ML14178B166
| ML14178B166 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 09/16/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML14178B165 | List: |
| References | |
| PROC-980916, NUDOCS 9809210085 | |
| Download: ML14178B166 (9) | |
Text
SITE AUDIT PLAN FOR THE STEP-2 REVIEW OF THE INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS SUBMITTAL AT THE H. B. ROBINSON (UNIT 2) PLANT September 1998 9809210085 980916 PDR ADOCK 05000261 P
TABLE OF CONTENTS 1
INTRODUCTION...........................................3 2
SITE AUDIT PLAN...
4 2.1 Principal Issues to be Investigated.........................
4 2.2 Plant Areas to be Included in the Walkdown...................
7 2.3 Licensee Personnel to be Interviewed.......................
7 2.4 Licensee/Site Documentation to be Audited...................
7 3
REFERENCES............................................7 2
I INTRODUCTION The initial "submittal only" review [1] of the Individual Plant Examination of External Events (IPEEE) submittal for the H. B. Robinson (HBR) plant [2] has raised some important concerns in the seismic area that require further consideration before a satisfactory review can be completed. Based both on the ongoing review of the Robinson 2 IPEEE submittal and on the licensee's responses to NRC's initial requests for additional information (RAls), it has been determined that a site audit should be conducted. This site audit will focus primarily on (a) the seismic fragility analyses (high confidence, low probability of failure [HCLPF] calculations), (b) the soil liquefaction/settlement analysis, and (c) a concern relating to an interfacing systems LOCA issue. The plant site audit is expected to assist the NRC in determining whether the licensee's IPEEE process meets the objectives of Supplement 4 to Generic Letter 88-20.
The objective of the site audit is to access and review information not contained in the IPEEE submittal, but nonetheless needed to properly evaluate the licensee's IPEEE process. The site audit will include the following activities:
An entrance/orientation meeting to discuss the site audit objectives and approach, and to satisfy requirements pertaining to radiological and security controls for plant walkdown.
An onsite audit of "Tier 2" IPEEE information, as described in Section 8 and Appendix C of NUREG-1407, related to the seismic analyses. For instance, such information may include system notebooks and analytical models, walkdown reports, supporting calculations and data, plant procedures supporting any credit taken for operator actions, plant configuration data, etc. However, the site audit will focus on a review of information pertaining to those issues (i.e., unresolved requests for additional information [RAls] and potential plant improvements) which have been documented as a result of the submittal-only review process.
Interviews with licensee personnel and/or licensee contractors who are familiar with the facets of the IPEEE analyses under review and who are also familiar with the aspects of plant operations, configuration, and design that are relevant to the issues under review consideration (as identified in Section 2 of this report).
Plant walkdowns to review and evaluate the appropriateness of IPEEE screening decisions, modeling assumptions, and identification of potential plant improvements.
Again, these walkdowns will focus on issues which have been documented from the submittal-only review and which can be better assessed by means of physical inspection. For any issues that may have broad relevance (i.e., are applicable to all components, to an entire safety system, or to a general class of components),as opposed to specific relevance to a particular area or component at the plant, the walkdown will be limited to a physical inspection of only representative items.
Identification and collection of information that may require subsequent evaluation to resolve a remaining review issue or a specific issue revealed as a result of the site audit.
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g0 An exit meeting to summarize the approach and results of the site audit (including any problems encountered), and to clarify further action items, if any.
Specific details regarding the site audit plan are provided in Section 2. Section 2.1 lists the principal issues to be investigated during the site audit. Section 2.2 identifies the plant areas to be included in the walkdown. Section 2.3 identifies the licensee and plant personnel to be interviewed during the site audit. Section 2.4 identifies the documents to be reviewed during the site audit.
2 SITE AUDIT PLAN 2.1 Principal Issues to be Investigated The principal issues to be investigated during the seismic IPEEE site audit have been documented in RAls to the licensee [4] and in a (draft) technical evaluation report (TER) [1]
resulting from the submittal-only review. These issues pertain to unresolved questions and the potential need for plant improvements. The specific issues are as follows:
2.1.1 Soil Failure, Soil Liquefaction and Slope Instability Analyses Experience from past earthquakes has shown soil failures, including soil liquefaction and slope instabilities, to be a significant concern. A number of issues have been raised with regard to the HBR IPEEE soil failure and liquefaction analyses. Of particular concern is the fact that soil liquefaction and seismically induced deformations of embankments or dams are sensitive to assumed earthquake magnitude and strong motion duration. The magnitude used for the HBR IPEEE.
submittal soils evaluation has not been determined to be consistent with the review level earthquake (RLE). (The selected magnitude is based on the mean magnitude for the Savannah River site.)
HB Robinson is a deep soil site. The submittal characterizes the top 50 ft of soil at the Robinson site as containing various beds of moderate to dense sands interspersed with layers of relatively weak to moderate strength silty sands, sandy silts, and silty clays. The submittal has indicated, from an initial liquefaction evaluation, that localized liquefaction lenses are likely to occur for a Mw 5.5 earthquake producing RLE motions; and based on an updated liquefaction analysis, a "statistically insignificant number of data points" indicated liquefaction. Thus, for an analysis based on higher magnitudes (for instance, Mw 6.0) significant liquefaction may be possible.
Also, as indicated in response to initial RAI A.2.4, an "equivalent static" factor of safety of Lake Robinson Dam, for SSE input (0.2g), was earlier assessed as being 1.08. For RLE motions, the factor of safety would likely be below unity, with resulting transient and permanent deformations. Again, considering higher magnitudes (e.g., Mw 6.0), it is likely that significant displacements of the dam would result. Furthermore, the treatment of submerged slopes and dispersal of lake sediments was based on "extrapolation of the soil boring logs" to conclude that the lake-bed sands are not 4
susceptible to liquefaction. However, no justification was provided in the response. All these assumptions and conclusions (and the data on which they are based) will be reviewed and discussed during the audit.
Earthquake experience has also identified seismically induced breaks of piping buried in soft soil or soils that have experienced liquefaction/settlement to be a significant concern. This possibility and the increased susceptibility associated with deterioration of piping (which the IPEEE indicates has been observed at Robinson-2 for buried service water piping), for the various possible site soil characteristics and beyond design-basis magnitudes, have not been adequately addressed in response to RAl A.2.3. The evaluation of the potential and effects of seismically induced failures of buried piping (e.g., service water piping and fuel oil transfer lines) founded in soil should be performed for critical (i.e., the most susceptible) soil conditions/locations subjected to RLE motions.
The IPEEE submittal has concluded that there are no concerns pertaining to soil failures at Robinson-2, and that, with respect to all soil failure modes and all earth structures, a HCLPF in excess of the 0.3g RLE exists. As noted above, sufficient information has not been provided to justify the conclusion.
In general, as part of the site audit, we will wish to discuss the HB Robinson soil failure analysis, including the data (soil properties, seismic capability characteristics of structures or components, plant configuration, dam configuration, slope configurations, earthquake characteristics, etc.), the methodological details, and the results of the HBR soil failure assessments which support the specific findings and conclusions.
Particular topics will include:
Choice of consistent earthquake magnitude to ensure that the investigation of soil failures (particularly for analyses of liquefaction susceptibility, dynamic instability, etc.) is consistent with RLE motions, Potential impact of assuming other magnitudes (e.g., Mw 5.5, 6.0, etc.) in the
- analyses, Magnitude and extent of liquefaction-induced soil shear strains at the plant site, within the slope and foundation materials of Lake Robinson Dam, and along submerged embankments, based on the critical observed soil properties, Potential for loss of soil strength and consequential reductions in lateral resistance of.foundation pile systems of essential structures, Potential impacts of pipe breaks and differential soil settlements/displacements on essential structures and components, Expected seismic-induced stress levels in buried piping for critical soil characteristics/locations (including deterioration in piping materials).
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2.1.2 Capacity (HCLPF) Calculations In the plant audit, HCLPF calculations for the following items will be reviewed:
Motor Operated Valves RHR-750 and RHR-751 Diesel Fuel Oil Storage Tank, RWST, CST Service Water Pumps 125 VDC MCCs A.& B.
Please make available HCLPF calculations, completed screening evaluation work sheets (SEWSs), walkdown notes/checklists and photographs for these components.
2.1.3 Concern With Combined Failures Of Two Motor-Operated Valves (With Cast Iron Yokes)
The seismic IPEEE identified a significant concern associated with potential combined failures of two low-capacity motor-operated valves (having cast-iron yokes) that may lead to an interfacing systems LOCA (ISLOCA) outside containment. An estimate of the frequency of this seismically induced ISLOCA was made in the IPEEE submittal.
However, the approach used for calculating this frequency was not provided in sufficient detail. No specific modifications have been proposed with respect to the two motor-operated valves.
The licensee originally committed to implement (by December 1998) related procedural enhancements in accordance with severe accident management guidelines. Subsequently, it was apparently determined that such procedural enhancements were unnecessary. As part of the audit, we would like to:
Identify and justify what actions, if any, will be taken to mitigate the ISLOCA concern. If procedural actions are being considered, te evaluate the effectiveness of these actions.
Identify what operator actions would be required, where the actions would need to take place, and the failure rates associated with such actions (in consideration of the potential for seismically induced failures that may interfere with such actions).
2.1.4 Containment Walkdown Results In your July 1, 1996 letter, Response A.2.6 states "We will perform a walkdown of the HBRSEP, Unit No. 2 containment heat removal systems and their anchorages, including the fan coolers, and report the findings." A letter discussing the results of the containment walkdown [5] was later received on September 2, 1998. During the site audit, please be prepared to discuss the walkdown approach and the observed configuration of containment heat removal systems.
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0 2.2 Plant Areas To Be Included In The Walkdown The seismic walkdown will include examination of the items discussed during the plant audit discussions, as determined by the reviewers and by plant area accessibility at the time. These will include the items whose HCLPF capacity calculations are to be reviewed, the two (cast-iron yolked) MOVs and, if determined to be necessary during the audit, examination of valves associated with the ISLOCA issue.
2.3 Licensee Personnel to be Interviewed Licensee personnel and/or licensee contractor personnel who participated in, and can explain in detail, the soil failure analyses, the seismic screening walkdown and its findings, the seismic HCLPF calculations, and the disposition approach and status for identified seismic outliers/anomalies should be available during the seismic site audit. At least one of these participants should be closely familiar with design documents and procedures for their ready retrieval during the site audit. A licensee participant familiar with the seismic success paths, plant systems, and operating procedures should also be available to discuss the seismic systems analysis and treatment of operator actions. Additionally, a plant operator who is familiar with plant systems, and who has reviewed the safe shutdown equipment list (SSEL),
should be on hand during the seismic review walkdown.
2.4 Licensee/Site Documentation to be Audited The licensee should provide the following documentation in support of the site audit of the H. B.
Robinson (Unit 2) seismic IPEEE:
Soils analysis data and reports as described above.
HCLPF calculation notes and supporting seismic review team (SRT) binders, engineering calculations, results of dynamic response calculations (i.e., in-structure spectra), and drawings.
Seismic IPEEE containment walkdown report, including screening evaluation work sheets (SEWS), walkdown notes, checklists, and summary of walkdown findings.
3 REFERENCES
- 1.
"Technical Evaluation Report on the Submittal-Only Review of the Individual Plant Examination of External Events at H B Robinson Steam Electric Plant, Unit 2," ERI/NRC 96-506, Final Report, March 1998.
- 2.
"H. B. Robinson Steam Electric Plant - Individual Plant Examination for External Events Submittal," Final Report, Carolina Power & Light Company, June 1995.
- 3.
"H. B. Robinson Steam Electric Plant, Unit 2 - Response to Request for Additional Information Regarding the Individual Plant Examination of External Events," letter from 7
R. M. Krich, Carolina Power & Light Company, to U. S. Nuclear Regulatory Commission, July 1, 1996.
- 4.
Letter from NRC to Carolina Power & Light Company, dated May 7, 1998,
Subject:
Request for Additional Information on Robinson IPEEE Submittal
- 5.
Letter from Carolina Power & Light Company to NRC, dated January 23, 1997,
Subject:
Results of Walkdown of the HBR2 Conatinment Heat Removal System.
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ATTENDEES FOR STAFF AUDIT NAME ORGANIZATION Alan M. Rubin NRC John T. Chen NRC Roger Kenneally NRC Mike Bohn Sandia National Laboratories