ML022380271
| ML022380271 | |
| Person / Time | |
|---|---|
| Site: | Salem, Hope Creek  |
| Issue date: | 08/26/2002 |
| From: | Reinhart F NRC/NRR/DSSA/SPSB |
| To: | Carpenter C, O'Reilly P NRC/NRR/DIPM, NRC/RES/DRAA |
| WONG, S.M., NRR/DSSA/SPSB, 415-1125 | |
| References | |
| Download: ML022380271 (17) | |
Text
August 26, 2002 NOTE TO: Cynthia Carpenter, Chief Inspection Program Branch Division of Inspection Program Management Office of Nuclear Reactor Regulation Patrick D. OReilly Operating Experience Risk Applications Branch Division of Risk Analysis and Applications Office of Nuclear Regulatory Research FROM: Mark F. Reinhart, Chief /RA/ M. Caruso for Licensing Section Probabilistic Safety Assessment Branch Division of Systems Safety and Analysis Office of Nuclear Reactor Regulation
SUBJECT:
RESULTS OF THE HOPE CREEK GENERATING STATION SDP PHASE 2 NOTEBOOK BENCHMARKING VISIT During June, 2002, NRC staff and a contractor visited the Salem/Hope Creek Nuclear Stations site to compare the Hope Creek Generating Station (HCGS) Significance Determination Process (SDP) Phase 2 notebook and licensees risk model results to ensure that the SDP notebook was generally conservative. HCGS's PSA did not include external initiating events; and therefore, no sensitivity studies were performed to assess the impact of these initiators on SDP color determinations. In addition, the results from analyses using the NRCs draft Revision 3i Standard Plant Analysis Risk (SPAR) model for HCGS were also compared with the licensees risk model. The results of the SPAR model benchmarking effort will be documented in a separate a trip report to be prepared by the Office of Nuclear Regulatory Research.
In the review of the HCGS SDP notebook, it was found that some changes to the SDP worksheets were needed to reflect how the plant is currently designed and operated.
Twenty-six hypothetical inspection findings were processed through the Rev. 0 SDP notebook, and the twenty-six hypothetical cases were processed after changes were made to the worksheets. Results from this effort indicated that the total risk impacts modeled in the Rev.
0 SDP notebook were underestimated by 0 percent, overestimated by 46 percent, and adequately estimated by 54 percent. The reviewers found that if eight fixes, including the changes to operator action credits for the loss of offsite power (LOOP) and loss of instrument air (LOIA) worksheets, were made to the SDP notebook, the results would be 4 percent underestimation, 23 percent overestimation, and 73 percent adequate estimation of risk impacts.
CONTACT: See-Meng. Wong, SPSB/DSSA/NRR 301-415-1125
C. Carpenter 2 Attachment A describes the process and results of the comparison of the HCGS SDP Phase 2 Notebook and the licensees PSA.
If you have any questions regarding this effort, please contact See-Meng Wong.
Attachments: As stated
C. Carpenter 2 Attachment A describes the process and results of the comparison of the HCGS SDP Phase 2 Notebook and the licensees PSA.
If you have any questions regarding this effort, please contact See-Meng Wong.
Attachments: As stated Accession#ML022380271 NRR-001 OFFICE SPSB/DSSA SC/SPSB/DSSA NAME S.Wong:nxh2 M. Reinhart /RA/ for M. Caruso DATE 08/26/02 08/26/02 OFFICIAL FILE COPY
SUMMARY
REPORT ON BENCHMARKING TRIP FOR HOPE CREEK GENERATING STATION (June 3-6, 2002)
Pranab K. Samanta Energy Sciences and Technology Department Brookhaven National Laboratory Upton, NY 11973-5000 July 2002
Table of Contents Page
- 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
- 2. Summary Results from Benchmarking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
- 3. Proposed Modifications to Rev. 0 SDP Notebook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1 Specific Changes to the Rev. 0 SDP Notebook for Hope Creek . . . . . . . . . . . . . 8 3.2 Generic Change in 0609 for Inspectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3 Generic Change to the SDP Notebook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
- 4. Discussion on External Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
- 5. List of Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 List of Tables Page Table 1. Comparison Table for Hope Creek Benchmarking . . . . . . . . . . . . . . . . . . . . . . . 4 Table 2. Comparative Summary of the Benchmarking Results . . . . . . . . . . . . . . . . . . . . . 7
-iv-
- 1. INTRODUCTION A benchmarking of the Risk-Informed Inspection Notebook for Hope Creek Nuclear Generating Station (HCGS) was conducted during a plant site visit on June 3-6, 2002. NRC staff (J. Trapp and S. Wong) and BNL staff (P. Samanta) participated in this Benchmarking exercise.
In preparation for the meeting, BNL staff reviewed the SDP notebook for the Hope Creek Generating Station and evaluated a set of hypothetical inspection findings using the Rev. 0 SDP worksheets. In addition, NRC staff provided the licensee with a copy of the meeting protocol.
The major milestones achieved during this meeting were as follows:
- 1. Recent licensees modifications to the HCGS PRA model were discussed for consideration in preparing the Rev. 1 notebook for the plant.
- 2. Importance measures, including the Risk Achievement Worths (RAWs) for the basic events in the internal event model for average maintenance, were obtained from the licensee.
- 3. Benchmarking was conducted using the Rev. 0 SDP model and the revised SDP model considering the licensees input and other modifications that were judged necessary based on comparison of the SDP model and the licensees detailed model.
- 4. For cases where the color evaluated by the SDP notebook differed from that determined based on the RAW values generated by the updated licensees PRA, results of the licensees model including the detailed minimal cutsets were requested from the licensee. The cutsets were reviewed to understand the reason for the differences. Applicable changes were defined for the SDP model.
Following the modification to the Rev. 0 SDP notebook for Hope Creek, a comparison of results between the notebook and the plants PRA model shows 1 case of underestimation (by one color) and 6 cases of overestimation (1 by two colors, and 5 by one color) out of 26 hypothetical cases studied. Similar colors are obtained for the remaining 19 cases. In another words, in 25 out of 26 cases, the notebook provides comparable, similar or conservative results by one color, and in 1 out of 26 cases, it shows a non-conservative result. Using the Rev. 0 notebook would have resulted in 12 cases of overestimation (4 by two colors and 8 by one color) out of the 26 cases studied. In summary, benchmarking has identified modifications which improve the matches (similar results) from 54% to 73%, reduce overestimation from 46% to 23%, but increase underestimation from 0%
to 4%.
- 2.
SUMMARY
RESULTS FROM BENCHMARKING This Section describes the results of the benchmarking exercise. The results are summarized in Table 1. Table 1 consists of six columns. The first column identifies the components or the case runs. The colors obtained using the SDP Rev. 0 worksheets without incorporating any modification from the benchmarking exercise are shown in the second column. The third column shows the internal RAW and the fourth column shows the associated colors estimated based on the licensees RAW values from the latest PRA model. The fifth column presents the colors for the inspection findings based on the revisions of the SDP Rev. 0 worksheets judged applicable during benchmarking. The last column provides comments explaining the differences between the SDPs and the plants PRA colors.
The colors obtained for inspection findings using the revised SDP notebook are observed to be underestimated in 1 case and overestimated in 6 cases out of the 26 cases studied. Conservative results are expected since the SDP model is a simplified tool and is intended to provide conservative colors. However, the reason for the differences is analyzed using the minimal cutsets for the cases where differences in colors are observed. These cases are discussed below.
Underestimation was noted for the HPCI pump. The reason for this underestimation is analyzed as follows:
- 1. The initiating event (IE) frequencies for transients with loss of PCS (TPCS), Stuck-open relief valve (SORV), and medium LOCA (MLOCA) are higher compared to the estimates used in the SDP notebook. The IE frequencies are respectively 0.5, 5E-02, and 9.3E-04 per reactor-yr. Comparable frequencies in the SDP notebook are 1E-01, 1E-02, and 1E-04 per reactor-yr. For the HPCI pump, the sequences obtained from the notebook and the PRA are same, but the differences in the IE frequency contribute to the underestimation.
Overestimation is noted in six cases: 1 SLC pump, 1 SSW train, 1 AC Bus, operator fails to use PCS, operator fails to vent, and operator fails to inhibit high pressure injection in ATWS. The reasons for these overestimations are discussed below.
- 1. The overestimation of the standby liquid control (SLC) pump is largely attributed to the difference in the ATWS frequency. The ATWS frequency used in the licensees PRA is approximately a factor of 20 lower compared to the estimate used in the SDP notebook.
- 2. Overestimation for 1 SSW train can be related to the licensees assumption of recovery of loss of service water with a probability of 0.1. Recovery credit is not provided in the SDP notebook; recovery credit will be judged as part of the inspection finding.
- 3. Overestimation for the loss of 1 AC bus is also related to the assumption used in counting the loss of SW sequences. In the SDP estimation LOSW frequency is increased an order of magnitude and also no recovery credit is given.
- 4. Overestimation of operator failing to use PCS is due to lower estimates used for suppression pool cooling (CHR in the notebook) and the late inventory makeup in the plants PRA.
- 5. Overestimation for the operator failing to inhibit is due to the differences in the ATWS frequency discussed earlier.
- 6. Overestimation for the operator failing to vent is due to a lower estimate used for suppression pool cooling used in the plants PRA and the use of recovery factor of 0.1 in loss of service water (LOSW).
Table 1. Comparison Table for Hope Creek Benchmarking CDF = 8.661E-6/yr, W = 1.115 (RAW), Y = 2.155 (RAW), R = 12.55 (RAW)
No. Basic Event Before RAW Plant CDF After Comments Name Color
- 1. RCIC R (O) 5.28 Y Y
- 2. HPCI R 14.2 R Y Underestimation; higher initiator frequencies for TPCS, SORV, and MLOCA in the licensees PRA contribute to higher RAW for licensee.
- 4. 1 LPCS train G 1.0 G G
- 5. MS/FW G NA G G
- 6. 1 G NA G G condensate pump
- 7. 1 RHR train G 1.0 G G (not A or B)
- 9. 1 CRD pump W (O) 1.0 G G
- 10. 1 Cond. Y (O) 1.0 G G transfer pump
- 11. 1 SLC pump G 1.06 G Y Overestimation by 2 colors.
Licensees ATWS frequency is a factor of 20 lower than the SDP frequency.
- 12. IA (one Y (O) 1.03 G G compressor fails)
No. Basic Event Before RAW Plant CDF After Comments Name Color
- 13. 1 Fire pump Y (O) 1.0 G G
- 14. 1 EDG W 1.64 W W
- 15. 2 EDGs W 1.64 W W
- 16. Salem gas W 1.19 W W turbine
- 17. 1 SSW train Y (O) 1.43 W Y Overestimation; Licensee assumes loss of SW can be recovered with 0.1 likelihood.
- 18. Containment Y (O) 1.39 W W venting path
- 20. 1 DC Bus R 14.20 R R (250 VDC Bus A)
Operator Actions
- 21. Operator R 2.39 Y R Overestimation; credit for fails to CV SPC (i.e., CHR function in the notebook) is conservative in the notebook.
- 22. Operator R 494.21 R R fails to DEP
- 24. Operator R R R fails to CHR
- 25. Operator Y (O) 1.29 W Y Overestimation; due to fails to INH differences in ATWS frequency.
No. Basic Event Before RAW Plant CDF After Comments Name Color
- 26. Operator W (O) 1.0 G G fails to use condensate train in M/LLOCA Note 1. In the Hope Creek plant, for loss of buses A and D, containment venting is lost. In those situations, operator can open the valve using hand-wheels from a remote control station. The human error probability (HEP) for this action is 0.1. For failure of RHR pump B, RHR pump A can be lost due to the loss of bus A and containment venting is conducted from remote control station.
The combined credit of the remaining RHR train and the operator failing to vent (HEP = 0.1) in the notebook is comparable to that in the PRA. In case of the RHR pump A, a loss of bus B does not require manual action from the remote control station, and the combined credit of the remaining RHR train and the operator failing to vent in the notebook is conservative compared to the plants PRA. The notebook does not distinguish these differences and provides a conservative estimate for RHR pump A.
Table 2: Comparative Summary of the Benchmarking Results Comparisons Rev. 0 SDP Notebook Rev. 1 SDP Notebook implementing the changes identified Total Number of Cases=26 Number of Cases Percentage Number of Cases Percentage SDP: Less 0 0 1 4 Conservative SDP: More 12 46 6 23 Conservative SDP: Matched 14 54 19 73
- 3. PROPOSED MODIFICATIONS TO REV. 0 SDP NOTEBOOK A set of modifications were proposed for the Rev. 0 SDP notebook as a result of the site visit.
These proposed modifications are based on the licensees revision to the plants PRA, better understanding of the current plant design features, revised Human Error Probabilities (HEPs),
modified initiator frequencies, and the results of benchmarking.
3.1 Specific Changes to the Rev. 0 SDP Notebook for Hope Creek Generating Station Several modifications have been identified for the Rev. 0 notebook based on the benchmarking at the plant. A summary of the major changes is provided below.
- 1. Table 1 is modified based on the plant-specific frequency of the special initiators. Loss of Instrument Air (LOIA) frequency is 1.6E-04/reactor-yr and is moved to Row IV. It is noted in a footnote that MLOCA and SLOCA frequencies are respectively 9.3E-04/reactor-yr and 6.5E-04/reactor-yr, i.e., MLOCA frequency is higher than SLOCA frequency.
- 2. Operator action credit for depressurization (DEP) is changed from 2 to 3. Revised estimate for the human error probability (HEP) in the plants PRA is 1.0E-03. In ATWS, an operator action credit of 1 is used because the plant-specific HEP is 5.6E-02.
- 3. Credit for Late Inventory, Makeup (LI) is changed from operator action = 2 to operator action = 3. Multiple options exist and the HEPs associated with these actions are low.
- 4. The description of LPCS mitigation capability is changed to state 1/4 LPCS pumps in 2 trains in all applicable worksheets.
- 5. At Hope Creek, the valves in the 12" Hard Pipe Containment Venting System and in the 6" hard pipe line can be operated from a remote control station using hydraulic hand pumps without any dependency on air or power. In the LOIA worksheet, containment venting is modified to be conducted from the remote control station. An operator action credit of 1 is assigned based on the Hope Creek HEP of 0.1 for this action.
- 6. In the LOOP worksheet, the operator action credit for recovery of offsite power in 5 hrs.
is changed from 2 to 1. The non-recovery probability in the PRA is 5.6E-02.
- 7. For loss of buses A and D, containment venting is lost. Operators can open the valves using hand-wheels from a remote control station. A footnote is provided so that operator action credit for containment venting can be adjusted for buses A and D.
3.2 Generic Change in 0609 for Inspectors None identified.
3.3 Generic Change to the SDP Notebook None identified.
- 4. DISCUSSION ON EXTERNAL EVENTS Integrated external event PRA model was not available for the Hope Creek plant. No evaluations were conducted for the external event risk during the benchmarking exercise.
- 5. LIST OF PARTICIPANTS Robert Buell INEEL Pranab Samanta BNL James Trapp USNRC/Region I See-Meng Wong USNRC/NRR John Lai PSE&G Tom Carrier PSE&G