ML021150523
| ML021150523 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 04/24/2002 |
| From: | Reinhart F Division of Systems Safety and Analysis |
| To: | Carpenter C, O'Reilly P NRC/NRR/DIPM, NRC/RES/DRAA |
| Wilson P, NRC/NRR/DSSA/SPSB, 415-1114 | |
| References | |
| Download: ML021150523 (12) | |
Text
April 24, 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/Signed by M. Caruso for Licensing Section Probabilistic Safety Assessment Branch Division of Systems Safety and Analysis Office of Nuclear Reactor Regulation
SUBJECT:
RESULTS OF THE PERRY NUCLEAR POWER PLANT UNIT 1 SDP PHASE 2 NOTEBOOK BENCHMARKING VISIT During July, 2001, NRC staff and a contractor visited the Perry Nuclear Power Plant Unit 1 to compare the Perry Significance Determination Process (SDP) Phase 2 notebook and licensees risk model results to ensure that the SDP notebook was generally conservative. Perrys PSA did not include external initiating events so no sensitivity studies were performed to assess the impact of these initiators on SDP color determinations.
In the review of the Perry 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 four hypothetical inspection findings were processed through the SDP notebook. Results from this effort indicated that the total risk impacts modeled in the SDP notebook were underestimated by 20 percent, overestimated by 24 percent, and adequately estimated by 56 percent. The reviewers found that if thirteen fixes were made to the SDP notebook, the results would be 4 percent underestimation and 38 percent overestimation of risk impacts.
Attachment A describes the process and results of the comparison of the Perry SDP Phase 2 Notebook and the licensees PSA.
If you have any questions regarding this effort, please contact Peter Wilson.
CONTACT: P. Wilson, SPSB/DSSA/NRR 301-415-1114 Attachments: As stated
April 24, 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/Signed by M. Caruso for Licensing Section Probabilistic Safety Assessment Branch Division of Systems Safety and Analysis Office of Nuclear Reactor Regulation
SUBJECT:
RESULTS OF THE PERRY NUCLEAR POWER PLANT UNIT 1 SDP PHASE 2 NOTEBOOK BENCHMARKING VISIT During July, 2001, NRC staff and a contractor visited the Perry Nuclear Power Plant Unit 1 to compare the Perry Significance Determination Process (SDP) Phase 2 notebook and licensees risk model results to ensure that the SDP notebook was generally conservative. Perrys PSA did not include external initiating events so no sensitivity studies were performed to assess the impact of these initiators on SDP color determinations.
In the review of the Perry 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 four hypothetical inspection findings were processed through the SDP notebook. Results from this effort indicated that the total risk impacts modeled in the SDP notebook were underestimated by 20 percent, overestimated by 24 percent, and adequately estimated by 56 percent. The reviewers found that if thirteen fixes were made to the SDP notebook, the results would be 4 percent underestimation and 38 percent overestimation of risk impacts.
Attachment A describes the process and results of the comparison of the Perry SDP Phase 2 Notebook and the licensees PSA.
If you have any questions regarding this effort, please contact Peter Wilson.
CONTACT: P. Wilson, SPSB/DSSA/NRR 301-415-1114 Attachments: As stated DISTRIBUTION: SPSB r/f Mreinhart PWilson G//SPSB/wilson/Perrybe1.wpd ACCESSION#ml021150523 NRR-096 OFFICE SPSB SC:SPSB NAME PWilson MReinhart DATE 04/23/02 04/24/02
OFFICIAL RECORD COPY
SUMMARY
REPORT ON BENCHMARKING TRIP TO Perry Nuclear Power Plant Unit 1 (July 10-12, 2001)
J. C. Higgins Brookhaven National Laboratory 9/20/01 Attachment A
1 Introduction This report compares the NRC Risk Informed Inspection Notebook, developed by BNL, and the licensee risk model for the Perry NPP to ensure that the Notebook is generally conservative. The benchmarking is being performed after the worksheets have been revised to include the appropriate licensee comments and recommendations and the special initiator worksheets have been completed.
2 Preparation for Benchmarking The Perry Inspection Notebook was originally prepared in January, 2001. Since that time some generic decisions have been made regarding the format and content of the Notebooks. Thus, Perry was reviewed prior to this Benchmarking visit in order to identify potential changes that may be needed. Some changes were made (Section 2.1), some areas were identified for clarification onsite (Section 2.2), and some areas were identified for changes that will be made subsequent to the site visit during the Maintenance Phase.
2.1 Main changes to Notebook prior to onsite visit C Added TPCS Event Tree (ET) and made related updates.
C LEAC worksheet should use TPCS ET not TRANS ET C Loop transfer on Seq. 1 should be to TPCS not TRANS C Changed CV from 1/2 to 1/3 paths.
C Changed PCS credit on TRANS from 2 to 3.
C Changed CHR credit on most ETs from (operator action = 2) to (multi-train system), credit of 3.
C On MLOCA changed credit for LPI from (operator action = 2) to a total of
C Corrected Table 2 - no RCIC on ATWS C Miscellaneous editorial changes.
2.2 Questions for Site C Confirm Sequence 9 on TRANS/SLOCA/SORV does not need CHR.
C We have changed our ATWS assumption to be MSIV closure / LOFW as initiator for ATWS. This implies no credit for PCS. Plan to change Perry SDP to reflect this.
C Should DEP for ATWS be 9/19 rather than 8/19? (4 for 20% power +
5/19).
C Are all 19 SRVs really required for OVERP on ATWS?
C On LSW - Is it proper to credit RCIC (is this because of recovery credit)?
C On the ATWS worksheet, is it correct to note LC with both INH and SLC?
Should SLC be a credit of 1 or 2? Note that as currently configured, the sequence ATWS-SLC has a base case color of white.
C How many total drywell to suppression pool vacuum breakers are there?
Are there two per line? How many are required to fail for EC failure? Is EC needed in MLOCA & SLOCA worksheets?
C Have we picked appropriate Perry basic events for the components out of service in Table 1 below?
C Need to obtain (if possible) PSA RAW values for selected components using the interval method delta CDF.
2.3 Proposed Changes to Worksheets in Maintenance Phase C Drop PCS/FW credit on ATWS C Will add train terminology throughout.
C Add more notes on Perry HEP values.
C Cleanup Table 2 and add more detailed information.
3 Summary Results from Benchmarking The onsite visit was conducted by a BNL representative, an NRC headquarters PRA representative and a Region III SRA. We met with the Perry PRA staff for two and one half days onsite to perform the benchmarking activities.
The initial activities included reviewing with the licensee the updates made to the Perry notebook as described in Section 2.1 above, and provided an updated copy of the Notebook to Perry We then provided Perry with the questions in Section 2.2. Perry researched the related information and provided answers to the team. Perry also gave the team a few added comments to the Notebook, which were valuable and improved the notebook. These were incorporated before beginning the benchmarking activities.
Notable changes made, based on the licensees comments and justifications, were:
- updated PCS components
- changed CV from 1 of 2 trains to 1 of 3 trains
- clarified information on LDEP
- dropped EC from LLOCA worksheet The licensee provided updated PSA information to the team based on the 2001 version of the PSA. This was supplemented by additional PSA information provided in response to team questions throughout the visit. Information included: definition of basic events, cutsets, RAW values, and event trees.
The team re-computed the break points in RAW values for the different SDP colors based upon a current PSA total internal events CDF of 5.9 E-6 events/reactor-year.
The team had pre-selected a fairly large list of components and human actions, as
listed in Table 1 below, that would be evaluated for the effect of having the component or human action fail. We then used the latest revised version of the notebook to develop the color corresponding to failure of each item and compared that to the color that would be implied by the items RAW value from the PSA.
In developing the colors from the notebooks, the team evaluated all sequences in each worksheet that contained the item (component or human action). A number was obtained for each re-evaluated sequence. We then used a counting rule to cascade lower value sequences to higher value ones as follows. For example three sequences of value 9 (shorthand for an estimated sequence frequency of 1 E-9 events/reactor-year) were equivalent to one sequence of value 8. Likewise 3 sequences of value 8 (3-8s) were equivalent 1 sequence of value 7(1-7). Also, 3-7s were equal to 1-6, and so on. Colors were developed as follows:
Sequences of value 7, 8, etc. Green Sequences of value 6 White Sequences of value 5 Yellow Sequences of value 4 or less Red When the above described counting rule was needed to obtain a color rather than a direct correlation from a sequence, then in Table 1 we note that it was obtained by the counting rule or bcr.
During the benchmarking the team noted some discrepancies and unexplainable aspects of the RAW values supplied by Perry. Some of the discrepancies were caused by truncation problems. The licensee addressed some of these by requantification during the onsite review. At the conclusion of the site visit, the NRC requested that Perry supply an updated list of RAW values for all components in the PSA. The licensee supplied this information by email on September 6, 2001. Not all of the components or basic events selected for quantification were contained in the RAW list sent to BNL (these are noted in the Table 1).
Table 2 provides a summary of the benchmarking results. The teams initial quantification of the Notebook had five non-conservative items and six that were more conservative than the colors that were based on the RAW values from the licensees PSA. Some items were off by two orders of magnitude. As a result, a few changes were made to the SDP worksheets, notably: moved the LOOP initiator from Row 2 to Row 1 in Table 1; removed the LEAC worksheet; changed credit for DFP and LDEP in the LOOP worksheet from 2 to 1; and changed the credit for CV from 2 to 3 in the worksheets. Some of the items were then re-quantified onsite and more consistent results were obtained. As noted above, the team requested that the licensee recalculate their RAW values. When the licensees updated RAW values were received (reference 2), all items in Table 1 were re-quantified. During this final re-quantification, the worksheets still had a few non-conservative items, namely: RCIC,
one CV train, condensate transfer alternate injection, and failure to recover offsite power in 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> (REC3).
BNL believes that it would be valuable for the licensee and/or the NRC to verify the RAW values since not all desired ones were available (seven noted as such in Table 1) and there are still a few potential anomalies, e.g.,
- RAW for EDG-3 higher than for the HPCS pump (this may be due to electrical cross-tie of EDG-3 on an SBO, but we could not verify that)
- RAW for condensate transfer seems high Also, it would be instructive to examine and understand the dominant non-minimal cutsets in the printouts provided onsite (check RCIC and RHR pumps C).
BNL notes that this was the first BWR-6 plant that has had a benchmarking visit and many useful Perry plant systems and PSA insights were obtained from the licensee. A benchmarking trip should be performed at another BWR-6 in order to consolidate the insights and enable the production of improved SDP notebooks for all BWR-6 plants.
Table 1: Comparison of Component Sensitivity Calculations Between Phase 2 Worksheets and Perry RAWs (CDF = 5.9E-6; RAW splits - 1.17, 2.69, 17.95)
SDP Color Work- Perry by Mod. SDP Item Out sheet Perry Basic RAW1 Perry Workshee Comment of Service Color Event ratio RAW1 t Color s Component HPCS R HPMPFR/FS 3.15 Y R bcr-con EDG-3 R DHDGFR/FS 3.91 Y R bcr-con RCIC W RCTPFR/FS 3.50 Y W non-con, note 1 SRV Y P1 3.89 Y Y same LPCS G LPMPFR/FS 1.142 G G same RHR- Y Pump failure 1.242 W Y bcr-con pump A event
SDP Color Work- Perry by Mod. SDP Item Out sheet Perry Basic RAW1 Perry Workshee Comment of Service Color Event ratio RAW1 t Color s RHR- Y Pump failure 1.202 W Y bcr-con pump B event RHR- G Pump failure 1.232 W G note 4 pump C event RHR HX Y LCHXPL1E12 1.1782 W Y bcr-con B0001A 1 CV valve W CVMVNO1G41 1.23 W G non-con F0140 note 5 Fire Pump G FPDPFR/FS 1.96 W W same Cond. Xfer G CTHICPPS4:4- 1.33 W G non-con pump ALT note 6 SPMU 1 G SMCLLF1G43 1.052 G G same train A or B SPMU-cc G SMMVCC 2.202 W Y con One SLC W SLMPFS/FR 1.002 G G same pump Both SLC Y SLMPCC 3.42 Y Y same pumps EDG 1 or Y DGDGFS1R43 3.17 Y Y same 2 S0001A/1B SA & IA W IACMCC 1.35 W W same item SRIA -- note 13 -- -- W bcr SW item G SWPFR... 1.02 G W con Both DW- -- note 13 -- -- Y SP vacuum breakers ECC-A Y ECMPFR1P42 6.19 Y R bcr-con C000A
SDP Color Work- Perry by Mod. SDP Item Out sheet Perry Basic RAW1 Perry Workshee Comment of Service Color Event ratio RAW1 t Color s ECC-B Y ECMPFR1P42 5.93 Y Y bcr C000B DC-Div 1 Y DCBDLC1R42 note 2 -- -- note 12 S0024 DC-Div 2 Y DCBDLC1R42 note 2 -- -- note 12 S0025 ESW A ESMPFR1P45 note 2 -- R bcr C0001A ESW B ESMPFR1P45 note 2 -- R bcr C0001B ESW C ESMPFR1P45 3.15 Y R bcr-con C0002 Operator Actions DEP R ADHICPEC2- 73.0 R R same ADS-T SLC Y SLHICPEQ6SL 3.97 Y Y same C1 CV R CVHICPEPC- 18.3 R R same COM REC3 G R15 1.73 W G non-con note 7 REC7 R R31 note 2 -- R Table 1 notes:
- 9. Perry RAW for internal events, average maintenance case. A final set of RAW values for use in the benchmarking were sent by Perry to BNL via email on September 6, 2001
- 10. In several cases when RAW values were not available on the email list sent to BNL. When possible BNL used the RAW value provided by Perry during the onsite visit in July, 2001.
- 12. RHR pump C: During onsite visit, a problem was identified with Perry cutsets and RAW calc for RHR-pump C, that makes related cutsets and RAW too high.
Top 3 cutsets containing pump C are non-minimal.
- 13. One CV path: RAW is just over threshold and we have 2 - 7s so we just miss white bcr.
- 14. Condensate transfer alternate injection: RAW is over threshold and we have only one 7.
HPCS - REC3 - DFP. This sequence is value 8 base case and REC3 has a credit of 1. This Failure of REC3 gives a value of 7, which is Green.
- 16. DC power has significant redundancy due to the Unit 2 DC that was kept after Unit 2 was cancelled.
- 17. EPRC not done because there are separate units per each pump room.
- 18. For a component such as a pump, we examined the RAW values for the basic events both for failure to start and failure to run, and selected the highest (or more conservative) value here.
- 19. RCIC: We get 2-6s on the benchmarking, so we do not quite get a yellow as per the RAW. The problem is on sequence 7 LOOP - EAC - HPCS - RCIC (14) on the LOOP worksheet. In the Perry PSA, this sequence has cutsets that total between 5 E-7 and 1 E-6. On our worksheet, the credit for the sequence is 7, which is more than the cutsets would indicate by almost an order of magnitude.
- 20. Not enough information was available to evaluate DC power.
- 21. Unable to identify a PSA modeled basic event.
Table 2: Comparative Summary of the Benchmarking Results SDP Worksheet SDP Worksheet Modified Number of Percentage Number of Percentag Cases Cases e SDP: Less 5 19 4 17 Conservative SDP: More 6 23 8 33 Conservative SDP: Matched 13 50 12 50 Total 26 100 24 100 In addition there were 6 items reviewed for benchmarking that we were not able to benchmark due to uncertainty in the RAW received from Perry.
4 Additional Proposed Modifications to SDP Worksheets 4.1 Specific Changes to the Rev-0 SDP Worksheet for Perry A number of changes were made to the Perry worksheet. Ones made before the onsite visit are noted is Section 2 above. A number of additional changes, made during and after the plant onsite visit, are summarized in Section 3 above and are contained in the updated notebook. This update has been supplied in draft form to the NRC Region III Senior Reactor Analyst.
4.2 GENERIC CHANGE IN 0609 FOR INSPECTORS None.
4.3 GENERIC CHANGE TO THE SDP WORKSHEET None.
5 Discussion on External Events As analyzed by the licensees updated PSA models, the core damage frequency estimates for internal initiators was 5.9E-6 events/reactor-year. Perry does not have an integrated external event PSA. The licensee noted that their IPEEE for fire, floods, and seismic events was a screening study only, and therefore there is not sufficient information to provide insights to potential changes in color evaluation based on consideration of external events.
6 Persons participating NRC:
Eugene Cobey Mike Parker BNL:
Jim Higgins Perry NPP:
Gerry Kindred Dennis Jondle Wallace Colvin Mark Rupp
- 6. References
- 7. Perry Cycle 9 PSA, March, 2001
- 8. Email of RAW values from Kindred to Higgins, September 6, 2001