ML14058A046
| ML14058A046 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 02/04/2014 |
| From: | Office of Information Services |
| To: | |
| Shared Package | |
| ML14055A421 | List:
|
| References | |
| FOIA/PA-2012-0325 | |
| Download: ML14058A046 (8) | |
Text
NRC Staff Comments to Duke Energy Request for Information Response Comment Duke Letter Duke Letter Response NRC Response Number Reference In addition, overtopping of the main dam and The NRC staff strongly feels that abutments from excessive pump back from Lake Duke cannot discount these types of Keowee to Lake Jocassee is considered not credible failures. There have been such 1ap.4 due to the redundant monitoring capabilities provided overtopping control system failures as from the Jocassee main control room and Hydro seen with the Taum Sauk Dam Central in Charlotte.
rupture in Missouri.
The two failure modes noted as Category II regarded Was soil liquefaction during a seismic the possible seepage at the east and west abutments event considered for this failure to the main dam that could result in piping/landslides mode?
and possibly a breach. For the east abutment, the failure mode was classified as Category II because high seepage could result in rock slope instability, resulting in damage to the switch yard and possibly 2 lacmet personnel, if the slide were extensive. The 2p.6 classification was also made to point out the importance of continued monitoring and treatment if seepage were to increase significantly. For the west abutment, the failure mode was classified as Category II because high seepage could result in slope instability, possibly piping and breach in the soils above the bedrock.
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NRC Staff Comment Duke Letter Duke Letter Response NRC Response Number Reference
- 3) Overtopping Causes Breach of Embankment or Duke cannot neglect the probability of Reservoir Rim (noted as PFM 6 in the study): The overtopping.
study evaluated the possibility of overtopping the main dam and embankments from pump-back operations and flooding. It noted the existence of redundant monitoring capabilities to detect the forebay elevation 3
p.6 and alert personnel to potential overtopping-events. It also noted that it would take a long time (60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br />) Io overtop the main dam and embankments from pump-back operations, neglecting the fact that the spillway gates would actually be overtopped first, and the resulting discharge would slow the reservoir rise.
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NRC Staff Comments to Duke Energy Request for Information Response Comment Duke Letter Duke Letter Response NRC Response Number Reference
- 3) p.6 Overtopping Causes Breach of Embankment or Reservoir Rim (noted as PFM 6 in the study):
The study evaluated the possibility of overtopping the main dam and embankments from pump-back operations and flooding. It noted the existence of redundant monitoring capabilities to detect the forebay elevation and alert personnel to potential overtopping events. It also noted that it would take a long time t60hours)to overtop the main dam and embankments from pump-back operations, neglecting the fact that the spillway gbtes would actually be overtopped first, and the resulting discharge would slow the reservoir rise.
The other possibility evaluated was the failure of the spillway gates to operate during a PMF scenario. The study noted that the gates are maintained, inspected, and tested under FERC regulations, and therefore are in good operating condition. The study further noted that there are redundant means to raise the gates. Thus the PFM was classified as Category IV.
In order to operate the spillway effectively, the gates must be fully open AND three-of-four turbines must be operable. The gates are tested every five years and have never been fully opened under load since stop logs are used. Referencing the FERC Dam Safety Performance Monitoring Program Chapter 14 potential failure mode categories do not directly relate to risk.
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NRC Staff Comments to Duke Energy Request for lnformation Response Comment Duke Letter Duke Letter Response NRC Response Number Reference In December, 2004, an independent engineering A PFMA study is not a PRA study.
company (Findlay Engineering) completed a FERC-The categories presented appear to requested potential failure modes analysis (PFMA) for be used for inspection resource the Jocassee project. The PFMA concluded that there allocation and are not probability are no Category I (scale of 1 to 4, with 1 being the frequencies. Due to the scarcity of 5
p.8 most significant) failure mechanisms applicable to the failure data, NRC staff feels that use Jocassee project. Further, the PFMA recommended of this study to parse (subdivide) data actions (which were adopted by Duke) for continued is inappropriate since it will introduce performance monitoring of Jocassee dam too high an uncertainty.
commensurate with identified potential failure modes.
In addition, UFSAR [Updated Final Safety Analysis The Review Level Earthquake (RLE)
Report] Chapter 2.4.4 indicates that Jocassee was for the Oconee site is 0.3g. Duke designed to the same seismic input conditions as needs to provide the basis for stating 6
p.2 ONS. Therefore, seismic failures of the Jocassee that Jocassee Dam has same seismic project are not considered credible, protection as the Oconee site.
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NRC Staff Comments to Duke Energy Request for Informaton Response Comment Duke Letter Duke Letter Response NRC Response Number Reference In 1992, in response to a FERC request, the Duke Hydro Department initiated a second flooding study that assumed a complete failure of the main dam at Jocassee, in accordance with FERC guidelines. This study used the DAMBRK program, Rev. 4, and evaluated two conditions: (1) a 'sunny day' break in the main dam at normal pond conditions, and (2) a break in the dam during PMF conditions. The purpose of the study was to determine the worst possible case flooding in downstream reservoirs for inclusion in the Emergency Action Plans (EAP) for these hydro-electric facilities. The resulting inundation provided the extent to which evacuation plans were developed.
The purpose of this study was not to assess credible flood heights for ONS.
Duke stated that the 1992 calculation was done to satisfy a regulatory requirement for the EAP and that NRC staff should ignore its results since i was not performed for nuclear regulation. However, in addressing Oconee site flooding, Duke based most of their assumptions on the FERC Potential Failure Modes Analysis (PFMA) in Attachment 1 as a basis that Jocassee was not susceptible to various random dam failure mechanisms which satisfied another regulatory requirement outside of nuclear. This is an inconsistent argument.
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NRC Staff Comments to Duke Energy Request for Information Response Comment Duke Letter Duke Letter Response NRC Response Number Reference Duke considers a random 'sunny day' failure of the This argument is specious from a Jocassee dam not credible because of the nature of PRA standpoint. Duke is inconsistent its design, its construction, the inspections conducted in their response citing that Jocassee during its construction, and those periodic inspections Dam cannot experience any failures that have occurred, and continue to occur, since its based solely on its design margins, construction. Jocassee was designed using the construction, inspections, and current state of practice technology, employing operation. The NRC staff has no 8
p.3 conservative assumptions and margin. The design evidence that Jocassee Dam is was created with two distinct oversight organizations, unique compared to other dams.
FERC and an Independent Board of Consultants. The NRC considered other dams, some of construction of the dam utilized a standardized quality which with the same FERC inspection control process. The dam is subject to a protocols, in development of the comprehensive monitoring program and an extensive random failure frequency.
inspection program. Its performance history is well documented through periodic inspection reports as required by the FERC.
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'eeaeea NRC Staff Comments to Duke Energy Request for Information Response Comment Duke Letter Duke Letter Response NRC Response Number Reference Duke understands that the NRC included the California seismic frequencies were Frenchman and Skagway failures, based on limited not used in any computation. In operating experience of rock-fill dams, when considering PMP, Colorado and determining the credibility of a Jocassee dam failure.
Montana do get less rainfall than However, Duke maintains inclusion of these two dam South Carolina thus making Jocassee failures in assessing the likelihood of a Jocassee dam more susceptible than Frenchman failure is inappropriate since it compares a set of and Skagway. externally initiated failures against the operating years 9
pof experience for rock-fill dams. As an example, the
- p. 5 occurrence of a dam failure due to an earthquake in California does not predict the likelihood of an earthquake in western SC exceeding the seismic capacity of the Jocassee dam. Similarly, flooding events in Montana and Colorado in 1952 and 1965, respectively, do not predict the likelihood of an inflow flood in excess of the capacity of Jocassee to successfully pass.
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I NRC Staff Comments to Duke Energy Request for Information Response Comment Duke Letter Duke Letter Response NRC Response Number Reference In previous discussions, the NRC staff has stated that NRC staff only considered dams of it had identified 35 potentially relevant earthen dam height greater than 50 feet. The failures. Significant differences in the assessment of statement that failures involving operating experience could be the result of differing embankment slides should be interpretation of important qualitative factors such as excluded does not agree with the data those described above, and may have counted from the FERC PMFA which shows flooding (PMF) events as discussed earlier. These an increase of embankment seepage differences may reduce the population of relevant dam and settling of the dam. Alhough not failures that should be considered. Duke noted that likely, these failure modes are still 10 p.6 many of the NPDP records were incomplete and credible for Jocassee.
required additional information from other sources to determine whether these failures are applicable to Jocassee. This was a common problem for many small dams. Also, Duke believes failures involving embankment slides should be excluded based on the characteristics of the rock-fill shells and the favorable results of slope stability analysis conducted for Jocassee.
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