ML20092A762
| ML20092A762 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 02/06/1992 |
| From: | Zeringue O TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9202100276 | |
| Download: ML20092A762 (12) | |
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1A Tennessee Vattey Authcuity Post Othce Boa 2000. DocAs Oatsma 3MA) 0,J.'ike'Zenngue,
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FEB 0 61992 U.S. Nuclear' Regulatory Commission ATTN -- Document Control Desk Washington,_D.C. 20555-4 Gentlemen In the-Matter of
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Docket Nos. 50-259 Tennessee Valley Authority
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50-260 50-296 BROWNS FERRY NUCLEAR PLANI-(BFN).- LOWER DRYWELL PLATFORMS AND
-MISCELLANEOUS' STEEL SEISMIC ~ CRITERIA Reference NRC letter dated December:12,-1991, " Request for Additional
.Information Regarding Browns Ferry Drywell and Miscellaneous Steel Design Criteria, Units 1, 2, and 3 (TAC NOS. M80618, M80619, and M80620)"
This letter _-is-in response to the referenced-request for: additional
~ information regarding BFN's criteria'for-the. seismic qualification'of the lower drywell steel platforms and miscellaneous-steel. The enclosure to this letter provides a point by point response to'each NRC. request.
There are no commitments contained in this letter.
If you-have any questions, please~ contact R.:R.-Baron,-Manager of Site Licensing, at (205) 729-7566.
. Sincerely, s
JO J. Zering e
. Enclosure cc:- Seefpage 2'
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-9202100276 920206-I PDRa-ADOCK 05000259
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2 U.S. Nuclear Regulatory Commisalon FEB 0 019M Enclosure ec (Enclosure):
NRC Resident InsPceter Brovns Ferry N.: lear Plant Dmi'- lo: Bo. 63/
Athens, Alt.oama 35611 Mr. Th brry M. Ross, Project Manager U.S. *.4uclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. B. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 e
l ENCLOSURE BROWNS FERRY NUCLEAR PLANT (BFN)
CRITERIA FOR THE SEISMIC QUALIFICATION OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL The NRC's December 12, 1991 request for additional information regarding the BFN criteria for the seismic qualification of the lower drywell steel platforms and miscellaneous steel was in response to TVA's June 12, 1991 letter.
TVA's letter is hereafter referred to as the " Reference".
NRC Request 1.
"On Page 8 of the Reference, it is stated that "TVA has demonstrated compliance of the design criteria with the FSAR requiremente."
(a)
Identify and provide the specific FSAR requirements."
TVA Responses As part of the Browns Ferry Unit 2 restart effort, TVA performed a FSAR verification program that reconciled licensing commitments with the design criteria. This included a verification that the FSAR and design criteria were in agreement. The FSAR commitments related to the seismic qualification of the lower drywell steel platforms are located in FSAR Section 12.2.2.7.1 and in Table 12.2-16.
The FSAR changes required to reflect the current criteria for the seismic qualification of the lower drywell steel platforms and miscellaneous steel have been made available for NRC review and will be incorporated into the next annual FSAR update.
There are no explicit FSAR commitments for the seismic qualification of miscellaneous steel as a class of
. commodities. However, there are discussions of the seismic qualification of individual miscellaneous steel commodities in the FSAR.
For example:
FSAR Section 3.5, Control Rod Drive Housing Supporte, states that the American Institute of Steel Construction (AISC) Specification was used in the design of the CRD housing support system. However, to provide a structure that absorbs as much energy as practical without yielding, the allowable tension and bending stresses were taken as 90 percent of yield, and the shear stress as 60 percent of yield. These are 1.5 times the corresponding AISC allowable stresses of 60 percent and 40 percene of yield.
FSAR Section 12.2.2.3.3, Reactor Support Pedestal, states that the ring girder is designed according to AISC code Specifications, t
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4 ENCLOSURE Pape 2 of 10 BROWNS FERRY NUCLEAR PLANT (BFN)
CRITERIA FOR THE SEISMIC QUALIFICATION OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL (CONTINUED)
FSAR Section 12.2.2.5, Reactor Building Crane, states that structural portions of the bridge and trolley were fabricated from A-36 steel, in accordance with section 1.23, Part I, of the " Specifications for the Design, Fabrication, and Erection of Structural Steel for Buildinge," as adopted by the American Institute of Stoel Construction.
Load combinationa used in designing the crane, with corresponding stressen, are listed ut Tables 12.2-14 and 12.2-15.
FSAR Section 12.2.2.6, Sacrificial Shield Wall, states that the AISc Specification for the Design, Fabrication, and Erection of Structural Steel for Duildings, adopted April 17, 1963, la used in the design of the steel in the sacrificial shield wall.
(NOTE: A change to the FSAR has been initiated which will revise this section to allow the une of the eighth edition of the AISC Specification for structural re-design or re-evaluation.)
FSAR Section 12.2.2.7.2, Support Steel for Pipe Guiden Inside Drywell states that the stresses in all componente of the supports are less than 90 percent of yield for tension and bending and 60 percent of yield for ahear.
These are 1.5 times the corresponding AIsc allowable stresses of 60 percent and 40 percent of yield.
The pipe guideo included in this section are for the Main Steam and Feedwater Systems. The guidea protect the nozzles, attached to the drywell, after a rupture of the pipe inside the-drywell.
- FSAR Section 12.2.5.2, Flood Protection Doors, states that all steel fabrication for the doors for the two exterior openings in the Radwaste Building was in accordance with the applicable requiremente of the American Institute of Steel Construction. Load combinations used in designing the doors with corresponding allowable stresses are listed in Tables-12.2-39 and 40.
FSAR Section 12.2.7.1.2, Personnel Access Doors, describes the doore that provide personnel access to the Residual Heat Removal Service Water (RHRSW) purap compartments. All steel fabrication was in accordance with the applicable requirements of the AISc. Load combinatione used in designing the (a)ra with corresponding allowable stresses are listed in Table 12.2-41.
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ENCLOSURE Page 3 of 10 BROWNS FERRY NUCLEAR PLANT (BFN)
CRITERIA FOR THE SEISMIC QUALIFICATION OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL (CONTINUED)
PSAR Section 12.2.8.2, Access Doors, describes the four doors that provide access to the diesel generator uni +.s and the one door that provides access to the Co ' room. All steel fabrication was in a
accordance with the applicable requirements of the American Institute of Steel Construction. Load combinations used in designing the doors with corresponding allowable stresses are listed in Table 12.2-30.
FSAR Section 12.2.8.4, Portable Bulkhead, discusses the portable bulkhead that is part of the Diesel-Generator Building flood protection.
Load combinations and corresponding allowable stresses used in designing the bulkhead are listed in Table 12.2-42.
All steel fabrication was in-accordance with the applicable requirements of the American Institute of steel Construction.
FSAR Section 12.2.9.2, Doors, describes the equipment access lock doors that provide an_ air lock betwee. the Reactor Building and outside entrance.
Load combinations used in designing the structural portions of the d(ors with corresponding allowable stresses are listed in Table 12.2-33.
All steel fabrication was in accordance with the applicable requirements of the American Institute of Steel Construction.
FSAR Section 12.2.9.3, Flood Gates, discusses the equipment access flood gate that is located on the outside face of the equipment access lock and is part of the Reactor Building flood protection.
Icad combinations and corresponding allowable stresses used in designing tne gate are listed in Table 12.2-43.
These examples are not intended to be an all inclusive list of miscellaneous steel commodities discussed in the FSAR.
However, they do represent a cross section of the types of commodities considered to be miscellaneous steel and the seismic design commitments and level of detail contained in the FSAR.
NRC Requents (b)
" Discuss if the FSAR requiremente cover steel platforms as well as miscellaneous steel.
If not, please provide the applicable requirements."
ENCLOSURE Page d of JO BROWNS FERRY NUCLEAR PLANT (BFN)
CRITERIA FOR THE SElSMIC QUALIFICATION OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL (CONTINUED)
TVA Response The FSAR commitments for the seismic qualification of the lower drywell steel platforms and miscellaneous steel are discussed in the response to Item 1(a) above. The detailed requirements for the seismic qualification of the lower drywell steel platforms and miscellaneous steel are provided in Attachment F t
BFM General Design Criteria BFN-50-C-7100, Design of Civil Structures, RevisaUn 2,-dated May 15, 1991, which was included as an enclosure to TVA's June 12, 1991 submittal.
NRC Requests (c)
" Describe how the design criteria submitted in the Reference satisfy each FSAR requirement."
TVA Respon=e Verification that the design criteria satisfy the FSAR commitments was based on an extensive comparison between the sixth and eighth edition of the AISC code. -The conclusion of this comparison was that the overall margins embodied in the FSAR requirements had not been reduced. The major areas that show the overall margins have not.been reduced are: -
- 1) The stress allowables for the operating basis earthquake use basic AISC code allowables without any increase in the code allowable stress.
- 2) The stress allowables for the safe shutdown earthquake use an increase in the basic AISC code allowable stress of 50 percent but has an upper cap of nine tenths of yield.
The comparison between sixth and eighth editions of the AISC code has been made available for NRC review.
As previously stated, the basic allowable stresses for miscellaneous steel commodities as a class are not explicitly specified in the FSAR.
However, the allowables currently used for the seismic qualification of miscellaneous steel commodities are in agreement with those used for the lower drywell steel platforms and envelope the FSAR commitments.
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ENCLOSURE' Page $ of 10 BROWNS FERRY NUCLEAR PLANT (BFN)
CRITERIA FOR THE SEISMIC QUALIFICATION OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL (CONTINUED)
NRC. Requests (d)
" Provide examples for key items demonstrating compliance of your proposed critoria with the applicable FSAR requirements."
TVA Response Refer to TVA's response to Question IC.
NRC Request:
2.
"Does miscellaneous steel mean structural steel other than lower drywell steel platfcrms at elevations 566' and 584' 9 "7 If so, are the criteria shown in FSAR Table 12.2-13 the criteria for miscellaneous steel? If not, provide a comprehensive discussion as to what the
-miscellaneous steals are and where in the FSAR applicable criteria are provided."
TVA Responses Miscellaneous steel includes structural shapes that range from main structural steel building features to items as small as ladders and hatch covers.
The allowables shown in Table 13 are for the reactor building super structure, which le net c llaneous steel commodity.
Pages 1 and 2 of to TVA's June 191 letter includes a listing of typical cormodities that are consin.ed to be miscellaneous steel.
Items'not criaidored to be miscellaneous steel include equipment casings (e.g. pump and mc housings), tanks, an' teat exchangers.
In response to Item la, examples of m acellaneous steel commodities discussed in the FSAR are provided.
NRC Request:
3.
'"Do the discussions on Page 7 of the reference apply to both steel platforms and miscellaneous steel with regard to compliance with FSAR requirements? If not, provide compliance-related discussions and examples for the miscellaneous steel (see Question 1)."
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ENCLOSURE Page 6 of M BROWNS FERRY NUCLEAR PLANT (BFN)
CRITI PIA FOR THE SEISMIC QUALIFICATION OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL (CONTINUED)
TVA Responso:
The discussiv e on Page 7 of the reference apply to both stool platforms and miscellaneous steel.
NRC Roquests 4.
" Provide a discussion for ductility ratio usage, including:
(a)
An exact definition with illustrative examples."
TVA Responsets The ductility ratio is definod a:J the ratio of deforras.tlon in a member to the def orrtation at yield.
Ductility ratios are used for the evaluation of stool structurce with thermal restraints to show that the thermal loads are secondary and self limiting in nature and that the material is ductile.
Exairples of the use of ductility ratios are discussed in Item 4C.
These ex..aples were previously roviewed by NRC.
NRC Poquents (b)
"Bason for une of ductility ratio in termo of physical test data and analytical demonstration regarding ductility ratio annociated with collapse mechanism (or other failuro mechanism of various structures). Describe how such ductility ration are calculated and why the calculation methodology is reliable, including any experimontal bases. Also discuss the impact of your ductility ratio usage on structural design safety margins compared to the margins which wov}d be provided if the applicable FSAR requirements and criteria wars strictly followed."
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i ENCLOSURE Papa 7 of to BROWNS FERRY NUCLEAR PLANT (BFN)
CRITERIA FOR THE SEISMIC QUALIFICATION l
OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL (CONTINUED)
TVA RGnponse The usage of the ductialty ratio of 3 was and ie provided in General Design r: rite.-la BFN-50-C7100, whl.ch is the long term design critoria f or this issue.
Thr.
ctions reviewed by NRO, which are documented in Inspection Por.
t 'c used GFN-50-C7100 as the basis for acceptance. The use of a de t. cv lo of 3 was explicitly reviawed and approved by NRC. for long term 4
use i
supplement 2 to the safety Evaluation Report on the Drowns Ferry Nuclear Performance Plep - NUREG-1232, Volume 3, dated January 23, 1991, Section 2.4, Plat form The-ul Grow +.h, states t "TVA has also evaluated the effects of platform thermal growth outside the drywell. The staff reviewed TVA's evaluations and concluded in IR $0-260/89-42 that the inspection concerns of IR 50-260/89-29 wore adequately resolved and that TVA's evaluation results and modifications
-were reasonable."
Physical testing was not performed for BFN and was not considered necessary since an appropriate non-linear analysis that models the members behavior was performed. There is no discussion in the FSAR regarding modeling of the behavior of structural steel featuren during a seismic evrnt or the use of ductility ration. Nor are ductility ratios specifind in the codes and specifications contained in FSAR commitments. Consequently, the present design criteria requirements for an evaluation that includes the impact of ductility is greater than the level of detail specified in the FSAR.
Due to the limited industry guidance in the evaluation of the thermal behavior of constrained structural memt. ors in plante licensed prior to 1976, the acceptability of the ductility ratio of 3 was negotiated with NRC as part of the overall seismic upgrade of BFN.
Its use is a separate issue from the two post-Unit 2 restart commiuments identified in NUREG-1232:
1)
The adequacy of using the 1978 edition of the AISC Specificat" in the restart evaluation in lieu of the 1963 edition specified in ths
$ 4R, and 2)
The review of the design criteria of determine if it conforms with the FSAR requirements.
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ENCLOSURE
'a9' 8 of 20 BROWNS FERRY NUCLEAR PLANT (BFN)
CRITERIA FOR THE SEISMIC QUALIFICATION OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL (CONTINUED)
The acceptability of this ductility ratio must be considered in the context of the overall seismic upgrade performed during the previous Unis 2 outage.
This overall seismic upgrade program included:
1)
The development of an artificial ground motion time history which enveloped the smoothed design response spectra f or all dartping values used in the analysis of structures, syste.se and components as specified by the current Standard Review Plan,
- 2) Used improved modeling and solemic analyses of rock and soil purported structures, and the reanalysis of the following structures and systems:
Large bore piping and supports, small bore piping and supports, Torus structures and piping (both internal and external),
control rod drive piping and supports, Instrument tubing, cable trays and supports, Electrical conduits and supports, Heating, ventilation, and air conditioning ductwork and supports, Drywell steel platforns, Hiscellaneous steel, Effect of the failures of Seismic class II features on class I
- features, Hochanical and electrical equipment, and secondary containment ptnotrations.
The restart of Unit 2 was based on the conservatism of the overall solemic analysis for each of these structures, ayatoms, and components; from the seismically induced ground motion to the response of the specific structures, syrtems, and components.
NRC Requests (c)
" Provide any specific references where the NRC staff approved such usage in the past."
iiiium.
ENCLOSURE l'*u*
- of 10 BROWNS FERRY NUCLEAR PLANT (BFN)
CRITERIA FOR THE SElSMIC QUALIFICATION OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL (CONTINUED)
TVA Responses i
The issue regarding the ductility ration of 3 was initially identified on the Browns Ferry docket in Section 3.4.3, Thermal Growth of Steel Platforms outside Drywell, of Inspection Report 89-30, dated September 20, 1989.
It states:
"The staff agreed to review the documentation and calculations presented by TVA at this meeting. The staff also stated that a ductility factor higher than 3 would not be acceptable because this is the limiting value that has been accepted by NRC, on a case-by-case basis.
This item remains open.
(CS0-34)"
The open item associated with ductility ratio was closed in Section 3.1.0, Thermal Expansion of Steel Structures outside Drywell, of Inspection Report 89-42, dated February 26, 1990.
It states:
"!R 50-260/89-30 stated tnat a ductility factor of 3 was the limiting value previously accepted by the NRC athff on a case-by* case basis. To address the team concern about the allowable ductility factor, TVA design input memorandum DIM-BFN-50-C-72.00-12 (B41 890505 003) specified the following limits for steel members, the maximum ductility factor equals 3; o
o for self-drilling concrete anchora, the maximum shear displacement equals 0.1D (where D = nominal diameter of anchor); and o for other types of concrete anchors, the maximum shear displacement equals 0.20.
The limit on concrete anchor shear displacement was based on TVA test data on concrete anchors (B04 890505 200). The team reviewed this TVA document and other test results and concluded that the TVA criteria are reasonable.
Therefore, the team concern about the allowable ductility factor criteria is resolved.
In summary, the team concluded that TVA's thermal growth evaluation of the structural steel outside drywell resolved all three team's concerns identified in IR 50-260/89-29, and the evaluation results and modifications are reasonable.
This item (CSO-34) is closed."
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ENCLOSURE rage so of to BROWNS FERRY NUCLEAR PLANT (BFN)
CRITERIA FOR THE SEISMIC QUALIFICATION OF THE LOWER DRYWELL STEEL PLATFORMS AND MISCELLANEOUS STEEL (CONTINUED)
The usage of the ductility ratio of 3 was and is provided in canoral Design criteria DFN-50-C/100, which is the long term design critoria for this isoue.
The calculations reviewed by HRC, which are documented in laspection Report 89-42, used DFN-50-C7100 as the basis for acceptance. Tho use of k ductility ratio of 3 was explicitly reviewed and approved by NHC for long term use.
Supplomont 2 to the safety Evaluation Report on the Browns Ferry Nucinar Pericrmance Plan - HUREG-1232, Volume 3, dated January 23, 1991, Section 2.4, platform Thermal Growth, states:
"TVA has also evaluated the effects of platform thermal growth outside the drywell. The staff reviewed TVA's evaluations and concluded in IR $0-260/89-42 that the inspection concerns of IR $0-260/89-29 were adequately resolved and that TVA's evaluation results and modifications were reasonable."
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