ML19257A279
| ML19257A279 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 12/19/1979 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Rubenstein L Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8001030533 | |
| Download: ML19257A279 (8) | |
Text
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TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 374ot 400 Chestnut Street Tower II December 19, 1979 Director of Nuclear Reactor Regulation Attention:
Mr. L. S. Rubenstein, Acting Chief Light Water Reactors Branch No. 4 Division of Proj ect Management U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Mr. Rubenstein:
In the Matter of the Application of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 Enclosed are IVA's responses to the questions asked by the Geosciences Branch Reviewer, J. Kane, in a telephone conversation on December 14, 1979. The Sequoyah Nuclear Plant Final Safety Analysis Report (FSAR) will be revised in accordance with these responses by Amendment 64.
Very truly yours, TENNESSEE VALLEY AUTHORITY J
.t y
_,\\. ! '
s
,u L. M. Mills, Manager Nuclear Regulation and Safety 9
Enclosure 1667 292 Ys An Eausi Occortuni:y Emetoyer 8001030
ENCLOSURE RESPONSE TO GEOSCIENCES BRANCH QUESTIONS 362.14 Question The estimated maximum pile loads to be imposed on the Waste Packaging Area and the Condensate Demineralizer Waste Evaporator Building provided in Table Q2.74-2 exceed the pile capacity which would be available if the driving criteria of 3 blows per in(Table Q2.65-1) was actually used in the field to control pile driving operations.
Please provide the actual pile driving records and pile load test for all Category I structures founded on H-piles.
If the field records that are available can not demonstrate a pile capacity which is capable of safely supporting the maximum pile loads to be imposed, please provide a proposed plan for remedial treatment with details that will assure an acceptable margin of safety during operation of the involved structures for NRC staff review and approval.
I
Response
TVA has developed the following program to resolve this i
item.
We will simultaneously pursue the following 4 courses of action.
Should the issue be resolved by any of these or any combination, we reserve the right to cancel any or all remaining activities.
1.
Review safety performance criteria and study possible structure and system modification to determine if the safety function of these structures can be modified.
2.
Discuss the behavior of the structures under earthquake loads with NRC structural people.
The static safety of the CDWEB and WPA is not questioned, only the earthquake conditions.
In our opinion these structures and their piles are adequate during an earthquake for the following reasons.
a.
The seismically imposed loads are overly conser-vative because of the analysis techniques used at that time.
The site motion is defined as a top of rock motion and is a nominal 0.18g (SSE).
This motion is linearly amplified in the 30 feet soil column to yield a top of ground motion of 0.42g.
This magnitude of ground motion is unrealistically high for the 362.14-1 1667 293
given rock motion.
This ground motion of 0.42g is then input to the structural model through foundation springs to yield a foundation mat motion of 0.50+g.
From this motion the structural response is determined.
b.
Even with these loads, should the maximum compression piles yield in bearing, no detrimental consequences will occur.
Should the pile move, the loads causing such a movement will be redistributed either (1) to the soil through activated skin friction as the pile tries to move downward with respect to the soil (This resistance could reach 216k per pile), (11) to the soil through bearing of the concrete foundation mat on the soil as if the pile was not present, (iii) to an adjacent pile by redistribution of load through the foundation mat, or (iv) by a combination of these.
c.
Considering the nature of the earthquake load and the extremely short duration of its maximum value, some adjustment needs to be made for pile performance under static versus dynamic loads.
d.
If the structures were soil supported only (no piles present), negligible settlement would occur due to an earthquake.
The site sofis are basically a clayey material.
The imposed seismic displacements would be essentially the sama with or without piles in the foundation system.
The presence of the piles would not adversely affect this performance.
3.
Seismic reanalysis of the CDWE3 and WPA to reduce the magnitude of the earthquake loads and thus increase the margin of safety in the pile system.
4.
Field pile load tests will be conducted to verify the adequacy of the piles under their anticipated loads.
Vertical and if necessary lateral load test will be performed.
The following steps will be involved.
a.
The pile load test will be conducted at a selected site away from the CDWEB and WPA areas.
New piles wi ll be driven and tested.
t667 294 362.14-2
pile during driving, unusual conditions, etc.
A continuous record of blows and resulting penetration will be maintained from five feet above anticipated set elevation to termination of driving. The driving criterion will be as originally used. We will ask either or both of of our consultants (Law Engineering and Testing Company and Woodward-Clyde Consultants) to assist in f.
Field load test will be performed in accordance with the procedures developed in step e.
The inspector will have authority to stop operations if the work is out of specification.
EN DES will have an observer and we will request our consultants to have an observer on site during all site driving and testing operations.
They will also have authority to stop work.
NRC will be notified before pile driving and testing and will be invited to observe either.
g.
The results of the pile load test will be evaluated by TVA with review by our consultants.
A precise time table of events has not been developed.
However - tentative plans are:
Seismic reanalysis of CDWE & WPA started 12/14/79 Rock exploration start 01/07/80 Soil exploration start 01/07/80- end mid-April Pile load test proc./NRC for review start 02/01/80 Pile driving and testing start mid-March Review results, prepare response 4-6 weeks after completion of testing Should all four courses of action just described not resolve the issue. TVA will undertake whatever measures are necessary, including underpinning of both structures, to resolve the issue.
1667 295 362.14-4
Existing pfles under either structure will not be tested.
b.
A rock exploration program consisting of core drilling will be conducted to determine t h e simil-arity of conditions at the CDWEB and WPA and the selected pile test site.
At least one boring will be made at each location.
The borings will be logged.
Part of this program will determine the material (efther shale, weathered shale, or in situ soil) at the pile tip elevation of the existing pfle.
To accomplish this rock boring will be performed as close as practical to both the CDWEB and WPA building and at a pile location.
Ualess obstructions exist, the selected pfle will be one of the maximum compression load piles.
The core boring at the test site will be used to establishe the similarity of soil and rock conditions (rock quality, depth, etc.).
If such similarity does not exist additional test sites will be considered until an acceptable site is located.
c.
A soll exploration program will be conducted to determine the soil properties.
The program will consist of three splitspoon borings (one each at CDWEB and WPA and one at the test site) and two undisturbed borings (one each at the CDWEB and WPA).
All soil borings will have continuous sampling from top of ground to " top of rock" (defined here as refusal of soil sampling equipment).
All soil samples will be classified.
Load-consolidation testing will be performed on selected undisturbed samples.
d.
Weathered shale samples from the rock exploration will be tested to determine the bearing capacity and other properties of this material.
e.
Pile load test procedures will be developed and test parameters defined.
This will include either the ASTM D-1143 method or the quick load test developed by B.
H.
Fellenius.
This will include detail requirements for recording all pertinent driving data.
These include plumbness, location accuracy, adherence to d riving or other criteria, length of pile, condi ti on of 362.14-3
SQNP 362.15 Question The apparent omission in the present FSAR concerning a discussion on the procedures and assumptions used in the dynamic analysis of structures founded on piles and
~
caissons should be corrected.
A discussion should be provided and important properties adopted for the foundation soils and piles should be identified along with the basis for the selected values.
The impact of changes (e.g. shear wave velocity) on design safety from presently reported FSAR information should be evaluated and discussed.
F
Response
The stated material is not in the FSAR.
The pile supported structures will be seismically reanalyzed in our response to Q362.14.
The reanalysis procedure will be different from the original procedure.
This procedure will be described and submitted concurrently with our response to Q362 14.
I667 297 362.15-1
SQNP 362.16 Question Indicate what portion of the maximum loads provided in Table Q2.74-2 represe t negative skin friction.
Response
Negative skin friction was not considered.
Our reasons for this will be detailed in our response to be submitted January 15, 1980.
1667 298 E
362.16-1
SQNP 362.17 Question Please clarify the discussion in the third paragraph of response to Q2.76 (362.11) concerning allowable and minimum lateral loads.
Response
This will be clarified in our response to be submitted January 15, 1980.
1667 299 F
362.17-1