.4LV-dll for total system performance assessment for the 
Viability Assessment and the total system performance assessment for the site recommendation. 
That version of ASHPLUME used erupted volume as a proxy for eruptive power to calculate 
plume height. Hence, uncertainties in erupted volume could affect plume height estimates, 
ash-dispersal patterns, and the resulting dose to the reasonably maximally exposed individual. 
A.3 RESPONSE 
The use of ash volume as a proxy for eruptive power can be traced back to total system 
performance assessment for the Viability Assessment, when the use of ASHPLUME V1.4LV-dll 
prompted the NRC to require additional information on the calculation of ash volumes and the 
basis upon which information from analogs had been incorporated into estimates of the range of 
erupted volume. Analysis of the volcanic direct release scenario in the total system performance 
assessment for the site recommendation used a version of the ASHPLUME code (ASHPLUME 
V1.4LV-dll, STN: 10022-1.4LV-dll-00) that used erupted volume as a proxy for eruptive power 
to calculate eruption column height. However, for TSPA-LA, ASHPLUME V2.0 (ASHPLUME 
V2.0, STN: 10022-2.0-00) will be used. ASHPLUME V2.0 is consistent with the original 
formulation of the ASHPLUME code (Jarzemba et al. 1997) and uses eruptive power to calculate 
column height. Results of preliminary studies indicate that the use of ASHPLUME V2.0 will 
result in greater column heights than those that were produced by ASHPLUME V1.4LV-dll. 
The basis for use of ASHPLUME V2.0 and descriptions of model inputs and outputs have been 
documented in Atmospheric Dispersal and Deposition of Tephra from a Potential Volcanic 
Eruption at Yucca Mountain, Nevada (BSC 2003a). 
The information need IA 2.03 AIN-1 incorporates three elements: (a) provide a technical basis 
for demonstrating how tephra volumes have been calculated based on eroded deposits in the 
Yucca Mountain region, (b) provide a technical basis for the inclusion of analog information, and 
(c) demonstrate how buried deposits, such as the flows from Little Cones, have been 
incorporated into the calculation of tephra volume. 
Provide a Technical Basis for Demonstrating How Tephra Volumes Have Been Calculated 
Based on Eroded Deposits in the Yucca Mountain RegionTephra volumes for eroded cones 
in Crater Flat have been estimated based on information from analog systems and by comparing 
the apparent levels of erosion at the analog sites with levels observed at the Crater Flat cones. 
Based on the comparisons, the original tephra volumes have been estimated at five times the 
November 2003 A-3 No. 13: Volcanic Events
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cone volume (Perry et al. 1998) and are listed in Characterize Eruptive Processes at Yucca 
Mountain, Nevada (BSC 2003b, Section 6.3.3.4.2). 
Provide a Technical Basis for the Inclusion of Analog InformationThe technical basis for 
inclusion of volume information from analog volcanoes is described in Characterize Eruptive 
Processes at Yucca Mountain, Nevada (BSC 2003b, Section 6.3.3.4.2). A set of analog 
volcanoes was established based on the results of searches of the technical literature. Then for 
erupted volume comparisons, the set was reviewed and reduced based on considerations of 
similarity of tectonic setting to that of the Lathrop Wells Cone (BSC 2003b, Section 6.3.3.4.2). 
The comparisons suggested that the smaller scoria cones are most appropriate to characterize 
disruptive volcanic events at Yucca Mountain. The technical basis for the selection of Lathrop 
Wells as an analog for a future eruption at the repository is described in Characterize Eruptive 
Processes at Yucca Mountain, Nevada (BSC 2003b, Sections 6.3.3 and 6.4). The choice of 
Lathrop Wells Cone as an analog for a potential disruptive volcano at the repository is based on 
geologic setting, its proximity to the repository, its composition, and its youth (approximately 
80,000 years). 
Demonstrate How Buried Deposits, Such as the Flows From Little Cones, Have Been 
Incorporated into the Calculation of Tephra VolumeLava volume is not included in DOE 
estimates of tephra volume. Lava volume is estimated separately from tephra volume 
(e.g., BSC 2003b, Table 34) because lava is considered to be a separate eruptive phase and to 
reflect different eruption parameters than tephra deposits. A sensitivity study that examined the 
effect of including the lava from Little Cones in the tephra volume estimate showed that the 
volume increased from 0.23 km3 to 0.26 km3 (Brocoum 1997, Enclosure 1, page 2). The 
13 percent increase was considered not significant. 
While eruptive volume is still important for documenting the diminishing volumes of basaltic 
eruptions over the past 5 m.y. in the Yucca Mountain region, it becomes irrelevant to the 
calculation of column height because ASHPLUME V2.0 will be used for TSPA-LA. To support 
the use of ASHPLUME V2.0, eruptive power for several historical eruptions has been calculated 
from estimations of time-averaged mass fluxes, heat capacities, and temperatures, and 
documentation has been provided in the update of Characterize Eruptive Processes at Yucca 
Mountain, Nevada (BSC 2003b). 
The information in this report is responsive to agreement IA 2.03 and the associated additional 
information needed (AIN-1). The report contains the information that the DOE considers 
necessary for NRC review for closure of this agreement. 
A.4 BASIS FOR THE RESPONSE 
During the development of information for the model report describing the ASHPLUME 
V1.4LV-dll code, the use of eruptive volume as a proxy for eruptive power was determined to be 
inappropriate. As a result, ASHPLUME V2.0 will be used for TSPA-LA analysis of the 
volcanism direct-release scenario. ASHPLUME V2.0 is consistent with ASHPLUME V1.0 code 
(Jarzemba et al. 1997) because it uses parameters for eruptive power to compute column height. 
Scoping calculations have shown that ASHPLUME V2.0 produces greater column heights than 
those obtained for the total system performance assessment for the site recommendation using 
November 2003 A-4 No. 13: Volcanic Events
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ASHPLUME V1.4LV-dll. Validation of the ASHPLUME model and its enumeration in 
ASHPLUME V2.0 have been documented in a new model report, Atmospheric Dispersal and 
Deposition of Tephra from a Potential Volcanic Eruption at Yucca Mountain, Nevada 
(BSC 2003a). The model report documents the qualification and validation of the ASHPLUME 
code from V1.4LV-dll to V2.0. 
Documentation of the erupted volumes of the scoria cone, lava flows, and tephra estimated for 
the Lathrop Wells Cone has been included in the revision of Characterize Eruptive Processes at 
Yucca Mountain, Nevada (BSC 2003b). The documentation also discusses the eruptive history 
of the volcano, deduced from analysis of the tephra deposits. Based on review of 
well-documented historical and older volcanoes, the report discusses the relevance of the 
Lathrop Wells Cone eruptive history to a potential volcanic eruption at the repository. The 
volumes of older, eroded volcanoes in Crater Flat (Perry et al. 1998) have not been updated 
because of the extensive erosion of the scoria cones, and erosion or burial of their respective 
tephra sheets; effort was instead focused upon the Lathrop Wells Cone due to the better 
preservation of the volcanic products there. 
Documentation of the total system performance assessment sensitivity to uncertainties in erupted 
volume was provided in the Total System Performance Assessment for the Site Recommendation 
(CRWMS M&O 2000b, Section 5.2.9.5). Because TSPA-LA analyses related to the 
direct-release (eruption) scenario will use ASHPLUME V2.0 rather than ASHPLUME 
V1.4LV-dll, it is no longer necessary to document the lack of sensitivity of repository 
performance to uncertainties in the range of tephra volumes used during simulations. It is also 
not necessary to justify the use of erupted volume as a proxy for eruptive power in the 
computation of column height. Hence, these analyses will not be included in the license 
application documentation. 
The technical basis for this response is the decision to use ASHPLUME V2.0-dll, which uses 
eruptive power (rather than erupted ash volume) to calculate eruptive column height. Because 
the range of calculated column heights will now include the higher altitudes that the NRC 
considers are possible in violent Strombolian phases of a volcanic eruption, the issues raised in 
the information need should be satisfied with the documentation provided in the new model 
report Atmospheric Dispersal and Deposition of Tephra from a Potential Volcanic Eruption at 
Yucca Mountain, Nevada (BSC 2003a). The ash-dispersal pattern resulting from advection and 
winds acting on the ash column will reflect the higher elevations expected with this approach and 
provide a better technical basis for evaluation of the potential dose to the reasonably maximally 
exposed individual. 
November 2003 A-5 No. 13: Volcanic Events
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A.5 REFERENCES 
A.5.1 Documents Cited 
Brocoum, S.J. 1997. Evaluation of Data Provided at U.S. Department of Energy (DOE) and 
U.S. Nuclear Regulatory Commission (NRC) Igneous Activity Technical Exchange, February 
25-26, 1997. Letter from S.J. Brocoum (DOE/YMSCO) to J.T. Greeves (NRC), June 4, 1997, 
with enclosure. ACC: MOL.19970722.0276; MOL.19970722.0277; MOL.19970722.0278. 
BSC (Bechtel SAIC Company) 2001a. Igneous Consequence Modeling for the TSPA-SR. ANLWIS-
MD-000017 REV 00 ICN 02. Las Vegas, Nevada: Bechtel SAIC Company. ACC: 
MOL.20011107.0005. 
BSC 2001b. Characterize Eruptive Processes at Yucca Mountain, Nevada. ANL-MGR-GS- 
000002 REV 00 ICN 01. Las Vegas, Nevada: Bechtel SAIC Company. ACC: 
MOL.20020327.0498. 
BSC 2003a. Atmospheric Dispersal and Deposition of Tephra from a Potential Volcanic 
Eruption at Yucca Mountain, Nevada. MDL-MGR-GS-000002 REV 00D. Las Vegas, Nevada: 
Bechtel SAIC Company. ACC: MOL.20030922.0197. 
BSC 2003b. Characterize Eruptive Processes at Yucca Mountain, Nevada. ANL-MGR-GS- 
000002 REV 01C. Las Vegas, Nevada: Bechtel SAIC Company. ACC: MOL.20030711.0107. 
CRWMS M&O (Civilian Radioactive Waste Management System Management and Operating 
Contractor) 2000a. Characterize Framework for Igneous Activity at Yucca Mountain, Nevada. 
ANL-MGR-GS-000001 REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.20001221.0001. 
CRWMS M&O 2000b. Total System Performance Assessment for the Site Recommendation. 
TDR-WIS-PA-000001 REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.20001220.0045. 
Jarzemba, M.S.; LaPlante, P.A.; and Poor, K.J. 1997. ASHPLUME Version 1.0A Code for 
Contaminated Ash Dispersal and Deposition, Technical Description and User's Guide. 
CNWRA 97-004, Rev. 1. San Antonio, Texas: Center for Nuclear Waste Regulatory Analyses. 
ACC: MOL.20010727.0162. 
Perry, F.V.; Crowe, B.M.; Valentine, G.A.; and Bowker, L.M., eds. 1998. Volcanism Studies: 
Final Report for the Yucca Mountain Project. LA-13478. Los Alamos, New Mexico: 
Los Alamos National Laboratory. TIC: 247225. 
Reamer, C.W. 2001. U.S. Nuclear Regulatory Commission/U.S. Department of Energy 
Technical Exchange and Management Meeting on Igneous Activity (June 21 - 22, 2001). Letter 
from C.W. Reamer (NRC) to S. Brocoum (DOE/YMSCO), June 29, 2001, with enclosure. 
ACC: MOL.20010918.0001. 
November 2003 A-6 No. 13: Volcanic Events
Revision 2 
Reamer, C.W. and Williams, D.R. 2000. Summary Highlights of NRC/DOE Technical 
Exchange and Management Meeting on Igneous Activity. Meeting held August 29-31, 2000, 
Las Vegas, Nevada, with attachments. Washington, D.C.: U.S. Nuclear Regulatory 
Commission. ACC: MOL.20001101.0105 through MOL.20001101.0128. 
Schlueter, J.R. 2002. Igneous Activity Agreement 2.03. Letter from J.R. Schlueter (NRC) to 
J.D. Ziegler (DOE/YMSCO), November 12, 2002, with enclosure: NRC Review of DOE 
Documents Pertaining to Igneous Activity Key Technical Issue Agreement Item 2.03. 
ACC: MOL.20030922.0139. 
Ziegler, J.D. 2002. Transmittal of Report Addressing Key Technical Issue (KTI) Agreement 
Item Igneous Activity (IA) 2.03. Letter from J.D. Ziegler (DOE/YMSCO) to J.R. Schlueter 
(NRC), July 30, 2002, with enclosure (Range of Tephra Volumes), OL&RC:TCG-1325. 
ACC: MOL.20021010.0006. 
A.5.2 Software Codes 
ASHPLUME V1.4LV-dll. STN: 10022-1.4LV-dll-00. 
ASHPLUME V2.0. STN: 10022-2.0-00. 
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A-8 No. 13: Volcanic Events 
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November 2003
WIND SPEEDS FOR VARIOUS HEIGHTS OF ERUPTIVE COLUMNS 
(RESPONSE TO IA 2.09 AIN-1) 
No. 13: Volcanic Events 
APPENDIX B 
Revision 2 
November 2003
Revision 2 
Note Regarding the Status of Supporting Technical Information 
This document was prepared using the most current information available at the time of its development. This 
Technical Basis Document and its appendices providing Key Technical Issue Agreement responses that were 
prepared using preliminary or draft information reflect the status of the Yucca Mountain Projects scientific 
and design bases at the time of submittal. In some cases this involved the use of draft Analysis and Model 
Reports (AMRs) and other draft references whose contents may change with time. Information that evolves 
through subsequent revisions of the AMRs and other references will be reflected in the License Application as 
the approved analyses of record at the time of its submittal. Consequently, the DOE will not routinely update 
either this Technical Basis Document or its Key Technical Issue Agreement appendices to reflect changes in 
the supporting references prior to submittal of the License Application. 
No. 13: Volcanic Events November 2003
Revision 2 
APPENDIX B 
WIND SPEEDS FOR VARIOUS HEIGHTS OF ERUPTIVE COLUMNS 
(RESPONSE TO IA 2.09 AIN-1) 
This appendix provides a response to Key Technical Issue (KTI) agreement Igneous Activity 
(IA) 2.09 additional information needed (AIN)-1. This KTI agreement relates to the wind speeds 
selected for analysis of the dispersal of various heights of volcanic eruptive columns. 
B.1 KEY TECHNICAL ISSUE AGREEMENT 
B.1.1 IA 2.09 AIN-1 
Agreement IA 2.09 was reached during the U.S. Nuclear Regulatory Commission (NRC)/U.S. 
Department of Energy (DOE) Technical Exchange and Management Meeting on IA, held 
August 29 to 31, 2000, in Las Vegas, Nevada (Reamer and Williams 2000). This agreement was 
later revised during the NRC/DOE technical exchange and management meeting on igneous 
activity held June 21 to 22, 2001 (Reamer 2001). 
For the total system performance assessment for site recommendation (TSPA-SR), the DOE used 
wind speed data described in Igneous Consequence Modeling for the TSPA-SR (BSC 2001a, 
Section 5.1.1). The NRC was concerned that modeling of a volcanic eruption through the 
repository had underestimated eruptive column heights. In general, wind speed increases with 
altitude, and underestimating column heights could lead to selection of wind speed data that is 
inappropriately biased toward lower wind speeds, which result in less dispersal of contaminated 
ash. Use of low wind speeds in the direct release scenario (volcanic eruption through Yucca 
Mountain) could underestimate the dose to the reasonably maximally exposed individual 
(RMEI). The result of this series of concerns was KTI agreement IA 2.09. 
The wording of the revised agreement is as follows: 
IA 2.09
Use the appropriate wind speeds for the various heights of eruption columns being 
modeled. DOE agreed and will evaluate the wind speed data appropriate for the 
height of the eruptive columns being modeled. This will be documented in a 
calculation document. This will be available to the NRC in FY 2002. 
The agreement was addressed in a previous report (Ziegler 2002). The report was based on 
results of analyses of the sensitivity of performance to uncertainties in wind direction and wind 
speed in the TSPA-SR (CRWMS M&O 2000, Sections 5.2.9.2 and 5.2.9.3). 
NRC concerns with the use of wind speed data from altitudes that are less than those associated 
with columns from a violent Strombolian eruption resulted in the request for specific additional 
information on this subject (Schlueter 2003). This resulted in IA 2.09 AIN-1. 
November 2003 B-1 No. 13: Volcanic Events
Revision 2 
The wording of the additional information needed is as follows: 
IA 2.09 AIN-1 
The DOE needs to demonstrate that the wind speed used in performance 
assessment is appropriate for the height of the eruption column. The DOE should 
demonstrate that neglecting the effects of higher velocity winds expressed during 
particle rise and lateral advection does not underestimate risk. If the DOE 
chooses to convolve wind-speed data into a single distribution for use in 
performance assessment, the DOE should document how appropriate weight was 
given in the distribution to upper altitude winds representative of lateral advection 
processes typically observed in volcanic eruption plumes. The DOE wind speed 
parameter distribution also should reflect the characteristics of the parameter 
distribution used for eruption column height, to avoid potential bias towards lower 
altitude wind speeds. As this information will be used in the TSPA-LA, the DOE 
needs to provide this information in a format that meets the requirements of the 
DOE quality assurance program. 
B.1.2 Related Key Technical Issue Agreements 
None. 
B.2 RELEVANCE TO REPOSITORY PERFORMANCE 
For the eruptive scenario at Yucca Mountain, an eruption column containing ash and some 
entrained waste particles may extend up to several kilometers above the growing volcanic cone. 
For the ASHPLUME model, the problem is one of modeling the distribution of ash/waste 
particles in the eruption column as it is subjected to a variable wind field and as the particles 
settle gravitationally onto the ground surface. For TSPA-SR, column height for each realization 
in ASHPLUME V1.4LV-dll (STN: 10022-1.4LV-dll-00) was calculated using erupted ash 
volume as a proxy for eruptive power (BSC 2001a, Section 6.1.2.1.8). In addition, column 
height was calibrated against observed eruptions whose column heights and erupted volumes had 
been measured (BSC 2001a). The NRC noted that column heights obtained in this manner did 
not extend to the higher column heights that the NRC considers reasonable (greater than 5 km). 
Lower column heights are subject to lower wind speeds (as measured with the Quiring 1968 
data), resulting in less dispersal of ash/waste particles, thinner deposition of ash/waste with 
distance, and a potential underestimation of dose to the RMEI. 
B.3 RESPONSE 
Agreement IA 2.09 was addressed in a report (Ziegler 2002). The report was based on results of 
analyses of the sensitivity of performance to uncertainties in wind direction and wind speed in 
the TSPA-SR (CRWMS M&O 2000, Sections 5.2.9.2 and 5.2.9.3). The results of the sensitivity 
studies showed that when wind directions were sampled, rather than specifying a constant wind 
blowing toward the RMEI the dose was decreased by about a factor of 5 (CRWMS M&O 2000, 
Section 5.2.9.2). Results also showed that when higher wind speeds were used, the dose was 
increased by about a factor of 2 (CRWMS M&O 2000, Section 5.2.9.3). The report also 
described the results of a separate analysis that used wind speed data from the Desert Rock 
November 2003 B-2 No. 13: Volcanic Events
Revision 2 
airstrip (NOAA n.d.). These data extend to altitudes much higher than those expected for a 
future basaltic eruption cloud in the Yucca Mountain region (BSC 2001b; BSC 2001c, 
Section 3.3.1.2.1). The analysis that used the data assumed that the wind blew constantly toward 
the RMEI. Analysis results showed that the probability-weighted mean annual dose increased by 
a factor of approximately 2 compared to TSPA-SR values. 
For TSPA for the license application (TSPA-LA), two fundamental changes in the DOE 
approach to modeling eruption columns have been made. These changes better reflect conditions 
that might be associated with an eruption that includes an ash column with a height in the range 
of 4-plus kilometers. First, eruption columns from a possible future volcano will be modeled 
using ASHPLUME V2.0 (STN: 1022-2.0-00), which uses eruptive power and event duration to 
calculate column height, mass flow rate, and total eruptive ash mass. This approach results in 
higher eruption columns (up to approximately 13 km) than those that result from calculations 
using ASHPLUME V.1.4LV dll, and captures uncertainty associated with the eruptive power 
parameter. Second, the modeling will use wind data (measured at the Desert Rock airstrip) 
(NOAA n.d.) that encompasses all eruptive column heights expected in a basaltic eruption at 
Yucca Mountain (BSC 2003, Table IV-7). The technical documentation for column height and 
wind speed and direction modeling is found in the new model report Atmospheric Dispersal and 
Deposition of Tephra from a Potential Volcanic Eruption at Yucca Mountain, Nevada (BSC 
2003), which has been prepared under the requirements of the DOE quality assurance program. 
The use of these approaches in TSPA-LA and in supporting documentation will provide more 
realistic modeling of ash column height, ash/waste dispersal by winds, advection, and 
gravitational settling, and the ability to calculate dose at appropriate distances from a volcano. 
The information in this report is responsive to agreement IA 2.09 and the associated additional 
information needed (AIN-1). The report contains the information that the DOE considers 
necessary for NRC review for closure of this agreement. 
B.4 BASIS FOR THE RESPONSE 
The DOE has developed additional information related to ASHPLUME parameters and has 
determined that ASHPLUME V. 2.0 is more appropriate for modeling atmospheric dispersal of 
contaminated ash than is ASHPLUME V.1.4LV-dll. 
For the Site Recommendation, the dose effects of using higher wind speeds were examined. One 
analysis documented in TSPA-SR (CRWMS M&O 2000, Section 5.2.9.3) described the effects 
of using the 95th percentile wind speed rather than the mean wind speed. Another analysis 
documented in FY01 Supplemental Science and Performance Analyses, Volume 2: Performance 
Analyses (BSC 2001c, Section 3.3.1.2.1) described the effects of using wind speed data collected 
at higher altitudes above the Desert Rock airstrip. The higher altitudes were consistent with the 
upper range of column heights proposed as possible for eruptions at Yucca Mountain. The 
analysis, documented in FY01 Supplemental Science and Performance Analyses, Volume 2: 
Performance Analyses (BSC 2001c, Section 3.3.1.2.1), showed that use of the Desert Rock data 
increases probability-weighted mean annual doses by a factor of approximately 2 compared to 
the TSPA-SR values. 
November 2003 B-3 No. 13: Volcanic Events
Revision 2 
The TSPA-LA will use comprehensive wind data from the Desert Rock airstrip that are 
consistent with the range of potential eruptive column heights (1 km to 13 km). For each 
realization of the ASHPLUME model, the value selected for wind speed will be appropriate for 
the column height selected for that realization. The distribution characteristics for wind speeds 
are described in the new model report Atmospheric Dispersal and Deposition of Tephra from a 
Potential Volcanic Eruption at Yucca Mountain, Nevada (BSC 2003). The documentation will 
describe the basis for the selection of ASHPLUME v. 2.0, consideration of alternative models, 
and the parameters that are used as inputs to the code. The model report was developed using 
the appropriate provisions of the DOE quality assurance program. Hence, NRC concerns about 
appropriate use of wind speed data consistent with column heights have been addressed. 
B.5 REFERENCES 
B.5.1 Documents Cited 
BSC (Bechtel SAIC Company) 2001a. Igneous Consequence Modeling for the TSPA-SR. 
ANL-WIS-MD-000017 REV 00 ICN 02. Las Vegas, Nevada: Bechtel SAIC Company. 
ACC: MOL.20011107.0005. 
BSC 2001b. FY01 Supplemental Science and Performance Analyses, Volume 1: Scientific 
Bases and Analyses. TDR-MGR-MD-000007 REV 00. Las Vegas, Nevada: Bechtel SAIC 
Company. ACC: MOL.20010712.0062. 
BSC 2001c. FY01 Supplemental Science and Performance Analyses, Volume 2: Performance 
Analyses. TDR-MGR-PA-000001 REV 00. Las Vegas, Nevada: Bechtel SAIC Company. 
ACC: MOL.20010724.0110. 
BSC 2003. Atmospheric Dispersal and Deposition of Tephra from a Potential Volcanic 
Eruption at Yucca Mountain, Nevada. MDL-MGR-GS-000002 REV 00D. Las Vegas, Nevada: 
Bechtel SAIC Company. ACC: MOL.20030922.0197. 
CRWMS M&O (Civilian Radioactive Waste Management System Management and Operating 
Contractor) 2000. Total System Performance Assessment for the Site Recommendation. 
TDR-WIS-PA-000001 REV 00 ICN 01. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.20001220.0045. 
NOAA (National Oceanic and Atmospheric Administration) n.d. Upper Air Data: Desert Rock, 
Nevada, 1978-1995. Reno, Nevada: National Oceanic and Atmospheric Administration, 
Western Regional Climate Center. TIC: 249335. 
Quiring, R.F. 1968. Climatological Data Nevada Test Site and Nuclear Rocket Development 
Station. ESSA Research Laboratories Technical Memorandum - ARL 7. Las Vegas, Nevada: 
U.S. Department of Commerce, Environmental Science Services Administration Research 
Laboratories. ACC: NNA.19870406.0047. 
November 2003 B-4 No. 13: Volcanic Events
Revision 2 
Reamer, C.W. 2001. U.S. Nuclear Regulatory Commission/U.S. Department of Energy 
Technical Exchange and Management Meeting on Igneous Activity (June 21 to 22, 2001). 
Letter from C.W. Reamer (NRC) to S. Brocoum (DOE/YMSCO), June 29, 2001, with enclosure. 
ACC: MOL.20010918.0001. 
Reamer, C.W. and Williams, D.R. 2000. Summary Highlights of NRC/DOE Technical 
Exchange and Management Meeting on Igneous Activity. Meeting held August 29 to 31, 2000, 
Las Vegas, Nevada, with attachments. Washington, D.C.: U.S. Nuclear Regulatory 
Commission. ACC: MOL.20001101.0105 through MOL.20001101.0128. 
Schlueter, J.R. 2003. Igneous Activity Agreement 2.09, Additional Information Needed. Letter 
from J.R. Schlueter to J.D. Ziegler, February 13, 2003. Washington, D.C., U.S. Nuclear 
Regulatory Commission, 2 pages with 4-page enclosure: NRC Review of DOE Letter Pertaining 
to Igneous Activity Key Technical Issue Agreement Item 2.09. BSC Correspondence 
Log #0319036515. ACC: MOL.20030918.0112. 
Ziegler, J.D. 2002. Transmittal of Report Addressing Igneous Activity (IA) Key Technical Issue 
(KTI) Agreement Items 2.02 and 2.09. Letter from J.D. Ziegler, DOE to J.R. Schlueter, NRC. 
Las Vegas, Nevada, U.S. Department of Energy, June 27, 2002, 4 pages with 2 enclosures: 
(1) Particle Size Sensitivity and (2) Wind Speed Data Appropriate for the Height of the Eruptive 
Columns Being Modeled. BSC Correspondence Log 0628023159. 
ACC: MOL.20020822.0149. 
B.5.2 Software Codes 
ASHPLUME V1.4lV-dll. STN: 10022-1.4lV-dll-00. 
ASHPLUME V2.0. STN: 10022-2.0-00. 
November 2003 B-5 No. 13: Volcanic Events
INTENTIONALLY LEFT BLANK 
B-6 No. 13: Volcanic Events 
Revision 2 
November 2003
APPENDIX C 
WASTE PACKAGE RESPONSE TO STRESSES FROM THERMAL AND 
MECHANICAL EFFECTS ASSOCIATED WITH EXPOSURE TO BASALTIC MAGMA 
(RESPONSE TO IA 2.19) 
No. 13: Volcanic Events 
Revision 2 
November 2003
Revision 2 
Note Regarding the Status of Supporting Technical Information 
This document was prepared using the most current information available at the time of its development. This 
Technical Basis Document and its appendices providing Key Technical Issue Agreement responses that were 
prepared using preliminary or draft information reflect the status of the Yucca Mountain Projects scientific 
and design bases at the time of submittal. In some cases this involved the use of draft Analysis and Model 
Reports (AMRs) and other draft references whose contents may change with time. Information that evolves 
through subsequent revisions of the AMRs and other references will be reflected in the License Application as 
the approved analyses of record at the time of License Application submittal. Consequently, the Project will 
not routinely update either this Technical Basis Document or its Key Technical Issue Agreement appendices to 
reflect changes in the supporting references prior to submittal of the License Application. 
No. 13: Volcanic Events November 2003
Revision 2 
APPENDIX C 
WASTE PACKAGE RESPONSE TO STRESSES FROM THERMAL AND 
MECHANICAL EFFECTS ASSOCIATED WITH EXPOSURE TO BASALTIC MAGMA 
(RESPONSE TO IA 2.19) 
This appendix provides a response to Key Technical Issue (KTI) agreement Igneous Activity 
(IA) 2.19. This KTI agreement relates to the evaluation of waste package response to stresses 
from thermal and mechanical effects associated with exposure to basaltic magma. 
C.1 KEY TECHNICAL ISSUE AGREEMENT 
C.1.1 IA 2.19 
Agreement IA 2.19 was reached during the U.S. Nuclear Regulatory Commission (NRC)/U.S. 
Department of Energy (DOE) Technical Exchange and Management Meeting on Igneous 
Activity held September 5, 2001, in Las Vegas, Nevada (Reamer 2001). 
The wording of the agreement is as follows: 
IA 2.19
DOE will evaluate waste package response to stresses from thermal and 
mechanical effects associated with exposure to basaltic magma, considering the 
results of evaluations attendant to IA Agreement 2.18. As currently planned, the 
evaluation, if implemented, would include (1) appropriate at-condition strength 
properties and magma flow paths, for duration of an igneous event; and (2) aging 
effects on materials strength properties when exposed to basaltic magmatic 
conditions for the duration of an igneous event, which will include the potential 
effects of subsequent seismically induced stresses on substantially intact waste 
packages. DOE will also evaluate the response of Zone 3 waste packages, or 
waste packages covered by backfill or rockfall, if exposed to magmatic gasses at 
conditions appropriate for an igneous event, considering the results of evaluation 
attendant to IA Agreement 2.18. If models take credit for engineered barriers 
providing delay in radionuclide release, DOE will evaluate barrier performance 
for the duration of the hypothetical igneous event. The results of this 
investigation would be documented in an update to the technical product Waste 
Package Behavior in Magma CAL-EBS-ME-000002, which would be available 
by the end of FY 2003, or other appropriate technical document. 
For total system performance assessment for the site recommendation (TSPA-SR), modeling of 
magma-waste package interactions was based on varying levels of damage that defined three 
damage zones in the repository. Waste packages in the path of an ascending dike (in Zone 1) 
were assumed to be damaged to the extent that they would provide no further protection for 
waste forms. Damage to waste packages in intersected drifts, but not in the path of the dike 
(Zone 2; three waste packages on either side of the point of intersection), was assumed limited to 
end-cap failure by fissuring. The final damage zone, Zone 3, was defined as repository areas 
proximal to Zone 2 and containing waste packages exposed to magmatic products but not 
November 2003 C-1 No. 13: Volcanic Events Revision 2 
directly exposed to magma. Models relied on assumptions about the durability of the waste 
package when exposed to magma or a magmatic environment. 
Analyses by the NRC indicated that intersection of the repository by an ascending basaltic dike 
could result in magma flow through the repository that would be sufficient to involve the entire 
inventory of waste. Other analyses (e.g., Reamer 2001, p. 5) indicated that insufficient technical 
information existed to constrain the extent of damage to waste packages exposed to thermal and 
gas effects from an intrusion. To address concerns associated with the effects on the waste 
package from interactions with magma and magmatic products, DOE agreed to evaluate the 
waste package response to stresses from thermal and mechanical effects associated with 
exposure to basaltic magma (Reamer 2001, p. 4). 
Waste package and waste form effects for TSPA for the license application (TSPA-LA) will be 
evaluated in the waste package and waste form impacts submodel of the TSPA-LA model. The 
effects analysis is based on the definition of two damage zones. Zone 1 includes all waste 
packages in drifts intersected by a dike, regardless of location relative to the ascent path of the 
dike. Zone 2 includes waste packages in drifts not directly intersected by a dike but potentially 
exposed to magmatic gases and thermal effects. Documentation of the submodel is provided in 
Igneous Intrusion Impacts on Waste Packages and Waste Forms (BSC 2003a). 
C.1.2 Related Key Technical Issue Agreements 
There are two KTI agreements related to IA 2.19. Agreements IA 2.18 and IA 2.20, 
respectively, are to provide inputs for the analysis of magma-waste package interactions and 
continue the analysis of effects on waste forms of exposure to magma and magmatic 
components. Agreement IA 2.18 is to ensure that information was obtained about the effects of 
repository structures on dike propagation and magma flow, exsolution of volatiles, and cooling 
and solidification of magma. These results could be incorporated in the analysis of effects on 
components of the engineered barrier system. Agreement IA 2.20 is to carry the analysis 
forward to the waste form and identify magma-waste form interaction effects that could increase 
the incorporation of waste in magma and potentially alter the waste chemistry in ways that could 
increase the mobility of the waste. 
C.2 RELEVANCE TO REPOSITORY PERFORMANCE 
For the igneous intrusiongroundwater release scenario, the risk of radiological dose is directly 
related to the number of waste packages contacted by the intrusion. The TSPA-LA approach to 
implementing the models for waste package and waste form response during igneous intrusion is 
based on identification of damage zones. Zone 1, which includes all emplacement drifts intruded 
by the basalt dike and Zone 2, which includes all other emplacement drifts in the repository that 
are not in Zone 1. Igneous Intrusion Impacts on Waste Packages and Waste Forms (BSC 2003a) 
documents the following model assessments: 
 Zone 1Impacts of magma intrusion on the drip shields, waste packages, and cladding 
directly contacted by magma and the fate of waste forms. Impacts of intrusion on 
Zone 1 in-drift thermal and geochemical environments, including seepage 
hydrochemistry. 
November 2003 C-2 No. 13: Volcanic Events Revision 2 
 Zone 2Impacts of conducted magmatic heat and diffused magmatic gases on the drip 
shields, waste packages, cladding, and waste packages adjacent to the intruded drifts 
Section 5.3 describes a variety of literature studies regarding the potential for enhanced corrosion 
in magmatic environments in Igneous Intrusion Impacts on Waste Packages and Waste Forms 
(BSC 2003a). These studies indicate that high temperatures and corrosive geochemical 
environments, which could accompany dike intrusion, can measurably increase the corrosion 
rates of steel and other metal alloys. 
Although none of the analyses indicate that the metallic engineered barriers would be destroyed 
or fail instantaneously, it appears that the effects would be rapid compared to the 10,000-year 
regulatory period for the repository. Therefore, because of the uncertainty associated with 
analyzing the effects of enhanced corrosion rates, performance assessment analyses for Yucca 
Mountain conservatively assume that any engineered materials contacted by magmas (e.g., drip 
shields, waste packages and cladding) during an intrusion will no longer provide any waste 
isolation function. 
For waste packages in drifts that are not directly intersected by a dike (Zone 2), model results 
indicate that significant thermal and volatile effects do not extend to the Zone 2 drifts. The 
model results indicate that thermal and chemical conditions that would adversely affect Zone 2 
waste packages do not develop. Hence, for TSPA-LA, waste package damage is limited by the 
analysis to the number of waste packages in Zone 1. 
C.3 RESPONSE 
The current model approach to be implemented for TSPA-LA features significant conservatisms 
in terms of volcanic process parameters associated with magma flow in drifts and effects on 
engineered barrier system components, specifically waste packages in drifts that are intersected 
by a dike. Alternative approaches are being reviewed, and the alternatives would feature less 
conservatism than the approach being implemented for TSPA-LA. 
Igneous Intrusion Impacts on Waste Packages and Waste Forms (BSC 2003a) defines two 
damage zones for the igneous activity scenarios. Zone 1 is characterized by intersection of the 
drifts by an ascending basaltic dike accompanied by waste package damage to the extent that 
waste packages in Zone 1 provide no further protection for the waste (BSC 2003a, Section 6.3). 
Zone 2 includes drifts not directly intersected by a dike but are adjacent to the intersected drifts 
(Zone 1) that waste packages and other engineered barrier system components could be exposed 
to heat and gases migrating from Zone 1. The TSPA-LA assumes that waste packages in Zone 1 
offer no protection from disruption by and interaction with the magma, and that all waste 
material is available for chemical interaction, between the fuel and metal/alloys of damaged 
waste canisters/assemblies and claddings, and transport. Simulations of heat conduction indicate 
that the maximum temperature rise in a drift that is not intersected by a dike, but that is adjacent 
to an intersected drift (Zone 2), is less than 10C (simulated maximum magma temperatures in 
an intersected drift was 1,150C) (BSC 2003a, Section 6.5.2.1.1). The rock provides an effective 
barrier to the thermal effects associated with the intrusion. The spatial and temporal heat 
conduction simulation results indicate that waste packages in Zone 2 emplacement drifts would 
November 2003 C-3 No. 13: Volcanic Events Revision 2 
not be affected by the heat conducting from the magma intruded into Zone 1 emplacement drifts 
(BSC 2003a, Section 6.5.2.1.1). 
Results of magma gas-flow simulations show that the gas-flow velocity decreases to near zero in 
about a year. The gas front in the wall rock (e.g., pillars) stops at about 3.6 m from the drift wall, 
and the gas front in the assumed backfill used in main drifts and turnouts of the repository stops 
at about 1.4 m into the backfill. Simulations of gas transport caused by diffusion, however, show 
that concentrations of gases entering Zone 2 drifts would be low (a maximum of 100 moles of 
gas) and would decrease after about 2 years. The concentrations of corrosive gas species in the 
volatile components could be expected to be significantly less than the concentration of water in 
the volatiles. These results indicate that waste packages in Zone 2 emplacement drifts would not 
be affected by the volatile gases exsolving from the basalt magma intruded into Zone 1 drifts 
(BSC 2003a, Section 6.5.2.2.3). 
The information in this report is responsive to agreement IA 2.19 made between the DOE and 
NRC. The report contains the information that DOE considers necessary for NRC review for 
closure of this agreement. 
C.4 BASIS FOR THE RESPONSE 
Discussions of each element of the agreements are provided in the following paragraphs. 
Evaluate Appropriate At-Condition Strength Properties and Magma Flow Paths, for 
Duration of an Igneous EventLimited analyses of the effects on waste packages to thermal 
and mechanical effects associated with exposure to basaltic magma have been completed. The 
results (BSC 2003a, Section 6.5.1.1) indicate that stresses associated with temperatures that are 
typical of basaltic magma could exceed the tensile strength of the waste package materials. In 
addition, as the magma cools, the volatile components of the magma could increase corrosion 
rates. The net result is that the analyses support the conservative assumption that waste packages 
in drifts intersected by an ascending basaltic dike (Zone 1) provide no further protection for the 
waste. This assumption makes it unnecessary to evaluate the at-condition strength properties for 
waste packages in intersected drifts. Evaluation of the effects of prolonged exposure to 
conditions in intersected drifts is also unnecessary. 
Results of numerical simulations of heat flow from Zone 1 emplacement drifts show that 
temperatures in the tuff wall rock decrease rapidly with distance from the intersected drift(s) 
(BSC 2003a, Section 6.5.2.1.1). The simulation results also show that the maximum temperature 
rise is less than 10C in a drift that is not intersected by a dike (Zone 2) but is adjacent to an 
intersected drift, and the rock provides an effective barrier to the thermal effects associated with 
the intrusion. The spatial and temporal heat conduction simulation results indicate that waste 
packages in Zone 2 emplacement drifts would not be affected by the heat conducting from the 
magma intruded into Zone 1 emplacement drifts (BSC 2003a, Section 6.5.2.1.1). 
Results of gas-flow simulations show that the gas-flow velocity decreases to near zero in about a 
year. The gas front in the wall rock stops at about 3.6 m from the drift wall, and the gas front in 
the backfill stops at about 1.4 m into the backfill. Simulations of diffusive gas flow show that 
concentrations of gas entering Zone 2 drifts would be low and would decrease after about 
November 2003 C-4 No. 13: Volcanic Events Revision 2 
2 years, and the concentrations of corrosive gases in the volatile components is expected to be 
significantly less than the concentration of water in the volatiles. These results indicate that 
waste packages in Zone 2 emplacement drifts would not be affected by the volatile gases 
exsolving from the basalt magma intruded into Zone 1 drifts (BSC 2003a, Section 6.5.2.2.3). 
Numerical simulations reported in Dike/Drift Interactions (BSC 2003b, Section 6.5.1.6) differ in 
detail but reach a similar conclusion that waste packages in unintruded drifts will not be exposed 
to adverse temperatures or gases. Results show a smaller increase in temperature and indicate 
that volcanic gases may be absorbed by host rock or diluted by air and backfill in connecting 
drifts before reaching Zone 2 drifts. 
Aging Effects on Materials Strength Properties when Exposed to Basaltic Magmatic 
Conditions for the Duration of an Igneous EventAging effects on strength properties of 
materials exposed to basaltic magmatic conditions have been evaluated in terms of effects of 
enhanced corrosion from heat and gases associated with a basaltic intrusion. As noted above, the 
analyses support the conservative TSPA assumption that waste packages in drifts intersected by 
an ascending basaltic dike (Zone 1) provide no further protection for the waste. On the other 
hand, heat or volatiles migrating from Zone 1 drifts are expected to produce no adverse effects 
on waste packages in Zone 2. Given that waste packages in Zone 1 are assumed compromised, 
and because simulation results indicate that Zone 2 packages will not be adversely affected by 
heat or volatiles, there is no need to evaluate aging effects beyond those considered in the 
nominal case. 
Potential Effects of Subsequent Seismically Induced Stresses on Substantially Intact Waste 
PackagesIt is not necessary to evaluate the effects of postintrusion seismically induced stresses 
on substantially intact waste packages. Waste packages in Zone 1 are already assumed to be 
compromised and to provide no further protection for the waste; so additional analyses to 
evaluate seismic effects for Zone 1 waste packages is unnecessary. Seismic effects on waste 
packages are being included in TSPA-LA, but Zone 2 waste packages are not expected to be 
damaged by effects from heat and/or gases migrating from Zone 1 drifts (BSC 2003a, 
Sections 6.5.2.1.1 and 6.5.2.2.3). The seismic analyses being included in TSPA-LA should be, 
therefore, adequate to address the concern. Hence, there is no need to further evaluate 
postintrusion seismic effects on Zone 2 packages. 
For additional information, see the discussion on the following page under the heading, 
Evaluate Barrier Performance for the Duration of the Hypothetical Igneous Event, If Credit Is 
Taken for Barrier Performance during an Igneous Event. 
Response of Zone 3 Waste PackagesFor TSPA-LA, no damage Zone 3 has been defined. 
TSPA-LA Zone 1 now includes all waste packages that were in Zones 1 and 2 for the TSPA-SR, 
and TSPA-LA Zone 2 includes waste packages that were in Zone 3 for TSPA-SR. 
Waste Packages Covered by Backfill or Rockfall, If Exposed to Magmatic Gases at 
Conditions Appropriate for an Igneous EventFor waste packages in Zone 1, the analyses 
support the conservative TSPA assumption that waste packages in Zone 1 provide no further 
protection for the waste. No credit is taken for presence of backfill (natural or man-made) in 
Zone 1 drifts. This assumption makes it unnecessary to evaluate the effects on waste packages 
November 2003 C-5 No. 13: Volcanic Events Revision 2 
covered by backfill or rockfall and exposed to magma or magmatic conditions in intersected 
drifts. For waste packages in Zone 2, results of gas flow simulations show that the gas flow 
velocity decreases to near zero in about a year. The gas front in the wall rock stops at about 
3.6 m from the drift wall, and the gas front in the backfill stops at about 1.4 m into the backfill. 
Simulations of diffusive gas flow show that concentrations of gas entering Zone 2 drifts would 
be low and would decrease after about 2 years, and the concentrations of corrosive gases in the 
volatile components is expected to be significantly less than the concentration of water in the 
volatiles. These results indicate that waste packages in Zone 2 emplacement drifts would not be 
affected by the volatile gases exsolving from the basalt magma intruded into Zone 1 drifts (BSC 
2003a, Section 6.5.2.2.3). 
Evaluate Barrier Performance for the Duration of the Hypothetical Igneous Event, If 
Credit Is Taken for Barrier Performance during an Igneous EventNo credit for barrier 
performance will be claimed for emplacement drifts intersected by a dike (Zone 1). All waste 
packages and drip shields in Zone 1 drifts will be assumed to be damaged to the extent that they 
provide no further protection for the waste. Simulation results show that the maximum 
temperature in drifts not intersected by a dike (Zone 2) would be less than 1C (BSC 2003b, 
Section 8.1.3). The rock provides an effective barrier to the thermal effects associated with the 
intrusion. 
Results of gas flow simulations show that the gas flow velocity decreases to near zero in about a 
year. The gas front in the wall rock stops at about 3.6 m from the drift wall, and the gas front in 
the backfill stops at about 1.4 m into the backfill. Simulations of diffusive gas flow show that 
concentrations of gas entering Zone 2 drifts would be low and would decrease after about 
2 years, and the concentrations of corrosive gases in the volatile components is expected to be 
significantly less than the concentration of water in the volatiles. These results indicate that 
waste packages in Zone 2 emplacement drifts would not be affected by the volatile gases 
exsolving from the basalt magma intruded into Zone 1 drifts (BSC 2003a, Section 6.5.2.2.3). 
Thermal and gas flow calculations show that the effects of intrusions on Zone 2 would be 
negligible (BSC 2003a, Section 6.7.2). Simulation results documented in the model report, 
Dike/Drift Interactions (BSC 2003b, Section 8.1.3) indicate that the maximum temperature 
increase in Zone 2 drifts would be less than 1C. This result is consistent with results 
documented in model report Igneous Intrusion Impacts on Waste Packages and Waste Forms 
(BSC 2003a, Section 6.5.2.1.1) that describe the maximum temperature in Zone 2 drifts as less 
than 10C. 
If the rise of the surface temperature of the affected waste packages in Zone 2 is less than 10C, 
and there is no impact on the chemistry of water in contact with the affected waste packages 
(BSC 2003a, Sections 6.5.2.1.1 and 5.5.2.2.3), the potential impact on localized corrosion 
susceptibility of the affected waste packages from the temperature rise is within the uncertainty 
of the localized corrosion initiation model for the waste packages for nondisrupted conditions 
(BSC 2003c, Sections 6.4.4.6). For nondisrupted conditions, the uncertainty range in the 
threshold temperature for initiation of waste package localized corrosion for a given water 
chemistry is approximately 30C, which is much larger than the potential temperature rises at the 
surface of the affected waste packages in Zone 2 (BSC 2003c, Sections 6.4.4.6). Hence, even the 
November 2003 C-6 No. 13: Volcanic Events Revision 2 
maximum increase in temperature of 10C is not expected to initiate localized corrosion of waste 
packages in Zone 2 drifts. 
For igneous effects on the invert, the current plan for revision of Igneous Intrusion Impacts on 
the Waste Packages and Waste Forms (BSC 2003a) includes describing disruption of the invert 
at the point of intersection of a dike with a drift. Outside the zone of intersection/disruption, the 
model report will show that the invert remains intact because magma is expected to enter a drift 
at the point of intersection and simply flow over the invert and down the drift. The update of the 
model report is expected to be ready in the second quarter of fiscal year 2004. For TSPA-LA, 
the invert nominal-case model will be used because, based on scoping analyses, the area of the 
invert disrupted by a basaltic dike compared to the total invert area is small. Because of the 
small disruption, explicit consideration of the disrupted invert for TSPA-LA analysis of the 
igneous intrusion groundwater-release scenario will likely have a negligible performance effect. 
C.5 REFERENCES 
BSC (Bechtel SAIC Company) 2003a. Igneous Intrusion Impacts on Waste Packages and Waste 
Forms. MDL-EBS-GS-000002 REV 00. Las Vegas, Nevada: Bechtel SAIC Company. 
ACC: DOC.20030819.0003. 
BSC 2003b. Dike/Drift Interactions. MDL-MGR-GS-000005 REV 00E. Las Vegas, Nevada: 
Bechtel SAIC Company. ACC: MOL.20030916.0259. 
BSC 2003c. General Corrosion and Localized Corrosion of Waste Package Outer Barrier. 
ANL-EBS-MD-000003 REV 01. Las Vegas, Nevada: Bechtel SAIC Company. 
ACC: DOC.20030916.0010. 
Reamer, C.W. 2001. U.S. Nuclear Regulatory Commission/U.S. Department of Energy 
Technical Exchange and Management Meeting on Igneous Activity (September 5, 2001). 
Letter from C.W. Reamer (NRC) to S. Brocoum (DOE/YMSCO), September 12, 2001, with 
enclosure. ACC: MOL.20011114.0008. 
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C-8 No. 13: Volcanic Events 
Revision 2 
November 2003
Revision 2 
APPENDIX D 
POTENTIAL FOR BASALTIC MAGMA 
TO INCORPORATE HIGH-LEVEL RADIOACTIVE WASTE 
(RESPONSE TO IA 2.20) 
November 2003 No. 13: Volcanic Events Revision 2 
Note Regarding the Status of Supporting Technical Information 
This document was prepared using the most current information available at the time of its development. This 
Technical Basis Document and its appendices providing Key Technical Issue Agreement responses that were 
prepared using preliminary or draft information reflect the status of the Yucca Mountain Projects scientific 
and design bases at the time of submittal. In some cases this involved the use of draft Analysis and Model 
Reports (AMRs) and other draft references whose contents may change with time. Information that evolves 
through subsequent revisions of the AMRs and other references will be reflected in the License Application as 
the approved analyses of record at the time of License Application submittal. Consequently, the Project will 
not routinely update either this Technical Basis Document or its Key Technical Issue Agreement appendices to 
reflect changes in the supporting references prior to submittal of the License Application. 
No. 13: Volcanic Events November 2003
Revision 2 
APPENDIX D 
POTENTIAL FOR BASALTIC MAGMA 
TO INCORPORATE HIGH-LEVEL RADIOACTIVE WASTE 
(RESPONSE TO IA 2.20) 
This appendix provides a response to Key Technical Issue (KTI) agreement igneous activity 
(IA) 2.20. This KTI agreement relates to the evaluation of the potential for basaltic magma to 
incorporate high-level radioactive waste. 
D.1 KEY TECHNICAL ISSUE AGREEMENT 
D.1.1 IA 2.20 
Agreement IA 2.20 was reached during the U.S. Nuclear Regulatory Commission (NRC)/U.S. 
Department of Energy (DOE) Technical Exchange and Management Meeting on Igneous 
Activity held September 5, 2001, in Las Vegas, Nevada (Reamer 2001). 
The wording of the agreement is as follows: 
IA 2.20
DOE will evaluate how ascent and flow of basaltic magma through repository 
structures could result in processes that might incorporate HLW, considering the 
results of evaluations attendant to IA Agreements 2.18 and 2.19. As currently 
planned, the evaluation, if implemented, would include the potential for HLW 
incorporation along reasonable potential flow paths that could develop during an 
igneous event. The evaluation would also include the physical and chemical 
response of HLW and cladding after heating and potential disruption of waste 
package and contents, for waste packages remaining in drifts. The evaluation 
would examine effects that may result in increased solubility potential relative to 
undisturbed HLW forms. The results of this investigation would be documented 
in a new AMR to document the waste form response to magmatic conditions, 
which is expected to be available by the end of FY 2003. DOE will describe the 
method of HLW incorporation used in DOE models, including consideration of 
particle aggregation and the effect on waste transport. If models take credit for 
engineered barriers providing delay in radionuclide release, DOE will evaluate 
barrier performance for the duration of the hypothetical igneous event. This will 
be documented in an update to the igneous consequences AMR, ANL-WIS-MD- 
000017, which is expected to be available in FY 2003, or another appropriate 
technical document. 
Analyses by the NRC indicated that intersection of the repository by an ascending basaltic dike 
could result in magma flow through parts of the repository and migration of heat and volatiles 
into drifts not directly intersected by a dike. The NRC questioned the extent of potential effects 
on the waste forms either from direct exposure to magma or from exposure to heat and exsolved 
volatiles. NRC was concerned that changes in the waste form and/or cladding, specifically 
changes that would increase solubility of the waste form, could occur, and that the changes could 
November 2003 D-1 No. 13: Volcanic Events Revision 2 
enhance the mobility of the radionuclides. To address concerns associated with the effects on the 
waste form from interactions with magma and magmatic products, DOE agreed to describe the 
method of high-level radioactive waste incorporation that will be used for total system 
performance assessment for the license application (TSPA-LA) (Reamer 2001). 
Waste package and waste form effects for TSPA-LA will be evaluated in the waste package and 
waste form impacts submodel of the TSPA-LA model. Documentation of the submodel is 
provided in Igneous Intrusion Impacts on Waste Packages and Waste Forms (BSC 2003). 
D.1.2 Related Key Technical Issue Agreements 
There are two KTI agreements related to IA 2.20. Agreements IA 2.18 and IA 2.19, respectively, 
are intended to provide inputs for the analysis of magma-drift and magmawaste package 
interactions to support the analysis of effects on waste forms of exposure to magma and 
magmatic components. Agreement IA 2.18 is intended to ensure that information was obtained 
about the effects of repository structures on dike propagation and magma flow, exsolution of 
volatiles, and cooling and solidification of magma so that the results could be incorporated in the 
analysis of effects on components of the engineered barrier system. Agreement IA 2.19 is 
intended to evaluate the damage to waste packages that could result from direct contact with 
magma (Zone 1) or from exposure to heat and gases that had exsolved from the magma and 
migrated to adjacent drifts (Zone 2). The analyses of effects of repository structures on dike 
propagation and magma flow and cooling and of magma and magmatic products on waste 
package durability determine the potential nature of the effects of igneous intrusion on the waste. 
RELEVANCE TO REPOSITORY PERFORMANCE D.2 
Changes in the thermal, mechanical, or chemical properties of waste forms from exposure to 
magmatic conditions could increase the mobility of radionuclides and increase the resulting dose 
to the reasonably maximally exposed individual for the igneous intrusiongroundwater release 
case. However, studies indicate that, even if changes in the waste could occur, the mobility of 
radionuclides is not increased (BSC 2003, Section 6.5.1.2). 
The TSPA-LA approach to implementing the models for waste package and waste form response 
during igneous intrusion is based on identification of damage zones. Zone 1 includes all 
emplacement drifts intersected by the basalt dike. Zone 2 includes all emplacement drifts in the 
repository that are not in Zone 1. Igneous Intrusion Impacts on Waste Packages and Waste 
Forms (BSC 2003) documents the following model assessments: 
 Zone 1Impacts of magma intrusion on the drip shields, waste packages and cladding 
directly contacted by magma, and the fate of waste forms. Impacts of intrusion on 
Zone 1 in-drift thermal and geochemical environments, including seepage 
hydrochemistry. 
 Zone 2Impacts of conducted magmatic heat and diffused magmatic gases on the drip 
shields, waste packages, cladding and waste packages adjacent to the intruded drifts. 
The current version of the model indicates that spent nuclear fuel in drifts intersected by a dike 
(Zone 1) would be assimilated by the magma, but the minerals or phases that are likely to result 
November 2003 D-2 No. 13: Volcanic Events Revision 2 
would be refractory. However, the specific properties of these refractory minerals or phases are 
unknown. While spent nuclear fuel in Zone 1 is expected be less soluble after exposure to 
magma and magmatic components, the spent nuclear fuel in Zone 1 is considered, in the basecase 
model, to be chemically unaffected by the magma intrusion. Because waste packages in 
Zone 2 will not be damaged by the effects of heat and volatiles migrating from Zone 1, spent 
nuclear fuel in Zone 2 will be treated the same as in the nominal scenario. 
D.3 RESPONSE 
The base-case conceptual model for damage to waste packages and waste forms from igneous 
intrusion include the following components (BSC 2003, Section 6.3): 
 Intrusion of basaltic magma (as a dike) into Zone 1 emplacement drifts (without surface 
eruption) 
 Damage to drip shields, waste packages and cladding in Zone 1 results in these 
components providing no further protection for the waste forms 
 Embedding or assimilation of waste materials into magma intruded into Zone 1 drifts 
 Postintrusion perturbations to the in-drift environmental conditions from cooling magma 
include heat loss by conduction, degassing, and fracturing of the intrusion. Following 
intrusion, the magma would cool, and the deleterious volatile gases that would exsolve 
from the magma would diffuse through the host rock (with the assumption of no 
chemical interactions to reduce their concentrations) and reach waste packages in drifts 
not intersected by the dike (Zone 2). 
 Reversion to normal in-drift environmental conditions would follow cooling of the 
magma. Seepage water entering the Zone 1 drifts would react and equilibrate with the 
cooled and fractured basalt. Seepage entering the Zone 2 drifts would not be 
equilibrated with basalt. 
The base-case model does not consider the effects of reactions between the waste forms and the 
basalt and any reactive exudates. For waste in Zone 1, TSPA-LA assumes that radionuclides in 
the waste forms will be available for dissolution immediately after water flow resumes in the 
cooled intrusion. The water is assumed to equilibrate with the basalt. Waste packages in Zone 2 
are unaffected by migrating heat and volatiles and must be breached before the waste is available 
for dissolution. When the waste reacts with water, the same solubility model is used for the 
radionuclides in Zone 1 and Zone 2. 
Section 5.3 describes a variety of literature studies regarding the potential for enhanced corrosion 
in magmatic environments, which are summarized in Igneous Intrusion Impacts on Waste 
Packages and Waste Forms (BSC 2003). These studies indicate that high temperatures and 
corrosive geochemical environments, which could accompany dike intrusion, could measurably 
increase the corrosion rates of steel and other metal alloys. 
November 2003 D-3 No. 13: Volcanic Events Revision 2 
Although none of the analyses indicate that the metallic engineered barriers would be destroyed 
or fail instantaneously, it appears that the effects would be rapid compared to the 10,000-year 
regulatory period. Therefore, because of the uncertainty associated with analyzing the effects of 
enhanced corrosion rates, performance assessment analyses for Yucca Mountain conservatively 
assume that any engineered materials contacted by magmas (e.g., drip shields, waste packages, 
cladding) during an intrusion will no longer provide any waste isolation function. However, the 
natural and engineered features and processes that act as barriers to limit dose will be 
documented in the license application. 
The alternative conceptual model described in Igneous Intrusion Impacts on Waste Packages and 
Waste Forms (BSC 2003, Section 6.4.1) indicates that spent nuclear fuel would be less mobile 
after exposure to magma and magmatic components. Oxidation of UO2 fuel would produce 
minerals that are less soluble than the phase that controls concentration of uranium in fluids 
transiting the repository. The results also indicate that some portion of the waste in drifts 
intersected by an ascending basaltic dike (Zone 1) would be assimilated in the magma. 
However, the alternative conceptual model indicates that mineral phases, which could result 
from interaction between magma and dispersed waste and waste package materials, would be 
refractory and of limited solubility (BSC 2003, Section 6.4.1). In addition, radionuclides in the 
waste could be incorporated into crystallizing silicate mineral phases, such as soddyite 
[(UO2)2(SiO4)  2 H2O], which would limit the concentration of uranium in fluids transiting the 
repository under the nominal scenario (BSC 2003, Section 6.4.1). Finally, the spent nuclear fuel 
is a hard ceramic material with a high melting point temperature of 2,800C. The commercial 
spent nuclear fuel and defense spent nuclear fuel wastes exposed to hot magma are not, 
therefore, expected to melt under temperatures no higher than the maximum magma temperature 
of 1,169C (BSC 2003, Section 6.4.1). The net effect is that the mobility of uranium would be 
reduced by exposure to magma or magmatic conditions. 
Conversely, in drifts that are not intersected by a dike (Zone 2), the effects of heat conduction 
and volatile migration are not expected to perturb the environment in these drifts to the extent 
that waste package integrity is compromised (BSC 2003, Section 6.7.2). If Zone 2 waste 
packages are not compromised, waste will not be exposed to the in-drift environmental 
conditions, and there are no mechanisms available to incorporate waste from Zone 2 drifts. 
Hence, for TSPA-LA, waste packages and waste in Zone 2 emplacement drifts will be treated the 
same as in the nominal scenario (BSC 2003, Section 6.7.2). 
The information in this report is responsive to agreement IA 2.20 made between the DOE and 
NRC. The report contains the information that DOE considers necessary for NRC review for 
closure of this agreement. 
D.4 BASIS FOR THE RESPONSE 
The technical basis for the response addresses the elements of the agreement, which are 
identified below in bold type. 
Evaluate Methods of High-Level Radioactive Waste Incorporation Used in 
U.S. Department of Energy Models, Including Consideration of Particle Aggregation and 
the Effect on Waste TransportThe DOE base-case conceptual model for magma-waste form 
November 2003 D-4 No. 13: Volcanic Events Revision 2 
interactions is described in Igneous Intrusion Impacts on Waste Packages and Waste Forms 
(BSC 2003, Section 6.3). Damage to drip shields, waste packages, and cladding in Zone 1 
results in these components providing no further protection for the waste forms followed by 
embedding or assimilation of waste materials into magma intruded into Zone 1 drifts. The model 
includes assimilation of material into magma intruded into Zone 1 drifts, but specific 
mechanisms have not been identified. Spent nuclear fuel is a hard ceramic material with a high 
melting point temperature of 2,800C. The commercial spent nuclear fuel and defense spent 
nuclear fuel wastes exposed to hot magma are not, therefore, expected to melt under 
temperatures no higher than the maximum magma temperature of 1,169C (BSC 2003, 
Section 6.4.1). The base-case model (BSC 2003) indicates that when the waste 
canisters/assemblies and fuel claddings are damaged, the fuel pellets/rods would be assimilated 
into the cooling basalt magma. Under this scenario, the alternative conceptual model (BSC 
2003, Section 6.4.1) indicates that two types of processes are expected: (a) interaction between 
waste forms and the magma and (b) interaction between the waste forms and the metal of waste 
canisters/assemblies and cladding in the presence of hot magma. 
In the first case, (a), the model shows that oxidation of some UO2 fuel would occur in the 
presence of water-rich volatiles exuding from cooling basalt magma. In addition, some 
radionuclides in the waste would be incorporated into crystallizing silicate mineral phases, such 
as soddyite [(UO2)2(SiO4)  2 H2O]. The solubility of soddyite is less than that of schoepite, 
which is considered to be the phase that controls concentration of uranium in fluids transiting the 
repository under the nominal scenario. This solubility information indicates that actinide 
concentrations in water passing through basalt-filled drifts would be decreased relative to 
actinide concentrations in the nominal case (BSC 2003, Sections 6.5.1.6 and 6.5.2.6). 
In the second case, (b), the model shows chemical interactions would occur between some of the 
fuel and metals/alloys of damaged waste canisters/assemblies and claddings in the presence of 
the cooling magma that would result in the formation of new phases. The alternative model 
indicates that these new phases would be refractory and of limited solubility (BSC 2003, Section 
6.4.1). Hence, particle aggregation effects that could increase local radionuclide concentrations 
in magma would likely be offset by the refractory nature and reduced solubilities of the mineral 
phases. 
In drifts that are not intersected by a dike (Zone 2), base-case model results (BSC 2003, 
Sections 6.5.2.1.1 and 6.5.2.2.3) show that the effects of heat conduction and volatile migration 
would not perturb the environment in Zone 2 drifts to the extent that waste package integrity is 
compromised (BSC 2003, Section 6.7.2). If Zone 2 waste packages are not compromised, waste 
will not be exposed to the in-drift environmental conditions, and there are no mechanisms 
available to incorporate waste from Zone 2 drifts. Hence, for TSPA-LA, waste packages and 
waste in Zone 2 emplacement drifts will be treated the same as in the nominal scenario. 
Evaluate the Potential for High-Level Radioactive Waste Incorporation along Reasonable 
Potential Flow Paths That Could Develop during an Igneous EventStudy results indicate 
that some portion of the waste in drifts intersected by an ascending basaltic dike (Zone 1) would 
be assimilated in the magma. Properties of assimilated waste phases and reactions of assimilated 
waste with magma are not known at this time. Therefore, the base-case model does not address 
November 2003 D-5 No. 13: Volcanic Events Revision 2 
details of reactions between assimilated waste and magma. Rather, depictions of selected 
reactions are used (BSC 2003, Section 6.4.1) until test results are available. 
Evaluate the Physical and Chemical Response of High-Level Radioactive Waste and 
Cladding after Heating and Potential Disruption of Waste Package and ContentsStudy 
results indicate that some portion of the waste in drifts intersected by an ascending basaltic dike 
(Zone 1) would be assimilated in the magma. However, the alternative conceptual model 
indicates that mineral phases, which could result from interaction between magma and dispersed 
waste and waste package materials, would be refractory and of limited solubility (BSC 2003, 
Section 6.4.1). In addition, radionuclides in the waste could be incorporated into crystallizing 
silicate mineral phases, such as soddyite [(UO2)2(SiO4)  2 H2O]. Development of soddyite 
would limit actinide concentrations in fluids exiting the repository. 
The spent nuclear fuel is a hard ceramic material with a high melting point temperature of 
2,800C; therefore, the commercial spent nuclear fuel and defense spent nuclear fuel wastes 
exposed to hot magma are not expected to melt under temperatures no higher than the maximum 
magma temperature of 1,169C (BSC 2003, Section 6.4.1). The alternative conceptual model 
presented in Igneous Intrusion Impacts on Waste Packages and Waste Forms (BSC 2003, 
Section 6.4.4) indicates that fracturing, fragmentation, and granulation of the waste form could 
result from thermal shock effects associated with exposure of waste to basaltic magma. For 
TSPA-LA, the waste is assumed to be exposed, and the radionuclides are assumed to be 
available for transport, but no explicit assumptions about conditions applicable to the waste form 
are made. 
For glass waste exposed to magma, even though magma temperatures could exceed the melting 
temperature of glass waste forms, the glass waste forms are likely to be minimally affected by 
exposure to magmatic thermal conditions because the thermal environment during an intrusion 
would be similar to that in which the glass was produced (BSC 2003, Section 6.4.4; Lichtner et 
al. 1999). 
Evaluate Effects That May Result in Increased Solubility Potential Relative to Undisturbed 
High-Level Radioactive Waste FormsAlternative conceptual models indicate that mineral 
phases, which could result from interaction between magma and dispersed waste and waste 
package materials, would be refractory and of limited solubility (BSC 2003, Section 6.4.1). In 
addition, radionuclides from the waste could be incorporated into crystallizing silicate mineral 
phases, such as soddyite [(UO2)2 (SiO4)  2 H2O]. Development of soddyite would limit actinide 
concentrations in fluids exiting the repository. Since the properties of these phases have not been 
determined, the TSPA-LA base case will apply the assumption that the waste is refractory and 
chemically unaffected by exposure to the intruding magma (BSC 2003, Sections 6.5.1.3 and 
6.7.1). 
D.5 REFERENCES 
BSC (Bechtel SAIC Company) 2003. Igneous Intrusion Impacts on Waste Packages and Waste 
Forms. MDL-EBS-GS-000002 REV 00. Las Vegas, Nevada: Bechtel SAIC Company. 
ACC: DOC.20030819.0003. 
November 2003 D-6 No. 13: Volcanic Events Revision 2 
Lichtner, P.C.; Keating, G.; and Carey, B. 1999. A Natural Analogue for Thermal-Hydrological- 
Chemical Coupled Processes at the Proposed Nuclear Waste Repository at Yucca Mountain, 
Nevada. LA-13610-MS. Los Alamos, New Mexico: Los Alamos National Laboratory. 
TIC: 246032. 
Reamer, C.W. 2001. U.S. Nuclear Regulatory Commission/U.S. Department of Energy 
Technical Exchange and Management Meeting on Igneous Activity (September 5, 2001). 
Letter from C.W. Reamer (NRC) to S. Brocoum (DOE/YMSCO), September 12, 2001, with 
enclosure. ACC: MOL.20011114.0008. 
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