ML14051A363
| ML14051A363 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 03/05/2014 |
| From: | Shawn Williams Plant Licensing Branch II |
| To: | Gatlin T South Carolina Electric & Gas Co |
| Williams, Shawn NRR/DORL 415-1009 | |
| References | |
| TAC MF2722 | |
| Download: ML14051A363 (7) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 March 5, 2014 Mr. Thomas D. Gatlin Vice President, Nuclear Operations South Carolina Electric & Gas Company Virgil C. Summer Nuclear Station Post Office Box 88, Mail Code 800 Jenkinsville, SC 29065
SUBJECT:
VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO. 1 (VCSNS)- CLOSURE LETTER CONCERNING 2012 ANNUAL EMERGENCY CORE COOLING SYSTEM EVALUATION MODEL REVISIONS REPORT (TAC NO. MF2722)
Dear Mr. Gatlin:
By letter dated June 13, 2013, the South Carolina Electric & Gas Company (SCE&G, the licensee) submitted an annual emergency core cooling system (ECCS) model revisions report pursuant to Title 10 of the Code of Federal Regulations (1 0 CFR}, Section 50.46. Staff requested additional information on December 2, 2013. SCE&G responded on January 13, 2014. The enclosure documents staff's closure evaluation.
The NRC staff determined that the licensee's June 13, 2013, report addressed the requirements contained in 10 CFR 50.46 related to estimating the effects of changes to the application of an evaluation model. However, as discussed in the enclosure, staff determined that the licensee failed to submit a 30 day report as required by 10 CFR 50.46(a)(3)(ii). The licensee has entered this issue in their corrective action program. Region II staff will follow up under the appropriate oversight process.
Docket No. 50-395
Enclosure:
Closure Evaluation cc w/encl: Distribution via Listserv Sincerely, Shawn Williams, Senior Project Manager Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
CLOSURE EVALUATION VIRGIL C. SUMMER NUCLEAR STATION, UNIT 1 EMERGENCY CORE COOLING SYSTEM EVALUATION MODEL REVISIONS REPORT INTRODUCTION Pursuant to 10 CFR 50.46(a)(3), South Carolina Electric and Gas Company, the licensee for Virgil C. Summer Nuclear Station, Unit 1, submitted a report describing "changes and enhancements to the ECCS [emergency core cooling system] Evaluation Models," and an estimate of the effects of the changes and enhancements on the predicted peak cladding temperature. The report was submitted by letter dated June 13, 2013 (Agencywide Document Access and Management System (ADAMS) Accession Number ML13169A054). The report was supplemented by letter dated January 13, 2014 (ADAMS Accession No. ML14015A139).
REGULATORY EVALUATION Acceptance criteria for emergency core cooling systems for light water nuclear power reactors are found in 10 CFR 50.46. In particular, 10 CFR 50.46(a)(3)(i) requires licensees to estimate the effect of any change to or error in an acceptable evaluation model or in the application of such a model to determine if the change or error is significant. For the purpose of 10 CFR 50.46, a significant change or error is one which results in a calculated peak fuel cladding temperature difference by more than 50 degrees Fahrenheit (°F) from the temperature calculated for the limiting transient using the last acceptable model, or is a cumulation of changes and errors such that the sum of the absolute magnitudes of the respective temperature changes is greater than 50°F.
For each change to or error discovered in an acceptable evaluation model or in the application of such a model, paragraph (a)(3)(ii) to 10 CFR 50.46 requires the affected licensee to report the nature of the change or error and its estimated effect on the limiting Emergency Core Cooling System (ECCS) analysis to the Commission at least annually. 1 If the change or error is significant, the licensee is required to provide this report within 30 days and include with the report a proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with § 50.46 requirements.
Additional clarification concerning the intent of the reporting requirements is discussed in the Federal Register (53 Fed. Reg. 35996):
[Paragraph (a)(3) of section 50.46] requires that all changes or errors in approved evaluation models be reported at least annually and does not require any further action by the licensee until the error is reported. Thereafter, although reanalysis is not required solely because of such minor error, any subsequent calculated evaluation of ECCS performance requires use of a model with such error, and any prior errors, corrected.
The NRC needs to be apprised of even minor errors or changes in order to ensure that they agree with the applicant's or licensee's assessment of the significance of the error or change and to maintain cognizance of modifications made subsequent to NRC review of the evaluation model...
1 The licensee stated in its June 13, 2013, letter that the subject report is an annual report.
Significant errors require more timely attention since they may be important to the safe operation of the plant and raise questions as to the adequacy of the overall evaluation model... More timely reporting is required for significant errors or changes... the final rule revision also allows the NRC to determine the schedule for reanalysis based on the importance to safety relative to other applicant or licensee requirements.
The NRC staff considered the discussion in the Federal Register in its evaluation of the report submitted by the licensee.
TECHNICAL EVALUATION Page 6 of 7 of Attachment II to the June 13, 2013, letter lists an "Upflow Conversion" under Line Item B., "Planned Plant Modification Evaluations," with an associated estimated effect on predicted peak cladding temperature (PCT) estimated as 148 °F. The NRC staff requested additional information to determine the nature of the upflow conversion, its implementation status, and its reporting history. In light of the fact that the estimated effect of the change was greater than 50°F, the NRC staff also requested a disposition for the requirement, pursuant to 10 CFR 50.46(a)(3)(ii) to "... include with the report a proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with 50.46 requirements... "
UPFLOW CONVERSION The supplemental letter dated January 13, 2014, described the upflow conversion in greater detail. The licensee stated, "The hardware change for this modification... consisted of plugging the existing flow holes in the core barrel between the top and second former level and machining new flow holes in the top former plates." Figure 1, included in Attachment 1 to the Enclosure to the January 13, 2014, letter provided an illustration of the core internal configuration.
Section 3-1-9, "Barrel/Baffle Effect," of WCAP-10081-NP-A, 'Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code," describes why this modification would have an effect on the ECCS evaluation. The section describes the nodalization for the barrel/baffle fluid volume differently for upflow and downflow plants. Thus, an upflow conversion would necessitate a switch from the downflow nodalization to the upflow nodalization. The NRC staff determined that this change could cause the effect on the small-break loss-of-coolant accident (SBLOCA) results that the licensee has estimated. In addition, since both the upflow and downflow nodalization schemes are explained in WCAP-10081-NP-A, the NRC staff concluded that the licensee's change did not affect the adequacy of the overall evaluation model.
Since the information provided by the licensee described the nature of the upflow conversion, and enabled the NRC staff to (1) determine its safety significance, and (2) verify the continued adequacy of the evaluation model as a whole, the NRC staff concluded that the licensee satisfied the intent of the 10 CFR 50.46(a)(3) reporting requirements.
REPORTING REQUIREMENTS The NRC staff requested additional information about the reporting and reanalysis status of the upflow conversion, because the 10 CFR 50.46 report identified it as a "planned facility modification." The wording gave the report the appearance of providing the estimated effect of a change that had not yet been implemented.
In its supplemental letter, the licensee clarified that the modification was made in fall 2009. The licensee stated that the Westinghouse SBLOCA evaluation model was used to estimate the effects of the change prior to the implementation of the upflow conversion. The licensee also provided the following information:
The results were utilized in the 1 0 CFR 50.59 evaluation for the Upflow Conversion. The SBLOCA evaluation included plant specific input values to explicitly model the impact of the Upflow Conversion on pre-accident initial conditions. These input changes were not considered changes in the Evaluation Model since {1) the SBLOCA Evaluation Model is applied to both upflow and downflow plants, (2) the input changes were not made to correct a prior error and (3) no modification in a feature of the Evaluation Model or in its application as described to the NRC in licensing documentation resulted. With the Upflow Conversion being a planned change, the peak clad temperature (PCT) change was not counted toward the accumulation of changes pertaining to 1 0 CFR 50.46 reporting requirements related to a significant change. Instead, consistent with Section 3.5 of WCAP-13451, the PCT change was included in the V. C. Summer Nuclear Station 2009 annual report provided to the NRC by SCE&G letter number RC-10-0073, dated June 7, 2010... It should be noted, Westinghouse typically shows all changes as planned until a new analysis of record is performed. In this context, planned does not mean future; it means a plant specific input change made under 10 CFR 50.59.
The licensee stated that it did not consider the upflow conversion to be an ECCS evaluation model change. However, 10 CFR 50.46(a)(3)(i) sates, "Each... holder of an operating license...
shall estimate the effect of any change to or error in an acceptable evaluation model or in the application of such a model... " While the NRC staff agrees that there was no change to the NOTRUMP Evaluation Model, the NRC staff determined that changing the analyzed nodalization to estimate the effect of an upflow conversion constitutes a change in the application of the Evaluation Model. Since the estimated effect of this change was an increase in the predicted PCT of 148°F, it was significant as described in 10 CFR 50.46(a)(3)(i).
Therefore, the portion of 10 CFR 50.46(a)(3)(ii), which states, "If the change or error is significant, the... licensee shall provide this report within 30 days and include with the report a proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with§ 50.46 requirements," was applicable with respect to this change.
In addition, the licensee referred to WCAP-13451, 'Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting," for its treatment of the PCT change. The NRC staff notes that, although this WCAP report is not NRC-approved, it defines "application" as, "The use of an Evaluation Model to calculate transient conditions during a LOCA at a specific plant. To perform this calculation, plant specific input values and initial conditions are generated and used." This definition does not specifically limit the consideration of the "application" of an evaluation model to those aspects described to the NRC in licensing documentation. Similarly, the NRC staff does not consider the application of an evaluation model to be limited to those aspects described to the NRC in licensing documentation, as the licensee suggested in its 3rd item explaining why the upflow conversion was not considered a change in the evaluation model. Furthermore, switching from one nodalization, which is better suited to model a downflow configuration, to another nodalization, which is suited to model the upflow configuration, is a change in the plant-specific input values. The NRC staff concluded that this change was a change in the application of the evaluation model.
The licensee's specific reference to WCAP-13451 2 is to a section that describes the relationship of the 10 CFR 50.46(a)(3) reporting requirements to 10 CFR 50.59. The NRC staff notes that this section of the WCAP provides additional context in determining whether an evaluation or a reanalysis is appropriate for LOCA results that are affected by plant changes. The guidance concludes that changes to the application of an evaluation model may be more appropriately addressed by 1 0 CFR 50.59, which also required annual reporting.
This section of WCAP-13451 is based on a prior revision of 10 CFR 50.59 that was eliminated in 1999, when the current form of the rule was promulgated. The NRC-endorsed guidance contained in NEI 96-07, "Guidelines for 10 CFR 50.59 Implementation," states that, 'Where changes to the facility or procedures are controlled by more specific regulations... 10 CFR 50.59 states that the more specific regulation applies." This guidance refers to 10 CFR 50.59(c)(4), which states, "The provisions in this section do not apply to changes to the facility or procedures when the applicable regulations establish more specific criteria for accomplishing such changes." Thus, the guidance contained in WCAP-13451 is based on a prior revision of 10 CFR 50.59, and the guidance is inapplicable to the current revision. The more specific reporting requirements contained in 10 CFR 50.46(a)(3) apply, especially given that the revised reporting requirement in 10 CFR 50.59(d) is now biennial, rather than annual.
In summary, the NRC staff determined that the licensee's estimation of the effect of the upflow conversion on the predicted PCT for the SBLOCA analysis, by using a different reactor vessel nodalization scheme, was a change in the application of the ECCS evaluation model. Because the estimated effect of the change exceeded 50°F, the change was significant. This conclusion was based on the following considerations:
The change in nodalization required to estimate the effect of the upflow conversion was a change in the plant-specific inputs, and thus to the application of the evaluation model.
The guidance contained in WCAP-13451, which the licensee referenced, refers to a prior revision of 10 CFR 50.59.
The licensee's invocation of 10 CFR 50.59 with respect to concluding that the conversion was not a change to the evaluation model, was irrelevant because 10 CFR 50.59 defers to the more specific regulations contained in 10 CFR 50.46.
The licensee stated that the effects of the upflow conversion were estimated by Westinghouse in a letter that was provided from Westinghouse to the licensee in January 2009. Since the upflow conversion was implemented in fall 2009, the licensee had estimated the effect of the change in the application of the ECCS evaluation model by the time the plant modification was implemented. Therefore, the NRC staff concluded that the licensee had already fulfilled the requirement, pursuant to 10 CFR 50.46(a)(3)(i), to estimate the effect of a change to the application of the evaluation model to determine whether it is significant, prior to the implementation of the plant modification. Thus, the licensee was required, pursuant to 10 CFR 50.46(a)(3)(ii), to submit a report describing the change to the application of the evaluation model and providing its estimated effect on the predicted peak cladding temperature for the limiting LOCA, and including a proposed schedule for providing a reanalysis or taking other 2 WCAP-13451 was published in 1992.
action as may be appropriate to show compliance with § 50.46 requirements, within 30 days.
Since the licensee included the estimated effect of the upflow conversion in its June, 2010, annual report of changes to the ECCS evaluation models, the NRC staff determined that the licensee did not provide the report within 30 days, as required.
RE-ANALYSIS REQUIREMENT In light of the fact that the estimated effect of the change was greater than 50°F, the NRC staff requested that the licensee provide a disposition for the requirement, pursuant to 10 CFR 50.46(a)(3)(ii) to"... include with the report a proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with 50.46 requirements... "
In its response dated January 13, 2014, the licensee stated the following:
The majority of the inputs for the Upflow Conversion remain unchanged from the V. C.
Summer SBLOCA analysis of record. Key changes included the plant as an upflow baffle-barrel configuration and associated reactor vessel hydraulic and geometric data.
A partial break spectrum with an upflow baffle-barrel configuration was evaluated using the NOTRUM-EM to confirm the limiting break size. Fuel burnup sensitivity studies were performed for the limiting break size to determine the worst times in life that maximize the resulting PCT and cladding oxidation. The results are summarized in Section 15.3.1.2.7 of the FSAR. Overall, the results demonstrate that the requirements of 10 CFR 50.46 continued to be met for this planned plant modification.
The NRC staff reviewed the information contained in the FSAR and verified that it reflected an updated analysis for the upflow conversion, and included consideration of a spectrum of break sizes sufficient to demonstrate that the limiting break had been identified. Since the licensee's estimate was generated by the use of explicit execution of the approved EM, and the estimate included consideration of a variety of break sizes, the NRC staff concluded that the licensee had inherently satisfied the re-analysis requirement contained in 10 CFR 50.46(a)(3)(ii), such that there was no need to propose a schedule for providing a reanalysis or taking other action as may be needed to show compliance with§ 50.46 requirements.
CONCLUSION Based on the considerations discussed above, the NRC staff determined that the licensee's report, dated June 13, 2013, and submitted pursuant to 10 CFR 50.46(a)(3), addressed the requirements contained in 1 0 CFR 50.46 related to estimating the effects of changes to the application of an evaluation model. However, the licensee's June, 2010, report identified a significant change to the application of the evaluation model related to the upflow conversion.
This significant change was not reported within 30 days, as required by 10 CFR 50.46(a)(3)(ii).
Because the estimated effect of the upflow conversion did not cause the results of the ECCS evaluation to exceed 10 CFR 50.46(b) acceptance criteria, and because the estimate was calculated using the NRC-approved NOTRUMP evaluation model, the NRC concluded that the estimate satisfied the intent of the 10 CFR 50.46 reporting requirements. In addition, since the licensee performed a sufficient break spectrum to demonstrate that the limiting break size had been identified, the NRC staff determined that the licensee had inherently satisfied the re-analysis requirement contained in 10 CFR 50.46(a)(3)(ii).
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