ML12024A393
| ML12024A393 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 01/19/2012 |
| From: | Hartz L Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC ME6695, 11-696 | |
| Download: ML12024A393 (12) | |
Text
Dominion Nuclear Connecticut, Inc.
5000 Dominion Boulevard, Glen Allen, Virginia 23060 Web Address: www.dom.com January 19, 2012 U. S. Nuclear Regulatory Commission Serial No.11-696 Attention: Document Control Desk NSSL/WDC RO Washington, DC 20555 Docket No. 50-423 License No. NPF-49 DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING RELOCATION OF SPECIFIC SURVEILLANCE FREQUENCY REQUIREMENTS TO A LICENSEE CONTROLLED PROGRAM (TAC NO. ME6695)
By letter dated July 5, 2011, as supplemented by letter dated September 12, 2011, Dominion Nuclear Connecticut, Inc. (DNC) submitted a license amendment request (LAR) for Millstone Power Station Unit 3 (MPS3). The proposed amendment would relocate certain technical specification (TS) surveillance frequencies to a licensee controlled program by adopting Technical Specification Task Force (TSTF)-425, Revision 3, "Relocate Surveillance Frequencies of Licensee Control - RITSTF [Risk-Informed Technical Specification Task Force Initiative] 5b." The proposed change would also add a new program, the Surveillance Frequency Control Program, to the TSs, in accordance with TSTF-425. TSTF-425 is approved for use by the Nuclear Regulatory Commission (NRC). In a letter dated December 8, 2011, the NRC transmitted a request for additional information (RAI) to DNC related to the LAR. DNC agreed to respond to the RAI by January 19, 2012. provides DNC's response to the NRC's RAI.
If you have any questions regarding this submittal, please contact Wanda Craft at (804) 273-4687.
Sincerely, L. N. Hartz Vice President - Nuclear Support Services
Attachment:
- 1. Response to Request for Additional Information Regarding Relocation of Specific Surveillance Frequency Requirements to a Licensee Controlled Program Commitments made in this letter:
- 1. None 4oo)
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Page 2 of 2 cc: U.S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406-1415 C. J. Sanders Project Manager - Millstone Power Station U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08-B3 Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 ATTACHMENT 1 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING RELOCATION OF SPECIFIC SURVEILLANCE FREQUENCY REQUIREMENTS TO A LICENSEE CONTROLLED PROGRAM DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Attachment 1, Page 1 of 9 By letter dated July 5, 2011, as supplemented by letter dated September 12, 2011, Dominion Nuclear Connecticut, Inc. (DNC) submitted a license amendment request (LAR) for Millstone Power Station Unit 3 (MPS3). The proposed amendment would relocate certain technical specification (TS) surveillance frequencies to a licensee controlled program by adopting Technical Specification Task Force (TSTF)-425, Revision 3, "Relocate surveillance Frequencies of Licensee Control - RITSTF [Risk-Informed Technical Specification Task Force Initiative] 5b. The proposed change would also add a new program, the Surveillance Frequency Control Program (SFCP), to the TSs, in accordance with TSTF-425. TSTF-425 is approved for use by the Nuclear Regulatory Commission (NRC). In a letter dated December 8, 2011, the NRC transmitted a request for additional information (RAI) to DNC related to the LAR. This attachment provides DNC's response to the NRC's RAI.
Question I The licensee has identified five "gaps"in the MPS3 probabilisticrisk assessment (PRA) model's conformance to the American Society of Mechanical Engineers internal events PRA standard. These gaps collectively cover eight deficiencies in meeting the supporting requirements (SRs) of the PRA standard, Capability Category II. The "description"and "current status" columns in Table 1, Attachment 2, of the July 5 submittal, adequately describe these gaps. However, the "importanceto application" column only restates that the gap is a model logic issue and that sensitivity studies will be conducted. The significance of these gaps to the overall PRA results and to the risk calculationssupporting changes to surveillance frequencies is not discussed, and must be addressed in order for the NRC staff to reach a conclusion on the significance of these gaps as relatedto this amendment request.
- 1. Provide a discussion of the significance of each of the five gaps identified in Table 1 of Attachment 2. Where applicable, provide a quantitative assessment of the sensitivity of core damage frequency (CDF) and large early release frequency (LERF) results. In addition, the following specific concerns should be addressed in your response:
Gap 1: The lack of modeling ventilation dependencies was specifically identified as a recommendation from the NRC staff's review of the MPS3 Individual Plant Examination (IPE). According to the model update timeline provided in the July 5, submittal, this was completed in December 1995. It is not clear how this same issue arises in a 2007 self assessment. What is unique about these three specific ventilation subsystems which led to them not being modeled as a requiredsupport system following the 1995 IPE?
Gap 2: Changes to surveillance test intervals can directly impact an associatedpre-initiator human error probability by reducing the opportunities for
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Attachment 1, Page 2 of 9 identification and restorationof a system misalignment. What is the scope of pre-initiatorhuman errors currently in the PRA model, and what is the basis for their inclusion in the model absent a review of plant procedures and practices? Is resolution of this gap expected to add to the pre-initiatorscope significantly?
Gap 4: The NRC staff review of the internal flooding analysis for the IPE also identified the lack of discussion regarding maintenance-induced flooding.
What internalflooding sources are currently consideredand what is the basis for their frequencies? Is resolution of this gap expected to increase the contribution of internal floods to CDF and LERF significantly? What is the schedule for addressing these contributors?
DNC Response The MPS3 PRA model is in the final stages of a model update. The updated PRA model, M31 OA, will address four of the five gaps previously identified in Table 1 of of the July 5 submittal. The nature of the gaps pertain to modeling of ventilation dependencies, pre-initiator Human Error Probabilities(HEPs), alignment specific basic event values, internal flooding frequencies associated with non-piping failures, and incorporating SAMG operation actions. Upon issuance of the updated PRA Model M31 OA, four of these five gaps will meet the ASME PRA standard supporting requirements. The significance of the remaining gap, Gap 4 is discussed below. The M31OA model will be completed prior to implementation of the SFCP.
GAP 1: Nothing is unique about these three ventilation subsystems. They were inadvertently not included in the PRA model. NRC Regulatory Guide (RG) 1.200, Revision 1, was issued in January 2007. Dominion performed a self-assessment based on guidance from R G 1.200 using the American Society of Mechanical Engineers (ASME) standard (RA-S-2002, RA-Sa-2003, and RA-Sb-2005). As part of the self-assessment, the Heating, Ventilation and Air Conditioning (HVAC) dependencies were reviewed in accordance with the ASME PRA Standard. This review identified lack of modeling for three HVAC dependencies. Completion of the updated MPS Model, M310A, will address the HVAC dependencies identified in Gap 1.
GAP 2: Upon issuance of the updated PRA Model, M31 OA, Gap 2 will meet SR HR-Al.
GAP 4: The current MPS3 PRA model includes maintenance-induced internal flooding initiating events. The internal flooding contributes -2% to overall CDF.
Resolution of Gap 4 is not anticipated to identify any new internal flooding scenarios. The majority of non-piping components (e.g., pumps, valves, tanks, etc) are identified and included in the internal flooding analysis. The remaining non-piping failures (expansion joints, bellows and inadvertent actuation of fire protection system) are bounded by already analyzed flow rates. Since the remaining non-piping failures make up a small percentage of the overall system
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Attachment 1, Page 3 of 9 piping failures, any changes in the internal flooding initiating event frequencies will not have a significant impact to the overall CDF/LERF or impact the SFCP.
Question 2 The licensee identified an industry peer review being conducted in 1999, and stated that the "A" and "B" findings from the review have been addressed. Are there other remaining open findings, from that review, which are related to different issues than those identified in the self-assessment conducted in 2007? Describe any such findings and theirpotentialimpact on this application.
DNC Response There are six level "C" facts and observations (F&Os) remaining open from the 1999 PRA peer review. The level "A" "B" and "D" level findings have previously been addressed. Level "C" F&Os are defined aS "considered desirable to maintain the maximum flexibility in PRA Applications and consistency in the industry, but not likely to significantly affect results or conclusions." The six level "C" F&Os will be closed with release of the updated MPS PRA model, M310A.
Question 3 The self-assessment results identified 39 SRs, related to documentation and uncertainty evaluations, which do not meet PRA Capability Category II. The details of these SRs are not discussed in the July 5, submittal. The characterization of uncertainties is essential to assure that PRA results supporting changes in test frequencies are understood by the independent decision-making panel in order to adequatelyimplement TSTF-425. Further,proper documentation is essential for maintaining the PRA model and understandingthe results. Finally,the NRC staff is concemed about the number of SRs in these specific areas, and notes that its review of the MPS3 IPE submittal also identified several specific areas where documentation needed enhancement.
Describe the nature of the deficiencies in documentation and uncertainty evaluations, including the current state of the PRA documentation and uncertainty analyses, and schedule for resolution of these items.
DNC Response In early 2007, Dominion started the self-assessment process for each of the five fleet PRA Models. In order to meet Category II for a supporting requirement, documented evidence that the supporting requirement was met was necessary. For example, supporting requirements IE-A6 and IE-C10 are categorized as not being met due to documentation issues only. Since each high level requirement of the standard has a separate documentation supporting requirement, these two supporting requirements (IE-A6 and IE-ClO) could have been categorized as met with the documentation
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Attachment 1, Page 4 of 9 supporting requirement categorized as not-met. Dominion's approach was to conservatively categorize IE-A6 and IE-C1 0 as not-met rather than categorize them as met with the documentation supporting requirement categorized as not-met. Therefore, the evaluation process used for the Dominion Fleet PRA models conservatively counts the number of not-met supporting requirements due to documentation issues.
Dominion agrees that documentation is essential in maintaining PRAs and understanding the results. With release of the updated MPS3 PRA model, M310A, 16 of the 39 not-met supporting requirements related to documentation will be addressed.
The remaining 23 not-met supporting requirements detailed in the attached table include 15 related to identification of model and assumptions uncertainties, with the remaining 8 related to non-significant model completeness issues (i.e., documentation issues). The table describes the nature of the current "not-met" supporting requirements and the importance to the application.
As part of the PRA model update process for M310A, the parametric and non-parametric uncertainties will be addressed. The model uncertainty evaluation will be completed before the SFCP is used to change a surveillance frequency.
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Attachment 1, Page 5 of 9 Millstone Power Station Unit 3 Not-Met Supporting Requirements using PRA Model M310A Not-Met Description Notes Importance To Application Supporting Requirement(s)
IE-D3, SC-C3, SY- Identification of These supporting requirements will be Non-Significant.
C3, IF-E6, IF-F3, assumptions and documented and evaluated in the MPS3 QU-B1, QU-E1, model notebook titled, ModelAssumptions And These supporting QU-E2, QU-E4, uncertainties. Uncertainties. Identification of assumptions requirements will be QU-F4, QU-F5, LE- and model uncertainties will ensure there is addressed before F2, LE-F3, LE-G2, no undue reliability on model uncertainty or implementation of the SFCP.
and LE-G4 assumptions in the SFCP evaluations IE-A6 and SY-A4 Documentation of The Dominion PRA staff has performed Non-significant.
interviews and many system walkdowns during the walkdowns development and maintenance of the Lack of interview and models. However, no formal documentation walkdown documentation is of these walkdowns exists at this time to not expected to significantly allow closure of ASME/ANS PRA Standard impact the SFCP risk supporting requirements. It is not evaluations for the reasons anticipated that not meeting this stated in the Notes column. In requirement will have a significant impact on addition, the risk evaluation will the model. Formal walkdown checklists be presented to the have been developed and will be completed Independent Decision-making in the future. As the walkdowns are Panel (IDP), which includes a completed, they will be included in PRA licensed senior reactor System Notebooks. operator, the subject matter expert, the surveillance Dominion PRA staff works closely with coordinator, and two MPS3 system engineers and operators Maintenance Rule expert while supporting the various risk informed panel members. The diverse programs such as Maintenance Rule, knowledge of the IDP
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Attachment 1, Page 6 of 9 Millstone Power Station Unit 3 Not-Met Supporting Requirements using PRA Model M310A Not-Met Description Notes Importance To Application Supporting Requirement(s)
Mitigating System Performance Indicator, members will compensate for Risk-Informed Inservice Inspection, Risk- the lack of documentation Informed TS submittals and Significance associated with these Determination Process resolution. The supporting requirements.
plant scheduling staff, along with the Shift Technical Advisors, use PRA for assessing plant risk as required by the Maintenance Rule (a)(4) program. This interaction with the plant staff provides valuable feedback on the PRA model. Also, the PRA staff has extensive plant knowledge with staff members who were previously system engineers, shift technical advisors, and senior reactor .operators. Although interviews with the plant staff have not been documented, which would allow closure of ASME/ANS PRA Standard supporting requirements, it is not anticipated that not meeting this requirement will have a significant impact on the model. In the future, formal interviews will be documented by inclusion in System Notebooks. Informal discussions pertinent to the model will also be included in the System Notebooks.
IE-A7 The MPS3 PRA Review of MPS3 plant-specific operating Non-significant.
model does not experience precursors is not expected to I
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Attachment 1, Page 7 of 9 Millstone Power Station Unit 3 Not-Met Supporting Requirements using PRA Model M310A Not-Met Description Notes Importance To Application Supporting Requirement(s) include a review identify any new initiating events. Several This is considered a of plant-specific PRA models in the Dominion Fleet have documentation issue based on operating completed this type of review and did not the discussion provided under experience for identify any significant new initiating events, the notes column.
initiating event The MPS3 model includes a review of plant-precursors. specific operating experience for initiating events that did occur. Additionally, the MPS3 PRA includes a systematic evaluation of the plant systems to assess the possibility of an initiating event occurring due to a failure of the system. Therefore, a review of plant-specific operating experience precursors should not result in the identification of any new significant initiating events.
IE-C10 Perform a The only expansion joint rupture frequency Non-significant.
reasonableness in the MPS3 PRA is for the service water check of the (SW) system, which is 1.14E-4/yr. The Model completeness issue expansion joint EPRI Pipe Rupture Frequencies (TR- only.
rupture 1013141) reports a circulating water (CW) frequencies expansion joint major flood as 1.22E-modeled in the 5/reactor-operating-component year. The PRA EPRI document does not delineate SW expansion joints from the pipe rupture rates.
The MPS3 SW expansion joint failure is considered conservative since the CW
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Attachment 1, Page 8 of 9 Millstone Power Station Unit 3 Not-Met Supporting Requirements using PRA Model M310A Not-Met Description Notes Importance To Application Supporting Requirement(s) system generally has a higher flow rate with large diameter pipe resulting in a theoretically higher failure rate for the CW expansion joint ruptures.
SY-B8 Identify spatial The majority of spatial analysis walkdowns Non-significant.
and have not been completed. The System environmental Analysis notebooks do contain a section to Identification of a potentially hazards that may document any spatial or environmental new spatial or environmental impact multiple hazard identified during plant walkdowns. hazard is not expected to systems or To date, spatial and environmental hazard significantly impact the risk redundant walkdowns have been performed and evaluations performed in components in documented for the internal flooding support of the SFCP.
the same system, analysis and for Component Cooling Water and account for and Charging & Chemical Control systems them in the with no new hazards identified. Since system fault tree comprehensive walkdowns were performed or the accident for the internal flooding analysis, it is not sequence expected that the spatial and environmental evaluation. walkdowns will identify any new significant spatial or environmental hazard.
IF-C3b M31OA does not The identification, documentation and Non-significant.
document the modeling of any potential flood barrier potential for flood unavailability or drain check valve failure is Any surveillance frequency barrier not expected to result in any significant increase for internal flooding unavailability or impact to the MPS3 PRA model. This is monitoring equipment will 1 provide a based on the conservative internal flooding include a sensitivity study to
Serial No.11-696 Docket No. 50-423 RAI Response for TSTF-425 Attachment 1, Page 9 of 9 Millstone Power Station Unit 3 Not-Met Supporting Requirements using PRA Model M310A Not-Met Description Notes Importance To Application Supporting Requirement(s) summary initiating event frequencies (see discussion address this not-met discussion of the for IF-D5) and small (-2%) contribution to supporting requirement. The locations of floor the overall CDF. sensitivity study will include drain check potential flood barrier valves and the unavailability and drain check considerations for valve failure probability.
their potential failure.
IF-C4A For multi-unit No credible multi-unit internal flooding Non-significant.
sites with shared scenarios exist. The path between MPS2 systems or and MPS3 has been addressed. However, Documentation issue only.
structures, propagation from the water treatment facility include multi-unit to MPS3 is non-credible but has not been scenarios documented as such.
IF-D5 Determine the The MPS3 PRA internal flooding initiating Non-significant.
flood-initiating event frequencies are based on "per reactor event frequency critical year" and does not account for the Internal flooding initiating event for each flood capacity factor. This is conservative since frequencies are conservatively scenario group by the internal flooding initiating event high and contribute only -2%
using the frequencies have not been multiplied by to the overall CDF.
applicable capacity factor. Addressing this supporting requirements requirement would result in lower internal I flooding initiating event frequencies.