ML20113J179
| ML20113J179 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/31/1992 |
| From: | Zeringue O TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M80618, TAC-M80619, TAC-M80620, NUDOCS 9208070129 | |
| Download: ML20113J179 (10) | |
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JUL 311992 U.S. Iluclear Regulatory Commission ATTil:
Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of
)
Docket 110s. 50-259 Tennessee Valley Authority
)
50-260 50-296 BROW!1S FERhY !!UCLEAR PLA!1T (BFN) - RESPONSE TO REQUEST FOR ADDITIO!1AL INFORMATIO!1 REGARDING DESIGN CRITERIA FOR LOWER DRYWELL STEEL PLATFORMS AllD MISCELLANEOUS STEEL (TAC NOS.
M80618, M80619, AND M80620)
Reference:
HRC letter, dated July 13, 1992, Safety Evaluation and Request for Additional Information Regarding Browns Ferry Nuclear Plant Units 1, and 3 Design Criteria for Lower Drywell Steel Platforms and Miscellaneous Steel This letter provides TVA's response to the referenced request for additional information regarding the design criteria for lower drywell steel platforms and miscellaneous steel.
An item by item response to each request is provided as to this letter.
TVA requests a Supplemental Safety Evaluation Report be issued to document the resolution of these open items as each item is resolved.
920D070129 920731 N
I PDR ADOCK 05000259
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4 U.
S. Nuclear Regulatory Commission JUL 311992 A summary list of commitments contained in this letter is provided as Enclosure 2.
If you have any questions, please contact R.
R.
Baron, Marager of Site Licensing, at (205) 7?9-7570.
Sincerely, f)
{$$tfh
- d. J. Zeringue Enclosures.
cc.(Enclosures):
HRC Resident Inspector Browns Perry Nuclear Plant Route 12, Box 637
-Athens, Alabama 35611 Mr. Thierry M. Ross, Project Manager U.S. Nuclear 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 k
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i ENCLOSURE 1 1
i BROWNS FERRY NUCLEAR PLANT (BFN) l LOWER DR(WELL PLATFORMS AND MISCELLANEOUS STEEL CRITERIA The cover letter to the NRC's July 13, 1993 Safety Evaluation Report (SER) and Roquest for Additional informatien lists four open items that requ!.re TVA's responso.
Listed below is TVA's response to each open item.
I l
NRC Request 1.
As noted in the enclosed SE Section 2.2, the staff does not agree j
tnat TVA hLs demonstrated compliance with the FSAR requirements for
]
steel design.
First, application of a ductility ratio is not permitted by the FSAR.
Second, the shear stress limit of 0.52 F, proposeid in the criteria submitted on June 12,.991 is greater that
)
the FSAR limit of 0.4 F,.
TVA has not provided a justification for j
j this increased limit.
TVA should justify the increased shear stress f
limit, as noted in SE Section 2.5.3.
TVA hau stated that the FSAR will be revised to reflert changes in the steel design criteria.
j This revision and the associated justification will be reviewed by the staff when it boromes available.
i TVA Response f
Ductility -
)
The original FSA toading combinations did not include thermal loads for i
steel structures and t here are no statements in the BFN FSAR that would prohibit the use of ductility to accommodate the effects of thermal conditions. TVA has e luated.the changes to its steel design critoria d
under the provision of av CFR 50.59 and voluntarily upgraded its design criteria and loading conbinations to explicitly address thermal conditions j
and to use the concept of ductility to relieve thermal loads. This j
upgraded design criteria provides specific methods to address Standard Review Plan (SRP) Section 3.8.4, which states, in part:
... thermal loads can be neglected when it can be shown that they are secondary and j
self-limiting in nature and where the material is ductile."
TVA and NRC met on April 30, 1992 to discuss the methodology used to 1-evaluate effects of thermal growth of steel structures.
As documented in the NRC's Hay 12, 1992 meeting notasi the NRC staff reques+.ed that TVA perform, and the NRC review, furth6r analysis of structures effected by i
thermal conditions following a postulated pipe breah.
7VA agreed to 3
develop a plan to perform this analysis and submitted this plan by TVA letter to NRC, dated July 20, 1992.
NRC also documented in its meeting notes that TVA would not have to perform any physical testing or verification of the ANSYS computer program.
TVA continues to pursue its proposed plan for the resolution of the
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to address the-thermal growth issue and will also perform linear anelysms thermal growth issue.
TVA will prepare a summary of the calculations used i
for those structural configurations that exhibit the highest lwvel-of thermally induced stress.
A_ summary Leport will be submitted to NRC and the supporting calculations made available for NRC review at TVA's Rockville office by September 30, 1992.
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ENCLOSURE 1 i
BROWNS FERRY NUCLEAR PLANT LOWER DRYWELL PLATFORMS AND MISCELLANEOUS STEEL CRITERIA (C ONTINUED) 3.
i Shear Stress Limit -
i
)
The shear stress limit of 0.52 F, is provided to ensure a margin similar i
to the 0.9 F, limit on tension and bending stresses.
Commentary l
Section 1.$.1.2 of the American Institute of Steel Construction (AISC)
I l
8'th edition states shear yield stress is frequently taken ast b
i 3
- 0. 9 F' = 0. 5 2 F,.
1 Thus.
4-l This allowable is in accordance with, or more conservative than, standard i
industry practice. An illustration of the margin provided by this shear stress limit with respect to industry practice is described below.
~
l The use of a shear stress limit of 0.52F, for DDE load combinations is within the bounds of acceptable practice permitted under the AISC oode.
Section 1.5.1.2 of the AISC's 8'th Edition of Manual of Steel Construction provides shear allowables. - A shear allowable of 0.4F, is the basic allowable on cross-sectional area effective in resisting shear.
It is i
used for service level load) and for the ODE at BFN.
Section 1.5.6 of the i
same code states that the. allowable stress may be-increased one third above'.the values otherwise provided when produced by wind.or seismic i
loading, acting alone or in combination with the design dead-and live-7 loads.
Considering a one third increase on the basic allowable for DBE loading combinations with wind or seismic-loads results'in an allowable shear stress ofi 1 f x'O.4F 0.533F
=
y y
4 l
The shear stress limit of 0.52F, for DBE load combinations that is specified in DFN's steel design criteria is-therefore more conservative i
that the 0.533F, allowed by the AISC.
4.
The stress allowables specified in-SRP Section 3.8.4 for DBE load combinations are 1.6 times the allowables of normal loading combinations.
This results in an allowable shear stress' oft
- 1.6 x 0.4F i 0.64F y
y
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-The shear stress limit of.0.52F, for DDE -load combinations that is specified in BFN's steel design criteria la therefore more conservative that the 0.64F, allowed by the SRP.
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b Page 3 of 6 ENCLOSURE 1 l
BROWNS FERRY NUCLEAR PLANT LOWER DRYWELL PLATFORMS AND MISCELLANEOUS STEEL CRITERW (CONTINUED) l The 0.52 F, value is consistent with the allowable used for the evaluation / design of other commodities at BFN.
For example, the NRC's j
July 16, it'92 SER on the Browns Ferry seismic design criteria for HVAC duct and their supports states that the shear stress limit of 0.52F, for 1
DDE load combinations is acceptable. The SER further states that this 4
stress limit is in accordance with, or more conservative than, current i
industry practices, i
FSAR Revisions -
1 j
TVA letter to NRC, dated July 23, 1992, transmitted Revision 9 of the Updated Browns Ferry Final Safety Analysis Report.
The FSAR has been updated to reflect tae steel design criteria.
TVA will further enhance FSAR Table 12.2-16 to more clearly describe stress allowables for drywell I
platforms.
I j
NRC Requeet a
2.
In the enclosed SE Section 2.4, TVA is requested to clarify the criteria to state that the absolute sum of dynamic forces will be i
used versus evaluation of dynamic force phase relationships.
The staff feels this request is consistent with previous TVA commitments.
TVA Response:
I TVA will clarify the criteria to state that the.various dynamic reactions from attached systems, such as piping, HVAC, and cable trays, are combined l
on an absolute sum basis.
i NRC Requests 3.
SE Section 2.5.1 requires TVA to clarify the PSAR with regard to j
circumstances where the upper stress limit should be applied.
TVA Responses j
TVA will further enhance FSAR' Table 12.2-16 to more clearly describe stress allowables for drywell platforms..
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Page 4 of 6 ENCLOSURE 1 BROWNS FERRY NUCLEAR PLANT LOWER DRYWELL PLATFORMS AND MISCELLANEOUS STEEL CRITERIA (CONTINUED) t l
d 11RC Request s i
4.
SE Section 2.5.2 states the staff does not accept 0.9 of the critical buckling streus, since this limit provides insufficient j
margin.
TVA is requested to submit a lower limit for staff review which demonstrates acceptable margin.
i TVA Response TVA's design criteris specifion a 1.5 increase in the basic AISC stress allowables for the DBE load combination. Ilowever, in no case shall allowables exceed 90 percent of critical buckling for axial compression.
The 0.9 Fen (Factor of Saf ety = 1.11) is only approached for very short compression members for which buckling is not a concern.
This allowable is in accordance_with, f.,r more conservative that, standard industry practice.
The allowables for columns are demonstrated by the following examples.
[
llote that 0.9 Fca is approached only for columns of very short length. As column length increases, the allowable stress is rapidly reduced to.
- 0. 7 8 Fem.
The example column has an allowable stress of 0.88 Fen at a 7.25 inch length. The allowable stress is reduced to 0.81 Fem at'a 48 inch length and declines to 0.78 Fe, at a length of 101.33 inches.
The factor of safety against critical buckling ranges from 1.11 for the short column,-
up to 1.28 for the longer column.
These factors of safety are consistent with those used fer tension and bending members for the DBE loading combination.
It has also been observed in physical tests that columns exhibit post-buckling strength and do.not fall abruptly-in compression.
The relationship between a 1.5 -increase in basic AISc stresses and 0.9 Fra is shown graphically in Figure 1.
1 The following examples assume a W6x25 main member, constructed from A36 steel, with an to of 1.52.
Using K = 2.1, K '/, < c, with Ce = 126 c
(Reference AISC.8th Edition, f4ection 1.5.1.3).
1.
Length = 7.25 inches K '/, = 2.1 ( 7. 2 5 ) / 1.52 =-10.0 Using K '/, = 10 AISC allowable = 21.16 kei (AISC 8th FJition, Table-3-36) _
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Page 3 of 6 ENCLOSURE 1 BROWNS FERRY NUCLEAR PLANT LOWER DRYWELL PL ATFORMS AND MISCELLANEOUS STEEL CRITERIA (CONTINUED)
For the DBE condition, Attachment F of TVA's design criteria allows a 1.5 increase.
Therefore, F 1.5 (21.16) 31.74 ksi
=
=
4 (Kl)8 303 I
r = [1-2 C/ ) F = (1, 2 (126)8) 36 = 35.89 kal
( A TSc h?q.1. 5 -1 wi thout ea 7,ggg,ofg,f,py) i
' i f
Factor of' safety = 35,89/31.74 = 1.13 i
Note for ovaluation purpocos, compute 0.9 Fra ij' O. 9 Fen = 0. 9 ( 3 5. 89 ) = 32.30 '<si i
q Compare to 1.5 F4 1.5 F 31.74 kai Controlling
+-
=
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2.
Length = 48 inches a.
l K '/, = 2.1 (48) / 1.52 = 66.3 Using K '/, = 67 4
AISC allowable = 16.74 kai (AISC 8th Edition, Table 3-36) l t
For the DBE condition, Attachment F of TVA's design critoria allows a 1.5 increase.
Therefore, F
= 1.5 (16.74) 25.11 kai
=
4 l
(gl):
r 67 i
F,
- li-
'l ) 7, g y. 2 (1#0I } 36 = 30.91 ksi (AJSC Eq.1. 5-1 wi thout e
Factor cf Safety)
Factor of safety = 30.91/25.11 = 1.23 Note for evaluation purposen, compute 0.9 Fe, 0.9 Fra = 0.9 (30.91) = 27.82 kai l
Compare to 1.5 F4 L
1.5 F
-25.11 kal Controlling
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Page 6 of 6 ENCLOSURE 1 BROWNS FERRY NUCLEAR PLANT LOWER DRYWELL PLATFORMS AND MISCELLANEOUS STEEL CRITERIA (CONTINUED)
For K '/, > C<
3.
Length = 101.33 inches K '/, = 2.1 (101.33) / 1.52 = 139.99 Using K'/,e 140 AISC allowable = 1,62 kai (AISC Bth Cdition, Table 3-36)
For the DBE condition, Attachment F of TVA's design criteria allows a 2.5 increate. Therefore, r, = 1.5 (7.62) = 11.43 kai (3.14) 2900J = 14.59 Asl (AISC Eq.1.5-2 wlthout Tc5 =
- =
(X
)*
100' Factor of Safety).
1 Factor of_ Safety = 14.59/11.43 = 1.28-e Note for evaluation purposes, compute 0.9 Fra O. 9 Fo = 0. 9 (14.59) = 13.13 kal Compare to 1.5 F4 1.5 F = 11.43 kai Controlling 4
The f actor of Safety against buckling ranges fron 1.13 to 1.28 for these i
examples.
CONC 1.,USION It is TVA's understanding that the. proposed steel design criteria is acceptable'to the NRC Staff except for the open items identified in the NRC's July-13,-1992 SER.
TVA's plan for. resolving the thermal growth issue was submitted for Staff review by letter, dated.Ju,1y 20, 1992.
t TVA's proposed use of the ductility ratio concept is compatible with the SRP philosophy of self-limiting and ductile materials, and is more conservative than the SRP since a upper bound of 3 was established on the allowable ductility rat.io.
The remainder of the open items are addressed in this submittal.
\\
TVA's_ steel criteria is' conservative and consistent with past TVA commitments.; TVA requests a Supplemental SER be issued-to_ document-the resolution of these open items as each item is resolved.
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ALLOWABLE STRESSES i
I FOR COMPRESSION MEMBERS OF 36 KSI YlELD STRESS STEEL BROWNS FERRY NUCLEAR PLANT DESIGN CRITERIA Fa (ksi) 40
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---90% CRITICAL 1
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--1.5 AISC
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- AISC W/O 1/3 INCR
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20 40 60.
80 100 120 140 160 180 200 i
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ENCLOSURE 2 1
BROWNS FERRY NUCLEAR PLANT
SUMMARY
OF COMMITMENTS l
l TVA will:
- 1) TVA will further enhance FSAR Table 12.2-16 to more clearly describe stress allowables for drywell platforms.
- 2) TVA will clarify the criteria to state that the various dynamic reactions from attached systems, such as piping, HVAC, and cable
)
trays, are combined on an absolute sum baslo.
i I