ML19347C098
| ML19347C098 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 10/14/1980 |
| From: | EARTHQUAKE ENGINEERING SYSTEMS, INC. |
| To: | |
| Shared Package | |
| ML19347C094 | List: |
| References | |
| NUDOCS 8010160577 | |
| Download: ML19347C098 (16) | |
Text
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O P-PRELIMINARY SEISMIC EVALUATION
SUMMARY
REPORT FOR YANKEE NUCLEAR POWER STATION Rowe, Massachusetts Y
S 3
Prepared For:
Yankee Atomic Electric Company h
Nuclear Services Division y
25 Research Drive Westborough, Massachusetts 01581 Prepared By:
1-Earthquake Engineering Systems, Inc.
,l 141 Battery Street, Suite 400 s
San Francisco, California 94111 October 14, 1980 h
8010160577r
f, TABLE OF CONTENTS 9
.ad Page l
m I.
INTRODUCTION........................................
1 E
l II.
REVIEW CF STRUCTURES.................................
2 III REVIEW OF PIPING SYSTEMS.............................
7 I
IV.
SUMMARY
OF RESULTS...................................
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j V.
REFERENCES...........................................
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I.
INTRODUCTION
' At' the requestL of YAEC, EES has conducted a brief study to extrapolate structural capacities -for the plants major Category 1 structures and systems based on two site specific spectra. utilizing the results of the preliminary seismic evaluation that has already been conducted by EES and which was based on the Housner average spectrum and the NRC Regulatory Guide 1.60 spectrum.
The two site specific spectra are the Yankee site specific spectrum (Ref. 1) and the LLL/ TERA spectrum (Ref. 2).
In addition, conclusions are presented relative to the-seismic resistance of structures and systems that were not included in the previous analyses, but which were' included.in the field walkdowns..
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II.
REVIEW OF STRUCTURES co o
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This study relied on analyses conducted during the preliminary an seismic review for the following Category 1 structures i
o Concrete Reactor Support Structure o
Steel Vapor Container o
Spent Fuel Pool Other Category 1 struchtres were visually inspected during a walkdown of the plant by an EES senior staff team.
This section describes briefly the methods used in the W
investigation.
E A.
Concrete Reactor Support Structure g
d EES conducted a
preliminary seismic evaluation of this l
structure and reported the aork in June, 1979 (Ref. 3).
y Linear three-dimensional finite element dynamic analysis methods were used.
Due to the lack of site specific seismic
- inputs, EES
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selected the Regulatory Guide 1.60 spectrum as an upper bound spectrum and the Housner Average Spectrum as a
spectrum approximating more closely a spectrum for the Rowe site.
In lieu of the standard process of inputting the ground motion and determining the resulting
- stresses, member capacities were calculated, and the resulting capacity of the overa
structure was determined.
Tois capacity was given in terms of a maximum ground acceleration for the I
aoove spectral shapes.
The work conformed to the Standard Review Plan.
Simultaneous three component earthquake input was applied using a damping factor of 7%.
In calculating d
the capacities, ultimate strength values were used.
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The abova r3fersnced report contains a dstalled description of the work, I
together with the results and suggested conceptual fixes.
l Two areas of deficiency were uncovered as a result of this investigation. The first relates to the column connection to the foundation. The existing base plate and anchor bolt system was found to be deficient in both moment and shear resistance. EES designed strengthening collars for this connection to allow resistance of the seismically induced moments and shears and to increase
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the ductility of that portion of the structure. This modification will be installed in the near future.
The other area of apparent deficiency was related to the embedment length of l
the reinforcing dowels connecting the tops of the columns to the superstructure. A special study was undertaken to determine the behavior of dowels under dynamic cyclic loads (Ref. 4).
It was concluded, based on that study, that these bars have sufficient length of embedment into the superstructure to allow the development of full yield stresses.
EES performed further work to extend the results of the report taking into 1
consideration the Yankee site specific spectrum developed by Weston Geophysical (Fig. 1).
Structural capacities in terms of maximum ground l
accelerations were developed for this spectral shape.. Table 1 shows a summary of the capacities based on RGl.60 spectrum and the Yankee site specific spec t rum. The work was also extended to include the LLL/TER) spectrum (Figure 1).
A summary of the results are given in Section IV of this report.
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COMPARISON OF SPECTRA 0.50 a
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PGA 0,19g, DAMPlNG 7%
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[@ US-NRC REGULATORY G PGA O.109, DAMPlNG 7%
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PGA 0,109. DAMPING 7%
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TABLE 1
PG A C AP ACITY (% G) p' (7% D AMPING, 3 DIR. INPUT, DUCT
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FR2QUENCY R.G. 1.60 SITE SPECIFIC MODEL 1 (cps)
SPECTRUM SPECTRUM (WESTON)
COMMENTS
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YA-3 1.11 3.1 12.5 AS IS I
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YA-7
'0.73 2.7 15.7 AS IS s"
YA-15 1.21.
5.9 22.6 COLUMN BASE FIX FOR MOMENT Y-5 1.69 3.8 11.0 COLUMN SHELL FIX BELOW BELLOWS o
Y-6 1.79 9.8 31.7 COLUMN SHELL FIX INT. BELOW BELLOWS
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YA-12 4.6 7.3 12.1 LOW WALL COLUMN FIX f
YA-14 4.6 13.0 20.6 HIGH WALL COLUMN FIX o
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B.
Stcel Vapor Container A detailed three-dimensional finite element model of the spherical structure'was' developed and was subjected to gravity, temperature, pressure, hydrostatic and seismic loadings. The seismic loading used was i
Regulatory Guide 1.60 spectrum anchored at 0.10 g.
The analysis l
considered three simultaneous earthquake components using 4% critical t
damping. Criteria and methods used in the investigation and analysis complied with the Standard Review Plan. The resulting stresses were w9 low the ' applicable allowables for the corresponding loading conditions with the exception of a region near the equipment hatch where some l.
exceedance of the allowable stress was indicated. While the model was a detailed one it did not have sufficient refinement to represent the complex geometry near the hatch.
_Therefore, a more detailed model was developed to more accurately predict the stresses in this region. This new model indicated that the overstress condition was a result of the modeling rather than the I
structure itself. A detailed description of the analysis and results of the investigation are given in a special EES report (Ref. 5).
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l The aralysis was subsequently extended to include the Yankee site specific spectrum ~and the LLL/ TERA spectrum.
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l-j A summary of the results are given.in -Section IV of this report.
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Spent Fuel Pool A ' detailed three-dimensional finite element analysis was performed on the spent fuel pool structure to determine the effects of a
proposed division wall.
The model was subsequently used to determine the seismic capability of the i
I structure.
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Regulatory Guide 1.60 spectrum anchored at 0.10 g was used as benchmark input.
The analysis considered three l
simultaneous components of earthquake using 7% of critical damping.
Standard Review Plan methods were adhered to.
The l
analysis indicated that all stresses were within allowable limits and that the seismic portion of the stresses were l
Very small.
The analysis also indicated that the structure can withstand double the seismic input and remain within allowable limits.
See Reference 6 for details of the l
analysis and results.
l D.
Other Category 1 Structures r
d The analytical effort on the other Category 1 structures has been recently initiated, and numerical results are not l-available yet.
However, some qualitative conclusions can be j
made based on a plant walkdown conducted by an EES Senior l
Review Team.
This walkdown of the Category 1 structures and l
system was conducted as part of the preliminary seismic evaluation project.
A cursory review of the structural drawings was also performed.
It was observed that considerable care and good judgement I
were exercised in the layout of the lateral structural l
- elements, and good conservative practices were used in detailing th, individu:1 s tru c tu r:.1 elements and their connections.
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.The material used and the detailing practices applied afforded these structures high damping and ductility both of which are essential.:gredients f
in good earthquake engineering design. These factors are key components contributing to.the inherent energy absorption capacity of these types of structures.
Additionally, most of these structures, because of their functional design, f
has e a larger number of lateral resisting elements (such as shear walls) than normally found in standard buildings. This feature helps to maintain low seismic stresses in each element since a large number of these elements are participating.
f Based on the above, and the fact these structures have been designed for high wind loadings and general lateral stability, it is the opinion of the review I
1 team that little damage is expected under the Yankee site specific earthquake. Under the LLL/ TERA spectrum earthquake, considerable demand will
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their structural integrity.
It is felt that these structures can meet this demand without excessive deformation? and hence without loss of'overall integrity.
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III. REVIEW OF PIPING SYSTEMS
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This section contains a brief description of the analytical work performed on 4
the Nuclear Steam Supply System.
It also describes the visual inspection of the other Category-1 piping systems in the plant.
A.
Nuclear Steam Supply System f
. A re%-esentative loop was analyzed using finite element spectral dynamic I
.cralysis methods. The model included the steam generator, main coolant pump, loop isolation valves and bypass-piping.
A seismic input was j
utilized consisting of three components of amplified response spectra at the appropriate elevations. The amplified spectra was developed using 4
Regulatory Guide 1.60, input motion at the base of the structure. This motion was used as benchmark for conducting structural capacity studies.
l The investigation indicated certain deficiencies in the system which were corrected by adding lateral seismic supports (snubbers) to each of the
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four steam generators at their centers of gravity.
4 This modification was designed and is being currently installed.
Details of the above investigation together with the results are given in Ref. 7 4
i Preliminary studies were: conducted to assess the effects of the Yankee site specific and the $LL/ TERA spectra..The results of this assessment are given in Section IV of this report.
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B.
Other Category 1 Piping Systems c
anal sis of the Category 1 piping systems Det' ailed seismic f
has been initiated recently and.will produce results in the near future.
Some qualitative conclusions regarding the seismic capability of these systems can be drawn from the rerolts of the EES senior review team walkdown as well as from the results of the IE Bulletins 79-32 and 79-14 inspections which vm conducted by EES (Refs. 8& 9),
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'?he 79-02 and 73-14 reviews indicated that the plant piping systems and. pipe supports were built in accordance with the original design drawings with the exception of a few non conformances which were reviewed and corrected.
Both walkdowns and a
review of the plant design drawings indicated that good practice was used in the original
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j design.
All piping in the plant was designed in accordance with the requirements of ASA B31.1 Code 1955 edition.
This version of the code was a
major departure from its predecessor in that it incorporated advanced concepts and philosophies relating to limiting thermal strain range, low cycle fatigue, self limiting thermal stresses, maximum shear stress theory and controlled flexibility.
Records of past earthquake damage indicate that piping b
designed to this code and earlier version have performed well.
Some examples are the Kern County Steam Station (1952 Tehachapi Earthquake, Mag 7.7),
Long Beach Steam Station (1933 Long Beach Earthquake, Mag 6.3), and the FN oach Power Plant at Anchorage (1964 Anchorage Earthquake, M%
.4).
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. Basad 'on._the walkdown rsview, the dssign coda ussd and expsrience with past f-earthquakes, it is expected ~ that the plant's piping systems s'hould perform h..
well under'the-Yankee site specific earthquake.. Under the LLL/ TERA spectrum earthquake, it'is-expected that localized damage will occur, however, the inherent flexibility and ductility of the system and its conservative design
'should. prevent loss of major integrity.
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IV.
SUMMARY
This section summarizes the results of the analytical work performed on the major Category 1' structures and systems, ins results are given in terms of maximum ground acceleration capacity in terms of the Yankee and the L!./fERA i
-spectra.
A.
Concrete Reactor Support Structure Based on the fix designed for the exterior column bases, the capacity of the structure is in excess of 0.2 g based on the Yankee site specific
-spectrum.
This capr. city assumes linear behaviour and full compliance with current regulatory criteria.
For the LLL/ TERA spectrum and based on the same assumptions above, the capacity of the structure is approximately 0.11 g.
In order to determine a capacity based on more realistic criteria taking into consideration the inherent reserve capacity of the. structure, a simplified 'non-linear elasto-plastic analysis was performed. The resulting capacity based on the LLL/ TERA spectrum exceeds 0.2 g.
This capacity assumes the same column fixes as above.
B.
Steel Vapor Container The capacity of the steel vapor container assuming current regulatory criteria exceeds 0.2 g based on both the Yankee and the LLL/ TERA spectra..The 0.2 g LLL/ TERA spectrum capacity would require a minor fix consisting of' stiffening the-bracing rods connecting the exterior columns.,.
C.
Spent Fuel Pool
.The analytical work conducted on this structure. indicated that the l
seismic stresses are a small fraccion of the total stresses.
A review of these stresses indicates a seismic capacity in excess of 0.2 g for both
.the Yankee and the LLL/ TERA spectra.
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i D.
Nuclear Steam Supply System l
Analysis of a representative loop indicates a capacity for this system in excess of 0.2 g based on the Yankee site specific spectrum and based on current seismic regulatory criteria and B31.1 piping code. The above also assumes the presence of the new steam generator lateral restraints.
No rigorous analysis has been made to determine the capacity of this system based on the LLL/ TERA spectrum. However, based on extrapolation of the available data, it is concluded that the capacity of the system is in-the range of 0.2 g.
E.
Other Category 1 Structures and Systems l
The analytical' effort on the other Category 1 structures and systems has been recently initiated, and numerical results are not available yet, j
.However, some qualitative conclusions have been made in Sections IID and IIIB based on'a plant walkdown conducted by an EES Senior Review Team and l.
l based on a cursory ~ review of. the design drawings.
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f V.
REFERENCES
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1.
" Yankee Site Specific Spectra",
Yankee Atomic Electric Company, letter and attachments-to EES, MEG 648/80, dated 2 October 1980.
i 2.
" Digitized Pseudo-Spectral Acceleration Data for SEP Plants,"
U.S.
Nuclear Regulatory Commission memorandum,
-dated 17 September 1980.
e 3.
" Preliminary Seismic Evaluation Concrete Reactor Support Structure for Yankee Nuclear Power Station," EES Report No.
E-Y-YR-80064, June 1979; Revision 1, August 1979.
4.
"A Study of Simplified Bond-Slip Relation," EES Report No.
E-Y-YR-80063, May 1979.
5.
" Seismic Analysis and Stress Report for the Steel Vapor Container Structure, Yankee Nuclear Power Station,"
EES Report No. E-Y-YR-80061, March 1979; Revision 1, April 1979.
6.
" Analysis and Stress Report for Yankee Nuclear Power Station Spent Fuel Pool for Effects of a Proposed Division Wall,"
EES Report No. E-Y-YR-80062, April 1979.
7.
" Preliminary Evaluation of NSSS Piping
Response
due to Support Structure Modification for Yankee Nuclear Power Station,"
EES Report No.
E-Y-YR-80065, June 1979; Revision 1, August 1979.
8.
" Inspection of Safety Related Piping Within the Vapor Container at Yankee Atomic Electric
- Company, Rowe, Massachusetts," EES Report No. BM-Y-YR-90041, August 1980.
4 9.
" Inspection of Safety Related Piping Outside the Vapor Container at Yankee Atomic Electric
- Company, Rowe, Massachusetts," EES Report No. BM-Y-YR-90041, August 1980.
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