ML20035A291
| ML20035A291 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/19/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20035A289 | List: |
| References | |
| REF-GTECI-A-46, REF-GTECI-SC, TASK-A-46, TASK-OR GL-87-02, GL-87-2, NUDOCS 9303250096 | |
| Download: ML20035A291 (5) | |
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ENCLOSURE SUPPLEMENTAL SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
OF THE TENNESSEE VALLEY AUTHORITY'S i
RESPONSE TO RE00EST FOR ADDITIONAL INFORMATION CONCERNING 120-DAY RESPONSE TO SUPPLEMENT NO. 1 i
0F GENERIC LETTER 87-02 i
FOR BROWNS FERRY NUCLEAR PLANT. UNITS 1. 2 AND 3 DOCKET NOS. 50-259. 50-260 AMD 50-296 i
INTRODUCTION l
By letter dated November 19, 1992, the staff issued a safety evaluation of the Tennessee Valley Authority's (TVA, the licensee),120-day response to l
Supplement No.1 of Generic Letter (GL) 87-02 for the Browns Ferry Nuclear Plant (BFN), Units 1, 2 and 3.
'Within this evaluation, the staff identified i
specific areas of the licensee's 120-day response which required additional l
information.
By letter dated January 19, 1993, the licensee provided its response to the staff's request. The staff's supplemental safety evaluation of the additional information is provided below.
DISCUSSION AND EVALUATION The licensee was requested to provide a more explicit commitment to the Generic Implementation Procedure, Revision 2 (GIP-2), as corrected on February 14, 1992, in its entirety, including' both the Seismic Qualification 1
Utility Group's (SQUG) commitments and the implementation guidance. The licensee responded that its program will be implemented in accordance with i
GIP-2, Part I, Section 1.3.
The licensee noted that under Section 1.3 of i
GIP-2, Unresolved Safety Issue (USI) A-46 licensees may substitute clearly equivalent methods'for implementation guidance without prior notification of NRC, but that significant or programmatic deviations should be reported as early as possible, but no later than the final summary report.
The staff's concern was whether the licensee intended to commit to the entire GIP-2, including both the SQUG commitments and the implementation guidance.
In a conference call on March 3,1993, the licensee clarified that it commits to comply with the entire GIP-2, including both the SQUG commitments and the implementation guidance, and that any deviations from the implementation i
guidance will be in accordance with Part I, Section 1.3 of GIP-2. The licensee's response is therefore considered acceptable.
y The licensee was requested to provide a more precise completion date, consistent with the provisions of Supplement No. I to GL 87-02, for resolution of USI A-46 at BFN Units 2 and 3.
The licensee responded that it will 9303250096 930319 U
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i complete its USI A-46 implementation program at BFN Units 2 and 3 by March 19, 1996, provided that the staff approves its in-structure response spectra to be used to resolve USI A-46 by March 19, 1993. Additionally, for Unit 3, the licensee stated that, in lieu of satisfying previous restart commitments pertaining to conduit and cable trays (including their supports) it will complete the portion of its USI A-46 program pertaining to these items prior t
to Unit 3 restart.
The staff finds the licensee's proposed implementation schedules acceptable for BFN Units 2 and 3.
The staff also finds that, for Unit 3, the licensee's plan to complete the portion of its implementation i
program addressing conduit (excluding flexible conduit which is discussed below) and cable trays, including their supports, prior to Unit 3 restart, is an acceptable alternative to implementing its previously approved restart programs for these items in Unit 3.
The staff notes that the licensee, in its September 21, 1992, 120-day response to the GL supplement, committed to completing its Unit 1 USI A-46 implementation program prior to unit restart.
This schedule was approved by the staff in its November 19, 1992 letter.
1 The staff requested that the licensee specify the criteria and procedures which it intends to use for the interim qualification of flexible conduit at BFN, Units 1 and 3, and for long-term qualification r flexible conduit at BFN Units 1, 2 and 3.
This issue was carried over fro: ne Unit 2 restart program, and only part of it is within the scope of the resolution of USI A-46.
During the Unit 2 restart effort, the staff reviewed and approved interim criteria for addressing seismic and thermal motion concerns with flexible conduit attached to electrical equipment covered by 10 CFR 50.49.
For flexible conduit attached to electrical equipment r.ot covered by 10 CFR 50.49 (i.e., important to safety but located in a mild environment), the licensee committed to evaluate this conduit as part of its resolution of USI A-46.
In its response, the licensee stated that, for BFN Units 1, 2 and 3, the seismic qualification of flexible conduit, other than flexible conduit connected to electrical equipment covered by 10 CFR 50.49, will be included as part of the resolution of USI A-46 in accordance with Section 8 of GIP-2.
Specifically, the guidance in GIP-2, Section 8 and Appendix D, Section D.4, which addresses seismic interactions including flexibility of attached lines to safety-related equipment, will be used to evaluate the adequacy of the flexible conduit. Additionally, for flexible conduit in BFN Units 1 and 3 which is attached to electrical equipment covered by 10 CFR 50.49, the licensee stated that it will inspect and evaluate this conduit prior to unit restart using the acceptance criteria reviewed and accepted by the staff for i
the Unit 2 restart program.
With regard to flexible conduit attached to electrical equipment not covered I
by 10 CFR 50.49, the licensee's plan to evaluate such conduit in accordance with the guidance in GIP-2, Section 8 and Appendix D is acceptable. However, i
since GIP-2 does not prescribe any specific procedure or acceptance criteria 4
for evaluating the conduit, the licensee should identify, and submit for staff review, the general approach, including the procedure and acceptance criteria, f
which it intends to use for performing the evaluations. The issue concerning flexible conduit attached to electrical equipment covered by 10 CFR 50.49 is i
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~ l not entirely within the scope of USI A-46, since, unlike the flexible conduit restart program, USl A-46 does not require the licensee to address potential thermal movement due to design basis accident conditions.
However, since this issue was identified in the licensee's response to the GL supplement, the j
staff provides the following evaluation of the licensee's position. The J
licensee's Unit ? restart program for flexible conduit attached to electrical equipment covered by 10 CFR 50.49 was previously reviewed and accepted on an interim basis only. Therefore, the staff finds that the licensee's plan to implement the Unit 2 restart program for Units 1 and 3 is acceptable as an interim measure to support unit restart. The licensee should submit long term criteria for staff review and approval, or alternatively, provide a justification why the interim position used for Unit,. restart is adequate for long term application for Units 1, 2 and 3.
Any future submittals addressing this issue should be made separate from the resolution of USI A-46.
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The licensee was requested to inform the staff if it intended to change its licensing basis via 10 CFR 50.59 to reflect a commitment to the USI A-46 methodology prior to receipt of the staff's plant-specific safety evaluation (SE).
The licensee indicated that it does not intend to change its licensing basis in the manner described prior to receipt of a plant-specific SE.
7 In the November 19, 1992 letter, the staff requested TVA to provide more j
explicit information regarding the methodology for generating the in-structure response spectra (IRS) for BFN.
From TVA's January 19, 1993 response, the staff determined the following:
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1.
TVA used the 1940 N-S El Centro earthquake time history with a peak ground acceleration of 0.2g as an input motion for development of the IRS for the Category I structures. TVA also used an artificial time history with a peak ground acceleration of about 0.29 as an alternative input motion for development of the IRS for the subsystems (i.e.,
structural elements, piping, and components) housed in the Category 1 i
s t ruc*.ure s.
This approach was accepted by NRC in the safety evaluation report (SER), NUREG-1232, Volume 3, Supplement 1.
This SER stated that the artificial time history can only be used to generate the IRS for the j
evaluation of. the subsystems, and the El Centro time history, as i
committed to in the Final Safety Analysis Report (FSAR), can only be used for calculating the se'smic loads of structures.
l TVA illustrated that both ground response spectra obtained from the time
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histories nearly enveloped the 5 percent damped ".icensing basis 1
spectrum.
However, no information is given in the licensee response, i
staff SER, or FSAR regarding the adequacy of the artificial time history for matching a target power spectral density (PSD) function compatible with the design response spectra.
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2.
Lumped mass stick models were used in generating the IRS. Modal j
analyses for the lumped mass systems were performed.
Using the mode shapes and frequencies together with the time history, the structural i
responses were obtained.
The 20-Hz cutoff frequency with the zero i
j period acceleration (ZPA) was used for the time history analyses, j
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3.
No soil-structure interaction was considered in the analyses of the reactor building, stack and pumping station structures since they are founded on bedrock. The' input motion was directly applied at the base of the structural models.
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For the analyses of the structures founded on soil (e.g., the diesel generator building, standby gas treatment building, etc.), TVA used soil amplification factors to account for the effects of soil-structure interaction. The methods of calculating the horizontal and vertical soil amplification factors were reviewed and accepted by NPC as described in the SER, NUREG-1232, Volume 3, Supplement 1.
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Three separate analyses were performed for the north-south, east-west, and vertical directions of the structures.
Coupling effects 'vetween the horizontal and vertical responses were considered for soil supported-structures. However, the coupling effects were not considered for rock supported structures.
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The developed IRS based on the El Centro time history were not peak broadened.
However, the developed IRS based on the artificial time history were peak broadened by 110 percent and 115 percent for rock supported structures and soil supported structures, respectively, to produce design IRS.
After reviewing the licensee's response, the staff concludes that the method used by the licensee to generate the IRS is adequate and acceptable. However, the IRS described by the licensee's response should be treated as median-centered response spectra due to the lack of considerations in the dynamic analyses of:
(1) the effect of the random adoption of the 20-Hz cutoff frequency, (2) the impact of use of soil amplification factors in lieu of a comprehensive soil-structure interaction analysis, (3) the extent of conformance to a target power spectral density (PSD) function of the artificial '.ime history used, and (4) the effect of insufficient peak broadening. These conclusions are based on an assumption that statements made in the licensee's response, and in procedures used to generate the floor response spectra, correctly reflect the FSAR and other licensing bases. The i
staff may perform an audit of the FSAR on an as needed basis.
1 CONCLUSIONS i
Based on the licensee's January 19, 1993, submittal, as clarified by the March 3, 1993 conference call, the staff finds that the licensee's commitment to implement the GIP-2 in its entirety, including both the SQUG commitments and the implementation guidance, is acceptable for resolving USI A-46 at BFN Units 1, 2 and 3.
The implementation schedules proposed by the licensee for BFN Units 2 and 3 are within the 3-year response period requested by the staff in Supplement No. I to GL 87-02 and are therefore acceptable.
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The licensee's plan to complete the conduit (excluding flexible conduit) and cable tray, including their supports, portions of its USl A-46 program for i
Unit 3 prior to restart, in lieu of completing the Unit 3 conduit and cable i
tray restart programs, is acceptable.
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The licensee's plan to use the guidance in GIP-2, Section 8 and Appendix D to l
evaluate flexible conduit attached to electrical equipment not covered by 10 CFR 50.49 (i.e., important to safety but located in a mild environment) is acceptable. However, the licensee should describe and submit for staff l
review, the general approach, including the procedure and acceptance criteria, which will be used to perform the evaluations.
The licensee's plan to implement the Unit 2 restart program for flexible l
conduit attached to electrical equipment covered by 10 CFR 50.49 is acceptable on an interim basis to support unit restart efforts.
The licensee should r
submit long term criteria for staff review and approval, or alternatively, l
provide a justification why the interim position used for Unit 2 restart is 4
adequate for long term application for Units 1, 2 and 3.
The licensee should l
address this issue separate from the resolution of USI A-46.
t The licensee's methodology for generating the IRS is acceptable, subject to the aforementioned considerations.
l Principal Contributors:
M. McBrearty and Y. Kim i
4 Date: March 19, 1993 l
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