ML013520130
| ML013520130 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 12/13/2001 |
| From: | Wichman K NRC/NRR/DE/EMCB |
| To: | Raghavan L NRC/NRR/DLPM/LPD1 |
| References | |
| +kBR1SISP20060530, FOIA/PA-2006-0179, TAC MB3328 | |
| Download: ML013520130 (6) | |
Text
December 13, 2001 MEMORANDUM TO: Lakshminaras Raghaven, Acting Chief Project Directorate Section I-1 Division of Licensing Project Management FROM: Keith R. Wichman, Chief /ra by BJElliot f/
Structural Integrity and Metallurgy Section Materials and Chemical Engineering Branch Division of Engineering
SUBJECT:
STAFF REVIEW OF THE LICENSEES RECONCILIATION OF FACILITY RCS LEAKAGE DETECTION CAPABILITY WITH THE TECHNICAL BASES CITED FOR INDIAN POINT UNIT 3 MAIN COOLANT LOOP LEAK-BEFORE-BREAK APPROVAL (TAC NO.:
MB3328)
By letter dated October 25, 2001, Entergy Nuclear Operations, Inc. (Entergy), the licensee for Indian Point Nuclear Generating Unit No. 3 (IP3), submitted a request for NRC review and approval of a technical reconciliation performed by Entergy concerning actual IP3 reactor coolant system (RCS) leakage detection capability and the technical bases cited by the NRC staff in our approval of leak-before-break (LBB) for the IP3 main coolant loop. The NRC staffs approval of LBB for the IP3 main coolant loop was issued by letter dated March 10, 1986. In our prior safety evaluation (SE), the NRC staff noted that the IP3 containment air radioactive particulate monitor and containment air radioactive gas monitor have, the capability of detecting one gpm [gallon per minute] change in leak rate in less than four hours. Based on current fuel performance and RCS activity, Entergy determined that the IP3 containment air radioactive gas monitor was no longer capable of achieving the referenced sensitivity. Since leakage detection sensitivity is a significant factor in demonstrating LBB behavior, Entergy submitted information in their October 25, 2001, letter to note all RCS leakage detection systems available at IP3 and requested NRC staff confirmation that the sensitivity of the installed IP3 leakage detection systems continued to support our prior LBB approval.
The staff has completed its evaluation of Entergys submittal. The information provided by Entergy was sufficient for the staff to determine that the installed IP3 leakage detection systems provide an adequate level of sensitivity to support the technical basis for the NRC staffs prior LBB approval. A supplement to our original IP3 main coolant loop LBB SE which further explains our determination regarding the adequate capability of the IP3 leakage detection systems is attached. The licensee shall conclude, therefore, that our original March 10, 1986, SE, as supplemented by the attachment, constitutes the technical basis for the NRC staffs approval of LBB for the IP3 main coolant loop. This completes our efforts for TAC No. MB3328.
Docket No.: 50-286
Attachment:
As stated CONTACT: M. A. Mitchell, EMCB/DE 415-3303
MEMORANDUM TO: Lakshminaras Raghaven, Acting Chief Project Directorate Section I-1 Division of Licensing Project Management FROM: Keith R. Wichman, Chief Structural Integrity and Metallurgy Section Materials and Chemical Engineering Branch Division of Engineering
SUBJECT:
STAFF REVIEW OF THE LICENSEES RECONCILIATION OF FACILITY RCS LEAKAGE DETECTION CAPABILITY WITH THE TECHNICAL BASES CITED FOR INDIAN POINT UNIT 3 MAIN COOLANT LOOP LEAK-BEFORE-BREAK APPROVAL (TAC NO.:
MB3328)
By letter dated October 25, 2001, Entergy Nuclear Operations, Inc. (Entergy), the licensee for Indian Point Nuclear Generating Unit No. 3 (IP3), submitted a request for NRC review and approval of a technical reconciliation performed by Entergy concerning actual IP3 reactor coolant system (RCS) leakage detection capability and the technical bases cited by the NRC staff in our approval of leak-before-break (LBB) for the IP3 main coolant loop. The NRC staffs approval of LBB for the IP3 main coolant loop was issued by letter dated March 10, 1986. In our prior safety evaluation (SE), the NRC staff noted that the IP3 containment air radioactive particulate monitor and containment air radioactive gas monitor have, the capability of detecting one gpm [gallon per minute] change in leak rate in less than four hours. Based on current fuel performance and RCS activity, Entergy determined that the IP3 containment air radioactive gas monitor was no longer capable of achieving the referenced sensitivity. Since leakage detection sensitivity is a significant factor in demonstrating LBB behavior, Entergy submitted information in their October 25, 2001, letter to note all RCS leakage detection systems available at IP3 and requested NRC staff confirmation that the sensitivity of the installed IP3 leakage detection systems continued to support our prior LBB approval.
The staff has completed its evaluation of Entergys submittal. The information provided by Entergy was sufficient for the staff to determine that the installed IP3 leakage detection systems provide an adequate level of sensitivity to support the technical basis for the NRC staffs prior LBB approval. A supplement to our original IP3 main coolant loop LBB SE which further explains our determination regarding the adequate capability of the IP3 leakage detection systems is attached. The licensee shall conclude, therefore, that our original March 10, 1986, SE, as supplemented by the attachment, constitutes the technical basis for the NRC staffs approval of LBB for the IP3 main coolant loop. This completes our efforts for TAC No. MB3328.
Docket No.: 50-286
Attachment:
As stated CONTACT: M. A. Mitchell, EMCB/DE 415-3303 DISTRIBUTION: EMCB RF PMilano DOCUMENT NAME: G:\MITCHELL\PLANTSPC\INDIAN POINT 3\LBB RECONCILIATION.WPD INDICATE IN BOX: C=COPY W/O ATTACHMENT/ENCLOSURE, E=COPY W/ATT/ENCL, N=NO COPY OFFICE DE:EMCB DSSA:SPLB DE:EMCB NAME MAMitchell:mam HWalker:hw KRWichman:bje f/
DATE 12 / 05 /2001 12 / 7 /2001 12 /13 /2001 OFFICIAL RECORD COPY
SAFETY EVALUATION SUPPLEMENT BY THE OFFICE OF NUCLEAR REACTOR REGULATION REGARDING THE NRC STAFFS PRIOR LEAK-BEFORE-BREAK APPROVAL FOR THE INDIAN POINT NUCLEAR GENERATING STATION UNIT 3 MAIN COOLANT LOOP ENTERGY NUCLEAR OPERATIONS, INC.
DOCKET NO.: 50-286
1.0 INTRODUCTION
By letter dated October 25, 2001, Entergy Nuclear Operations, Inc. (Entergy), the licensee for Indian Point Nuclear Generating Unit No. 3 (IP3), submitted a request for NRC review and approval of a technical reconciliation performed by Entergy concerning actual IP3 reactor coolant system (RCS) leakage detection capability and the technical bases cited by the NRC staff in our approval of leak-before-break (LBB) for the IP3 main coolant loop.[1] The NRC staffs approval of LBB for the IP3 main coolant loop was issued by letter dated March 10, 1986.[2] In our prior safety evaluation (SE), the NRC staff noted that the IP3 containment air radioactive particulate monitor and containment air radioactive gas monitor have, the capability of detecting one gpm [gallon per minute] change in leak rate in less than four hours. Based on current fuel performance and RCS activity, Entergy determined that the IP3 containment air radioactive gas monitor was no longer capable of achieving the referenced sensitivity. Since leakage detection sensitivity is a significant factor in demonstrating LBB behavior, Entergy submitted information in their October 25, 2001, letter to note all RCS leakage detection systems available at IP3 and requested NRC staff confirmation that the sensitivity of the installed IP3 leakage detection systems continued to support our prior LBB approval.
2.0 REGULATORY REQUIREMENTS AND STAFF POSITIONS As addressed in Title 10 of the Code of Federal Regulations Part 50, Appendix A, General Design Criteria 4, nuclear power plant structures, systems, and components important to safety shall be appropriately protected against dynamic effects, including the effects of missiles, pipe whipping, and discharging fluids, that may result from equipment failures and from events and conditions outside the nuclear power unit. However, dynamic effects associated with postulated pipe ruptures may be excluded from the facility design basis when analyses reviewed and approved by the Commission demonstrate that the probability of fluid system piping rupture is extremely low under conditions consistent with the design basis for the piping. Formal, rigorous, leak-before-break (LBB) evaluations consistent with NRC staff guidance (e.g., NUREG-1061, Volume 3, draft Standard Review Plan 3.6.3) have been accepted by the staff as an acceptable demonstration of this extremely low probability of piping rupture.[3,4]
LBB evaluations require that the throughwall critical crack size which could lead to pipe rupture under design basis loading conditions and the throughwall leakage crack size which would provide a readily detectable amount of RCS leakage under normal operating conditions be established.
The leakage crack size is established by determining what length throughwall flaw will provide ten times the amount of leakage that is expected to be detectable by the facilitys RCS leakage detection systems. The factor of ten multiplier is included as a safety factor to account for uncertainties in the evaluation of two-phase fluid leakage through the postulated crack and uncertainties in the actual capability of the facilitys RCS leakage detection system. The evaluation should then demonstrate that an acceptable margin on crack length (usually a factor of 2) exists between the critical and leakage crack sizes.
ATTACHMENT
2 As such, the leakage crack size for the LBB evaluation is directly affected by the sensitivity of installed facility RCS leakage detection systems. Generally, acceptable LBB evaluations have included the condition that facility RCS leakage detection systems be able to detect 1 gallon per minute (gpm) of leakage over an established time period. In the case of IP3, the NRC staffs original LBB approval was based on the licensees ability to detect 1 gpm of RCS leakage in the course of four hours. This capability was related to the sensitivity of the IP3 containment air radioactive particulate monitor and containment air radioactive gas monitor in the NRC staffs March 10, 1986, approval of LBB for the IP3 main coolant loop.
3.0 LICENSEE'S DETERMINATION In their October 26, 2001, letter, the licensee stated that the capability of the IP3 RCS leakage detection systems had been reassessed. Based on improved fuel integrity and lower RCS activity, the licensee concluded that although the containment air radioactive particulate monitor would continue to be able to detect 1 gpm of RCS leakage in course of four hours, the containment air radioactive gas monitor would detect 1 gpm of RCS leakage in course of 70 hours8.101852e-4 days <br />0.0194 hours <br />1.157407e-4 weeks <br />2.6635e-5 months <br />. Therefore, the licensee questioned whether the IP3 RCS leakage detection system capability remained consistent with the specific bases cited in the NRC staffs LBB approval.
The licensee concluded that, consistent with the technical requirements for demonstrating LBB behavior, the entire package of RCS leakage detection systems should be considered when reviewing the capability of the IP3 facility to monitor RCS leakage. In general, Entergy noted that the overall integrated method of leak detection at IP3 has remained essentially unchanged since the 1986 NRC SE approving LBB for the facilitys main coolant loop. Entergy noted that in addition to the IP3 containment air radioactive particulate monitor and containment air radioactive gas monitor, several other RCS leakage detection systems are available. Table 1 summarizes the licensees assessment of the current capability of two of these other leakage detection systems.
Table 1 RCS Leakage Detection System Present Assessed Capability(1)
Containment Air Radioactive Particulate Monitor (R-11) 1 gpm within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> Containment Air Radioactive Gas Monitor (R-12) 1 gpm within 70 hours8.101852e-4 days <br />0.0194 hours <br />1.157407e-4 weeks <br />2.6635e-5 months <br /> Vapor Containment (VC) Sump Monitor 1 gpm within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> Fan Cooler Unit Condensate Weir Monitor 0.5 to 1 gpm (per weir) with operator action (1)
The assessed capability of each system may be affected by specific plant operating conditions, background levels, etc.
The values listed are presented as reasonable, point value, estimates of system performance.
In addition, Entergy noted that a VC humidity detector, which was discussed in the NRC staffs 1986 LBB SE, is also available as an additional means of measuring overall leakage from water and steam systems inside containment. Further, the licensee stated that VC temperature and pressure monitoring methods may also be used to infer identified leakage inside containment. The licensee provided no specific assessment of the sensitivity level that may be expected from these systems.
3 In conclusion, the licensee determined that the overall IP3 RCS leakage detection capability remains diverse and reasonably sensitive (i.e., demonstrating an acceptable capability relative to the capability necessary to support assumptions in the original 1986 LBB approval) for RCS leakage detection. Based on this conclusion, the licensee requested that the NRC staff review and modify the specific leakage detection bases cited in the original SE consistent with the existing leakage detection systems capability at IP3.
4.0 STAFF EVALUATION The NRC staff has reviewed the information provided by the licensee. The staff has concluded that the licensee has demonstrated that the current IP3 leakage detection system capability is adequate to continue to support the technical bases cited in the staffs March 10, 1986, SE approving LBB for the IP3 main coolant loop. Additional details regarding the staffs conclusion are provided below.
An appropriate LBB evaluation may be assumed to begin with the evaluation of RCS leakage during normal power operation. The normal power operation condition is to be used since LBB approval is based on the philosophy that a subcritical throughwall flaw can be identified during normal power operation and the facility brought to cold shutdown conditions to effect a repair prior to realizing the potential for piping failure under any design basis loading condition. The concept of identifying a leak of a given magnitude (e.g. 1 gpm) in some specified period of time (e.g., one hour, four hours) ensures that the information necessary to take prompt action to place the facility in a safe condition would be readily available to the licensees operators.
Based on this integrated assessment of RCS leakage detection capability, a leakage limit can then be established consistent with the technical bases and safety factors specified in staffs guidance on LBB evaluations (e.g., NUREG-1061, Volume 3, draft Standard Review Plan Section 3.6.3). For LBB evaluations, this leakage limit is taken to be the demonstrated facility leakage detection capability multiplied by a safety factor of ten to account for uncertainties in the estimation of two-phase leakage through a postulated throughwall pipe flaw and uncertainties in the actual capability of the facilitys RCS leakage detection system. Hence, a typical facility RCS leakage detection capability of 1 gpm would result in a 10 gpm leakage limit within the LBB evaluation.
This leakage limit is then related to a specific throughwall crack length which is expected to provide that amount of leakage under normal operating conditions. This relation of the leakage limit to the corresponding throughwall flaw size is performed through the application of thermal-hydraulic computer codes which model two-phase flow through tight flaws. The leakage flaw which meets this leakage limit is then compared in length to the critical flaw which would fail the pipe under the most severe design basis loading conditions. In order to adequately demonstrate LBB, the postulated critical flaw must be greater in length then the leakage flaw by approximate a factor of 2 (or more). Finally, the leakage flaw must be shown to be stable under loads equivalent to or slightly greater than (by a specified safety factor) the limiting design basis loads.
Given the overall evaluation process described above, the NRC staff concludes that it is consistent to permit a licensee to credit or evaluate all available RCS leakage detection systems for the purpose of establishing the facilitys leakage detection capability. Reliance only on RCS leakage detection systems which are based on the assessment of containment air activity has not been imposed in prior NRC staff LBB approvals. Frequently, prior NRC staff LBB approvals have been based on facility commitments to utilize sump level/flow monitoring; containment particulate/gaseous radioactivity monitoring; containment temperature, pressure, and humidity monitoring; and/or containment air cooler condensate flow rate monitoring to establish their leakage
4 detection capability. Therefore, the licensees request to credit systems other than their containment air radioactive particulate monitor and containment air radioactive gas monitor as part of the RCS leakage detection system reassessment was consistent with the considerations accepted in other NRC staff LBB approvals.
Further, based on the considerations specified in the licensees submittal, the NRC staff has concluded that an overall IP3 RCS leakage detection system capability for detecting 1 gpm of leakage in an acceptable time frame (relative to the bases of the existing IP3 main coolant loop LBB assessment) has been established. The two systems (the containment air radioactive particulate monitor and the VC sump monitor) capable of identifying 1 gpm of RCS leakage in the course of four hours coupled with the availability of the supporting systems identified in Section 3.0 is sufficient to justify the use of a 1 gpm capability in the IP3 LBB analysis, even in the event that one of the two systems capable of detecting 1 gpm in the course of four hours becomes unavailable. Additional operator actions which may be taken or required by IP3 Technical Specifications (performance of RCS inventory balance or containment atmosphere grab sampling) also serve to further enhance the robustness of the overall IP3 leakage detection capability.
5.0 CONCLUSION
The NRC staff concludes that, based on the information provided in the licensees October 25, 2001, submittal, the demonstrated IP3 leakage detection system capability continues to support the technical bases cited in the staffs March 10, 1986, IP3 main coolant loop LBB safety evaluation.
Specifically, the licensee has supported the continued use of a 1 gpm RCS leakage detection capability to determine the length of the leakage size flaw in the facilitys licensing basis main coolant loop LBB evaluation. The licensee shall, therefore, conclude that our original March 10, 1986, SE, as supplemented by the information in this SE supplement, constitutes the technical basis for the NRC staffs approval of LBB for the IP3 main coolant loop.
6.0 REFERENCES
[1] R.J. Barrett (Entergy) to U.S. Nuclear Regulatory Commission Document Control Desk, Reconciliation of the Technical Bases of the IP3 Leak Before Break RCS Leakage Detection Capability Licensing Design Basis Documented in Mary 1986 Safety Evaluation Report, October 26, 2001.
[2] S.A. Varga (USNRC) to J.C. Brons (State of New York), Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Elimination of Large Primary Loop Ruptures as a Design Basis, March 10, 1986.
[3] United States Nuclear Regulatory Commission NUREG-1061, Volume 3, Report of the U.S.
Nuclear Regulatory Commission Piping Review Committee, Evaluation of Potential for Pipe Breaks, November 1984.
[4] United States Nuclear Regulatory Commission Draft Standard Review Plan Section 3.6.3, Leak-Before-Break Evaluation Procedures, published for comment at 52 Federal Register 32626, August 28, 1987.