0CAN081401, Response to Request for Additional Information (RAI) Associated with Near-Term Task Force (NTTF) Recommendation 2.1, Seismic Hazard and Screening Report

Response to Request for Additional Information (RAI) Associated with Near-Term Task Force (NTTF) Recommendation 2.1, Seismic Hazard and Screening Report

ML14233A275
Person / Time
Site:	Arkansas Nuclear
Issue date:	08/21/2014
From:	Jeremy G. Browning Entergy Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
0CAN081401
Download: ML14233A275 (6)

Text

Entergy Operations, Inc.

1448 S.R. 333 Russellville, AR 72802 Tel 479-858-3110 Jeremy G. Browning Site Vice President Arkansas Nuclear One 0CAN081401 August 21, 2014 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk 11555 Rockville Pike Rockville, MD 20852

SUBJECT:

Response to Request for Additional Information (RAI) Associated with Near-Term Task Force (NTTF) Recommendation 2.1, Seismic Hazard and Screening Report Arkansas Nuclear One - Units 1 and 2 Docket Nos. 50-313 and 50-368 License Nos. DPR-51 and NPF-6

REFERENCES:

1. NRC letter to Entergy, Request for Information (RFI) Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3 of the NTTF Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 2012 (0CNA031208)

(ML12053A340)

2. Entergy Letter to NRC, Seismic Hazard and Screening Report (Central Eastern United States Sites), Response to NRC RFI Pursuant to 10 CFR 50.54(f) Regarding Recommendation 2.1 of the NTTF Review of Insights from the Fukushima Dai-ichi Accident, dated March 28, 2014 (0CAN031404) (ML14092A021)

3. NRC Letter to Entergy, RAI Associated with NTTF Recommendation 2.1, Seismic Hazard and Screening Report, dated July 16, 2014 (0CNA071401) (ML14195A059)

Dear Sir or Madam:

On March 12, 2012, the NRC issued Reference 1 to all power reactor licensees. By Reference 2, Entergy Operations, Inc. (Entergy) provided the Seismic Hazard and Screening Reports for Arkansas Nuclear One (ANO) requested by Reference 1. In Reference 3, the NRC issued RAIs related to these reports with a response requested by August 15, 2014. During a subsequent teleconference with the NRC staff, the Entergy Senior Manager of Fleet Regulatory Assurance discussed a due date extension to August 21, 2014. The attachment to this submittal provides Entergys responses to the RAIs.

This letter contains no new regulatory commitments. If you have any questions or require additional information, please contact Stephenie Pyle at 479.858.4704.

0CAN081401 Page 2 of 2 I declare under penalty of perjury that the foregoing is true and correct. Executed on August 21, 2014.

Sincerely, ORIGINAL SIGNED BY JEREMY G. BROWNING JGB/nbm

Attachment:

RAI Responses cc: Mr. Marc L. Dapas Regional Administrator U. S. Nuclear Regulatory Commission, Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Mr. John Hughey MS 13-C5 One White Flint North 11555 Rockville Pike Rockville, MD 20852

Attachment to 0CAN081401 Request for Additional Information (RAI) Responses

Attachment to 0CAN081401 Page 1 of 3 RAI Responses

1. The licensee states, in Appendix B of the submittal date March 28, 2014, that the minimum plant level high-confidence-low-probability of failure (HCLPF) for Units 1 and 2 is 0.3 gravity (g) peak ground acceleration (PGA). Section 2.0 of the submittal states that the Individual Plant Examination of External Events (IPEEE) commitments and modifications that were required to achieve the plant level HCLPF have been completed.

For the purpose of understanding the significant IPEEE commitments made by the licensee, the NRC staff reviewed the Staff Evaluation Report (SER) for ANO, Units 1 and 2, dated February 27, 2001 (ADAMS Accession No. ML010600244). The staff noted a few potential discrepancies between the SER and the licensee's technical basis for assuming a 0.3g plant HCLPF in the screening report. For example, SER, Table 3.5-1, reported that emergency diesel fuel tanks A/B (Units 1 and 2) have HCLPFs of 0.2g PGA (capacity controlled by bolt shear). Another example is the Unit 2 480 volt (V) load switchgear which has a reported HCLPF of 0.27g PGA (controlled by tension on the plug welds). In addition, SER Table 7-1, "Opportunities for Plant Improvements," states that the emergency diesel fuel tank bolt and 480V switchgear issues were being resolved by either making plant improvements or determining that further plant improvements are not cost beneficial relative to the corresponding safety improvement.

Based on the above observations, it is not clear if the current designs of the emergency diesel fuel tank and 480V switchgear have been enhanced to have a HCLPF greater than 0.3g PGA. In order for the staff to confirm the licensees basis for satisfying the Screening, Prioritization and Implementation Details (SPID) prerequisites (SPID, Section 3.0), the staff requests clarification on this issue.

Based on a review of the HCLPF calculations for ANO, Unit 1 (ANO-1) and Unit 2 (ANO-2),

Entergy Operations Inc. (Entergy) concluded the switchgear referenced as an example in RAI#1 intended to refer to ANO-2 4160 V switchgear 2A-3 and 2A-4 Shutdown Equipment List (SSEL) components. An internal review determined 2A-3 and 2A-4 to be the only switchgear having a HCLPF of < 0.30 g. As such, the following response addresses ANO-2 4160 V 2A-3 and 2A-4 SSEL components.

The current configurations for both the ED fuel tank and the 4160 V switchgear have demonstrated seismic HCLPF levels at or above the 0.3 g Review Level Earthquake (RLE) levels as reported in responses to the NRC original IPEEE RAIs. No physical equipment modifications were required to achieve the plant level HCLPF for the ED fuel tanks or the 4160 V vital switchgear. Reassessments of the original IPEEE HCLPF calculations were conducted using the accepted criteria for IPEEE seismic evaluations to verify meeting the 0.3 g HCLPF values reported for ANO. Overly conservative assumptions had been used previously for both items of equipment, which had resulted in the original HCLPF values being below the 0.3 g level. The assumptions, as well as their associated reassessments, are described below.

1. ED Fuel Tanks IPEEE HCLPF Assessment

Attachment to 0CAN081401 Page 2 of 3 The ED fuel tanks are horizontal saddle supported tanks anchored to a concrete base slab of a storage vault in the ANO yard. The original IPEEE HCLPF evaluation used the Unresolved Safety Issue A-46 (USI A-46) model and methodologies to develop a conservative estimate of 0.2 g for the HCLPF that was reported in the IPEEE report.

The A-46 evaluation used anchorage capacity criteria which was valid for the A-46 program, but was somewhat conservative relative to the structural code criteria allowed for the IPEEE assessments using the seismic margin methodology (e.g. EPRI 6041). A reevaluation of the anchorage capacity following the guidance of Appendix D of ACI 349-06 provides a more appropriate HCLPF level capacity of the anchorage. Using the revised anchorage capacity and the RLE loads determined from the original IPEEE calculation (Calculation 95-SQ-1021-02), the HCLPF is calculated to be 0.36 g PGA.

Thus, the ED Fuel Tanks have been shown to have seismic capacity exceeding the 0.3 g RLE using the criteria established for the IPEEE evaluations.

2. 4160 V Switchgear IPEEE HCLPF Assessment The original IPEEE evaluation of the 4160 V switchgear (SSEL Components 2A-3 and 2A-4) was based on the anchorage configurations that could be physically verified during the ANO IPEEE plant walkdown. Cabinet access was restricted at the time of the walkdown, and the walkdown team was able to view only part of the weld locations anchoring the switchgear. The anchorage confirmed during these walkdowns consisted of two rows of welded connection points, one set in the front of the cabinet and one set towards the middle of the cabinet. The back section of the switchgear assembly could not be visually verified by the walkdown team without complete removal of the large switchgear breaker. However, a third row of anchorage locations was illustrated on the switchgear design/installation drawings. The IPEEE team conservatively based the original seismic HCLPF calculation on weld locations visually confirmed in the field and did not account for the third row of welds. This evaluation resulted in the HCLPF value of 0.27g, which was reported in the original IPEEE submittal for ANO. In order to address the 0.27 g HCLPF being slightly below the 0.3 g RLE target, Entergy performed a subsequent walkdown during an ANO outage and was able to confirm the additional welds that anchored the switchgear to the third embedded steel anchor plate. Based on this actual anchorage configuration, the revised (more realistic and in conformance with IPEEE anchorage methods/criteria) HCLPF is calculated to be 0.42 g.

Since both the ED fuel tanks and the 4160 V switchgear units demonstrate a 0.3 g PGA or greater HCLPF, no enhancements to either piece of equipment were required or implemented to meet the 0.3 g PGA plant level HCLPF.

2. In Section 4. 7 of Appendix B to the licensee's Near-Term Task Force (NTTF)

Recommendation 2.1 submittal dated March 28, 2014, non-seismic failures and human actions are discussed, including Reference 6.13 (Entergy Letter to NRC, Arkansas Nuclear One - Units 1 and 2, Docket Nos. 50-313 and 50-368, License Nos.

DPR-51 and NPF-6, Additional Information Pertaining to Generic Letters 87-02 and 88-20, dated March 30, 1999 (0CAN039901), ADAMS Accession Number ML080070325) in an IPEEE RAI response on this topic. However, the subsequent text in the NTTF Recommendation 2.1 submittal that describes what the licensee did to address this

Attachment to 0CAN081401 Page 3 of 3 topic appears to differ from the IPEEE RAI response description. Specifically, the NTTF Recommendation 2.1 submittal states that the developed fault tree took no credit for components on the IPEEE Safe Shutdown Equipment List (SSEL) in calculating a conditional core damage probability. However, the IPEEE RAI response states that the fault tree was developed by removing components not on the IPEEE SSEL and, as such, the calculation only credits the IPEEE SSEL components. Please clarify how non-seismic failures were determined to be insignificant contributors for the IPEEE seismic evaluation.

Appendix B, Section 4.7, of the March 28, 2014 submittal (Entergy Letter 0CAN031404) refers to the IPEEE RAI responses with respect to non-seismic failures. Entergy intended the description of the treatment of non-seismic failures in the March 28, 2014, submittal would to be identical to the IPEEE RAI response.

To clarify, a fault tree was developed from the detailed plant fault tree, taking no credit for components not on the IPEEE SSEL, and quantified to determine the conditional core damage probability, ignoring seismic failures of components.

For additional clarification, the following excerpt from the original RAI response (Entergy Letter 0CAN039901) is included below:

"To assess just this point, a fault tree was constructed by removing the components not on the IPEEE safe shutdown component list from the detailed plant fault tree for each of the units. The quantification of these fault trees using the nominal equipment reliability values provided a 0.3g peak ground acceleration conditional core damage probability of less than .1178 independent of the seismic event. Therefore, the overall core damage frequency from a 0.3 peak ground acceleration event is insignificant."