Characterize Framework for Igneous Activity at Yucca Mountain, Nevada REV 02, ICN 00 

ANL-MGR-GS-000001

October 2004 

1. PURPOSE 
The purpose of this scientific analysis report is threefold: 
 
Present a conceptual framework of igneous activity in the Yucca Mountain region 
(YMR) consistent with the volcanic and tectonic history of this region and the 
assessment of this history by experts who participated in the probabilistic volcanic 
hazard analysis (PVHA) (CRWMS M&O 1996 [DIRS 100116]1). Conceptual models 
presented in the PVHA are summarized and applied in areas in which new information 
has been presented. Alternative conceptual models are discussed, as well as their impact 
on probability models. The relationship between volcanic source zones defined in the 
PVHA and structural features of the YMR are described based on discussions in the 
PVHA and studies presented since the PVHA. 
 
Present revised probability calculations based on PVHA outputs for a repository 
footprint proposed in 2003 (BSC 2003 [DIRS 162289]), rather than the footprint used at 
the time of the PVHA. This analysis report also calculates the probability of an eruptive 
center(s) forming within the repository footprint using information developed in the 
PVHA. Probability distributions are presented for the length and orientation of volcanic 
dikes located within the repository footprint and for the number of eruptive centers 
(conditional on a dike intersecting the repository) located within the repository footprint. 
 
Document sensitivity studies that analyze how the presence of potentially buried basaltic 
volcanoes may affect the computed frequency of intersection of the repository footprint 
by a basaltic dike. These sensitivity studies are prompted by aeromagnetic data 
collected in 1999, indicating the possible presence of previously unrecognized buried 
volcanoes in the YMR (Blakely et al. 2000 [DIRS 151881]; OLeary et al. 2002 
[DIRS 158468]). The results of the sensitivity studies are for informational purposes 
only and are not to be used for purposes of assessing repository performance. 
The U.S. Department of Energy (DOE) considers volcanism to be a potentially disruptive event 
in the total system performance assessment (TSPA) analysis supporting the License Application 
(LA) for the proposed Yucca Mountain repository (DOE 1998 [DIRS 100550]). The two 
volcanic scenarios (with individual probabilities and consequences) modeled by the TSPA-LA 
are: 
 
Ascent of a basaltic dike or dike system (i.e., a set or swarm of multiple dikes 
comprising a single intrusive event) to repository level where it intersects drifts 
 
Development of volcanoes within the repository footprint with one or more conduits that 
intersect waste packages. 
In this report, a unique six-digit numerical identifier (the Document Input Reference System [DIRS] number) is placed in the 
text following the reference callout (e.g., BSC 2002 [DIRS 156605]), the purpose of which is to assist the reader in locating a 
specific reference in the DIRS database. Within the reference list (Section 8), multiple sources by the same author and date 
(e.g., BSC 2002) are sorted alphabetically by title. 

As a consequence of the first event, which is non-eruptive, waste from breached packages may 
provide a source of radionuclides when groundwater moves through the damaged packages at 
some time in the future (igneous intrusion groundwater release). The potential consequence of 
the second event is that waste packages entrained within a conduit may be breached, releasing 
radionuclides to the erupting ash plume where they can be dispersed downwind to a reasonably 
maximally exposed individual (RMEI) (10 CFR 63 [DIRS 156605], Section 63.2; 66 FR 55794) 
in the accessible environment at the controlled area boundary (10 CFR 63 [DIRS 156605], 
Section 63.302; 66 FR 55813). According to 10 CFR Part 63 this location is to be approximately 
18 km from the southern boundary of the repository. 
This report, Characterize Framework for Igneous Activity at Yucca Mountain, Nevada, Revision 
(REV) 02, describes the conceptual framework for volcanism near Yucca Mountain and how the 
conceptual framework provides the basis for probability calculations. This report also presents 
the probability results and associated uncertainties for intersection of the proposed repository by 
a volcanic event and the probability of an eruption through the repository, conditional on a dike 
intersection. In the context of the PVHA, a volcanic event is 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 [DIRS 100116], Appendix E). For the purposes of the probability models 
discussed in this report, a volcanic event is defined as a point (x,y) 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 a probability model by a line element defined in terms 
of a length, azimuth, and location relative to the point event (Figure 6-8 and Figure 6-10). 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 (e.g., multiple dikes) has width or consists of multiple 
parallel dikes is not part of the calculations in this report. Both the width of the dikes and the 
number of parallel dikes affect the consequences of an intersection and are included in Number 
of Waste Packages Hit by Igneous Intrusion (BSC 2004 [DIRS 170001]). 
The probability results documented in this report provide the basis for all further igneous 
consequences analysis. These probability results remain unchanged from those presented in 
REV 01 of this report (BSC 2003 [DIRS 163769]) and no new output data were generated in this 
version. The output data tracking numbers (DTNs) carried forward as output from this revision 
are listed in Section 7.2. The results of this report provide direct input into the Number of Waste 
Packages Hit by Igneous Intrusion scientific analysis report and direct input to the TSPA-LA. 
This document uses information on conduit size developed in Characterize Eruptive Processes 
at Yucca Mountain, Nevada, to define a buffer zone around the repository footprint. 
The following documents also use information developed in this analysis report: 
Screening Analysis of Criticality Features, Events, and Processes for License Application 
Features, Events, and Processes: System Level 
Features, Events, and Processes in UZ Flow and Transport 
Features, Events, and Processes: Disruptive Events. 

Consideration of the number of volcanic events that have occurred during selected periods of 
time in the YMR was one of the key parameters the PVHA used to calculate the probability of a 
basaltic dike intersecting the repository footprint. Volcanic features counted as volcanic events 
included individual volcanoes, alignments of volcanoes, and aeromagnetic anomalies in the 
region that are known (by drilling) or inferred to be buried volcanoes. In 1999, three years after 
the PVHA was completed, a new aeromagnetic survey of the YMR was completed under the 
direction of the U.S. Geological Survey (USGS) (Blakely et al. 2000 [DIRS 151881], OLeary et 
al. 2002 [DIRS 158468]). REV 01 of this report (BSC 2003 [DIRS 163769]) presented 
sensitivity studies addressing the potential impact of the new aeromagnetic survey results. This 
report documents an additional sensitivity analysis that uses alternative conceptual models to 
assess the potential impact of undetected (buried) volcanic events on the probability of 
intersection of the repository footprint by a basaltic dike. This scientific analysis report is 
governed by the Technical Work Plan For: Igneous Activity Assessment for Disruptive Events 
(TWP) (BSC 2004 [DIRS 171403]). The TWP specifies the activities to be carried out in 
updating information in the revision of this report. The activities documented in this report do 
not deviate from those specified in the TWP. 

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2. QUALITY ASSURANCE 
Development of this scientific analysis report and the supporting analyses was subject to the 
Office of Civilian Radioactive Waste Management quality assurance program (BSC 2003 
[DIRS 171403], Section 8.1). Approved quality assurance procedures identified in the TWP 
(BSC 2004 [DIRS 171403], Section 4) were used to conduct and document the activities 
described in this report. The TWP also identifies the methods used to control the electronic 
management of data (BSC 2004 [DIRS 171403], Section 8.4). The TWP also described the 
methods to be used for the electronic management of information, as identified in AP-SV.1Q, 
Control of the Electronic Management of Information. These methods were followed in 
developing this report. 
This report documents the volcanic history of the YMR, recalculates the frequency of 
intersection and development of distributions for length and orientation of dikes, and recalculates 
the number of eruptive centers within the repository footprint (subsurface facilities). The 
subsurface facilities are classified on the Q-List (BSC 2004 [DIRS 168361], Appendix A) as a 
Safety Category because of their importance to waste isolation, as defined in AP-2.22Q, 
Classification Analyses and Maintenance of the Q-List. The results of this report are important 
to the demonstration of compliance with the postclosure performance objectives prescribed in 10 
CFR 63.113 [DIRS 156605]. This report contributes to the analysis and modeling data used to 
support performance assessment; the conclusions do not directly impact engineered features 
important to safety, as defined in AP-2.22Q. 

INTENTIONALLY LEFT BLANK 

3. USE OF SOFTWARE 
3.1 SOFTWARE TRACKED BY CONFIGURATION MANAGEMENT 
The calculations presented in this scientific analysis report were performed with the set of 
software routines described below. This software was qualified and placed on the Software 
Baseline under AP-SI.1Q, Software Management, in 2000. The qualified calculations presented 
in this report were conducted in REV 01 (BSC 2003 [DIRS 163769]) in 2003, again under the 
software procedures active at that time. Although those software procedures have been 
superseded by a more recent procedure (LP-SI.11Q-BSC), the software used in this analysis has 
not been modified from the original baseline software. The software and routines used in 
support of this work are appropriate for this application and are used within their range of 
validation as described in the qualification documentation. The software is written in 
FORTRAN77 and operates on a personal computer equipped with a 486 or Pentium processor 
under a disk operating system or in a Microsoft Windows operating system window. The 
computations were performed using the software routines acquired from Software Configuration 
Management. The software used was selected because it was designed to perform the 
calculations defined by the PVHA (CRWMS M&O 1996 [DIRS 100116]), and it was used 
within the parameter limits defined by the PVHA. There are no limitations on the use of the 
results due to use of the selected software. 
The software routine titles are listed with the standard FORTRAN .FOR extension in the 
Software Configuration Management database, the DIRS database, and in Section 8.3 of this 
report. The routines are listed by their titles without the .FOR extension in Table 3-1 and 
Table 3-2, Figure 3-1 and Figure 3-2, and in the text of this report. 
Table 3-1 lists the software routines used to compute the frequency of intersection of the 
repository footprint by a volcanic event through full enumeration of the PVHA experts logic 
trees. Figure 3-1 shows the data flow through the routines in Table 3-1. The software routines 
listed in Table 3-1 are qualified versions of the routines used in the PVHA calculation (CRWMS 
M&O 1996 [DIRS 100116]). 
Table 3-2 lists the software routines used to compute the conditional distributions for the length 
and azimuth of an intersecting dike within the repository footprint and the number of eruptive 
centers within this footprint. The data flow through the software routines for this calculation is 
shown in Figure 3-2. 
In addition, the software routine COMBDELD.FOR V1.0 (LANL 2000 [DIRS 148617]) was 
used to calculate aggregate dike length and event length distributions across all 10 PVHA experts 
for display in Figures 6-2 and 6-4. 
Software used to convert Nevada State Plane coordinates to Universal Transverse Mercator 
(UTM) coordinates for the repository footprint is listed in Table 3-3. 

Table 3-1. Software Routines Used to Compute Frequency of Intersection of the Proposed Repository 
by a Dike 
Software Routine 
(Software Tracking 
Number) Function 
FITCD V1.0 
(10262-1.0-00) [DIRS 
148532] 
Computes discrete cumulative probability distributions for dike length from cumulative 
probabilities specified at selected values of length. 
SFCD V1.0 
(10275-1.0-00) [DIRS 
148533] 
Computes discrete cumulative probability distributions for dike length using user-
specified distribution forms. 
DCPELD V1.0 
(10258-1.0-00) [DIRS 
148534] 
Computes discrete probability distribution for dike length from expert-specified 
distributions (output of FITCD). 
CPDI V1.0 
(10257-1.0-00) [DIRS 
148535] 
Computes conditional probability of intersection from volcanic events on an x,y grid 
using output of DCPELD and expert-specified azimuth distributions. 
UZVH V1.0 
(10277-1.0-00) [DIRS 
148536] 
Computes frequency of intersection from volcanic source zones using output of CPDI. 
FKVH V1.0 
(10265-1.0-00) [DIRS 
148567] 
Computes frequency of intersection using kernel density estimation with specified h 
and output of CPDI. 
UZVPVH V1.0 
(10279-1.0-00) [DIRS 
148537] 
Computes frequency of intersection from volcanic source zones using volume 
predictable volcanic event rate model and output of CPDI. 
FKVPVH V1.0 
(10267-1.0-00) [DIRS 
148538] 
Computes frequency of intersection using kernel density estimation using volume 
predictable volcanic event rate model and output of CPDI. 
ZBCKVH V1.0 
(10283-1.0-00) [DIRS 
148539] 
Computes frequency of intersection using kernel density estimation with h constrained 
by a source zone boundary and output of CPDI. 
FITFIELD V1.0 
(10263-1.0-00) [DIRS 
148540] 
Computes parameters of a bivariate Gaussian distribution that approximates 
boundaries of a defined polygon. 
FIT2CNTR V1.0 
(10261-1.0-00) [DIRS 
148541] 
Computes parameters of a bivariate Gaussian distribution from locations of volcanic 
events. 
PFGVH V1.0 
(10273-1.0-00) [DIRS 
148542] 
Computes frequency of intersection using a bivariate Gaussian distribution with 
specified field parameters and output of CPDI. Bivariate Gaussian distribution 
parameters obtained from programs FIT2CNTR or FITFIELD. 
FPFGVH V1.0 
(10269-1.0-00) [DIRS 
148543] 
Computes frequency of intersection using a bivariate Gaussian distribution with 
parameters fit to volcanic event locations and output of CPDI. 
VHTREE V1.0 
(10282-1.0-00) [DIRS 
148544] 
Computes mean and fractiles of frequency of intersection over an individual experts 
volcanic hazard logic tree and aggregate over all experts using outputs of UZVH, 
UZVHB, FKVH, UZVPVH, FKVPVH, ZBCLVH, PFGVH, and FPFGVH. 

Table 3-2 Software Routines Used to Compute Conditional Distributions for Dike Length, Azimuth, and 
Number of Eruptive Centers within the Proposed Repository 
Software Routine 
(Software Tracking Number) Function 
FITCD V1.0 
(10262-1.0-00) [DIRS 148532] 
Computes discrete cumulative probability distributions for dike length from 
cumulative probabilities specified at selected values of length. 
SFCD V1.0 
(10275-1.0-00) [DIRS 148533] 
Computes discrete cumulative probability distributions for dike length using user-
specified distribution forms. 
DCPELD V1.0 
(10258-1.0-00) [DIRS 148534] 
Computes discrete probability distribution for dike length from expert-specified 
distributions (output of FITCD). 
CPDI V1.0 
(10257-1.0-00) [DIRS 148535] 
Computes conditional probability of intersection from volcanic events on an x,y 
grid using output of DCPELD and expert-specified azimuth distributions. 
UZVHLH V1.0 
(10278-1.0-00) [DIRS 148545] 
Computes simulations of contributions to frequency of intersection on an x,y grid 
from volcanic source zones using Latin Hypercube sampling and output from 
CPDI. 
FKVHLH V1.0 
(10266-1.0-00) [DIRS 148546] 
Computes simulations of contributions to frequency of intersection on an x,y grid 
using kernel density estimation with specified h, Latin Hypercube sampling, and 
output from CPDI. 
UZVPVHLH V1.0 
(10280-1.0-00) [DIRS 148547] 
Computes simulations of contributions to frequency of intersection on an x,y grid 
from volcanic source zones using volume predictable volcanic event rate model, 
Latin Hypercube sampling, and output from CPDI. 
FKVPVHLH V1.0 
(10268-1.0-00) [DIRS 148551] 
Computes simulations of contributions to frequency of intersection on an x,y grid 
with kernel density estimation using volume predictable volcanic event rate 
model, Latin Hypercube sampling, and output from CPDI. 
ZBCKVHLH V1.0 
(10284-1.0-00) [DIRS 148550] 
Computes simulations of contributions to frequency of intersection on an x,y grid 
using kernel density estimation with h constrained by a source zone boundary, 
Latin Hypercube sampling, and output from CPDI. 
FITFIELD V1.0 
(10263-1.0-00) [DIRS 148540] 
Computes parameters of a bivariate Gaussian distribution that approximates 
boundaries of a defined polygon. 
FIT2CNTR V1.0 
(10261-1.0-00) [DIRS 148541] 
Computes parameters of a bivariate Gaussian distribution from locations of 
volcanic events. 
PFGVHLH V1.0 
(10274-1.0-00) [DIRS 148552] 
Computes simulations of contributions to frequency of intersection on an x,y grid 
using a 2D-Gaussian distribution with specified parameters, Latin Hypercube 
sampling, and output from CPDI. Gaussian distribution parameters obtained 
from programs FIT2CNTR or FITFIELD. 
FPFGVHLH V1.0 
(10270-1.0-00) [DIRS 148553] 
Computes simulations of contributions to frequency of intersection on an x,y grid 
using a 2D-Gaussian distribution with parameters fit to volcanic event locations, 
Latin Hypercube sampling, and output from CPDI. 
VHTIELHS V1.0 
(10281-1.0-00) [DIRS 148554] 
Computes mean and fractiles of simulations of contributions to frequency of 
intersection on an x,y grid over an individual experts volcanic hazard logic tree 
using Latin Hypercube sampling and output from UZVHLH, FKVHLH, 
UZVPVHLH, FKVPVHLH, ZBCLVHLH, PFGVHLH, and FPFGVHLH. 
NECPDS V1.1 
(10272-1.1-00) [DIRS 168238] 
Computes distributions for number of eruptive centers per volcanic event and 
average spacing between eruptive centers. 
FITIDSR V1.0 
(10264-1.0-00) [DIRS 148557] 
Computes discrete incremental probability distributions for dike length using 
input to FITCD. 
SFIDSR V1.0 
(10276-1.0-00) [DIRS 148571] 
Computes discrete incremental probability distributions for dike length using 
input to SFCD. 
DLECD V1.0 
(10260-1.0-00) [DIRS 148558] 
Computes joint discrete probability distributions for dike length and number of 
eruptive centers per volcanic event using output from FITIDSR. 

Table 3-2 Software Routines Used to Compute Conditional Distributions for Dike Length, Azimuth, and 
Number of Eruptive Centers within the Proposed Repository (Continued) 
Software Routine 
(Software Tracking Number) Function 
DILECDLH V1.1 
(10259-1.1-00) [DIRS 168221] 
Computes joint conditional distribution of dike intersection length, dike azimuth, 
and number of eruptive centers within the repository footprint from outputs of 
program VHTIELHS using Latin hypercube sampling of dike length and volcanic 
event location distributions from DIECDIST. 
CFRAC V1.0 
(10254-1.0-00) [DIRS 148560] 
Locates individual experts simulation results that represent specified percentiles 
of the composite distribution for frequency of intersection from outputs of 
VHTIELHS. 
COMBSM V1.1 
(10256-1.1-00) [DIRS 168220] 
Computes composite joint distribution of dike intersection length, dike azimuth, 
and number of eruptive centers within the repository footprint across experts 
from outputs of DILECDLH and VHTIELHS for mean hazard. 
COMBSF V1.1 
(10255-1.1-00) [DIRS 168218] 
Computes composite joint distribution of dike intersection length, dike azimuth, 
and number of eruptive centers within the repository footprint across experts 
from outputs of DILECDLH for selected percentiles of the hazard. 
MARGIN V1.1 
(10271-1.1-00) [DIRS 168223] 
Computes marginal distributions for dike intersection length, dike azimuth, and 
number of eruptive centers within the repository footprint from output of 
COMBSM and COMBSF. 
For Information Only 
NOTE: Names in the boxes denote software routines listed in Table 3-1. 
Figure 3-1. Flowchart for Computation of Frequency of Intersection of Proposed Repository by a Dike 
ANL-MGR-GS-000001 REV 02 3-4 October 2004 

For information only 
NOTE: Names in boxes denote software routines listed in Table 3-2. 
Figure 3-2. Flowchart for Computation of Conditional Distributions for Length and Azimuth of Intersecting 
Dike and Number of Eruptive Centers within the Repository Given Intersection of Repository 
Footprint by a Dike 

Table 3-3. Software Used to Convert Emplacement Drift End Points for the Repository Footprint from 
Nevada State Plane Coordinates to Universal Transverse Mercator 
Software Name 
Software Tracking 
Computer and Platform 
and Version (V) 
Number 
Description 
Identification 
EarthVision 5.1 
10174-5.1-00 
Commercial GIS software used for 
Silicon Graphics/ 
[DIRS 167994] 
coordinate conversion. 
IRIX 6.5 
3.2 EXEMPT SOFTWARE 
Commercial, off-the-shelf software used in support of this scientific analysis is listed in 
Table 3-4. This software is exempt from the requirements of LP-SI.11Q-BSC, Software 
Management. 
Table 3-4. Exempt Software 
Software Name and 
Version 
(V) 
Software 
Tracking 
Number Description 
Computer and 
Platform 
Identification 
Microsoft Excel, 97 N/A The commercial software, Microsoft Excel, 97 was 
used for plotting graphs and preparing tables. No 
software routines or macros were used with this 
PC, Windows 98 
software to prepare this report. The output was 
visually checked for correctness. 

4. INPUTS 
4.1 DIRECT INPUTS 
The location, a brief description, and the data tracking number (DTN) used as input for this 
scientific analysis report are listed in Table 4-1. The qualification status of data input is provided 
in the Technical Data Management System and listed in the Document Input Reference System 
(DIRS) database. 
Table 4-1. Direct Input Data 
Data Name Data Source DTN 
PVHA (CRWMS M&O 1996 CRWMS M&O 1996 [DIRS 100116] MO0002PVHA0082.000 
[DIRS 100116]): Expert Assessment of [DIRS 148234] 
Volcanic Hazard in the YMR 
Conduit Diameter BSC 2004 [DIRS 169980] LA0407DK831811.001 
[DIRS 170768] 
The primary source of input data for this analysis is the PVHA expert interpretations presented in 
Probabilistic Volcanic Hazard Analysis for Yucca Mountain, Nevada (CRWMS M&O 1996 
[DIRS 100116]). Because this report is an analysis of the PVHA (CRWMS M&O 1996 
[DIRS 100116]), the use of the PVHA as input to this report is appropriate. The PVHA expert 
interpretations are used as inputs to the calculations described in Section 6.5 and Appendix C. 
Interpretations and inputs provided by the PVHA to perform the calculations described in 
Section 6.5 are discussed in Section 6.5.1. The interpretations are also discussed in the 
conceptual framework described in Sections 6.1 through 6.4. The distribution of conduit 
diameters is used in Appendix B to develop a buffer zone surrounding the repository footprint 
that is used to account for the effect of conduit size on the calculation of the frequency of dike 
intersection and the distribution for number of eruptive centers within the repository footprint. 
Other input to this analysis is listed in Table 4-2. 
Table 4-2. Other Direct Input to This Scientific Analysis 
Name Description DTN 
Repository footprint Repository footprint determined from information described N/A 
in BSC 2003 [DIRS 162289] 
All other DTNs presented in this scientific analysis report are not used as direct input to this 
report and are used as reference only. 
4.2 CRITERIA 
The general requirements to be satisfied by the TSPA are stated in 10 CFR 63.114 
[DIRS 156605]. Technical requirements to be satisfied by the TSPA are identified in the Yucca 
Mountain Project Requirements Document (Canori and Leitner 2003 [DIRS 166275]). The 
acceptance criteria that will be used by the Nuclear Regulatory Commission (NRC) to determine 
whether the technical requirements have been met are identified in the Yucca Mountain Review 

Plan, Final Report (NRC 2003 [DIRS 163274]). Criteria that are applicable to this scientific 
analysis report, and details of how the criteria have been addressed, are described in Appendix D. 
The Yucca Mountain Review Plan, Final Report (NRC 2003 [DIRS 163274]) lists acceptance 
criteria pertaining to the above requirements. Criteria that are applicable to this scientific 
analysis report are described in Appendix D. 
The Yucca Mountain Review Plan, Final Report Acceptance Criteria are intended to ensure that 
the requirements of 10 CFR 63.114(a)(c) and (e)(g) [DIRS 156605] are met. 
4.3 CODES, STANDARDS, AND REGULATIONS 
No specific formally established codes, standards, or regulations have been identified as applying 
to this activity, except for those discussed in Section 4.2. This activity does not directly support 
LA design. 

5. ASSUMPTIONS 
This section describes the assumptions used for the analyses in Section 6.5 and Appendix C. 
The calculation of the updated distribution for frequency of intersection of the repository 
footprint by a basaltic dike requires no assumptions because it uses the outputs defined by the 
PVHA (CRWMS M&O 1996 [DIRS 100116]) without modification. The update involves only a 
change in the repository footprint. 
The calculation of conditional distributions for the length and azimuth of intersecting dikes 
within the proposed repository requires no assumptions because it involves only a modification 
of the software to output an intermediate step of the frequency of intersection of the repository 
footprint by a dike calculation. 
The calculation of conditional distributions for the number of eruptive centers within the 
repository footprint requires an assessment of the number of eruptive centers associated with a 
volcanic event and the spatial distribution for eruptive centers along the length of the dike. As 
explained in Section 6.5.2.2, this analysis uses the PVHA experts assessment of volcanic event 
counts and the number of separate eruptive centers to develop a distribution for the number of 
eruptive centers per volcanic event. The number of eruptive centers associated with a volcanic 
event is derived using the following assumptions. 
5.1 USE OF QUATERNARY VOLCANOES 
Assumption: The mapped Quaternary volcanoes in the YMR are representative of the type of 
volcanoes characterized for calculation of the consequences of an eruptive event through the 
proposed repository. For the purposes of this analysis report and for performance assessment 
(PA) calculations, each eruptive center or vent equates to one subsurface conduit. 
Basis: As stated by the Igneous Consequences Peer Review Panel, the history of volcanism 
and eruptive styles of Pliocene to Quaternary volcanoes in the Crater Flat Volcanic Zone (CFVZ) 
represents the best guide to possible future activity at the YMR (Detournay et al. 2003 
[DIRS 169660], Section 2.1.1). Therefore, the characteristics of Quaternary volcanoes in the 
YMR are used to define the distributions for the characteristics of future volcanic events (BSC 
2004 [DIRS 169980]). The assumption that each volcano is associated with a conduit is 
consistent with the description of the eruptive process for YMR volcanoes described in the 
scientific analysis report Characterize Eruptive Processes at Yucca Mountain, Nevada (BSC 
2004 [DIRS 169980]). Volcanoes were also used by the PVHA experts as indicators of the 
occurrence of past volcanic events. 
Use in the Analysis: This assumption is used in Appendix C to derive distributions for the 
number of eruptive centers per volcanic event and the average spacing between eruptive centers. 
Confirmation Status: This assumption needs no further confirmation. 

5.2 ALL VOLCANIC EVENTS PRODUCE AT LEAST ONE ERUPTIVE CENTER 
Assumption: Each hypothetical volcanic event for which the associated dike intersects the 
repository has at least one eruptive center located somewhere along the length of the dike. 
Basis: This assumption is reasonable on the basis of the PVHA expert panels general belief that 
magma that ascends to within a few hundred meters of the surface will produce a surface 
manifestation of the volcanic event (CRWMS M&O 1996 [DIRS 100116], 
Appendix E, pp. RC-10, BC-6, WD-6, WH-6, MK-12). The assumption is conservative because 
the PVHA experts allowed for the possibility that not all past volcanic events reached the surface 
in assessing the rate of volcanic events. The rate of volcanic events used to compute the 
frequency of intersection of the repository footprint by a dike was obtained by multiplying the 
rate based on past volcanic events with observed surface manifestations by a hidden events factor 
greater than or equal to 1.0. The hidden events factor was used by the PVHA experts to account 
for past volcanic events that may not have reached the surface, but did ascend high enough in the 
crust to reach the level of the repository. The hidden event factors assessed by the PVHA 
experts ranged from 1.0 to 5.0 with a composite mean value of approximately 1.4. Assuming all 
future volcanic events will produce an eruptive center produces the maximum rate of eruptive 
center occurrence. 
Use in the Analysis: This assumption is used in Appendix C to develop distributions for the 
number of eruptive centers per volcanic event and in Section 6.5.2.2 in the computation of the 
conditional distribution for number of eruptive centers within the repository. 
Confirmation Status: The assumption is consistent with the expert panels general 
consideration that magma ascending to within a few hundred meters of the surface would erupt 
and need not be confirmed. 
5.3 LOCATION OF ERUPTIVE CENTERS ALONG THE LENGTH OF A DIKE OR 
DIKE SEGMENT 
Assumption: The location of an eruptive center (a volcanic cone and associated conduit) along 
the length of a dike or dike segment is defined by a uniform probability distribution. 
Basis: A distribution for the location of eruptive centers along the length of the dike system 
associated with a volcanic event was not assessed as part of the PVHA. Therefore, an 
assumption about the form of this distribution is needed in order to complete the calculations in 
this analysis report. The assumption of a uniform distribution is justified on the basis that it is 
the minimum information assumption that maximizes the uncertainty in location of the eruptive 
centers. Any other form of a probability distribution requires more information than the range of 
possible locations (in this case, the end points of a dike or dike segment). The assumption is 
conservative because it maximizes the probability for the occurrence of multiple eruptive centers 
within the repository footprint (i.e., no clustering of eruptive centers on a dike segment falling 
partly outside the repository footprint). The PVHA experts did assess the location of the dike 
with respect to the volcanic event, typically specifying that the dike was most likely to be 
centered on the volcanic event. An alternative for Assumption 5.3 would be to assume that the 
assessed location of dikes relative to the volcanic event also applies to the location of eruptive 

centers along the length of a dike; i.e., that eruptive centers are most likely to occur at the center 
of the dike. However, this alternative assumption imposes more information on the process than 
the assumption of a uniform distribution and is expected to produce slightly lower hazard. In 
addition, applying this alternative to the case of multiple eruptive centers during a single event is 
not straightforward. Therefore, the assumption of a uniform distribution is considered to be 
more appropriate. 
Use in the Analysis: This assumption is used in Section 6.5.2.2 in the computation of the 
conditional distribution for number of eruptive centers within the proposed repository. 
Confirmation Status: The assumption does not need to be confirmed because it does not 
impose any additional information beyond the length of the dike, which is obtained from the 
PVHA experts interpretations. Furthermore, in this report an alternative assumption is used in 
which the presence of the repository induces, with a probability of 1.0, the formation of at least 
one eruptive center within the repository footprint, given an intersection by a volcanic event. 

INTENTIONALLY LEFT BLANK 

6. SCIENTIFIC ANALYSIS 
6.1 INTRODUCTION 
In this report, a conceptual framework for volcanism at Yucca Mountain consistent with output 
and results of the PVHA is described. This report describes how this framework and alternative 
conceptual frameworks influence the results of estimations of the probability of dike intersection 
and volcanic eruption at the proposed geologic repository at Yucca Mountain. 
This report summarizes and extends the findings of the PVHA (CRWMS M&O 1996 
[DIRS 100116]). For the PVHA, an expert panel was convened in 1995 to review all pertinent 
data relating to volcanism at Yucca Mountain and based on these data, to quantify both the 
annual probability and associated uncertainty of a volcanic event intersecting a proposed 
repository sited at Yucca Mountain. The data the experts reviewed was comprehensive, 
consisting of two decades of data collected by volcanologists who conducted studies to quantify 
the probability that a future volcanic eruption would disrupt the proposed repository (e.g., 
CRWMS M&O 1998 [DIRS 105347] and references therein). This report also describes the 
relationship between volcanic source zones defined in the PVHA and the current understanding 
of structural controls on volcanism in the YMR. 
The results of the PVHA are a set of alternative models for assessing the volcanic hazard at 
Yucca Mountain, probabilities that each model is the appropriate model, and probability 
distributions for the parameters of the models. As such, the PVHA defines the scientific 
uncertainty in applying models to assess the volcanic hazard. The PVHA experts documented 
the basis for their assessments of the validity of the alternative models in Probabilistic Volcanic 
Hazard Analysis for Yucca Mountain, Nevada (CRWMS M&O 1996 [DIRS 100116], 
Appendix E). Therefore, the results of the PVHA are considered valid for assessing the 
uncertainty in the volcanic hazard at Yucca Mountain. 
In the context of the PVHA, the volcanic hazard is defined as the annual frequency of 
intersection of the repository by a volcanic event. A volcanic event was defined in the PVHA 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 [DIRS 100116], Appendix E). For the 
purposes of the probability models developed in the PVHA and discussed in this report, a 
volcanic event is defined as a point (x,y) 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 probability model by a line element defined in terms of a length, azimuth, and 
location relative to the point event. 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 (e.g., multiple 
dikes) has width or consists of multiple parallel dikes does not significantly affect the 
intersection probability and is not part of the calculations in this report. Both the width of the 
dikes and the number of parallel dikes affect the consequences of an intersection and are 
included in the consequence analyses presented in Number of Waste Packages Hit by Igneous 
Intrusion (BSC 2004 [DIRS 170001]). 

Based on the PVHA outputs and assumptions in Section 5 of this report, probability distributions 
are developed for the length and orientation of intersecting dikes within the repository footprint 
and for the number of eruptive centers located within the repository footprint (conditional on a 
dike intersecting the repository). Lastly, the probability of dike intersection is recalculated based 
on the 2003 repository footprint (BSC 2003 [DIRS 162289]) and the probability of an eruptive 
center(s) forming within the repository footprint is calculated (the latter is a calculation that was 
not included in the PVHA). 
The analysis presented in this report is based on the volcanic hazard model developed in the 
PVHA (CRWMS M&O 1996 [DIRS 100116]). Therefore, the computational methods and 
software used to perform the analysis are based on the original software developed to implement 
the PVHA hazard model. Other software to implement the 1996 PVHA volcanic hazard model 
does not exist. 
6.1.1 Summary of Conceptual Model for Igneous Activity 
This section provides a summary of the conceptual model for igneous activity near Yucca 
Mountain. The conceptual model consists of three components, each related to an aspect of 
igneous processes that may impact the repository. The three components are: 
Igneous Frameworkdescribes the igneous and tectonic history and features of the Yucca 
Mountain region, and the assessment of the history and features by PVHA experts as a 
basis to determine the probability of intersection of the repository by a volcanic event (this 
report). 
Igneous Processesdescribes the physical processes expected to occur during a potential 
future volcanic event (BSC 2004 [DIRS 169980]; BSC 2004 [DIRS 170001]; BSC 2003 
[DIRS 168960]; BSC 2004 [DIRS 170028]; BSC 2004 [DIRS 170026]; BSC 2004 
[DIRS 168504]). 
Post-Igneous Processesdescribes the surficial processes of erosion and deposition 
expected to occur when a contaminated tephra sheet covers the landscape and is 
redistributed following a potential future volcanic eruption through the repository 
(BSC 2004 [DIRS 170026]). 
6.1.1.1 Igneous Framework 
Basaltic volcanism is the most common form of volcanism on earth and has occurred repeatedly 
throughout the western United States over the past 5 million years (Perry et al. 1998 
[DIRS 144335], Figure 4.1). Basaltic volcanoes, primarily scoria cones, generally form in 
clusters of several, to several hundred volcanoes that define a volcanic field. In the western 
United States, the largest basaltic volcanic fields erupted approximately 100 to 300 cubic 
kilometers of lava, generally over periods of less than a few million years (Perry et al. 1998 
[DIRS 144335], Figure 4.2). The larger volcanic fields tend to occur along the margins of major 
physiographic provinces, such as the Colorado Plateau and Great Basin. Smaller-volume 
volcanic fields of less than tens of cubic kilometers tend to occur within the interior of the Basin 
and Range Province, including the interior of the Great Basin where Yucca Mountain is located. 
Basaltic volcanism in the western United States is generally correlated with regions of 

extensional tectonics. It is not uncommon for relatively large-volume basaltic volcanism to be 
spatially and temporally associated with regions of relatively high extension rate (Section 6.2 of 
this report). 
The earliest volcanism in the Yucca Mountain region was dominated by a major episode of 
caldera-forming, silicic volcanism that occurred primarily between about 15 and 11 million years 
ago, forming the southwestern Nevada volcanic field (Sawyer et al. 1994 [DIRS 100075]). 
Silicic volcanism was approximately synchronous with a major period of extension, which 
occurred primarily between 13 and 9 million years ago (Sawyer et al. 1994 [DIRS 100075], 
Figure 4). Silicic volcanism has not occurred in the Yucca Mountain region in the last 7 or 
8 million years and is not included as part of the igneous conceptual model. The commencement 
of basaltic volcanism occurred during the latter part of the silicic caldera-forming phase as 
extension rates waned. Small-volume basaltic volcanism has continued into the Quaternary as 
part of a general decline in eruption volume over the past 11 million years (Perry et al. 1998 
[DIRS 144335], Chapter 2). 
Post-Miocene volcanism (younger than 5 million years) has occurred in six episodes in the 
Yucca Mountain region, at approximately 4.8, 3.7, 3.1, 1.0, 0.4, and 0.08 million years ago, as 
summarized in Figure 6-1 and Table 6-2 (Perry et al. 1998 [DIRS 144335] Table 2.B; Heizler 
et al. 1999 [DIRS 107255]). The total eruption volume of the post-Miocene 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 about 0.5 km3 (Perry et al. 1998 
[DIRS 144335], Table 3.1). The Quaternary volcanoes are of small volume (about 0.1 km3 or 
less) and typically consist of a single main scoria cone surrounded by a small field of aa basalt 
flows, which commonly extend about 1 km from the scoria cone (Section 6.2 of this report). 
In addition to surface exposures of basaltic volcanism, several magnetic anomalies in the 
Amargosa Desert identified in aeromagnetic surveys conducted in the early 1990s have 
characteristics that indicate buried basaltic volcanic centers (Langenheim et al. 1993 
[DIRS 148622], p. 1840). One of these anomalies ([DIRS 148622], Anomaly B of Langenheim 
et al. 1993), was drilled and basalt cuttings were dated at 3.85 million years using the 40Ar/39Ar 
method (CRWMS M&O 1998 [DIRS 105347], Chapter 2, Table 2.B). A more recent survey 
conducted by the USGS in 1999 (OLeary et al. 2002 [DIRS 158468]) suggests the possibility of 
additional buried volcanic centers. Results of sensitivity studies indicate these data do not 
significantly impact the results of the PVHA (Section 6.5.4.1 of this report). 
The decreased eruptive volume through time, together with geochemical evidence (Perry et al. 
1998 [DIRS 144335], p. 4-8), indicates that the intensity of mantle melting processes that 
produce basaltic magma beneath the Yucca Mountain region has waned over the past 5 million 
years (Perry and Crowe 1992 [DIRS 106488], p. 2359). Considered in terms of total eruption 
volume, frequency of eruptions, and duration of volcanism, basaltic volcanic activity in the 
Yucca Mountain region in the past 5 million years defines one of the least active basaltic 
volcanic fields in the western United States (CRWMS M&O 1998 [DIRS 105347], Figure 4-2). 

The probability of intersection of the repository footprint by a volcanic event depends on the 
recurrence rate of volcanic events multiplied by the likelihood that a volcanic event will intersect 
the repository (CRWMS M&O 1996 [DIRS 100116], Section 3.1.1). Because volcanic events 
have occurred very infrequently on average in the past 5 million years (every few hundred 
thousand years), recurrence rates for volcanic events are proportionally low (10-5 to 10-6 events 
per year). The low recurrence rate of volcanism in the Yucca Mountain region is the primary 
reason that the probability of intersection is extremely low, with a mean of 1.7  10-8 
intersections per year (Section 6.5.3.1 of this report), or approximately one in 6,000 over the 
10,000-year performance period of the repository. The probability that a volcano will erupt 
through the repository is conditional on dike intersection and is slightly less than the probability 
of dike intersection (mean of 1.3  10-8 eruptions per year) (Section 6.5.3.2 of this report), 
because a volcano may not necessarily erupt at a location along the length of an intersecting dike 
that lies within the repository footprint (Section 6.5.1.3 of this report). 
Post-Miocene volcanoes of different ages in the Yucca Mountain region are spatially clustered 
(Figure 6-1). Clustering of volcanism is potentially significant to probability models because it 
indicates spatial control on location of past volcanism that may predict the location of future 
volcanism. The most significant clustering of post-Miocene volcanism occurs in the Crater Flat 
structural domain (Fridrich et al. 1999 [DIRS 107333), both in terms of number of episodes 
(three of six post-Miocene episodes) and proximity to Yucca Mountain (Figure 6-1). Two of the 
three episodes of Quaternary volcanism, including the youngest episode at Lathrop Wells, occur 
within the Crater Flat structural domain, as does the repository. The structural and geophysical 
features of the domain and the extent to which they influence the location of volcanism within 
the domain were key factors in conceptual models of volcanism and assessments of the 
probability of volcanic disruption of the repository. 
Structural data indicate that the southwestern part of the Crater Flat domain is more extended 
than the northeastern part of the domain (Fridrich 1999 [DIRS 118942]; Fridrich et al. 1999 
[DIRS 107333]). Post-Miocene basaltic centers of the Crater Flat domain lie within the extended 
southwestern part of the domain. The youngest volcano in the Crater Flat domain, the 80 
thousand years ago (ka) Lathrop Wells volcano, lies within the most active site of late 
Quaternary faulting in the Crater Flat domain (Fridrich et al. 1999 [DIRS 107333], p. 211). 
Thus, a close spatial and temporal relationship exists between sites of extension and volcanism 
throughout the Crater Flat domain (Fridrich et al. 1999 [DIRS 107333], p. 211). The restriction 
of three episodes of post-Miocene volcanism to the more extended part of the Crater Flat domain 
suggests that volcanism is less likely to occur at Yucca Mountain, which lies outside of the more 
extended part in an area where no post-Miocene volcanism has occurred (Fridrich et al. 1999 
[DIRS 107333], p. 210, Figure 17a). The PVHA experts recognized the close association 
between volcanism and areas of maximum extension in the Yucca Mountain region (CRWMS 
M&O 1996 [DIRS 100116], pp. RC-5, BC-12, AM-5, MS-2, GT-2). Subsequent geologic and 
geophysical studies provide corroborative evidence that areas of maximum extension in the 
Crater Flat domain correspond closely to volcanic source zones defined in the PVHA 
(Stamatakos et al. 1997 [DIRS 138819]; Brocher et al. 1998 [DIRS 100022]; Fridrich et al. 1999 
[DIRS 107333]). 

DTNs: LAFP831811AQ97.001 [DIRS 144279]; MO0003YMP98126.001 [DIRS 149605] (both are reference only). 
Source: Numbers by each volcano indicate approximate age in millions of years (CRWMS M&O 1998 
[DIRS 105347], Chapter 2, Tables 2.B and 2.C; DTN: LAFP831811AQ97.001). 
TM =Thirsty Mesa; PCF = Pliocene Crater Flat; BM = Buckboard Mesa; QCF = Quaternary Crater Flat; (MC = Makani 
Cone; BC = Black Cone; RC = Red Cone; LC = Little Cones); HC = Hidden Cone; LBP = Little Black Peak; 
LW = Lathrop Wells 
Figure 6-1. Location and Age of Post-Miocene (less than 5.3 million years (m.y.)) Volcanoes (or Clusters 
Where Multiple Volcanoes Have Indistinguishable Ages) in the Yucca Mountain Region 

6.1.1.2 Igneous Processes 
The formation of a volcanic event in the Yucca Mountain region begins with ascent of magma 
from the mantle source as a dike (magma-filled crack). During magma ascent and 
decompression, volatile gases, such as H2O and CO2, escape, increasing the volume of the 
magma. This resulting volume expansion drives the basaltic magma upward through the upper 
few kilometers of crust. Because volatiles are concentrated near the crack tip of the ascending 
magma, the start of volcanism is typically characterized by pyroclastic eruptions (volcanic 
explosions and aerial expulsion of clastic rock from a volcanic vent) of gas-rich magma. Based 
on analogue studies, the concentration of volatile species in basalts of the Yucca Mountain 
region is likely to range from 1 to 3 wt %, or more (BSC 2004, [DIRS 169980], Section 7). This 
range is higher than in most alkali (sodium or potassium-rich) basalt magmas, possibly because 
the volatile species originated in small percentages of partial melt of a hydrous lithospheric 
mantle source. The incompatible-element-enriched nature of these alkali basalts relative to other 
alkali basalts in the western United States is consistent with this conclusion (BSC 2004 
[DIRS 169980], Sections 6.3.2 and 6.3.3). 
Basaltic magma is transported from a region of melting in the mantle to the surface through 
dikes. In the Yucca Mountain region, dikes are typically 1 to 2 m in width and have an average 
length of 4 km (CRWMS M&O 1996 [DIRS 100116]). The longest expected dike length in the 
Yucca Mountain region is about 10 km. Based on the regional stress field of the upper crust, 
dikes are expected to have an orientation that centers on N30E, although other orientations are 
possible and are observed within the region (BSC 2004, [DIRS 169980], Section 6.3). 
Although an ascending dike could be influenced by topographic or thermal-mechanically 
induced stress, the model described here assumes that the dike propagates through the repository 
(BSC 2004 [DIRS 170028], Section 6.3.9.2.2.2). As the dike approaches the level of the drifts, 
the crack tip advances ahead of the magma front and will intersect the repository drifts first. 
When the magma front within the dike reaches the level of the repository, magma will be 
available to flow into drifts. There are two possibilities for the behavior of the magma as it 
approaches the drifts. One is that the magma steadily releases gas into the host rock as it 
approaches the drifts so that a relatively gas-poor magma flows effusively into the drifts. A 
more likely scenario, based on analogue studies of historic eruptions, is that the initial magma 
encountering the drifts will be gas-rich, resulting in pyroclastic flow into the drifts. In either 
case, the dike tip will precede the magma by several seconds to a few hours. Because the entry 
of magma from the dike into the drift is not necessarily instantaneous with intersection, it is 
unlikely that dike intersection will result in an abrupt explosion into the drift (BSC 2004 
[DIRS 170028]). At the analogue Parcutin volcano, the initial crack broke the surface several 
hours before the first manifestation of weak pyroclastic eruptions began (BSC 2004 
[DIRS 170028]). 
The most likely scenario following dike intersection of repository drifts is that the dike continues 
to follow the path established by the dike tip and erupts to the surface without being influenced 
by the presence of the repository. An alternative scenario is that the lateral diversion of magma 
into drifts results in sufficient pressurization of drifts to propagate a dike to the surface at a 
location some distance from the site of the initial dike intersection. This scenario could 
potentially lead to more waste entrained during an eruption compared to the case of conduits 

developed only above the site of initial dike intersection. The amount of waste potentially 
entrained in this scenario would depend on the length of drifts that transport magma to the site of 
the down-drift dike, assuming the magma is able to incorporate and transport waste. 
The rate and degree to which an intersected drift fills with magma depends on variables, such as 
magma rise rate, magma viscosity, and the nature (effusive or pyroclastic) of the flow into the 
drifts (BSC 2004 [DIRS 170028]). Magma rise rates are assumed to range between 1 and 
10 m/s, while viscosities are assumed to range between 10 and 100 Pas (BSC 2004 
[DIRS 169980]). 
The potential ascent of dikes and the formation of conduits at Yucca Mountain has been 
analyzed relative to the configuration of the repository, which consists of approximately one 
hundred waste-emplacement drifts of 5-m diameter, spaced about 80 m apart and encompassing 
a total area of approximately 5 km2. The number of waste-emplacement drifts intersected would 
depend on the orientation of a dike system intersecting the repository, the number of dikes in a 
dike swarm, and the lengths of the dikes lying within the repository footprint. 
Formation of a volcano begins with a fissure eruption as a dike or dike swarm intersects the 
surface (BSC 2004 [DIRS 169980]). The formation of a basaltic volcano is complex with total 
eruption durations typically ranging from weeks to months and possibly years. During the 
eruption, activity includes effusion of gas-poor lava flows and explosive, gas-rich pyroclastic 
eruptions. Both types of eruptions can occur simultaneously or in alternating cycles that include 
periods of inactivity (BSC 2004 [DIRS 169980], Section 6.4). Intrusive processes 
simultaneously occur in the subsurface. Analogue studies of shallowly eroded volcanoes in the 
Yucca Mountain region demonstrate that subsurface intrusive processes may include the 
formation of multiple dikes (dike swarm) and sills (horizontal emplacement of magma into the 
host rock). Evolution of the intrusion beneath an erupting volcano can also lead to changes in 
the location or migration of eruptive vents during the period of eruption (BSC 2004 
[DIRS 169980], Sections 6.3.1 and 6.3.3). 
At a relatively early stage of the eruption, the fissure eruption localizes to one or more conduits 
that transport magma to the surface for the remainder of the eruption. Conduit formation 
provides a mechanism to transport waste to the surface. The physical processes that would 
influence the exact location of a conduit within the repository (e.g., at drifts or within pillars) 
depend on multiple complex factors. Conduit localization is assumed to be random along the 
length of a given dike (BSC 2004 [DIRS 169980], Section 6.3.1.1). Conduit diameters are 
typically a few tens of meters. A value of 150 m is used in the TSPA-LA as an upper bound for 
conduit diameter. Basalt conduit depths probably reach several hundred meters and are assumed 
in this model to reach the depth of the repository to allow interaction with waste emplacement 
drifts (BSC 2004 [DIRS 169980], Sections 6.3.3 and 6.3.1). 
Magma flux through the conduit during explosive phases of the eruption typically varies from 
approximately 104 kg/s for normal Strombolian (eruption of ballistic magma fragments) activity 
to approximately 106 kg/s for violent Strombolian (sustained eruption column producing an ash 
plume) activity (BSC 2004 [DIRS 169980], Section 6.3). Commonly, high magma flux and 
explosive eruptions occur during the early stage of the eruption, with an increase in effusive 

(lava flows) activity as the eruption proceeds. At Lathrop Wells, however, field observations 
indicate that early volcanism was Strombolian, followed by violent Strombolian eruptions. 
Lathrop Wells is one of eight small-volume (about 0.01 km3 to 0.1 km3) basaltic volcanoes that 
formed during the Quaternary within 50 km of Yucca Mountain (Figure 6-1). Based on 
observations of preserved eruptive deposits, these volcanoes share a similar eruptive history of a 
pyroclastic phase that led to the formation of a main scoria cone and effusion of aa lava flows. 
The scoria cone and lava flow deposits, excluding tephra fall from violent eruptions, typically 
cover a few square kilometers. The fundamental similarity of all Quaternary volcanoes in the 
YMR suggests that a future volcano that could potentially disrupt the repository will share these 
same characteristics (BSC 2004 [DIRS 169980], Section 6.3.3). 
A violent Strombolian eruption is the most energetic eruption expected in the Yucca Mountain 
region (BSC 2004 [DIRS 169980]; BSC 2004 [DIRS 170026]). These eruptions involve a 
sustained, vertical eruption column (a gas-particle jet) that propels the tephra to heights of 
several kilometers above the scoria cone. The tephra plume eventually reaches a level of neutral 
buoyancy in the atmosphere, spreads laterally as an anvil cloud, and is transported downwind. 
Tephra particles fall out of the vertical eruption column and the anvil-shaped cloud. The 
atmospheric dispersal and deposition of the fine tephra forms a sheet-like deposit of volcanic ash 
characterized by decreasing thickness and grain size with distance from the volcano. Tephra 
deposits might extend 10 km or more from the volcano and cover several hundred square 
kilometers (BSC 2004 [DIRS 169980], Section 6.3.3). In the TSPA-LA, only the violent 
Strombolian phase of volcanism is modeled for atmospheric dispersal because this is the only 
mechanism for the ash column to reach the heights necessary to deposit ash 18 km downwind 
from the volcano to the location of the RMEI (BSC 2004 [DIRS 169980], Sections 6.3.3.4.1 
and 6.3.3.4.3). 
If a dike intersects the repository, waste packages can be disrupted by magma entering the 
emplacement drifts and contacting the waste packages (intrusion case), or by direct entrainment 
of waste packages within conduits to the surface (eruption case). In the intrusion case, the 
number of packages disrupted depends on the number of emplacement drifts filled by magma, 
which is conditional on the number of drifts intersected by dikes. For the eruption case, the 
number of packages disrupted depends on the diameter and number of conduits that form within 
the repository footprint (BSC 2004 [DIRS 170001], Section 6.4). 
If magma fills a drift, post-emplacement processes become important (BSC 2004 
[DIRS 170028]). Magmatic volatiles are expected to degas from the cooling magma within the 
intruded drift and infiltrate the tuff host rock. Thermal energy from the cooling magma would 
also be transferred into the host rock (BSC 2004 [DIRS 170028], Section 6.9). 
6.1.1.3 Post-Igneous Processes 
After the deposition of a violent Strombolian tephra sheet, volcanic ash is subject to 
redistribution by normal sedimentary processes (erosion and deposition) (BSC 2004 
[DIRS 170026]). A hypothetical violent Strombolian eruption through the repository would 
produce tephra dispersed to the northeast, blanketing part of the Fortymile Wash drainage system 
with particles less than 2 mm in size (BSC 2004 [DIRS 170026], Section 6). Redistribution of 

the tephra would be dominated by southward fluvial transport in Fortymile Wash. Tephra 
deposited on slopes would be moved downslope as small debris flows, eventually reaching a 
distributary channel at the base of a slope. The general result is downstream movement of 
tephra-bearing sediment that is progressively diluted and dispersed. This mixing and dilution of 
the sedimentary components from the drainage system occurs in environments where sediment is 
transported by water or wind. Such mechanisms might transport contaminated ash to the RMEI, 
even if the original volcanic eruption did not deposit tephra at the reasonably maximally exposed 
location. 
6.1.2 Features, Events, and Processes 
Table 6-1 describes the features, events, and processes (FEPs) that are included in the TSPA-LA 
through the use of the results of the analysis described in this document. The complete set of 
FEPs is contained in DTN: MO0407SEPFEPLA.000 [DIRS 170760]. This analysis report 
addresses the annual frequency (essentially equivalent to annual probability) of the events 
addressed by the FEPs. The effects of these events are addressed by the reports described in 
Section 6.1.1.2. 
Table 6-1. Included Features, Events, and Processes for This Scientific Analysis Report 
FEP Number FEP Name Relevant Section 
1.2.04.03.0A Igneous intrusion into Section 6.5 describes the 
repository calculation of the annual 
frequency of igneous 
intrusion into the repository 
1.2.04.06.0A Eruptive conduit to surface 
intersects repository 
Section 6.5 describes the 
calculation of the annual 
frequency of intersection of 
the repository by an 
eruptive conduit 
6.1.3 Summary of Output Data 
The primary output data of this analysis are contained in the following two data sets: 
 
Output DTN: LA0302BY831811.001 contains the computed distribution for frequency 
of intersection of the repository footprint by a basaltic dike and the conditional 
distributions for the length and azimuth of intersecting dikes within the repository 
footprint and conditional distributions for the number of eruptive centers. These outputs 
are described in Section 6.5.3.1 and 6.5.3.2. 
 
Output DTN: LA0307BY831811.001 contains the distribution for the frequency of 
intersection of the repository in a modified format appropriate for submittal to TSPA. 
File PVHA-4P.DST (Output DTN: LA0302BY831811.001) was modified by adding a 
zero point and by eliminating a few intermediate points that did not result in a 
perceptible increase in the cumulative probability distribution. The resulting modified 
file, PVHA-4PA.DST in Output DTN: LA0307BY831811.001, conforms to the TSPA 
requirement for a monotonic increase in an input discrete probability distribution. 

Output DTN: LA0307BY831811.001 also contains data presented in summary tables in 
Section 6.5.3 and 7.1. 
The output data in these two output DTNs are based on the 2003 repository footprint (BSC 2003 
[DIRS 162289]) and are to be used as input to revisions of the Number of Waste Packages Hit by 
Igneous Intrusion report (BSC 2004 [DIRS 170001]), and as inputs to the TSPA-LA. These data 
were computed during REV 01 of this report (BSC 2003 [DIRS 163769]) and have not changed 
from that revision. 
In addition, there are three other data sets associated with this analysis report: 
 
Output DTN: LA0303BY831811.001 contains the repository footprint polygon 
developed in Appendix B and data used to generate figures and tables in Section 6 of 
this report. The data files are referenced by the figure and table numbers in REV 01 of 
this report (BSC 2003 [DIRS 163769]). 
 
Output DTN: LA0009FP831811.001 contains the data files for the PVHA 1996 
volcanic hazard model used as input to the calculations and data used to generate some 
figures in Section 6 and Appendix C. This DTN also contains output files from Rev 0 of 
this report based on earlier repository designs. 
 
Output DTN: LA0009FP831811.004 contains additional data from Appendix C and 
output files from Rev 0 of this report based on earlier repository designs. 
Section 6.5.4 presents sensitivity analyses conducted to assess the impact of recent data and 
proposed models for volcanic event locations. The results of these sensitivity studies are for 
information only and are not to be used for purposes of assessing repository performance. They 
were conducted with non-qualified input data and non-qualified software. 
6.2 VOLCANIC HISTORY OF THE YUCCA MOUNTAIN REGION 
Because several Quaternary basaltic volcanoes exist within 20 km of the proposed Yucca 
Mountain repository (Figure 6-1), volcanism must be assessed as a possible future disruptive 
event in TSPA. Two major types of volcanism have occurred in the YMR: an early phase of 
Miocene silicic volcanism, the recurrence of which is considered extremely unlikely in the next 
million years, and a more recent phase of Miocene and post-Miocene basaltic volcanism that 
indicates recurrence of volcanism somewhere in the YMR is likely (Reamer 1999 
[DIRS 119693], p. 5). 
The earliest volcanism in the YMR was dominated by a major episode of caldera-forming, silicic 
volcanism that occurred primarily between approximately 15 and 11 m.y., forming the 
southwestern Nevada volcanic field (Sawyer et al. 1994 [DIRS 100075]). Silicic volcanism was 
approximately coincident with a major period of extension, which occurred primarily between 
13 and 9 m.y. (Sawyer et al. 1994 [DIRS 100075], Figure 4). Yucca Mountain is an uplifted, 
erosional remnant of voluminous ash-flow tuff deposits formed during the early phase of silicic 
volcanism. 

The commencement of basaltic volcanism occurred during the latter part of the caldera-forming 
phase, as extension rates waned, and small-volume basaltic volcanism has continued into the 
Quaternary. In terms of eruption volume, the 15 m.y. history of volcanism in the YMR is 
viewed as a magmatic system that peaked between 13 and 11 m.y. with the eruption of over 
5000 km3 of ash flow tuffs and has been in decline since, with relatively minor volumes of basalt 
erupted since 11 m.y. ago (CRWMS M&O 1998 [DIRS 100129], Figure 3.9-2). Approximately 
99.9 percent of the volume of the southwestern Nevada volcanic field erupted by about 7.5 m.y. 
ago 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 entirely of basalt erupted since 7.5 m.y. ago (CRWMS 
M&O 1998 [DIRS 100129], Figure 3.9-5). Considered in terms of total eruption volume, 
frequency of eruptions, and duration of volcanism, basaltic volcanic activity in the YMR defines 
one of the least active basaltic volcanic fields in the western United States (e.g., CRWMS M&O 
1998 [DIRS 105347], Chapter 4, Figure 4-2, for post-Miocene basalts of Crater Flat). 
Post-caldera basalts in the YMR can be divided into two episodes: Miocene (eruptions between 
approximately 9 and 7.3 m.y.) and post-Miocene (eruptions between approximately 4.8 and 
0.08 m.y.). The time interval of about 2.5 m.y. between these episodes is the longest eruptive 
hiatus of basalt in the YMR during the last 9 m.y. (CRWMS M&O 1998 [DIRS 105347], 
Chapter 3, Table 3.1). This eruptive hiatus also marks a distinct shift in the locus of post-caldera 
basaltic volcanism in the YMR to the southwest (CRWMS M&O 1998 [DIRS 100129], 
Figure 3.9-6). The Miocene basalts and post-Miocene basalts are thus, both temporally and 
spatially distinct. This observation emphasizes the importance of considering the age and 
location of the post-Miocene basalts (approximately the past 5 m.y. of the volcanic history of the 
YMR) when calculating the volcanic hazard to the proposed Yucca Mountain repository. The 
PVHA experts almost exclusively considered the time period of interest to be post5 m.y. (with 
significant weight given to the post1 m.y. period) as the time period of interest in assessing 
volcanic hazard at Yucca Mountain (CRWMS M&O 1996 [DIRS 100116], Figure 3-62). 
The post-Miocene basalts formed during at least six episodes of volcanism (based on age 
groupings) that occurred within 50 km of the proposed Yucca Mountain repository (Figure 6-1). 
These six episodes, in order of decreasing age, consist of the: 
 
Basalt of Thirsty Mesa 
 
Pliocene Crater Flat and Amargosa Valley 
 
Buckboard Mesa 
 
Quaternary Crater Flat 
 
Hidden Cone and Little Black Peak (the Sleeping Butte centers) 
 
Lathrop Wells. 
Three basalt episodes are in, or near the Crater Flat topographic basin within 20 km of Yucca 
Mountain. Several aeromagnetic anomalies in the Amargosa Valley have characteristics that 
indicate buried basaltic volcanic centers (Langenheim et al 1993 [DIRS 148622], p. 1840). One 
of these anomalies (Anomaly B of Langenheim et al. 1993 [DIRS 148622]) was drilled and 
basalt cuttings were dated at 3.85 m.y. using the 40Ar/39Ar method (CRWMS M&O 1998 
[DIRS 105347], Chapter 2, Table 2.B). Because of the similarity in age to the 3.75 m.y. Pliocene 

Crater Flat episode, the buried basalts of Amargosa Valley are considered here as part of the 
same episode. 
The total eruption volume of the post-Miocene 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 1998 [DIRS 100129], Figure 3.9-2; 
Table 3-3). All of the Quaternary volcanoes are similar because they are of small volume 
(approximately 0.1 km3 or less, Table 6-2) 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. 
Table 6-2. Estimated Volume and 40Ar/39Ar Agea of Quaternary Volcanoes in the Yucca Mountain 
Repository 
Volcano Volume (km3)b Volume (km3)c Age (m.y.)f 
Makani Cone 0.006 1.161.17 
Black Cone 0.105 0.07c 0.941.10 
Red Cone 0.105 0.921.08 
Little Cones 0.002 >0.01c,d 0.771.02 
Hidden Cone 0.03 0.320.56 
Little Black Peak 0.03 0.360.39 
Lathrop Wells Cone 0.14 0.086e 0.0740.084 
DTNs: LA0004FP831811.002 [DIRS 149593]; LAFP831811AQ97.001 [DIRS 144279] (both are used for 
reference only).
a
40Ar/39Ar dates provide the most complete and self-consistent chronology data set for Quaternary volcanoes 
of the YMR. A full discussion of other chronology methods used to date basaltic rocks in the YMR can be 
found in CRWMS M&O (1998 [DIRS 105347], Chapter 2). Other chronology methods may not provide 
b 
consistent or accurate estimates of the time of eruption. 
CRWMS M&O (1998 [DIRS 105347], Chapter 3, Table 3.1), (DTN: LA0004FP831811.002 [DIRS 149593]). 
d 
Stamatakos et al. (1997 [DIRS 138819], p. 327). 
Accounts for volume of buried flows detected by ground magnetic surveys. 
e 
BSC (2004 [DIRS 169980]), Table C-18), (DTN: LA0305DK831811.002 [DIRS 164026]). Minimum volume 
based on calculated volume of fall sheet, cone, and flows. 
f 
Range of ages from CRWMS M&O (1998 [DIRS 105347], Chapter 2, Table 2.B). Lathrop Wells ages (Heizler 
et al. 1999 [DIRS 107255], Table 3) represent the range of plateau ages measured, except for sample LW157, 
a statistical outlier (DTN: LAFP831811AQ97.001 [DIRS 144279]). 
The seven or eight (if Little Cones is counted as two volcanoes) Quaternary volcanoes in the 
YMR 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 [DIRS 100973], p. 328). Five 
of seven Quaternary volcanoes are in or near Crater Flat and lie within 20 km of the Yucca 
Mountain site (Figure 6-1). Models that attempt to relate volcanism and structural features in the 
YMR have emphasized the Crater Flat basin because of the frequency of volcanic activity 
associated with Crater Flat and its proximity to the proposed Yucca Mountain repository 
(e.g., Smith et al. 1990 [DIRS 101019], p. 84; Connor and Hill 1995 [DIRS 102646], p. 10122). 

6.3 THE PROBABILISTIC VOLCANIC HAZARD ANALYSIS 
In 1995 to 1996, the DOE sponsored the PVHA project to assess the probability of a future 
volcanic event intersecting the proposed repository at Yucca Mountain. To ensure that a wide 
range of approaches was considered for the PVHA, the DOE identified 10 experts in the field to 
participate in the project and evaluate the data. Their evaluations (elicitations) were then 
combined to produce an integrated assessment of the volcanic hazard that reflects a range of 
alternative scientific interpretations. This assessment, which focused on the volcanic hazard at 
the site expressed as the probability of intersection of the proposed repository by a basaltic dike, 
provided input to an assessment of volcanic risk. 
6.3.1 The Probabilistic Volcanic Hazard Analysis Process 
The major procedural steps in the PVHA were selecting the expert panel members, identifying 
the technical issues, eliciting the experts judgments, applying temporal and spatial aspects of 
probability models, and compiling and presenting the results. 
6.3.1.1 Selecting the Expert Panel Members 
From more than 70 nominees, 10 individuals were selected to participate in the PVHA project. 
Efforts were made to balance the panel with respect to technical expertise (geology, 
geochemistry, and geophysics) and institutional/organizational affiliation. The 10 experts and 
their affiliations are listed in Table 6-3 (CRWMS M&O 1996 [DIRS 100116], Table 1-2). 
Table 6-3. Probabilistic Volcanic Hazard Analysis Panel Members 
Expert Abbreviation Affiliation 
Dr. Richard W. Carlson RC Carnegie Institute of Washington 
Dr. Bruce M. Crowe BC Los Alamos National Laboratory 
Dr. Wendell A. Duffield WD United States Geological Survey, Flagstaff 
Dr. Richard V. Fisher RF University of California, Santa Barbara (Emeritus) 
Dr. William R. Hackett WH WRH Associates, Salt Lake City 
Dr. Mel A. Kuntz MK United States Geological Survey, Denver 
Dr. Alexander R. McBirney AM University of Oregon (Emeritus) 
Dr. Michael F. Sheridan MS State University of New York, Buffalo 
Dr. George A. Thompson GT Stanford University 
Dr. George P. L. Walker GW University of Hawaii, Honolulu 
Source: DTN: MO0002PVHA0082.000 [DIRS 148234]. 
6.3.1.2 Identifying Technical Issues 
The PVHA panel of experts convened between February and December 1995. A technical 
facilitator/integrator led carefully structured, intensive interactions among the panel members. 
The experts participated in workshops, field trips, and other interactions that were used to 
identify sources of agreement and disagreement among them. 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 consideration of alternative interpretations. In all the interactions, 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. 
At the core of the PVHA project were four workshops. The primary objective of the workshops 
was to ensure the experts understanding of the issues, alternative volcanic hazard models, and 
the available data on which they would base their technical assessments. The first three 
workshops focused on the data, volcanic hazard models, and interpretations relevant to the 
PVHA. The workshops included presentations of data and interpretations by technical 
specialists from the Los Alamos National Laboratory, the USGS, the University of Nevada, 
Las Vegas, and the Center for Nuclear Waste Regulatory Analysis, as well as from some PVHA 
experts. During the fourth workshop, the experts reviewed the preliminary assessments 
developed by the panel members, after which the individual elicitations were revised, based on 
feedback received. Two field trips held during the course of the PVHA provided the opportunity 
for the panel members to observe geologic relationships pertaining to eruptive style, the 
definition of volcanic events, and the distribution and timing of volcanic activity in the YMR. 
6.3.1.3 Temporal and Spatial Aspects of Probability Models 
Before the third PVHA workshop, an interactive meeting was held for the benefit of the expert 
panel in order to focus on the methods available to calculate volcanic hazard. The methods were 
used to calculate the two main aspects of volcanic hazard probability models: the temporal and 
spatial aspects. 
Temporal models describe the frequency of occurrence of volcanic activity and include 
homogeneous and non-homogeneous models. Many of the 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. Non-homogeneous 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 believed was relevant to hazard 
analysis. 
Spatial models describe the spatial distribution (location) of future volcanic activity. The most 
common PVHA models considered the future occurrence of volcanoes to be homogeneous 
within particular defined regions or source zones (CRWMS M&O 1996 [DIRS 100116], 
Figure 3-62). Source zones were defined based on several criteria: the spatial distribution of 
observed basaltic volcanoes (especially post-5 m.y. volcanoes), structurally-controlled regions, 
regions defined based on geochemical affinities, tectonic provinces, and other criteria. 
Non-homogeneous parametric spatial distributions of future volcano occurrences were also 
modeled (for example, a model was developed showing that the location of future volcanoes will 
follow a bivariate Gaussian distribution based on the location of volcanoes in Crater Flat). 
Finally, non-homogeneous, 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. 
6.3.1.4 Eliciting the Experts Judgments 
Formal elicitation followed the third workshop. The process consisted of a two-day individual 
interview with each expert. To provide consistency, the same interview team was used for all 
elicitations. Following the elicitation interview, each expert was provided with a written 
summary of his elicitation, which was prepared by the interview team. The expert reviewed and 
clarified the summary and had the opportunity to revise any assessments. To promote a full 
understanding of each individuals judgment, the preliminary assessments made by each member 
of the expert panel were presented and discussed at the fourth workshop. Following this 
workshop, each expert had a final opportunity to revise his assessments before the results of the 
PVHA were finalized (CRWMS M&O 1996 [DIRS 100116], Appendix E). 
6.3.1.5 Probabilistic Volcanic Hazard Analysis Results and Uncertainty 
The product of the PVHA was a quantitative assessment of the probability of a volcanic event 
intersecting the proposed repository and the uncertainty associated with the assessment 
(CRWMS M&O 1996 [DIRS 100116], 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 PVHA components are described in 
Probabilistic Volcanic Hazard Analysis for Yucca Mountain, Nevada (CRWMS M&O 1996 
[DIRS 100116], Section 4.2). 
Each of the 10 experts independently arrived at a probability distribution for the annual 
frequency of intersection of the repository footprint by a dike that typically 
spanned approximately 2 orders of magnitude (CRWMS M&O 1996 [DIRS 100116], 
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 that reflected the uncertainty across the entire expert panel (CRWMS M&O 1996 
[DIRS 100116], Figure 4-32). The individual experts distributions were combined using equal 
weights to obtain the aggregate probability distribution. The mean value of the aggregate 
probability distribution was 1.510-8 dike intersections per year, with a 90 percent confidence 
interval of 5.410-10 to 4.910-8 (CRWMS M&O 1996 [DIRS 100116], p. 4-10). Note that these 
values are updated in this report for the 2003 repository footprint (BSC 2003 [DIRS 162289]) in 
Section 6.5.3. 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 
[DIRS 100116], Figure 4-32). The variance for frequency of intersection defined by the 
composite distribution was disaggregated to identify the contributions from each of the sources 
of uncertainty, including variability between the experts interpretations (CRWMS M&O 1996 
[DIRS 100116], Figure 4-33). Most of the uncertainty in characterizing the hazard arose from 
uncertainty in an individual experts interpretations of the hazard rather than differences in 
scientific interpretation between the experts (CRWMS M&O 1996 [DIRS 100116], p. 4-10, 
Figure 4-33). The probability distribution arrived at by the PVHA accounted for undetected 
events (buried volcanic events, or intrusive events that never reached the surface). The 

undetected event frequency ranged from 1 to 5 times that of observed events, with most 
estimates in the range of 1.1 to 1.5 (CRWMS M&O 1996 [DIRS 100116], Figure 3-62). 
The PVHA results indicated that the statistical uncertainty in estimating the event rate was the 
largest component of intra-expert uncertainty (CRWMS M&O 1996 [DIRS 100116], 
Figure 4-33). The next largest uncertainty was uncertainty in the appropriate spatial model. 
Other important spatial uncertainties included the spatial smoothing distance, Gaussian field 
parameters, zonation models, and event lengths. The temporal issues of importance included the 
time period of interest, event counts at a particular center, and the frequency of hidden events 
(CRWMS M&O 1996 [DIRS 100116], Figure 4-33). 
6.3.1.6 Consideration of Alternative Conceptual Models 
The PVHA was in essence an exercise in combining multiple alternative conceptual models into 
a single distribution that captured the uncertainty in the experts conceptual models of the 
physical behavior of volcanism in the YMR. Alternative conceptual models incorporated into 
the results of the PVHA consisted primarily of alternative temporal and spatial models that 
describe expected behavior (based on past behavior) of volcanism in the YMR. No single 
base-case conceptual model is appropriate in the area of volcanism because the underlying 
physical processes that control the precise timing and location of volcanic events within a 
particular region remain largely unknown to science. 
Although numerous alternative conceptual models were incorporated in the PVHA, several 
alternative models not considered in the PVHA have emerged since the PVHA was completed in 
1996. These models are summarized in Table 6-4 and are discussed in the following section. 
Table 6-4. Alternative Conceptual Models Not Considered in the Probabilistic Volcanic Hazard Analysis 
Alternative Models Key Conclusions Assessment 
Anomalous strain rate in the Anomalously high current strain Not considered plausible based on later 
YMR (Wernicke et al. 1998 
[DIRS 103485]) 
rate based on GPS 
measurements indicates volcanic 
event rate may be 
underestimated by factor of 10. 
measurements from Savage et al. 
(1999 [DIRS 118952]) that show low 
strain rate as well as questionable 
assumptions about links between strain 
rate and volcanic event rate. 
Mantle hotspot beneath the Anomalously high mantle basalt Not considered plausible based on 
YMR (Smith et al. 2002 source temperatures lead to weight of documented scientific 
[DIRS 158735]) underestimation of future evidence showing that mantle hotspot is 
volcanic event rate. not present beneath YMR (e.g., Farmer 
et al. 1989 [DIRS 105284]. 
Tectonically weighted Weighting of certain tectonic Not considered plausible based on 
probability models (Connor et elements in probability models observation that tectonically weighted 
al. 2000 [DIRS 149935], 
p. 427) 
lead to probability estimates as 
high as 10-7 . 
probability models are poor predictors 
of location of volcanism in YMR 
(Section 6.3.3 of this report). 

Table 6-4. Alternative Conceptual Models Not Considered in the Probabilistic Volcanic Hazard 
Analysis (Continued) 
Alternative Models Key Conclusions Assessment 
Significant number of buried or Aeromagnetic anomalies suggest Significance of buried volcanoes on 
undetected volcanic centers in that significant number of probability estimates cannot be 
the YMR (Hill and Stamatakos volcanic events were assessed without further data collection 
2002 [DIRS 159500]) unaccounted for in the PVHA, and update of the PVHA. Sensitivity 
underestimating the volcanic studies documented in Section 6.5.4 of 
hazard. this report are for information purposes 
only. The results of the 1996 PVHA, as 
summarized in Section 7.1 of this 
report, are the results that will be used 
in TSPA-LA. 
6.3.1.7 Significance of Buried Volcanic Centers on Probabilistic Volcanic Hazard 
Analysis Results 
The uncertainty in the event rate accounted for about 40 percent of the total intra-expert 
uncertainty (CRWMS M&O 1996 [DIRS 100116], 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/year/square kilometer (CRWMS M&O 1996 [DIRS 100116], p. 3-2; 
Figure 6-11a of this report). A key parameter for estimating event rates is, therefore, an estimate 
of the number of volcanic events that have occurred in the YMR, particularly since the Miocene. 
Since all post-Miocene volcanic centers observable at the surface in the YMR have been 
identified (Figure 6-1), the only factor that could significantly change PVHA estimates of event 
counts and the event rate would be evidence of a significant number of previously unidentified 
buried volcanic centers or intrusions not considered by the PVHA. 
Langenheim et al. (1993 [DIRS 148622]) presented data for aeromagnetic anomalies in the 
Amargosa Valley and interpreted them as shallowly buried basaltic volcanic centers. These data 
were available to the PVHA experts (CRWMS M&O 1996 [DIRS 100116], p. B-4), and data and 
interpretations concerning the Amargosa Valley anomalies were also presented by Langenheim 
during Workshop 1 of the PVHA project (CRWMS M&O 1996 [DIRS 100116], p. C-3). In the 
PVHA, 9 of 10 experts included volcanic events of the Amargosa Valley in their YMR event 
counts (CRWMS M&O 1996 [DIRS 100116], Appendix E, pp. RC-8, BC-17, WD-5, WH-7, 
MK-10, AM-8, MS-8, GT-6, GW-6). The only expert who did not include events of the 
Amargosa Valley in their YMR event counts considered only the past 2 m.y. to be the relevant 
time period (CRWMS M&O 1996 [DIRS 100116], Appendix E, RF-6), thus, excluding the 
period of time during which the anomalies were probably formed. The most common expert 
assessment 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 [DIRS 100116], Figure 3-63). In addition, the PVHA experts assessed a hidden event 
factor, allowing for additional undetected events not counted in the total YMR event counts that 
already included the Amargosa Valley event counts (CRWMS M&O 1996 [DIRS 100116], 
Figure 3-62, 3-63). These factors typically resulted in an increase of 10 to 50 percent in the rate 
of volcanic events over that computed from the observed volcanic events. 

New data that could potentially change the assessment of the number of volcanic events by the 
PVHA experts include an analysis of existing aeromagnetic data for the YMR (Earthfield 
Technology 1995 [DIRS 147778]) and new ground magnetic surveys of aeromagnetic anomalies 
(Connor et al. 1997 [DIRS 135969]; Magsino et al. 1998 [DIRS 147781]). A map presented by 
Earthfield Technology (1995 [DIRS 147778], Appendix II) indicates the presence of as many as 
40 to 60 aeromagnetic anomalies within approximately 35 to 40 km of Yucca Mountain that are 
interpreted as intrusive bodies; six of these lie within approximately 5 km of the proposed 
repository site. The Earthfield Technology (1995 [DIRS 147778]) results were based on the 
merging of three aeromagnetic data sets: the Timber Mountain, Lathrop Wells, and Yucca 
Mountain surveys. Subsequent to release of the Earthfield Technology (1995 [DIRS 147778]) 
report, it was discovered that the report was flawed by an incomplete and mislocated Timber 
Mt. Survey (Feighner and Majer 1996 [DIRS 105078], p. 1). Inspection of the flight survey 
map in Earthfield Technology (1995 [DIRS 147778], Figure 2) and a corresponding map 
enclosed in Results of the Analysis of the Timber Mt., Lathrop Wells, and Yucca Mt. 
Aeromagnetic Data (Feighner and Majer (1996 [DIRS 105078], Appendix I) indicates that the 
Timber Mountain Survey, which encompasses about 50 percent of the coverage area and the 
majority of the aeromagnetic anomalies, was mislocated approximately 20 km to the 
south-southwest of its correct location. For this reason, further analysis of the anomalies that 
were presented by Earthfield Technology (1995 [DIRS 147778], Appendix II) and that lie within 
the Timber Mountain survey is not warranted. The six anomalies located within 5 km of the 
proposed repository site (the Yucca Mountain survey) are associated with mapped faults and are 
probably due to magnetic variation resulting from fault-controlled juxtaposition of rock masses 
with differing magnetic properties (Feighner and Majer 1996 [DIRS 105078], p. 2; Reamer 1999 
[DIRS 119693], p. 32). 
The most reliable and detailed data available for magnetic anomalies in the YMR is presented in 
Connor et al. (1997 [DIRS 135969]) and Magsino et al. (1998 [DIRS 147781]). These data were 
obtained using ground magnetic surveys of fourteen selected aeromagnetic anomalies located to 
the north, east, west, and south of the proposed repository site (Magsino et al. 1998 
[DIRS 147781], Figure 1-1). Collectively, these surveys represent a comprehensive assessment 
of aeromagnetic anomalies nearest the proposed repository site and provide confidence that the 
geologic record of basaltic volcanism near Yucca Mountain is adequately understood. Of the 
fourteen surveys, seven provide no evidence of buried basalt and three were conducted over 
areas with known surface exposures of basalt, partly to enhance understanding of the relationship 
between volcanism and geologic structure (Magsino et al. 1998 [DIRS 147781], Section 4). 
Four of the 14 surveys provide evidence of buried volcanic centers. Two of these (Anomalies A 
and F/G of the PVHA) were known to the PVHA experts as possible buried basaltic volcanic 
centers (from the data of Langenheim et al. 1993 [DIRS 148622]; Crowe et al. 1995 
[DIRS 100110], Figure 2.5), but the data presented in Connor et al. (1997 [DIRS 135969]) and 
Magsino et al. (1998 [DIRS 147781]) provide increased detail and confidence of 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 tuff (Magsino et al. 1998 [DIRS 147781], Sections 4.4 and 4.11). 
Each of the four anomalies representing probable buried volcanic centers occur within volcanic 
source zones previously specified by the PVHA experts (CRWMS M&O 1996 [DIRS 100116], 

Appendix E), except for the anomalies in the Steves Pass area, which lie slightly to the 
southwest of most experts volcanic source zones in a direction away from Yucca Mountain. 
On the basis of evidence for buried volcanic centers presented in Connor et al. (1997 
[DIRS 135969]), Brocoum (1997 [DIRS 147772]) conducted sensitivity analyses to assess the 
potential impact on the PVHA results of increased event counts in Amargosa Valley and Crater 
Flat. Considering the experts 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 [DIRS 147772], Enclosure 1, p. 5). 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 [DIRS 147772], Enclosure 1, p. 5). Given the uncertainty factored into the 
PVHA by assessment of alternative event counts and hidden event factors, small changes in the 
PVHA event counts have a minor impact on the annual frequency of intersection distribution 
derived from the PVHA. A later sensitivity analysis presented by Synthesis of Volcanism Studies 
for the Yucca Mountain Site Characterization Project (CRWMS M&O 1998 [DIRS 105347], 
Chapter 6, pp. 6-83 and 6-84) conservatively assumed that all known aeromagnetic anomalies in 
Crater Flat and the Amargosa Valley were of Quaternary age, instead of Pliocene. Using this 
assumption, the most likely number of Quaternary volcanic events near Yucca Mountain based 
on PVHA event counts was increased from 3.8 to 8 events. This increase in the Quaternary 
event count resulted in a disruption probability of approximately 2.510-8 per year (CRWMS 
M&O 1998 [DIRS 105347], Chapter 6, p. 6-84), a result not significantly different from the 
mean PVHA result of 1.510-8 per year (CRWMS M&O 1996 [DIRS 100116], pp. 4-10, 4-14). 
The data presented by Connor et al. (1997 [DIRS 135969]) and Magsino et al. (1998 
[DIRS 147781]) provide stronger evidence that Anomalies A and F/G (as defined in the PVHA) 
represent buried volcanic centers, and that at least one anomaly not considered by the PVHA 
experts represents a probable buried volcanic center. Sensitivity studies (Brocoum 1997 
[DIRS 147772]; CRWMS M&O 1998 [DIRS 105347], Chapter 6) show that the addition of 
several volcanic events located within already defined volcanic source zones does not 
significantly impact the results of the PVHA. Significantly, the four anomalies east of Yucca 
Mountain (Magsino et al. 1998 [DIRS 147781], Figure 1-1) show no evidence of buried volcanic 
centers and provide confirmatory 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 post-Miocene volcanism in the YMR. 
In 1999, the USGS conducted a regional aeromagnetic survey for the purpose of assessing 
potential hydrologic pathways in the Yucca Mountain/Death Valley region (Blakely et al 2000 
[DIRS 151881]). Subsequent interpretation of these data indicated that 20 to 24 aeromagnetic 
anomalies present to the west and south of Yucca Mountain could potentially represent buried 
basalt (OLeary et al. 2002 [DIRS 158468]; Hill and Stamatakos 2002 [DIRS 159500]). 
Section 6.5.4 of this report documents an assessment of how the potential presence of additional 
buried volcanoes in the YMR could impact the frequency of intersection. 

6.3.1.8 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 6-5). 
As discussed in the following section (6.3.2), volcanic events in hazard calculations have been 
represented as both points and lines (Table 6-5). 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. The shorter the event length, the more 
comparable intersection probability results are for calculations representing volcanic events as 
points. Intersection probabilities near 10-7 intersections per year (Ho and Smith 1998 
[DIRS 140152], pp. 507 and 508; Reamer 1999, p. 61 [DIRS 119693]) reflect unusually small 
volcanic source zone areas or unusually long event lengths (Table 6-5). 
Most of the published intersection probabilities, including the mean intersection probability 
estimated in the PVHA, cluster at values slightly greater than 10-8 per year (Table 6-5), 
indicating that this probability estimate is robust, given the range of alternative temporal and 
spatial models, and the different event geometries considered in the probability calculations. 
Table 6-5. Published Estimates of the Probability of Intersection of the Proposed Repository at Yucca 
Mountain by a Volcanic Event 
Intersection Event 
Reference Probability (per year) Comment Representation 
Crowe et al. (1982 [DIRS 
102741]), pp. 184 through 185 
3.3 10-10 - 4.7 10-8 Range of alternative probability 
calculations. 
point 
Crowe et al. (1993 [DIRS 
100026]), p. 188 
2.6 10-8 Median value of probability 
distribution. 
point 
Connor and Hill (1995 [DIRS 
102646]), p. 10121 
15 10-8 Range of 3 alternative models. point 
Crowe et al. (1995 [DIRS 
100110]), Table 7.22 
1.8 10-8 Median value of 22 alternative 
probability models. 
point 
Ho and Smith (1998 [DIRS 
140152]), pp. 507 through 508 
(1) 1.5 10-8 , 
(2) 1.09 10-8 , 
2.83 10-8 , 
(3) 3.14 10-7 
3 alternative models; 3rdrd 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 
point 
within a small zone enclosing Yucca 
Mountain. 
CRWMS M&O (1998 [DIRS 
105347]), Chapter 6, p. 6-84 
2.5 10-8 Sensitivity analysis that 
conservatively assumes all 
aeromagnetic anomalies in 
Amargosa Valley are Quaternary 
point 
age. 

Table 6-5. Published Estimates of the Probability of Intersection of the Proposed Repository at Yucca 
Mountain by a Volcanic Event (Continued) 
Intersection Event 
Reference Probability (per year) Comment Representation 
Connor et al. (2000 [DIRS 
149935]), p. 427 
10-8-10-7 Value of 10-7 assumes maximum 
event length of 20 km, regional 
recurrence rates of 5 events/m.y., 
line 
and that crustal density variations 
contribute to event location. 
6.3.2 Definitions and Parameters of a Volcanic Event and Implications for Alternative 
Probability Calculations 
An important issue in the PVHA and in alternative volcanic hazard assessments of the proposed 
Yucca Mountain 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 
compare the results of alternative probability calculations meaningfully. 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 [DIRS 100116], 
Appendix E). The physical manifestations of a volcanic event include the dike or dike system 
and any surface eruption deposits. For the purposes of probability models discussed in this 
report (Section 6.5), a volcanic event is defined as a point (x,y) 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 6-8 and Figure 6-10). 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 calculations in this report. 
The width of the dikes and the number of parallel dikes does affect the consequences of an 
intersection and is incorporated into the igneous intrusion scenario presented in Number of Waste 
Packages Hit by Igneous Intrusion (BSC 2004 [DIRS 170001]). Although the PVHA assumed 
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 proposed repository by an intrusive 
basaltic dike (CRWMS M&O 1996 [DIRS 100116], Section 4.2, Figure 4-32). The PVHA did 
not calculate the conditional probability that a dike intersecting the proposed repository would 
result in an extrusive volcanic eruption through the repository. 
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 [DIRS 100116], Appendix E; Figure 6-2). The most likely values for maximum dike 
lengths were estimated to be in the range of 17 to 22 km (CRWMS M&O 1996 [DIRS 100116], 
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 individual PVHA expert dike length 
distributions can be aggregated to derive a PVHA aggregate dike length distribution. 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 6-2). The most commonly 
assigned dike orientation centers around N30oE (CRWMS M&O 1996 [DIRS 100116], 
Figure 3-62). 
Prior to the PVHA, most assessments of volcanic hazard to the proposed repository represented 
volcanic events as points having no physical dimension (CRWMS M&O 1996 [DIRS 100116], 
p. 3-16). The physical dimension of events was generally taken into account by appropriately 
expanding the area of the proposed repository or of volcanic source zones (e.g., Crowe 
et al. 1995 [DIRS 100110], p. 7-64). The PVHA and probability calculations presented by the 
NRC since the PVHA have represented volcanic events as having both length and orientation 
(Reamer 1999 [DIRS 119693]). It is important to compare the different representations of 
volcanic events in order to compare probability results meaningfully. The PVHA intersection 
probability represents the probability of a dike intersecting the repository footprint (CRWMS 
M&O 1996 [DIRS 100116], Section 3.1.6). The NRC intersection probability represents the 
intersection of the repository footprint by a vent or vent alignment (Reamer 1999 
[DIRS 119693], Sections 4.1.6.3.2 and 4.1.6.3.3, Figures 29 and 30) and assumes that all vents 
along the alignment are contemporaneous and represent a single volcanic event (e.g., the 
alignment of Quaternary vents from Makani Cone to Little Cones ([Reamer 1999 
[DIRS 119693]]) (see Figure 6-1 in this report). In contrast, the PVHA allowed that an 
alignment of volcanoes could represent one to several volcanic events that are not necessarily 
contemporaneous. Conceptually, use of either the PVHA or NRC volcanic event should result in 
the same intersection probability if the same temporal/spatial models and assumptions are used, 
as well as the same probability distributions for event length and orientation (Figure 6-3). 
However, these probabilities represent different physical occurrences and PVHA and NRC 
model parameters are not equivalent. Since the PVHA intersection probability represents the 
probability of a dike intersection, the probability of an eruption (conditional on dike intersection) 
through the proposed repository is equal to, or lower than the intersection probability 
(Figure 6-3). The NRC intersection probability values are based on the interpretation that every 
intersection of a vent alignment with the repository footprint results in an eruption through the 
repository (Reamer 1999 [DIRS 119693], p. 57) and that the probability of intersection by 
shallow intrusive events that do not erupt is necessarily higher, possibly by a factor of 2-5 
(Reamer 1999 [DIRS 119693], p. 60, Figure 5). 

Output 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 6-2. Composite Distribution for Dike Length Averaged Across All 10 Probabilistic Volcanic Hazard 
Analysis Experts 

on 
PVHA di iiii?? 
intrusion 
probability 
eruption 
probability 
kentersectprobability 
NRC vent algnment 
intersecton probability 
lower probability annual probability higher probability 
For Information Only. 
Source: Reamer 1999 [DIRS 119693] 
Figure 6-3. Conceptual Diagram Comparing Event Definitions from the Probabilistic Volcanic Hazard 
Analysis and Reamer: Implications for Eruption and Intrusion Probabilities Based on 
Different Event Definitions 
The NRC assumes that every vent alignment intersection will result in an eruption through the 
repository because they conclude that vent spacing along alignments is small compared to the 
repository footprint (Reamer 1999 [DIRS 119693], Sections 4.1.4.3.3 and 4.1.6.3.2). The 
technical basis for this conclusion is unclear. In Section 6.5.1.3, a number of alternative 
approaches for the number and spatial distribution of vents along the dike associated with a 
volcanic event are formulated based on PVHA expert output and observed vent spacing in the 
YMR to test for sensitivity of model choice. Using these approaches, the eruption probability is 
approximately 78 percent of the dike intersection probability because of cases where no vents 
form within the repository footprint (Table 6-11). 
6.3.2.1 Intrusive Versus Extrusive Events: Evidence from Analogue Sites 
Another issue requiring discussion is whether dikes or dike systems can reach the near surface 
without any portion of the system erupting. The NRC (Reamer 1999 [DIRS 119693]) 
assumption that all vent alignment intersections result in eruption through the proposed 
repository implies that intrusive events that intersect the proposed repository and do not erupt 
represent entirely separate temporal events. Using the San Rafael volcanic field as an analogue, 
the NRC assumes for PA purposes that the probability of separate intrusive events that do not 
erupt is 2 to 5 times higher than the probability of eruptive events (Reamer 1999 [DIRS 119693], 
Section 4.1.6.4). Thus, for example, if 5 volcanic events resulting in volcanic eruptions have 
occurred in the YMR in the past 1 m.y., the NRCs assumption requires that 10 to 25 additional 
intrusive events have also occurred, independent in time and location from the events that 
produced the volcanic eruptions. In the PVHA definition of a volcanic event, intrusive and 
extrusive events in the YMR are generally considered to be linked on a one-to-one basisa 
volcanic event is defined as an extrusive volcano and its associated intrusive dike or dike system. 

Dikes that reach depths of less than 0.5 to 1 km are thought to erupt at some point along the 
length of the dike, mainly because of volatile exsolution (CRWMS M&O 1996 [DIRS 100116], 
Appendix E, pp. RC-10, BC-6, WH-6, MK-12). The most common multiplier assigned in the 
PVHA for undetected intrusive events was 1.1 to 1.2 times that of known volcanic events 
(CRWMS M&O 1996 [DIRS 100116], Figure 3-62), which is a number lower than the NRC 
multiplier of 2 to 5. 
An appropriate analogue in the YMR for understanding the relationship between intrusive and 
extrusive components of a volcanic event is the Paiute Ridge intrusive/extrusive center (Byers 
and Barnes 1967 [DIRS 101859]) 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 1998 [DIRS 105347], 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, represent a single 
volcanic event (Ratcliff et al. 1994 [DIRS 106634]; CRWMS M&O 1998 [DIRS 105347], 
Chapter 5, p. 5-29). The vents and associated dike system formed within an NNW-trending 
extensional graben provide excellent exposures of a variety of depths of the system including 
remnants of surface lava flows, volcanic conduits, and dikes and sills intruded into tuff country 
rock at depths of up to 300 m (CRWMS M&O 1998 [DIRS 105347], Chapter 5, pp. 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 [DIRS 101859]; 
CRWMS M&O 1998 [DIRS 105347], Chapter 5, pp. 5-27 through 5-28). Dike lengths at Paiute 
Ridge range from less than 1 to 5 km (CRWMS M&O 1998 [DIRS 105347], Chapter 5, p. 5-31), 
comparable to the range estimated for post-Miocene volcanism near Yucca Mountain 
(Figure 6-2). 
Field observations at Paiute Ridge clearly show that, while some portions of individual dikes 
stagnated within about 100 m of the surface without erupting, other portions of the same volcanic 
event did erupt, as evidenced by associated lava flows and volcanic conduits (Byers and Barnes 
1967 [DIRS 101859]; CRWMS M&O 1998 [DIRS 105347], Chapter 5, pp. 5-29 through 5-33). 
During the time period considered most significant by the PVHA experts for evaluating volcanic 
hazard (the past 5 m.y., CRWMS M&O 1996 [DIRS 100116], Figure 3-62), there is no known 
episode of dike intrusion to within a few hundred meters of the surface in the YMR that has not 
been accompanied by an extrusive component. Thus, there is no evidence in the YMR geologic 
record to suggest that dike intrusions without accompanying eruptions occur 2 to 5 times more 
frequently than eruptions (Reamer 1999 [DIRS 119693], Figure 5, Sections 4.1.6.3.4 and 
4.1.6.4). 
The NRC assumption of higher intrusion probabilities in the YMR is based on analogy to the San 
Rafael volcanic field on the western Colorado Plateau, where an extensive system of shallowly 
intruded dikes is well exposed (Delaney and Gartner 1997 [DIRS 145370]). Delaney and 
Gartner (1997 [DIRS 145370], p. 1180) estimate that 174 dikes are represented in the San Rafael 
dike swarm. Breccias are present along portions of 45 of these dikes, which are interpreted to 
represent the subsurface beneath eruptive centers (Delaney and Gartner 1997 [DIRS 145370], 
pp. 1178 and 1191). No attempt is made in Delaney and Gartner (1997 [DIRS 145370]) 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; or may have erupted as is observed at 
Paiute Ridge. Given the Paiute Ridge analogy and the Delaney and Gartner (1997 
[DIRS 145370]) interpretation that the San Rafael swarm likely represents the subsurface 
beneath a large volcanic field active for about a million years (Delaney and Gartner 1997 
[DIRS 145370], pp. 1177, 1178, and 1179), it is likely that many individual intrusive/extrusive 
events are represented at San Rafael, with some portion of a dike system erupting during each 
event and other portions of the same dike system not erupting. Thus, while the data and 
discussion presented in Delaney and Gartner (1997 [DIRS 145370]) have been used to argue that 
intrusive events without an eruptive component occur 2 to 5 times more frequently than intrusive 
events with an eruptive component, an alternative interpretation is that the intrusion/extrusion 
ratio is closer to 1. This alternative interpretation is more consistent with the geologic record of 
the YMR, as demonstrated at the Paiute Ridge analogue site, and by the conclusions of the 
PVHA (CRWMS M&O 1996 [DIRS 100116]). 
6.3.2.2 Alternative Event Lengths 
The length of dikes or vent alignments (Reamer 1999 [DIRS 119693], Figure 30) can 
significantly affect intersection probabilities, depending partly on the distance of high-event-
frequency areas from the proposed repository. When volcanic events primarily occur far from 
the proposed repository, they must have sufficient length to intersect the repository, and longer 
event lengths will result in higher intersection probabilities. When volcanic events occur more 
frequently nearer the proposed repository, volcanic events with shorter lengths are able to 
intersect the repository with higher frequency. 
As evaluated by experts in the PVHA, the mean dike length associated with a volcanic event in 
the YMR is 4 km and 95 percent of dikes are shorter than 10.1 km (Figure 6-2). These values 
are based on observed volcanic features in the YMR. For instance, the maximum vent spacing in 
the YMR is 5.4 km between Black and Makani Cones, and volcanic vent alignments 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 
YMR, assuming it represents one volcanic event, is the Quaternary Crater Flat alignment with a 
length of about 11 km (Figure 6-1). Observed dikes, such as at Paiute Ridge, range in length 
from less than 1 to 5 km. Dike and vent alignments of the 3.7 m.y. basalts in southeast Crater 
Flat (Figure 6-1) are no more than 4 km in length. 
Event lengths used in probability models by researchers from the University of Nevada, 
Las Vegas (e.g., Smith et al. 1990 [DIRS 101019]) and the NRC (Reamer 1999 [DIRS 119693], 
Figures 29 and 30) are significantly longer than those assessed by the experts in the PVHA. For 
example, Smith et al. (1990 [DIRS 101019], p. 81) based the dimensions of high-risk volcanic 
source zones, which were used as a spatial control on event distribution in probability models, on 
the length of volcanic vent alignments at analogue sites. The analogue site chosen to define the 
dimensions of the high-risk zone is the relatively large-volume Fortification Hill volcanic field 
near Lake Mead, 200 km southeast of Yucca Mountain. In terms of volume, Smith et al. (1990 
[DIRS 101019], p. 85) acknowledge that this volcanic field is not analogous to Quaternary 
volcanism near Yucca Mountain. The vent alignment length defined at Fortification Hill is 
25 km (Smith et al. 1990 [DIRS 101019], p. 85). Smith et al. (1990 [DIRS 101019], p. 87) 

consider this length to be an upper bound, and it corresponds to the greater than 99th percentile 
value of the PVHA event length distribution (Figure 6-2). 
Vent alignment lengths are used directly in NRC probability calculations (Reamer 1999 
[DIRS 119693], Sections 4.1.6.3.2 and 4.1.6.3.3, Figures 29 and 30) and have a maximum 
half-length range of 5.2 to 10.2 km, corresponding to a total-length range of 10.4 to 20.4 km. 
These values are based on the half-length of the Quaternary Crater Flat vent alignment (5.6 km, 
the longest half-length observed in the YMR) and the observation that vent alignment 
half-lengths of 10 km or more occur in other volcanic fields (Reamer 1999 [DIRS 119693], 
p. 40). It is notable that approximately 97 percent of the 174 dike lengths measured in the 
San Rafael volcanic field (discussed above), which the NRC uses as a YMR analog, have total 
lengths of less than 5 km (Delaney and Gartner 1997 [DIRS 145370], 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 [DIRS 145370], Figure 4), a distribution not dissimilar to 
that used in the PVHA (Figure 6-2). 
A measure comparable to dike half-length, the distance from the end of the dike nearest the 
proposed repository to the point of origin of the volcanic event, can be derived from information 
elicited in the PVHA (Figure 6-4). This distribution has a 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 YMR. Note that the range of 
maximum event length values (10 to 20 km) used in NRC probability models (Reamer 1999 
[DIRS 119693], Figures 29 and 30), are comparable to the maximum dike lengths assessed by 
the PVHA experts. However, the NRCs use of a uniform distribution for dike half-length 
results in a much greater weighting in NRC probability models for dike lengths that represent the 
greater than 95th percentile values assessed by the 10 PVHA experts (Figure 6-2). The NRC 
intersection probability value of 10-7 per year, assumed for purposes of NRC PA (Reamer 1999 
[DIRS 119693], p. 61), depends on a maximum vent alignment length of 20 km (Reamer 1999 
[DIRS 119693], Figure 30), which is inconsistent with observed vent alignment lengths in the 
YMR. 
6.3.3 Conceptual Models of Volcanism and Formulation of Probability Models 
In the PVHA and alternative assessments of volcanic hazard to the proposed Yucca Mountain 
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 volcanoes 
has a fundamental impact on how probability models are formulated and on the results of 
probability models (e.g., Smith et al. 1990 [DIRS 101019]; CRWMS M&O 1996 
[DIRS 100116]; Reamer 1999 [DIRS 119693]). 
In general, the PVHA experts viewed the YMR 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, 
but several members of the panel noted the possible additional influence on volcanism of the 
Walker-Lane structural zone (CRWMS M&O 1996 [DIRS 100116], Appendix E, e.g., pp. WD-1 
and WH-1). The smaller volumes of basalt erupted in the YMR since the Miocene reflects 
waning of both tectonism and magmatism in this part of the Basin and Range Province 

(CRWMS M&O 1996 [DIRS 100116], Appendix E, e.g., pp. RC-1, BC-3, WD-2, RF-3, WH-1, 
MK-1, AM-3). 
Output DTN: LA0009FP831811.001. 
NOTE: This distribution is obtained by convolving the distributions for dike length with those for the location of the 
point event relative to the dike. The 5th percentile, mean, and 95th percentile values are 0.2, 2.0, and 5.6, 
km, respectively. The distribution contains a very long upper tail extending to 86 km. 
Figure 6-4. Composite Distribution for the Distance from the Point Volcanic Event to the End of the Dike 
Averaged Across All 10 PVHA Experts 
Some PVHA 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 [DIRS 100116], Appendix E, pp. MK-2 and 
AM-1). The PVHA experts generally view volcanism in the YMR as a regional-scale 
phenomenon because of 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 1998 [DIRS 105347], Chapter 4, 
p. 4-4). The exact mechanism of mantle melting in the YMR is poorly understood, but may be 
controlled by a complex combination of processes including the effect of residual heat in the 
lithospheric mantle from previous episodes of volcanism and the presence of a 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 
[DIRS 100116], Appendix E). Researchers who have analyzed magmatic processes in the YMR 
generally agree that the magnitude of mantle melting has drastically decreased since the middle 
Miocene and that all melts in the past few million years have been generated within relatively 
cool (compared to asthenospheric mantle) ancient lithospheric mantle, which is a factor that may 
contribute to the relatively small and decreasing volume of basaltic melt erupted in the YMR 
since the Miocene (Farmer et al. 1989 [DIRS 105284]; Yogodzinski and Smith 1995 
[DIRS 136262]; CRWMS M&O 1996 [DIRS 100116], Appendix E; Reamer 1999 
[DIRS 119693], pp. 17 and 47). 
An alternative to the hypothesis of melting within lithospheric mantle was presented by 
Smith et al. (2002 [DIRS 158735]), who hypothesized instead, that basaltic melts beneath the 
YMR are generated within hot, upwelling asthenospheric mantle (mantle hotspot model). This 
model raises the possibility that the recurrence rate of basaltic volcanism near Yucca Mountain 
(the Crater Flat volcanic field) could increase in the next few thousand years to a level 
comparable to the more active Lunar Crater volcanic field, 150 km to the north. This hypothesis 
is based on a proposed correlation between the timing of volcanic episodes between the Lunar 
Crater and Crater Flat fields and a proposal that anomalously hot mantle underlies the region 
beneath both volcanic fields, providing a common mechanism that controls the timing of 
volcanic activity. If this hypothesis were valid, probability models that estimate the probability 
of volcanic disruption of the repository might need to be revised to account for the possibility of 
higher recurrence rates in the future. 
The hypothesis that recurrence rates of volcanism could suddenly increase because of 
anomalously hot mantle beneath the Yucca Mountain area is inconsistent with the following 
observations: 
 
The Crater Flat volcanic field is one of the least active volcanic fields in the western 
United States, while the Lunar Crater field is one of the most active fields within the 
Basin and Range interior. This fundamental difference in eruptive behavior does not 
suggest a common physical mechanism that links the two fields. Basaltic volcanic fields 
are common throughout the western United States, with at least 20 to 30 fields active in 
the last 5 m.y. Many of these volcanic fields consist of 50 to 100 individual volcanoes, 
with several of the largest containing more than 300 individual volcanoes. Eruption 
rates for most fields range from 10 to more than 100 km3/m.y. (Perry and Bowker 1998 
[DIRS 159502]). The Lunar Crater field consists of 70 to 100 individual volcanoes, 
with an eruption rate of approximately 20 km3/m.y. over the past 4 m.y. In contrast, the 
Crater Flat field consists of about 10 to 15 individual volcanoes with an eruption rate of 
less than 1 km3/m.y. over the past 4 m.y. (Perry and Bowker 1998 [DIRS 159502]). 
These data indicate a recurrence rate in the Lunar Crater field that is approximately an 
order of magnitude greater than in the Crater Flat field. If, as proposed, the common 

link between the two fields is anomalously hot mantle, the lower volume, eruption rate, 
and recurrence rate of the Crater Flat field indicates that the underlying mantle is not as 
hot or prone to melt as mantle beneath Lunar Crater. The low activity of the Crater Flat 
field compared to nearly every other volcanic field in the western U.S. indicates that the 
underlying mantle is not particularly hot. Therefore, there is no evidence to indicate that 
the recurrence rate of volcanism near Yucca Mountain will ever reach values equivalent 
to those at Lunar Crater. 
 
Neodymium isotopic compositions of basalts in the Lunar Crater and Crater Flat 
volcanic fields are significantly different, indicating fundamentally different mantle 
sources or fundamental differences in processes that produced the basalts. 
Smith et al. (2002 [DIRS 158735]) recognized the isotopic differences between the two 
volcanic fields and speculated that the unusual Nd isotopic compositions of basalt near 
Yucca Mountain are due to (1) contamination of asthenospheric melts passing through 
lithospheric mantle or (2) modification of asthenospheric mantle by fluids or melts 
derived from subducted crust. Either mechanism would not be expected to affect the 
basalts near Yucca Mountain selectively, but would instead operate on a much larger 
scale. For example, because subducted crust existed beneath most of the western United 
States for tens of millions of years, modifying fluids of melts derived from subducted 
crust would be expected to modify asthenospheric mantle on a continental scale, not just 
the small region surrounding Yucca Mountain. Basalts from Lunar Crater have isotopic 
compositions similar to ocean island basalts, indicating a source in relatively warm and 
convecting asthenospheric mantle. The unusual Nd isotopic composition of basalts in 
the Crater Flat field indicate derivation from a lithospheric mantle source that is old, 
stable, and cold (nonconvecting) compared to asthenospheric mantle (Perry et al. 1987 
[DIRS 162311]; Farmer et al. 1989 [DIRS 105284]; Livaccari and Perry 1993 
[DIRS 162310]). Wernicke et al. (1987 [DIRS 107250]), citing tectonic evidence, 
suggested that the relative lack of volcanism in the YMR until 15 m.y. ago left the 
lithosphere cold and difficult to extend, compared to more volcanically active and earlier 
extended regions of the Basin and Range province. The preponderance of evidence 
indicates that the small volume of basalt and limited volcanic activity near Yucca 
Mountain reflect an underlying mantle source that is cold and unable to produce 
significant volcanic activity. 
On a more local and shallow crustal scale, most researchers conclude that (1) volcanism is 
correlated with zones of past or present crustal extension, and (2) once dikes feeding volcanoes 
enter the shallow upper crust, their location and orientation is influenced by the orientation of the 
local stress field and the presence of faults that may locally control vent location and alignment. 
The evidence cited for these two conclusions includes several northeast-oriented vent alignments 
in the YMR and the association of eruptive centers with known or inferred faults 
(Smith et al. 1990 [DIRS 101019], p. 83; CRWMS M&O 1996 [DIRS 100116], Appendix E, 
p. AM-4; Connor et al. 1997 [DIRS 135969], p. 78; Reamer 1999 [DIRS 119693], 
Section 4.1.3.3.3; Fridrich et al. 1999 [DIRS 107333], p. 211). 
A mechanistic model relating mantle melting and lithospheric extension has recently been 
proposed for the YMR by Connor et al. (2000 [DIRS 149935]) and additionally, is used as the 
geologic basis for weighting spatial density models based on crustal density variations across the 

YMR (Reamer 1999 [DIRS 119693], Section 4.1.6.3.3). The conceptual basis of the model is 
that crustal density variations across the YMR control variations in lithostatic pressure at the 
base of the crust. These pressure variations in turn control the location of decompression melting 
within the mantle, which, in turn, controls the location of future igneous activity within the YMR 
(Connor et al. 2000 [DIRS 149935], pp. 419 through 422). 
As formulated, a finite-element model that calculates lateral pressure changes in the YMR based 
on upper crustal density variations (Connor et al. 2000 [DIRS 149935], p. 420) is a poor 
predictor of volcano distribution in the YMR. The model predicts that maximum melting (and, 
hence, more frequent occurrence of volcanism) will occur farthest from the region of high crustal 
density (Connor et al. 2000 [DIRS 149935], Figure 3). But this model prediction is the opposite 
of what is observed for the occurrence of post-Miocene volcanism in the YMR because 
volcanism is concentrated near high-density crust of the Bare Mountain domain, rather than 
farther to the east (Figure 6-5). 
A map of apparent crustal density variation (Connor et al. 2000 [DIRS 149935], Plate 1) shows 
that low average crustal density extends fairly uniformly for a distance of at least 50 km east of 
the Bare Mountain Fault. Within the context of the conceptual model proposed by Connor et al. 
(2000 [DIRS 149935]) (i.e., crustal density exerts a primary control on location of volcanism), 
post-Miocene volcanism should occur somewhat randomly across this broad region. Instead, all 
post-Miocene volcanism near Yucca Mountain is located within 5 to 10 km of the Bare 
Mountain fault or near the southern ends of the Windy Wash and Stagecoach Road faults 
(Fridrich et al. 1999 [DIRS 107333], p. 211), indicating that local zones of extension and upper 
crustal faulting may exert more direct control on the location of volcanism than the effect of 
shallow crustal processes on mantle processes (CRWMS M&O 1996 [DIRS 100116], 
Appendix E, e.g., pp. AM-5 and MS-2; Fridrich et al. 1999 [DIRS 107333], p. 211; Reamer 1999 
[DIRS 119693], Section 4.1.5.3.3). This does not mean that areas of low crustal density and 
volcanism do not often coincide, but instead means that both are independently influenced or 
caused by upper crustal faulting and extension. 
Connor et al. (2000 [DIRS 149935]) use crustal density as a primary tectonic or geologic 
control on volcano distribution (Reamer 1999 [DIRS 119693], Section 4.1.6.3.3), even though 
volcanoes are not randomly distributed over broad areas of low crustal density as predicted by 
this model. An alternative method of weighting spatial density models would be to weight by 
estimated percent of extension within the Crater Flat basin (e.g., Fridrich et al. 1999 
[DIRS 107333], Figure 5), thereby tying probability models more directly to a geologic process 
(faulting and extension) that many researchers agree exerts an important geologic control on 
volcano location (Smith et al. 1990 [DIRS 101019], p. 83; CRWMS M&O 1996 [DIRS 100116], 
Appendix E, pp. AM-5 and MS-2; Connor et al. 1997 [DIRS 135969], p. 78; Reamer 1999 
[DIRS 119693], Section 4.1.3.3.3, p. 47). The strong southward and westward increase in 
extension rate across the Crater Flat basin corresponds well to sites of most recent volcanism in 
the basin (Fridrich et al. 1999 [DIRS 107333], Figures 1 and 5), as opposed to crustal density 
variations that are hypothesized to control volcano location, but do not correspond well with 
volcano location (Reamer 1999 [DIRS 119693], Figure 22). In terms of alternative conceptual 
models, models based on observable geologic features in the YMR provide a more defensible 
framework and technical basis for probability calculations than models relying on unobservable 

processes that remain largely speculative (i.e., Reamer 1999 [DIRS 119693], Section 4.1.5.3.2; 
see also Probability Acceptance Criteria 3, Reamer 1999 [DIRS 119693], p. 24). 
In summary, the probability model proposed by Connor et al. (2000 [DIRS 149935]) that relies 
on spatial density functions weighted by crustal density is not well supported based on 
observations of volcano distribution within the YMR. Significantly, this probability model is the 
basis for calculating the highest annual probability value for a volcanic eruption within the 
proposed repository boundary (9  10-8 per year, Reamer 1999 [DIRS 119693], Figure 30), 
which is the value (rounded up to 10-7 per year) that the NRC will use for the purposes of PA 
(Reamer 1999 [DIRS 119693], p. 61). It should also be noted that this probability model results 
in an approximately two-fold increase in the intersection probability compared to unweighted 
spatial density models (Reamer 1999 [DIRS 119693], Figure 29). As discussed previously in 
Section 6.3.2.2, the results of this probability model also depend to a large extent on dike lengths 
that are inconsistent with the geologic record of the YMR. 
6.4 THE CRATER FLAT STRUCTURAL DOMAIN 
Clearly, post-Miocene volcanoes in the YMR are spatially clustered (Crowe et al. 1995 
[DIRS 100110], Chapter 3; Connor and Hill 1995 [DIRS 102646], Figure 2). For probability 
models that incorporate clustering of volcanoes (Connor and Hill 1995 [DIRS 102646]) or 
specify volcanic source zones based primarily on the location or clustering of volcano centers 
(CRWMS M&O 1996 [DIRS 100116]), estimation of the hazard to Yucca Mountain is often 
dominated by the presence of the Crater Flat cluster. This dominance is due to the relatively 
high occurrence and Quaternary age of volcanoes in the Crater Flat basin (including Lathrop 
Wells, which lies within the Crater Flat structural domain and is the youngest volcano in the 
YMR), and because of the close proximity of Crater Flat volcanoes to Yucca Mountain, 
compared to other volcanic clusters in the YMR (Figure 6-1). 
The Crater Flat structural domain as defined by Fridrich (1999 [DIRS 118942], pp. 170 through 
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 6-5). It includes the Crater Flat 
topographic basin on the west and Yucca Mountain near the center of the structural basin 
(Figure 6-5). Because the proposed Yucca Mountain repository lies within the Crater Flat 
structural domain, 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 formulating 
conceptual models of volcanism. Such models are important for assessing hazards to the 
proposed repository. 
The following sections describe the internal structure of the Crater Flat basin, as well as how the 
PVHA experts and subsequent investigators have interpreted the influence of structural 
characteristics of the basin to estimate the locations of future volcanic events. Based largely on 
work published since the PVHA, the evidence that the northeastern and southwestern parts of the 
basin have different extensional histories that may have influenced the location of basaltic 
volcanism within the basin is summarized below. 

Source: Basalts of different ages are shown in relation to basin structure (modified from Fridrich et al. 1999 
[DIRS 118942], Figure 1). The 70-ka age of the Lathrop Wells volcano indicated in the legend was 
estimated based on preliminary data subsequently published in Heizler et al. (1999) [DIRS 107255], which 
indicates an age closer to 80 k.y. 
NOTE: PCF = Pliocene Crater Flat; MC = Makani Cone; BC = Black Cone; RC = Red Cone; LC = Little Cones; 
LW = Lathrop Wells; ka = thousand years ago; k.y = thousand years. 
Figure 6-5. 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 

6.4.1 Internal Structure and Boundaries of the Crater Flat Basin 
The Crater Flat structural domain (also referred to as the Crater Flat basin) comprises the Crater 
Flat topographic basin (west of Yucca Mountain), Yucca Mountain, and the western part of 
Jackass Flats. Based on geologic mapping and the interpretation of subsurface structures from 
geophysical surveys (discussed below), the Crater Flat structural domain appears to comprise a 
single, westward-sloping, faulted basin (Figure 6-6). The western boundary of the Crater Flat 
basin coincides with the Bare Mountain fault and the northward extension of the fault into the 
Tram Ridge and Tates Wash faults (Fridrich 1999 [DIRS 118942], p. 174). The Bare Mountain 
fault dips steeply (64  5 near the southern end) and can be imaged by seismic reflection to 
depths of at least 3.5 km and possibly to depths of 6 km (Brocher et al. 1998 [DIRS 100022], 
pp. 956 and 966). Logically, 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 
[DIRS 118942], p. 174). As defined by Fridrich (1999 [DIRS 118942], pp. 174 and 176), the 
northeastern boundary coincides with Yucca Wash, which is an alluvium-filled valley inferred to 
be underlain by a small northwest-striking right-lateral strike slip fault or zone of faults 
(Fridrich 999 [DIRS 118942], pp. 174 and 176). The fault is nowhere exposed, but is inferred 
from the fact that Yucca Wash is a linear valley separating Yucca Mountain from a domain to 
the northeast in which the 12.7 to 12.8 m.y. Paintbrush Group and older rocks are more 
extended than on northern Yucca Mountain (Fridrich 1999 [DIRS 118942], p. 176). Day et al. 
(1998 [DIRS 100027], p. 11) summarize evidence indicating that a major fault is not present 
beneath Yucca Wash. 
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 
basin is probably a buried down-to-the-west fault known as the Gravity Fault (Fridrich 999 
[DIRS 118942], p. 176, Figure 7). 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 
[DIRS 118942], p. 176). Fundamental changes in the style, timing, and magnitude of 
extensional deformation occur across all of the boundaries of the Crater Flat basin. 
6.4.1.1 Fault Orientations, Dip Directions, and Displacements 
In the center of the Crater Flat basin, a sequence of 12.7 to 12.8 m.y. ash-flow tuffs (primarily 
the Tiva Canyon and Topopah Spring Tuffs of the Paintbrush Group) crop out. These exposed 
tuff units comprise Yucca Mountain and adjacent mesas. Much of the information about 
orientation, offset, and timing of faulting is based on examination of faults that cut through the 
exposed tuffs. Because both Crater Flat and Jackass Flats are basins that have undergone 
alluviation in the late Quaternary, much of the structure of these basins is not accessible to direct 
observation. Information on structures beneath Crater Flat and Jackass Flats is derived mainly 
from seismic, gravity, and aeromagnetic and ground magnetic data. 

Source: Modified from Brocher et al. 1998 [DIRS 100022]. 
NOTE: Location of cross section is indicated in Figure 6-5. 
Figure 6-6. Schematic Cross Section of the Crater Flat Basin, from Seismic Reflection, Surficial 
Geology, and Borehole Information 
The Crater Flat basin is characterized by an array of closely spaced, small-to-moderate sized 
extensional faults that generally dip towards the center of the basin (Figure 6-6). Normal faults 
within the Crater Flat basin strike northerly in the northeastern part of the basin, but change to 
increasingly northeasterly to the south and west across the basin (Figure 6-5). These orientations 
can be measured directly where faults are exposed on Yucca Mountain and can be inferred from 
the strike of aeromagnetic and gravity anomalies buried beneath young basin fill. In general, the 
fault pattern within Crater Flat basin is roughly radial to the caldera complex to the north and is 
curved from north to south across the basin. Based on the strike directions of faults within the 
Crater Flat basin, a northwest-trending hinge line can be defined (Fridrich et al. 1999 
[DIRS 107333], 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 6-5). 
The hinge line also 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 
[DIRS 107333], p. 208; Stamatakos et al. 1997 [DIRS 138819], p. 327). These observations are 
consistent with a division of the Crater Flat basin into two parts, separated at the approximate 
position of the hinge line (Figure 6-5): (1) a northeastern, less extended part, and (2) a 
southwestern, more extended part (Fridrich et al. 1999 [DIRS 107333], p. 208; Stamatakos et al. 
1997 [DIRS 138819], pp. 327 through 328). 
Seismic reflection surveys show that the Crater Flat basin is deepest to the west 
(Brocher et al. 1998 [DIRS 100022], Figure 6; Ferrill et al. 1996 [DIRS 105315], Figure 1b), 
implying that extension is also greatest to the west. Stratigraphic thickening of Miocene 
volcanic rocks to the west support this interpretation (Fridrich et al. 1999 [DIRS 107333], 

p. 198). Thus, Crater Flat basin is a single, westward-dipping graben with less fault 
displacement in the eastern half within which no major faults dominate (Figure 6-6). 
Nearly all faults of the Crater Flat basin have at least a small component of oblique offset 
(Fridrich 1999 [DIRS 118942], p. 177). Stratal tilts increase strongly to the west and south from 
an area of minimum tilts in the northeastern part of the basin on north Yucca Mountain. Faults 
in the southern part of the basin have a shallower dip and generally greater hanging wall tilt. In 
the northeastern part of the basin, cumulative extension is 7 to 15 percent. In contrast, 
cumulative extension in the southwestern part of the basin is at least 50 to 100 percent. This 
greater extension results from decreased spacing between the intrabasin faults and to increased 
average throw of the major faults (Fridrich et al. 1999 [DIRS 107333], pp. 197-198). 
6.4.1.2 Rotation of Faults 
The curved pattern of faults and the difference in orientation of faults from northeast to 
southwest, in the Crater Flat basin is attributed to southward increasing clockwise vertical-axis 
rotation where fault blocks, together with their bounding faults were rotated from their original 
positions. On the scale of the basin as a whole, the spatial variation of declination 
(i.e., interpreted as vertical-axis rotation) is very smooth (Rosenbaum et al. 1991 [DIRS 106708], 
pp. 1976 and 1977; Hudson et al. 1996 [DIRS 106194]; Fridrich et al. 1999 [DIRS 107333], 
Figure 8). The hinge line that is defined from the strike directions of faults corresponds 
approximately to the contour of 20o clockwise rotation of the Tiva Canyon Tuff. In general, 
more than 20o of clockwise rotation is present southwest of this line, and less than 20o of rotation 
is present northeast of the hinge line. In the northeastern part of the basin, cumulative clockwise 
rotation is generally less than 5o; in contrast, cumulative rotation in the southwestern part of the 
basin is greater than 45o (Fridrich et al. 1999 [DIRS 107333], p. 197). Paleomagnetic data from 
the Crater Flat basin are interpreted to show that older stratigraphic units are rotated more than 
younger units and that the major pulse of vertical-axis rotation followed the major episode of 
extension by about 1 m.y. The major pulse of rotation occurred between 11.6 and 11.45 m.y. 
(Hudson et al. 1996 [DIRS 106194]; Fridrich et al. 1999 [DIRS 107333], p. 210). The close 
association in the areal pattern of vertical-axis rotation with the magnitude of extension in the 
Crater Flat basin suggests that the rotation and extension are related as a consequence of the 
fan-like opening of the basin (Fridrich et al. 1999 [DIRS 107333], p. 210). 
6.4.1.3 Quaternary Slip Rate 
Based on the areal variation in the pattern of late Quaternary extension in the Crater Flat basin, a 
strong southward increase in deformation rate exists. Slip rates determined on individual faults 
generally increase to the south (Fridrich et al. 1999 [DIRS 107333], pp. 197 and 208; 
Fridrich 1999 [DIRS 118942], p. 177). In addition, cumulative late Quaternary (900 to 100 k.y.) 
extension measured along three profiles yields 0.025, 0.1, and 0.2 percent per m.y. from north to 
south across the basin (Fridrich et al. 1999 [DIRS 107333], p. 207). Thus, the original fan-like 
pattern of basin opening established in the Miocene still persists. The continuing pattern of 
oblique basin opening indicates that vertical-axis rotation must still be occurring at a rate that is 
significant relative to the rate of extension (Fridrich et al. 1999 [DIRS 107333], pp. 207 
and 208). 

Wernicke et al. (1998 [DIRS 103485], p. 2098) presented data from global positioning system 
surveys that they interpreted as indicating a strain rate near Yucca Mountain three to four times 
the Basin and Range average. Based on this conclusion, they suggested that the volcanic hazard 
at Yucca Mountain may have been underestimated by an order of magnitude (Wernicke et 
al. 1998 [DIRS 103485], p. 2099). A more recent study (Savage et al. 1999 [DIRS 118952]) 
using data covering a longer time period than Wernicke et al. (1998 [DIRS 103485]) interpreted 
the data to suggest that within the error of the measurements, the strain rate near Yucca 
Mountain measured between 1983 to 1998 was not significantly different from zero (Savage et 
al. 1999 [DIRS 118952], p. 17631). 
The suggestion that postulated anomalous strain rates near Yucca Mountain would lead to an 
order-of-magnitude increase in the volcano recurrence rate is not consistent with the 
post-Miocene volcanic record of the YMR. The total volume of basalt erupted during the past 
million years near Yucca Mountain is less than 0.5 km3 and is part of a systematic decline in the 
volume of basalt erupted over the past 5 m.y. (CRWMS M&O 1998 [DIRS 105347], Chapter 4, 
p. 4-12). This million-year record of low-volume volcanism is inconsistent with the hypothesis 
that approximate 100,000 year time intervals within this period have involved particularly high 
strain rates that would lead to an order-of-magnitude increase in magmatic activity, as stated by 
Wernicke et al. (1998 [DIRS 103485], p. 2099). Furthermore, the youngest episode of 
volcanism near Yucca Mountain occurred as a temporally isolated event approximately 80 k.y. 
ago at Lathrop Wells, with no volcanism occurring since (CRWMS M&O 1998 [DIRS 105347], 
Chapter 2, Sections III and IV). This observation is inconsistent with the Wernicke et al. (1998 
[DIRS 103485], p. 2099) hypothesis that Lathrop Wells may represent the onset of a cluster of 
volcanic events that may continue for several tens of thousands of years. Savage et al. (1998 
[DIRS 145359], p. 1007b) calculated that an order-of-magnitude increase in the volcano 
recurrence rate would result in a 90 percent probability of a new volcano forming between 80 ka 
and the present. No such event has occurred. Savage et al. (1998 [DIRS 145359], Figure 1) also 
presented fault displacement data showing that deformation rates in the YMR have decreased 
since about 60 k.y. ago, suggesting that the region is not currently within a period of anomalous 
strain rate that would couple to an increased volcano recurrence rate. 
6.4.1.4 Basin Subsidence and Fault Displacement 
A greater subsidence in the southwestern part of the Crater Flat basin can be inferred from a 
lower elevation and therefore, a greater sedimentation rate compared to the northeastern part of 
the basin. A subtle topographic decline (lower on the southwest side) corresponds with the hinge 
line, defined from the strike directions of faults (discussed above) along most of its length. The 
lower elevation is a function of greater total amount of extension to the southwest of the hinge 
line. Most faults that cross the hinge line show a pronounced southward increase in both 
Quaternary displacement and total bedrock displacement across it (Fridrich et al. 1999 
[DIRS 107333], pp. 197 and 208; Fridrich 1999 [DIRS 118942], p. 177), especially near the 
western margin (Bare Mountain fault) and central part (southern Yucca Mountain) of the basin. 
Miocene and Pliocene sediments are only slightly offset at the northern end of the Bare 
Mountain fault, while Holocene sediments are significantly offset near the southern end of the 
fault (Stamatakos et al. 1997 [DIRS 138819], p. 327). Also, growth of alluvial fans is greater 
along the southern part of the fault. Differences in fan growth are indicative of increased fault 
slip in the southwestern part of the basin and are compatible with measured slip rates along the 

Bare Mountain fault from 0.02 mm/yr in the north to 0.21 mm/yr along the southern part of the 
fault (Ferrill et al. 1996 [DIRS 105315], p. 562). Along the eastern side of Crater Flat, 
cumulative offset on the Solitario Canyon fault is approximately 1000 m greater to the south 
compared to the north (Stamatakos et al. 1997 [DIRS 138819], p. 327). Greater differential 
subsidence in the southwestern part of the Crater Flat basin is correlated with a greater thickness 
of Quaternary alluvium in this part of the basin compared to adjacent parts. For example, lava 
flows associated with Little Cones are buried beneath approximately 15 m of alluvium, while the 
Red and Black Cones of approximately the same age are more completely exposed. 
To summarize, a variety of structural data, including fault orientations, direction of dip, total and 
late Quaternary extension, vertical-axis rotation, and basin subsidence, are interpreted to show 
that the northeastern part of the Crater Flat basin is significantly different from the southwestern 
part of the basin. That is, each part of the basin has a distinctive style of deformation; the two 
regions of the basin can be distinguished from each other across a well-defined though 
gradational boundary, the hinge line extending obliquely across the Crater Flat basin 
(Figure 6-5). Thus, the northeastern and southwestern parts of the Crater Flat basin are 
structurally distinct, with the southwestern part characterized by a history of greater extension. 
6.4.1.5 Correlation with Volcanism 
The post-Miocene basaltic centers of the Crater Flat basin lie within the southwestern part of the 
basin (Figure 6-5). This part of the basin is coincident with the zone of greatest transtensional 
deformation, between the hinge line of the basin and the Bare Mountain fault, suggesting that 
this extensional zone controlled the ascent of basalt through the upper crust (Fridrich et al. 1999 
[DIRS 107333], p. 210). 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 
[DIRS 107333], p. 211). Thus, there is a close spatial and temporal relationship between sites of 
extension and volcanism throughout the Crater Flat basin (Fridrich et al. 1999 [DIRS 107333], 
p. 211). The restriction of three episodes of post-Miocene volcanism to the transtensional zone 
in 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 [DIRS 107333], p. 210, Figure 17a). As discussed in the next section, the 
PVHA experts recognized the close association between volcanism and areas of maximum 
extension in the YMR (CRWMS M&O 1996 [DIRS 100116], pp. RC-5, BC-12, AM-5, MS-2, 
GT-2). Subsequent geologic and geophysical studies provide corroborative evidence that areas 
of maximum extension in the Crater Flat basin correspond closely to volcanic source zones 
defined in the PVHA (Stamatakos et al. 1997 [DIRS 138819]; Brocher et al. 1998 
[DIRS 100022]; Fridrich et al. 1999 [DIRS 107333]). 
6.4.2 Probabilistic Volcanic Hazard Analysis Volcanic Source Zones: Relationship to 
Crater Flat Structural Features and the Probability of Dike Intersection 
The correlation between the structurally active part of the Crater Flat basin and sites of 
volcanism within the basin indicate that Yucca Mountain is near, but not within, a local volcanic 
zone that may produce small volumes of future volcanism (CRWMS M&O 1996 
[DIRS 100116], Appendix E, expert zone maps). Although local source zones were chosen by 

PVHA experts based largely on the location of past volcanic events, they correspond to the areas 
of highest cumulative extension and most recent faulting in the Crater Flat basin 
(Fridrich et al. 1999 [DIRS 107333], Figures 5 and 6), an association recognized by several of 
the PVHA experts (CRWMS M&O 1996 [DIRS 100116], pp. RC-5, BC-12, AM-3 through 5, 
GT-2). In all cases in which local zones were defined, the zones were restricted to the 
southwestern part of the Crater Flat basin or defined elongated, northwest-trending belts that 
included the southwestern part and stretched to the Timber Mountain area (Figure 6-7a and 
Figure 6-7b). All of the local zones excluded the northeastern part of the Crater Flat basin, in 
which the proposed Yucca Mountain repository is located (Figure 6-7a and Figure 6-7b). Based 
on structural arguments and the past patterns showing the close association of volcanism and 
extension, the eastern boundaries of local volcanic source zones defined in the PVHA separate 
more tectonically active and less tectonically active parts of the Crater Flat basin and may be 
reasonable predictors of the eastern extent of volcanism expected in the future. 
In terms of probability calculations, the volcanic source zones defined in the PVHA represent 
local regions of higher event frequency (southwestern Crater Flat), while northeastern Crater Flat 
(which includes Yucca Mountain) falls within a regional background source zone of lower event 
frequency (Figures 6-7a and 6-7b). According to the intersection probability models used in the 
PVHA, two mechanisms can generate a disruptive event at Yucca Mountain: either (1) 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 proposed repository, or (2) a volcanic event is generated within a regional 
background zone (lower probability event) and intersects the repository. Because the probability 
of intersection of a volcanic event with the proposed 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 
conclusion 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 the source zone. 
In summary, many models of the experts related the areas of greatest likelihood for future 
volcanic activity to the region where previous volcanism has occurred and in which extensional 
deformation has been, and continues to be greatest, i.e., to the southwestern part of the Crater 
Flat basin (CRWMS M&O 1996 [DIRS 100116], pp. RC-5, BC-12, AM-5, MS-2, GT-2, and 
expert zone maps; Figure 6-7a and Figure 6-7b). Analysis by the NRC also indicates that the 
highest likelihood of future volcanic activity is in southwestern Crater Flat (Reamer 1999 
[DIRS 119693], Sections 4.1.5.4 and 4.1.6.3.3; Figure 6-26). Given that the southern and 
southwestern part of the Crater Flat basin is the most extended (Ferrill et al. 1996 
[DIRS 105315]; Stamatakos et al. 1997 [DIRS 138819]; Fridrich et al. 1999 [DIRS 107333]; 
Reamer 1999 [DIRS 119693], p. 47) and that the locus of post-Miocene volcanism in the Crater 
Flat basin lies in the south and southwestern part of the basin (Fridrich et al. 1999 
[DIRS 107333]; Reamer 1999 [DIRS 119693], p. 47), volcanic source zones defined in the 
PVHA and centered in southwestern Crater Flat are consistent with the tectonic history and 
structural features of the Crater Flat structural domain (Figure 6-7a and Figure 6-7b). 

DTN: MO0002PVHA0082.000 [DIRS 148234] (for zone boundaries only). 
Source: Superimposed on the Fridrich et al. (1999 [DIRS 107333], Figure 1) map are boundaries of selected 
volcanic source zones (locally homogeneous spatial and temporal model, CRWMS M&O 1996 
[DIRS 100116] Section 3.13) that were defined by the PVHA experts and that lie within the Crater Flat 
basin (CRWMS M&O 1996 [DIRS 100116], Appendix E). 
NOTE: MC = Makani Cone; BC = Black Cone; RC = Red Cone; LC = Little Cones; LW = Lathrop Wells. 
Figure 6-7a. 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 

DTN: MO0002PVHA0082.000 [DIRS 148234] (for zone boundaries only). 
Source: Superimposed on the Fridrich et al. (1999 [DIRS 107333], Figure 1) map are boundaries of selected 
volcanic source zones (locally homogeneous spatial and temporal model, CRWMS M&O 1996 
[DIRS 100116], Section 3.13) that were defined by the PVHA experts and that lie within the Crater Flat 
basin (CRWMS M&O 1996 [DIRS 100116], Appendix E). 
NOTE: MC = Makani Cone; BC = Black Cone; RC = Red Cone; LC = Little Cones; LW = Lathrop Wells. 
Figure 6-7b. 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 

6.5 PROBABILISTIC VOLCANIC HAZARD ANALYSIS FOR THE REPOSITORY 
FOOTPRINT 
The PVHA (CRWMS M&O 1996 [DIRS 100116]) presented a methodology for calculating the 
frequency of intersection of the proposed repository by a volcanic event. The interpretations of 
10 experts were used to compute a distribution for the frequency of intersection and quantify the 
scientific uncertainty in the PVHA assessment. The configuration of the repository emplacement 
area (BSC 2003 [DIRS 162289]) has a different outline from that used in the PVHA (CRWMS 
M&O 1996 [DIRS 100116]). Consequently, the distribution for frequency of intersection is 
recalculated in this section of the report, based on the volcanic hazard model developed in the 
PVHA, but using the 2003 repository footprint (BSC 2003 [DIRS 162289]). 
To evaluate the consequences of an intersection, information is needed on the length and 
orientation of the intersecting dike or dikes and the probability that an eruptive center (the vent 
above the conduit feeding an erupting volcano) forms within the emplacement area of the 
repository. Although not computed in the original PVHA study, the length and orientation of 
intersecting dikes can be obtained as part of the calculation process without any additional 
assumptions. This section of the report develops these assessments from the PVHA volcanic 
hazard model. The PVHA experts were not asked to make assessments of the number and 
location for eruptive centers along the length of the dike system associated with a volcanic event. 
The PVHA experts did assess the number of volcanic events represented by the observed 
eruptive centers in the YMR. These assessments, together with the characteristics of Quaternary 
volcanoes in the YMR and a limited number of assumptions (described in Section 5), are used to 
derive empirical distributions for the number of eruptive centers per volcanic event. Application 
of these assessments in the calculation of the number of eruptive centers within the proposed 
repository requires assessment of the possible correlation between number of eruptive centers 
and dike length and on the spatial distribution of eruptive centers along the length of the dike. 
Calculations are performed in this report using a range of possible assessments to incorporate 
these uncertainties into the analysis. 
6.5.1 Description of the PVHA Volcanic Hazard Model Formulation 
In the context of the PVHA volcanic hazard model, a volcanic event is 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 [DIRS 100116], Appendix E). The 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 PVHA probability model by 
a line element defined in terms of a length, azimuth, and location relative to the point event 
(Figure 6-8). 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 width of the dikes and the number of parallel dikes does affect the 
consequences of an intersection and is included in Number of Waste Packages Hit by Igneous 
Intrusion (BSC 2004 [DIRS 170001]). 

This section describes the formulation of the volcanic hazard model developed in the PVHA 
(CRWMS M&O 1996 [DIRS 100116], Section 3), its extension to compute the distributions for 
the length and azimuth of intersecting dikes within the repository footprint, and the number of 
eruptive centers within this footprint. The mathematical description of the formulation is 
presented in Appendix A. The calculations were performed utilizing the 2003 repository layout 
(BSC 2003 [DIRS 162289]) and the repository footprint polygon, which was developed as 
described in Appendix B. 
6.5.1.1 Frequency of Intersection of the Repository Footprint by a Dike 
The approach used to compute the frequency of intersection of the proposed repository by a 
volcanic event is illustrated in Figure 6-8, Figure 6-9, and Figure 6-10. The PVHA experts 
specified spatial and temporal models that define the frequency of occurrence of volcanic events 
in the region around Yucca Mountain. A grid is constructed over this region with a spacing of 
0.5 km in the x (east-west) and y (north-south) directions (a 1-km spacing was used in the 
original PVHA calculation, CRWMS M&O 1996 [DIRS 100116]). At each location in the grid, 
x and y, the annual frequency of occurrence of volcanic events is computed from the experts 
spatial and temporal models. The volcanic events occurring at any point will have an associated 
dike. The experts defined distributions for the length and orientation of the possible dike or dike 
system that may be associated with volcanic events. Shown schematically on Figure 6-8 are four 
possible alternative geometries of the dike system associated with the volcanic event. Of these 
four, two are at the proper orientation and of sufficient length to intersect the repository 
footprint. Using the distributions for dike length and orientation, the fraction of all of the 
possible alternative dike systems associated with volcanic events at any point that intersect the 
proposed repository is computed. This fraction is defined as the conditional probability of 
intersection for volcanic events at a point. (The probability is called a conditional probability 
because it is conditional on the occurrence of a volcanic event.). 
Figure 6-9 illustrates how the conditional probability of intersection is computed. The dike 
system associated with a volcanic event at point (x,y) has a total length L. The distance d from 
the point (x,y) to the end of the dike system in the direction of the repository is important for 
determining whether or not intersection of the repository footprint occurs. Distance d is some 
fraction of the total length L depending on how the dike system is oriented with respect to the 
volcanic event. (How distance d is determined is discussed in the paragraph below.) Given a 
distance d, all dikes with azimuths between f1 and f2 will intersect the repository footprint. The 
probability that the dike will have an azimuth between f1 and f2 is determined by the PVHA 
experts distributions for dike orientation. The probability that the dike system will have length 
d is determined by the PVHA experts distributions for the total length of the dike system L and 
the location of the dike system with respect to the volcanic event. Combing these two 
probability distributions produces the conditional probability of intersection for point (x,y). 

For Information Only 
NOTE: Dikes labeled 1 through 4 represent four alternative geometries for the dikes associated with a volcanic event at 
point (xi,yj). 
Figure 6-8. Schematic Illustrating Procedure for Computing the Frequency of Intersection of the 
Proposed Repository by a Volcanic Event 
For Information Only 
NOTE: L is the length of the dike, d is the distance from the volcanic event at point (x,y) to the end of the dike, f1 
and f2 are the range in azimuths for which a dike extending a distance d from point (x,y) will intersect the 
repository, and LIm is the length of the intersecting dike within the repository when the dike is at azimuth fn. 
Figure 6-9. Illustration of the Process Used to Compute the Conditional Probability of Intersection of the 
Proposed Repository by a Volcanic Event 

For Information Only 
Figure 6-10. Example Distributions for Dike Length, L, (part a); Normalized Location of the Point 
Volcanic Event Relative to the Total Length of the Dike, EL, (part b); and the Resulting 
Distribution for Distance from the Point Volcanic Event to the End of the Dike, d (part c) 

Figure 6-10 illustrates how the distribution for distance d is obtained. Part (a) of Figure 6-10 
shows an example probability distribution for the total length L of the dike system associated 
with a volcanic event. Typically, these distributions were defined by the PVHA experts to be 
skewed with long upper tails. Part (b) shows a distribution for the normalized location of the 
dike system relative to the point volcanic event, parameter EL. If all dike systems were centered 
on the volcanic event, then EL would always equal 0.5 and d would always equal L/2. However, 
the PVHA volcanic hazard model allowed for the possibility that the dike system near the 
surface was not necessarily centered on the volcanic event and EL was allowed to vary over the 
range of 0 to 1. The PVHA experts specified distributions for EL that were symmetric about 0.5 
(the expected center of the event relative to the total length of the dike) and typically had higher 
probability for locations at the midpoint (the dike centered on the event point) than at the ends 
(the dike extending for its full length in one direction away from the event point). It is because 
the parameter EL is allowed to vary between 0 and 1, that the point volcanic event is defined as 
the expected center (the mean value of EL is equal to 0.5 in all cases) rather than just the 
center of the volcanic event. Part (c) shows the resulting probability and cumulative probability 
distributions for the distance d from the proposed repository to the end of the dike obtained by 
convolving the distributions from (a) and (b). 
The frequency of intersecting volcanic events occurring at point (x,y) in Figure 6-8 is then 
obtained by multiplying the frequency of volcanic events occurring at that point by the 
conditional probability of intersection for that point. The process is repeated for all locations in 
the grid, producing the frequency of intersection at each point. The sum of these values over all 
locations in the grid is the annual frequency of intersection of the proposed repository by 
volcanic events, the computed result of the PVHA volcanic hazard model. 
Figure 6-11 shows the components of this calculation. Part (a) shows the spatial distribution of 
volcanic event frequency. The contour value at any point represents the expected annual 
frequency of volcanic events per square kilometer. These values represent the weighted average 
of all of the PVHA experts alternative spatial and temporal models for the occurrence of 
volcanic events. Areas with the highest event frequency (contoured intervals from orange to red) 
outline Crater Flat and a small region around the Lathrop Wells volcano. Areas with the next 
level of event frequency (yellow contoured areas) extend to the northwest to Sleeping Buttes and 
to the south into Amargosa Valley. There is also a small yellow area at Buckboard Mesa 
northeast of the repository location. The areas of higher event frequency represent areas of 
post-Miocene volcanism in the YMR and areas where future volcanism is considered more likely 
to occur. Part (b) of Figure 6-11 shows a map of the product of the volcanic event frequency 
(part a) and the conditional probability of intersection for each point (x,y). It is a map of the 
spatial distribution of volcanic events that contribute to the mean annual frequency of 
intersection (the integral of the displayed densities equals the mean annual frequency of 
intersection). In those areas that are shown in white, the conditional probability of intersection is 
very low and dike systems for volcanic events that occur in these areas are very unlikely to 
intersect the repository. The north-northeastsouth-southwest elongation of the region shown 
on Part (b) of Figure 6-11 reflects the highest weighted orientation of dike systems in the PVHA 
volcanic hazard model. The shape of the yellow region to the southwest of the repository 
location matches that of the high frequency region for Crater Flat on part (a), with a high 
intensity point at Lathrop Wells. The Buckboard Mesa region to the northeast of the repository 
also shows a contribution to the intersection frequency. 

(a) (b) 
Intersection 
Volcanic Events4150 
Events 
4150 
per year
per year 
per sq km 
per sq km 
1E-010 
1E-007 
4100 
1E-011 
UTM Northing (km) 
UTM Northing (km) 
4100 
1E-008 
1E-012 1E-009 
1E-010 1E-013 
4050 
4050 
1E-011 
1E-014 
1E-012 
1E-015 
1E-013 4000 
1E-016 
4000 
500 550 600 500 550 600 
UTM Easting (km) UTM Easting (km) 
Output DTNs: (a) LA0009FP831811.001; (b) LA0303BY831811.001. 
NOTE: The maps represent the mean results averaged over 10 experts and over each experts logic tree 
(CRWMS M&O 1996 [DIRS 100116], Appendix E). The black area in the center of the maps is the location 
of the proposed repository. 
Figure 6-11. Spatial Distribution of Volcanic Hazard Defined by the Probabilistic Volcanic Hazard 
Analysis Expert Panel: (a) Spatial distribution of Expected Volcanic Event Frequency and 
(b) Spatial Distribution of Expected Intersection Frequency 
In all assessments of the effects of rare phenomena, there is considerable uncertainty in selecting 
the appropriate models and model parameters arising from limited data and (or) alternative 
interpretations of the available data. The PVHA experts quantified the uncertainty in the annual 
frequency of intersection of the proposed repository by developing sets of alternative probability 
models and model parameters for all aspects of the hazard calculation. These models were 
organized in the logic tree format shown in Figure 6-12a and Figure 6-12b. 
A logic tree consists of a series of nodes or levels representing the sequence of assessments that 
must be made to perform the analysis. The order of these nodes reflects a progression from 
general or global assessments of alternative models, to the specific assessment of individual 
model parameters. In a logic tree, all assessments are made conditional on the path leading to a 
particular node. As a simple example, the first node of the tree may address assessing the 
relative credibility of two alternative conceptual models, Model A or Model B. The second level 
of the tree would then address the assessment of the model parameters. On the Model A branch 
from the first node, the assessment at the second level node would address only the parameters 
for Model A under the assumption that Model A applies to the problem. On the Model B branch, 
the assessment at the second level node would address only the parameters for Model B under 
the assumption that Model B applies. The logic tree methodology allows for alternative models, 
hypotheses, and parameter values to be weighted and incorporated into the analysis in a logical 
and transparent way. Thus, it provides a convenient approach for breaking a large, complex 
assessment into a sequence of smaller, simpler components that can be more easily addressed. 

Source: Modified from CRWMS M&O 1996 [DIRS 100116]. 
Figure 6-12a. Logic Tree Structure Used to Characterize Uncertainty in Volcanic Hazard 
Source: Modified from CRWMS M&O 1996 [DIRS 100116]. 
NOTE: These sub-trees are attached to the overall logic tree shown on Figure 6-12a. 
Figure 6-12b. Logic Tree Structure for Sub-trees Addressing Uncertainty in Volcanic Hazard from 
Specific Sources 

At each node, a set of branches is used to define discrete alternatives for alternative credible 
models or parameter values that characterize the uncertainty in the assessment. The alternative 
branches are defined to be a mutually exclusive and collectively exhaustive set of alternatives. 
The weights are assigned to each branch to represent the relative likelihood or degree of belief 
that the branch represents the correct value or state of the input parameter. The weights on the 
branches at each node are treated as conditional probabilities, with the branch weights summing 
to unity at each node. 
For assessments such as the PVHA, the weights depend strongly upon expert judgment 
(subjective probabilities) because the available data are too limited to allow for objective 
statistical analysis and because scientific judgment is needed to weigh alternative scientific 
interpretations of the available data. The logic tree approach simplifies these subjective 
assessments because the uncertainty in a single parameter is considered individually and all other 
parameters leading up to that parameter assessment are assumed to be known with certainty. 
Thus, the nodes of the logic tree are sequenced to provide for the conditional aspects or 
dependencies among the parameters and to provide a logical progression of assumptions from 
the general to the specific in defining the input parameters for an evaluation. 
Figure 6-12a and Figure 6-12b show the general logic tree structure used to represent the 
scientific uncertainties in the PVHA computation. The logic tree is structured to move from the 
assessment of the general framework on the left (Figure 6-12a) to specific assessments of 
individual volcanic zones and volcanic centers on the right (Figure 6-12b). The specific 
definition of volcanic source zone or the estimate of the number of events that may have 
occurred at a volcanic center are often dependent upon more general assessments of the 
appropriate time period or region of interest. Thus, the dependent assessments are placed to the 
right, and the independent assessments are placed to the left. 
The first two nodes of the logic tree address specification of alternative distributions for the 
length and orientation of dikes associated with the events. These parameters are used to compute 
the conditional probability of intersection. The assessments of these two distributions are placed 
first in the logic tree because they apply to all events that may occur in the region and are not 
dependent on the spatial or temporal models used to model volcanic event occurrence. 
The remaining levels of the logic tree shown on Figure 6-12a address the alternative spatial and 
temporal models used to characterize the occurrence of volcanic events in the Yucca Mountain 
region. These assessments include various time periods representative of the current rate of 
volcanic events, alternative temporal models, alternative regions over which the hazard is 
evaluated, and alternative spatial models. 
At this point, the logic tree is expanded into sub-trees, one for each of the identified volcanic 
sources. The vertical bar without a dot denotes additive hazard from multiple sources, (e.g., a 
local source zone and a background source). To the right of this point of the logic tree each 
source is considered to be acting independently, and the distribution in the total computed hazard 
is obtained by convolving the independent distributions obtained for each source. 

The logic tree structure for each volcanic source sub-tree is shown on Figure 6-12b. These logic 
trees address the parameters for the various spatial and temporal models for the individual 
volcanic sources and the number of volcanic events that have occurred at each of the major 
volcanic centers. The final node addresses the statistical uncertainty in estimating the volcanic 
rate parameter for the given temporal model and data set. This statistical uncertainty includes the 
uncertainty in the homogenous or non-homogeneous Poisson rates and the uncertainty in the 
volume predictable rate. Detailed descriptions of the PVHA volcanic hazard model are 
presented in Probabilistic Volcanic Hazard Analysis for Yucca Mountain, Nevada (CRWMS 
M&O 1996 [DIRS 100116], Section 3 and Appendix E). 
Each pathway through the composite logic tree (Figure 6-12a and Figure 6-12b) represents a 
complete interpretation of the volcanic hazard at the site for which a frequency of intersection is 
computed. Each pathway is associated with a probability equal to the product of the conditional 
probabilities of all the branches along the way. The result of computing the hazard for all 
pathways is a discrete distribution for frequency of intersection, representing the uncertainty in 
the volcanic hazard at a site. 
6.5.1.2 Conditional Distribution for Length and Azimuth of an Intersecting Dike 
The PVHA analysis did not make any assessment of the consequences of an intersection of the 
repository footprint by a dike. Consequently, a potential dike that extended all the way through 
the proposed repository, such as Dike 2 on Figure 6-8, has the same contribution to the frequency 
of intersection as a shorter dike that only extends part way into the proposed repository, such as 
Dike 4 on Figure 6-8. However, an assessment of consequences requires information on the 
length and orientation of the intersecting dikes within the proposed repository. This information 
is obtained by breaking down (disaggregating) the intersection frequency into relative 
frequencies for discrete increments of dike intersection length and azimuth. 
Referring to Figure 6-9, the pictured dike system has a specific azimuth of fn. and a length of 
intersection within the repository footprint of LIm. A series of bins with length increments of 
50 meters and azimuth increments of 5 were defined. This discretization is sufficiently fine to 
provide an accurate picture of the distribution of lengths and azimuths of intersecting dikes. 
Then, when a volcanic event produces an intersection in the hazard calculation, the resulting 
length and azimuth within the repository footprint are computed and the event is assigned to the 
appropriate bin. At the end of the calculation, the value in each bin represents the frequency of 
intersections that produce the specific values of length and azimuth represented by the bin 
parameters. The sum of the numbers in all of the length-azimuth bins equals the frequency of 
intersection. The values in each bin divided by the frequency of intersection provide a 
conditional distribution for length and azimuth, given an intersection. The only parameters that 
affect the calculation of the conditional distributions for dike intersection length and azimuth are 
the dike length, dike location on the volcanic event, and dike azimuth distributions. Thus, this 
calculation is completely defined by the interpretations developed by the PVHA expert panel 
(CRWMS M&O 1996 [DIRS 100116], Appendix E) and requires no additional assumptions. 

6.5.1.3 Conditional Distribution for the Number of Eruptive Centers 
This section discusses the formulation for assessing the conditional distribution for the number 
of eruptive centers within the footprint of the proposed repository. The development is based on 
the concept that eruptive centers will occur at uncertain locations along the length of the dike 
system associated with a volcanic event. The length of intersection within the repository 
footprint, compared to the total length of the dike system, the number of eruptive centers per 
volcanic event, and the spatial distribution of eruptive centers along the length of the dike system 
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 system and the length of intersection within 
the proposed repository are computed as part of the formulation presented above in 
Sections 6.5.1.1 and 6.5.1.2, and are completely defined by the PVHA experts interpretations 
without any additional assumptions. 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 
PVHA expert elicitation. However, with the limited set of assumptions (Section 5), 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 PVHA, 
these alternatives were used to develop alternative assessments of the conditional distribution for 
the number of eruptive centers within the repository footprint. These alternative assessments are 
then combined using relative weights assigned to each to produce a composite assessment. 
Number of Eruptive Centers Associated with a Volcanic EventThe assumptions described 
in Section 5.1 and 5.2 provide the basis for using the mapped volcanoes in the YMR to derive 
assessments of the number of eruptive centers per volcanic event from the PVHA experts 
interpretations. Two alternative approaches are used as described below. 
The first approach uses the number of mapped volcanoes to derive empirical distributions for the 
number of eruptive centers per volcanic event independent of any assessment of the total length 
of the dike system associated with the volcanic event. In this approach, volcanic events can have 
from 1 to 5 eruptive centers, the range in number of individual volcanoes associated with a single 
volcanic event, as defined by the PVHA experts using the YMR data. For example, the observed 
five volcanoes in Crater Flat are assumed to correspond to five eruptive centers using the 
assumption described in Section 5.1. These eruptive centers may have been caused by 1 to 5 
volcanic events, with each PVHA expert providing a probability distribution for the number of 
volcanic events. These assessments can be used to produce a distribution for the number of 
eruptive centers per volcanic event. If the Crater Flat volcanoes were produced by five 
individual volcanic events, then the data indicate one eruptive center per volcanic event. If, on 
the other hand, the five volcanoes (and their associated eruptive centers) were created by one 
volcanic event, then the data indicate five eruptive centers per volcanic event. Using each 
experts assessments of volcanic event counts and the number of separate eruptive centers that 
have occurred in the Quaternary, distributions for the number of separate eruptive centers per 
volcanic event were developed. These distributions are developed in Appendix C and shown in 
Figure 6-13. 

0 
1 2 3 4 5 
Probability 
AM 
BC 
GT 
GW 
MK 
MS 
RC 
RF 
WD 
WH 
0.1 
0.2 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
0.9 
Number of Eruptive Centers per Volcanic Event 
Output DTN: LA0009FP831811.001. 
Source: from Appendix C, Figure C-1. 
NOTE: The two-letter code refers to the initials of the 10 PVHA experts in Table 6-3. 
Figure 6-13. Distributions for Number of Eruptive Centers per Volcanic Event Derived from the 
Probabilistic Volcanic Hazard Analysis Experts Interpretations 
The distributions shown on Figure 6-13 were developed without explicit consideration of the 
length of the dike system associated with the volcanic events. The PVHA experts distributions 
for dike length were also assessed without consideration of the number of eruptive centers 
associated with a volcanic event. However, the calculation of the conditional probability of the 
number of eruptive centers with the repository footprint requires the conditional distribution of 
the number of eruptive centers given the dike length (Appendix A). The limiting conditions that 
define the relationship between two variables are complete independence and complete 
dependence. These two limiting conditions are used to define alternatives for the influence of 
dike length on the number of eruptive centers on a dike. Complete independence implies that the 
conditional distribution for number of eruptive centers is equal to the distributions shown on 
Figure 6-13, regardless of the total length of the dike system. Complete dependence implies that 
the number of eruptive centers varies directly with dike length (it is considered unrealistic to 
have a negative correlation). The correlation between dike length and number of eruptive 
centers per event was set to the maximum value by making the distributions for number of 
eruptive centers per volcanic event shown on Figure 6-13 rank correlated with the corresponding 
experts dike length distribution. 
The longest proposed single-event dike represented by the Quaternary volcanoes in the YMR is 
the 11.2-km spacing between Little Cones SW and Makani Cone in Crater Flat. However, many 
of the PVHA experts specified distributions for dike length with upper tails that greatly exceed 
this length. Thus, the distributions shown on Figure 6-13 may not be representative of 
conditions for very long dikes. To address this issue, an alternative approach for defining the 
number of eruptive centers was included. In the second approach, the number of eruptive centers 

is defined on the basis of an average density per kilometer of dike length or equivalently, by the 
average spacing between eruptive centers. For a given dike length, the number of eruptive 
centers is found by dividing the dike length by the average spacing (rounding to the nearest 
integer). 
The same process used to derive the distribution for number of eruptive centers per volcanic 
event from the PVHA experts assessments was used to evaluate the average spacing between 
eruptive centers. For example, if the five volcanoes in Crater Flat are considered to constitute a 
single volcanic event, then the 11.2-km distance between Little Cones SE and Makani Cone in 
Crater Flat divided by 4 (the number of intervals between eruptive centers) gives an average 
spacing of 2.8 km. An alternative assessment might be that Crater Flat contains two volcanic 
events. One volcanic event may consist of Makani and Black Cones. These two cones are 
located 5.4 km apart. The other volcanic event would then consist of Red Cone and the two 
Little Cones. The distance between Red Cone and Little Cone SW is 3.2 km, resulting in an 
average spacing for this volcanic event of 1.6 km. The other Quaternary volcano cluster with 
multiple cones is Hidden Cone and Little Black Peak near Sleeping Butte, 2.5 km apart. If these 
are considered to be the result of a single volcanic event, the average spacing between eruptive 
centers for this event is 2.5 km. Empirical distributions for the average spacing between eruptive 
centers in an individual volcanic event were developed as described in Appendix C, by 
considering all of the alternative volcanic event assessments made by each expert. These 
distributions are listed in Table 6-6. Note that the minimum value of the average spacing of 
eruptive centers in the empirical distributions is 0.46 km (the spacing between Little Cones NE 
and Little Cones SW). Using this average spacing and the maximum repository dimensions, the 
maximum possible number of eruptive centers within the repository footprint is 13. Table 6-7 
lists the mean or expected value of the distributions given in Table 6-6 for each of the PVHA 
experts to provide a basis for comparison. 
In this second approach the total number of eruptive centers is directly correlated with the total 
length of the dike system. 
Table 6-6. Empirical Distribution for Average Spacing between Eruptive Centers Calculation Results 
PVHA Expert Empirical Distribution for Average Spacing between Eruptive Centers (km) 
Alex McBirney (AM) 0.46 (0.0272), 2.01 (0.0492 ), 2.45 (0.0253 ), 2.80 (0.8859 ), 2.88 (0.0124) 
Bruce Crowe (BC) 0.46 (0.4031), 1.62 (0.0489), 2.45 (0.1874), 2.80 (0.0914), 2.88 (0.2203), 5.35 (0.0489) 
George Thompson (GT) 0.46 (0.4720), 2.01 (0.1279), 2.45 (0.1839), 2.80 (0.1705), 2.88 (0.0457) 
George Walker (GW) 0.46 (0.5916), 2.45 (0.1767), 2.80 (0.0800), 2.88 (0.1517) 
Mel Kuntz (MK) 0.46 (0.0550), 2.01 (0.2100), 2.45 (0.2950), 2.80 (0.4200), 2.88 (0.0200) 
Michael Sheridan (MS) 0.46 (0.0388), 2.01 (0.1330), 2.45 (0.3238), 2.80 (0.4656), 2.88 (0.0388) 
Richard Carlson (RC) 0.46 (0.1186), 2.45 (0.3608), 2.80 (0.4020), 2.88 (0.1186) 
Richard Fisher (RF) 0.46 (0.0842), 1.62 (0.0192), 2.45 (0.3383), 2.80 (0.5199), 2.88 (0.0192), 5.35 (0.0192) 
Wendell Duffield (WD) 0.46 (0.6445), 2.45 (0.0322), 2.80 (0.0833), 2.88 (0.1560), 4.09 (0.0840) 
William Hackett (WH) 0.46 (0.4078), 2.45 (0.1844), 2.80 (0.0851), 2.88 (0.1844), 4.09 (0.1383) 
OUTPUT DTN: LA0009FP831811.004. 
Source: from Appendix C, Table C-13 of this document. 
NOTE: The values in ( ) are the empirical probability for the preceding value of average spacing. 
ANL-MGR-GS-000001 REV 02 6-53 October 2004 

Table 6-7. Expected Value for Average Eruptive Center Spacing 
PVHA Expert 
Expected Value for Average Spacing 
Between Eruptive Centers (km) 
Alex McBirney (AM) 2.7 
Bruce Crowe (BC) 1.9 
George Thompson (GT) 1.5 
George Walker (GW) 1.4 
Mel Kuntz (MK) 2.4 
Michael Sheridan (MS) 2.5 
Richard Carlson (RC) 2.4 
Richard Fisher (RF) 2.5 
Wendell Duffield (WD) 1.4 
William Hackett (WH) 2.0 
Output DTN: LA0009FP831811.001. 
Source: from Appendix C, Table C-12. 
Spatial Distribution of Eruptive Centers Along a Dike SystemThe assumption described in 
Section 5.3 provides the basis for specification of the spatial distribution of eruptive centers 
along the length of the dike system. The minimum information probability distribution for the 
random location of a point on a line is the uniform distribution between the limits of the line 
length. The assumption listed in Section 5.3 applies the uniform distribution to eruptive center 
location. Two alternative applications of the uniform distribution were used to capture the range 
of possible behaviors when multiple eruptive centers occur along the length of the dike system 
for a single volcanic event, as illustrated in Figure 6-14. 
The first approach specifies the location of each eruptive center independently of the others and 
is designated the independent, uniformly distributed (IUD) approach. The probability that an 
individual eruptive center will occur within the repository is equal to the length of intersecting 
dike within the proposed repository divided by the total length of the dike system. Over many 
volcanic events, this approach on average will produce eruptive centers spaced out over the total 
length of the volcanic events. However, for an individual event, a range of behaviors may occur. 
Part (a) of Figure 6-14 shows 20 simulations using the IUD approach. Some of the simulations 
produce relatively uniform spaced eruptive centers and some produce highly clustered eruptive 
centers. 
Dense clustering of multiple eruptive centers can be prevented by imposing a minimum spacing 
between the eruptive centers. Taking this approach to the limit would result in uniform spacing 
of eruptive centers along the length of the dike. Part (b) of Figure 6-14 shows 20 simulations 
using an approach in which the length of the dike is divided into equal length segments, one 
segment for each eruptive center. Applying the assumption described in Section 5.3, each 
eruptive center is randomly located within its segment following a uniform distribution. This 
approach, designated the uniformly spaced, randomly distributed (USRD) approach, produces a 
broader spread between the eruptive centers in each simulation compared with the IUD 
approach, while still allowing for clustering of two eruptive centers along the length of the dike. 
Some clustering is expected to occur on occasion, given the close spacing between Little Cones 
SW and Little Cones NE. The probability that the eruptive center associated with each 

dike-length segment will occur within the repository footprint now becomes the length of that 
segment within the repository divided by the length of that segment. 
For Information Only 
NOTE: Each row of triangles represents a separate simulation of the locations of five eruptive centers along the 
length of a dike system. The solid triangles show the locations of the individual eruptive centers for each 
simulation. 
Figure 6-14. Example Simulations of the Distribution of Eruptive Centers along the Length of a Dike for: 
(a) the Independent, Uniformly Distributed (IUD) Spatial Distribution and (b) the Uniformly 
Spaced, Randomly Distributed (USRD) Spatial Distribution 

r
Figure 6-15a and Figure 6-15b compare the probabilities of eruptive centers occurring within the 
repository footprint as a function of dike length using these two approaches for the spatial 
distribution of eruptive centers. In Figure 6-15a, the length of intersection within the repository 
is held fixed at 1 km and the number of eruptive centers associated with the volcanic event is 
held fixed at 2. The three plots grouped on the left show the probability of 0, 1, or 2 eruptive 
centers occurring within the repository footprint as a function of the total length of the dike 
system, and the single plot on the right shows the probability of at least one eruptive center 
within the repository. The parameter rEC indicates the number of eruptive centers within the 
repository. For a total length L of 1 km, the entire dike lies within the repository (the length of 
intersection is fixed at 1). Therefore, the probability for rEC = 3 is 1.0 and the probability forEC = 1 or rEC = 0 is zero (no portion of the dike lies outside of the repository). As length L 
increases while holding the length of intersection fixed at 1, some portion of the dike now lies 
outside of the repository. For the IUD spatial distribution there is now a finite probability that 
both eruptive centers will lie outside of the repository (rEC = 0). The probability increases 
continuously with increasing length L. For the USRD spatial distribution, over half of the dike 
lies within the repository until the total length L reaches 2 km. Thus, the probability for rEC = 0 
remains at zero until L reaches 2 km. At that point, the probability rEC = 1 becomes 1.0 for the 
USRD approach because half of the dike, and thus one complete dike segment, lies within the 
repository. For L greater than 2, the probability rEC = 2 becomes zero for the USRD approach in 
this example because it was computed assuming that one end of the dike system was penetrating 
the repository footprint. If the dike system were straddling the repository, then the probability 
the rEC = 2 would be greater than 0. 
For Information Only 
NOTE: Results are shown for the independent, uniformly distributed (IUD) and the uniformly spaced, randomly 
distributed (USRD) spatial distributions. 
Figure 6-15a. Probability for the Number of Eruptive Centers Within the Repository Footprint, rEC, as a 
Function of Dike Length, L, for the Length of Intersection Equal to 1 km and the Number 
of Eruptive Centers Associated with the Volcanic Event Equal to 2 

For Information Only 
NOTE: Results are shown for the independent, uniformly distributed (IUD) and the uniformly spaced, randomly 
distributed (USRD) spatial distributions. 
Figure 6-15b. Probability for the Number of Eruptive Centers Within the Repository Footprint, rEC, as a 
Function of Dike Length, L, for the Length of Intersection Equal to 1 km and the Number 
of Eruptive Centers Associated with the Volcanic Event Equal to 3 
Figure 6-15b repeats this example calculation with the total number of eruptive centers 
associated with the volcanic event increased to 3. The behavior is similar to that shown on 
Figure 6-15a. For all total lengths, the USRD spatial distribution approach produces a higher 
probability that at least one eruptive center will occur within the repository footprint (rEC is 
greater than 0). Except for short dike lengths, use of the IUD spatial distribution produces a 
higher probability of multiple eruptive centers within the repository footprint for a fixed length 
of intersection. 
The USRD spatial density approach is also consistent with the concept of determining the 
number of eruptive centers associated with a volcanic event on the basis of an average spacing 
between eruptive centers and total dike system length. In this approach the density of eruptive 
centers is fixed at a specified average spacing and the number of eruptive centers is determined 
by dividing this average spacing into the total length of the dike system, L. The total length of 
the dike system is divided into segments with lengths equal to the average spacing between 
eruptive centers. The location of the eruptive center within each segment is then specified by a 
uniform distribution following the assumption discussed in Section 5.3. This modified form of 
the USRD spatial distribution is designated the USRD-FD approach for uniformly 
spaced-randomly distributed with fixed density. 
Figure 6-16 shows an example calculation of the probability of one or more eruptive centers 
occurring within the repository footprint for the USRD-FD approach. The example is the same 
one as that shown in Figure 6-15a. For short dike lengths, the USRD-FD approach results in a 
lower probability for one or more centers within the proposed repository than the other two 

approaches. However, as the dike length increases, the USRD-FD approach reaches a nearly 
constant probability of 0.4 for intersection by one eruptive center (0.4 equals the intersection 
length of 1 km divided by the fixed average spacing of 2.5 km). 
For Information Only 
NOTE: Results are shown for the independent, uniformly distributed (IUD), the uniformly spaced, randomly 
distributed (USRD), and the uniformly spaced, randomly distributed with fixed density (USRD-FD) spatial 
distributions. Total number of eruptive centers is fixed at 2 for the IUD and USRD approaches and is 
determined from the total dike length and an average spacing of 2.5 km for the USRD-FD approach. As in 
Figure 6-15a, the length of intersection is fixed at 1 km. 
Figure 6-16. Example Probabilities for the Number of Eruptive Centers within the Repository Footprint, 
EC
r, Computed with the Total Number of Eruptive Centers Defined by an Average Spacing 
of 2.5 km between Eruptive Centers Compared to Probabilities Computed Using a Fixed 
Total Number of 2 Eruptive Centers 
Computation of the Conditional Distribution for the Number of Eruptive CentersThe 
process for computing the conditional distribution for number of eruptive centers can now be 
described. Referring back to Figure 6-9, the pictured dike system has a total length L and a 
length of intersection within the repository of LIm. Given the total number of eruptive centers 
associated with the volcanic event and one of the alternative approaches for the spatial 
distribution of eruptive centers along the length of the dike system, the probability of 0, 1, 2, etc. 
eruptive centers within the repository is computed. These probabilities are multiplied by the 
frequency of volcanic events at point (x,y) that produce intersection lengths of LIm for total dike 
system lengths L defined in Section 6.5.1.2. The process is repeated for the full distribution of 
possible dike lengths and then over the spatial grid for possible volcanic event locations. The 
sum of event frequencies that produce 0, 1, 2, etc. eruptive centers within the repository footprint 
is then divided by the total frequency of intersection (Section 6.5.1.1) to produce the conditional 
distribution for number of eruptive centers within the repository. 

The approaches developed above for specifying the total number of eruptive centers associated 
with a volcanic event and their spatial distribution along the length of the dike system lead to 
five alternative assessments for the conditional probability distribution for number of eruptive 
centers within the repository footprint. The five approaches are summarized below: 
1. 
The independent, uniformly distributed, uncorrelated (IUD-UC) approach. The 
distribution for the total number of eruptive centers per volcanic event is derived from 
the PVHA experts interpretations (Figure 6-13). These distributions are uncorrelated 
with the distributions for dike length. The location for each eruptive center is defined 
by a uniform distribution over the total length of the dike, and if multiple eruptive 
centers occur in a volcanic event, the distributions for their locations are independent. 
2. 
The independent, uniformly distributed, correlated (IUD-C) approach. The 
distribution for the total number of eruptive centers per volcanic event is derived from 
the PVHA experts interpretations (Figure 6-13). These distributions are completely 
correlated with the distributions for dike length. The location for each eruptive center 
is defined by a uniform distribution over the total length of the dike and if multiple 
eruptive centers occur in a volcanic event, the distributions for their locations are 
independent. 
3. 
The uniformly spaced, randomly distributed, uncorrelated (USRD-UC) approach. The 
distribution for the total number of eruptive centers per volcanic event is derived from 
the PVHA experts interpretations (Figure 6-13). These distributions are uncorrelated 
with the distributions for dike length. The total length of the dike is divided into equal 
segments, one for each eruptive center. Within each segment, the location of the 
eruptive center is defined by a uniform distribution over the length of the segment. 
4. 
The uniformly spaced, randomly distributed, correlated (USRD-C) approach. The 
distribution for the total number of eruptive centers per volcanic event is derived from 
the PVHA experts interpretations (Figure 6-13). These distributions are completely 
correlated with the distributions for dike length. The total length of the dike is divided 
into equal segments, one for each eruptive center. Within each segment, the location 
of the eruptive center is defined by a uniform distribution over the length of the 
segment. 
5. 
The uniformly spaced, randomly distributed, fixed density (USRD-FD) approach. The 
total number of eruptive centers per volcanic event is determined by dividing the total 
length of the dike by an average distance between eruptive centers derived from the 
PVHA experts interpretations (Table 6-6). The total length of the dike is divided into 
equal segments, one for each eruptive center. Within each segment, the location of the 
eruptive center is defined by a uniform distribution over the length of the segment. 
Application of the results of this report in assessing the impact of disruptive events requires a 
rule for combining the results obtained from these five approaches. In the overall framework of 
the PVHA, this is accomplished by assigning weights to each model. These weights are derived 
by separately examining the three issues addressed by the alternative approaches. 

The first issue is the overall approach for evaluating the number of eruptive centers per volcanic 
event. The two approaches are to define a distribution for the total number based on the 
observed Quaternary data, or to define the average spacing using the Quaternary data and 
compute the number for each dike length. These two approaches are considered to be equally 
credible. They both rely to an equal degree on the observed data and the PVHA experts 
interpretations of these data to define the characteristics of volcanic events in the YMR. Thus, 
the two approaches are given equal weight. 
The second issue is the appropriate spatial distribution for eruptive centers along the length of 
the dike or dike system. Two alternative approaches are used, one in which the location of each 
eruptive center is independent of the others (IUD), and one in which the eruptive centers are 
spaced out along the total length of the dike system (USRD). The simulations shown on 
Figure 6-14 indicate that the IUD spatial model often produces tight clustering of multiple 
eruptive centers. This is somewhat at odds with the limited observations for eruptive centers in 
the vicinity of Yucca Mountain. Therefore, the URSD model is strongly preferred over the IUD 
model by a ratio of 3:1, yielding weights of 0.75 for the USRD models and 0.25 for the IUD 
models. Note that this assessment applies to the cases where the number of eruptive centers is 
derived from the distributions shown on Figure 6-13. When the number of eruptive centers is 
derived from an average spacing, only the USRD model is applied because it is consistent with 
the basis for determining the number of eruptive centers. 
The third issue addresses the correlation between the distributions for number of eruptive centers 
per volcanic event shown on Figure 6-13 and the distributions for the length of the dike 
associated with a volcanic event developed by the PVHA experts. Two alternatives are 
used: the two distributions are uncorrelated and the two distributions are fully correlated. It is 
likely that there is some degree of correlation because longer total dike lengths would provide 
more opportunity for the formation of vents and presumably result from volcanic events with 
larger volumes. Thus, the fully correlated model is slightly favored (0.6) to the uncorrelated 
model (0.4). Again, this assessment applies only to the cases where the number of eruptive 
centers is derived from the distributions shown in Figure 6-13. Determining the number of 
eruptive centers for a volcanic event using the average spacing and the total length produces full 
correlation between length and number of eruptive centers. 
Combining these three sets of weights yields the following relative weighting of the five 
approaches for computing the conditional distribution for number of eruptive centers within the 
repository footprint: 
 
The weight for the IUD-UC approach is equal to 0.5 for the approach for number of 
centers, times 0.25 for the spatial approach, times 0.4 for uncorrelated number of 
eruptive centers and dike length distributions, yielding a weight of 0.05. 
 
The weight for the IUD-C approach is equal to 0.5 for the approach for number of 
centers, times 0.25 for the spatial approach, times 0.6 for correlated number of eruptive 
centers and dike length distributions, yielding a weight of 0.075. 

 
The weight for the USRD-UC approach is equal to 0.5 for the approach for number of 
centers, times 0.75 for the spatial approach, times 0.4 for uncorrelated number of 
eruptive centers and dike length distributions, yielding a weight of 0.15. 
 
The weight for the USRD-C approach is equal to 0.5 for the approach for number of 
centers, times 0.75 for the spatial approach, times 0.6 for uncorrelated number of 
eruptive centers and dike length distributions, yielding a weight of 0.225. 
 
The weight for the USRD-FD approach is 0.5 for the approach, with only the USRD 
spatial approach applying because the correlation issue is not pertinent, yielding a 
weight of 0.5. 
These weights are used to combine the results for the five alternative approaches to number of 
eruptive centers to produce a composite result of the analyses. 
Incorporation of Potential Effect of Repository OpeningsThe above approaches developed 
for assessing the spatial distribution of eruptive centers along the length of the dike or dikes 
associated with a volcanic event assume that the presence of the repository drifts has no impact 
on the likelihood of an eruptive conduit forming within the repository footprint. There exists 
some potential that the presence of the repository opening may induce formation of an eruptive 
center if intersection occurs. Therefore, two approaches are used to address the effect of the 
repository openings. The first approach considers the repository openings to have no effect and 
uses the weighted combination of the five approaches described above to develop the conditional 
distributions for 0, 1, 2, 3, etc. intersecting eruptive centers. The second approach considers that 
the repository openings will induce at least one eruptive center. For this approach the 
distribution for the number of intersecting eruptive centers is derived from the results of the first 
approach by setting the conditional probability of no intersecting eruptive centers to zero and 
renormalizing the probabilities for 1, 2, 3, etc. intersecting eruptive centers to sum to unity. For 
example, if the first approach resulted in a conditional distribution for the number of intersecting 
eruptive centers of {0 (0.4), 1 (0.3), 2 (0.2), 3 (0.1)}, then the second approach would result in 
the distribution for the number of intersecting eruptive centers of {1 (0.5), 2 (0.333), 3 (0.167)}. 
Because there has not been significant study of the issue and the PVHA experts were not elicited 
on this question, maximum uncertainty weights of 0.5 are applied to these two approaches for 
assessing the effect of the repository openings. As a result, the composite distribution for the 
number of eruptive centers intersecting the proposed repository in the above example would be 
{0 (0.2), 1 (0.4), 2 (0.267), 3 (0.133)}. 

6.5.2 Description of Probabilistic Volcanic Hazard Calculation 
This section briefly describes the implementation of the formulation presented in Section 6.5.1. 
A complete description is presented in Appendix A. 
6.5.2.1 Computation of Frequency of Intersection of the Repository Footprint by a Dike 
The computational scheme used in Probabilistic Volcanic Hazard Analysis for Yucca Mountain, 
Nevada (CRWMS M&O 1996 [DIRS 100116]) and repeated in this report consists of the steps 
shown on Figure 3-1. These steps are performed for each of the volcanic hazard models 
developed by the 10 PVHA experts. 
Step 1: Discrete cumulative distributions for dike length are developed from the experts 
assessments using software routines FITCD V1.0 (LANL 2000 [DIRS 148532]) or SFCD V1.0 
(LANL 2000 [DIRS 148533]) (e.g., part (a) of Figure 6-10). These distributions are then 
convolved with the experts event location on the dike distribution (e.g., part (b) of Figure 6-10) 
to produce distributions for volcanic event length (e.g., part (c) of Figure 6-10) using software 
routine DCPELD V1.0 (LANL 2000 [DIRS 148534]). This step develops the distribution for 
parameter d shown on Figure 6-9. 
Step 2: The conditional probability of intersection is computed for each set of parameters 
defined by a unique event length distribution from Step 1 and a unique dike azimuth distribution 
using software routine CPDI V1.0 (LANL 2000 [DIRS 148535]). The output from individual 
runs of software routine CPDI is stored for use in the next step of the calculation. 
Step 3: The rate of intersection is computed for individual volcanic hazard source models using 
software routines specific to the type of source: 
 
Software routines UZVH V1.0 (LANL 2000 [DIRS 148536]) and UZVPVH V1.0 
(LANL 2000 [DIRS 148537]) for source zones 
 
Software routines FKVH V1.0 (LANL 2000 [DIRS 148567]), FKVPVH V1.0 (LANL 
2000 [DIRS 148538]), and ZBCKVH V1.0 (LANL 2000 [DIRS 148539]) for kernel 
density sources 
 
Software routines PFGVH V1.0 (LANL 2000 [DIRS 148542]) and FPFGVH V1.0 
(LANL 2000 [DIRS 148543]) for 2-D Gaussian field sources. 
The characterization of individual volcanic sources is defined by the alterative parameters 
indicated on the right hazard side of the volcanic source logic tree shown on Figure 6-12b. 
These parameters depend upon the alternative source definitions, temporal models, and time 
periods of interest. The software routines used to compute the hazard from an individual source 
contain a set of 12 nested DO loops to enumerate all of the alternative parameter sets (see 
Figure 6-12b). Given a set of parameters, the frequency of volcanic events is computed for a 
specific source using the formulation appropriate for the source type. This frequency is 
multiplied by the conditional probability of intersection, from the output of routine CPDI V1.0 
and summed over all points within the source to obtain the frequency of intersection from 
volcanic events associated with the source. The software routines store the mean frequency of 

intersection and the distribution in the frequency of intersection in output files for use in the final 
step of the computation. Separate output files are created for all of the alternative sets of source 
model parameters and for the alternative parameters that describe the associated dikes. 
Step 4: The results from Step 3 are combined over the distributions for both the source model 
parameters and the associated dikes (see Figure 6-12a and Figure 6-12b) to compute the full 
distribution for frequency of intersection specified by an individual PVHA experts 
interpretations. The results for each expert are then combined with equal weights to obtain the 
composite distribution. These calculations are performed using software routine VHTREE V1.0 
(LANL 2000 [DIRS 148544]). Complete enumeration of all of the alternative parameter sets is 
achieved by a series of nested DO loops. The mean value and various percentiles of the 
distribution for frequency of intersection of the repository footprint by a dike are computed from 
the discrete distribution for frequency of intersection defined by the alternative end branches of 
the volcanic hazard model logic trees. 
The 2003 repository footprint used for the calculations in this report is shown on Figure 6-17a 
(BSC (2003 [DIRS 162289]), but this footprint has been superseded by a more recent design 
(BSC 2004 [DIRS 164519]). The calculations performed in the PVHA (CRWMS M&O 1996 
[DIRS 100116]) used the repository footprint shown in Figure 6-17b. The 2003 repository 
design (BSC 2003 [DIRS 162289]) calls for a longer and narrower emplacement area compared 
to the design used at the time of the PVHA (Figure 6-17b). Appendix B presents the coordinates 
of the drifts in the 2003 repository footprint and their transformation to UTM kilometers. The 
repository footprint polygon used for calculations in this report uses values obtained from 
Repository Design, Repository/PA IED Subsurface Facilities (BSC 2003 [DIRS 162289]) and 
modified to provide a clearance of approximately 55 m around the drift coordinates 
(see Figure 6-17a) to account for the effect of the size of eruptive centers in the calculations 
(see Appendix B). The final footprint polygon used for calculation information is contained in 
output DTN: LA0303BH831811.001. 

Output DTN: LA0303BY831811.001. 
Figure 6-17a. Repository Emplacement Drifts and Footprint Polygon Encompassing the Emplacement 
Panels 
The most recent proposed repository design differs from the design used for the calculations in 
this report by having one less emplacement drift at the north end of panel 3 (BSC 2004 
[DIRS 164519]). This decreases the north-south extent of the footprint by approximately 100 m 
but has a negligible impact on the current calculations. For comparison, the difference in 
north-south dimension between the repository footprint used for the current calculation (BSC 
2003 [DIRS 162289]) and the footprint used in the PVHA is approximately 1500 m (Figure 16b). 
This difference resulted in a difference in the calculated mean of the frequency of intersection of 
about 13%. Based on this comparison, the difference in the mean frequency of intersection 
caused by the small change in the most recent proposed repository design (BSC 2004 
[DIRS 164519] is expected to be less than 1%, which is negligible given the overall range of 
uncertainty in the results. 

Output DTN: LA0303BY831811.001. 
NOTE: PVHA reference in figure is CRWMS M&O (1996 [DIRS 100116]). 
Figure 6-17b. Location of 2003 Repository Footprint (BSC 2003 [DIRS 162289]) Compared to 
Repository Footprint Used in the Probabilistic Volcanic Hazard Analysis 
6.5.2.2 Computation of Distributions for Length, Azimuth, and Number of Eruptive 
Centers 
The computations performed in Probabilistic Volcanic Hazard Analysis for Yucca Mountain, 
Nevada (CRWMS M&O 1996 [DIRS 100116]) were made for all possible sets of parameters 
(full enumeration of the logic tree branches) defined by the volcanic hazard characterization of 
each of the PVHA experts (CRWMS M&O 1996 [DIRS 100116], Appendix E). However, the 

objective of this analysis is a disaggregation of the intersection frequency into intersection 
frequencies with specific values of intersecting dike length, dike azimuth, and number of 
eruptive centers. Repeating the calculation including this disaggregation would require 
exhaustive computation and storage of the spatial disaggregation of the hazard for all possible 
parameter sets. Therefore, a simulation approach was used to develop random sample parameter 
sets from the PVHA experts logic trees and to speed up the computation process. As discussed 
subsequently in the results (Section 6.5.3), the mean and distribution for the frequency of 
intersection of the repository footprint by a dike computed by full enumeration and by simulation 
for each PVHA experts interpretation and for the composite result generally agree within a few 
percent. The approach used to obtain the spatial disaggregation of the frequency of intersection 
consists of the following steps (see Figure 3-2). 
Step 1: The conditional probability of intersection was taken directly from the computation for 
the frequency of intersection discussed above. The files containing the conditional probability of 
intersection for each set of parameters were created using routine CPDI V1.0 (LANL 2000 
[DIRS 148535]) and using inputs processed through routines FITCD V1.0 (LANL 2000 
[DIRS 148532]), SFCD V1.0 (LANL 2000 [DIRS 148533]), and DCPELD V1.0 (LANL 2000 
[DIRS 148534]). This process is a repeat of steps 1 and 2 discussed in Section 6.5.2.1. 
Step 2: The second step in the calculation involved computation of the spatial disaggregation of 
frequency of intersection hazard for the individual sources specified by the alternative source 
parameter sets and for the alternative dike parameters. For the reasons discussed at the 
beginning of this section, simulation is used to select random samples of the parameter subset, 
which is used to compute the frequency of intersection for an individual source type. The 
approach used to generate these parameter subsets is Latin hypercube sampling (McKay et al. 
1979 [DIRS 127905], pp. 243-245). The software routines used to compute the frequency of 
intersection replace the 12 nested DO loops with simulation of 50 parameter sets using Latin 
hypercube sampling from the 12 independent and discrete parameter distributions representing 
the right hand side of the individual source logic tree shown on Figure 6-12b. The product of the 
Latin hypercube sampling is 50 equally likely outcomes from each experts model for an 
individual volcanic source. 
The simulation software routines are designated UZVHLH V1.0 (LANL 2000 [DIRS 148545), 
UZVPVHLH V1.0 (LANL 2000 [DIRS 148547]), FKVHLH V1.0 (LANL 2000 
[DIRS 148546]), FKVPVHLH V1.0 (LANL 2000 [DIRS 148551]), ZBCKVHLH V1.0 (LANL 
2000 [DIRS 148550]), PFGVHLH V1.0 (LANL 2000 [DIRS 148552]), and FPFGVHLH V1.0 
(LANL 2000 [DIRS 148553]). They use the same input files used to compute the frequency of 
intersection by full enumeration (Step 3 in Section 6.5.2.1). 
Step 3: The third step in the calculation is computation of the distribution for the spatial 
disaggregation of the hazard for each PVHA experts interpretation. The full enumeration of the 
possible parameter sets is again replaced by simulation of 50 equally likely parameter sets using 
Latin hypercube sampling. The software routine VHTIELHS V1.0 (LANL 2000 
[DIRS 148554]) is used to perform this calculation for the volcanic hazard model developed by 
each of the PVHA experts. The result of this calculation is the frequency of intersection at each 
point in the 0.5 km  0.5 km grid covering the Yucca Mountain region. Part (b) of Figure 6-11 
shows a map of this result, averaged over all 10 of the PVHA experts models. 

Step 4: The composite distribution for the frequency of intersection of the repository footprint 
by a dike is now represented by the 2,500  10 simulation results for the 10 PVHA experts. 
Each experts distribution was assigned equal weight in the PVHA aggregation process. Thus, 
the composite 25,000 simulations of annual frequency of intersection are all equally likely. The 
25,000 simulations of annual frequency of intersection are ranked and the simulations that 
produce various percentiles of the distribution are identified (e.g., the 95th percentile is the 
simulation with rank 0.95  25,000 = 23,750). Simulation results that are close to each 
percentile (within a rank of 250) and that are from different experts are also identified to 
capture the range of expert interpretations. These simulations are identified using software 
routine CFRAC V1.0 (LANL 2000 [DIRS 148560]). 
Step 5: Steps 1 through 4 provide the values of disaggregated frequency of intersection and the 
expected value for the spatial disaggregation of the frequency of the intersection for each of the 
possible dike geometry distributions (the first two levels of the logic tree shown on 
Figure 6-12a). The final step is the discretization of the conditional probability of intersection 
into increments of intersection length, intersection azimuth, and number of eruptive centers 
within the repository footprint for each volcanic event location. Software routine DILECDLH 
V1.0 (BSC 2000 [DIRS 168221]) is used to discretize the conditional probability of intersection 
into the designated bins for length and azimuth within the proposed repository. The inputs to 
program DILECDLH are: (1) the spatial disaggregation of the frequency of intersection; (2) the 
dike length and volcanic event location distributions for the corresponding parameter set; (3) a 
joint distribution for dike length and the number of eruptive centers on a dike, which is computed 
using software routines FITIDSR V1.0 (LANL 2000 [DIRS 148557], SFIDSR V1.0 (LANL 
2000 [DIRS 148571]), and DLECD V1.0 (LANL 2000 [DIRS 148558]); and (4) the spatial 
distribution of eruptive centers along the dike. 
As discussed in Section 6.5.1.3, five alternative approaches are used to compute the number and 
spatial distributions of eruptive centers along the length of the dike system associated with a 
volcanic event. All five of these approaches are used to obtain conditional distributions for the 
number of eruptive centers within the repository footprint given an intersection by a volcanic 
event. A weighted average of the results of these five approaches is computed using the weights 
developed in Section 6.5.1.3. As a final step, the potential effect of the repository opening is 
incorporated as described at the end of Section 6.5.1.3. 
The calculations performed in Step 5 are carried out at three levels of the distribution for 
frequency of intersection: the mean frequency of intersection, the 5th percentile frequency of 
intersection, and the 95th percentile frequency of intersection. The resulting conditional 
distributions for intersection length, intersection azimuth, and number of eruptive centers with 
the repository footprint do not represent the mean, 5th percentile, and 95th percentile values of 
these distributions. Instead, they represent the distribution of length, azimuth, and number of 
eruptive centers conditional on the frequency of intersection equaling the mean, 5th percentile 
and 95th percentile value. 

6.5.3 Results 
6.5.3.1 Frequency of Dike Intersection of the Repository Footprint 
Table 6-8 lists the mean annual frequency of intersection of the repository footprint and 
percentiles of the distribution for the frequency of intersection computed by full enumeration and 
by simulation with Latin hypercube sampling for the repository footprint. The results are listed 
for each expert, indicated by the experts initials from Table 6-3, and for the composite 
distribution over all 10 experts, with equal weight assigned to the individual expert assessments. 
The results computed by full enumeration of the experts logic trees are indicated by the 
suffix-FEn in the column headings (e.g., AM-FEn) and the results computed by simulation are 
indicated by the suffix-Sim in the column headings (e.g., AM-Sim). The percent difference in 
the frequency of intersection is also listed in the tables. The differences between the frequencies 
of intersection computed by full enumeration and by simulation are generally small, ranging 
from -25.7 percent to +20.5 percent, indicating that simulation with Latin hypercube sampling 
reliably represents the full distribution for frequency of intersection. 
Table 6-8. Frequency of Intersection for the Repository Footprint 
AM1-FEn2 AM-Sim2 
% 
Difference3 BC-FEn BC-Sim 
% 
Difference GT-FEn GT-Sim 
% 
Difference 
Mean 0.696E-08 0.698E-08 0.2 0.136E-07 0.135E-07 -0.3 0.379E-07 0.374E-07 1.3 
0.05 0.199E-08 0.212E-08 6.3 0.118E-08 0.118E-08 -4.9 0.123E-07 0.117E-07 -4.8 
0.1 0.245E-08 0.253E-08 3.0 0.195E-08 0.179E-08 -8.5 0.148E-07 0.149E-07 0.7 
0.15 0.282E-08 0.303E-08 7.5 0.251E-08 0.238E-08 -5.1 0.174E-07 0.172E-07 -0.9 
0.2 0.316E-08 0.318E-08 0.4 0.295E-08 0.278E-08 -5.8 0.204E-07 0.192E-07 -5.8 
0.3 0.363E-08 0.364E-08 0.2 0.398E-08 0.389E-08 -2.3 0.229E-07 0.226E-07 -1.2 
0.4 0.407E-08 0.402E-08 -1.3 0.550E-08 0.542E-08 -1.4 0.263E-07 0.265E-07 0.6 
0.5 0.457E-08 0.467E-08 2.1 0.832E-08 0.819E-08 -1.5 0.316E-07 0.322E-07 1.8 
0.6 0.549E-08 0.529E-08 -3.7 0.132E-07 0.136E-07 3.5 0.372E-07 0.387E-07 4.3 
0.7 0.676E-08 0.646E-08 -4.4 0.178E-07 0.176E-07 -1.2 0.447E-07 0.436E-07 -2.3 
0.8 0.851E-08 0.827E-08 -2.8 0.240E-07 0.240E-07 -0.2 0.525E-07 0.501E-07 -4.6 
0.85 0.102E-07 0.111E-07 8.6 0.263E-07 0.265E-07 0.6 0.617E-07 0.575E-07 -6.7 
0.9 0.141E-07 0.138E-07 -2.7 0.309E-07 0.307E-07 -0.8 0.676E-07 0.656E-07 -3.0 
0.95 0.209E-07 0.214E-07 2.4 0.417E-07 0.402E-07 -3.6 0.776E-07 0.756E-07 -2.6 

Table 6-8. Frequency of Intersection for the Repository Footprint (Continued) 
GW-FEn GW-Sim 
% 
Difference MK-FEn MK-Sim 
% 
Difference MS-FEn MS-Sim 
% 
Difference 
Mean 0.675E-08 0.695E-08 3.1 0.123E-07 0.120E-07 -2.0 0.190E-07 0.186E-07 -1.7 
0.05 0.126E-08 0.121E-08 -3.9 0.437E-09 0.468E-09 7.3 0.324E-08 0.341E-08 5.3 
0.1 0.174E-08 0.180E-08 3.6 0.912E-09 0.103E-08 13.4 0.468E-08 0.436E-08 -6.8 
0.15 0.219E-08 0.216E-08 -1.5 0.174E-08 0.186E-08 7.0 0.589E-08 0.539E-08 -8.4 
0.2 0.257E-08 0.233E-08 -9.2 0.251E-08 0.247E-08 -1.8 0.708E-08 0.629E-08 -11.2 
0.3 0.331E-08 0.312E-08 -5.7 0.398E-08 0.390E-08 -2.1 0.977E-08 0.841E-08 -13.9 
0.4 0.407E-08 0.401E-08 -1.6 0.603E-08 0.576E-08 -4.4 0.126E-07 0.110E-07 -12.4 
0.5 0.501E-08 0.493E-08 -1.7 0.813E-08 0.791E-08 -2.7 0.155E-07 0.148E-07 -4.3 
0.6 0.631E-08 0.587E-08 -7.0 0.107E-07 0.106E-07 -0.9 0.195E-07 0.188E-07 -3.4 
0.7 0.794E-08 0.791E-08 -0.4 0.141E-07 0.139E-07 -1.7 0.234E-07 0.238E-07 1.4 
0.8 0.102E-07 0.104E-07 1.4 0.186E-07 0.186E-07 0.0 0.282E-07 0.286E-07 1.6 
0.85 0.120E-07 0.123E-07 2.2 0.219E-07 0.216E-07 -1.3 0.316E-07 0.318E-07 0.7 
0.9 0.138E-07 0.139E-07 0.4 0.275E-07 0.265E-07 -3.7 0.363E-07 0.366E-07 0.8 
0.95 0.174E-07 0.155E-07 -10.6 0.363E-07 0.357E-07 -1.7 0.447E-07 0.443E-07 -0.8 
RC-FEn RC-Sim 
% 
Difference RF-FEn RF-Sim 
% 
Difference WD-FEn WD-Sim 
% 
Difference 
Mean 0.157E-07 0.151E-07 -3.7 0.199E-07 0.197E-07 -0.8 0.166E-08 0.200E-08 20.5 
0.05 0.123E-08 0.130E-08 5.8 0.437E-08 0.437E-08 0.1 0.138E-09 0.134E-09 -3.0 
0.1 0.191E-08 0.177E-08 -7.3 0.617E-08 0.573E-08 -7.0 0.204E-09 0.205E-09 0.3 
0.15 0.251E-08 0.237E-08 -5.8 0.759E-08 0.687E-08 -9.5 0.257E-09 0.256E-09 -0.4 
0.2 0.339E-08 0.310E-08 -8.4 0.891E-08 0.816E-08 -8.4 0.339E-09 0.352E-09 3.9 
0.3 0.468E-08 0.439E-08 -6.1 0.112E-07 0.111E-07 -1.2 0.537E-09 0.539E-09 0.3 
0.4 0.741E-08 0.736E-08 -0.7 0.138E-07 0.141E-07 2.5 0.100E-08 0.743E-09 -25.7 
0.5 0.977E-08 0.992E-08 1.5 0.170E-07 0.173E-07 1.8 0.123E-08 0.124E-08 0.7 
0.6 0.129E-07 0.130E-07 0.5 0.200E-07 0.196E-07 -1.8 0.123E-08 0.124E-08 0.8 
0.7 0.174E-07 0.176E-07 1.2 0.234E-07 0.234E-07 -0.3 0.151E-08 0.153E-08 0.9 
0.8 0.229E-07 0.230E-07 0.4 0.282E-07 0.283E-07 0.3 0.263E-08 0.229E-08 -12.9 
0.85 0.309E-07 0.303E-07 -2.0 0.316E-07 0.321E-07 1.5 0.295E-08 0.293E-08 -0.7 
0.9 0.372E-07 0.348E-07 -6.4 0.363E-07 0.379E-07 4.4 0.380E-08 0.382E-08 0.4 
0.95 0.525E-07 0.437E-07 -16.7 0.457E-07 0.444E-07 -2.8 0.457E-08 0.535E-08 16.9 
WH-FEn WH-Sim % Difference Composite4 Fen Composite4 Sim % Difference 
Mean 0.353E-07 0.357E-07 0.9 0.169E-07 0.168E-07 -0.6 
0.05 0.692E-08 0.702E-08 1.5 0.741E-09 0.743E-09 0.2 
0.1 0.871E-08 0.874E-08 0.4 0.148E-08 0.149E-08 0.4 
0.15 0.102E-07 0.102E-07 -0.1 0.229E-08 0.227E-08 -1.1 
0.2 0.120E-07 0.120E-07 -0.5 0.302E-08 0.296E-08 -2.0 
0.3 0.170E-07 0.164E-07 -3.5 0.457E-08 0.449E-08 -1.8 
0.4 0.234E-07 0.233E-07 -0.6 0.692E-08 0.673E-08 -2.7 

Table 6-8. Frequency of Intersection for the Repository Footprint (Continued) 
WH-FEn WH-Sim % Difference Composite4 Fen Composite4 Sim % Difference 
0.5 0.295E-07 0.299E-07 1.3 0.100E-07 0.992E-08 -0.8 
0.6 0.355E-07 0.363E-07 2.2 0.145E-07 0.142E-07 -1.9 
0.7 0.437E-07 0.440E-07 0.8 0.204E-07 0.203E-07 -0.8 
0.8 0.537E-07 0.542E-07 0.9 0.269E-07 0.276E-07 2.6 
0.85 0.603E-07 0.607E-07 0.8 0.331E-07 0.330E-07 -0.5 
0.9 0.692E-07 0.696E-07 0.5 0.407E-07 0.410E-07 0.7 
0.95 0.871E-07 0.891E-07 2.3 0.550E-07 0.533E-07 -3.0 
Output DTN: LA0303BY831811.001. 
1 AM = Alex McBirney, BC = Bruce Crowe, GT = George Thompson, GW = George Walker, MK = Mel Kuntz, MS = 
Michael Sheridan, RC = Richard Carlson, RF = Richard Fisher, WD = Wendell Duffield, WH = William Hackett. 
2 FEn = results from full enumeration, Sim = results from simulations with Latin hypercube sampling. 
The percent difference is computed as (Sim - FEn)/FEn. It represents the percent difference between the 
frequency of intersection computed by full enumeration and by simulation. 
4 The composite distributions are computed giving equal weight to the individual experts distributions. 
The computed distribution for the annual frequency of intersection of the repository footprint by 
a dike is shown in Figure 6-18. Part (a) of Figure 6-18 shows the computed distributions for the 
frequency of intersection aggregated over all of the 10 PVHA experts interpretations, together 
with the median and mean values obtained for each experts interpretation. Part (b) of 
Figure 6-18 compares the 5th to 95th percentile range for frequency of intersection obtained for 
each experts interpretation with that for the aggregate distributions. 
The computed mean annual frequency of intersection of the repository footprint by a dike is 1.7 
 10-8 for the 2003 repository footprint (BSC 2003 [DIRS 162289]) as compared to 1.5  10-8 
obtained in the PVHA (CRWMS M&O 1996 [DIRS 100116], p. 4-10). The computed 5th and 
95th percentiles of the uncertainty distribution for frequency of intersection are 7.4  10-10 and 
5.5  10-8, respectively, as compared to 5.4 10-10 and 4.9 10-8 obtained in the PVHA 
(CRWMS M&O 1996 [DIRS 100116], p. 4-10). 
The composite uncertainty distributions for frequency of intersection that are the output of these 
calculations are located in the output file PVHA-4P.DST in Output 
DTN: LA0302BY831811.001 The file consists of a title record, a record giving the number of 
points in the composite distribution, and n records containing the n discrete values of frequency 
of intersection, the associated probability mass, and the cumulative probability, which together 
define the cumulative probability density function (CDF). 

Output DTN: LA0303BY831811.001. 
NOTE: (a) Aggregate distribution and median and means for individual PVHA expert interpretations. (b) Range for 
5th to 95th percentiles for results from individual PVHA expert interpretations compared to range for 
aggregate distribution. Two-letter code indicates initials of experts from Table 6-3. 
Figure 6-18. Annual Frequency of Intersecting the Repository Footprint 
6.5.3.2 Conditional Distributions for Intersection Length, Azimuth, and Number of 
Eruptive Centers within the Repository Footprint 
The Latin hypercube sampling process described in Section 6.5.2.2 was used to compute joint 
distributions for length and azimuth of dike intersection at the mean, 5th, and 95th percentile 
frequencies of intersection. At each of these frequencies of intersection, distributions for the 
number of eruptive centers within the repository footprint were developed, conditional on the 
length and azimuth within the repository of the intersecting dike system. The joint distributions 
are listed in three output files (Output DTN: LA0303BY831811.001): file CCSM-LA.CMP 
provides the joint distribution for length and azimuth of dike intersection and conditional 
distributions for the number of eruptive centers corresponding to the mean frequency of 

5
intersection; file CC05-LA.CMP provides the joint distribution for length and azimuth of dike 
intersection and conditional distributions for the number of eruptive centers corresponding to the 
th percentile frequency of intersection; and file CC95-LA.CMP provides the joint distribution 
for length and azimuth of dike intersection and conditional distributions for the number of 
eruptive centers corresponding to the 95th percentile frequency of exceedance. Each file consists 
of a title record, a record giving the number of points in the joint distribution for dike intersection 
length and azimuth, and n records containing the n pairs of intersection length (LIm) and azimuth 
(fn) and the joint probability of an intersection having that length and azimuth within the 
proposed repository. Also listed for each LIm and fn 
pair, is the composite conditional 
distribution for the number of eruptive centers within the proposed repository given the pair LIm 
and fn. 
Figure 6-19, Figure 6-20, and Figure 6-21 show the marginal distributions for intersection length, 
intersection azimuth, and number of eruptive centers for the repository footprint, respectively, 
computed from the joint distributions described above (a marginal distribution represents the 
variation in a single parameter averaged over the variations in the other parameters). These 
results are also summarized in Table 6-9, Table 6-10, and Table 6-11. The marginal distributions 
are computed from the joint distributions using software routine MARGIN V1.1 (BSC 2000 
[DIRS 168223]) (Figure 3-2). The results indicate the degree to which the distributions for 
length and azimuth of intersecting dikes and the number of eruptive centers vary with frequency 
of intersection. For example, results listed in Table 6-9 indicate that similar marginal 
distributions for dike intersection length are obtained at the 5th, mean, and 95th frequencies of 
intersection. The marginal distributions for intersection azimuth obtained at the 5th, mean, and 
95th frequencies of intersection (Table 6-10) are also similar. 
Figure 6-21 shows the marginal distributions for the number of eruptive centers within the 
repository footprint obtained using the five alternative approaches for the number and spatial 
distribution of eruptive centers along the length of the dike system. The IUD-UC approach 
produces the lowest probability of one or more eruptive centers within the proposed repository, 
approximately 0.4, and the USRD-FD approach produces the highest probability, approximately 
0.6. The values plotted in Figure 6-21 are those computed using the five alternative approaches 
for evaluating the number and spatial distribution of eruptive centers under the assumption that 
the presence of the proposed repository opening has no effect on the location of eruptive centers. 
These distributions are listed in the second through sixth columns of Table 6-11 under the overall 
subheading of Random Location for the formulation of eruptive center spatial distribution. 
The seventh column of Table 6-11 shows the marginal distribution for the weighted average 
results of the five approaches, using the weights described at the end of Section 6.5.1.3 and 
indicated in the column headings. The eighth column of Table 6-11 shows the marginal 
distribution for number of eruptive centers within the repository footprint under the assumption 
that the presence of the repository openings results in at least one eruptive center within the 
repository footprint, given an intersection. The last column of Table 6-11 lists the final 
composite marginal distribution, which represents an equally weighted average of the random 
location assumption and the renormalized random distributions with P(rEC = 0) = 0 (eighth 
column). Similar marginal distributions for the number of eruptive centers are obtained at the 
5th, mean, and 95th frequencies of intersection. 

Output DTN: LA0303BY831811.001. 
NOTE: These distributions are conditional on the occurrence of an intersection. The distributions are developed for 
the specified value of the frequency of intersection. 
Figure 6-19. Marginal Distributions for Dike Intersection Length, LI, for the 5th Percentile, Mean, and 
95th Percentile Frequency of Intersection 
Output DTN: LA0303BY831811.001. 
NOTE: These distributions are conditional on the occurrence on an intersection. The distributions are developed for 
the specified value of the frequency of intersection. 
Figure 6-20. Marginal Distributions for Dike Intersection Azimuth, f, for the 5th Percentile, Mean, and 
95th Percentile Frequency of Intersection for the Repository Footprint 

5th Percentile Hazard 
0 
0.1 
0.2 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
Probability 
IUD-UC 
USRD-UC 
IUD-C 
USRD-C 
USRD-FD
1 23 4 56 78 910111213 
0 
Num ber of Eruptive Centers w ithin Repository Footprint 
Mean Hazard 
0 
0.1 
0.2 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
Probability 
IUD-UC 
USRD-UC 
IUD-C 
USRD-C 
USRD-FD
0 1 23 4 56 78 910111213 
Num ber of Eruptive Centers w ithin Repository Footprint 
95th Percentile Hazard 
0 
0.1 
0.2 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
Probability 
IUD-UC 
USRD-UC 
IUD-C 
USRD-C 
USRD-FD 
0 1 23 4 56 78 910111213 
Num ber of Eruptive Centers w ithin Repository Footprint 
Output DTN: LA0303BY831811.001. 
NOTE: IUD = independent; uniformly distributed; USRD = uniformly spaced; randomly distributed; 
UC = uncorrelated length and number of eruptive centers per volcanic event distributions; C = correlated 
length and number of eruptive centers per volcanic event distributions; FD = fixed density for number of 
eruptive centers per volcanic event. These distributions are conditional on the occurrence on an 
intersection. The distributions are developed for the specified value of the frequency of intersection. 
r
Figure 6-21. Marginal Distributions for the Number of Eruptive Centers within the Repository Footprint, 
EC, for the 5th Percentile, Mean, and 95th Percentile Frequency of Intersection 

Table 6-9. Marginal Distributions for Dike Intersection Length for the 5th Percentile, Mean, and 95th 
Percentile Frequency of Intersection of the Repository Footprint 
Dike Intersection 
Length (km) 
Probability Mass 
5th Percentile Frequency 
of Intersection 
Mean Frequency 
of Intersection 
95th Percentile 
Frequency of Intersection 
0.0-0.255 0.1288 0.1088 0.1051 
>0.255-0.505 0.1159 0.1048 0.1012 
>0.505-0.755 0.1114 0.1054 0.1047 
>0.755-1.005 0.1336 0.1128 0.1105 
>1.005-1.255 0.1208 0.1189 0.1137 
>1.255-1.505 0.0821 0.0909 0.0888 
>1.505-1.755 0.0583 0.0674 0.0679 
>1.755-2.005 0.0492 0.0553 0.0591 
>2.005-2.255 0.0382 0.0430 0.0433 
>2.255-2.505 0.0353 0.0421 0.0417 
>2.505-2.755 0.0296 0.0323 0.0324 
>2.755-3.005 0.0255 0.0318 0.0334 
>3.005-3.255 0.0219 0.0263 0.0285 
>3.255-3.505 0.0190 0.0226 0.0230 
>3.505-3.755 0.0104 0.0089 0.0106 
>3.755-4.005 0.0044 0.0055 0.0065 
>4.005-4.255 0.0028 0.0043 0.0046 
>4.255-4.505 0.0025 0.0050 0.0062 
>4.505-4.755 0.0036 0.0028 0.0066 
>4.755-5.005 0.0039 0.0033 0.0031 
>5.005-5.255 0.0016 0.0036 0.0044 
>5.255-5.505 0.0013 0.0042 0.0043 
>5.505-5.755 0.0001 0.0003 0.0003 
Output DTN: LA0307BY831811.001. 

Table 6-10. Marginal Distribution for Intersecting Dike Azimuth for the 5th Percentile, Mean, and 95th 
Percentile Frequency of Intersection of the Repository Footprint 
Intersecting Dike 
Azimuth () 
Probability Mass 
5th percentile 
Frequency of 
Intersection 
Mean Frequency of 
Intersection 
95th percentile 
Frequency of 
Intersection 
>-2.5-12.5 0.0560 0.0861 0.1072 
>12.5-22.5 0.1240 0.1485 0.1636 
>22.5-32.5 0.2030 0.2717 0.2491 
>32.5-42.5 0.2015 0.2372 0.2060 
>42.5-52.5 0.1463 0.1146 0.0955 
>52.5-62.5 0.0841 0.0464 0.0402 
>62.5-72.5 0.0431 0.0157 0.0188 
>72.5-82.5 0.0209 0.0053 0.0099 
>82.5-92.5 0.0102 0.0023 0.0055 
>92.5-102.5 0.0043 0.0011 0.0031 
>102.5-112.5 0.0013 0.0005 0.0017 
>112.5-122.5 0.0005 0.0004 0.0009 
>122.5-132.5 0.0019 0.0011 0.0015 
>132.5-142.5 0.0072 0.0037 0.0049 
>142.5-152.5 0.0193 0.0100 0.0145 
>152.5-162.5 0.0327 0.0182 0.0280 
>162.5-172.5 0.0316 0.0230 0.0325 
>172.5-177.5 0.0121 0.0142 0.0170 
Output DTN: LA0307BY831811.001. 

Table 6-11. Marginal Distribution for Number of Eruptive Centers within the Proposed Repository for the 
5th Percentile, Mean, and 95th Percentile Frequency of Intersection of the Repository 
Footprint 
Number of 
Eruptive 
Centers in 
Proposed 
Repository 
rEC 
Formulation for Eruptive Center Spatial Distribution 
Final 
Composite 
Marginal 
Probability 
Random Location 
(weight 0.5) 
Repository 
Induces 
Eruptive 
Center 
(weight 0.5) 
Independent, 
Uniformly 
Distributed, 
Uncorrelated, 
(weight 0.05) 
Uniformly 
Spaced, 
Randomly 
Distributed, 
Uncorrelated, 
(weight 0.15) 
Independent, 
Uniformly 
Distributed, 
Correlated, 
(weight 
0.075) 
Uniformly 
Spaced, 
Randomly 
Distributed, 
Correlated, 
(weight 
0.225) 
Uniformly 
Spaced, 
Randomly 
Distributed, 
Fixed Density, 
(weight 0.5) 
Weighted 
Average 
For 
Random 
Location 
Renormalized 
such that 
P(rEC=0)=0 
Conditional Distributions for 5th Percentile Frequency of Intersection 
0 0.693 0.672 0.571 0.516 0.391 0.490 0 0.245 
1 0.232 0.264 0.328 0.419 0.369 0.355 0.738 0.546 
2 0.0489 0.0414 0.0775 0.0537 0.102 0.0775 0.140 0.109 
3 0.0108 0.0098 0.0171 0.0088 0.0495 0.0300 0.0539 0.0419 
4 0.00688 0.00566 0.00520 0.00159 0.0301 0.0170 0.0273 0.0222 
5 0.00903 0.00728 0.00105 0.00015 0.0186 0.0109 0.0157 0.0133 
6 0 0 0 0 0.0151 0.00755 0.00985 0.00870 
7 0 0 0 0 0.0120 0.00598 0.00762 0.00680 
8 0 0 0 0 0.00677 0.00339 0.00423 0.00381 
9 0 0 0 0 0.00227 0.00114 0.00134 0.00124 
10 0 0 0 0 0.00269 0.00135 0.00166 0.00151 
11 0 0 0 0 0.00078 0.00039 0.00044 0.00041 
12 0 0 0 0 0.00033 0.00016 0.00018 0.00017 
13 0 0 0 0 0.00005 0.00002 0.00003 0.00002 
Conditional Distributions for Mean Frequency of Intersection 
0 0.590 0.568 0.521 0.477 0.348 0.435 0 0.218 
1 0.312 0.347 0.383 0.454 0.390 0.394 0.740 0.567 
2 0.0661 0.0576 0.0756 0.0585 0.104 0.0829 0.134 0.108 
3 0.0140 0.0129 0.0148 0.0085 0.0540 0.0327 0.0533 0.0430 
4 0.00746 0.00616 0.00477 0.00137 0.0349 0.0194 0.0282 0.0238 
5 0.0103 0.00833 0.00097 0.00012 0.0240 0.0139 0.0187 0.0163 
6 0 0 0 0 0.0181 0.00903 0.0111 0.0101 
7 0 0 0 0 0.01271 0.00636 0.00763 0.00699 
8 0 0 0 0 0.00617 0.00308 0.00362 0.00335 
9 0 0 0 0 0.00269 0.00135 0.00154 0.00144 
10 0 0 0 0 0.00171 0.00086 0.00098 0.00092 
11 0 0 0 0 0.00149 0.00075 0.00086 0.00080 
12 0 0 0 0 0.00084 0.00042 0.00049 0.00045 
13 0 0 0 0 0.00010 0.00005 0.00006 0.00005 

Table 6-11. Marginal Distribution for Number of Eruptive Centers within the Proposed Repository for the 
5th Percentile, Mean, and 95th Percentile Frequency of Intersection of the Repository 
Footprint (Continued) 
Number of 
Eruptive 
Centers in 
Proposed 
Repository 
rEC 
Formulation for Eruptive Center Spatial Distribution 
Final 
Composite 
Marginal 
Probability 
Random Location 
(weight 0.5) 
Repository 
Induces 
Eruptive 
Center 
(weight 0.5) 
Independent, 
Uniformly 
Distributed, 
Uncorrelated, 
(weight 0.05) 
Uniformly 
Spaced, 
Randomly 
Distributed, 
Uncorrelated, 
(weight 0.15) 
Independent, 
Uniformly 
Distributed, 
Correlated, 
(weight 
0.075) 
Uniformly 
Spaced, 
Randomly 
Distributed, 
Correlated, 
(weight 
0.225) 
Uniformly 
Spaced, 
Randomly 
Distributed, 
Fixed Density, 
(weight 0.5) 
Weighted 
Average 
For 
Random 
Location 
Renormalized 
such that 
P(rEC=0)=0 
Conditional Distributions for 95th Percentile Frequency of Intersection 
0 0.576 0.551 0.511 0.464 0.393 0.451 0 0.225 
1 0.316 0.355 0.385 0.459 0.410 0.406 0.789 0.597 
2 0.0699 0.0628 0.0795 0.0648 0.087 0.0768 0.118 0.0972 
3 0.0169 0.0155 0.0177 0.0102 0.0362 0.0249 0.0393 0.0321 
4 0.00948 0.00765 0.00591 0.00188 0.0242 0.0146 0.0209 0.0177 
5 0.0114 0.00893 0.00126 0.00017 0.0167 0.0104 0.0142 0.0123 
6 0 0 0 0 0.0126 0.00629 0.00764 0.00696 
7 0 0 0 0 0.00940 0.00470 0.00558 0.00514 
8 0 0 0 0 0.00469 0.00234 0.00271 0.00253 
9 0 0 0 0 0.00225 0.00113 0.00126 0.00119 
10 0 0 0 0 0.00173 0.00086 0.00098 0.00092 
11 0 0 0 0 0.00145 0.00073 0.00082 0.00077 
12 0 0 0 0 0.00079 0.00040 0.00045 0.00042 
13 0 0 0 0 0.00007 0.00003 0.00004 0.00004 
Output DTN: LA0307BY831811.001. 
NOTE: Results presented in this table were rounded to at most three significant digits after calculation. 
The results summarized in Table 6-9, Table 6-10, and Table 6-11 indicate that the conditional 
distributions for intersecting dike length, intersecting dike azimuth, and number of eruptive 
centers within the repository footprint are not sensitive to the underlying frequency of 
intersection, as there is little variation between the results obtained at the 5th, mean, and 95th 
frequencies of intersection. Therefore, the results obtained for the mean frequency of 
intersection can be used to assess the consequences of intrusive and extrusive distribution for all 
frequencies of intersection. 
6.5.4 Sensitivity Studies 
Sensitivity studies are documented in this section to assess (1) the impact of new aeromagnetic 
data (Blakely et al. 2000 [DIRS 151881]; OLeary et al. 2002 [DIRS 158468]; Hill and 
Stamatakos 2002 [DIRS 159500]) on the frequency of intersection of the repository footprint, 
and (2) the impact of alternative conceptual models (i.e., the potential for buried volcanic events 
undetectable by previous geophysical surveys) on the frequency of intersection. These 
sensitivity studies test whether additional buried basalts suggested by new aeromagnetic data or 

postulated in alternative conceptual models could lead to significant changes in the results of the 
1996 PVHA (CRWMS M&O 1996 [DIRS 100116]). Significant is defined in Brocoum (1997 
[DIRS 147772]) as a change in the mean of the probability distribution by half an order of 
magnitude or more. Compared to the mean annual frequency of intersection of 1.510-8 
determined in the 1996 PVHA, significant changes would correspond to mean annual 
frequencies of greater than approximately 510-8 or less than approximately 510-9. 
The results of these sensitivity studies are considered non-Q because the input data (OLeary et 
al. 2002 [DIRS 158468]; Hill and Stamatakos 2002 [DIRS 159500]) were not obtained using 
Yucca Mountain Project quality procedures and additional postulated buried volcanic events 
used for the sensitivity studies are strictly hypothetical with no basis in existing data. The results 
are for information only and are not to be used for purposes of assessing repository performance. 
6.5.4.1 Impact of 1999 Aeromagnetic Data on Frequency of Intersection 
Anomalies observed in aeromagnetic and ground magnetic data gathered by the USGS and the 
Center for Nuclear Waste Regulatory Analysis, respectively, since completion of the PVHA 
suggest the possibility that a number of basaltic volcanic centers are buried beneath alluvium in 
Crater Flat and the northern Amargosa Valley (Blakely et al. 2000 [DIRS 151881]; OLeary et 
al. 2002 [DIRS 158468]; Hill and Stamatakos 2002 [DIRS 159500]). Interpretation of these data 
indicates that 20 to 24 magnetic anomalies occur within Crater Flat and the northern Amargosa 
Valley that could represent buried basaltic volcanoes (OLeary et al. 2002 [DIRS 158468]; Hill 
and Stamatakos 2002 [DIRS 159500]). Of these anomalies, 8 were known at the time of the 
PVHA from previous surveys and were considered as possible volcanic events as part of the 
PVHA (Figure 6-22). 
This section summarizes the methodology and results of an evaluation carried out as part of this 
report to determine the effect of the possible presence of buried volcanic centers on the results of 
the PVHA. The results of the evaluation are considered non-Q because the input data (OLeary 
et al. 2002 [DIRS 158468]; Hill and Stamatakos 2002 [DIRS 159500]) were not obtained using 
Yucca Mountain Project quality procedures. The results are for information only and are not to 
be used for purposes of assessing repository performance. 
Evaluation of the effect on the probability estimate from potential buried volcanic centers 
requires an estimate of the age of possible buried centers and an assessment of the likelihood that 
anomalies or groups of anomalies represent buried basaltic volcanic centers. 
The probable age range of potential buried volcanic centers was estimated by 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 [DIRS 158468]. For two cases, the basalt in Crater Flat 
encountered in drill hole VH-2 and the basalt of Anomaly B, sedimentation rates were calculated 
by dividing the known depth (from drilling) of the buried basalt by the measured age of the 
basalt. These calculations give sedimentation rates of 0.03 and 0.04 mm/yr, respectively. A 
third case, Little Cones, has buried flows that have been characterized by ground magnetic 
surveys (Stamatakos et al. 1997 [DIRS 138819]). Using a modeled depth to the top of the flows 
of 15 m, a flow thickness of 10 m, and an age of 0.77-0.98 m.y. (Stamatakos et al. 1997 
[DIRS 138819], p. 328), the calculated sedimentation rate is 0.025-0.32 mm/yr. 

Source: Magnetic Anomaly designations are from Hill and Stamatakos 2002. [DIRS 159500]; (Coordinates from 
Hill and Stamatakos 2002 [DIRS 159500]). 
NOTE: MC = Makani Cone; BC = Black Cone; RC = Red Cone; LC = Little Cones; LW = Lathrop Wells. 
PCF = Pliocene Crater Flat. 
Figure 6-22. Locations of Potential Buried Basalt Inferred from Aeromagnetic Data 

Using the range of calculated sedimentation rates discussed above and the modeled burial depth 
of anomalies (OLeary et al. 2002 [DIRS 158468]), minimum and maximum ages were 
estimated for individual anomalies. Maximum ages for anomalies range from 2.5 to 8.3 m.y. and 
minimum ages range from 1.25 to 6.25 m.y. The exception to this age range is Anomaly T, 
which was estimated to be approximately 11 m.y. in age. Consideration of magnetic polarity 
data adds another age constraint and a most likely age was chosen for each anomaly within the 
age range estimated for that anomaly. This approach leads to most likely ages for the anomalies 
that range from 2.6 to 6.3 m.y. All age ranges represent minimum ages (and, thus, are 
conservative for the purposes of volcanic hazard analysis) because they do not account for the 
thickness of the basalt bodies in calculating the depth of sediments deposited after basalt was 
emplaced. 
The PVHA experts made evaluations of the likelihood that the magnetic anomalies identified at 
that time represented buried volcanic centers. An individual experts confidence that an anomaly 
represented buried basalt generally depended on the experts interpretation of the shape, 
magnetic signature, and geologic setting of the anomaly (CRWMS M&O 1996 [DIRS 100116]). 
OLeary et al. (2002 [DIRS 158468]) and Hill and Stamatakos (2002 [DIRS 159500]) used 
similar criteria to rank their confidence that the 20 to 24 anomalies identified in their reports 
represent buried basalt using a scale of 1 to 4 (OLeary et al. 2002 [DIRS 158468]) and high, 
medium, and low (Hill and Stamatakos 2002 [DIRS 159500]). Qualitatively, the rankings used 
in these two reports lead to similar conclusions regarding scientific confidence that particular 
anomalies represent buried basalt. The number of magnetic anomalies identified in these reports 
that may represent buried basalt depends upon the resolution of the aeromagnetic data. Hill and 
Stamatokos (2002 [DIRS 159500]) suggest that basaltic features with areas smaller than 1 km2 
are generally undetectable using the data presented in OLeary et al. (2002 [DIRS 158468]). 
The potential impact of the aeromagnetic and ground magnetic data on the probability of igneous 
disruption of the proposed repository was assessed by developing distributions for the number of 
volcanic events represented by the anomalies, assigning these events to the volcanic sources 
defined by the experts in the 1996 PVHA, and calculating the annual frequency of intersection of 
the repository footprint. The distributions for the number of volcanic events were developed 
using the tendency of each expert to group, or not group, aligned anomalies into single or 
multiple volcanic events. Two cases were developed. In the 1996 PVHA, the experts did not 
consider all of the anomalies identified at that time to be buried volcanic centers. Instead, to 
varying degrees, they factored the likelihood that the anomalies represented buried volcanic 
centers into their assessments of the number of volcanic events that have occurred. Case 1 for 
this study was developed to be consistent with this approach. The distributions for the number of 
volcanic events represented by the magnetic anomalies for Case 1 were developed by the authors 
of this scientific analysis report using the qualitative likelihood that the anomalies represent 
buried volcanic centers discussed in the previous paragraph, and using each experts tendency for 
including anomalies with various levels of confidence into those experts 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 by the authors of this report 
based only on each experts tendency for grouping aligned volcanic centers into events. 
The PVHA experts considered the time period of interest for computing the rate of volcanic 
events in the YMR to range from the past 1 m.y. to the past 10 m.y., with the most likely time 

period to be the past 4.5 to 5 m.y. With the exception of Anomaly T, the age estimates for the 
anomalies generally fall within the past 6 m.y. For purposes of these sensitivity analyses, it was 
assumed that the ages of 22 anomalies (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, 1, 2, 
3, and 4) fall within the past 4.5- to 5-m.y. time period. The age of Anomaly T was assumed to 
fall within the past 9 to 10 m.y. time period. Two of the PVHA experts considered a time period 
of the past 2 m.y. The range in age estimates for Anomalies O, 1, and 2 overlaps the 2 m.y. time 
period and, for these sensitivity analyses, these anomalies were given a 50 percent probability of 
being less than 2 m.y. in age. 
Table 6-12 lists the results of the sensitivity analyses in terms of the mean number of volcanic 
events occurring within the time period used by the experts to define the rate of volcanic events. 
For those experts who considered a 5 m.y. time period, the sensitivity analyses indicate an 
approximate 50 percent increase in the mean number of events for Case 1 (which incorporates 
the likelihood that the anomalies represent buried volcanic centers) and an approximate 
100 percent increase in the mean number of events for Case 2 (which assumes that all of the 
anomalies represent buried volcanic centers). 
Table 6-12. Comparison of Mean Number of Volcanic Events for 1996 Probabilistic Volcanic Hazard 
Analysis Assessment with Sensitivity Analysis Values 
Expert 
Time Period 
Quaternary Plio-Quaternary 
1996 Case 1b Case 2b 1996 Case 1b Case 2b 
AM ---14.5 21.8 27.2 
BC ---16.7 24.0 29.7 
GT ---14.5 22.3 29.0 
GW ---14.8 22.8 30.6 
MK 4.1 4.6 5.6 11.1 17.9 25.6 
MS ---14.4 24.5 25.6 
RC ---12.0 18.5 24.4 
RF 4.4 5.1 5.9 ---
WD 6.6 6.6 6.6 ---
WH ---15.7 18.4 30.4 
Average 5.0 5.4 6.0 14.2 21.3 27.8 
Source: Ziegler (2002 [DIRS 171274]). 
a 
AM = Alexander McBirney; BC = Bruce Crowe; GT = George Thompson; GW = George Walker; 
MK = Mel Kuntz; MS = Michael Sheridan; RC = Richard Carlson; RF = Richard Fisher; WD = 
Wendell Duffield; WH = William Hackett. 
b 
Case 1 and Case 2 were developed by the authors of this report based on the 1996 PVHA 
experts preferences for grouping aligned volcanic centers into volcanic events. 
For the two experts who considered a 2 m.y. time period, the sensitivity analyses result in 
increases of 10 and 20 percent for Case 1 and Case 2, respectively. Duffield considered only a 
1 m.y. time period but assigned low probabilities that some of the anomalies are less than 1 m.y. 
in age (CRWMS M&O 1996 [DIRS 100116]). Applying this assessment to the larger population 
of anomalies results in less than a 1 percent increase in the mean number of volcanic events. 
For each expert in this sensitivity study, the distributions for the number of volcanic events 
developed were assigned to the appropriate volcanic sources defined by the PVHA experts. In 
general, the magnetic anomalies lie within or slightly to the west of the experts Crater Flat and 

Amargosa Valley sources. Therefore, for these sensitivity analyses, the volcanic events 
represented by the magnetic anomalies were assigned to the experts Crater Flat and Amargosa 
Valley sources (i.e., source zones, Gaussian fields, kernel density functions) rather than to larger 
background source zones. 
Figure 6-23 and Figure 6-24 show the results of the sensitivity analyses in terms of the computed 
distributions for the frequency of intersection of the repository footprint by a basaltic dike. The 
footprint used for these analyses is the 70,000- metric tons of uranium (MTU) no-backfill 
repository layout (primary-plus-contingency blocks) used in REV 01 (BSC 2003 
[DIRS 163769]) of this report. Use of this footprint results in approximately 6 percent lower 
frequencies of intersections than if the 2003 repository footprint (BSC 2003 [DIRS 162289]) had 
been used to assess the impact (based on comparison of the mean annual frequency of 
intersection from the two footprints). The results are summarized in Table 6-13. 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 more active volcanic 
sources to the west of the site. As indicated in Figure 6-11, a significant portion of the volcanic 
hazard results from the occurrence of volcanic events near or to the northeast of the proposed 
repository, areas in which the estimated rate of volcanic events is not greatly affected by 
inclusion of the additional magnetic anomalies in the volcanic event count distributions. 
6.5.4.2 Impact of Potential Undetected Volcanic Events on Frequency of Intersection 
In addition to potential buried volcanoes identified in the 1999 USGS aeromagnetic survey, the 
possibility exists that additional undetected buried volcanoes may also exist in the YMR. This is 
of particular concern in areas immediately to the east and west of the repository (Jackass Flats 
and Crater Flat, respectively; Figure 6-22). These areas have a complex magnetic background 
signal due to underlying faulted-Miocene-tuff bedrock, making it more difficult to identify 
possible buried volcanoes using existing data (Hill and Stamatakos [DIRS 159500], p. 2-22). 
The presence of undetected volcanoes, depending on their age and location, could impact 
estimates of the frequency of intersection of the repository footprint estimated in the 1996 
PVHA. 
To evaluate the effect of potential undetected buried volcanic events on the estimate of the 
annual frequency of intersection of the repository footprint, an additional number of volcanic 
events beyond the maximum number suggested by existing data (OLeary et al. 2002 
[DIRS 158468]; Hill and Stamatakos 2002 [DIRS 159500]) are postulated in this report to be 
buried in the alluvial-filled basins east and west of Yucca Mountain. The results of this 
sensitivity study are considered non-Q because the input data (OLeary et al. 2002 
[DIRS 158468]; Hill and Stamatakos 2002 [DIRS 159500]) were not obtained using Yucca 
Mountain Project quality procedures and the additional postulated buried volcanic events used 
for the sensitivity study are strictly hypothetical with no basis in existing data. The results are 
for information only and are not to be used for purposes of assessing repository performance. 

Source: Ziegler (2002 [DIRS 171274]). 
NOTE: Results labeled 1996 use the PVHA volcanic event counts; results labeled Case 1 and Case 2 use the 
volcanic event counts developed in this sensitivity analysis. 
Figure 6-23. Composite Annual Frequency of Intersection of the Repository Footprint for Sensitivity 
Cases for the Primary-plus-Contingency Block Case of the 70,000 Metric Tons of Uranium 
No-Backfill Layout 
ANL-MGR-GS-000001 REV 02 6-84 October 2004 

Source: Ziegler (2002 [DIRS 171274]). 
NOTE: Results labeled 1996 use the PVHA volcanic event counts; results labeled Case 1 and Case 2 use the 
volcanic event counts developed for the sensitivity cases. 
Figure 6-24. Individual Expert Results for Annual Frequency of Intersection of the Repository Footprint 
for Sensitivity Cases for the Primary-plus-Contingency Block Case of the 70,000 Metric 
Tons of Uranium No-Backfill Layout 

Table 6-13. Summary of Computed Frequency of Intersection for 70,000-Metric Tons of Uranium 
No-Backfill Repository Layout (primary + contingency blocks) from Sensitivity Cases 
Input Parameters 
Annual Frequency of Intersection 
5th percentile 50th percentile Mean 95th percentile 
1996 PVHA 7.9E-10 9.8E-09 1.6E-08 5.2E-08 
Sensitivity Case 1 7.8E-10 1.0E-08 1.9E-08 6.5E-08 
Sensitivity Case 2 7.9E-10 1.1E-08 2.2E-08 7.6E-08 
Source: Ziegler (2002 [DIRS 171274]). 
6.5.4.2.1 Scenario Development 
To evaluate the impact of potential undetected buried volcanic events on the frequency of 
intersection of the repository footprint, a basis was derived for postulating the number and 
location of undetected volcanic events. 
The basis for the number of potential undetected volcanic events was determined using the 
following steps: 
1. 
An area of approximately 130 km2 was defined in the northern Amargosa Desert that 
encompasses twelve magnetic anomalies (1, 2, 3, F, G, H, I, J, L, M, N, O). Assuming 
that buried volcanic centers cause magnetic anomalies, that all anomalies are due to 
volcanic centers, and that the maximum density of magnetic anomalies is readily 
discernable by visual inspection, this area can be used to define a reasonable 
maximum buried volcanic center density in the Yucca Mountain region (Figure 6-25). 
2. 
It is assumed that all buried volcanic centers, and therefore potential undetected 
volcanic events, are between approximately 2 and 5 m.y. old (Pliocene age). Two 
million years is assumed to be the minimum time necessary to completely bury a 
volcanic center. 
3. 
Based on groupings of anomalies with medium to high confidence of representing 
buried basalt (Hill and Stamatakos 2002 [DIRS 159500], Table 1) and the tendency for 
experts to group aligned volcanic centers into volcanic events, the twelve anomalies 
were interpreted by the authors of this report as likely to represent six volcanic events 
(1, [L+M+N+O+2 (=2 events)], 3, I, [F+G+H]). Anomaly J was not considered in the 
event count because it has a low confidence of representing buried basalt (Hill and 
Stamatakos 2002 [DIRS 159500], Table 1). These six volcanic events occur within an 
area of approximately 130 km2, resulting in an event density of 0.046 events/km2. 
4. 
Assuming the event density derived in Step 3 represents a reasonable maximum event 
density for Pliocene volcanic events in Crater Flat and Jackass Flats, the event density 
was applied to the approximate areas of Crater Flat (200 km2) and western Jackass 
Flats (185 km2) to derive an expected maximum number of Pliocene volcanic events in 
each area. This approach resulted in a maximum of nine expected Pliocene volcanic 
events in both Crater Flat and Jackass Flats (numbers are rounded to whole numbers). 

5. 
Assuming four known Pliocene volcanic events in Crater Flat and zero known 
Pliocene volcanic events in Jackass Flats, five additional volcanic events are required 
in Crater Flat and nine additional volcanic events are required in Jackass Flats. The 
four known Pliocene volcanic events in Crater Flat include two events at the surface in 
southeastern Crater Flat (CRWMS M&O 1996 [DIRS 100116]) and two magnetic 
anomalies (A and Q) with medium to high confidence of representing buried basalt 
(Hill and Stamatakos 2002 [DIRS 159500], Table 1). 
Locations of each event were assumed to be random within the areas defined for event locations 
in Crater Flat and western Jackass Flats (Figure 6-25). 
6.5.4.2.2 Impact of Scenario on Frequency of Intersection 
The impact of the scenario defined in Section 6.5.4.2.1 on the annual frequency of intersection 
was assessed by comparing the results of the following two cases: 
Case 1: Best estimate input parameters were developed from the PVHA defined inputs 
(CRWMS M&O 1996 [DIRS 100116]) and the results of the 1999 USGS aeromagnetic survey 
discussed in Section 6.5.4.1. The selected time period of interest was the past 5 m.y. The 
volcanic event counts were set to 1 for Lathrop Wells, 2 for Sleeping Buttes, 3 for Northwest 
Crater Flat (combined Little Cones, combined Red and Black Cones, and Makani Cone), 1 for 
Buckboard Mesa, 2 for Southeast Crater Flat, 1 for Thirsty Mesa, and 12 buried events (A, B, C, 
D, E, combined F-G-H, I, combined L-M-N-O, Q, 1, 2, and 3). The average hidden-event factor 
distribution was set to {1.0 (0.18), 1.15 (0.47), 1.5 (0.17), 2, (0.13), 4 (0.05)}. The event length 
distribution was taken to be the composite distribution shown in Figure 6-4. The average dike 
orientation distribution was set at 90 percent of the events oriented N27E (standard deviation 
15 degrees) and 10 percent of the events oriented N19W (standard deviation 12 degrees). 
Case 2: An additional five buried events in Crater Flat and nine buried events in Jackass Flat 
were added to Case 1. These additional events were placed at random (uniform likelihood of 
location) within the areas shown on Figure 6-25. Ten simulations of event locations were 
generated, which are shown in Figure 6-26. The additional events were also assumed to have 
occurred within the past 5 m.y. 
The scenario calculations were performed using two spatial models defined in the PVHA 
(CRWMS M&O 1996 [DIRS 100116]): the parametric field shape model (2-D Gaussian) and 
the kernel density model. Only these two models were used because the postulated additional 
hidden-event locations could be directly incorporated within their framework without additional 
assumptions. 
Gaussian kernels were used in the kernel density spatial model with the distribution for the 
smoothing parameter h set to {3.6 km (0.333), 6.2 km (0.245), 8.9 km (0.311), and 12 km 
(0.111)}. 

2 
2 
2 
185 km130 km200 km
Source: Perry et al. (2003 [DIRS 171285], pp. 25-27, 29-31). 
Figure 6-25. Areas Used to Define the Hidden-Events Scenario
ANL-MGR-GS-000001 REV 02 6-88 October 2004 

Source: Perry et al. (2003 [DIRS 171285], pp. 25-27, 29-31). 
NOTE: The location of simulated events is shown by solid triangles. The location of the proposed repository is 
shown by the filled polygon. 
Figure 6-26. Simulated Hidden-Event Locations in Crater Flat and Jackass Flats Used in Scenario 
Calculation 
Figure 6-27 shows example results for the 2-D Gaussian parametric field shape model (events at 
Sleeping Butte, Thirsty Mesa, and Buckboard Mesa were considered to be separate fields 
consistent with PVHA interpretations and were not included in fitting the field shape to the event 
locations). Including the additional events in Jackass Flat broadens the fitted volcanic field 
shape and places the field center between the two concentrations of events. An alternative model 
not included in this analysis would be to assume that the events in Jackass Flat represent a 
separate field from those in Crater Flat. This alternative model would result in a smaller increase 
in the volcanic event density in the immediate vicinity of the proposed repository location. 

Case 1 Case 2 
Events/ yr/ sq km 
4150 
4150 
1E-007 
4125 
4125 
1E-008 
4100 
4100 
1E-009 
4075 
4075 
1E-010 
4050 
1E-011 4050 
1E-012 4025 
4025 
1E-013 4000 
4000 
500 525 550 575 600 500 525 550 575 600 
For Information Only 
NOTE: The location of simulated events is shown by solid triangles: black for Case-1 events, red for additional 
Case-2 events. The location of the proposed repository is shown by the filled polygon. Events at Sleeping 
Butte, Thirsty Mesa, and Buckboard Mesa were not included in the field. 
Figure 6-27. Example of Effect of Hidden-Event Scenario on the Spatial Density of Volcanic Events 
Computed Using the 2-D Gaussian Parametric Field Shape Model 
Figure 6-28 shows example results for the kernel density spatial model. For small values of h, 
the additional events produce a second concentration east of Yucca Mountain. For large values 
of h, the two concentrations merge, producing a spatial density pattern similar to that generated 
by the parametric field shape model (Figure 6-27). 
Table 6-14 summarizes the results of the hidden-events scenario calculations. The inclusion of 
additional events in Crater Flat and Jackass Flat produce an increase in the annual frequency of 
intersection by a factor of 3 to 13, depending upon the spatial model. This increase is primarily a 
result of the effect of events in Jackass Flat on the spatial density of volcanic events (Figure 6-27 
and Figure 6-28). Note that the additional hidden events represent an increase of a factor of 1.6 
in the total number of events. 

Characterize Framework for Igneous Activity at Yucca Mountain, Nevada 
ANL-MGR-GS-000001 REV 02 6-91 October 2004 
500525550575402540504075410041251E-0131E-0121E-0111E-0101E-0091E-0081E-007500525550575402540504075410041255005255505754025405040754100412550052555057540254050407541004125h = 8.9 kmh = 8.9 kmh = 3.6 kmh = 3.6 kmEvents/yr/sq kmCase 1Case 2500525550575402540504075410041251E-0131E-0121E-0111E-0101E-0091E-0081E-007500525550575402540504075410041255005255505754025405040754100412550052555057540254050407541004125h = 8.9 kmh = 8.9 kmh = 3.6 kmh = 3.6 kmEvents/yr/sq kmCase 1Case 2 
For Information Only 
NOTE: The location of simulated events is shown by solid triangles: black for Case-1 events, red for additional 
Case-2 events. The location of the proposed repository is shown by the filled polygon. 
Figure 6-28. Example of Effect of Hidden-Event Scenario on the Spatial Density of Volcanic Events 
Computed Using the Kernel Density Spatial Model 
Table 6-14. Summary of Computed Frequency of Intersection for 70,000 Metric Tons of Uranium No-
Backfill Repository Layout (primary + contingency blocks) from Hidden-Events Scenario 
Cases 
Annual Frequency of Intersection 
Spatial Model Case 1 Case 2 
Parametric Field Shape 0.7 x 10-8 9.7 x 10-8 
Kernel Density 2.2 x 10-8 6.3 x 10-8 
Equally Weighted Average 1.5 x 10-8 8.0 x 10-8 
Source: Perry et al. (2003 [DIRS 171285], pp. 25-27, 29-31). 

INTENTIONALLY LEFT BLANK 

7. CONCLUSIONS OF SCIENTIFIC ANALYSIS 
7.1 SUMMARY 
The result of the PVHA (CRWMS M&O 1996 [DIRS 100116]), the annual frequency of 
intersection of the proposed repository by a volcanic event (dike), has been recalculated using 
PVHA outputs to account for the 2003 repository footprint (the outline of the waste emplacement 
area) and extended to include the probability of an eruption within the repository footprint, 
conditional on a dike intersection (Table 7-1). The change in the annual frequency of 
intersection due to differences between the 2003 repository footprint and the repository footprint 
used at the time of PVHA is small (1.710-8 per year versus 1.510-8 per year), constituting an 
increase in the annual probability of intersection of approximately 13 percent. A conceptual 
framework for the probability calculations, based on PVHA outputs and subsequent studies, 
accounts for deep (mantle) and shallow (structural control) processes that influence volcanic 
event distribution and recurrence rate in the YMR. The framework presented here emphasizes 
the close correlation between the distribution of volcanic events and areas of crustal extension 
and faulting in the YMR, and within this context, the appropriateness of volcanic source zone 
boundaries defined in the PVHA. The framework also emphasizes the appropriate selection of 
parameter distributions that affect probability models and provides support for comparison of 
alternative scenarios and parameter selection within the framework of the volcanic history of the 
YMR. Alternative models presented by Connor et al. (2000 [DIRS 149935]) that result in higher 
eruption probabilities (10-7 versus 1.710-8 per year) than those presented here, are found to 
employ input parameters that either represent extreme values (e.g., event length) or assume a 
specific geologic control (i.e., crustal density) on spatial distribution while not considering more 
defensible and observable controls (i.e., crustal extension and structure). Spatial density models 
weighted by crustal density result in higher event frequencies at the proposed repository site, 
while the same models weighted by an alternative geologic control, such as cumulative crustal 
extension across the Crater Flat structural domain would likely lead to decreased event 
frequencies at the site. Connor et al. (2000 [DIRS 149935]) state that the highest value (10-7 per 
year) in their range of calculated probability values (10-8 to 10-7 per year) cannot be considered 
more or less likely than any other value they have calculated using alternative probability 
models. The analysis in this report suggests that the choice of input parameters used by Connor 
et al. (2000 [DIRS 149935]), compared to those used in the PVHA, logically places their highest 
probability value at the extreme upper tail of a probability distribution. 
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 proposed repository have been recalculated based on the 2003 
repository footprint (BSC 2003 [DIRS 162289]). These results are summarized in Table 7-1. 
The annual frequency of disruption of the repository by one or more eruptive centers is obtained 
by multiplying the frequency of intersection from Figure 6-18, by the conditional probability of 
the occurrence of at least one eruptive center (1 minus the conditional probability of 0 centers) 
from the right-hand column of Table 6-11. The reported probability values represent the annual 
frequencies of intrusive and extrusive disruption of the repository waste emplacement footprint 
by a volcanic event, which may consist of multiple parallel dikes (see definition of volcanic 
event at the beginning of Section 6.5). Users of the results of this scientific analysis must 

consider the distribution for the number of parallel dikes associated with a volcanic event in 
assessing the consequences of igneous intrusion. 
Conditional distributions for the length and azimuth of the intersecting dike and the number of 
eruptive centers occurring within the repository footprint are developed for the three values of 
frequency of intersection in Table 7-1. These distributions are very similar for the three levels of 
frequency of intersection. Because of this similarity, it is appropriate to use the conditional 
distributions obtained for the mean frequency of intersection to perform consequence analyses 
and as input to TSPA. 
The inputs to this scientific analysis report are the results of an expert elicitation conducted in a 
manner consistent with the guidance in the Branch Technical Position on Expert Elicitation 
(Kotra et al. 1996 [DIRS 100909]). The PVHA experts explicitly quantified the uncertainties in 
their interpretations, and these uncertainties are represented in the outputs of this report in the 
form of probability distributions. Thus, it is concluded that the results of this report form an 
appropriate basis for the evaluation of the consequences of volcanic hazards in the YMR. Yucca 
Mountain Review Plan, Final Report (NRC 2003 [DIRS 163274]) acceptance criteria have been 
met as described in Appendix D of this report. 
Table 7-1. Summary Frequencies of Disruptive Volcanic Events for the License Application Footprint 
Annual Frequency of Intersection 
of Proposed Repository by a 
Volcanic Event 
Composite Conditional 
Probability of at Least One 
Eruptive Center 
Annual Frequency of Occurrence 
of One or More Eruptive Centers 
within Proposed Repository 
7.410-10 (5th percentile) 0.75 5.610-10 
1.710-8 (mean) 0.78 1.310-8 
5.510-8 (95th percentile) 0.77 4.310-8 
Output DTN: LA0307BY831811.001. 
NOTE: Results presented in this table were rounded to two significant digits after calculation. 
7.2 OUTPUT DATA 
The outputs of this scientific analysis report based on the 2003 repository footprint (BSC 2003 
[DIRS 162289]) are described in detail in Section 6.5.3. They are summarized as the following: 
1. 
A discrete probability distribution for the annual frequency of intersection of the 
repository emplacement area footprint by a dike or dike system. This distribution is 
given in output file PVHA-4PA.DST (Output DTN: LA0307BY831811.001). The 
file contains three columns of data. The first column contains discrete values for the 
annual frequency of intersection. The second column contains the probability mass 
associated with each frequency of intersection. The third column contains the 
cumulative probability that the frequency of intersection is equal to, or lower than the 
corresponding value in the first column. This data file was modified from file 
PVHA-4P.DST (Output DTN: LA0302BY831811.001) to conform to the 
requirements of input distributions to TSPA. 

2. 
A discrete probability distribution for the annual frequency of disruption of the 
repository emplacement area footprint by one or more eruptive centers. This 
distribution is obtained by multiplying the first column of output file PVHA-4PA.DST 
(Output DTN: LA0307BY831811.001) by 0.782, the conditional probability of 
disruption by at least one eruptive center, given intersection of the repository. As 
discussed in Sections 6.5.3.2 and 7.1, it is considered appropriate to use the 
conditional probability obtained for the mean frequency of intersection to define the 
full distribution for frequency of extrusive disruption. 
3. 
Conditional joint probability distributions for length and azimuth of an intersecting 
dike and number of eruptive centers within the repository footprint, output files 
CCSM-LA.CMP, CC05-LA.CMP, and CC95-LA.CMP (Output 
DTN: LA0302BY831811.001). As discussed in Sections 6.5.3.2 and 7.1, it is 
considered appropriate to use the distributions obtained for the mean frequency of 
intersection (output file CCSM-LA.CMP) to evaluate consequences at all frequencies 
of intersection. 
In addition, there are a number of other data sets associated with this analysis report. Output 
DTN: LA303BY831811.001 contains the repository footprint polygon developed in Appendix B 
and data used to generate figures and tables in Section 6 of this report. Output 
DTN: LA307BY831811.001 contains additional data used to generate figures and tables in 
Section 6 and 7. Output DTN: LA0009FP831811.001 contains the data files for PVHA 1996 
volcanic hazard model and data used to generate some figures in Section 6 and Appendix C. 
Output DTN: LA0009FP831811.004 contains additional data from Appendix C. See 
Section 6.1.3 for a fuller description. 
7.3 UNCERTAINTIES 
The data and parameter inputs to the PVHA, as well as their uncertainty, were defined as part of 
the expert elicitation process. All of the uncertainties defined by the elicitation process were 
fully propagated through the probability models and are reflected in the final probability 
distribution. Selection of particular parameter values, ranges, and bounding assumptions for 
conceptual models were arrived at through the process of expert elicitation. The contributions to 
uncertainty from each of the PVHA components are described in Probabilistic Volcanic Hazard 
Analysis for Yucca Mountain, Nevada (CRWMS M&O 1996 [DIRS 100116], Section 4.2) and 
Section 6.3.1.5 of this scientific analysis report. 

INTENTIONALLY LEFT BLANK 

8. INPUTS AND REFERENCES 
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OL&RC: TCG-1820, with enclosure. ACC: MOL.20021104.0351. 
8.2 CODES, STANDARDS, REGULATIONS, AND PROCEDURES 
10 CFR 63. Energy: Disposal of High-Level Radioactive Wastes in a Geologic 156605 
Repository at Yucca Mountain, Nevada. Readily available. 
AP-2.22Q, Rev. 1 ICN 1. Classification Analyses and Maintenance of the Q-List 
AP-SIII.9Q, 1 ICN 7. Scientific Analysis 
AP-SV.1Q, Rev. 1 ICN 1. Control of the Electronic Management of Information 
8.3 QUALIFIED SOFTWARE 
LANL (Los Alamos National Laboratory) 2000. Software Routine: CFRAC.FOR 148560 
V1.0. V1.0. 10254-1.0-00. 
LANL 2000. Software Routine: FITFIELD.FOR V1.0. V1.0. 10263-1.0-00. 148540 
LANL 2000. Software Routine: FIT2CNTR.FOR V1.0. V1.0. 10261-1.0-00. 148541 
LANL 2000. Software Routine: UZVPVHLH.FOR V1.0. V1.0. 10280-1.0-00. 148547 
LANL 2000. Software Routine: ZBCKVHLH.FOR V1.0. V1.0. 10284-1.0-00. 148550 
LANL 2000. Software Routine: FKVPVHLH.FOR V1.0. V1.0. 10268-1.0-00. 148551 
LANL 2000. Software Routine: PFGVHLH.FOR V1.0. V1.0. 10274-1.0-00. 148552 
LANL 2000. Software Routine: FPFGVHLH.FOR V1.0. V1.0. 10270-1.0-00. 148553 
LANL 2000. Software Routine: VHTIELHS.FOR V1.0. V1.0. 10281-1.0-00. 148554 

LANL 2000. Software Routine: FITIDSR.FOR V1.0. V1.0. 10264-1.0-00. 148557 
LANL 2000. Software Routine: COMBDELD.FOR V1.0. V1.0. 10288-1.0-00. 148617 
LANL 2000. Software Routine: FITCD.FOR V1.0. V1.0. 10262-1.0-00. 148532 
LANL 2000. Software Routine: SFCD.FOR V1.0. V1.0. 10275-1.0-00. 148533 
LANL 2000. Software Routine: DCPELD.FOR V1.0. V1.0. 10258-1.0-00. 148534 
LANL 2000. Software Routine: CPDI.FOR V1.0. V1.0. 10257-1.0-00. 148535 
LANL 2000. Software Routine: UZVH.FOR V1.0. V1.0. 10277-1.0-00. 148536 
LANL 2000. Software Routine: UZVPVH.FOR V1.0. V1.0. 10279-1.0-00. 148537 
LANL 2000. Software Routine: FKVPVH.FOR V1.0. V1.0. 10267-1.0-00. 148538 
LANL 2000. Software Routine: ZBCKVH.FOR V1.0. V1.0. 10283-1.0-00. 148539 
LANL 2000. Software Routine: PFGVH.FOR V1.0. V1.0. 10273-1.0-00. 148542 
LANL 2000. Software Routine: FPFGVH.FOR V1.0. V1.0. 10269-1.0-00. 148543 
LANL 2000. Software Routine: VHTREE.FOR V1.0. V1.0. 10282-1.0-00. 148544 
LANL 2000. Software Routine: UZVHLH.FOR V1.0. V1.0. 10278-1.0-00. 148545 
LANL 2000. Software Routine: FKVHLH.FOR V1.0. V1.0. 10266-1.0-00. 148546 
LANL 2000. Software Routine: DLECD.FOR V1.0. V1.0. 10260-1.0-00. 148558 
LANL 2000. Software Routine: FKVH.FOR V1.0. V1.0. 10265-1.0-00. 148567 
LANL 2000. Software Routine: SFIDSR.FOR V1.0. V1.0. 10276-1.0-00. 148571 
BSC 2000. Software Routine: COMBSF. V 1.1. PC, Windows 95. 10255-1.1-00. 168218 
BSC 2000. Software Routine: COMBSM. V 1.1. PC, Windows 95. 10256-1.1-00. 168220 
BSC 2000. Software Routine: DILECDLH. V 1.1. PC, Windows 95. 168221 
10259-1.1-00. 
BSC 2000. Software Routine: MARGIN. V 1.1. PC, Windows 95. 10271-1.1-00. 168223 

BSC 2000. Software Routine: NECPDS. V 1.1. PC, Windows 95. 10272-1.1-00. 168238 
Dynamic Graphics 2000. Software Code: EARTHVISION. V5.1. SGI/IRIX 6.5. 167994 
10174-5.1-00. 
8.4 INPUT DATA AND OTHER REFERENCED DTNS 
LA0004FP831811.002. Volume of Volcanic Centers in the Yucca Mountain 149593 
Region. Submittal date: 04/14/2000. 
LA0305DK831811.002. Locations and Thicknesses of Tephra (Ashfall) from 164026 
Lathrop Wells Cone, Nevada. Submittal date: 05/09/2003. 
LA0407DK831811.001. Physical Parameters of Basaltic Magma and Eruption 170768 
Phenomena. Submittal date: 07/15/2004. 
LAFP831811AQ97.001. Chemical and Geochronology Data for the Revision and 144279 
Final Publication of the Volcanism Synthesis Report. Submittal date: 08/29/1997. 
MO0002PVHA0082.000. Probabilistic Volcanic Hazard Analysis for Yucca 148234 
Mountain, Nevada. Submittal date: 02/17/2000. 
MO0003YMP98126.001. Quaternary and Pliocene Basalt. Submittal date: 149605 
03/02/2000. 
MO0407SEPFEPLA.000. LA FEP List. Submittal date: 07/20/2004. 170760 
8.5 OUTPUT DATA 
LA0009FP831811.001. Compilation and Summaries of Data Supporting 
Computation of Volcanic Event Intersection Frequencies. Submittal date: 
09/01/2000. 
LA0009FP831811.004. Data Summaries Supporting Computation of Volcanic 
Event Intersection Frequencies for the 70,000 MTU Repository Layout. Submittal 
date: 09/14/2000. 
LA0302BY831811.001. Characterize Igneous Framework and Probability. 
Submittal date: 02/05/2003. 
LA0303BY831811.001. Characterize Igneous Framework Figures and Tables. 
Submittal date: 04/07/2003. 
LA0307BY831811.001. Characterize Igneous Framework Additional Output. 
Submittal date: 07/29/03. 

APPENDIX A 
DESCRIPTION OF MATHEMATICAL FORMULATION AND IMPLEMENTATION 
OF PROBABILISTIC VOLCANIC HAZARD ANALYSIS 


Section A1 of this Appendix describes the mathematical formulation used to compute the 
conditional distributions for the length and azimuth of intersecting dikes and the conditional 
distribution for the number of eruptive centers within the repository footprint. Section 2 of this 
Appendix describes the implementation of that formulation. 
A1 MATHEMATICAL FORMULATION 
The mathematical formulation used to compute the frequency of intersection of the repository 
footprint by a volcanic event is described in detail in the PVHA report (CRWMS M&O 1996 
[DIRS 100116], Section 3). The focus of this section is to describe the extension of that 
mathematical formulation to the computation of the conditional distributions for length and 
azimuth of intersecting dikes and the conditional distributions for number of eruptive centers 
within the repository footprint. 
A1.1 Frequency of Intersection of the Repository Footprint by a Dike 
This section restates the PVHA formulation (CRWMS M&O 1996 [DIRS 100116], Section 3) to 
introduce terms and notation. 
The PVHA study provided a distribution for the annual frequency of intersection of the proposed 
repository, .I(t), computed using the relationship (CRWMS M&O 1996 [DIRS 100116], p. 3-2): 
.
I (t) =.(x, y, t) PI( 
x, y)dxdy (Eq. A-1) 
..
R 
where .(x,y,t) is the rate density of volcanic events at location (x,y) for the current time 
t; PI(.x,y) is the conditional probability that a dike associated with the volcanic event at point 
(x,y) intersects the proposed repository boundary; and R is the region surrounding the proposed 
repository. Note that the notation for intersection has been changed from a subscript I in 
Probabilistic Volcanic Hazard Analysis for Yucca Mountain, Nevada (CRWMS M&O 1996 
[DIRS 100116]) to a superscript I in this report for clarity. 
The actual calculation was performed on a 0.5-km  0.5-km grid spacing using the numerical 
summation: 
.
I (t) = ...(xi , yj , t)  PI ( xi ,yj ).x.y (Eq. A-2) 
ij 
The PVHA experts quantified the uncertainty in . I(t) by developing a set of alternative 
probability models and model parameters for all aspects of the hazard calculation. These models 
were organized in the logic tree format shown in Figure 6-12a and Figure 6-12b. 
The end branches of these logic trees define a discrete joint distribution for the parameters, T, 
required to perform the calculation. Thus, Equation A-2 becomes: 
.
I (t.) =...(xi , yj ,t.)  PI ( xi ,y,.).x.y (Eq. A-3) 
S 
S 
jS 
ij 

where .S 
is the parameter set associated with an individual end branch of one experts logic tree. 
The probability that . I(t|.S) is the correct frequency of intersection, given the experts 
characterization of the uncertainty in the process, is given by the probability that the parameter 
set T takes on the specific values defined by .S, P(T = .S). This discrete probability is obtained 
by multiplying all of the conditional probabilities at each node along the path through the logic 
tree that leads to .S. The mean or expected frequency of intersection is given by: 
E .I (t)[]= ..I (t.) P(T=.) (Eq. A-4) 
SS 
s 
.I
and the percentiles of the distribution for .I(t) are obtained by ordering the values of .(t|.S) and 
then summing the probabilities P(T = .S) until the desired percentiles are reached. 
The models used to obtain .(x,y,t|.S) are described in Section 3 of the PVHA report (CRWMS 
M&O 1996 [DIRS 100116]). They are not described here because they do not impact the 
development of the conditional distributions for length and azimuth of intersecting dikes and the 
number of eruptive centers within the repository. 
A1.2 Conditional Distribution for Length and Azimuth of an Intersecting Dike 
The above formulation for the PVHA hazard computation gives the overall frequency of 
intersection, .I(t). However, to compute the consequences of an intersection, one needs to know 
the distribution for length and orientation of the intersecting dikes. This distribution is 
developed by breaking down (disaggregating) the total frequency, .I(t|.S), into frequencies for 
specific values of intersecting dike length, LIm, and dike azimuth, fn. 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 proposed repository, .I (t .S ) (see 
xi , yj 
Figure 6-8). At each point (xi,yj), the conditional probability of intersection is the probability that 
dikes or dike systems of all lengths and azimuths will intersect the proposed repository. The 
conditional probability of intersection can be divided into probabilities for intersection from 
dikes with specific lengths and azimuths (see Figure 6-9). 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, LIm, and azimuth, fn, within 
the repository footprint, .I (t, LI ,f
.
S ). Summing these frequencies over all locations gives 
xi , yj mn 
the frequency of intersection with a specific value of length and azimuth from all volcanic 
events, .I(t,LIm,fn|.S). Dividing this frequency by the total frequency of intersection, .I(t|.S), 
gives the conditional probability that an intersecting dike will produce a specific value of length 
and azimuth within the proposed repository. 
The conditional probability of intersection, PI(.x,y,.S), in Equation A-3 is computed using the 
relationship (CRWMS M&O 1996 [DIRS 100116], p. 3-17): 
x, y, d
f 2
Lmax .S
P
I ( xi , yj ,.) = 
f (d.). 
..f
f (f.)df. (Eq. A-5) 
S 
S 
S
. 0 
x ,y ,d 
.dd
1 

where: 
f(d|.S) is the probability that a dike associated with a volcanic event at (x,y) will extend a 
distance d toward the proposed repository 
Lmax is the maximum length of a dike 
f(f|.S) is the density function for dike azimuth 
f1.x,y,d and f2.x,y,d define the range of azimuths over which a dike extending d from a 
volcanic event at (x,y) will intersect the footprint of the proposed repository. 
These parameters are illustrated on Figure 6-9. The integration over dike length in Equation A-5 
is also computed by summation. 
The density function f(d|.S) is computed by convolving the distribution for the total length of the 
dike, f(L|.S), with a distribution for the normalized location of the dike relative to the volcanic 
event, f(EL|.S). Figure 6-10 illustrates the process using example distributions defined by one of 
the PVHA expert panel members. Part (a) of Figure 6-10 shows the probability distribution for 
the total length of the dike associated with a volcanic event, f(L|.S). Typically, these 
distributions were defined by the PVHA experts to be skewed with long upper tails. Part (b) 
shows a distribution for the normalized location of the point event (point (x,y)) relative to the 
total length of the dike, f(EL|.S). These distributions were defined as symmetric distributions 
over the range of 0 to 1, typically with higher probability for locations at the midpoint (the dike 
centered on point (x,y)) than at the ends (the dike extending for its full length in one direction 
away from point (x,y)). Part (c) shows the resulting probability and cumulative probability 
distributions for distance from the proposed repository to the end of the dike (d = ELL) obtained 
by convolving the distributions from (a) and (b). Using these definitions, the summation form of 
Equation A-5 becomes: 
f=f2 
x ,y ,EL  Lp
o
Lp = Lmax .S EoL =1 n 
P
I ( xi , yj ,.) =. P(Lp .) .P(EL .) . P(f.) (Eq. A-6) 
S 
So 
Sn 
S 
L 
n 1
Lp = 0 Eo = 0 f=f
x, y, EL  Lp
o 
where: 
P(Lp|.S) is a discrete probability mass function for dike length 
P(EL .S ) is a discrete probability mass function for the relative location of the dike on the 
o 
volcanic event 
P(fn|.S) is a discrete probability mass function for dike azimuth 
f
1 x,y, EL  Lp and f
x, y,EL  Lp again define the range of azimuths over which a dike 
o 2 
o 
extending d = EL  Lp from a volcanic event at (x,y) will intersect the repository footprint. 
o 

The three probability mass functions are obtained by discretizing the continuous probability 
density functions developed for L, EL, and f by the PVHA experts. 
As the summation in Equation A-6 is performed, it can be disaggregated into bins defined by 
azimuth increments, fn, and intersection length increments, LIm, where LI is the length of 
penetration of a dike into the proposed repository (see Figure 6-9). As a result, Equation A-6 can 
be rewritten as: 
I
P
I ( xi , yj ,.) = .. PI (L,f
x
i , yj ,.) (Eq. A-7) 
S mn 
S 
mn 
The quantity PI(LIm,fn.xi,yj,.S) is the probability that a dike associated with a volcanic event at 
location (xi,yj) will intersect the proposed repository with length LIm and azimuth fn, and is given 
by: 
EL
.So =1
Lp = Lmax 
I 
I
P
I ( L,f
x
i , yj ,.) =. P(Lp .) .P(EL .)d(LI = L) P(f.) (Eq. A-8) 
mn S 
So 
S mn 
S 
Lp = 0 EoL = 0 
IL
where d( LI = L) = 1 for those combinations of Lp, E , and fn 
that result in LI = LIm for a
mo
I
volcanic event at (x,y), and d(LI = L) = 0 otherwise.
m 
Multiplying Equation A-8 by the frequency of volcanic events at (xi,yj) and summing over all 
locations yields the frequency of occurrence for intersections of the proposed repository of 
length LIm and azimuth fn: 
I 
I
.
I (t, L,f.) = ...( xi , y,t.)  PI (L,f
x
i , yj ,.) (Eq. A-9) 
mn 
Sj S mn 
S 
ij 
Because the summation of .I(t,LIm,fn|.S) over the mn LI and f intervals equals .I(t|.S) 
I
.
.I (t.) =...I (t,L,f.)
.. 
. 
, the ratio .I(t,LIm,fn|.S)/.I(t|.S) defines the relative frequency
S mn
S
.
. mn 
of intersection events with length LIm and azimuth fn. 
Equation A-9 can be recast into the form: 
I 
x
i , yj ,.). 
mn S
I
.
I (t, L,f.) =..[.(xi , y ,t.)  PI ( 
x
i , yj ,.)]
. PI (
PLI (
,f
mn 
Sj 
S 
S . 
ij 
x
i , yj ,.) . 
S .
. 
or, if we define : .I (t.) =.(xi ,yj , t.)  PI ( xi ,yj ,.) (Eq. A-10) 
S 
S 
S
xi , yj 
I 
x
i , yj ,.). 
mn S
I 
I
.
I (t, L,f.) =..[.(t.)]
. PI (
PLI (
,f
mn 
S xi , yj 
S . 
ij 
x
i , yj ,.) . 
S .
. 

The first term in brackets defines the contribution to the frequency of intersection from volcanic 
events occurring at point (x,y), .I (t .S ). The second term in brackets defines the joint 
xi , yj 
distribution for intersection length and azimuth from volcanic events at point (x,y) conditional on 
intersection occurring. 
The only parameters of .S 
that affect the second term are the specification of the dike length, 
dike location on the volcanic event, and dike azimuth distributions. The PVHA experts specified 
these distributions to be independent of the distributions that characterized the spatial density and 
frequency of volcanic events (Figure 6-12a). Thus T can be broken into two independent 
sets: TD and TE . Parameters TD are those that define the distributions for total length, 
location relative to the point volcanic event, and azimuth of the dike associated with the volcanic 
event (the parameters used in the computation of the conditional probability PI(.x,y)). These 
parameters are defined by the first two levels of the logic tree shown on Figure 6-12a. 
Parameters TE are those that define the distribution for volcanic event frequency, .(x,y,t). 
These parameters are defined by all of the remaining levels of the logic trees shown on 
Figure 6-12a and Figure 6-12b. Therefore, the expected or mean value of . I(t,LIm,fn|.S) 
(Equation A-4) can be written as: 
. I 
x
i , yj ,.D ). 
mn 
SD
I 
D
E[.I (t, L,f
T)]= .P(T D =.)...
. 
. 
PI (
PLI (
,f
mn 
SD 
D 
T D ij 
x
i , yj ,.) .  
SD .
. . 
.
E 
EI
.P(T E =.) .(xi , yj ,t.) PI (L,f
x
i , yj ,.D ).
SE mn
SE 
SD 
T E 
. 
or, again using .I ( t.) =.( xi , yj ,t.) PI( 
x
i , yj ,.) (Eq. A-11)
S 
S 
S
xi ,yj 
. I 
x
i , yj ,.D ) . . 
mn
I 
D SD I 
D
E[.I (t, L,f
T)]= . P(T D =.)...
. 
. 
PI (L,f
mn 
SD
D xi , yj 
T D 
SD 
. ij . PI ( xi , yj ,.) .E[.(t.)]. 
SD . . 
I DI
where E.(t. )] is the expected value of . (t) conditional on the set of dike parameters 
[ 
xi, yj 
SD xi , yj 
.
SDD 
. The form of Equation A-11 greatly improves the efficiency of the calculation because the 
terms involving the conditional probability of intersection need to be computed only once for 
E
each dike parameter set, .SDD , rather than for every combination of the parameters .SE that define 
the distribution for volcanic event frequency. 
A1.3 Conditional Distribution for the Number of Eruptive Centers 
This section develops the mathematical formulation for assessing the conditional distribution for 
the number of eruptive centers within the footprint of the proposed repository. The development 
is based on the concept that eruptive centers will occur at uncertain locations along the length of 
the dike associated with a volcanic event. 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 
proposed repository are computed as part of the formulation presented in Section A1.2 of this 
appendix and are completely defined by the PVHA experts interpretations. 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 PVHA expert elicitation. However, with the 
limited set of assumptions (Section 5), the number of eruptive centers and their spatial 
distribution were derived from the experts interpretations. Section 6.5.1.3 describes the 
alternative ways that these assumptions were applied. 
Using the approaches for the spatial distribution of eruptive centers described in Section 6.5.1.3, 
the formulation from Section A1.2 is expanded to define the distribution for the number of 
eruptive centers that occur within the proposed repository. In the previous section, the 
contributions to the frequency of intersection from each location (x,y) in the spatial grid around 
the proposed repository, .I (t .S ), were divided into probabilities for intersection with specific 
xi , yj 
lengths and azimuths, .I (t, LI ,f
.
S ). This calculation involved looping over the possible dike
xi , yj mn 
lengths and azimuths. During this calculation, the models for number and spatial distribution of 
eruptive centers above can be used to compute the number of volcanic events that produce 0, 1, 
2, 3, etc. eruptive centers in the proposed repository. As a result, .I (t, LI ,f
.
S ) is divided into 
xi , yj mn 
the frequency of intersection from volcanic events at point (x,y) that produce specific numbers of 
I EC
eruptive centers, rEC, within the proposed repository, . (t, LI ,fn ,r 
.
S ). Summing these 
xi , yj m 
values over all locations (x,y) gives the frequency of intersection with a specific number of 
I EC
eruptive centers in the proposed repository, .I (t, L,fn ,r 
.
S ). Dividing this frequency by the
m 
total frequency of intersection, .I (t .S ), gives the conditional probability that an intersecting 
event will produce a specific number of eruptive centers in the proposed repository. 
EC
The disaggregation of .I (t, LI ,f
.
S ) into .I (t, LI ,fn ,r 
.
S ) for rEC = 0, 1, 2,  eruptive 
xi , yj mn 
xi , yj m 
centers is accomplished by computing the conditional distribution for rEC, given the total length 
of the dike, L, the length of intersection within the repository footprint, LI, the number of 
eruptive centers associated with the volcanic event, nEC, and the spatial distribution for the 
location of eruptive centers. Note that the assumption listed in Section 5.2 results in nEC=1. 
Two alternative approaches were used to define the spatial distribution of eruptive centers along 
the length of the dike system associated with a volcanic event. 
The first approach, the IUD approach, specifies the location of each eruptive center 
independently of the others using a uniform distribution over the length of the dike system. The 
second approach, the USRD approach, divides the length of the dike into equal length segments, 
one segment for each eruptive center. Each eruptive center is randomly located within its 
segment following a uniform distribution. 

Independent, Uniformly Distributed (IUD) Spatial Distribution 
In this approach, the location of each eruptive center is uniformly distributed along the total 
length of the dike and the location of each eruptive center is independent of all of the others. 
Thus, the occurrence of each eruptive center within the footprint of the proposed repository is an 
independent Bernoulli trial with probability of success, p, equal to the length of intersecting dike 
within the proposed repository, LI, divided by the total length of the dike, L. Under these 
conditions, the conditional probability distribution for the number of eruptive centers within the 
repository footprint, rEC, given nEC eruptive centers associated with the volcanic event, is given 
by the binomial distribution: 
EC 
. . LI . r 
..
1- 
LI . nEC -r EC
n
EC 
P
EC
IUD (rEC
n, L, LI ) = 
.. 
rEC 
. . (Eq. A-12) 
. . . L . . L . 
n
EC
. 
where . .. 
is the binomial coefficient and the subscript IUD refers to independent, uniformly 
r 
EC
. . 
distributed eruptive centers. 
Uniformly Spaced, Randomly Distributed (USRD) Spatial Distribution 
The alternative approach for the spatial distribution of eruptive centers is that they are spaced 
more or less equidistant along the length of the dike. If nEC eruptive centers are generated along 
the length of the dike, then each eruptive center is located within a segment of length Ls = L/nEC . 
If the location of the eruptive center within each segment is defined by a uniform distribution, 
the probability that an eruptive center associated with segment q will occur within the repository 
footprint is equal to the length of segment q within the boundary of the proposed repository, LsIq, 
divided by the total length of the segment, Lsq. There can be at most two segments of a dike that 
have partial penetration of the repository footprint in one volcanic event (there may be more 
segments that lie entirely within the repository footprint). If only the qth segment penetrates into 
the repository footprint, then the probabilities for zero or one eruptive center within the proposed 
repository are given by: 
sI
L
q
r 
EC
P
USRD(= 0 
n
EC , L, LI ) = 1- 
s
L
q 
r
L
sI (Eq. A-13) 
EC 
q
P
USRD (= 1nEC , L, LI ) = 
s
L
q 

If the qth and (q+1)th segments penetrate into the repository footprint, then the probabilities for 
zero, one, or two eruptive centers within the proposed repository are given by: 
sI . . sI
. 
q
r 
EC
P
USRD (= 0 
n
EC , L, LI ) =.1- 
L. .1 - 
Lq+1 .
. 
ss
. Lq . . Lq+1 . 
sI . . sI
. L
EC q 
. LsI . . Lq +1 .
. (Eq. A-14) 
P
USRD( rEC = 1 n, L, LI ) =. . .1 - 
Lq+1 .
. 
+.1 - q . . 
sI 
ss ss
. Lq . . Lq+1 . . Lq . . Lq +1 . 
sI . . sI
. L
EC q
P
USRD (rEC = 2n, L, LI ) =. . . Lq+1 .
. 
ss
. Lq . . Lq+1 . 
If one or more segments lie entirely within the repository footprint, then the probability of an 
eruptive center occurring within the proposed repository is unity for these segments. In such a 
case, the value of rEC in Equations A-13 and A-14 is increased by the number of wholly 
contained segments. For example, if one segment lies completely within the proposed repository 
and one spans the boundary of the proposed repository, then Equation A-13 becomes: 
L
P
USRD (rEC = 0 nEC , L,LI ) = 0 
sI 
EC q
P
USRD(rEC = 1n, L, LI ) = 1- (Eq. A-15) 
s
L
q 
sI
L
q
r
EC
P
USRD ( = 2 
n
EC ,L, LI ) = 
s
L
q 
Conditional Distribution 
In evaluating the consequences of an intersection of the repository footprint by the dike system 
associated with a volcanic event, it is more informative to define P(rEC) conditional on the length 
of intersection, LIm. Equation A-8 defines the joint probability of intersection length and azimuth 
I
for a volcanic event at point (xi,yj), PI ( L,f
x
i , yj ,.D ). As indicated in developing
mn 
SD 
Equation A-11, the only parameters that affect the calculation of the conditional probability of 
DI
intersection are .SD . Thus PI ( L,f
x
i , yj ,.) in Equation A-8 can be rewritten as 
mn 
S 
I
P
I ( L,f
x
i , yj ,.D ). In addition, the probability for the number of eruptive centers within the 
mn 
SD 
proposed repository, Equations A-12, A-13, and A-14, is dependent on the number of eruptive 
EC
centers per volcanic event, nEC . Appendix C develops distributions for nEC , P(n=.Lp,.D ),
SD 
which may be conditional on the total length of the dike, Lp. 

D
The parameter set .SD is expanded to include any alternatives for assessing P(nEC =.). Using 
these definitions, the joint probability of rEC eruptive centers in the proposed repository for a 
volcanic event at (x,y) producing a length of intersection of LIm at an azimuth of fn 
is given by: 
DLp =Lmax .SD 
EoL =1
I
n ,rEC D 
D 
DI 
D
P
I (L,f
x
i , yj ,.) =. P(Lp.SD ) . P(EL .)d(LI = L) P(f.) 
m 
o 
SD mn
SD 
SD 
L =0 EL =0
po 
(Eq. A-16)
.=nEC 
max 
n
EC 
D rEC 
I ,nEC
.P( =.Lp ,.)P(
Lp, L=.)
m
SD 
.=1 
EC
with P(rEC 
Lp, LI , n =.) given by either Equation A-12 or Equations A-13 and A-14. 
m 
Multiplying Equation A-16 by .(xi , yj , t.D ) , the frequency of volcanic events at (xi,yj), and 
SD 
summing over all locations yields the frequency of occurrence for intersections of the proposed 
repository of length LIm and azimuth fn 
with rEC eruptive centers within the repository: 
I 
E IEC
.(t, LI ,fn ,rEC .) =...( xi , yj ,t. ) PI (L,fn,r 
x
i , yj ,.D ) (Eq. A-17) 
m S 
m 
SD 
ij 
SE 
IECECEC I
Because the summation of .(t,LIm,fn,r|.S) over rEC = 0 to r = n equals .(t,LIm,fn|.S), the 
max
ratio .I(t,LIm,fn,rEC|.S)/.I(t,LIm,fn|.S) defines the relative frequency of intersection events with 
length LIm and azimuth fn. that produce rEC eruptive centers within the proposed repository. 
In the same manner that Equation A-9 was recast as Equation A-10, Equation A-17 can be recast 
into the form: 
In,rEC
.PI(L,f
x
i , yj ,.D ). 
m 
SD
I 
I 
ED
.(t, LI ,fn ,rEC .) =...xi , yj (t.,.)
. 
. PI( 
x
i , yj ,.) . (Eq. A-18) 
m S 
SE SD 
D 
ij 
SD . 
ED 
E 
D
where the substitution .I (t.,.) =.(xi , yj ,t.) PI ( xi ,y,.)has been made. 
j SDSE SD 
SE
xi , yj 
Equation A-18 may be adapted in a manner similar to Equation A-11 to improve the efficiency 
IEC
of the computation of the expected value of .(t,LIm,fn,r|.S), producing: 
In,rEC D
E[.I (t, L,f
T)]= .P(TD =.SD )  
m 
TD 
I EC 
.(Eq. A-19)
. .PI (L,fn,r
m 
SD I
x
i , yj ,.D ) 
. 
. 
E[.(t.D )].
.... 
SD
xi , yj
x
i , yj ,.D )
. 
ij . PI ( 
SD . . 

A2 IMPLEMENTATION OF MATHEMATICAL FORMULATION 
This section describes the implementation of the formulation presented in Section A1 of this 
appendix. Equations A-3 and A-5 provide the relationships used to compute the frequency of 
intersection, .I(t). Equations A-10, A-11, A-18, and A-19 provide the relationships used to 
compute the frequency of intersecting volcanic events that produce an intersection length of LIm, 
at an azimuth of fn, with rEC eruptive centers occurring within the repository footprint. 
A2.1 Frequency of Intersection of the Repository Footprint by a Dike 
The computational scheme used in Probabilistic Volcanic Hazard Analysis for Yucca Mountain, 
Nevada (CRWMS M&O 1996 [DIRS 100116]) and repeated in this report consists of the steps 
shown on Figure 3-1 (repeated for each experts interpretation). 
Step 1: Discrete cumulative distributions for dike length are developed from the experts 
assessments using software routines FITCD V1.0 (LANL 2000 [DIRS 148532]) or SFCD V1.0 
(LANL 2000 [DIRS 148533]) (e.g., part (a) of Figure 6-10). These distributions are then 
convolved with the event location of the dike on the volcanic event (e.g., part (b) of Figure 6-10) 
to produce distributions for volcanic event length (e.g., part (c) of Figure 6-10) using software 
routine DCPELD V1.0 (LANL 2000 [DIRS 148534]). 
D
Step 2: The conditional probability of intersection, PI ( xi , yj ,.) , is computed for each set of 
SD 
parameters .SDD (defined by a unique event length distribution from Step 1 and a unique azimuth 
distribution) using software routine CPDI V1.0 (LANL 2000 [DIRS 148535]). 
Step 3: The rate of intersection, .I(t), is computed using software routines specific to the type of 
source (software routines UZVH V1.0 (LANL 2000 [DIRS 148536]) and UZVPVH V1.0 
(LANL 2000 [DIRS 148537]) for source zones; routines FKVH V1.0 (LANL 2000 
[DIRS 148567]), FKVPVH V1.0 (LANL 2000 [DIRS 148538]), and ZBCKVH V1.0 (LANL 
2000 [DIRS 148539]) for kernel density sources; and routines PFGVH V1.0 (LANL 2000 
[DIRS 148542]) and FPFGVH V1.0 (LANL 2000 [DIRS 148543]) for 2-D Gaussian field 
sources). The characterization of individual volcanic sources is defined by a 12-parameter subset 
of .SEE . The distribution for these parameters depends upon the alternative source definitions, 
temporal models, and time periods of interest. To denote this breakdown of .SEE , the parameter 
set .SEASM represents the alternative source models (including temporal models) and parameter set 
E 
represents the individual source parameters, which are conditional on the chosen 
.
SEISP .SASM 
source and temporal models .SEASM . The software routines used to compute the hazard from an 
individual source contain a set of 12 nested DO loops to enumerate all of the alternative versions 
E
of .SISP .E (see Figure 6-12b). Given a set of parameters, the frequency of volcanic events, 
SASM 
.( xi , yj ,t.E ) , is computed for a specific source, a, using the formulation appropriate for the 
a
SISP 
source type. This frequency is multiplied by the conditional probability of intersection, 
D
P
I ( xi , yj ,.) , from the output of routine CPDI V1.0 and summed over all points within the 
SD 
source to obtain the frequency of intersection from volcanic events associated with source a. 

The software routines store the mean frequency of intersection and the distribution in the 
frequency of intersection (computed over the distributions for .E 
in output files for use in 
SISP 
.
SEASM 
the final step of the computations). Separate output files are created for all of the alternative sets 
of source model parameters, .SEASM , and for the alternative parameters that describe the associated 
dikes, .SDD . 
D
Step 4: The results from Step 3 are combined over the distributions for .SEASM and .SD 
(see Figure 6-12a and Figure 6-12b) to compute the full distribution for frequency of intersection 
specified by an individual PVHA experts interpretations. The results for each expert are then 
combined to obtain the composite distribution. These calculations are performed using software 
routine VHTREE V1.0 (LANL 2000 [DIRS 148544]). Complete enumeration of all of the 
alternative parameter sets .SEASM is again achieved by a series of nested DO loops. The mean 
value and various percentiles of the distribution for frequency of intersection of the repository 
DE
footprint by a dike were computed from the discrete distribution for .I(t|.SD ,.SE ) as described 
above in Section A1.1. These computations are then combined using equal weights to produce a 
composite distribution for frequency of intersection. 
A2.2 Distributions for Length, Azimuth, and Number of Eruptive Centers 
The computations performed in Probabilistic Volcanic Hazard Analysis for Yucca Mountain, 
D
Nevada (CRWMS M&O 1996 [DIRS 100116]) were made for all possible sets of .SD and .SEE 
defined by the volcanic hazard characterization of each of the PVHA experts (full enumeration 
of the logic tree branches (CRWMS M&O 1996 [DIRS 100116], Appendix E)). However, the 
DE
objective of this analysis is a disaggregation of the intersection frequency, .I(t|.SD ,.SE ), into 
EC
intersection frequencies with specific values of LIm, fn, and r. Repeating the calculation for 
the spatial disaggregation would require exhaustive computation and storage of the spatial 
EE
disaggregation of the hazard, .I (t.,.D ), for all possible parameter sets .SE . Therefore, a 
SE SD
xi , yj 
simulation approach was used to develop random sample parameter sets .SEE from the PVHA 
experts logic trees to speed up the computation process. The approach used to obtain the spatial 
disaggregation of the frequency of intersection consists of the following steps (see Figure 3-2). 
D
Step 1: The conditional probability of intersection, PI ( xi , yj ,.) , was taken directly from the 
SD 
computation for the frequency of intersection discussed above. The files containing 
DD
P
I ( xi , yj ,.) for each set of parameters .SD were created using routine CPDI V1.0 (LANL 2000 
SD 
[DIRS 148535]) using inputs processed through routines FITCD V1.0 (LANL 2000 
[DIRS 148532]), SFCD V1.0 (LANL 2000 [DIRS 148533]), and DCPELD V1.0 (LANL 2000 
[DIRS 148534]). 
Step 2: The second step in the calculation involved computation of the spatial disaggregation of 
frequency of intersection hazard for the individual sources specified by the alternative source 
D
parameter sets .SEASM and for the alternative dike parameters .SD . For the reasons discussed 
above, simulation is used to select random samples of the parameter subset .E used to
SISP 
.
SEASM 

compute the frequency of intersection for an individual source type. The approach used to 
generate these parameter subsets is Latin hypercube sampling (McKay et al. 1979 
[DIRS 127905], pp. 243245). The software routines used to compute the frequency of 
intersection replace the 12 nested DO loops with simulation of 50 parameter sets, 
E 
E 
, simISP = 50 to 1 , using Latin hypercube sampling from the 12 independent, discrete 
.
simISP 
.SASM 
E
parameter distributions that define TISP .SEASM . Once a parameter subset is defined, the spatial 
distribution of .(x,y,t) for source a is computed using the same algorithms employed for the 
PVHA calculation (CRWMS M&O 1996 [DIRS 100116]). The disaggregated frequency of 
I 
ED
intersection, .a, xi , yj (t.sim ISP ,.SEASM ,.), from each simulation for each source ais output to a file
SD 
along with the mean frequency of intersection for the source. Each simulated parameter set 
E
.
simISP .E is an equally likely realization of the possible parameter sets from the joint
SASM 
E
distribution for T ISP .SEASM . Therefore, the mean frequency of intersection for source a, given 
EI 
ED
source model parameter set .SASM and dike parameters .SDD , E[.(t.,.)], and its spatial 
a 
SASM SD 
I 
ED
disaggregation E.[ (t. ,. )], may be estimated by the average of the results from the 50 
a, xi , yj 
SASM SD 
simulations. 
= 50 
I 
ED I 
ED
E[.(t.,.)]~
1 simISP 
..( t.E ,.)
a 
SD
SASM SD simISP ,.S-ASM
50 
sim ISP =1 
a 
and (Eq. A-20) 
I 
ED I 
ED
E[.a,xi ,yj (t.,.)]~1 simISP = 50 
.
E ,.)
50
SASM SD .a,xi ,yj (t.simISP ,.S- ASM SD 
sim ISP =1 
The simulation software routines are designated UZVHLH V1.0 (LANL 2000 [DIRS 148545), 
UZVPVHLH V1.0 (LANL 2000 [DIRS 148547]), FKVHLH V1.0 (LANL 2000 
[DIRS 148546]), FKVPVHLH V1.0 (LANL 2000 [DIRS 148551]), ZBCKVHLH V1.0 (LANL 
2000 [DIRS 148550]), PFGVHLH V1.0 (LANL 2000 [DIRS 148552]), and FPFGVHLH V1.0 
(LANL 2000 [DIRS 148553]). They use the same input files used to compute the frequency of 
intersection by full enumeration. 
Step 3: The third step in the calculation is computation of the distribution for the spatial 
disaggregation of the hazard for each the PVHA experts interpretation. The full enumeration of 
D
the possible parameter sets .SD and .SEASM is again replaced by simulation of 50 equally likely 
parameter sets. The software routine VHTIELHS V1.0 (LANL 2000 [DIRS 148554]) is used to 
perform the following operations for the interpretation developed by each of the PVHA experts. 
E
Step 3a. First, all of the possible sets .SDD in the joint distribution for T D and T ASM are
,.SEASM 
enumerated. The joint probability of each set is computed from the PVHA experts logic tree. 

Step 3b. The mean frequency of intersection for each set of .SDD and its spatial 
,.SEASM 
disaggregation are estimated from the sum of all the individual source results from Step 2, for 
those sources present in the parameter set .SEASM , 
ED I 
ED
E[.I (t.,.)]~ 
. E[.( t.,.)]
a
SASM SD 
SASM SD 
a.SEASM 
and (Eq. A-21) 
I 
ED I 
ED
E[.(t.,.)]~ .E[.a, xi , yj (t.,.)]
xi ,yj 
SASM SD 
SASM SD 
a.SEASM 
Step 3c. The sets of .SDD are then ranked in terms of increasing mean frequency of 
,.SEASM
ED
ED
intersection, E [.I (t.,.)], defining a distribution for E [.I (t.,.)].
SASM SD 
SASM SD 
D
Step 3d. Then, 50 parameter sets, .simD 
E , are selected using Latin hypercube sampling 
,.sim ASM 
ED
from the distribution for E [.I (t.,.)]. For each of these sets, the frequency of intersection 
SASM SD 
and its spatial disaggregation are computed for the 50 simulations of parameters 
E
.
EE 
simISP 
(.=.sim ASM ) by:
SASM 
EED I
.
EE DI (t.sim ISP ,.simASM ,.sim D )~ . .a(t.sim ISP ,.simASM ,.sim D ) 
a.E 
sim ASM 
and (Eq. A-22) 
I 
EED I 
EE D
.(t.sim ISP ,.simASM ,.sim D )~ ..
a,xi ,yj (t.simISP ,.sim ASM ,.simD ) 
a.E 
xi , yj 
sim ASM 
EE
In Equation A-22, .I (t.,.simASM ,.D ) , and its spatial disaggregation,
a 
simISP simD 
I 
E
(t.E ,.simASM ,.D ), are the values for source a for the simulated parameter set 
sim ISP simD 
.a, xi , yj 
E 
DDED
.
simISP .E ,.SD from (2) with .SEASM ,.SD =.simASM ,.simD , the source model and dike parameter set 
SASM 
selected in one simulation. The result is 2,500 equally likely values for frequency of 
intersection. The resulting values of the spatial disaggregation of the frequency of intersection, 
E
.I (t.E ,.simASM ,.D ), are written to separate files for each of the 2,500 simulated parameter 
simISP simD
xi , yj 
sets. 

Step 3e. Finally, the expected value for the spatial disaggregation of the frequency of 
intersection for each of the possible dike parameter sets is estimated from the average of all of 
D
the results from Step 3d for which .simD =.SDD . 
sim ISP, ASP,D =2500 
I 
E
..(t.E ,.simASM ,.D 
sim D 
=.D )
simD )d(.D 
sim ISP SD 
I 
xi ,yj 
D sim ISP, ASP,D =1E[.(t.SD )]~ simISP ,ASP, D =2500 (Eq. A-23) 
xi ,yj 
D
.d(.=.D )
simD SD 
simISP ,ASP, D =1 
DD D
where d(.simD =.SD ) =1 for those simulations where .simD =.SDD , and zero otherwise. Note that 
simISP, ASP, D =2500
1 DD
2,500 .d(.=.)~ P(TD =.D ).
simD SD SD
sim ISP, ASP, D =1
I 
D
Figure 6-11, part (b), shows a map of E.[ (t. )] averaged across all 10 experts. This figure 
xi , yj 
SD 
indicates the locations of volcanic events that contribute to the frequency of intersection. Also 
shown on Figure 6-11, part (a), is a map of the expected frequency of volcanic events, 
D
E[.( xi , yj ,t.)], averaged across all experts. This map was obtained by repeating the 
SD 
D
calculation for part (b) with the conditional probability of intersection, PI ( xi , y,.), set to 1 at 
j SD 
every point (x,y). 
Step 4: The composite distribution for the frequency of intersection of the repository footprint 
by a dike is now represented by the 2,500  10 simulation results for the 10 PVHA experts. 
Each experts distribution was assigned equal weight in the PVHA aggregation process. Thus, 
I
the composite 25,000 simulations of .I(t) are all equally likely. The 25,000 simulations of .(t) 
are ranked and the simulations that produce various percentile of the distribution for .I(t) are 
identified (e.g., the 95th percentile is the simulation with rank 0.95  25,000 = 23,750). 
Simulation results that are close to each percentile (within a rank of 250) and that are for 
different experts are also identified to capture the range of expert interpretations. These 
simulations are identified using software routine CFRAC V1.0 (LANL 2000 [DIRS 148560]). 
EI 
D
Step 5: Steps 1 through 4 provide the values of .I (t.E ,.simASM ,.D ) and E[. (t. )]
simISP simD xi , yj 
SD
xi , yj 
needed for Equations A-10, A-11, A-18, and A-19. What remains is the calculation of 
I 
D IEC
P
I (L,f
x
i , yj ,.) and PI ( L,fn ,r
x
i , yj ,.D ) , the discretization of the conditional probability 
mn SD m 
SD 
of intersection into increments of intersection length, intersection azimuth, and number of 
eruptive centers within the repository footprint for each volcanic event location (x,y). Software 
routine DILECDLH V1.0 (BSC 2000 [DIRS 168221]) is used to discretize the conditional 
D
probability of intersection, PI ( xi , y,.) , into the designated bins for length and azimuth within 
j SD 
the proposed repository. The inputs to program DILECDLH are: 
 
The spatial disaggregation of the frequency of intersection (either the mean result 
conditional on .SDD for one expert from Step 3 or for one of the hazard simulations 
representative of the 95th percentile of the composite distribution from Step 4) 

 
The dike length and volcanic event location distributions for the corresponding 
parameter set .SDD 
 
A joint distribution for dike length and the number of eruptive centers on a dike, 
D
P(nEC =.Lp,.) (computed using software routines FITIDSR V1.0 (LANL 2000 
SD 
[DIRS 148557], SFIDSR V1.0 (LANL 2000 [DIRS 148571]), and DLECD V1.0 (LANL 
2000 [DIRS 148558]) 
 The spatial distribution of eruptive centers along the dike. 
With the exception of the assessments for the number and spatial distribution of eruptive centers, 
all of the probability distributions required to perform this calculation are defined in 
Probabilistic Volcanic Hazard Analysis for Yucca Mountain, Nevada (CRWMS M&O 1996 
[DIRS 100116]). 
Two alternative approaches are developed for the spatial distribution of eruptive centers in 
Section 6.5.1.3 and A1.3. In the first approach (designated IUD) the location of each eruptive 
center is specified by an independent, uniform distribution over the total length of the dike, Lp. 
In the second approach (designated USRD) the eruptive centers are spaced out over the full 
length of the dike with the location each of the nEC eruptive centers uniformly distributed in a 
I EC
segment of length Lp/nEC . Calculations of PI ( L,fn ,r
x
i , yj ,.D ) are performed for both
m 
SD 
D
approaches. Distributions for the number of eruptive centers on a dike, P(nEC =.Lp,.) , are
SD 
developed below from the PVHA experts assessments of the number of eruptive centers 
associated with a volcanic event. 
D
The distributions for P(nEC =.Lp,.) derived in Appendix C for total number of eruptive 
SD 
centers associated with a volcanic event (Figure 6-13) are marginal distributions in the sense 
that they are independent of assessments of dike length and are averaged over an experts 
interpretations, TE . The calculations need to use the conditional distribution of number of 
eruptive centers given dike length. The limiting conditions that define the relationship between 
two variable parameters are complete independence and complete dependence. These two 
D
limiting conditions are used to define the influence of dike length on P(nEC =.Lp,.).
SD 
Complete independence implies that the conditional distribution for number of eruptive centers is 
D EC
equal to the marginal distribution, and P(nEC =.Lp,.) = P(n=.TE ) is used in
SD 
Equation 16. The resulting discretizations of the frequency of intersection are designated: 
II
.
IUD-UC (t,Lm ,fn, rEC .S ) for independent, uniformly distributed spatial locations with the number 
II
of eruptive centers uncorrelated with dike length; and .USRD -UC (t, L,fn,rEC .S ) for uniformly 
m 
spaced, randomly distributed spatial locations with the number of eruptive centers uncorrelated 
with dike length. 
Complete dependence implies that the number of eruptive centers varies directly with dike length 
(it is considered unrealistic to have a negative correlation). The correlation between dike length 
and number of eruptive centers per event was set to the maximum value by making the marginal 

distributions for dike length and number of eruptive centers per volcanic event rank correlated. 
This correlation is achieved by specifying a one-to-one correspondence of the marginal CDFs for 
the two parameters. The resulting discretizations of the frequency of intersect are designated: 
I EC
.
IUD-C (t, LI ,fn ,r 
.
S ) for independent, uniformly distributed spatial locations and the number of 
m
I
eruptive centers correlated with dike length; and .USRD -C (t,LI ,fn, rEC .S ) for uniformly spaced, 
m 
randomly distributed spatial locations and the number of eruptive centers correlated with dike 
length. These two approaches span the range of correlation considered reasonable (zero to 
maximum). 
The alternative approach for specifying the total number of eruptive centers associated with a 
volcanic event is to define a distribution for the average spacing between volcanic events and use 
this distribution, together with the total dike length, to obtain the total number of eruptive 
centers. Consistent with the number of eruptive centers being defined by an average spacing 
between eruptive centers, the USRD method is used to defining the spatial distribution for 
location of eruptive centers along the length of the dike system. 
The computation procedure used in software routine DILECDLH V1.1 is as follows: 
Step 5a. An input file is created that contains the probability distributions for the length of the 
dike, L, and number of eruptive centers per volcanic event, nEC . The probability distribution for 
L is discretized into the probability mass for Lp in 0.05-km increments using module FITIDSR 
V1.0 (LANL 2000 [DIRS 148557]) or SFIDSR V1.0 (LANL 2000 [DIRS 148571]). The 
marginal distribution for nEC is listed at the top of the file and the rank correlated value for nEC is 
listed for each value of L by determining the value in the marginal distribution for nEC that has 
the same cumulative probability as Lp in the marginal distribution for L. 
Step 5b. For each of the dike parameter sets, .SDD , the spatial disaggregation of the hazard 
computed in Steps 3 and 4 is then input into the program. At each location (x,y) that contributes 
EI 
D
to the frequency of intersection {.I (t.E ,.simASM ,.D ) or E [.xi ,yj (t.)] > 0}, the direction
simISP simD 
SD
xi , yj 
toward the proposed repository is sampled over 5 increments in azimuth, with the probability 
D
distribution for PI (f.) obtained by computing the probability mass in the interval fn-2.5 =f
nSD 
L
=fn-2.5. At each azimuth, fn, 100 simulations of Lsim and Esim are created by Latin hypercube 
sampling from the distributions defined for each. For those combinations of Lp and EL at
o 
azimuth fn 
that result in intersections with the repository footprint, LI is computed. The 
I
probability PI (L,f
x
i ,yj ,.D ) defined in Equation A-8 is now approximated by the expression: 
mn 
SD 
I 
1 I
P
I ( L,f
x
i , yj ,.S )~ 100 d(LI = L)  P(f.) (Eq. A-24) 
mn 
mn S 

EC
and the probability PI (r , LI ,f
x
i , yj ,.D ) in Equation A-16 is approximated by 
mn 
SD 
r 
sim =100
EC I
I 
D
P
I (, L,f
x
i , yj ,.D )~ 1 .d( LI = L) P(f.) 
mn 
SD 100 mn
SD 
sim =1 
(Eq. A-25) 
EC 
n
.=nmax 
EC D rEC 
I ,nEC
.
P( =.Lsim,.SD ) P(
L
sim , Lm =.) 
.=1 
IL
where d(L = LI ) = 1 for those simulation values of Lsim and Esim at azimuth fn 
that result in 
m
I
LI=LIm for a volcanic event at (x,y), and d(LI = L) = 0 otherwise. An increment of 0.05 km is 
m 
chosen for the intersection length bin size. This length bin size, together with the azimuth bin 
size of 5, are sufficient to define clearly the variability in the length and azimuth of intersecting 
dikes. (The computation of the frequency of intersection is independent of these bin sizes.) 
D
Equation A-25 is used five times for the five alternative approaches for P(nEC =.Lsim ,.SD ) and 
I
P(rEC 
L
sim ,Lm ,nEC =.) described in Section 6.5.1.3. 
Step 5c. The results of Step 5b are then used in Equations A-11 and A-19 to estimate the 
II 
II EC
expected frequencies of intersection E [.(t, L,fT)] and E [.(t, L,fn,r 
T)], respectively for 
mn 
m 
each of the PVHA experts interpretations. The definition for P(TD =.SDD ) used in 
Equation A-23 is used in this calculation. The results for each expert are then averaged to obtain 
an estimate of the composite expected frequencies over all experts using the expressions: 
expert 10
II II
E[.(t, L,f)]~1 .E[.(t,L,f
T)]
mn 10 mn 
expert 1 
and (Eq. A-26) 
expert 10
I In, rEC IIn, rEC
E[.(t, L,f)]~1 .E[.(t,L,f
T)]
m 10 m 
expert 1 
This calculation is performed using software routine COMBSM (BSC 2000 [DIRS 168220]). 
The resulting partial frequencies of intersection are then normalized to produce conditional 
II EC
distributions. At each value of LIm and fn, the computed vales of E [.(t, L,fn,r )]are divided
m
II
by E[.(t, L,f)]to produce a distribution for rEC conditional on LIm and fn. The values of
mn
II I
E[.(t, L,f)] are, in turn, divided by E [.(t)]to produce a joint distribution for LIm and fn
mn 
conditional on the mean frequency of intersection. Because Latin hypercube sampling was used 
instead of full enumeration in Step 2 at a few of the points (x,y) that contribute to the frequency
L
of intersection computed in Step 3, the 100 simulated values of Lsim and Esim do not produce any 
intersections. These intersections occur at locations where only the longest possible dikes 
combined with values of EL very near 1.0 result in intersections of the repository footprint. As a 
II
result, the sum of E [.(t, L,f
T)]over LIm and fn 
for each expert typically equaled about 
mn 

97 percent to 99 percent of E [.I (t 
T)]. Because the purpose of Step 5 is to obtain a conditional 
I
distribution, the computed values of E [.I (t, L,fT)] for each expert were normalized in 
mn 
software routine COMBSM V1.0 to sum to the value of E [.I (t 
T)] computed in Step 3 (The true 
value of E [.I (t 
T)] was computed by full enumeration of the individual expert interpretations.) 
.
Step 5d. Step 4 identified those simulation results that represented the 5th and 95th percentiles 
of the composite distribution for frequency of intersection. For these parameter sets, designated 
0.05and .0.95, the results of Step 5b are used in Equations A-10 and A-18 to compute the values 
I .0.05 I
of .I (t, L,f
) and .I (t, L,fn ,rEC .0.05), respectively, for the 5th percentile hazard and 
mn 
m 
I .0.95 I
.
I (t, L,f
) and .I (t, L,fn ,rEC .0.95), respectively, for the 95th percentile hazard. The
mn 
m 
results of the individual simulations are averaged using software routine COMBSF (BSC 2000 
I .0.05), I EC .0.05),
[DIRS 168218]) to produce the final values of .I (t, L,f
.
I (t, L,fn ,r
mn 
m 
I .0.95)I EC .0.95).
.
I (t, L,f 
and .I (t, L,fn ,r 
Routine COMBSF performs this calculation, 
mn 
m 
I .0.xx t.0. xx )
) over LIm and fn 
equals .I (
including the normalization so that the sum of .I (t, L,f
mn 
obtained in Step 4. The resulting disaggregated frequencies of intersection are then normalized 
to produce conditional distributions. At each value of LIm and fn, the computed values of 
I EC .0.05 I .0.05 I EC .
.
I (t, L,fn ,r 
) are divided by .I (t, L,f
) and the values of .I (t, L,fn ,r 
0.95) are 
m 
mn 
m 
I .0.95 
divided by .I (t, L,f) to produce a distribution for rEC conditional on LIm and fn. The
mn 
I .0.05 t.0.05 I
values of .I (t, L,f
) are, in turn, divided by .I (
) and the values .I (t, L,f.0.95) are 
mn 
mn 
t.0.95 
) to produce joint distributions for LIm and fn 
conditional on the 5th and 
95th percentile values for the frequency of intersection. 
divided by .I (

APPENDIX B 
DEVELOPMENT OF FOOTPRINT POLYGON 
FOR THE PROPOSED REPOSITORY 


The coordinates of the emplacement drifts for the 2003 repository design were obtained from the 
Repository Design, Repository/PA IED Subsurface Facilities (BSC 2003 [DIRS 162289]). 
These coordinates are given in terms of the Nevada State Plane Coordinate System, Central 
Zone. The coordinate system used in the PVHA hazard assessment is UTM. The Nevada State 
Plane coordinates for the emplacement drifts were transformed to UTM (Zone 11) using the 
coordinate conversion utility in EarthVision 5.1 (Dynamics Graphics 2000 [DIRS 167994]). The 
transformed coordinates are listed in Table B-1. Subsequent to REV 01 of this report, the 
emplacement area of the repository has been modified slightly (BSC 2004 [DIRS 164519]). As 
discussed in Section 6.5.2, this slight decrease in the size of the emplacement area is expected to 
have a negligible effect on the calculated frequency of intersection. 
The calculations performed in this scientific analysis use input data from files that contain the 
vertices of a polygon for the repository footprint. For the purpose of this analysis, the repository 
footprint is defined as the outline of the waste emplacement area. A polygon was constructed to 
encompass the emplacement drifts in panels 1, 2, 3, and 5 of the repository design. A buffer 
zone was added around the emplacement area defined by the drift coordinates in Table B-1 to 
account for the effect of eruptive conduit size on the calculation of the frequency of dike 
intersection and the distribution for number of eruptive centers within the repository footprint. 
The width of the buffer zone (55 m) was defined in REV 01 of this report (BSC 2003 
[DIRS 163769]) as the sum of the mean diameter for eruptive conduits (52.2 m) and the drift 
half-width of 2.75 m. The resulting polygon vertices were placed in input file LA2002.FP used 
in the calculations presented in this report. The footprint polygon file is shown in Figures 6-17a 
and 6-17b, Section 6.5. 
The Characterize Eruptive Processes at Yucca Mountain, Nevada, report (BSC 2004 
[DIRS 169980]) has redefined the distribution for eruptive conduit diameter to be triangular with 
a mode at 50 m and a maximum at 150 m. The mean of this distribution is approximately 67 m. 
If the repository footprint polygon were to be adjusted to account for a 15 m difference in the 
width of the buffer zone, the difference in the total length of the footprint polygon would be 
approximately 0.5 percent and the difference in the area of the repository footprint would be 
3 percent. The change in area and length from the 1996 PVHA footprint to the repository 
footprint represent increases of 12 percent and 41 percent, respectively. These changes produced 
only a 13 percent increase in the mean frequency of intersection. Thus, increasing the width of 
the buffer zone by 15 m is expected to have a very small effect on the computed frequency of 
intersection and a recalculation is not warranted at this time. It should be noted that the buffer 
zone width does accommodate the mode of the conduit diameter distribution. Also, the increase 
in size is partially offset by the modification to the repository design discussed at the beginning 
of this appendix. 

Table B-1. Repository Drift Coordinates for 2003 Repository Design 
East Side West Side 
UTM UTM UTM UTM 
Panel Drift 
Easting 
(km) 
Northing 
(km) 
Easting 
(km) 
Northing 
(km) 
2 1 548.966 4081.495 548.434 4081.320 
2 2 548.962 4081.408 548.392 4081.221 
3 2 548.364 4081.212 547.959 4081.079 
2 3 548.921 4081.310 548.351 4081.122 
3 3 548.323 4081.113 547.782 4080.935 
2 4 548.879 4081.211 548.309 4081.023 
3 4 548.281 4081.014 547.711 4080.827 
2 1 549.441 4081.310 548.997 4081.164 
2 5 548.837 4081.112 548.267 4080.925 
3 5 548.239 4080.915 547.669 4080.728 
3 6 547.627 4080.629 548.198 4080.816 
2 6 548.226 4080.826 548.796 4081.013 
2 2 548.956 4081.065 549.532 4081.255 
2 3 549.582 4081.186 548.914 4080.966 
2 7 548.754 4080.913 548.184 4080.726 
3 7 548.156 4080.717 547.586 4080.529 
3 8 547.544 4080.431 548.114 4080.618 
2 8 548.142 4080.627 548.713 4080.815 
2 4 548.872 4080.868 549.610 4081.110 
2 5 549.563 4081.009 548.831 4080.769 
2 9 548.671 4080.716 548.101 4080.528 
3 9 548.073 4080.519 547.503 4080.332 
3 10 547.446 4080.228 548.032 4080.421 
2 10 548.061 4080.430 548.626 4080.616 
2 6 548.770 4080.664 549.511 4080.907 
2 7 549.459 4080.805 548.738 4080.567 
2 11 548.622 4080.529 548.046 4080.340 
3 11 547.994 4080.323 547.425 4080.136 
3 12 547.421 4080.049 547.990 4080.236 
2 12 548.042 4080.253 548.618 4080.443 
2 8 548.735 4080.481 549.408 4080.703 
2 9 549.356 4080.601 548.730 4080.394 
2 13 548.613 4080.356 548.038 4080.167 
3 13 547.986 4080.150 547.417 4079.963 
3 14 547.412 4079.876 547.981 4080.063 
2 14 548.033 4080.080 548.609 4080.269 
2 10 548.726 4080.307 549.304 4080.498 
2 11 549.253 4080.395 548.722 4080.221 
2 15 548.605 4080.183 548.030 4079.993 
3 15 547.978 4079.977 547.407 4079.789 
3 16 547.404 4079.703 547.973 4079.890 

Table B-1. Proposed Repository Drift Coordinates for License Application Design (Continued) 
East Side West Side 
UTM UTM UTM UTM 
Panel Drift 
Easting 
(km) 
Northing 
(km) 
Easting 
(km) 
Northing 
(km) 
2 16 548.025 4079.907 548.601 4080.096 
2 12 548.718 4080.134 549.201 4080.293 
2 13 549.164 4080.196 548.713 4080.048 
2 17 548.596 4080.009 548.021 4079.820 
3 17 547.969 4079.803 547.399 4079.616 
3 18 547.395 4079.529 547.965 4079.717 
2 18 548.016 4079.733 548.593 4079.923 
2 14 548.710 4079.962 549.142 4080.104 
2 15 549.115 4080.010 548.705 4079.875 
2 19 548.588 4079.836 548.012 4079.647 
3 19 547.961 4079.630 547.391 4079.443 
3 20 547.387 4079.356 547.956 4079.543 
2 20 548.008 4079.560 548.584 4079.750 
2 16 548.701 4079.789 549.106 4079.921 
2 17 549.087 4079.830 548.696 4079.702 
2 21 548.580 4079.663 548.003 4079.474 
3 21 547.951 4079.457 547.382 4079.269 
3 22 547.381 4079.184 547.948 4079.370 
2 22 548.000 4079.387 548.575 4079.576 
2 18 548.693 4079.615 549.067 4079.738 
2 19 549.049 4079.647 548.688 4079.529 
2 23 548.571 4079.490 547.995 4079.300 
3 23 547.946 4079.284 547.389 4079.101 
3 24 547.396 4079.018 547.962 4079.204 
1 1 548.112 4079.254 548.566 4079.403 
1 2 548.563 4079.316 548.012 4079.135 
3 25 547.959 4079.118 547.403 4078.935 
3 26 547.411 4078.852 547.954 4079.031 
1 3 548.006 4079.048 548.558 4079.230 
1 4 548.554 4079.143 548.002 4078.961 
3 27 547.950 4078.944 547.419 4078.770 
3 28 547.426 4078.687 547.946 4078.858 
1 5 548.003 4078.877 548.550 4079.056 
1 6 548.546 4078.970 548.044 4078.805 
3 29 547.944 4078.772 547.437 4078.605 
3 30 547.470 4078.531 547.977 4078.697 
1 7 548.541 4078.883 548.128 4078.747 
3 31 548.074 4078.645 547.528 4078.465 
1 8 548.538 4078.796 548.215 4078.691 
5 1 548.525 4078.537 547.794 4078.297 
5 2 547.793 4078.211 548.520 4078.450 
5 3 548.516 4078.363 547.791 4078.125 

Table B-1. Proposed Repository Drift Coordinates for License Application Design (Continued) 
East Side West Side 
UTM UTM UTM UTM 
Panel Drift 
Easting 
(km) 
Northing 
(km) 
Easting 
(km) 
Northing 
(km) 
5 4 547.790 4078.040 548.511 4078.277 
5 5 548.508 4078.190 547.789 4077.954 
5 6 547.788 4077.869 548.503 4078.103 
5 7 548.499 4078.017 547.786 4077.783 
5 8 547.786 4077.697 548.495 4077.930 
5 9 548.491 4077.843 547.784 4077.612 
5 10 547.783 4077.526 548.486 4077.757 
5 11 548.483 4077.670 547.785 4077.441 
5 12 547.787 4077.356 548.478 4077.583 
5 13 548.473 4077.497 547.788 4077.272 
5 14 547.789 4077.187 548.469 4077.410 
5 15 548.465 4077.324 547.792 4077.102 
5 16 547.793 4077.018 548.461 4077.237 
5 17 548.456 4077.150 547.795 4076.933 
5 18 547.800 4076.849 548.453 4077.064 
5 19 548.448 4076.977 547.805 4076.766 
5 20 547.807 4076.681 548.444 4076.890 
5 21 548.440 4076.804 547.807 4076.596 
5 22 547.805 4076.510 548.436 4076.717 
5 23 548.431 4076.630 547.806 4076.425 
5 24 547.807 4076.340 548.428 4076.544 
5 25 548.416 4076.455 547.815 4076.257 
5 26 547.843 4076.181 548.381 4076.358 
5 27 548.337 4076.259 547.892 4076.113 
Output DTN: LA0303BY831811.001. 

APPENDIX C 
DEVELOPMENT OF DISTRIBUTIONS FOR NUMBER OF ERUPTIVE CENTERS 
PER VOLCANIC EVENT AND AVERAGE SPACING BETWEEN 
ERUPTIVE CENTERS 


C1 INTRODUCTION 
This appendix presents the derivation of discrete distributions for the number of eruptive centers 
per volcanic event, nEC, and the average spacing between eruptive centers. These assessments 
are derived from the PVHA experts assessments of the number of volcanic events at the three 
Quaternary volcanic centers in the site region, Lathrop Wells (LW), Sleeping Butte (SB), and 
Northwest Crater Flat (NWCF) using the first two assumptions described in Section 5. As 
defined in the PVHA (CRWMS M&O 1996 [DIRS 100116]), the number of eruptive centers at 
each of these sites is: two at Sleeping Butte (Little Black Peak and Hidden Cone); five at Crater 
Flat (Little Cones southwest, Little Cones northeast, Red Cone, Black Cone, and Makani Cone); 
and one at Lathrop Wells. 
C2 ILLUSTRATION OF THE PROCESS 
The process is illustrated using the assessments of Alex McBirney (AM) (from Table AM-1, 
p. AM-13 of Appendix E in Probabilistic Volcanic Hazard Analysis for Yucca Mountain, 
Nevada (CRWMS M&O 1996 [DIRS 100116])). For Lathrop Wells (LW), AM assigned 
probabilities of 0.3, 0.2, 0.4, and 0.1, for possible volcanic events 1, 2, 3, and 4, respectively. If 
only one event occurred, then the data from LW are one event with one eruptive center per event 
(nEC = 1). If there were two events, then the data are two events with nEC = 1. For the three and 
four volcanic event scenarios the data are three events with nEC = 1 and four events with nEC = 1, 
respectively. These assessments are summarized in Table C-1. 
n
For Sleeping Butte (SB), AM assigned probabilities of 0.05, 0.8, and 0.15 to there being 1, 2, or 
3 volcanic events, respectively. For the one event scenario, the data are one event with nEC = 2 
(Hidden Cone and Little Black Peak). For the two-event scenario, the data are two events with 
EC = 1. For the three-event scenario, the data are three events with nEC = 1. 
For Northwest Crater Flat (NWCF), AM assigned probabilities of 0.9, 0.05, 0.025, 0.015, and 
0.01, because there were 1, 2, 3, 4, or 5 volcanic events, respectively. For the one event 
scenario, the data are one event with nEC = 5 (Little Cones SW, Little Cones NE, Red Cone, 
Black Cone, and Makani Cone). For the two-event scenario, AM linked Little Cones (SW and 
NE), Red Cone, and Black Cone into one event and considered Makani Cone to be the second 
event. Thus, the data are one event with nEC = 4 and one event with nEC = 1. For the three-event 
scenario, AM considered Red Cone and Black Cone to be one event, Little Cones SW and NE to 
be one event, and Makani Cone to be the third event. Thus, the data are two events with nEC = 2 
and one event with nEC = 1. For the four-event scenario, AM considered Little Cones SW and 
NE to be one event, and Red Cone, Black Cone, and Makani Cone to each be separate events. 
EC
Thus, the data are one event with nEC = 2 and four events with n = 1. Finally, for the 
five-event scenario, the data are five events with nEC = 1. 
The PVHA experts defined their assessments at each of the volcanic centers to be independent of 
the assessments at the other centers. As a result, for the assessments from Alex McBirney, there 
are 435 = 60 possible combined scenarios for the number of Quaternary volcanic events. 
Each of these combined scenarios represents a possible empirical data set for evaluating the 
distribution for nEC . For example, if LW scenario 1, SB scenario 1, and NWCF scenario 1 are 
the correct assessments for the number of events, then the combined data set consists of one 

event with nEC = 1, one event with nEC = 2, and one event with nEC = 5. The resulting empirical 
distribution defining the relative frequency for various values of nEC is: 
( 
EC 
( 
n P = 1)= 1/3 = 333.0 
EC 
( 
n P = 2)= 1/3 = 333.0 
EC
n P = 3)= 0/3 = 0 
(
n P EC = 4)= 0/3 = 0 
(n P EC = 5)= 1/3 = 333.0 
The joint probability that this combined scenario represents the correct data is the product of the 
three independent probabilities for each scenario and is equal to 0.30.050.9 = 0.0135. There 
are 59 other possible combined data sets, each resulting in an empirical distribution for nEC . The 
weighted average of these distributions is used to represent the expected distribution for nEC 
based on the assessments of Alex McBirney. 
A similar process is followed to compute the average spacing between eruptive centers. 
Whenever a volcanic event is defined to contain more than one of the eruptive centers, then the 
assessment provides a data point that can be used to evaluate the average spacing between 
eruptive centers. In the above combined scenario, there are two volcanic events with multiple 
eruptive centers. The single event at Sleeping Butte consists of eruptive centers at Little Black 
Peak and Hidden Cone. These cones are located 2.45 km apart. The single event at Crater Flat 
consists of five eruptive centers. The distance between Makani Cone and Little Cones SW is 
11.19 km. Dividing this distance by 4, which is the number of intervals between eruptive 
centers, gives an average spacing of 2.80 km. Thus the empirical distribution consists of a 
sample of two points, 2.45 km with a probability of 0.5 and 2.80 km, with a probability of 0.5. 
This distribution is weighted by the probability for the scenario of 0.0135. Repeating the process 
for the 59 other scenarios, weighting each empirical distribution by its scenario probability 
provides a composite empirical distribution for the average spacing between eruptive centers in 
future volcanic events. In performing this calculation, those scenarios that result in only volcanic 
events with no multiple eruptive centers are removed from the weighting process. 
C3 CALCULATION INPUT AND RESULTS 
The inputs to the calculation are the distributions for the number of volcanic events represented 
by the mapped Quaternary volcanoes defined by the PVHA experts and the locations of the 
volcanoes. Tables C-1 through C-10 summarize the interpretations of the assessments made by 
the 10 PVHA experts. 

Table C-1. Assessments from Alex McBirneys Volcanic Hazard Model 
Volcanic 
Center Scenario 
Number of 
Events * Probability 
Number of Events with nEC = 
1 2 3 4 5 
1 1 
LW 0.3 1 
2 2 
LW, LW 0.2 2 
Lathrop Wells 
3 3 
LW, LW, LW 0.4 3 
4 
4 
LW, LW, LW, 
LW 
0.1 
4 
1 1 
LBP+HC 0.05 1 
Sleeping 
Butte 2 2 
LBP, HC 0.8 2 
3 3 
LBP, HC, ? 0.15 3 
1 
1 
MC+BC+RC+ 
LCne+LCsw 
0.9 
1 
2 
2 
MC, BC+RC+ 
LCne+LCsw 
0.05 
1 1 
Crater Flat 3 
3 
MC, BC+RC, 
LCne+LCsw 
0.025 
1 2 
4 
4 
MC, BC, RC, 
LCne+LCsw 
0.015 
3 1 
5 
5 
MC, BC, RC, 
LCne, LCsw 
0.01 
5 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table AM-1, p. AM-13). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; MC = Makani 
Cone; BC = Black Cone; RC = Red Cone; Lcne = Little Cones North East; LCsw = 
Little Cones southwest, undetected. A + indicates eruptive centers considered to 
be part of a single volcanic event. 

Table C-2. Assessments from Bruce Crowes Volcanic Hazard Model 
Volcanic Number of Number of Events with nEC = 
Center Scenario Events * Probability 1 2 3 4 5 
1 1 
LW 0.9 1 
2 2 
LW, LW 0.06 2 
Lathrop Wells 
3 3 
LW, LW, LW 0.03 3 
4 
4 
LW, LW, LW, 
LW 
0.01 4 
1 1 
LBP+HC 0.35 1 
Sleeping Butte 2 2 
LBP, HC 0.45 2 
3 3 
LBP, HC, ? 0.2 3 
1 
1 
MC+BC+RC+ 
LCne+LCsw 
0.1 
1 
2 
2 
MC+BC, 
RC+LCne+LC 
sw 
0.1 
1 1 
3 
3 
MC, BC+RC, 
LCne+LCsw 
0.45 1 
2 
Crater Flat 4 
4 
MC, BC, RC, 
LCne+LCsw 
0.2 3 
1 
5 
5 
MC, BC, RC, 
Lcne, LCsw 
0.1 5 
6 
6 
MC, BC, RC, 
Lcne, LCsw, ? 
0.025 6 
7 
7 
MC, BC, RC, 
Lcne, LCsw, 
?, ? 
0.025 7 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table BC-3, p. BC-39). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; MC = Makani 
Cone; BC = Black Cone; RC = Red Cone; Lcne = Little Cones North East; LCsw = 
Little Cones southwest, undetected. A + indicates eruptive centers considered to 
be part of a single volcanic event. 

Table C-3. Assessments from George Thompsons Volcanic Hazard Model 
Volcanic Number of Number of Events with nEC = 
Center Scenario Events* Probability 1 2 3 4 5 
1 1 
LW 0.75 1 
2 2 
LW, LW 0.09 2 
Lathrop Wells 
3 3 
LW, LW, LW 0.08 3 
4 
4 
LW, LW, LW, 
LW 
0.08 4 
Sleeping Butte 
1 1 
LBP+HC 0.35 1 
2 2 
LBP, HC 0.65 2 
1 
1 
MC+BC+RC+ 
LCne+LCsw 
0.2 
1 
2 
2 
MC, BC+RC+ 
LCne+LCsw 
0.15 1 
1 
Crater Flat 3 
3 
MC, BC+RC, 
LCne+LCsw 
0.1 1 
2 
4 
4 
MC, BC, RC, 
LCne+LCsw 
0.5 3 
1 
5 
5 
MC, BC, RC, 
Lcne, LCsw 
0.05 5 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table GT-1, p. GT-11). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; MC = Makani 
Cone; BC = Black Cone; RC = Red Cone; Lcne = Little Cones North East; LCsw = 
Little Cones southwest, undetected. A + indicates eruptive centers considered to 
be part of a single volcanic event. 

Table C-4. Assessments from George Walkers Volcanic Hazard Model 
Volcanic Number of Number of Events with nEC = 
Center Scenario Events* Probability 1 2 3 4 5 
1 1 
LW 0.9 1 
2 2 
LW, LW 0.07 2 
Lathrop Wells 
3 3 
LW, LW, LW 0.02 3 
4 
4 
LW, LW, LW, 
LW 
0.01 4 
Sleeping Butte 
1 1 
LBP+HC 0.4 1 
2 2 
LBP, HC 0.6 2 
1 
1 
MC+BC+RC+ 
LCne+LCsw 
0.1 
1 
Crater Flat 3 
3 
MC, BC+RC, 
LCne+LCsw 
0.35 1 
2 
4 
4 
MC, BC, RC, 
LCne+LCsw 
0.55 3 
1 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table GW-1, p. GW-11). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; MC = Makani 
Cone; BC=Black Cone; RC = Red Cone; Lcne = Little Cones North East; 
LCsw = Little Cones southwest, undetected. A + indicates eruptive centers 
considered to be part of a single volcanic event. 

Table C-5. Assessments from Mel Kuntzs Volcanic Hazard Model 
Volcanic Number of Number of Events with nEC = 
Center Scenario Events * Probability 1 2 3 4 5 
1 1 
LW 0.95 1 
2 2 
LW, LW 0.03 2 
Lathrop Wells 
3 3 
LW, LW, LW 0.019 3 
4 
4 
LW, LW, LW, 
LW 
0.001 4 
1 1 
LBP+HC 0.6 1 
Sleeping 
Butte 2 2 
LBP, HC 0.3 2 
3 3 
LBP, HC, ? 0.1 3 
1 
1 
MC+BC+RC+ 
LCne+LCsw 
0.6 
1 
Crater Flat 
2 
2 
MC, BC+RC+ 
LCne+LCsw 
0.3 1 
1 
3 
3 
MC, BC+RC, 
LCne+LCsw 
0.05 1 
2 
4 
4 
MC, BC, RC, 
LCne+LCsw 
0.05 3 
1 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table MK-1, p. MK-18). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; M = Makani 
Cone; BC = Black Cone; RC = Red Cone; Lcne = Little Cones North East; 
LCsw = Little Cones southwest, undetected. A + indicates eruptive centers 
considered to be part of a single volcanic event. 

Table C-6. Assessments from Michael Sheridans Volcanic Hazard Model 
Volcanic Number of Number of Events with nEC = 
Center Scenario Events * Probability 1 2 3 4 5 
Lathrop Wells 
1 1 
LW 0.9 1 
2 2 
LW, LW 0.1 2 
Sleeping Butte 
1 1 
LBP+HC 0.67 1 
2 2 
LBP, HC 0.33 2 
1 
1 
MC+BC+RC 
+ 
LCne+LCsw 
0.7 
1 
Crater Flat 2 
2 
MC, 
BC+RC+ 
LCne+LCsw 
0.2 1 
4 
3 
3 
MC, 
BC+RC, 
LCne+LCsw 
0.1 1 
2 2 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table MS-1, p. MS-16 and from 
text on pages MS-6 to MS-7). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; MC = Makani 
Cone; BC = Black Cone; RC = Red Cone; Lcne = Little Cones North East; 
LCsw = Little Cones southwest, undetected. A + indicates eruptive centers 
considered to be part of a single volcanic event. 

Table C-7. Assessments from Richard Carlsons Volcanic Hazard Model 
Volcanic Number of Number of Events with nEC = 
Center Scenario Events * Probability 1 2 3 4 5 
Lathrop Wells 
1 1 
LW 0.95 1 
2 2 
LW, LW 0.05 2 
1 1 
LBP+HC 0.7 1 
Sleeping 
Butte 2 2 
LBP, HC 0.2 2 
3 3 
LBP, HC, ? 0.1 3 
1 
1 
MC+BC+RC+ 
LCne+LCsw 
0.6 
1 
Crater Flat 3 
3 
MC, BC+RC, 
LCne+LCsw 
0.3 1 
2 
5 
5 
MC, BC, RC, 
Lcne, LCsw 
0.01 5 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table RC-1, p. RC-16). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; MC = Makani 
Cone; BC = Black Cone; RC = Red Cone; Lcne = Little Cones North East; 
LCsw = Little Cones southwest, undetected. A + indicates eruptive centers 
considered to be part of a single volcanic event. 

Table C-8. Assessments from Richard Fishers Volcanic Hazard Model 
Volcanic Number of Probabilit Number of Events with nEC = 
Center Scenario Events * y 1 2 3 4 5 
1 1 
LW 0.6 1 
Lathrop Wells 2 2 
LW, LW 0.3 2 
3 3 0.05 3 
4 4 0.05 4 
1 1 
LBP+HC 0.7 1 
Sleeping Butte 2 2 
LBP, HC 0.25 2 
3 3 
LBP, HC, HC 0.05 3 
1 
1 
MC+BC+RC+ 
LCne+LCsw 
0.8 
1 
Crater Flat 
2 
2 
MC+BC, 
RC+LCne+LCs 
w 
0.05 
1 1 
3 
3 
MC, BC+RC, 
LCne+LCsw 
0.05 1 
2 
4 
4 
MC, BC, RC, 
LCne+LCsw 
0.1 3 
1 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table RF-1, p. RF-12). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; MC = Makani 
Cone; BC = Black Cone; RC = Red Cone; LCne = Little Cones North East; 
LCsw = Little Cones southwest, undetected. A + indicates eruptive centers 
considered to be part of a single volcanic event. 

Table C-9. Assessments from Wendell Duffields Volcanic Hazard Model 
Volcanic Number of Number of Events with nEC = 
Center Scenario Events* Probability 1 2 3 4 5 
Lathrop Wells 
1 1 
LW 0.9 1 
2 2 
LW, LW 0.1 2 
Sleeping 
Butte 
1 1 
LBP+HC 0.05 1 
2 2 
LBP, HC 0.95 2 
1 
1 
MC+BC+RC+ 
LCne+LCsw 
0.07 
1 
2 
2 
MC+BC+RC, 
LCne+LCsw 
0.14 
1 1 
Crater Flat 3 
3 
MC, BC+RC, 
LCne+LCsw 
0.26 1 
2 
4 
4 
MC, BC, RC, 
LCne+LCsw 
0.34 3 
1 
5 
5 
MC, BC, RC, 
Lcne, LCsw 
0.19 5 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table WD-1, pp. WD-11 and 
page WD-5). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; MC = Makani 
Cone; BC = Black Cone; RC = Red Cone; Lcne = Little Cones North East; 
LCsw = Little Cones southwest, undetected. A + indicates eruptive centers 
considered to be part of a single volcanic event. 

Table C-10. Assessments from William Hacketts Volcanic Hazard Model 
Volcanic Number of Number of Events with nEC = 
Center Scenario Events* Probability 1 2 3 4 5 
1 1 
LW 0.4 1 
2 2 
LW, LW 0.1 2 
Lathrop Wells 
3 3 
LW, LW, LW 0.4 3 
4 
4 
LW, LW, LW, 
LW 
0.05 4 
5 
5 
LW, LW, LW, 
LW, LW 
0.05 5 
1 1 
LBP+HC 0.4 1 
Sleeping 
Butte 2 2 
LBP, HC 0.5 2 
3 3 
LBP, HC, ? 0.1 3 
1 
1 
MC+BC+RC+ 
LCne+LCsw 
0.1 
1 
2 
2 
MC+BC+RC, 
LCne+LCsw 
0.3 
1 1 
Crater Flat 
3 
3 
MC, BC+RC, 
LCne+LCsw 
0.4 1 
2 
4 
4 
MC, BC, RC, 
LCne+LCsw 
0.1 3 
1 
5 
5 
MC, BC, RC, 
Lcne, LCsw 
0.05 5 
6 
6 
MC, BC, RC, 
Lcne, LCsw, ? 
0.05 6 
DTN: MO0002PVHA0082.000 [DIRS 148234]. 
Source: CRWMS M&O (1996 [DIRS 100116], Appendix E, Table WH-1, pp. WH-16). 
NOTE: * LW = Lathrop Wells; HC = Hidden Cone; LBP = Little Black Peak; MC = Makani 
Cone; BC = Black Cone; RC = Red Cone; Lcne = Little Cones North East; LCsw = 
Little Cones southwest, undetected. A + indicates eruptive centers considered to 
be part of a single volcanic event. 

The locations of the Quaternary volcanoes are listed in Table C-11. These values were used in 
the PVHA calculation (CRWMS M&O 1996 [DIRS 100116]) and were taken from Connor and 
Hill (1995 [DIRS 102646]). 
Table C-11. Volcano Locations 
UTM East (km) UTM North (km) Volcano 
543.780 4060.380 Lathrop Wells 
523.230 4112.530 Hidden Cone 
522.130 4110.340 Little Black Peak Cone 
540.330 4079.130 Makani Cone (North Cone) 
538.840 4073.990 Black Cone 
537.450 4071.470 Red Cone 
535.500 4069.490 Little Cone northwest 
535.131 4069.220 Little Cone southeast 
Source: DTN: MO0002PVHA0082.000 [DIRS 148234]. 
The calculation of the distribution for the number of eruptive centers per volcanic event and the 
average spacing between eruptive centers was performed using the software routine NECPDS 
(BSC 2000 [DIRS 168238]). The data in Tables C-1 through C-11 were used to create the 
following input files. The resulting output files are listed after each input file. 
**** File: AMNECPDS.IN **** 
vxy.dat
amnecpds.out
AM no ec on dikes at LW, SB, NWCF
4 0.3 0.2 0.4 0.1 
1 1 1 
2 1 1 1 1 
3 1 1 1 1 1 1 
4 1 1 1 1 1 1 1 1 
3 0.05 0.8 0.15 
1 2 2 3 
2 1 2 1 3 
3 1 2 1 3 1 3 
5 0.9 0.05 0.025 0.015 0.01 
1 5 4 5 6 7 8 
2 4 5 6 7 8 1 4 
3 2 7 8 2 5 6 1 4 
4 2 7 8 1 5 1 6 1 4 
5 1 4 1 5 1 6 1 7 1 8 
q 
**** File: AMNECPDS.OUT **** 
AM no ec on dikes at LW, SB, NWCF
NEC 1 2 3 4 5 
0.797067 0.020689 0.000000 0.008057 0.174188 
average spacing = 2.69
Average spacing distribution
5 0.46 0.6445 2.45 0.0322 2.80 0.0833 2.88 0.1560 4.09 0.0840 
average spacing from distribution = 1.40 

**** File: BCNECPDS.IN **** 
vxy.datbcnecpds.outBC no ec on dikes at LW, SB, NWCF4 0.9 0.06 0.03 0.01 
1 1 1 
2 1 1 1 1 
3 1 1 1 1 1 1 
4 1 1 1 1 1 1 1 1 
3 0.35 0.45 0.2 
1 2 2 3 
2 1 2 1 3 
3 1 2 1 3 1 3 
7 0.1 0.1 0.45 0.2 0.1 0.025 0.025 
1 5 4 5 6 7 8 
2 3 6 7 8 2 4 5 
3 2 7 8 2 5 6 1 4 
4 2 7 8 1 4 1 5 1 6 
5 1 4 1 5 1 6 1 7 1 8 
6 1 4 1 5 1 6 1 7 1 8 1 8 
7 1 4 1 5 1 6 1 7 1 8 1 8 1 8 
q 
**** File: BCNECPDS.OUT **** 
BC no ec on dikes at LW, SB, NWCFNEC 1 2 3 4 5 
0.681609 0.271645 0.020588 0.000000 0.026158 
average spacing = 1.87Average spacing distribution6 0.46 0.4030 1.62 0.0489 2.45 0.1874 2.80 0.0914 2.88 0.2202 5.35 
0489 
average spacing from distribution = 1.88 
**** File: GTNECPDS.IN **** 
vxy.datGTnecpds.outGT no ec on dikes at LW, SB, NWCF4 0.75 0.09 0.08 0.08 
1 1 1 
2 1 1 1 1 
3 1 1 1 1 1 1 
4 1 1 1 1 1 1 1 1 
2 0.35 0.65 
1 2 2 3 
2 1 2 1 3 
5 0.2 0.15 0.1 0.5 0.05 
1 5 4 5 6 7 8 
2 4 5 6 7 8 1 4 
3 2 7 8 2 5 6 1 4 
4 2 7 8 1 5 1 6 1 4 
5 1 4 1 5 1 6 1 7 1 8 
q 
**** File: GTNECPDS.OUT **** 
GT no ec on dikes at LW, SB, NWCFNEC 1 2 3 4 5 
0.744308 0.174364 0.000000 0.030266 0.051062 
average spacing = 1.53Average spacing distribution5 0.46 0.4720 2.01 0.1279 2.45 0.1839 2.80 0.1705 2.88 0.0457 
average spacing from distribution = 1.53 

**** File: GWNECPDS.IN **** 
vxy.datgwnecpds.outGW no ec on dikes at LW, SB, NWCF
4 0.9 0.07 0.02 0.01 
1 1 1 
2 1 1 1 1 
3 1 1 1 1 1 1 
4 1 1 1 1 1 1 1 1 
2 0.4 0.6 
1 2 2 3 
2 1 2 1 3 
3 0.1 0.35 0.55 
1 5 4 5 6 7 8 
3 2 7 8 2 5 6 1 4 
4 2 7 8 1 4 1 5 1 6 
q 
**** File: GWNECPDS.OUT **** 
GW no ec on dikes at LW, SB, NWCFNEC 1 2 3 4 5 
0.690211 0.282237 0.000000 0.000000 0.027552 
average spacing = 1.36 
**** File: MKNECPDS.IN **** 
vxy.datMKnecpds.outMK no ec on dikes at LW, SB, NWCF
4 0.95 0.03 0.019 0.001 
1 1 1 
2 1 1 1 1 
3 1 1 1 1 1 1 
4 1 1 1 1 1 1 1 1 
3 0.6 0.3 0.1 
1 2 2 3 
2 1 2 1 3 
3 1 2 1 3 1 3 
4 0.6 0.3 0.05 0.05 
1 5 4 5 6 7 8 
2 4 5 6 7 8 1 4 
3 2 7 8 2 5 6 1 4 
4 2 7 8 1 4 1 5 1 6 
q
Average spacing distribution
4 0.46 0.5917 2.45 0.1767 2.80 0.0800 2.88 0.1517 
average spacing from distribution = 1.37 
**** File: MKNECPDS.OUT **** 
MK no ec on dikes at LW, SB, NWCFNEC 1 2 3 4 5 
0.559011 0.199381 0.000000 0.067184 0.174424 
average spacing = 2.40 
**** File: MSNECPDS.IN **** 
vxy.datMSnecpds.outMS no ec on dikes at LW, SB, NWCF
2 0.9 0.1 
1 1 1 
2 1 1 1 1 
2 0.67 0.33 
1 2 2 3 
2 1 2 1 3 

3 0.7 0.2 0.1 
1 5 4 5 6 7 8 
2 4 5 6 7 8 1 4 
3 2 7 8 2 5 6 1 4 
qAverage spacing distribution5 0.46 0.0550 2.01 0.2100 2.45 0.2950 2.80 0.4200 2.88 0.0200 
average spacing from distribution = 2.40 
**** File: MSNECPDS.OUT **** 
MS no ec on dikes at LW, SB, NWCFNEC 1 2 3 4 5 
0.509542 0.235628 0.000000 0.045810 0.209020 
average spacing = 2.49Average spacing distribution5 0.46 0.0388 2.01 0.1330 2.45 0.3238 2.80 0.4655 2.88 0.0388 
average spacing from distribution = 2.49 
**** File: RCNECPDS.IN **** 
vxy.datRCnecpds.outRC no ec on dikes at LW, SB, NWCF2 0.95 0.05 
1 1 1 
2 1 1 1 1 
3 0.7 0.2 0.1 
1 2 2 3 
2 1 2 1 3 
3 1 2 1 3 1 3 
3 0.6 0.3 0.1 
1 5 4 5 6 7 8 
3 2 7 8 2 5 6 1 4 
5 1 4 1 5 1 6 1 7 1 8 
q 
**** File: RCNECPDS.OUT **** 
RC no ec on dikes at LW, SB, NWCFNEC 1 2 3 4 5 
0.518637 0.301513 0.000000 0.000000 0.179850 
average spacing = 2.40Average spacing distribution4 0.46 0.1186 2.45 0.3608 2.80 0.4021 2.88 0.1186 
average spacing from distribution = 2.41 
**** File: RFNECPDS.IN **** 
vxy.datRFnecpds.outRF no ec on dikes at LW, SB, NWCF4 0.6 0.3 0.05 0.05 
1 1 1 
2 1 1 1 1 
3 1 1 1 1 1 1 
4 1 1 1 1 1 1 1 1 
3 0.7 0.25 0.05 
1 2 2 3 
2 1 2 1 3 
3 1 2 1 3 1 3 
4 0.8 0.05 0.05 0.1 
1 5 4 5 6 7 8 
2 3 6 7 8 2 4 5 
3 2 7 8 2 5 6 1 4 
4 2 7 8 1 4 1 5 1 6 
q 
ANL-MGR-GS-000001 REV 02 C-16 October 2004

**** File: RFNECPDS.OUT **** 
RF no ec on dikes at LW, SB, NWCFNEC 1 2 3 4 5 
0.540624 0.232107 0.010571 0.000000 0.216698 
average spacing = 2.51Average spacing distribution6 0.46 0.0842 1.62 0.0192 2.45 0.3383 2.80 0.5200 2.88 0.0192 5.35 
0.0192 
average spacing from distribution = 2.51 
**** File: WDNECPDS.IN **** 
vxy.datWDnecpds.outWD no ec on dikes at LW, SB, NWCF2 0.9 0.1 
1 1 1 
2 1 1 1 1 
2 0.05 0.95 
1 2 2 3 
2 1 2 1 3 
5 0.07 0.14 0.26 0.34 0.19 
1 5 4 5 6 7 8 
2 2 7 8 3 4 5 6 
3 2 7 8 2 5 6 1 4 
4 2 7 8 1 4 1 5 1 6 
5 1 4 1 5 1 6 1 7 1 8 
q 
**** File: WDNECPDS.OUT **** 
WD no ec on dikes at LW, SB, NWCFNEC 1 2 3 4 5 
0.782655 0.172043 0.027872 0.000000 0.017430 
average spacing = 1.40Average spacing distribution5 0.46 0.6445 2.45 0.0322 2.80 0.0833 2.88 0.1560 4.09 0.0840 
average spacing from distribution = 1.40 
**** File: WHNECPDS.IN **** 
vxy.datWHnecpds.outWH no ec on dikes at LW, SB, NWCF5 0.4 0.1 0.4 0.05 0.05 
1 1 1 
2 1 1 1 1 
3 1 1 1 1 1 1 
4 1 1 1 1 1 1 1 1 
5 1 1 1 1 1 1 1 1 1 1 
3 0.4 0.5 0.1 
1 2 2 3 
2 1 2 1 3 
3 1 2 1 3 1 3 
6 0.1 0.3 0.4 0.1 0.05 0.05 
1 5 4 5 6 7 8 
2 3 4 5 6 2 7 8 
3 2 5 6 2 7 8 1 4 
4 2 7 8 1 4 1 5 1 6 
5 1 4 1 5 1 6 1 7 1 8 
6 1 4 1 5 1 6 1 7 1 8 1 8 
q 

**** File: WHNECPDS.OUT **** 
WH no ec on dikes at LW, SB, NWCF
NEC 1 2 3 4 5 
0.668581 0.256513 0.053095 0.000000 0.021812 
average spacing = 1.97 
Average spacing distribution
5 0.46 0.4078 2.45 0.1844 2.80 0.0851 2.88 0.1844 4.09 0.1383 
average spacing from distribution = 1.97
The distributions for nEC for each expert are plotted in Figure C-1. The expected value for the 
average spacing between eruptive centers computed from each PVHA experts hazard model is 
listed in Table C-12 and the empirical distributions for the average spacing between eruptive 
centers are listed in Table C-13. 
Table C-12. Summary of Expected Average Spacing Between Eruptive Centers Calculation Results 
PVHA Expert 
Expected Average Spacing 
Between Eruptive Centers (km) 
Alex McBirney (AM) 2.7 
Bruce Crowe (BC) 1.9 
George Thompson (GT) 1.5 
George Walker (GW) 1.4 
Mel Kuntz (MK) 2.4 
Michael Sheridan (MS) 2.5 
Richard Carlson (RC) 2.4 
Richard Fisher (RF) 2.5 
Wendell Duffield (WD) 1.4 
William Hackett (WH) 2.0 
Output DTN: LA0009FP831811.001. 

Table C-13. Empirical Distribution for Average Spacing Between Eruptive Centers Calculation Results 
PVHA Expert 
Empirical Distribution for Average Spacing between 
Eruptive Centers (km) 
Alex McBirney (AM) 0.46 (0.0272), 2.01 (0.0492 ), 2.45 (0.0253 ), 2.80 (0.8859 ), 
2.88 (0.0124) 
Bruce Crowe (BC) 0.46 (0.4031), 1.62 (0.0489), 2.45 (0.1874), 2.80 (0.0914), 
2.88 (0.2203), 5.35 (0.0489) 
George Thompson (GT) 0.46 (0.4720), 2.01 (0.1279), 2.45 (0.1839), 2.80 (0.1705), 
2.88 (0.0457) 
George Walker (GW) 0.46 (0.5916), 2.45 (0.1767), 2.80 (0.0800), 2.88 (0.1517) 
Mel Kuntz (MK) 0.46 (0.0550), 2.01 (0.2100), 2.45 (0.2950), 2.80 (0.4200), 
2.88 (0.0200) 
Michael Sheridan (MS) 0.46 (0.0388), 2.01 (0.1330), 2.45 (0.3238), 2.80 (0.4656), 
2.88 (0.0388) 
Richard Carlson (RC) 0.46 (0.1186), 2.45 (0.3608), 2.80 (0.4020), 2.88 (0.1186) 
Richard Fisher (RF) 0.46 (0.0842), 1.62 (0.0192), 2.45 (0.3383), 2.80 (0.5199), 
2.88 (0.0192), 5.35 (0.0192) 
Wendell Duffield (WD) 0.46 (0.6445), 2.45 (0.0322), 2.80 (0.0833), 2.88 (0.1560), 
4.09 (0.0840) 
William Hackett (WH) 0.46 (0.4078), 2.45 (0.1844), 2.80 (0.0851), 2.88 (0.1844), 
4.09 (0.1383) 
Output DTN: LA0009FP831811.004. 
NOTE: The values in ( ) are the empirical probability for the preceding value of average 
spacing. 
0 
1 2 3 4 5 
Probability 
AM 
BC 
GT 
GW 
MK 
MS 
RC 
RF 
WD 
WH 
0.1 
0.2 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
0.9 
Number of Eruptive Centers per Volcanic Ev ent 
Output DTN: LA0009FP831811.001. 
NOTE: The two-letter code indicates the PVHA experts initials from Table C-12. 
Figure C-1. Distributions for Number of Eruptive Centers per Volcanic Event, nEC, Derived from the 
Probabilistic Volcanic Hazard Analysis Experts Interpretations 

INTENTIONALLY LEFT BLANK 

APPENDIX D 
ADDRESSING YUCCA MOUNTAIN REVIEW PLAN, FINAL REPORT ACCEPTANCE 
CRITERIA RELATED TO SITE CHARACTERIZATION, IDENTIFICATION OF 
EVENTS WITH PROBABILITIES GREATER THAN 10-8 PER YEAR, AND 
VOLCANIC DISRUPTION OF WASTE PACKAGES 


The probability of intersection of the repository by an ascending basaltic dike has been estimated 
to be 1.7  10 -8 per year. Therefore, to meet the requirements of 10 CFR 63.114(d), the 
probability of intersection has been identified as an event that must be evaluated as part of the 
analysis of repository postclosure performance. Section 1.5.2 of the Yucca Mountain Review 
Plan, Final Report, and Section 1.5.3 of NUREG-1804 (NRC 2003 [DIRS 163274]) provides the 
acceptance criteria that apply to the description of site characterization activities. NUREG-1804, 
Section 2.2.1.2.2.3 contains Acceptance Criteria related to the integrated subissue of 
identification of events with probabilities greater than 10-8 per year. NUREG-1804, 
Section 2.2.1.3.2.3 contains the acceptance criteria related to the integrated subissue of 
mechanical disruption of waste packages. NUREG-1804, Section 2.2.1.3.10.3 contains the 
acceptance criteria related to the integrated subissue of volcanic disruption of waste packages. 
The following information identifies sections of this report that contain information relevant to 
future igneous events at Yucca Mountain. The applicable acceptance criteria may also be 
addressed in other analysis and model reports and are considered fully addressed when this 
report is considered in conjunction with those reports. 
Section 1.5.3 Acceptance Criterion 1: The General Information section of the License 
Application contains an adequate description of site characterization activities 
1. An adequate overview is provided of the site characterization activities related to 
geology; hydrology; geochemistry; geotechnical properties and conditions of the host 
rock; climatology, meteorology, and other environmental sciences; and the reference 
biosphere. 
Section 6.1.1 describes the conceptual model for igneous activity, and Section 6.2 
describes the volcanic history of the Yucca Mountain region. Section 6.3 describes the 
PVHA (CRWMS M&O 1996 [DIRS 100116]), including the process used 
(Section 6.3.1), the definition of a volcanic event, and the technical basis for the 
definition ( 6.3.2). Section 6.4 describes the Crater Flat structural domain and its 
relationship to volcanism. 
Section 1.5.3 Acceptance Criterion 2: The General Information section of the 
License Application contains an adequate description of site characterization results. 
2. A sufficient understanding is provided of current features and processes present in the 
Yucca Mountain region. 
FEPs associated with igneous activity and addressed by information in this report are 
identified in Section 6.1.2. The analysis report describes the volcanic history of the 
YMR and separates the Miocene eruptions of huge volumes of silicic tephra from the 
Pliocene and Quaternary eruptions of very modest amounts of basalt that ended with 
the eruption(s) at the Lathrop Wells cone about 80,000 years ago. Internal structure 
and boundaries of the Crater Flat structural domain are described in Section 6.4.1. The 
correlation of volcanism with features of the structural domain is described in 
Section 6.4.1.5. The relationship of volcanic source zones described in the PVHA) to 
the structural domain is described in Section 6.4.2. 

The PVHA established that the annual probability of intersection of the repository by a 
basaltic dike is very low but still large enough that volcanism must be considered in 
the TSPA-LA. The estimate of the annual probability of intersection of the repository 
by an ascending basaltic dike was done using an expert elicitation process described in 
the PVHA. Topics of special interest include (a) discussion of PVHA results and 
uncertainty (Section 6.3.1.5), (b) consideration of alternative conceptual models 
(Section 6.3.1.6), (c) discussion of the significance of buried volcanic centers on 
PVHA results (Section 6.3.1.7), (d) discussion of alternative estimates of intersection 
probabilities, (e) discussion of the definitions and parameters of a volcanic event and 
implications for alternative probability calculations (Section 6.3.2), and (f) discussion 
of conceptual models of volcanism and formulation of probability models 
(Section 6.3.3). 
3. An adequate understanding is provided of future events and processes likely to be 
present in the Yucca Mountain region that could affect repository safety. 
The PVHA established that the annual probability of intersection of the repository by a 
basaltic dike is very low but still large enough that volcanism must be considered in 
the TSPA-LA. The estimate of the annual probability of intersection of the repository 
by an ascending basaltic dike was done using an expert elicitation process described in 
the PVHA. Topics of special interest include (a) discussion of PVHA results and 
uncertainty (Section 6.3.1.5), (b) consideration of alternative conceptual models 
(Section 6.3.1.6), (c) discussion of the significance of buried volcanic centers on 
PVHA results (Section 6.3.1.7), (d) discussion of alternative estimates of intersection 
probabilities, (e) discussion of the definitions and parameters of a volcanic event and 
implications for alternative probability calculations (Section 6.3.2), and (f) discussion 
of conceptual models of volcanism and formulation of probability models 
(Section 6.3.3). 
For TSPA-LA, volcanic disruption of the repository will be modeled by two disruption 
scenarios. The first is a direct release scenario, which features a basaltic eruption 
through the repository and ejection and dispersal of contaminated ash to the location of 
the RMEI. The second is an indirect release scenario, which features intrusion of a 
basaltic dike into the repository without eruption, damage to waste packages, and 
exposure of the waste to transport by normal groundwater mechanisms. In each case, 
the dose is multiplied by the annual probability to provide a probability-weighted 
mean annual dose. The annual probability is documented in this report and other 
reports document the other parameters needed to complete the models for the two 
scenarios. 
4. The description of the reference biosphere is consistent with present knowledge of 
natural processes in and around the Yucca Mountain site, including the location of the 
RMEI. 
This report does not address the characteristics of the reference biosphere or the 
location of the RMEI. 

Section 2.2.1.2.2.3, Identification of Events with Probabilities Greater Than 10-8 Per Year 
Acceptance Criterion 1: Events Are Adequately Defined 
5. 
Events or event classes are defined without ambiguity and used consistently in 
probability models, so that probabilities for each event or event class are estimated 
separately. 
For the PVHA (CRWMS M&) 1996 [DIRS 100116]), an expert panel was convened 
in 1995 to review all pertinent data relating to volcanism at Yucca Mountain and, 
based on these data, to quantify both the annual probability and associated uncertainty 
of a volcanic event intersecting a proposed repository sited at Yucca Mountain. The 
data the experts reviewed was comprehensive, consisting of two decades of data 
collected by volcanologists who conducted studies to quantify the probability that a 
future volcanic eruption would disrupt the proposed repository. PVHA results and 
uncertainties are summarized in Section 6.3.1.5. Section 6.3.2 describes how the 
experts defined a volcanic event and the implications of the definition for alternative 
probability calculations. Based on the description in Section 6.3.2, although the 
experts defined a volcanic event differently, the product of the expert elicitation 
process was an unambiguous definition of a volcanic event and the descriptions in 
Sections 6.3.2 and 6.3.3 show how the definitions were consistently used in the 
development and evaluation of probability models that supported the estimate of the 
probability of intersection of the proposed repository by a future igneous event. 
6. 
Probabilities of intrusive and extrusive igneous events are calculated separately. 
Section 6.5.3 describes the results of the estimation of the probability of intersection of 
the repository footprint by an ascending basaltic dike. The section also describes the 
results of the estimation of the number of eruptive centers that could occur within the 
repository footprint. Probability values, presented in Table 6-14, show the annual 
frequency of intersection of the repository by a dike, the conditional probability of at 
least one eruptive center (given intersection), and the annual frequency of occurrence 
of one or more eruptive centers within the proposed repository. 
Acceptance Criterion 2: Probability Estimates For Future Events Are Supported By 
Appropriate Technical Bases 
1. Probabilities for future natural events have considered past patterns of the natural 
events in the Yucca Mountain region considering the likely future conditions and 
interactions of the natural and engineered system. These probability estimates have 
specifically included igneous events. 
Section 6.2 describes the volcanic history of the YMR. Section 6.3.1 describes the 
PVHA process and includes documentation of the measures used to include 
information about past patterns of igneous activity in the YMR were incorporated into 
alternative spatial and temporal distributions of potential future volcanic activity in the 
region (Section 6.3.1.3). Section 6.3.1.7 describes the methods used to evaluate the 
significance of buried volcanic centers on the PVHA results, and Section 6.3.1.8 

describes the measures used to include alternative estimates of the intersection 
probability. Section 6.3.2 includes examples of how information about vents and vent 
alignments in the YMR was incorporated into the probability calculations. 
Acceptance Criterion 3: Probability Model Support Is Adequate 
(1) Probability models are justified through comparison with output from 
detailed process-level models and/or empirical observations (e.g., laboratory 
testing, field measurements, or natural analogs, including Yucca Mountain 
site data). Specifically: 
(a) For infrequent events, the U.S. Department of Energy justifies, to the 
extent appropriate, proposed probability models with data from 
reasonably analogous systems. Analog systems should contain 
significantly more events that the Yucca Mountain system, to provide 
reasonable evaluations of probability model performance. 
Section 6.3.1.3 describes the temporal and spatial aspects of probability models and 
the methods that were used to ensure that alternative spatial and temporal models were 
considered by the experts and included in the development of probability models. 
Section 6.3.1.6 describes the consideration of alternative conceptual models of the 
tectonic environment of Yucca Mountain that have emerged since the PVHA was 
completed. Section 6.3.1.7 describes the methods used to consider the significance of 
buried volcanic centers on the PVHA results. Section 6.3.1.8 describes the alternative 
estimates of intersection probability and provides comments about the relevance of 
each of the models to estimating the probability of intersection. Section 6.3.2 
describes definitions and parameters of a volcanic event and describes implications of 
these elements for alternative probability calculations. Section 6.3.2.1 specifically 
addresses use of analogue information and describes evidence from analogue sites 
related to determining whether dikes or dike systems can reach the near-surface 
without any portion of the system erupting. Data from the analogue systems shows 
that field observations do not support the multipliers assigned for undetected intrusive 
events by the NRC. Rather, the analogue information supports the interpretation that 
the intrusion/extrusion ratio is close to 1. 
(b) The U.S. Department of Energy justifies, to the extent appropriate, the 
ability of probability models to produce results consistent with the 
timing and characteristics (e.g., location and magnitude) of successive 
past events in the Yucca Mountain system. 
The DOE probability estimate for intersection of the proposed repository by a basaltic 
dike is a combined estimate developed from inputs of 10 experts but modified to 
reflect a more current repository design. The experts models were based on the 
igneous characteristics of the YMR; hence, the probability models they developed 
were consistent with the timing and characteristics of past events in the YMR. The 
information used by the experts and the results of their deliberations are extensively 
documented in the PVHA (CRWMS M&O 1996 [DIRS 100116]). The ability of the 

probability model to produce results consistent with timing and characteristics of past 
events is described in detail in Section 6.5.3, and the effects of new aeromagnetic 
information on the hazard estimate is evaluated in Section 6.5.4. 
Based on structural arguments and the past patterns of the close association of 
volcanism and extension, the eastern boundaries of local volcanic source zones defined 
in the PVHA separate more tectonically active and less tectonically active portions of 
the Crater Flat basin and may be reasonable predictors of the eastern extent of 
volcanism expected in the future (Section 6.4.2). The correlation between volcanism 
and internal structures and boundaries of the Crater Flat basin is described in 
Section 6.4.1.4. The relationship between the probability of dike intersection and 
structural features of Crater Flat is described in Section 6.4.2. The area of most likely 
future volcanism is not at the repository but rather is in the southwest part of the Crater 
Flat basin in the area with the most extension (Section 6.4.2). 
(c) The U.S. Department of Energy probability models for natural events 
use underlying geologic bases (e.g., tectonic models) that are consistent 
with other relevant features, events, and processes evaluated, using 
Section 2.2.1.2.1 
Consistency of experts models with tectonic models is discussed in Section 6.4, which 
presents a detailed description of the Crater Flat structural domain. Consideration of 
relevant FEPs is discussed in Section 6.1.2. 
Acceptance Criterion 4: Probability Model Parameters Have Been Adequately Established 
(1) Parameters used in probability models are technically justified and 
documented by the U.S. Department of Energy. Specifically: 
(a) Parameters for probability models are constrained by data from the 
Yucca Mountain region and engineered repository system to the extent 
practical. 
Section 6.2 describes the volcanic history of the YMR. Section 6.3.1 describes the 
PVHA process and includes documentation of the measures used to include 
information about past patterns of igneous activity in the YMR were incorporated into 
alternative spatial and temporal distributions of potential future volcanic activity in the 
region (Section 6.3.1.3). Section 6.3.1.7 describes the methods used to evaluate the 
significance of buried volcanic centers on the PVHA results, and Section 6.3.1.8 
describes the measures used to include alternative estimates of the intersection 
probability. Section 6.3.2 includes examples of how information about vents and vent 
alignments in the YMR was incorporated into the probability calculations. 
(b) The U.S. Department of Energy appropriately establishes reasonable and 
consistent correlations between parameters. 

The volcanic history of the YMR is described in Section 6.2. The correlations 
between volcanism and the internal structure and boundaries of the Crater Flat basin 
are described in Section 6.4.1.5, and the relationship between Crater Flat structural 
features and the probability of dike intersection with the repository is described in 
Section 6.4.2. The reasonableness and consistency of the relationship between 
intrusive and extrusive event, and the effects of consideration of alternative models of 
the relationship based on analogue information, is described in detail in 
Section 6.3.2.1. Alternative event (dike) lengths and their consistency with data from 
the YMR and with data from analogues are considered in Section 6.3.2.2. Conceptual 
models of volcanism and the use of these models in the development of probability 
models are described in Section 6.3.3. 
(c) Where sufficient data do not exist, the definition of parameter values and 
conceptual models is based on appropriate use of other sources, such as 
expert elicitation conducted in accordance with appropriate guidance. 
The DOE probability estimate is based on the results of formal elicitations of ten 
experts (Section 6.3.1.1). The data considered by the experts was described in detail in 
the PVHA report (CRWMS M&O 1996 [DIRS 100116], e.g., Table 3-1). The 
development of the probability estimate is summarized in Section 6.3 of this report, 
and the elicitation process is summarized in Section 6.3.1.4. Elicitation results are 
extensively documented in the PVHA report (CRWMS M&O 1996 [DIRS 100116], 
Sections 4.1 and 4.2) and are summarized in this report in Section 6.3.1.5. DOE and 
NRC guidance relevant to the elicitation process and adherence to that guidance during 
the elicitation process was described in the PVHA (CRWMS M&O 1996 
[DIRS 100116], Section 2.1.1). 
Acceptance Criterion 5: Uncertainty In Event Probability Is Adequately Evaluated 
(1) Probability values appropriately reflect uncertainties. Specifically: 
(a) The U.S. Department of Energy provides a technical basis for 
probability values used, and the values account for the uncertainty in the 
probability estimates. 
The technical basis for the probability values described in this report are extensively 
documented in Sections 6.3.2 and 6.4, and the PVHA process is summarized in 
Section 6.3.1. The formulations and methods used to recalculate the frequency of 
intersection, develop distributions for length and orientation of dikes, and estimate the 
number of eruptive centers within the repository footprint are described in 
Sections 6.5.1 and 6.5.2. The results of the calculations are described in Section 6.5.3. 
Uncertainties in the PVHA elicitation process are summarized in Section 6.3.1.5, and 
uncertainties in the technical basis supporting the probability values calculated in this 
report are described in Sections 6.3.2 and 6.3.3. The correlation of volcanism in the 
YMR with the Crater Flat structural domain is discussed in Section 6.4.1.5, and the 
relationship of the PVHA volcanic source zones to Crater Flat structural features and 

the probability of dike intersection is described in Section 6.4.2. Propagation of 
uncertainties in the analyses is specifically described in Section 6.5.3 and is shown, for 
example, in Figure 6-18. 
(b) The uncertainty for reported probability values adequately reflects the 
influence of parameter uncertainty on the range of model results 
(i.e., precision) and the model uncertainty, as it affects the timing and 
magnitude of past events (i.e., accuracy). 
Propagation of uncertainties in the analyses is specifically described in Section 6.5.3 
and shown, for example, in Figure 6-18. Methods to include uncertainties associated 
with specific parameter are described in the formulation of the probability models in 
Section 6.5.1. 
Integrated Subissue: Mechanical Disruption of Engineered Barriers 
Acceptance criteria related to mechanical disruption of engineered barriers are presented in 
Section 2.2.1.3.2.3 of NUREG-1804 (NRC 2003 [DIRS 163274]). Because this section of 
NUREG-1804 addresses the consequences of an igneous event intersecting the repository, the 
applicability of the information in this report to the acceptance criteria is limited. Information in 
this report about the segment lengths and orientations of dikes that intersect the repository and 
the spacing between dikes is needed to evaluate the effects of igneous intrusion on the repository. 
However, this report does not address issues related to the nature of the possible interactions 
between a dike and repository drifts; nor does this report address waste package damage caused 
by exposure to magmatic conditions or the incorporation of such damage models into TSPA-LA. 
Acceptance Criterion 1: System Description and Model Integration Are Adequate 
1. 
Total System Performance Assessment (TSPA) adequately incorporates important 
design features, physical phenomena, and couplings, and uses consistent and 
appropriate assumptions throughout the mechanical disruption of engineered barrier 
abstraction process. 
The subjects identified in this acceptance criterion are not addressed by information in 
this report. 
2. 
The description of geological and engineering aspects of design features, physical 
phenomena, and couplings that may affect mechanical disruption of engineered 
barriers, is adequate. For example, the description may include materials used in the 
construction of engineered barrier components, environmental effects 
(e.g., temperature, water chemistry, humidity, radiation, etc.) on these materials, and 
mechanical failure processes and concomitant failure criteria used to assess the 
performance capabilities of these materials. Conditions and assumptions in the 
abstraction of mechanical disruption of engineered barriers are readily identified and 
consistent with the body of data presented in the description. 
The subjects identified in this acceptance criterion are not addressed by information in 
this report. 

3. 
The abstraction of mechanical disruption of engineered barriers uses assumptions, 
technical bases, data, and models that are appropriate and consistent with other related 
U.S. Department of Energy abstractions. For example, assumptions used for 
mechanical disruption of engineered barriers are consistent with the abstraction of 
degradation of engineered barriers (Section 2.2.1.3.1 of the Yucca Mountain Review 
Plan). The descriptions and technical bases provide transparent and traceable support 
for the abstraction of mechanical disruption of engineered barriers. 
The subjects identified in this acceptance criterion are not addressed by information in 
this report. 
4. 
Boundary and initial conditions used in the TSPA abstraction of mechanical disruption 
of engineered barriers are propagated throughout the abstraction approaches. 
The subjects identified in this acceptance criterion are not addressed by information in 
this report. 
5. 
Sufficient data and technical bases to assess the degree to which features, events, and 
processes have been included in this abstraction are provided. 
This report provides the mean annual frequency of intersection of the repository 
footprint by an igneous event (Section 6.5.3.1). The report also provides the 
conditional distributions for one or more eruptive centers forming within the 
repository, and distributions for dike length and azimuth (Section 6.5.3.2). 
6. 
The conclusion, with respect to the impact of transient criticality on the integrity of the 
engineered barriers, is defensible. 
Transient criticality is not addressed in this report. 
7. 
Guidance in NUREG-1297 (Altman et al. 1988 [DIRS 103597]) and NUREG-1298 
(Altman et al. 1988 [DIRS 103750]) or other acceptable approaches, is followed. 
NUREG-1297 describes the generic technical position with respect to the use of peer 
reviews on high-level waste repository programs. Peer review was not used in the 
development of this report. NUREG-1298 describes the generic technical position 
with respect to qualification of existing data. When external sources have provided 
unqualified data that have been used as direct input to this document, the inputs from 
those sources are qualified for intended use within the document using the criteria 
found in AP-SIII.9Q, Scientific Analyses. These criteria represent a subset of the 
methods and attributes required for qualification of data per AP-SIII.2Q, Qualification 
of Unqualified Data. These methods and attributes are based on those that are 
presented in NUREG 1298, which are meant to provide the level of confidence in the 
data  commensurate with their intended use. 

Acceptance Criterion 2: Data Are Sufficient for Model Justification 
1. 
Geological and engineering values used in the license application to evaluate 
mechanical disruption of engineered barriers, are adequately justified. Adequate 
descriptions of how the data were used, and appropriately synthesized into the 
parameters, are provided. 
This report provides the mean annual frequency of intersection of the repository 
footprint by an igneous event (Section 6.5.3.1). The report also provides the 
conditional distributions for one or more eruptive centers forming within the 
repository, and distributions for dike length and azimuth (Section 6.5.3.2). 
2. 
Sufficient data have been collected on the geology of the natural system, engineering 
materials, and initial manufacturing defects, to establish initial and boundary 
conditions for the TSPA abstraction of mechanical disruption of engineered barriers. 
This report provides the mean annual frequency of intersection of the repository 
footprint by an igneous event (Section 6.5.3.1). The report also provides the 
conditional distributions for one or more eruptive centers forming within the 
repository, and distributions for dike length and azimuth (Section 6.5.3.2). The 
volcanic history of the region is described in Section 6.2, and the characteristics of the 
Crater Flat Structural Domain are described in Section 6.4. Other inputs needed to 
establish initial and boundary conditions for the TSPA abstraction of mechanical 
disruption of engineered barriers are beyond the scope of this report. 
3. 
Data on geology of the natural system, engineering materials, and initial 
manufacturing defects used in the TSPA abstraction, are based on appropriate 
techniques. These techniques may include laboratory experiments, site-specific field 
measurements, natural analogue research, and process-level modeling studies. As 
appropriate, sensitivity or uncertainty analyses used to support the U.S. Department of 
Energy TSPA abstraction are adequate to determine the possible need for additional 
data. 
This report provides the mean annual frequency of intersection of the repository 
footprint by an igneous event (Section 6.5.3.1). The report also provides the 
conditional distributions for one or more eruptive centers forming within the 
repository, and distributions for dike length and azimuth (Section 6.5.3.2). The 
volcanic history of the region is described in Section 6.2, and the characteristics of the 
Crater Flat Structural Domain are described in Section 6.4. Use of analogue data for 
differentiation of intrusive and extrusive events is described in Section 6.3.2.1. 
Analyses examining the sensitivity of the volcanic hazard estimate to potential buried 
volcanic centers are described in Section 6.5.4. Other inputs needed to support the 
TSPA abstraction of mechanical disruption of engineered barriers are beyond the 
scope of this report. 

4. 
Engineered barrier mechanical failure models for disruption events are adequate. For 
example, these models may consider effects of prolonged exposure to the expected 
emplacement drift environment, material test results not specifically designed or 
performed for the Yucca Mountain site, and engineered barrier component fabrication 
flaws. 
Analysis of mechanical failure models for disruption events is beyond the scope of this 
report. 
Acceptance Criterion 3: Data Uncertainty Is Characterized and Propagated Through the 
Model Abstraction 
1. 
Models use parameter values, assumed ranges, probability distributions, and bounding 
assumptions that are technically defensible, reasonably account for uncertainties, and 
variabilities, and do not result in an under-representation of risk. 
This report provides the mean annual frequency of intersection of the repository 
footprint by an igneous event (Section 6.5.3.1). The report also provides the 
conditional distributions for one or more eruptive centers forming within the 
repository, and distributions for dike length and azimuth (Section 6.5.3.2). Analyses 
examining the sensitivity of the volcanic hazard estimate to potential buried volcanic 
centers are described in Section 6.5.4. 
2. 
Process-level models used to represent mechanically disruptive events, within the 
emplacement drifts at the proposed Yucca Mountain repository, are adequate. 
Parameter values are adequately constrained by Yucca Mountain site data, such that 
the estimates of mechanically disruptive events on engineered barrier integrity are not 
underestimated. Parameters within conceptual models for mechanically disruptive 
events are consistent with the range of characteristics observed at Yucca Mountain. 
This report provides the mean annual frequency of intersection of the repository 
footprint by an igneous event (Section 6.5.3.1). The report also provides the 
conditional distributions for one or more eruptive centers forming within the 
repository, and distributions for dike length and azimuth (Section 6.5.3.2). Analyses 
examining the sensitivity of the volcanic hazard estimate to potential buried volcanic 
centers are described in Section 6.5.4. The analyses described in this report do not 
include development of parameters for conceptual models of mechanically disruptive 
events. 
3. 
Uncertainty is adequately represented in parameter development for conceptual 
models, process-level models, and alternative conceptual models considered in 
developing the TSPA abstraction of mechanical disruption of engineered barriers. 
This parameter development may be done either through sensitivity analyses or use of 
conservative limits. 
Uncertainties associated with the PVHA results are described in Section 6.3.1.5. The 
frequency of intersection of repository footprint by a dike is described in 
Section 6.5.3.1, and the conditional distributions for intersection length and azimuth 

and number of eruptive centers within the repository footprint are described in 
Section 6.5.3.2. These distributions include uncertainties associated with each 
parameter. 
4. Where sufficient data do not exist, the definitions of parameter values and conceptual 
models are based on appropriate use of expert elicitation, conducted in accordance 
with NUREG-1563 (Kotra et al. 1996 [DIRS 100909]). If other approaches are used, 
the U.S. Department of Energy adequately justifies their use. 
The volcanic hazard estimate (frequency of intersection of the repository by an 
igneous event) documented in the PVHA is based on an expert elicitation 
(Section 6.3.1). The elicitation was done in accordance with the DOE procedure for 
expert elicitation and was consistent with NRC draft guidance for expert elicitations 
that was the basis for NUREG-1563. 
Acceptance Criterion 4: Model Uncertainty Is Characterized and Propagated Through the 
Model Abstraction 
1. 
Alternative modeling approaches of features, events, and processes are considered and 
are consistent with available data and current scientific understanding, and the results 
and limitations are appropriately considered in the abstraction. 
Definitions and parameters of a volcanic event and implications for alternative 
probability calculations are described in Section 6.3.2, and alternative estimates of the 
intersection probability are described in Section 6.3.1.8. Consistency of the frequency 
of intersection estimates with volcanic source zones defined by the PVHA experts is 
described in Section 6.4.2, and the correlation of internal structures and boundaries of 
the Crater Flat structural domain with volcanism are described in Section 6.4.1.5. 
Propagation of uncertainties associated with the frequency of intersection is described 
in Section 6.5.3.1, and with dike lengths, azimuths, and the number of eruptive centers 
is described in Section 6.5.3.2. Sensitivity studies that examined the effects of buried 
volcanic centers (variations in the number of events) on the volcanic hazard estimate 
are described in Section 6.5.4. 
2. 
Consideration of conceptual model uncertainty is consistent with available site 
characterization data, laboratory experiments, field measurements, natural analogue 
information and process-level modeling studies; and the treatment of conceptual 
model uncertainty does not result in an under-representation of the risk estimate. 
As described in Section 6.1.1, the results of the PVHA are a set of alternative models 
for assessing the volcanic hazard at Yucca Mountain, probabilities that each model is 
the appropriate model, and probability distributions for the parameters of the models. 
As such, the PVHA defines the scientific uncertainty in applying models to assess the 
volcanic hazard. The PVHA experts documented the basis for their assessments of the 
validity of the alternative models in Probabilistic Volcanic Hazard Analysis for Yucca 
Mountain, Nevada (CRWMS M&O 1996 [DIRS 100116], Appendix E). Therefore, 

the results of the PVHA are considered valid for assessing the uncertainty in the 
volcanic hazard at Yucca Mountain. 
In the context of the PVHA the volcanic hazard is defined as the annual frequency of 
intersection of the repository by a volcanic event. A volcanic event was defined in the 
PVHA 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 
[DIRS 100116], Appendix E). For the purposes of the probability models developed 
in the PVHA and discussed in this report, a volcanic event is defined as a point (x,y) 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 
probability model by a line element defined in terms of a length, azimuth, and location 
relative to the point event. 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 (e.g., multiple dikes) has width or consists of multiple 
parallel dikes does not significantly affect the intersection probability and is not part of 
the calculations in this report. The width of the dikes and the number of parallel dikes 
does affect the consequences of an intersection and is included in the consequence 
analyses presented in Number of Waste Packages Hit by Igneous Intrusion (BSC 2004 
[DIRS 170001]). 
Based on the PVHA outputs and assumptions in Section 5 of this report, probability 
distributions are developed for the length and orientation of intersecting dikes within 
the repository footprint and for the number of eruptive centers located within the 
repository footprint (conditional on a dike intersecting the repository). These 
distributions provide estimates of the uncertainties associated with the parameters. 
3. Appropriate alternative modeling approaches are investigated that are consistent with 
available data and current scientific knowledge and that appropriately consider their 
results and limitations using tests and analyses that are sensitive to the processes 
modeled. 
Section 6.3.2 describes the definitions and parameters of a volcanic event and 
implications for alternative probability calculations. In addition, Section 6.3.1 
explains that the PVHA resulted in the development of alternative models for 
volcanism by each expert. The alternatives were combined in the PVHA to produce a 
composite mean annual frequency of intersection as well as 5th and 95th percentile 
frequencies. Finally Section 6.5.4 describes studies of the sensitivity of the hazard 
estimate to variations in the number of buried volcanic centers near Yucca Mountain. 

Acceptance Criterion 5: Model Abstraction Output Is Supported by Objective 
Comparisons 
1. 
Models implemented in this TSPA abstraction provide results consistent with output 
from detailed process-level models and/or empirical observations (laboratory and field 
testing and/or natural analogues). 
The direct input provided to TSPA by the analysis described in this report is the 
volcanic hazard or the mean annual frequency of intersection of the repository by a 
basaltic dike. The hazard was determined during the PVHA (Section 6.3.1.5), and the 
methods selected for the PVHA were used specifically to ensure that uncertainties 
associated with the hazard estimate were quantified. The PVHA estimate has been 
updated to consider the 2003 repository footprint (BSC 2003 [DIRS 162289]), and the 
hazard magnitude has increased from 1.5  10-8 per year to 1.7  10-8 per year because 
of the area of the 2003 footprint is greater than the area of the footprint used for the 
PVHA (Section 6.5.3). Consistency of the volcanic hazard analysis with detailed 
process-level models is described in Section 6.4.2, and use of information from natural 
analogue sites is described in Section 6.3.2.1. 
2. 
Outputs of mechanical disruption of engineered barrier abstractions reasonably 
produce or bound the results of corresponding process-level models, empirical 
observations, or both. 
This report does not address the effects of disruption of the engineered barriers. Such 
effects are described in analysis report Number of Waste Packages Hit by Igneous 
Intrusion (BSC 2004 [DIRS 170001]) and model reports Dike/Drift Interactions (BSC 
2004 [DIRS 170028]) and Atmospheric Dispersal and Deposition of Tephra from a 
Potential Volcanic Eruption at Yucca Mountain, Nevada (BSC 2004 [DIRS 170026]). 
3. 
Well-documented procedures that have been accepted by the scientific community to 
construct and test the mathematical and numerical models are used to simulate 
mechanical disruption of engineered barriers. 
This report does not describe simulations used to evaluate mechanical disruption of 
engineered barriers or the results of such simulations. See previous item. 
4. 
Sensitivity analyses or bounding analyses are provided to support the TSPA 
abstraction of mechanical disruption of engineered barriers that cover ranges 
consistent with site data, field or laboratory experiments and tests, and natural 
analogue research. 
This report does not describe analyses used to evaluate mechanical disruption of 
engineered barriers or the results of such simulations. Studies to evaluate the 
sensitivity of the mean annual frequency of intersection are described in Section 6.5.4. 

Integrated Subissue: Volcanic Disruption of Waste Packages 
Acceptance criteria related to the volcanic disruption of waste packages are presented 
in Section 2.2.1.3.10.3 of NUREG-1804 (NRC 2003 [DIRS 163274] NUREG-1804). 
Because this section of NUREG-1804 addresses the consequences of an igneous event 
intersecting the repository, the applicability of the information in this report to the 
acceptance criteria is limited. Information in this report about the segment lengths and 
orientations of dikes that intersect the repository, the number of eruptive centers that 
could form along a dike segment within the repository footprint, and the spacing 
between centers is needed to evaluate eruptive processes. However, this report does 
not address issues related to the nature of the possible interactions between a dike and 
repository drifts; nor does this report address waste package damage caused by 
exposure to magmatic conditions or the incorporation of such damage models into 
TSPA-LA. 
Acceptance Criterion 1: System Description And Model Integration Are Adequate 
1. 
Total system performance assessment adequately incorporates important design 
features, physical phenomena, and couplings, and uses consistent and appropriate 
assumptions throughout the volcanic disruption of waste packages abstraction process. 
The element is not addressed by information in this report. Information about the 
effects of exposure of waste packages to the environmental conditions attending 
intersection of the repository by a basaltic dike is provided in the model report, 
Dike/Drift Interactions [DIRS 170028]. 
2. 
Models used to assess volcanic disruption of waste packages are consistent with 
physical processes generally interpreted from igneous features in the Yucca Mountain 
region and/or observed at active igneous systems. 
Information in this report addresses the relationship between an ascending dike and the 
number of eruptive centers that could occur within the repository footprint 
(Section 6.5.3.2). The formulations and implementation methods needed to support 
the analyses are described in Sections 6.5.1.2 and 6.5.2.2, respectively. Models that 
are used to support the analysis of the effects of exposure of waste packages to the 
environmental conditions attending intersection of the repository by a basaltic dike 
will be described in the report, Dike/Drift Interactions [DIRS 170028]. 
3. 
Models account for changes in igneous processes that may occur from interaction with 
engineered repository systems. 
Changes in igneous processes that may occur from interactions with the engineered 
repository systems are not addressed in this report. Changes in igneous processes will 
be addressed in the update of the report, Dike/Drift Interactions [DIRS 170028]. 

4. 
Guidance in NUREG-1297 and NUREG-1298 (Altman et al. 1998 a, b) or other 
acceptable approaches is followed. 
NUREG-1297 provides guidance for the use of peer review. Peer review was not used 
in the development or evaluation of this report; so the guidance in NUREG-1297 is not 
relevant. 
External sources have provided unqualified data that have been used as direct inputs to 
the analyses described in this report. The inputs from these sources are qualified for 
intended use within the document using the criteria found in AP-SIII.9Q, Scientific 
Analyses. These criteria represent a subset of the methods and attributes required for 
qualification of data per AP-SIII.2Q, Qualification of Unqualified Data. These 
methods and attributes are meant to provide the level of confidence in the data  
commensurate with their intended use. 
Acceptance Criterion 2: Data Are Sufficient For Model Justification 
1. 
Parameter values used in the license application to evaluate volcanic disruption of 
waste packages are sufficient and adequately justified. Adequate descriptions of how 
the data were used, interpreted, and appropriately synthesized into the parameters are 
provided. 
The parameters developed in this report and needed in the analysis of volcanic 
disruption of waste packages are the results of calculations of the length and 
orientation of dikes and the number of eruptive centers within the repository. These 
parameters are documented in Section 6.5.3. 
2. 
Data used to model processes affecting volcanic disruption of waste packages are 
derived from appropriate techniques. These techniques may include site-specific field 
measurements, natural analogue investigations, and laboratory experiments. 
This report does not provide information about processes affecting volcanic disruption 
of waste packages, except for the frequency of intersection (Section 6.5.3.1), and 
conditional distributions for intersection length, azimuth, and number of eruptive 
centers within the license application footprint (Section 6.5.3.2). Information about 
and descriptions of the modeling of, processes affecting volcanic disruption of waste 
packages will be provided in the following analysis reports: 
 Characterize Eruptive Processes and Ash Redistribution at Yucca Mountain, 
Nevada (BSC 2004 [DIRS 169980]) 
 Dike/Drift Interactions (BSC 2004 [DIRS 170028]) 
 
Number of Waste Packages Hit by Igneous Intrusion (BSC 2004 [DIRS 170001]) 
 
Atmospheric Dispersal and Deposition of Tephra from a Potential Volcanic 
Eruption at Yucca Mountain, Nevada (BSC 2004 [DIRS 170026]) 

3. 
Sufficient data are available to integrate features, events, and processes, relevant to 
volcanic disruption of waste packages into process-level models, including 
determination of appropriate interrelationships and parameter correlations. 
This report does not provide information about processes affecting volcanic disruption 
of waste packages, except for the frequency of intersection (Section 6.5.3.1), and 
conditional distributions for intersection length, azimuth, and number of eruptive 
centers within the license application footprint (Section 6.5.3.2). Table 6-1 identifies 
the FEPs that are included in this analysis report. However, this report does not 
provide that FEPs disposition documentation. That documentation will be provided in 
the update of the disruptive events FEPs analysis report (BSC 2004 [DIRS 170017]). 
4. 
Where sufficient data do not exist, the definition of parameter values and associated 
conceptual models is based on appropriate use of expert elicitation, conducted in 
accordance with NUREG-1563 (Kotra et al 1996 [DIRS 100909]). If other approaches 
are used, the U.S. Department of Energy adequately justifies their use. 
The DOE probability estimate is based on the results of formal elicitations of 10 
experts (Section 6.3.1). The data considered by the experts was described in detail in 
the PVHA report (CRWMS M&O 1996 [DIRS 100116], e.g., Table 3-1). The 
identification of the technical issues considered in the PVHA is summarized in 
Section 6.3.1.2 of this report, and the elicitation process is summarized in 
Section 6.3.1.4. Elicitation results are extensively documented in the PVHA report 
(CRWMS M&O 1996 [DIRS 100116], Sections 4.1 and 4.2) and are summarized in 
this report in Section 6.3.1.5. DOE and NRC guidance relevant to the elicitation 
process and adherence to that guidance during the elicitation process was described in 
the PVHA (CRWMS M&O 1996 [DIRS 100116], Section 2.1.1). 
Acceptance Criterion 3: Data Uncertainty Is Characterized And Propagated Through The 
Model Abstraction 
1. Models use parameter values, assumed ranges, probability distributions, and bounding 
assumptions that are technically defensible, and reasonably account for uncertainties 
and variabilities, and do not result in an under-representation of the risk estimate. 
The formulations support the probability estimate and propagate parameter 
uncertainties, methods used to implement the analyses, and results of the analyses are 
described in detail in Sections 6.5.1, 6.5.2, and 6.5.3, respectively, of this report. In 
addition, the definitions and parameters of a volcanic event and their implications for 
alternative probability calculations are described in Section 6.3.2. PVHA results and 
associated uncertainties are discussed in Section 6.3.1.5. Consideration of alternative 
probability models in the PVHA process is described in Section 6.3.1.6, and the 
significance of buried volcanic centers on the PVHA results is described in 
Section 6.5.4. Alternative estimates of the intersection probability are described in 
Section 6.3.1.8. The robustness of the estimate of the probability of intersection has 
been demonstrated through sensitivity analyses (e.g., Brocoum 1997 [DIRS 147772]), 

and some published estimates of the probability of intersection of the repository by a 
dike are presented in Table 6-5. 
2. 
Parameter uncertainty accounts quantitatively for the uncertainty in parameter values 
observed in site data and the available literature (i.e., data precision), and the 
uncertainty in abstracting parameter values to process-level models (i.e., data 
accuracy). 
The uncertainties associated with the temporal and spatial aspects of models of the 
probability of intersection are described in Section 6.3.1.3. PVHA results and 
uncertainty are described in Section 6.3.1.5. Similarly, the formulations, 
implementation, and results of the recalculation of the frequency of intersection and 
the development of distributions for length and orientation of dikes are explained in 
Sections 6.5.1, 6.5.2, and 6.5.3, respectively. These sections also explain the 
development of the probability distributions for the number of eruptive center that 
could occur within the repository. The process for abstracting the recalculated values 
is not addressed in this report. 
3. 
Where sufficient data do not exist, the definition of parameter values and associated 
uncertainty is based on appropriate use of expert elicitation, conducted in accordance 
with NUREG-1563 (Kotra et al 1996 [DIRS 100909]). If other approaches are used, 
the U.S. Department of Energy adequately justifies their use. 
The DOE probability estimate is based on the results of formal elicitations of 10 
experts (Section 6.3.1.1). The data considered by the experts was described in detail in 
the PVHA report (CRWMS M&O 1996 [DIRS 100116], Table 3-1). The development 
of the probability estimate is summarized in Section 6.3.1 of this report, and the 
elicitation process is summarized in Section 6.3.1.4. Elicitation results are extensively 
documented in the PVHA report (CRWMS M&O 1996 [DIRS 100116], Sections 4.1 
and 4.2) and are summarized in this report in Section 6.3.1.5. DOE and NRC guidance 
relevant to the elicitation process and adherence to that guidance during the elicitation 
process was described in the PVHA (CRWMS M&O 1996 [DIRS 100116], 
Section 2.1.1). 
Acceptance Criterion 4: Model Uncertainty Is Characterized And Propagated Through 
The Model Abstraction 
1. 
Alternative modeling approaches to volcanic disruption of the waste package are 
considered and are consistent with available data and current scientific understandings, 
and the results and limitations are appropriately considered in the abstraction. 
This report does not address modeling of the volcanic disruption of waste packages. 
Modeling of the volcanic disruption of waste packages is addressed in Number of 
Waste Packages Hit [DIRS 170001] and Atmospheric Dispersal and Deposition of 
Tephra from a Potential Volcanic Eruption at Yucca Mountain, Nevada 
[DIRS 170026]. 

2. 
Consideration of conceptual model uncertainty is consistent with available site 
characterization data, laboratory experiments, field measurements, natural analogue 
information and process-level modeling studies; and the treatment of conceptual 
model uncertainty does not result in an under-representation of the risk estimate. 
This report does not directly address the processes and associated models of volcanic 
disruption of waste packages. Modeling of the volcanic disruption of waste packages 
is addressed in Number of Waste Packages Hit by Igneous Intrusion (BSC 2004 
[DIRS 170001]) and Atmospheric Dispersal and Deposition of Tephra from a 
Potential Volcanic Eruption at Yucca Mountain, Nevada (BSC 2004 [DIRS 170026]). 
Uncertainties in conceptual models used to estimate the probability of intersection of 
the repository, distributions of dike length and orientation, and the number of eruptive 
centers within the proposed repository are explained in Section 6.5.1, which describes 
the formulation of the analyses and 6.5.4, which describes studies of the sensitivity of 
the frequency of intersection to increases in the number of buried volcanic centers. 
Acceptance Criterion 5: Model Abstraction Output Is Supported By Objective 
Comparisons 
This report does not address model abstraction. Analysis outputs consist of the 
frequency of intersection of the repository (Section 6.5.3.1), and conditional 
distributions for intersection length, azimuth, and number of eruptive centers within 
the repository footprint (Section 6.5.3.2).