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| issue date = 03/15/2010
| issue date = 03/15/2010
| title = Email from J. Mitman, NRR to L. James, NRR on Generic Failure Rate Evaluation for Jocassee
| title = Email from J. Mitman, NRR to L. James, NRR on Generic Failure Rate Evaluation for Jocassee
| author name = Mitman J T
| author name = Mitman J
| author affiliation = NRC/NRR
| author affiliation = NRC/NRR
| addressee name = James L M
| addressee name = James L
| addressee affiliation = NRC/NRR
| addressee affiliation = NRC/NRR
| docket = 05000269, 05000270, 05000287
| docket = 05000269, 05000270, 05000287
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=Text=
=Text=
{{#Wiki_filter:Mitman, JeffreyIFrom:Sent:To:Cc:
{{#Wiki_filter:Mitman, Jeffrey                                                                                          I From:                       Mitman, Jeffrey i (' (
Sent:                       Monday, March 15, 2010 5:55 PM To:                         James, Lois Cc:                         Ferrante, Fernando; Vail, James; Laur, Steven


==Subject:==
==Subject:==
Attachments:
Generic Failure Rate Evaluation for Jocassee Attachments:                GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM.doc; Memo OFI Dam Failure Rate Rl.doc Importance:                High Lois, attached is the final version of the subject document. It has been reviewed by Steve, all of his comments and concerns have been addressed. I've also drafted a transmittal memo to Mark (through Melanie) from you.
Importance:
It also is attached. If these meet with you concurrence we will enter the documents formally into Adams and transmit them to Mark.
Mitman, Jeffrey i (' (Monday, March 15, 2010 5:55 PMJames, LoisFerrante, Fernando; Vail, James; Laur, StevenGeneric Failure Rate Evaluation for JocasseeGENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM.doc; Memo OFI DamFailure Rate Rl.docHighLois, attached is the final version of the subject document.
Jeff Tracking:
It has been reviewed by Steve, all of his commentsand concerns have been addressed.
 
I've also drafted a transmittal memo to Mark (through Melanie) from you.It also is attached.
SU.S.NRC          UNITED STATES NUCLEAR REGULATORY COMMISSION ProtectingPeople and the Environment Generic Failure Rate Evaluation for Jocassee Dam March 15, 2010 Probabilistic Risk Assessment (PRA) Analyst:         James Vail, Reliability and Risk Analyst, NRR/DRA/APOB Probabilistic Risk Assessment (PRA) Analyst:        Fernando Ferrante, Reliability and Risk Analyst, NRR/DRA/APOB Probabilistic Risk Assessment (PRA) Analyst:        Jeff Mitman, Senior Reliability and Risk Analyst, NRRJDRAIAPOB Peer Reviewer:                                       Steven A. Laur, Senior Technical Advisor NRR/DRA SENSITIVE INFORMATION         OFFICIAL U~     UNLY~
If these meet with you concurrence we will enter the documents formally into Adams andtransmit them to Mark.JeffTracking:
 
SU.S.NRCUNITED STATES NUCLEAR REGULATORY COMMISSION Protecting People and the Environment Generic Failure Rate Evaluation for Jocassee DamMarch 15, 2010Probabilistic Risk Assessment (PRA) Analyst:Probabilistic Risk Assessment (PRA) Analyst:Probabilistic Risk Assessment (PRA) Analyst:James Vail, Reliability and Risk Analyst,NRR/DRA/APOB Fernando  
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM BY DIVISION OF RISK ASSESSMENT'S PRA OPERATIONAL SUPPORT BRANCH The following documents a generic dam failure rate analysis applicable to the Jocassee Dam performed by the PRA Operational Support Branch (APOB) of the Division of Risk Assessment (DRA) in the Office of Nuclear Reactor Regulation (NRR). The analysis, technical justifications, and databases used in support of the calculations for the derived value are briefly discussed.
: Ferrante, Reliability and RiskAnalyst, NRR/DRA/APOB Jeff Mitman, Senior Reliability and RiskAnalyst, NRRJDRAIAPOB Peer Reviewer:
Portions of this evaluation were initially performed in 2007 but not formally documented at that time.
Steven A. Laur, Senior Technical AdvisorNRR/DRASENSITIVE INFORMATION OFFICIAL U~ UNLY~
Approach The approach used in deriving a generic failure rate value applicable to the Jocassee Dam included: (i) an evaluation of the physical characteristics and description of the dam, (ii) an assessment of the overall U.S. dam population for those with similar features to the Jocassee Dam, (iii) a study of U.S. dam performance information for failure events that may be applicable to this subset of the overall population, and (iv) a calculation of a point estimate, as well as consideration of the uncertainty involved, for the failure rate given the observed failure events and the observed time period (in dam-years).
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).docGENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAMBY DIVISION OF RISK ASSESSMENT'S PRA OPERATIONAL SUPPORT BRANCHThe following documents a generic dam failure rate analysis applicable to the Jocassee Damperformed by the PRA Operational Support Branch (APOB) of the Division of Risk Assessment (DRA) in the Office of Nuclear Reactor Regulation (NRR). The analysis, technical justifications, and databases used in support of the calculations for the derived value are briefly discussed.
Jocassee Dam Description The Jocassee Dam is located in northwest South Carolina, forming a reservoir (Lake Jocassee) with a 7565-acre surface area, a water volume of 1,160,298 acre-feet, and a total drainage area of 147 sq-miles at full pond (1,110 feet elevation above mean sea level). The reservoir was created in 1973 with the construction of the dam. The Jocassee Dam is an embankment dam with an earthen core and rockfilled and random rockfilled zones (see Figure 1).
Portions of this evaluation were initially performed in 2007 but not formally documented at thattime.ApproachThe approach used in deriving a generic failure rate value applicable to the Jocassee Damincluded:  
(b)(7)(F)
(i) an evaluation of the physical characteristics and description of the dam, (ii) anassessment of the overall U.S. dam population for those with similar features to the JocasseeDam, (iii) a study of U.S. dam performance information for failure events that may be applicable to this subset of the overall population, and (iv) a calculation of a point estimate, as well asconsideration of the uncertainty  
SENZITI'.'E INFORftiLA.TION   - OFFICIAL U3~ ~
: involved, for the failure rate given the observed failure eventsand the observed time period (in dam-years).
1
Jocassee Dam Description The Jocassee Dam is located in northwest South Carolina, forming a reservoir (Lake Jocassee) with a 7565-acre surface area, a water volume of 1,160,298 acre-feet, and a total drainage areaof 147 sq-miles at full pond (1,110 feet elevation above mean sea level). The reservoir wascreated in 1973 with the construction of the dam. The Jocassee Dam is an embankment damwith an earthen core and rockfilled and random rockfilled zones (see Figure 1).(b)(7)(F)
 
SENZITI'.'E INFORftiLA.TION  
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc The dam is 385 feet in height (1,125 crest elevation above mean sea level) and 1,825 feet in length and, along with two homogeneous earthfill dikes and a reinforced concrete spillway, is part of a hydroelectric station and pumped storage project. The underground powerhouse generating units receive water from two cylindrical intake towers through eight openings. The water is channeled from the intake towers to four hydro turbines by two bifurcated power tunnels which are constructed through the bedrock of the east abutment. Two gates 33 feet in height and 38 feet in width control the outflow of the spillway.
-OFFICIAL U3~ ~1 GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).docThe dam is 385 feet in height (1,125 crest elevation above mean sea level) and 1,825 feet inlength and, along with two homogeneous earthfill dikes and a reinforced concrete  
Databases The staff used two databases to obtain information about the population of dams in the US: the National Inventory of Dams (NID), maintained by the US Army Corps of Engineers, and the National Performance of Dams Program (NPDP), developed by the Department of Civil and Environmental Engineering at Stanford University. The NID database contains data describing multiple attributes such as dimensions, type, impoundment characteristics, etc. The NPDP database contains a collection of dam incident reports searchable by various parameters including dam type, incident type, and consequences.
: spillway, ispart of a hydroelectric station and pumped storage project.
Failure Events Table 1 lists the applicable dam failures initially derived from the NPDP database. To choose these 13 failures, the analysts used criteria based on the previously discussed dam characteristics (i.e., dam type and height). However, due to the ambiguity in the classification of the dam type (i.e., based on material composition) between and within the NID and NPDP databases, as well as the lack of information to establish an exact link with the Jocassee Dam characteristics for every data point, the staff considered both rockfill dams and mixed-rockfill dams (i.e., those classified exclusively as rockfill dams as well as mixed dam types that include rockfill in their categorization). It should be noted that the NPDP database does not list any failures post-2006 and at least two well-known large dam failures in the U.S. are not included:
The underground powerhouse generating units receive water from two cylindrical intake towers through eight openings.
the Big Bay Dam in Mississippi (March 2004) and the Taum Sauk Reservoir (December 2005) in Missouri. While the Big Bay Dam was an earthen dam (i.e., excluded based on dam type),
Thewater is channeled from the intake towers to four hydro turbines by two bifurcated power tunnelswhich are constructed through the bedrock of the east abutment.
the Taum Sauk Reservoir consisted of a concrete-faced rockfill dam approximately 100 feet in height and was, therefore, included in the current analysis.
Two gates 33 feet in heightand 38 feet in width control the outflow of the spillway.
Additionally, the list was screened to take into consideration (i) failure events observed between 1900 and 2005, and (ii) failure events observed between 1940 and 2005; under the assumption that events prior to these construction periods could produce different results representative of distinct design practices. In part, this choice was due to the lack of information on the exact construction date of several dams in the database. The staff expended an extensive effort to determine the construction completion date for several dams for which the information was missing in the NPDP database (this information is included in Table 1).
Databases The staff used two databases to obtain information about the population of dams in the US: theNational Inventory of Dams (NID), maintained by the US Army Corps of Engineers, and theNational Performance of Dams Program (NPDP), developed by the Department of Civil andEnvironmental Engineering at Stanford University.
Several failures listed in Table 1 have (or are assumed to have) occurred within a few years of either the start or completion of construction (e.g., the Lower Hell Hole Dam and the Frenchman Dam failures). Based on the information available and the estimated completion dates, the staff screened out such failures since the occurrence of the events was assumed to be related to the construction phase and, therefore, not applicable to a mature dam such as Jocassee.
The NID database contains data describing multiple attributes such as dimensions, type, impoundment characteristics, etc. The NPDPdatabase contains a collection of dam incident reports searchable by various parameters including dam type, incident type, and consequences.
Finally, the analysts chose to include the Dresser No. 4 Dam failure, because they deemed this dam to be similar to the Jocassee Dam in composition (i.e., a large mixed earthfill-rockfill dam),
Failure EventsTable 1 lists the applicable dam failures initially derived from the NPDP database.
3ENSITIVE INFORMATION           OFFC'IAL USE OL-2
To choosethese 13 failures, the analysts used criteria based on the previously discussed damcharacteristics (i.e., dam type and height).  
 
: However, due to the ambiguity in the classification ofthe dam type (i.e., based on material composition) between and within the NID and NPDPdatabases, as well as the lack of information to establish an exact link with the Jocassee Damcharacteristics for every data point, the staff considered both rockfill dams and mixed-rockfill dams (i.e., those classified exclusively as rockfill dams as well as mixed dam types that includerockfill in their categorization).
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc despite the fact that it is listed as a tailings dam (i.e., a dam theoretically built under lower standards of quality and maintenance).
It should be noted that the NPDP database does not list anyfailures post-2006 and at least two well-known large dam failures in the U.S. are not included:
Therefore, the final list of failures of dams similar to, and therefore applicable to, the Jocassee Dam includes 6 failures occurring between 1900 and 2005. These six failures are highlighted in Table 1. The staff included these failures based on the following criteria: (i) rockfill or mixed-rockfill dam type, (ii) dam height above 50 feet, (iii) failure occurring after 1900, and (iv) no failures during or within a few years of completion of construction. Note that iffailures occurring prior to 1940 are screened, then only 4 events remain: (1) Taum Sauk, (2) Dresser No.4 Dam, (3) Skagway, and (4) Kern Brothers Reservoir. It should be noted that there are 1 to 3 failures of dams built between 1940 and 2005 depending on whether the entries with unknown construction dates are excluded or not, respectively (in similar fashion, there are 3 to 5 failures for dams constructed between 1900-2005 excluding or not entries with unknown construction dates, respectively).
the Big Bay Dam in Mississippi (March 2004) and the Taum Sauk Reservoir (December 2005)in Missouri.
Total Dam-years Calculation To calculate the dam failure rate, the staff needed to obtain the total number of dam-years of both failed and non-failed dams. The analysts extracted a subset of dams from the NID database based on a set of parameters to narrow the US population of dams to those reflecting the characteristics of the Jocassee Dam discussed above, i.e., large rockfill dams. They assumed that dams above 50 feet in height appropriately reflect design practices and structural characteristics of larger dams such as Jocassee. This height criterion was consistent with the large dam definition (WCD, 2000) established by the International Commission on Large Dams (ICOLD) which "defines a large dam as a dam with a height of 15m or more from the foundation." If dams are between 5-15 meters high and have a reservoir volume of more than 3 million cubic meters, ICOLD also classified such dams as large. Hence, the staff used this definition as a screening criterion. The dams considered for calculation of the total dam-years were those in the NID database that were categorized exclusively as 'Rockfill' dams (i.e., those listed under the 'ER' abbreviation, intended to correspond to rockfill dams for NID cataloguing purposes).
While the Big Bay Dam was an earthen dam (i.e., excluded based on dam type),the Taum Sauk Reservoir consisted of a concrete-faced rockfill dam approximately 100 feet inheight and was, therefore, included in the current analysis.
The staff included the dam-year contributions from Skagway and the replacement for the failed Frenchman Dam, while those from Kern Brothers Reservoir, Dresser No. 4 Dam, Penn Forest, and the failed Frenchman Dam were not included. This was because the staff judges that including the dam-year contribution from these specific dams would not significantly impact the resulting dam-year total. The staff calculated the final result using the difference between the last year in the available data (2005) and either 1900 or 1940. For the 1900-2005 period, the staff obtained a total of 21,490 dam-years; while for 1940-2005 the result was 13,889 dam-years. See Appendix A for a tabulation of the dams and the associated dam-years.
Additionally, the list was screened to take into consideration (i) failure events observed between1900 and 2005, and (ii) failure events observed between 1940 and 2005; under the assumption that events prior to these construction periods could produce different results representative ofdistinct design practices.
3
In part, this choice was due to the lack of information on the exactconstruction date of several dams in the database.
 
The staff expended an extensive effort todetermine the construction completion date for several dams for which the information wasmissing in the NPDP database (this information is included in Table 1).Several failures listed in Table 1 have (or are assumed to have) occurred within a few years ofeither the start or completion of construction (e.g., the Lower Hell Hole Dam and the Frenchman Dam failures).
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc
Based on the information available and the estimated completion dates, the staffscreened out such failures since the occurrence of the events was assumed to be related to theconstruction phase and, therefore, not applicable to a mature dam such as Jocassee.
              '2005,                                                 Overtopped due to overjunipi of reservoir. Independent analysis Taum Sauk              1963                  RoM              94 indicated several root causes(e,, lack of monitoring, spillway).
: Finally, the analysts chose to include the Dresser No. 4 Dam failure, because they deemed thisdam to be similar to the Jocassee Dam in composition (i.e., a large mixed earthfill-rockfill dam),3ENSITIVE INFORMATION OFFC'IAL USE OL-2 GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).docdespite the fact that it is listed as a tailings dam (i.e., a dam theoretically built under lowerstandards of quality and maintenance).
Dresser Dam No.4       1975 Unknown Ppg....         EarthRoddl Ea ill           105   Catastrophic failure that created a breach 300 feet wide inthe levee.
Therefore, the final list of failures of dams similar to, and therefore applicable to, the JocasseeDam includes 6 failures occurring between 1900 and 2005. These six failures are highlighted inTable 1. The staff included these failures based on the following criteria:  
Indow FbWed Skagway        1965   1925   " logic Event   Rockill           79   The dam failed during afood in1965.
(i) rockfill or mixed-rockfill dam type, (ii) dam height above 50 feet, (iii) failure occurring after 1900, and (iv) nofailures during or within a few years of completion of construction.
Hell Hole       1964   1964 Not Known       RocdlI           410   Dam failed during construction. Overtopped by 100 feet- washing out most of the fill.
Note that if failures occurring prior to 1940 are screened, then only 4 events remain: (1) Taum Sauk, (2) Dresser No.4 Dam,(3) Skagway, and (4) Kern Brothers Reservoir.
Penn Forest     1960   1960 Piping           Concrete Earth   151   Partial failure. Sinkhole occurred inupstream slope of dam.
It should be noted that there are 1 to 3 failuresof dams built between 1940 and 2005 depending on whether the entries with unknownconstruction dates are excluded or not, respectively (in similar fashion, there are 3 to 5 failuresfor dams constructed between 1900-2005 excluding or not entries with unknown construction dates, respectively).
Rockfi ll Frenchman      1952   1951 Inflow Flood-   RockhIll         63   Runoff from melting snow. Adike section was overtopped early Dam                          Hydrologic Event                         morning April 15, 1952. Later that day, dam breached.
Total Dam-years Calculation To calculate the dam failure rate, the staff needed to obtain the total number of dam-years ofboth failed and non-failed dams. The analysts extracted a subset of dams from the NIDdatabase based on a set of parameters to narrow the US population of dams to those reflecting the characteristics of the Jocassee Dam discussed above, i.e., large rockfill dams. Theyassumed that dams above 50 feet in height appropriately reflect design practices and structural characteristics of larger dams such as Jocassee.
Kern Brothers   1949 Unknown Settlement       Earth Rockilll   54   Failure due to excessive settlement of fill.
This height criterion was consistent with thelarge dam definition (WCD, 2000) established by the International Commission on Large Dams(ICOLD) which "defines a large dam as a dam with a height of 15m or more from thefoundation."
Reservoir Blowout failure under concrete spillway weir structure during period Lake Francis   1899   1899 Piping           Earth Rockfill   79   of heavy spillway flow. Spillway failure thought to be due to piping in soft saturated foundation.
If dams are between 5-15 meters high and have a reservoir volume of more than 3million cubic meters, ICOLD also classified such dams as large. Hence, the staff used thisdefinition as a screening criterion.
Lafayette       1928   1928 Embankment Slide Earth Rockfill   132   Foundation slide during construction (at 120 feet). Height raised to L170 feet in1932. Not sure ifthis isconsidered afailure.
The dams considered for calculation of the total dam-years were those in the NID database that were categorized exclusively as 'Rockfill' dams (i.e., thoselisted under the 'ER' abbreviation, intended to correspond to rockfill dams for NID cataloguing purposes).
Manitou         1924   1917 Seepage         Earth Rockill   123   Partial failure was dlsintegrating and converted into gravel fill.
The staff included the dam-year contributions from Skagway and the replacement for the failedFrenchman Dam, while those from Kern Brothers Reservoir, Dresser No. 4 Dam, Penn Forest,and the failed Frenchman Dam were not included.
Failure by piping through abutment; undermined by passage of water Lyman          1915   1912 Piping           Earth Rockfill   76.4   under cap of lava rock which flanked dam and extended beneath
This was because the staff judges thatincluding the dam-year contribution from these specific dams would not significantly impact theresulting dam-year total. The staff calculated the final result using the difference between thelast year in the available data (2005) and either 1900 or 1940. For the 1900-2005 period, thestaff obtained a total of 21,490 dam-years; while for 1940-2005 the result was 13,889 dam-years. See Appendix A for a tabulation of the dams and the associated dam-years.
_        spillway. Main part of dam uninjured.
3 GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).docTaum Sauk'2005,1963RoM94Overtopped due to overjunipi of reservoir.
Lower Otay     1916   1897 Spillway         Earth Rockdil   154   Foundation slide during construction (at 120 feel). Height raised to 170 feet in1932. Not sure ifthis isconsidered afailure.
Independent analysisindicated several root causes(e,,
Failure by piping through abutment; undermined by passage of water Black Rock     1909   1908 Piping           Earth Rockflll   7     under cap of lava rock which flanked dam and extended beneath spillway. Portion of spillway dropped 7feet; some fill at south end washed out. Main part of dam uninjured.
lack of monitoring, spillway).
SeENBIIE-NF9RMA:Hie-eF~eIAHUeE ONLY-4
Dresser No.4 ....EarthRoddl Dam 1975 Unknown Ppg Ea ill 105 Catastrophic failure that created a breach 300 feet wide in the levee.Indow FbWedSkagway 1965 1925 " logic Event Rockill 79 The dam failed during a food in 1965.Hell Hole 1964 1964 Not Known RocdlI 410 Dam failed during construction.
 
Overtopped by 100 feet- washingout most of the fill.Penn Forest 1960 1960 Piping Concrete Earth 151 Partial failure.
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc Generic Point Estimate of the Dam Failure Rate The staff calculated the point estimate by dividing the number of applicable dam failures (see Table 1 above) by the total applicable dam-years (derived as described previously). Assuming a 1900-2005 range for the year of occurrence of the failure events and the dam-year estimation (based on completion year), the analysts obtained a failure rate of 2.8E-4 per dam-year. When considering a 1940-2005 range, the staff obtained a result of 2.9E-4 per dam-year.
Sinkhole occurred in upstream slope of dam.Rockfi llFrenchman 1952 1951 Inflow Flood- RockhIll 63 Runoff from melting snow. A dike section was overtopped earlyDam Hydrologic Event morning April 15, 1952. Later that day, dam breached.
Because the NID database does not give information regarding the quality of design, construction and/or maintenance, and the NPDP database does not consistently supply information on the dam health (i.e., is it well maintained?) at time of failure, the staff could not derive failure rates for above or below average built and maintained dams. This lack of information precluded the staff from making any judgment as to whether Jocassee is or is not an above average designed, constructed and maintained dam deserving of a failure frequency different than an average failure frequency.
Kern Brothers 1949 Unknown Settlement Earth Rockilll 54 Failure due to excessive settlement of fill.Reservoir Blowout failure under concrete spillway weir structure during periodLake Francis 1899 1899 Piping Earth Rockfill 79 of heavy spillway flow. Spillway failure thought to be due to piping insoft saturated foundation.
Additionally, the staff recognizes that ambiguity and lack of complete information with respect to dam type, construction completion data, and dam incident reporting, may result in variations in the failure rate estimation. Therefore, the staff performed a simple sensitivity study in order to evaluate the changes due to screening failure events and cut-off year criteria. The results are shown in Table 2 for an assumed number of failures and clearly indicated that the results exhibit small variations for the period cut-off selected (1900-2005 and 1940-2005) and the number of failures considered (6 and 4, respectively). Additionally, the extent of the variation in the point estimate is shown for other number of failures and cut-off years based on the subset of dams selected. The table illustrates that the order-of-magnitude failure frequency estimate does not change significantly if the number of failures is increased or decreased slightly.
Lafayette 1928 1928 Embankment Slide Earth Rockfill 132 Foundation slide during construction (at 120 feet). Height raised toL 170 feet in 1932. Not sure if this is considered a failure.Manitou 1924 1917 Seepage Earth Rockill 123 Partial failure was dlsintegrating and converted into gravel fill.Failure by piping through abutment; undermined by passage of waterLyman 1915 1912 Piping Earth Rockfill 76.4 under cap of lava rock which flanked dam and extended beneath_ spillway.
Table 2: Failure Rate Sensitivity Analysis ASSUMED NUMBER OF FAILURES CUT-       DAM-OFF       YEARS       #DAMS         1         2         3         4           5           6       7 ALL      25137        484      4.OE-05    8.OE-05    1.2E-04    1.6E-04    2.OE-0.4    2.4E-04    2.8E-04 1900      21490        466      4.7E-05   9.3E-05   1.4E-04   1.9E-04   2.3E-04     2.8E6.44 3.3E-04 1910      19778        449      5.1E-05   1.OE-04   1.5E-04   2.OE-04   2.5E-04   "3.0E-04   3.5E-04 1920      18389        434      5.4E-05   1.1E-04   1.6E-04   2.2E-04   2.7E-04     3.3E-04: 3.8E-04 1930      16475        410      6.1E-05   1.2E-04   1.8E-04   2.4E-04   3.OE-04     3.6E-04   4.2E-04 1940      13889        373      7.2E-05   1.4E-04   2.2E-04   2.9E-04 I 3.6E-04       4.3E-04   5.OE-04 1950      12269        346 1960        8453        270 1970        3242        143 1980        1339        82 1990        381        36 I  FAILURE RATE GIVEN # NUMBER OF FAILURES AND CUTOFF YEAR INFORMAT-         -FCILUE 5
Main part of dam uninjured.
 
Lower Otay 1916 1897 Spillway Earth Rockdil 154 Foundation slide during construction (at 120 feel). Height raised to170 feet in 1932. Not sure if this is considered a failure.Failure by piping through abutment; undermined by passage of waterBlack Rock 1909 1908 Piping Earth Rockflll 7 under cap of lava rock which flanked dam and extended beneathspillway.
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc Bayesian Estimate of the Dam Failure Rate To evaluate the dam failure rate uncertainty, the staff conducted a Bayesian analysis of the failure rate for the 1900-2005 period via a Bayesian analysis approach (Atwood et al, 2003). In this approach, a prior distribution was assumed from the number of failures and dam-years for all large dams (according to the ICOLD definition) identified in the NID and NPDP databases.
Portion of spillway dropped 7 feet; some fill at south endwashed out. Main part of dam uninjured.
Failures identified as 'infantile failures' in NPDP were excluded and only dams built since 1900 according to NID were used for total dam-year calculation. Under these assumptions, the total number of failures for all large dams for 1900-2005 was 84 with a total of 260,960 dam-years.
SeENBIIE-NF9RMA:Hie-eF~eIAHUeE ONLY-4 GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).docGeneric Point Estimate of the Dam Failure RateThe staff calculated the point estimate by dividing the number of applicable dam failures (seeTable 1 above) by the total applicable dam-years (derived as described previously).
This corresponds to a point estimate of the failure rate equivalent to 3.2E-4/dam-year. A distribution was fitted around this mean. The number of dam failure events was modeled as a Poisson distribution for which its conjugate prior was assumed to follow a Gamma distribution (i.e., the conjugate prior in a Gamma-Poisson model). The staff, based on judgment, chose a Gamma distribution with the point estimate obtained from the large dam failure rate above and a 5 th percentile corresponding to 1 E-5/dam-year. With these assumptions, the staff obtained a prior Gamma distribution with parameters a = 0.8333 and 13= 2589, which has a 5 th percentile equivalent to 1E-5/dam-year and a 9 5 1h percentile corresponding to 1 E-3/dam-year. The staff updated this prior distribution with the data used to obtain the large rockfill dam point estimate (e.g., 6 failures in 21,490 dam-years) to calculate the posterior distribution. The resulting posterior has a mean of 2.8E-4/dam-year, a 5 th percentile of 1.3E-4(dam-years, and a 950' percentile of 4.8E-4/dam-years (with parameters a = 6.8333 and 13= 24,079). Figure 2 shows both the generic large dam prior and the posterior specific to rockfill dams.
Assuminga 1900-2005 range for the year of occurrence of the failure events and the dam-year estimation (based on completion year), the analysts obtained a failure rate of 2.8E-4 per dam-year.
Conclusions The staff estimated generic dam failure rates for large rockfill dams, which it considers applicable to the Jocassee Dam, as 2.8E-4/dam-year. Given the nature of the data and the assumptions involved in narrowing the applicable failure events and subset of the U.S. dam population comparable to this specific dam, the staff performed a Bayesian analysis. Using available data on the domestic inventory of dams and dam failures, the range obtained varies between 1.3E-4/dam-year and 4.8E-4/dam-year (5 th - 9 5 th percentile) around a mean of 2.8E-4/dam-year.
Whenconsidering a 1940-2005 range, the staff obtained a result of 2.9E-4 per dam-year.
A literature review performed by the authors for statistical studies of dam failures appears to corroborate this conclusion. Such studies were found in Baecher et al (1980), Martz and Bryson (1982), Donnelly (1994), ICOLD (1995), Foster (2000a), and Foster et al (2000b).
Because the NID database does not give information regarding the quality of design,construction and/or maintenance, and the NPDP database does not consistently supplyinformation on the dam health (i.e., is it well maintained?)
6
at time of failure, the staff could notderive failure rates for above or below average built and maintained dams. This lack ofinformation precluded the staff from making any judgment as to whether Jocassee is or is not anabove average designed, constructed and maintained dam deserving of a failure frequency different than an average failure frequency.
 
Additionally, the staff recognizes that ambiguity and lack of complete information with respect todam type, construction completion data, and dam incident reporting, may result in variations inthe failure rate estimation.
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc Figure 2: Failure Rate Probability Distributions Used in Bayesian Updating 5000 4500-Prior 4000                                - Posterior
Therefore, the staff performed a simple sensitivity study in order toevaluate the changes due to screening failure events and cut-off year criteria.
                  ,   3500-(D 3000-\
The results areshown in Table 2 for an assumed number of failures and clearly indicated that the results exhibitsmall variations for the period cut-off selected (1900-2005 and 1940-2005) and the number offailures considered (6 and 4, respectively).
2500 -
Additionally, the extent of the variation in the pointestimate is shown for other number of failures and cut-off years based on the subset of damsselected.
22000 O.1500         "",
The table illustrates that the order-of-magnitude failure frequency estimate does notchange significantly if the number of failures is increased or decreased slightly.
1000" 500 0
Table 2: Failure Rate Sensitivity AnalysisASSUMED NUMBER OF FAILURESCUT- DAM-OFF YEARS #DAMS 1 2 3 4 5 6 7ALL19001910192019301940195019601970198019902513721490197781838916475138891226984533242133938148446644943441037334627014382364.OE-058.OE-051.2E-041.6E-042.OE-0.42.4E-042.8E-044.7E-05 9.3E-05 1.4E-04 1.9E-04 2.3E-04 2.8E6.44 3.3E-045.1E-05 1.OE-04 1.5E-04 2.OE-04 2.5E-04 "3.0E-04 3.5E-045.4E-05 1.1E-04 1.6E-04 2.2E-04 2.7E-04 3.3E-04:
2        4         6           8       10 Failure Rate (per dam-years)         x 10-4 References Baecher, G. B., M. E. Patd, and R. De Neufville (1980), "Risk of Dam Failure in Benefit-Cost Analysis," Water Resource Research, 16(3), 449-456.
3.8E-046.1E-05 1.2E-04 1.8E-04 2.4E-04 3.OE-04 3.6E-04 4.2E-047.2E-05 1.4E-04 2.2E-04 2.9E-04 I 3.6E-04 4.3E-04 5.OE-04I FAILURE RATE GIVEN # NUMBER OF FAILURES AND CUTOFF YEARINFORMAT-  
Martz, H.F., and M.C. Bryson (1982), "Predicting Low-Probability/High-Consequence Events,"
-FCILUE5 GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).docBayesian Estimate of the Dam Failure RateTo evaluate the dam failure rate uncertainty, the staff conducted a Bayesian analysis of thefailure rate for the 1900-2005 period via a Bayesian analysis approach (Atwood et al, 2003). Inthis approach, a prior distribution was assumed from the number of failures and dam-years forall large dams (according to the ICOLD definition) identified in the NID and NPDP databases.
Proceedings of the Workshop on Low-Probability/High-Consequence Risk Analysis, June 15-17, 1982, Arlington, Virginia.
Failures identified as 'infantile failures' in NPDP were excluded and only dams built since 1900according to NID were used for total dam-year calculation.
Donnely, R. (1994), "Issues in Dam Safety, ACRES International Innovations Autumn Edition":
Under these assumptions, the totalnumber of failures for all large dams for 1900-2005 was 84 with a total of 260,960 dam-years.
http://www.hatch.com.cn/Hatcheneravy/Innovations/autumn2OO4/feature.html ICOLD (1995), "Dam Failures Statistical Analysis," Bulletin 99, International Commission on Large Dams.
This corresponds to a point estimate of the failure rate equivalent to 3.2E-4/dam-year.
WCD (2000), "Dams and Development: A New Framework for Decision-Making - overview," The Report of the World Commission on Dams.
Adistribution was fitted around this mean. The number of dam failure events was modeled as aPoisson distribution for which its conjugate prior was assumed to follow a Gamma distribution (i.e., the conjugate prior in a Gamma-Poisson model). The staff, based on judgment, chose aGamma distribution with the point estimate obtained from the large dam failure rate above and a5th percentile corresponding to 1 E-5/dam-year.
Foster M, Fell R, Spannagle M (2000a), "The statistics of embankment dam failures and accidents," CanadianGeotechnicalJournal,37, 1000-1024.
With these assumptions, the staff obtained aprior Gamma distribution with parameters a = 0.8333 and 13 = 2589, which has a 5th percentile equivalent to 1 E-5/dam-year and a 951h percentile corresponding to 1 E-3/dam-year.
Foster M, Fell R, Spannagle M (2000b) "A method for assessing the relative likelihood of failure of embankment dams by piping," CanadianGeotechnicalJournal,37, 1025-1061 SENS1il~.1114RAT 7
The staffupdated this prior distribution with the data used to obtain the large rockfill dam point estimate(e.g., 6 failures in 21,490 dam-years) to calculate the posterior distribution.
 
The resulting posterior has a mean of 2.8E-4/dam-year, a 5th percentile of 1.3E-4(dam-years, and a 950'percentile of 4.8E-4/dam-years (with parameters a = 6.8333 and 13 = 24,079).
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc C.L. Atwood, J.L. LaChance, H.F. Martz, D.J. Anderson, M. Englehardt, D. Whitehead, and T.
Figure 2 showsboth the generic large dam prior and the posterior specific to rockfill dams.Conclusions The staff estimated generic dam failure rates for large rockfill dams, which it considers applicable to the Jocassee Dam, as 2.8E-4/dam-year.
Wheeler (2003), "Handbook of Parameter Estimation for Probabilistic Risk Assessment,"
Given the nature of the data and theassumptions involved in narrowing the applicable failure events and subset of the U.S. dampopulation comparable to this specific dam, the staff performed a Bayesian analysis.
NUREG/CR-6823, US NRC.
Usingavailable data on the domestic inventory of dams and dam failures, the range obtained variesbetween 1.3E-4/dam-year and 4.8E-4/dam-year (5th -95th percentile) around a mean of2.8E-4/dam-year.
                    '"'"" ..... R.....T. "'   O,-FICiAL USEQNLY-"
A literature review performed by the authors for statistical studies of dam failures appears tocorroborate this conclusion.
8
Such studies were found in Baecher et al (1980), Martz and Bryson(1982), Donnelly (1994), ICOLD (1995), Foster (2000a),
 
and Foster et al (2000b).6 GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).docFigure 2: Failure Rate Probability Distributions Used in Bayesian Updating50004500-Prior4000 -Posterior
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc S DAM MPOL2NDMENT IPOUNDMENT RAGE APOUNDMENTDAM CENSITIVE INrORMA lION - oFFICIAL UZE ONLY 9
, 3500-(D 3000-\2500 -22000O.1500 "",1000"50002 4 6 8 10Failure Rate (per dam-years) x 10-4References
 
: Baecher, G. B., M. E. Patd, and R. De Neufville (1980), "Risk of Dam Failure in Benefit-Cost Analysis,"
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc 400  73.000    28 CA01116                50    420    29 1ST2                    CAO1108                77    870    29 CA01128              101    250      29 E                  CA01 122            123    42300    29 mA                CA018124            225    1.970    29 OR00B12              345  500,000    29 CA01092                55    89      30 CA01120              80    117      30 CA01084              108    2,500    30 (ON                      CA01123              183    5.700    so CAD1101                55    300      31 OCH                NC01524              112    762      31 CA01080              179  285400    31 CA01111                52    52      32 CA01054                53    570      32 CAD0D87                56    1,820    32 lAY                  SC02757              64  1,287,788   32 CA0 112              93     180    32 PA00734              102    71,000    32 R                    CA00223              109    43.800 32 CA00309              114      r1800 32 CA00054              133  131 452 32 KY03048              282  435600 32 340  323r700 32 385  1,257,788 32 CO                                                58   2,950 33 63    887 33 87    550 33 79    1.250 33
Water Resource  
      .A                                        80    340 33 135    4,080 33 158    8r200 33 WALINGS  DAM                              570    7,200 34 52      74 34 62    185 34 89    14,200 93    2.342    34 34 111    2to0 34 124    11100 34 162    3r300 34 568  2,030,000 38 55     117 35 67    730 35 75    3,840 35 78    240 35 87.7   4230 35 116    2,500 35 180    8o000 37 53    844 36 Creek Dam                                        ili    4,000 37 120    7.850    38 163  29.101    38 166    52500 37 84    1,490 37 92    3,375 37 124    220 37 127    58903 37 I4YON                                        157    356 37 N                                            187    2,570 37 222    77100 38
: Research, 16(3), 449-456.Martz, H.F., and M.C. Bryson (1982), "Predicting Low-Probability/High-Consequence Events,"Proceedings of the Workshop on Low-Probability/High-Consequence Risk Analysis, June 15-17,1982, Arlington, Virginia.
    'RINIS LAKE                                  54      37 38 59    550 38 ANL;H                                            60    210 38 8a  4.150 38 71    3160 38 LANTDAM                                  75    380 38
: Donnely, R. (1994), "Issues in Dam Safety, ACRES International Innovations Autumn Edition":
        .LL                                      152      25 38 108    877 39
http://www.hatch.com.cn/Hatcheneravy/Innovations/autumn2OO4/feature.html ICOLD (1995), "Dam Failures Statistical Analysis,"
        ;3                                      118    309 38 128  61,000 3a 215    1 808 38 ECT                                      285    45 70 4,020    39 51 39 68    140 83    680      39 97    18000 100    8,542    34 115    83,000    39 38 DAM                                    122    111293    39 224    3036      39 410  208, 0    39 50    300      40
Bulletin 99, International Commission onLarge Dams.WCD (2000), "Dams and Development:
        ;;; Dike                                52    4900      40 07    5,870    40 70    240      40 75    2,56      40 77    185      40 81    121000    40 OLLOWTALINGS DAM                          129    1,260 146    11500    40 40 105    2,040 193    221000 vS                                        195    525500 INFPM~TQN
A New Framework for Decision-Making  
                      ~ENSII'.'           -CrI'Ar-u           USE-NLY 10
-overview,"
 
TheReport of the World Commission on Dams.Foster M, Fell R, Spannagle M (2000a),  
GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc 205    1251000  40 214    24.300  40 231    111.333  45 36.30D  45 240 413400  45 kM                                        390 50            4' 71 so            41 130  41 54
"The statistics of embankment dam failures andaccidents,"
      )am 91                                    55            41 K                                          59        20  41 Dam                                        90      120  41 03      1r140  41 Dam 92                                    65      157  41 95      390  41 a5        29  41 76        73  41 AM                                        150      1,156  41 41 113    22*5*6  41 193            41 273    67,520  41 440    535,D    41 S19    219,00 42 RK                                        51      109
Canadian Geotechnical
                                                      -- 25    42 54            42 55      310  42 57      4820  42 ows Reservolr                            So 59            42 4.425  42 71      I30  42 73            42 85      390  42 94        37  42 1PER                                      94      4,350 42 95            42 102    75,500  42 108    76,500 119    15T800  42 42 148      147  42 152    57T050 42 165      Bo0  42 171    417120  42 185            42 DAM DN                                  250            42 453    230.,000 43 51      376  43 VOIR                                                  19  43 55      912  43 50        37  43 75    3500    43 892    2,754 43 100        46  43 I      1. 2 DAM EWS 124 140 145 150 185 25.000 519500 43 43 43 4,750  42 10              42 192    20000    42 200      9,790  44 90        94 75        45 82      244  44 95    5,250 115      3415s  44 120 129    55,477  43 44 4                                                    58.200  44" S                                      175 S                                      200      31680  44 210    03,010  44 OAM                                          150,290  451 43 DAM                                    239    659050 271            473 1.670,700 45 300            43 56      116  40 43 59      193  45 43r 66        340  45 71      234  45 90        23  45 107        68  45 138    12.250  49 192      89991  46 193    409062  45 400    123,600  49 65        180  45 79            45 25400  47 95 ISO 190    37,120  47 164      2,400  47 ky, 200    59r500  47 47 5o        45  47 50      109 52      107 I1,240 72 72      280 320
: Journal, 37, 1000-1024.
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Foster M, Fell R, Spannagle M (2000b) "A method for assessing the relative likelihood of failureof embankment dams by piping,"
 
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Latest revision as of 08:42, 4 November 2019

Email from J. Mitman, NRR to L. James, NRR on Generic Failure Rate Evaluation for Jocassee
ML14058A059
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Issue date: 03/15/2010
From: Jeffrey Mitman
Office of Nuclear Reactor Regulation
To: Lois James
Office of Nuclear Reactor Regulation
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Mitman, Jeffrey I From: Mitman, Jeffrey i (' (

Sent: Monday, March 15, 2010 5:55 PM To: James, Lois Cc: Ferrante, Fernando; Vail, James; Laur, Steven

Subject:

Generic Failure Rate Evaluation for Jocassee Attachments: GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM.doc; Memo OFI Dam Failure Rate Rl.doc Importance: High Lois, attached is the final version of the subject document. It has been reviewed by Steve, all of his comments and concerns have been addressed. I've also drafted a transmittal memo to Mark (through Melanie) from you.

It also is attached. If these meet with you concurrence we will enter the documents formally into Adams and transmit them to Mark.

Jeff Tracking:

SU.S.NRC UNITED STATES NUCLEAR REGULATORY COMMISSION ProtectingPeople and the Environment Generic Failure Rate Evaluation for Jocassee Dam March 15, 2010 Probabilistic Risk Assessment (PRA) Analyst: James Vail, Reliability and Risk Analyst, NRR/DRA/APOB Probabilistic Risk Assessment (PRA) Analyst: Fernando Ferrante, Reliability and Risk Analyst, NRR/DRA/APOB Probabilistic Risk Assessment (PRA) Analyst: Jeff Mitman, Senior Reliability and Risk Analyst, NRRJDRAIAPOB Peer Reviewer: Steven A. Laur, Senior Technical Advisor NRR/DRA SENSITIVE INFORMATION OFFICIAL U~ UNLY~

GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM BY DIVISION OF RISK ASSESSMENT'S PRA OPERATIONAL SUPPORT BRANCH The following documents a generic dam failure rate analysis applicable to the Jocassee Dam performed by the PRA Operational Support Branch (APOB) of the Division of Risk Assessment (DRA) in the Office of Nuclear Reactor Regulation (NRR). The analysis, technical justifications, and databases used in support of the calculations for the derived value are briefly discussed.

Portions of this evaluation were initially performed in 2007 but not formally documented at that time.

Approach The approach used in deriving a generic failure rate value applicable to the Jocassee Dam included: (i) an evaluation of the physical characteristics and description of the dam, (ii) an assessment of the overall U.S. dam population for those with similar features to the Jocassee Dam, (iii) a study of U.S. dam performance information for failure events that may be applicable to this subset of the overall population, and (iv) a calculation of a point estimate, as well as consideration of the uncertainty involved, for the failure rate given the observed failure events and the observed time period (in dam-years).

Jocassee Dam Description The Jocassee Dam is located in northwest South Carolina, forming a reservoir (Lake Jocassee) with a 7565-acre surface area, a water volume of 1,160,298 acre-feet, and a total drainage area of 147 sq-miles at full pond (1,110 feet elevation above mean sea level). The reservoir was created in 1973 with the construction of the dam. The Jocassee Dam is an embankment dam with an earthen core and rockfilled and random rockfilled zones (see Figure 1).

(b)(7)(F)

SENZITI'.'E INFORftiLA.TION - OFFICIAL U3~ ~

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GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc The dam is 385 feet in height (1,125 crest elevation above mean sea level) and 1,825 feet in length and, along with two homogeneous earthfill dikes and a reinforced concrete spillway, is part of a hydroelectric station and pumped storage project. The underground powerhouse generating units receive water from two cylindrical intake towers through eight openings. The water is channeled from the intake towers to four hydro turbines by two bifurcated power tunnels which are constructed through the bedrock of the east abutment. Two gates 33 feet in height and 38 feet in width control the outflow of the spillway.

Databases The staff used two databases to obtain information about the population of dams in the US: the National Inventory of Dams (NID), maintained by the US Army Corps of Engineers, and the National Performance of Dams Program (NPDP), developed by the Department of Civil and Environmental Engineering at Stanford University. The NID database contains data describing multiple attributes such as dimensions, type, impoundment characteristics, etc. The NPDP database contains a collection of dam incident reports searchable by various parameters including dam type, incident type, and consequences.

Failure Events Table 1 lists the applicable dam failures initially derived from the NPDP database. To choose these 13 failures, the analysts used criteria based on the previously discussed dam characteristics (i.e., dam type and height). However, due to the ambiguity in the classification of the dam type (i.e., based on material composition) between and within the NID and NPDP databases, as well as the lack of information to establish an exact link with the Jocassee Dam characteristics for every data point, the staff considered both rockfill dams and mixed-rockfill dams (i.e., those classified exclusively as rockfill dams as well as mixed dam types that include rockfill in their categorization). It should be noted that the NPDP database does not list any failures post-2006 and at least two well-known large dam failures in the U.S. are not included:

the Big Bay Dam in Mississippi (March 2004) and the Taum Sauk Reservoir (December 2005) in Missouri. While the Big Bay Dam was an earthen dam (i.e., excluded based on dam type),

the Taum Sauk Reservoir consisted of a concrete-faced rockfill dam approximately 100 feet in height and was, therefore, included in the current analysis.

Additionally, the list was screened to take into consideration (i) failure events observed between 1900 and 2005, and (ii) failure events observed between 1940 and 2005; under the assumption that events prior to these construction periods could produce different results representative of distinct design practices. In part, this choice was due to the lack of information on the exact construction date of several dams in the database. The staff expended an extensive effort to determine the construction completion date for several dams for which the information was missing in the NPDP database (this information is included in Table 1).

Several failures listed in Table 1 have (or are assumed to have) occurred within a few years of either the start or completion of construction (e.g., the Lower Hell Hole Dam and the Frenchman Dam failures). Based on the information available and the estimated completion dates, the staff screened out such failures since the occurrence of the events was assumed to be related to the construction phase and, therefore, not applicable to a mature dam such as Jocassee.

Finally, the analysts chose to include the Dresser No. 4 Dam failure, because they deemed this dam to be similar to the Jocassee Dam in composition (i.e., a large mixed earthfill-rockfill dam),

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GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc despite the fact that it is listed as a tailings dam (i.e., a dam theoretically built under lower standards of quality and maintenance).

Therefore, the final list of failures of dams similar to, and therefore applicable to, the Jocassee Dam includes 6 failures occurring between 1900 and 2005. These six failures are highlighted in Table 1. The staff included these failures based on the following criteria: (i) rockfill or mixed-rockfill dam type, (ii) dam height above 50 feet, (iii) failure occurring after 1900, and (iv) no failures during or within a few years of completion of construction. Note that iffailures occurring prior to 1940 are screened, then only 4 events remain: (1) Taum Sauk, (2) Dresser No.4 Dam, (3) Skagway, and (4) Kern Brothers Reservoir. It should be noted that there are 1 to 3 failures of dams built between 1940 and 2005 depending on whether the entries with unknown construction dates are excluded or not, respectively (in similar fashion, there are 3 to 5 failures for dams constructed between 1900-2005 excluding or not entries with unknown construction dates, respectively).

Total Dam-years Calculation To calculate the dam failure rate, the staff needed to obtain the total number of dam-years of both failed and non-failed dams. The analysts extracted a subset of dams from the NID database based on a set of parameters to narrow the US population of dams to those reflecting the characteristics of the Jocassee Dam discussed above, i.e., large rockfill dams. They assumed that dams above 50 feet in height appropriately reflect design practices and structural characteristics of larger dams such as Jocassee. This height criterion was consistent with the large dam definition (WCD, 2000) established by the International Commission on Large Dams (ICOLD) which "defines a large dam as a dam with a height of 15m or more from the foundation." If dams are between 5-15 meters high and have a reservoir volume of more than 3 million cubic meters, ICOLD also classified such dams as large. Hence, the staff used this definition as a screening criterion. The dams considered for calculation of the total dam-years were those in the NID database that were categorized exclusively as 'Rockfill' dams (i.e., those listed under the 'ER' abbreviation, intended to correspond to rockfill dams for NID cataloguing purposes).

The staff included the dam-year contributions from Skagway and the replacement for the failed Frenchman Dam, while those from Kern Brothers Reservoir, Dresser No. 4 Dam, Penn Forest, and the failed Frenchman Dam were not included. This was because the staff judges that including the dam-year contribution from these specific dams would not significantly impact the resulting dam-year total. The staff calculated the final result using the difference between the last year in the available data (2005) and either 1900 or 1940. For the 1900-2005 period, the staff obtained a total of 21,490 dam-years; while for 1940-2005 the result was 13,889 dam-years. See Appendix A for a tabulation of the dams and the associated dam-years.

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GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc

'2005, Overtopped due to overjunipi of reservoir. Independent analysis Taum Sauk 1963 RoM 94 indicated several root causes(e,, lack of monitoring, spillway).

Dresser Dam No.4 1975 Unknown Ppg.... EarthRoddl Ea ill 105 Catastrophic failure that created a breach 300 feet wide inthe levee.

Indow FbWed Skagway 1965 1925 " logic Event Rockill 79 The dam failed during afood in1965.

Hell Hole 1964 1964 Not Known RocdlI 410 Dam failed during construction. Overtopped by 100 feet- washing out most of the fill.

Penn Forest 1960 1960 Piping Concrete Earth 151 Partial failure. Sinkhole occurred inupstream slope of dam.

Rockfi ll Frenchman 1952 1951 Inflow Flood- RockhIll 63 Runoff from melting snow. Adike section was overtopped early Dam Hydrologic Event morning April 15, 1952. Later that day, dam breached.

Kern Brothers 1949 Unknown Settlement Earth Rockilll 54 Failure due to excessive settlement of fill.

Reservoir Blowout failure under concrete spillway weir structure during period Lake Francis 1899 1899 Piping Earth Rockfill 79 of heavy spillway flow. Spillway failure thought to be due to piping in soft saturated foundation.

Lafayette 1928 1928 Embankment Slide Earth Rockfill 132 Foundation slide during construction (at 120 feet). Height raised to L170 feet in1932. Not sure ifthis isconsidered afailure.

Manitou 1924 1917 Seepage Earth Rockill 123 Partial failure was dlsintegrating and converted into gravel fill.

Failure by piping through abutment; undermined by passage of water Lyman 1915 1912 Piping Earth Rockfill 76.4 under cap of lava rock which flanked dam and extended beneath

_ spillway. Main part of dam uninjured.

Lower Otay 1916 1897 Spillway Earth Rockdil 154 Foundation slide during construction (at 120 feel). Height raised to 170 feet in1932. Not sure ifthis isconsidered afailure.

Failure by piping through abutment; undermined by passage of water Black Rock 1909 1908 Piping Earth Rockflll 7 under cap of lava rock which flanked dam and extended beneath spillway. Portion of spillway dropped 7feet; some fill at south end washed out. Main part of dam uninjured.

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GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc Generic Point Estimate of the Dam Failure Rate The staff calculated the point estimate by dividing the number of applicable dam failures (see Table 1 above) by the total applicable dam-years (derived as described previously). Assuming a 1900-2005 range for the year of occurrence of the failure events and the dam-year estimation (based on completion year), the analysts obtained a failure rate of 2.8E-4 per dam-year. When considering a 1940-2005 range, the staff obtained a result of 2.9E-4 per dam-year.

Because the NID database does not give information regarding the quality of design, construction and/or maintenance, and the NPDP database does not consistently supply information on the dam health (i.e., is it well maintained?) at time of failure, the staff could not derive failure rates for above or below average built and maintained dams. This lack of information precluded the staff from making any judgment as to whether Jocassee is or is not an above average designed, constructed and maintained dam deserving of a failure frequency different than an average failure frequency.

Additionally, the staff recognizes that ambiguity and lack of complete information with respect to dam type, construction completion data, and dam incident reporting, may result in variations in the failure rate estimation. Therefore, the staff performed a simple sensitivity study in order to evaluate the changes due to screening failure events and cut-off year criteria. The results are shown in Table 2 for an assumed number of failures and clearly indicated that the results exhibit small variations for the period cut-off selected (1900-2005 and 1940-2005) and the number of failures considered (6 and 4, respectively). Additionally, the extent of the variation in the point estimate is shown for other number of failures and cut-off years based on the subset of dams selected. The table illustrates that the order-of-magnitude failure frequency estimate does not change significantly if the number of failures is increased or decreased slightly.

Table 2: Failure Rate Sensitivity Analysis ASSUMED NUMBER OF FAILURES CUT- DAM-OFF YEARS #DAMS 1 2 3 4 5 6 7 ALL 25137 484 4.OE-05 8.OE-05 1.2E-04 1.6E-04 2.OE-0.4 2.4E-04 2.8E-04 1900 21490 466 4.7E-05 9.3E-05 1.4E-04 1.9E-04 2.3E-04 2.8E6.44 3.3E-04 1910 19778 449 5.1E-05 1.OE-04 1.5E-04 2.OE-04 2.5E-04 "3.0E-04 3.5E-04 1920 18389 434 5.4E-05 1.1E-04 1.6E-04 2.2E-04 2.7E-04 3.3E-04: 3.8E-04 1930 16475 410 6.1E-05 1.2E-04 1.8E-04 2.4E-04 3.OE-04 3.6E-04 4.2E-04 1940 13889 373 7.2E-05 1.4E-04 2.2E-04 2.9E-04 I 3.6E-04 4.3E-04 5.OE-04 1950 12269 346 1960 8453 270 1970 3242 143 1980 1339 82 1990 381 36 I FAILURE RATE GIVEN # NUMBER OF FAILURES AND CUTOFF YEAR INFORMAT- -FCILUE 5

GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc Bayesian Estimate of the Dam Failure Rate To evaluate the dam failure rate uncertainty, the staff conducted a Bayesian analysis of the failure rate for the 1900-2005 period via a Bayesian analysis approach (Atwood et al, 2003). In this approach, a prior distribution was assumed from the number of failures and dam-years for all large dams (according to the ICOLD definition) identified in the NID and NPDP databases.

Failures identified as 'infantile failures' in NPDP were excluded and only dams built since 1900 according to NID were used for total dam-year calculation. Under these assumptions, the total number of failures for all large dams for 1900-2005 was 84 with a total of 260,960 dam-years.

This corresponds to a point estimate of the failure rate equivalent to 3.2E-4/dam-year. A distribution was fitted around this mean. The number of dam failure events was modeled as a Poisson distribution for which its conjugate prior was assumed to follow a Gamma distribution (i.e., the conjugate prior in a Gamma-Poisson model). The staff, based on judgment, chose a Gamma distribution with the point estimate obtained from the large dam failure rate above and a 5 th percentile corresponding to 1 E-5/dam-year. With these assumptions, the staff obtained a prior Gamma distribution with parameters a = 0.8333 and 13= 2589, which has a 5 th percentile equivalent to 1E-5/dam-year and a 9 5 1h percentile corresponding to 1 E-3/dam-year. The staff updated this prior distribution with the data used to obtain the large rockfill dam point estimate (e.g., 6 failures in 21,490 dam-years) to calculate the posterior distribution. The resulting posterior has a mean of 2.8E-4/dam-year, a 5 th percentile of 1.3E-4(dam-years, and a 950' percentile of 4.8E-4/dam-years (with parameters a = 6.8333 and 13= 24,079). Figure 2 shows both the generic large dam prior and the posterior specific to rockfill dams.

Conclusions The staff estimated generic dam failure rates for large rockfill dams, which it considers applicable to the Jocassee Dam, as 2.8E-4/dam-year. Given the nature of the data and the assumptions involved in narrowing the applicable failure events and subset of the U.S. dam population comparable to this specific dam, the staff performed a Bayesian analysis. Using available data on the domestic inventory of dams and dam failures, the range obtained varies between 1.3E-4/dam-year and 4.8E-4/dam-year (5 th - 9 5 th percentile) around a mean of 2.8E-4/dam-year.

A literature review performed by the authors for statistical studies of dam failures appears to corroborate this conclusion. Such studies were found in Baecher et al (1980), Martz and Bryson (1982), Donnelly (1994), ICOLD (1995), Foster (2000a), and Foster et al (2000b).

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GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc Figure 2: Failure Rate Probability Distributions Used in Bayesian Updating 5000 4500-Prior 4000 - Posterior

, 3500-(D 3000-\

2500 -

22000 O.1500 "",

1000" 500 0

2 4 6 8 10 Failure Rate (per dam-years) x 10-4 References Baecher, G. B., M. E. Patd, and R. De Neufville (1980), "Risk of Dam Failure in Benefit-Cost Analysis," Water Resource Research, 16(3), 449-456.

Martz, H.F., and M.C. Bryson (1982), "Predicting Low-Probability/High-Consequence Events,"

Proceedings of the Workshop on Low-Probability/High-Consequence Risk Analysis, June 15-17, 1982, Arlington, Virginia.

Donnely, R. (1994), "Issues in Dam Safety, ACRES International Innovations Autumn Edition":

http://www.hatch.com.cn/Hatcheneravy/Innovations/autumn2OO4/feature.html ICOLD (1995), "Dam Failures Statistical Analysis," Bulletin 99, International Commission on Large Dams.

WCD (2000), "Dams and Development: A New Framework for Decision-Making - overview," The Report of the World Commission on Dams.

Foster M, Fell R, Spannagle M (2000a), "The statistics of embankment dam failures and accidents," CanadianGeotechnicalJournal,37, 1000-1024.

Foster M, Fell R, Spannagle M (2000b) "A method for assessing the relative likelihood of failure of embankment dams by piping," CanadianGeotechnicalJournal,37, 1025-1061 SENS1il~.1114RAT 7

GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc C.L. Atwood, J.L. LaChance, H.F. Martz, D.J. Anderson, M. Englehardt, D. Whitehead, and T.

Wheeler (2003), "Handbook of Parameter Estimation for Probabilistic Risk Assessment,"

NUREG/CR-6823, US NRC.

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GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc S DAM MPOL2NDMENT IPOUNDMENT RAGE APOUNDMENTDAM CENSITIVE INrORMA lION - oFFICIAL UZE ONLY 9

GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc 400 73.000 28 CA01116 50 420 29 1ST2 CAO1108 77 870 29 CA01128 101 250 29 E CA01 122 123 42300 29 mA CA018124 225 1.970 29 OR00B12 345 500,000 29 CA01092 55 89 30 CA01120 80 117 30 CA01084 108 2,500 30 (ON CA01123 183 5.700 so CAD1101 55 300 31 OCH NC01524 112 762 31 CA01080 179 285400 31 CA01111 52 52 32 CA01054 53 570 32 CAD0D87 56 1,820 32 lAY SC02757 64 1,287,788 32 CA0 112 93 180 32 PA00734 102 71,000 32 R CA00223 109 43.800 32 CA00309 114 r1800 32 CA00054 133 131 452 32 KY03048 282 435600 32 340 323r700 32 385 1,257,788 32 CO 58 2,950 33 63 887 33 87 550 33 79 1.250 33

.A 80 340 33 135 4,080 33 158 8r200 33 WALINGS DAM 570 7,200 34 52 74 34 62 185 34 89 14,200 93 2.342 34 34 111 2to0 34 124 11100 34 162 3r300 34 568 2,030,000 38 55 117 35 67 730 35 75 3,840 35 78 240 35 87.7 4230 35 116 2,500 35 180 8o000 37 53 844 36 Creek Dam ili 4,000 37 120 7.850 38 163 29.101 38 166 52500 37 84 1,490 37 92 3,375 37 124 220 37 127 58903 37 I4YON 157 356 37 N 187 2,570 37 222 77100 38

'RINIS LAKE 54 37 38 59 550 38 ANL;H 60 210 38 8a 4.150 38 71 3160 38 LANTDAM 75 380 38

.LL 152 25 38 108 877 39

3 118 309 38 128 61,000 3a 215 1 808 38 ECT 285 45 70 4,020 39 51 39 68 140 83 680 39 97 18000 100 8,542 34 115 83,000 39 38 DAM 122 111293 39 224 3036 39 410 208, 0 39 50 300 40
Dike 52 4900 40 07 5,870 40 70 240 40 75 2,56 40 77 185 40 81 121000 40 OLLOWTALINGS DAM 129 1,260 146 11500 40 40 105 2,040 193 221000 vS 195 525500 INFPM~TQN

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GENERIC FAILURE RATE EVALUATION FOR JOCASSEE DAM (2).doc 205 1251000 40 214 24.300 40 231 111.333 45 36.30D 45 240 413400 45 kM 390 50 4' 71 so 41 130 41 54

)am 91 55 41 K 59 20 41 Dam 90 120 41 03 1r140 41 Dam 92 65 157 41 95 390 41 a5 29 41 76 73 41 AM 150 1,156 41 41 113 22*5*6 41 193 41 273 67,520 41 440 535,D 41 S19 219,00 42 RK 51 109

-- 25 42 54 42 55 310 42 57 4820 42 ows Reservolr So 59 42 4.425 42 71 I30 42 73 42 85 390 42 94 37 42 1PER 94 4,350 42 95 42 102 75,500 42 108 76,500 119 15T800 42 42 148 147 42 152 57T050 42 165 Bo0 42 171 417120 42 185 42 DAM DN 250 42 453 230.,000 43 51 376 43 VOIR 19 43 55 912 43 50 37 43 75 3500 43 892 2,754 43 100 46 43 I 1. 2 DAM EWS 124 140 145 150 185 25.000 519500 43 43 43 4,750 42 10 42 192 20000 42 200 9,790 44 90 94 75 45 82 244 44 95 5,250 115 3415s 44 120 129 55,477 43 44 4 58.200 44" S 175 S 200 31680 44 210 03,010 44 OAM 150,290 451 43 DAM 239 659050 271 473 1.670,700 45 300 43 56 116 40 43 59 193 45 43r 66 340 45 71 234 45 90 23 45 107 68 45 138 12.250 49 192 89991 46 193 409062 45 400 123,600 49 65 180 45 79 45 25400 47 95 ISO 190 37,120 47 164 2,400 47 ky, 200 59r500 47 47 5o 45 47 50 109 52 107 I1,240 72 72 280 320

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