RBG-46944, Supplement to Request for Alternative - Implementation of a Risk-Informed Inservice Inspection Program Based on ASME Code Case N-716 (RBS-ISI-013)
| ML092290106 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 08/11/2009 |
| From: | Roberts J Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-46944, TAC ME1507 | |
| Download: ML092290106 (46) | |
Text
Entergy River Bend Station 5485 U.S. Highway 61N St. Francisville, LA 70775 Tel 225-381-4149 Jerry C. Roberts Director, Nuclear Safety Assurance RBG-46944 August 11, 2009 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
SUBJECT:
Supplement to Request for Alternative - Implementation of a Risk-Informed Inservice Inspection Program Based on ASME Code Case N-716 (RBS-ISI-013)
River Bend Station, Unit 1 Docket No. 50-458 License No. NPF-47 Reference
- 1. Entergy Letter to NRC dated June 16, 2009, Request for Alternative -
Implementation of a Risk-Informed Inservice Inspection Program Based on ASME Code Case N-716 (RBS-ISI-013 / RBG 46922)
- 2. NRC letter to Entergy July 29, 2009, River Bend Station, Unit 1 -
Supplemental Information Needed For Acceptance Of Requested Licensing Action Re: Risk-informed Relief Request Based On ASME Code Case N-716 (TAC ME1507)
Dear Sir or Madam:
On June 16, 2009, Entergy Operations, Inc. (Entergy) submitted a request to implement a risk-informed Inservice Inspection (RI ISI) program based on the methodology of American Society of Mechanical Engineers (ASME) Code Case N-716, as documented in the attachment to Request for Alternative RBS-ISI-01 3, Reference 1.
On July 28, 2009, the NRC Staff and Entergy personnel met to discuss Reference 1, and the associated submittal (RBS-ISI-01 3) requesting approval to use the methodology of ASME Code Case N-716. During this meeting the NRC discussed additional information needed to continue review of the request. On July 29, 2009, the NRC Staff identified the additional information needed as indicated in Reference 2. This letter responds to the NRC Staff request in Reference 2.
The request for additional information contained two questions, with the first necessary for completionof the acceptance review and the second to support continued review by the NRC Staff.
Acw-r
RBG-46944 Page 2 of 3 In the first question, additional information was requested on those gaps in the PRA analysis identified as documentation issues with the guidance given in Regulatory Guide 1.200 Revision 1. Attachment 1 contains further discussion on these issues. Also, the associated tables include additional information and clarifications further explaining the basis of the determination that these gaps do not affect the conclusions of the Relief Request.
The second NRC question concerned the PRA Capability category for certain Internal Flooding (IF) element Supporting Requirements (SR's). Attachment 2 contains the response to the NRC question. The RBS IF-PRA meets Capability Category III for the four SR's which are the subject of question 2.
This information does not include new commitments. If you have any questions or require additional information, please contact David Lorfing, Manager, Licensing at (225) 381-4157.
Sincerely, D/irect/oNuclear Safety Assurance River Bend Station - Unit 1 JCR/DNL/bmb Attachments:
- 1.
Supplement to Request for Alternative RBS-ISI-01 3, Response to Question 1
- 2.
Supplement to Request for Alternative RBS-ISI-013, Response to Question 2 cc:
Regional Administrator U. S. Nuclear Regulatory Commission Region IV 612 E. LamarBlvd., Suite 400 Arlington, TX 76011-4125 NRC Senior Resident Inspector P. 0. Box 1050 St. Francisville, LA 70775 U. S. Nuclear Regulatory Commission Attn: Mr. Alan B. Wang MS 0-7 D1 Washington, DC 20555-0001
RBG-46944 Page 3 of 3 Mr. Jeffrey P. Meyers Louisiana Department of Environmental Quality Office of Environmental Compliance Attn. OEC - ERSD P. 0. Box 4312 Baton Rouge, LA 70821-4312
ATTACHMENT 1 TO RBG-46944 SUPPLEMENT TO REQUEST FOR ALTERNATIVE RBS-ISI-013 to RBG-46944 Page 1 of 38 SUPPLEMENT TO REQUEST FOR ALTERNATIVE ENTERGY OPERATIONS, INC.
RIVER BEND STATION - UNIT 1 RBS-ISI-013 From NRC letter to Entergy July 29, 2009, River Bend Station, Unit 1 -Supplemental Information Needed For Acceptance Of Requested Licensing Action Re: Risk-informed Relief Request Based On ASME Code Case N-716 NRC Question #1:
(1)
Table 1 in the relief request provides the results of the RBS probabilistic risk assessment (PRA) self-assessment and identifies the 72 ASME (RA-Sb-2005) supporting requirements (SR) that could require a sensitivity study or other disposition to more fully support the RI-ISI analysis. In numerous entries, the importance of the gap between the ASME SR and the RBS PRA analysis is deemed not significant based on the gap being a documentation issue which requires no model changes.
RBS should explain how it reached the conclusion that each of these gaps are solely a lack of documentation and not an important (for RI-ISI) difference between the attributes of RBS PRA analysis and the ASME SR's.
Enterqy Response:
As described in Attachment 1 to letter RBG-46922 dated June 16, 2009, Entergy performed a self-assessment of the River Bend PRA against the ASME PRA Standard, ASME RA-Sb-2005, as endorsed by Regulatory Guide 1.200 Revision 1. This self-assessment was primarily conducted in late 2008. Table 1 of letter RBG-46922 provided the results of the River Bend self-assessment and provided a disposition, including characterization, for the list of 72 supporting requirements which were categorized as having gaps with respect to fulfilling the ASME PRA Standard. The self-assessment documented the recommended actions for these gaps to address in the next Revision of the RBS PRA so that the RBS PRA would meet Capability Category II of the ASME PRA Standard.
River Bend Internal Flooding PRA (IFPRA) was completed in June 2009. The River Bend IFPRA meets at least Capability Category II for all Internal Flooding (IF) SRs per the ASME PRA standard, and meets the more rigorous Capability Category III for a number of SRs. The River Bend IFPRA provides a robust and high quality basis for the CDF and LERF screenings which are one of the multiple screening elements in a N-716 RI-ISI application.
As discussed in RBG-46922 and RG-1.174, it is recognized that RI-ISI applications are less reliant upon PRA risk insights than other risk-informed applications. For the N-716 RI-ISI approach, PRA risk metrics are one of five selection criteria for the inspection population.
PRA criteria are applied solely for the purpose of capturing any potential high risk piping elements which are not otherwise identified for inclusion as part of the other four screening criteria.
This methodology further uses an absolute risk ranking approach. As such, conservatism in either the consequence assessment or the failure potential assessment will result in a larger inspection population rather than masking other important components. That is, providing more realism into the PRA model (e.g., by meeting higher Capability Categories) would most to RBG-46944 Page 2 of 36 likely result in a smaller inspection population. These facts of the methodology reduce the importance and influence of PRA on the final list of candidate welds. On this basis, River Bend provided in Table I information on the gaps (to Capability Category I of the ASME PRA Standard) identified in the RBS PRA. This same approach has been used in other N-716 RI-ISI submittals to the NRC.
Table 1 of RBG-46922 listed all gaps identified in the RBS PRA to the minimum requirements of the ASME PRA Standard. This would correspond to gaps to Capability Category I. Of the 72 identified gaps, only 7 involved SR's for which there is a differentiation between Capability Categories I and II. The disposition of those gaps is based upon addressing those gaps with respect to Capability Category II.
The PRA self-assessment conducted by Entergy also identified 28 SR's which were categorized as meeting Capability Category I of the ASME PRA Standard. These are listed in Table E of this letter with a disposition to explain why there is no negative impact on the RBS N-716 RI-ISI application associated with these Capability Category I SR's. 12 of these SR's are in the LE (Large Early Release Fraction) element of the ASME PRA Standard and are assigned Capability Category I on the basis of a NUREG/CR-6595 simplified LERF model.
Many of the SR's in the ASME PRA Standard LE element section explicitly direct assignment of Capability Category I when the NUREG/CR-6595 methodology has been adopted.
The NUREG/CR-6595 methodology is a simplified approach which uses accident sequence information from the Level 1 PRA to estimate the frequencies of various containment failure modes. The split fractions applied in NUREG/CR-6595 to the simplified Containment Event Trees reflect reasonably conservative estimates of the likelihood of early containment failure for different containment design types (e.g., BWR Mark III containment for Rivet Bend), and are bounding in nature to encompass the plants within a particular containment type. As documented in Appendix B of NUREG/CR-6595, this approach results in generally higher LERF values than those obtained from a traditional Level 2 PRA. NUREG/CR-6595 approaches have been characterized as Capability Category I under the ASME standard because of this conservatism.
Thus, the fact that a number of LERF element SR's are judged as Capability Category I will not detract from the RI-ISI decision process. As a result, the bounding nature of the NUREG/CR-6595 approach would tend to increase the scope of High Safety Significance (HSS) piping and therefore the size of the inspection population. This would,add to the robustness of the selection process in terms of its thoroughness in identifying an inspection population that meets N-716 requirements.
River Bend had performed a full Level 2 PRA update in support of the Amendment 116 to the RBS operating license that allowed removal of the Inclined Fuel Transfer System blind flange at power. While these results have not been updated for subsequent revisions to the Level 1 PRA, the River Bend LERF/Level 2 PRA provides substantial additional documentation beyond the scope associated with NUREG/CR-6595. The detailed documentation associated with this Level 2 application was generally not included in the scope of the RG-1.200 self-assessment and provides assurance of additional rigor for the River Bend LERF model.
River Bend has provided expanded and clarified information upon the gaps to the ASME Standard which were identified in Table 1 of letter RBG-46922. As part of the clarification, the 72 gaps identified in the June 16, 2009, letter have been grouped into the following Tables:
to RBG-46944 Page 3 of 36 Table A: (6 gaps)
Table B: (21 gaps)
Table C: (10 gaps)
These are the gaps which were originally identified as Potentially Applicable to the RBS N-716 RI-ISI submittal and which were dispositioned in Table 2 of RBG-46922.
These are the gaps for which potential model refinements or sensitivity studies were recommended for consideration' as part of the PRA self-assessment but these gaps were considered "NOT SIGNIFICANT" for the purposes of the RBS N-716 RI-ISI submittal and decision processes.
This Table also includes several gaps which are addressed via addressing the items in Table A, as well as a small number of gaps which need not be addressed for RI-ISI applications (Ref:
EPRI TR-1018427).
The RG 1.200 endorsement of the ASME PRA Standard has included a requirement to document the assumptions and sources of uncertainty associated with each PRA element. As of the performance of this self-assessment, the BWROG had mandated that these SR's be identified as gaps to the Standard pending agreement on exactly what is entailed under these SR's.
These SR's are identified as items that need not be met for the purpose of RI-ISI per EPRI TR-1018427, thus do not impact RI-ISI decisions.
Subsequent to the RBS PRA self-assessment, the NRC has issued NUREG-1855, "Guidance on the Treatment of Uncertainties Associated with PRA's in Risk-Informed Decision Making." This has clarified requirements for meeting the ASME PRA Standard. Thus, the SR's in Table C are concluded to constitute documentation issues which, as discussed in EPRI TR-101*8427, do not impact RI-ISI applications.
These are the gaps in Documentation that would not result in PRA model changes and which do not impact the applicability of the RBS PRA in support of RI-ISI decision making. Entergy has explained in Table D why each of these gaps is a documentation issue and is not an important (for RI-ISI) difference between the attributes of RBS PRA analysis and the ASME PRA Standard SR's.
Table D: (35 gaps)
All items identified in letter RBG-46922 are included in Tables A through D, including several items which are considered resolved due to subsequent review. Note that experience from recent revisions to other Entergy site PRA models provides insights to support characterization of issues as documentation in nature and not affecting the content of the PRA model, since the same processes are used in the development and maintenance of these Entergy PRA models.
Table E presents discussions concerning SR's where the RBS PRA is judged Capability Category I and why the difference in these areas to Capability Category II would not impact RI-ISI decision making. EPRI report TR-1018427 identifies that Capability Category II would be appropriate for SR IE-A4 but that Capability Category I would be appropriate for all other SR's in Table E.
to RBG-46944 Page 4 of 36 Note that substantial margins to acceptance criteria exist for the RBS N-716 RI-ISI application.
The risk impact documented in RBG-46922 demonstrates significant margins to the acceptance guidelines of RG 1.174:
Metric:
RBS Risk Impact:
RG 1.174 acceptance guidelines (Region III)
ACDF 4.42E-09
< 1E-06 ALERF 2.86E-10
< 1E-07 Also, the sensitivity analyses documented in Table 2 of RBG-46922 demonstrate the robustness of the RI-ISI decision process and of the use of the RBS PRA for RI-ISI applications.
Thus, the additional information provided herein continues to support the previous conclusions that the RBS PRA models are suitable for use in the RI-ISI application. This conclusion has been supplemented by the information provided herein that provides additional explanations regarding SR's for which identified gaps are to be documentation issues and on additional information assessing the RBS PRA against Capability Category II of the ASME PRA Standard for the purposes of RI-ISI applications.
ATTACHMENT 2 TO RBG-46944 SUPPLEMENT TO REQUEST FOR ALTERNATIVE RBS-ISI-013 to RBS-46944 Page 1 of 5 SUPPLEMENT TO REQUEST FOR ALTERNATIVE RBS-ISI-01 3 From NRC letter to Entergy July 29, 2009, River Bend Station, Unit 1 -Supplemental Information Needed For Acceptance Of Requested Licensing Action Re: Risk-informed Relief Request Based On ASME Code Case N-716 NRC Question #2:
Page 27 of 68 in the relief request states that, "[t]he RBS Internal Flooding Analysis (IFA) was significantly upgraded to meet the requirements of RG 1.200 in 2009." The NRC staff interprets this to mean that the flooding SR's are all at least consistent with Capability Category II (CCII) supporting requirements. The NRC staff has concluded that additional work may be needed beyond CCII in order for the PRA technical adequacy to be consistent with that determined to be acceptable for PRAs that supported the EPRI TR-1 12657 RI-ISI process. Please explain how the following three issues are addressed.
Supporting requirement IF-C3 (IFSN-A8) identifies the failure mechanisms that shall be evaluated to determine the susceptibility of each structure, system, and component (SSC) in a flood area to flood-induced failures. Capability category II identifies failure by submergence and spay as requiring identification but may not require assessment. Capability category III requires identification and assessment of all failure modes including submergence, spray, jet impingement, pipe whip, and humidity, condensation, and temperature concerns. RI-ISI methods require that all SSC failures induced by a pipe break be considered. Please demonstrate that all SCCs failures that are induced by a pipe break are adequately assessed in your analysis.
Supporting requirement IF-D3a (IFEV-A3) Category II permits grouping or subsuming flood initiated scenarios with existing plant initiating event groups. A category III analysis which does not permit grouping is more consistent with previous RI-ISI analyses. If grouping of flood scenarios with other initiating events groups was done, please confirm that the subsumed flooding scenarios were identified during the flooding analysis and extracted during the RI-ISI analysis in order to insure that their contribution to the RI-ISI analysis was properly included.
Supporting requirement IF-C6 (IFSN-A14) and IF-C8 (IFSN-A16) permits screening-out of flood areas and sources respectively based on, in part, the success of human actions to isolate and terminate the flood before equipment is damaged. RI-ISI methods require determination of the flood scenario with and without human intervention which corresponds to the capability category III, i.e. scenarios are not screened out based on human actions.
Therefore a category III analysis is more consistent with previous RI-ISI analyses. If capability category II is used, high reliability of the human actions relied upon to screen out scenarios should be demonstrated using methods consistent with the supporting requirement IF-E5 (IFQU-A5) in the standard. Please re-evaluate the credit given to human actions to provide confidence that scenarios that might exceed the quantitative guideline are identified.
to RBG-46944 Page 2 of 5
,Entergy response:
In support of the N-716 relief request, Entergy developed the River Bend Station (RBS)
Internal Flooding PRA (IFPRA) to meet Capability Category II for all Internal Flooding (IF)
Supporting Requirements (SR's) of the ASME Standard for Probabilistic Risk Assessment for Nuclear Power Plant Applications, ASME RA-Sb-2005. There are 8 IF SR's in the ASME PRA Standard with differentiation between Category II and Capability Category Ill; the RBS IFPRA meets Category III requirements for over half of these.
EPRI TR-1018427 dated December 2008, "Non-Destructive Evaluation: Probabilistic Risk Assessment Technical Adequacy Guidance for Risk-Informed In-Service Inspection Programs," discusses technical adequacy expectations of PRA's.
"A PRA meeting Capability Category II of the PRA Standard [ASME RA-Sb-2005] is a major step forward in the PRA maturation process and is an acceptable starting point for almost all risk assessment applications. This viewpoint is supported by the general trend that Capability Category I supporting requirements (SR's) have a conservative bias, whereas Capability Category III SR's represent more realism in the analysis. In addition, an increasing Capability Category tends to increase the completeness as well as the documentation requirements of the PRA."
The conclusion of the EPRI review is that only one SR (IF-D5a) is recommended for Capability Category III for N-716 RI-ISI applications. Only four SR's (IE-A4, IF-C3, IF-C6, and IF-C8) are recommended for Capability Category II of the approximately 300 SR's in the ASME PRA Standard.
The River Bend IFPRA exceeds these quality expectations of EPRI TR-1018427 and meets Capability Category II or III for all IF SR's. The RBS IFPRA meets Capability Category III for the four SR's discussed in the NRC letter. Discussion of these individual SR's follows.
Supporting Requirement IF-C3:
Capability Categories I and II:
For the SSCs identified in IF-C2c, IDENTIFY the susceptibility of each SSC in a flood area to flood-induced failure mechanisms.
INCLUDE failure by submergence and spray in the identification process.
EITHER:
(a) ASSESS qualitatively the impact of flood-induced mechanisms that are not formally addressed (e.g., using the mechanisms listed under Capability Category III of this requirement), by using conservative assumptions; OR (b) NOTE that these mechanisms are not included in the scope of the evaluation.
Capability Category II:
For the SSCs identified in IF-C2c, IDENTIFY the susceptibility of each SSC in a flood area to flood-induced failure mechanisms. INCLUDE failure by submergence, spray, jet impingement, pipe whip, humidity, condensation, temperature concerns, and any other identified failure modes. in the identification process.
to RBG-46944 Page 3 of 5 Discussion:
The RBS IFPRA has accounted for flood-induced equipment failure mechanisms including submergence, spray, jet impingement, pipe whip, humidity, condensation, and temperature in identifying equipment which is assumed to fail in the quantification process for the IFPRA.
This meets Capability Category III of the ASME PRA Standard for SR IF-C3. All IF-C3.failure mechanisms are accounted for in the scope of the IFPRA.
As part of scenario development for the River Bend IFPRA, equipment which would be damaged due to submergence and/or spray and subsequent plant impact was specifically considered for all release scenarios. Detailed analyses of submergence levels and propagation paths were conducted as part of the IFPRA.
Per EPRI TR-1018427, N-716 RI-ISI applications should meet Capability Category II for SR IF-C3. Note the NRC's comment in RG 1.200 R1 on the ASME standard for this SR requires, for Capability Category II, an assessment of Capability Category III mechanisms (e.g.
submergence) by using conservative assumptions. Thus, Capability Category II is conservative as compared to Capability Category I1l. At worst, this would from a N-716 perspective increase the scope of HSS piping and therefore the size of the inspection population. Note that resolution of NRC comments on SR IF-C3 led to the Capability Category II requirement to qualitatively assess the impact of flood-induced damage mechanisms by using conservative assumptions. Thus, Capability Category II would be conservative with respect to Capability Category III; at worst, this would from a N716 perspective increase the scope of HSS piping and therefore the size of the inspection population. Therefore, meeting Capability Category II is more conservative for RI-ISI applications than meeting Capability Category Ill.
Concerns related to jet impingement, pipe whip, temperature, and humidity are associated with High Energy Line Breaks (HELB's) and Moderate Energy Line Cracks (MELC's). Protection against dynamic effects associated with postulated piping failure is discussed in Section 3.6A of the RBS SAR. Pipe breaks are evaluated for the effects of pipe whip, jet impingement, spray, pressurization, and environmental effects (e.g., temperature, humidity, condensation).
Moderate energy piping is evaluated for spray and other environmental effects. IFPRA's account for releases from all piping, i.e., considers both HELB's and MELC's.
The possibility of these damage mechanisms has been addressed with regard to the postulated rupture of high energy piping. High energy fluid systems are defined as those systems that during normal plant operation are maintained pressurized where the maximum temperature exceeds 200°F and/or the maximum pressure exceeds 275 psig. High energy piping outside containment for River Bend, per SAR Table 3.6A-22, includes the Main Steam system (and its drains), the Main Feedwater System, RCIC steam supply, RWCU, and CRD.
Pipe whip analyses for these systems are documented in SAR Section 3C. Most of this high energy piping is in the RBS Auxiliary Building steam tunnel (zone AB 114-2/7). RCIC steam piping in the RCIC pump room would only affect the RCIC equipment in that room. High energy CRD piping outside containment is only in the Fuel Building, and, as discussed in SAR Section 3C.2.10.1, the only targets of any CRD pipe whip would be floors and walls of the building which have been designed to ensure their structural integrity.
HELB analyses are conducted to demonstrate that other systems and trains not subject to the break are capable of bringing the reactor to safe shutdown conditions using qualified equipment, i.e., are capable of being credited in an IFPRA. Safety related electrical equipment that is located in a harsh environment has been qualified by test or other methods as required to RBG-46944 Page 4 of 5 by 1 0CFR50.49(f). Equipment credited for safe shutdown is qualified for the accident conditions specified in the RBS Environmental Design Criteria. These conditions are developed based upon worst case maximum break energy releases, whereas IFPRA considers all spectra of releases, that is, will consider the higher probability releases with smaller and less severe release rates as well as the lower probability maximum release rates.
Thus, the environmental effects analyzed for design basis HELB's are bounding compared to the values that would be experienced for smaller release rates.
Scenario development for IFPRA identified equipment which would be damaged due to various damage mechanisms and quantified Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) based on equipment modeled in the PRA which would remain available. This included crediting environmentally qualified equipment. The RBS Environmental Qualification program is described in SAR Section 3.11. The environmental design basis conditions which have been used to establish the design basis for RBS are specified for normal, abnormal, and accident conditions. The environmental data for temperature, pressure, humidity, and radiation are defined for each building zone. Under the RBS Equipment Qualification program, Auxiliary Building zones are qualified for a bounding value of 100% relative humidity.
The RBS Auxiliary Building is of a high compartmentalized design. Thus, any large releases in the Auxiliary Building 70' elevation (bottom level) would be postulated to result in failure of the equipment in those rooms (ECCS pump rooms, containment penetration area, and a piping tunnel) due to submergence, if not already failed due to spray effects; each room has independent drain sumps that do not communicate.
In developing the RBS IFPRA, all scenarios identified equipment important to risk which could be impacted due to releases. This includes tracking the propagation of releases and determining which equipment would be damaged due to all effects from the release. This includes the effects of spray and/or submergence as the floodwater propagates from its source to the location where it would eventually accumulate (e.g., building basement flood zones).
It is thus concluded that the RBS IFPRA has accounted for flood-induced equipment failure mechanisms including submergence, spray, jet impingement, pipe whip, humidity, condensation, and temperature in identifying equipment which is assumed to fail in the quantification process. This meets Capability Category III of the ASME PRA Standard for SR IF-C3.
Supportinq Requirement IF-D3a:
Capability Categories I and II:
GROUP OR SUBSUME the flood-initiating scenarios with an existing plant-initiating event group, if the impact of the flood (i.e., plant response and mitigating system capability) is the same as a plant-initiating event group already considered in the PRA in accordance with the applicable requirements of Table 4.5.1-2(b).
Capability Category IIl:
DO NOT GROUP AND DO NOT SUBSUME flood-initiating scenarios with other plant-initiating event groups.
to RBG-46944 Page 5 of 5 Discussion:
In developing the River Bend Internal Flooding PRA, the flooding scenario that would result from a pipe rupture in a given system and a given flood zone would identify the initiating event and associated system and component failures that would occur as a result of the specific flooding event. Even when the consequences of the release was the same as an established Initiating Event, a separate quantification of the specific flooding initiator was performed as part of the IFPRA. Approximately 500 separate quantifications were performed for the RBS IFPRA. Flooding scenarios were not subsumed into existing Internal Events PRA initiating events. Thus, the River Bend Internal Flooding PRA did not group and did not subsume flood-initiating scenarios with other plant-initiating event groups.
EPRI report TR-1018427 identifies that combined Capability Category I/1l is appropriate for IF-D3a. However, the RBS IFPRA does meet Capability Category III for this Supporting Requirement.
Supporting Requirement IF-C6:
Capability Category II:
USE potential human mitigative actions as additional criteria for screening out flood areas if all the following can be shown:
(a) flood indication is available in the control room (b) the flood sources in the area can be isolated (c) the mitigative action can be performed with high reliability for the worst flooding initiator. High reliability is established by demonstrating, for example, that the actions are procedurally directed, that adequate time is available for response, that the area is accessible, and that there is sufficient manpower available to perform the actions.
Capability Category IIl:
DO NOT SCREEN OUT flood areas based on reliance on operator action to prevent challenges to normal plant operations.
The River Bend Internal Flooding PRA meets Capability Category III of ASME RA-Sb-2005 for these supporting requirements. The IFPRA does not screen out flooding areas or flooding sources based on operator action to prevent challenges to normal plant operations. Although the vast majority of flooding scenarios would result in alarms due to high sump level alarms in the Main or Auxiliary Control Room which would allow operators to quickly respond and secure the source of the flooding, no flooding areas and no flooding sources were screened from quantification by crediting for such alarms and/or operator actions. Approximately 500 separate quantifications were performed for the RBS IFPRA. A plant transient or operator action to shut down the plant was assumed for almost all releases. Only a very small number of releases were evaluated as not resulting in a plant transient, primarily for where there was a very limited release, such as from an isolated section of piping which would not damage any equipment which could result in a plant transient.
While EPRI report TR-1 018427 identifies that Capability Category II is appropriate for IF-C6 and IF-C8 for N-716 RI-ISI applications, the RBS IFPRA does meet Capability Category III for these Supporting Requirements.