ML20090A703
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DEPARTMENT OF THE ARMY NCRTM CENTRAI., OlveSION. CORPS OF ENGINEERS
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534 south CLAM < STRECT g.
CMIC AGO. ILLINCes GCooS scDan 10 JUL F' Dr. Robert Jseksen U.S. Nuclear Regulatory f**=sion Division of Systems Safety Mail Stop P-314 Washington, D.C.
20535 Dear Mr. Jackson; i
The inclosed Letter Report, covering subtask No.1 of Interagency Agreement No. NRC-03-79-167 concerning Units 1 and 2 of Midland Nuclear Plant, is hereby transmitted to you f reu the Detroit District.
Sincerely.
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_ ZANE M. CQOmmt. P.E.
As Stat-d Chief. Eng'ineering Division 9 03 m
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!GCDED 10 AL 1980 li Dr. Robert Jachsen U.S. leeelaar teamlatory e - imaion Divisima of Syetano dafety Mail Stop P-314 usatdaston, D.C.
20555 Dear Mr. Jeekson; The inciesed Imeter Report, coverina subtask No.1 of Interagency Agreement No. 31tC-03-79-167 concereias Unite 1 and 2 of ? tid 1m=J W1aar Flast, is hereby transmitted to yee from Elne Detroit District.
Sincerely.
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?JLW M. C000Utt F.E.
As Stated Chief. Distineering Division
DEPARTMENT OF THE ARMY sene,sommer. cease os mamamme SWEIWF savuon sommamaan 7JE W
SUBJECT:
Interagency Agreement No. NRC-03-79-167, Task No. 1 - Midland Plant Units 1 and 2. Subcask No.1 - i.etter Report
_l THRU: Divistan Engineer, March Central ATTN: NCDED-G (James Simpson)
TO:
U.S. Nuclear Regulatory hf ssion ATTK' Dr. Robert E. Jackson e
Division of Systems Safety Mail Stop F-314 Washington, D. C.
20555 1.
The Detroit Distri -
hereby submits this letter report with regard to completion of subtask Mo. 1 of the subject Interagency Agreement concerning the Midland Nuclear Pla.ut, Units 1 and 2.
The purpose of this report is to identify unresolved issws and aske recommendations on a course of action ad/or cite additional inforancion necessary to settle these matters prior to preparation of the Safety Evaluation Report.
2.
The Detroit Dis t ric t 's team providing geotechnfeal engineering support to the NRC to date has ande a review of furnished doeuesnts concerning f oundations for structures, has jointly participated in briefing meetings with the NRC staf f, Consumers Power C.>epany (the applicant) and personnel from North Central Division of the Corps of Engineers and has made detailed site inspections.
The data reviewed includes all documents received through Ame ndmen t 78 to the operating License request, Revision 28 of the FSAR, Revision 7 to the 10 CM 50.5=(f) requests and MCAR No. 24 through Interim Report No. 8.
Generally, each structure within the complex was studied as a separate entity.
3.
A listing of specif te problems in review of Midland 'Jnits 1 and 2 follws l
for Category 1 structures.
The issues are unresolved in many instances, because of inadequate or sissing information.
The structures to be addressed i
. follow the descriptiun of the problem.
Inadequate presentation of subsurface information from earspleted a.
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borings on :ssaningful profiles and sectional views.
\\11 st ruetures.
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i 7 JUL 1980 X:EED-T SUM ECT:
Interagency Agreeneat No. NRC-03-79-167 Task No. 1 - Midland Plant Units 1 and 2. Subtssk No.1 - Letter Report i
b.
Discrepancies between soil descriptions and classifications on boring logs with submitted laboratory test results susseries.
Examples of such discrepancies are found la boring T-14 (Borated water tank) which shows stiff to very stiff clay where laboratory tests indicate sof t clay with shear strength of only 500 p.s.f.
The los of boring T-15 shows stiff, silty clay, Wile the lab tests show sof t, clayey sand with shear strength of 120 p.s.f.
All structures.
c.
I4ck of discussion about the criteria used to select soil samples for lab testing. Also, identificaciou of the basis for selecting specific values for the various parameters used in foundation design from the lab test results. All structures. -
d.
'the inability to completely identify the soil behavior from lab testing (prior to design and constriaccion) of individual samples, because in general, only final test values in sumanry form have been provided. All structures.
(1) Lack of site specific infor:aation in estimating allowable bearing l
pres sure s.
Only textbook type information has been provided. If necessary, be.::ing capacity should be revised based on latest soils data. All structures on, oe partially on, fill.
(2) Additional information is needed to indicate the design methods used, design assumptions and computations in estiaating settlement for safety related structures and systems. All structures except Diesel Generator Building where surcharging was performed.
s.
A complete detailed presentation of foundation design regarding remedial measures for structures undergoing distress is required. Areas of l
remedial amasures except Diesel Generator Building.
f.
There are inconsistencies in presentation of seismic design information as af facted by changes due to poor compaction of plant f111.
Response to TRC question 35 (10 CFR 50.54f) indicates that the lower bouad of i
shear ways velocity is 500 feet per second. We understand that the same velocity will be used to analyze the dynamic response of structures built on i
fill. However, from inforancion provided by the applicant at the site meeting on 27 and 2S February 1980, it was stated that, except for the Diesel l
Cenerator Building, higher shear wave velocities are being used to re-evaluate the dynamic response of the structures on fill asterial.
Structures on fill or partially on fill except Diesel Generator Building.
4.
A listing of specific issues and inforancion necessary to resolve them.
a.
Reactor auilding Foundation (1) Settlement / Consolidation. 3ssis for settlement / consolidation of the reactor foundation as fiscussed in the ? JAR assumes the plant site would 2
7 JUL 150 NCEED-T
SUBJECT:
Interagency Agreement No. NRC-03-79-167 Task No.1 - Midland Plant Units 1 and 2. Subtask No.1 - Letter Report not be dewatered.
Discuss and furnish computation for settlement of the 2eactor Buildings in respect to the changed unter table level as the result of l
site dewatering.
Include the effects of bouyancy, which were used in previous calc,14tions, and fluctuations in water table which could happen if the dewatering system became inoperable.
(2) Bearing Capacity. Bearing capacity computations should be provided and should include method used, foundation design, design l
assumptions, adopted soil properties, and basis for selecting ultimate bearing l
capacity and resulting factor of safety.
b.
Diesel Generator Building.
(1) Se c clement / Consolidation.
In the response to NRC Question 4 and 27, (10 CFR 50.54f), the applicant has furnished the results of his computed settlements due to various kinds of loading conditions. From his explanation of the results, it appears that compressibility parameters obtained by the preload tasts have been used to cogute the static settlements.
In formation pertaining to dynamic response including the amplitude of vibration of i
generator pedestals have also been f urnished. The observed settlement pattern of the Diesel Generator Building indicates a direct correlation with soil types and properties within the backfill asterial. To verify the preload test settlement predictions, compute settlements based on test results on samples from new borings which we have requested in a separate meno and present the result s.
Reduced ground water levels resulting from dewatering and diesel plus seismic vibration should be considered in settlement and seismic a nalys is.
Furnish the computation details for evaluattag amplitude of vibration for diesel generator pedestals including angnitude of exciting f orces, wherher they are constant or frequency dependent.
(2) Bearing Capacity. Applicant's response to NRC Question 35 (10 CFR 50.54f) relative to bearing capacity of soil is not sa t is f ac tory.
Fi uce d
35-3, which has been the basis of selection of shear strength for computing bearing capacity does not reflect the characteristics of the soils under the Diesel Generator 3uilding. A bearing capacity computation should be subsitted based on the test results of samples from new borings which we have requested in a separate aseo. Bis information should include method used, foundation design assugtions, adopted soil properties and basis for selection, ultiste bearing capacity and resulting factor of safety.
(3)
Preload Ef fectiveness.
Me ef fectiveness of the preload should be stud.ied with regard to the moisture content of the fill at the time of p reloading.
De heidht of the water table, its time duration at this level, and whether the plant fill was piaced wat or dry of optimum would be all tiportant considerations.
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7 EL 1980 NCEED-T SURJECT: Interagency Agreement No. NRC-03-79-167 Task No.1 - ltidiand Plant Units 1 and 2, Subtask No.1 - Letter Report (a) Cranular Soils.
When sufficient load is applied to granular soils it usually causes a reorientation of grains and enovement of particles into more stable positions plus (at high streeses) fracturing of particles at their points of contact.
Reorientation and breakage creates a chain reaction among these and adjacent particles resulting in settlement.
Reorientation is resisted by friction between particles. Capillary tension would tend to increase this friction. A soisture increase causing saturation, such as a rise in the water table as occurred here, would decrease capillary tension resulting in more compaction.
Present a discussion on the water table and capillary water effect on the granular portion of the plant fill Loch above and below the eter table during and af ter the preload.
(b) tapervious and/or Clay Soils.
Clay fill placed dry of optimuss would not compset and voids could exist between particles and/or chunks.
In this situation SPT blow countih would give aisleading information as to strength.
Discuss the raising of the y
water table and deter: sine if the time of saturation was long enough to saturate possible clay lumps so that the consolidation could take place that would preclude furthe r settienent.
Discuss the preload ef fect on clay soils lying above the weer table j
(7 feet +) that were possibly compacted dry of optimum.
It would appear only limited consolidation froe the preload could take place in this situation and the potential for further settlement would exist.
Discuss the ef fect of the preload on clays placed wet of optinua.
It would appear consolidation along sich a anin in strengtJ. would take pl. ace.
Determine if the new soil strength is adequate for bearing capacity.
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Conclusion:==
Since the reliability of existing fill and compaction information is uncertairs, additional borings and tests ta determine void ratio (3ranu14r i
soils) relative density, soisture content, density, consolidation properties and strength (trianial tests) would appear to be desirable in order to 44tisfactorily answer the above questions.
3orings should be contin ~,un push eith undisturbed cohesive soil samples taken.
(1. ) 'tiscellaneous.
- A contour map, showing t'io set tieaant conf 1 ur4 tion of the Diesel ':enerator luilding, furnished by the apolicant at 4
the weting of 27 and 21 February 1990 indicates that the base of the buildin g has uurped due to dif ferential settlements.
Additional stresses vill be induced in the varias conponents of the structure.
- he appiteint should evaluate these stresses due t > tha dif ferential settlement and furnish the conputistions and results far review.
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7 AL 1990 scaso-r
SUBJECT:
Interagency Agreement No. NRC-03-79-167, Task No. 1 - Midland Plant Units 1 and 2 Subtask No.1 - Letter Report Service unter Building Foundation.
c.
t (1) Searing Capacity. A detailed pile design based upon pertinent soil data should be developed in order to more ef fectively evaluate the proposed pile support systen prior to load testing of test piles.
Provide adopted soil properties, reference to test data on which they are based, and method and assumptions used to estiaste pile design espacity including computations.
Provide estimated maximum static and dynamic loads to be I
imposed and individual contribution (DL, LL, OBE, SSE) on the anximum loaded pile. Provide factor of safety against soil failure due to maximum pile load.
(2) Set tleasse s.
(a) Discuss and provide analysis evaluating possible dif ferential settlement that could occur between the pile supported end and the portion plaeed on fill.
(b) Present discussion why the retaining wall adjacent to the intake structure is not required to be Seismic Category I structure. Evaluate the observed settlement of both the service water pumphouse retaining walls and the intake structure retaining well and the significance of the settlement including future settleanne prediction on the safe operation of the Midland 4
Nuclear Plant.
(3) Seismic Analysis.
Provided the proposed 100 ton ultimate pile load espacities are achieved and reasonable asesin of safety is available, the vertical pile support proposed for the overhang section of the Service Water
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Pump Structure will provide the support necessary for the structure under combined static and seismic inertial loadings even if the soit under the overhang portion of the structure should liquef y.
There is no reason to think this won't be achieved at this time, and the applicant has couaitted to a load test to demonstrate the pile capacity.
The dynamic response of the structure, including the inertial loads for which the structure itself is designed and the mechanical equipment contained therein, would :hange as a result of the introduction of the piles. The refo re (a) Please summarize or provide copies of reports on the dynamic analysis of the structure in its old and proposed configuestion.
For the latter, provtje detailed information on the stif fness assigned to the piles and the way in whteh the stif foesses wre obtained and show the largest change in interior floor vertical response spectra resulting frw the proposed modifiestion.
If the proposed configuration has not yet been analyzed, describe the analyses that are to be perfor34d giving partleular attention to i
the basis for calculation or selection, of and the range of numerical stiffnese val'ues assigned to the vertiest piles.
(b)
Provide af ter ospletion of the new plie foundation, in sesordance with eoenitzent No. 6, ites 125 Consumers Power Company sencrandus 5
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7 JUL 1980
'ICEED-T
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l SUMECT:
Interagency Agreement No. NRC-03-79-167, Task No. 1 - Midland Plant l
Units 1 and 2, Subtask No.1 - Letter Report dated 13 March 1980, the results of meas-resents of vertical applied load and absolute pile head vertical deformation which will be made when the structural load is jacked on the piles so that the pile stif fnesu can be determined and compared to that used in the dynamic analysis.
d.
Auxiliary Butiding Electrical Penetration Areas and Feeduster Isolation Valve Pits.
(1) Settlement. Provide the assumptions, method, computation and estiante of expected allowable lateral and vertical defleccians under static and seismic loadings.
(2) Provide the construction plans, and specifications for underpinning operations beneath the Electrical Penetration Area and Feeduster Valve Pit.
The requested information to be submitted should cover the following in suf ficient details for evaluations (a) Details of dewatering systes (locations, depth, size and espacity of wells) including the monitoring program to be required, (for example, 1
wesuring drawdown, flow, frequency of observations, etc.) to evaluate the performance and adequacy of the installed systes.
(b) Location, sectional vicvs and di aensions of access shaf t and drift ta and below auxiliary butiding wings.
(c) Details of temporary surface support system for the valve pits.
(d) Dewstering before underpinnin4 is recommended is order to preclude 4tf ferential settlement between pile and soil supported elements and negative drag forces.
(e) Provide adopted soil properties, method and assumptions used to estimate caisson and/or pile design capacities, and computational results.
Provide estinst::d uximum static and dynamic load (compresstun, upitf t and lateral) to be 1:sposed and the individual contribution (DL, LL, 05E, SSE) on l
Saxinurs loaded caisson and/or pile.
Provide factor of safety against soil f allure due to anxisua pile load.
(f) Discuss and furnish conputations for settienent af the portion of the Auxiliarv lu11 ding (valve pits, and electrical penetrattan area) in respect to changed veter level as a result af the site devatering.
Include the ef fect of houyancy, which was used in previous e ticulations, and fluctuations in vater table which could happen, if dewatering system becomes inocerable.
(1) Discuss protection measures to be required a pinst carrosion, if pilt: 3 is selected.
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SUBJECT:
Interagency Agreement No. NRC-03-79-167 Task No. 1 - Midland Plant Units 1 and 2, Subtask No.1 - Letter Report (h) Identify specific information, data and anthod of presentation to be submitted for regulatory review at completion of underpinning operation.
This report should sumerize construction activities, field inspection recorda, results of field load tests on caissons and piles and an evaluation of the completed fix for assuring the stable foundation.
e.
Berated Water Tanks.
(1) Settlement.
The settlement estimate for the Borated Water Storage Tanks furnished by the applicant in response to NRC Question 31 (10 CFR 50.54f) is based upon the results of two plate load tests conducted at the foundation elevation (EL 627.001) of the tacks.
Since a place load test is not of factive in providing information regarding the soil beyond a depth more than twice the diameter of the bearing place used in the test, ' i.e e s t ias t e o f the settlement furnished by the applicant does not include the contribution of the sof t clay layers located at depth more than 5' below the bottom of the tanks (see Boring No. T-14 and T-15, and T-22 thru T-26;.
(a) Compute settlements which include contribution of all the soll layers influenced by the total load on the tanks. Discuss and provide for review the analysis evaluating dif ferential settlement that cou1J occar between the ring (foundations) and the center of the tanks.
(b) The bottom of the borated tanks being flexible could warp under dif ferencial settlement.
Evaluate what additional stresses could be induced in the ring beams, tank walls, and tank bottoes, because of the settlement, and compare with allowable stresses.
Furnish the computations on stresses including asthod, assuspcions and adopted soil properties in the analysis.
/2) Bearing Capacity.
Laboratory test results on samples f ron bo.4ag T-15 show a sof t stratue of soil below the tank bottoa. Consideration has not been given to using these test results to evaluate bearing capacity information furnished oy the applicant in response to NRC Question 35 (10 CTR 50.54f).
Provide bearing capacity computations based on the test results of the samples from relevant boriegs.
This information should include method used, foundation design assumptions, adopted soil properties, ultimate bearing capacity and resulting factor of safety for tjle. static and the retsmic loa ds.
f.
L*nderground Diesel Fuel Tank Foundation Design (1) Beartr's esoscity.
Provide hearing capacity computation based on the test resuita of samples from talavent borings, including ne thod used, foundation design assumptions, adopted soil properties, ultiaste bearing espaetty and the resulting factor of safety.
i (2) Provide tank gettlement analysis due to static and dynamie loads including methods, assunptions nade, etc.
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7 JUL ?g60 NCEED-T SCBJECT:
Interagency Agreement No. NRC-03-79-167, Task No.1 - Midland Plant Units 1 and 2, Subtask No.1 - Letter Report (3) What will L. ;ffects of uplift pressure on the stability of the tanks and the associates piping system if the deintering system becomes inoperable?
3 Underground Utilities:
1 (1) Settlement (a) Inspect the interior of water circulation piping with video cameras and sensing devices to show pipe cross section, possible areas of crackings and openings, and slopes of piping following consolidation of the plant fill beneath ths imposed surcharge loading.
(b) The applicant has stated in his response to NRC Question 7 (10 CFA 50.54f) that if the duct banks remain intact af ter the preload program has been completed, they will be able to withstand all future operating loads.
Provide the results of the observations made, during the preload test, to determine the stability of the duct banks, with your discussion regarding their reliability to perform their design functions.
l (c) The responsa to Question 17 of " Responses to VRC Requests Regardi ng Plant F121" states that 'there is no reason to believe that the i
stresses in Seismic Category I piping systems will ever approach the Code allowable." We question the above statement based on the follosing:
Profile 26" - OH3C-54 on Fig. 19-1 shows a swiden drop of approx. 0.2 feet within a distance of only 20 feet. Using the procedure on p. 17-2, g b = E(e) = E ( D ) = E ( D ) ( 86 )
2R 2
L2 gg = 30000 ( 26 ) [ 8(0.2)(12)_l = 130.0 KSr 2
(20 12)-
Furthermore, the Eq.
10(a) of Article :5C-3652.3, Sec.111, Division 1, of the i
ASME code requires that some Stress Intansification Factor "i" be assigned to all camputed settlement stresses.
Yet, Table 17-2 lists only $2.5 KS1 stress for this pipe.
This setter revitres f arther review.
Please respond to l
apparent discrepancy and also specify the location of each camputed settlement stress at the pipeline stationing shown on the profiles. : fore than one critical stress location is possible along the same pipeline.
(d) During the site visit on 19 February !?io, we observed three instances of what appeared to be degradation of rattlespace at penetrations of Category I piping through eonerete walls as follows:
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Ncr.zo-T c
SUBJECT:
Interagency Agreement No. NRC-03-79-167, Task No. 1 - Midland Plant Units I and 2, Subtask No.1 - Letter Raport 1
West Borated Water Tank - in the volve pit attached to the base of the structure, a Israe disaster steel pipe ec: ended through a steel sleeve placed in the um12.
i Because the alceve was not cut flush with the waL11, clearance between the sleeve and the pipe was very small.
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eg -Q.4sup A sse Service Water Structure - Two of the service uter pipes penetrating the northwust us11 of the service water structs.re had settled dif ferentia11y with respect to the structure and were resting on slightly squashed short pieces of 2 x 4 placed in the bottom of the penetration. From the inclination of the pipe, there is a suggestion that the portions of the pipe further back in the all opening (which was not visible) were actually bearing on the invert of the opening. The bottoe surface of one of the steel pipes had small surface irregularities around the edges of j
the area in contact with the 2 x 4 Whether these irregularities are normal manufacturing irregularities or the result of concentration of load on this temporary support caused by the settlement of the fill, was not known.
These instances are sufficient to warrant an examination of those penetrati'ons where Category I pipe derives support from plant fill on one or both sides of a penetration.
In view of the above facts, the following information is req uired.
(1) What is the minisua seisale rattlespace required between a Category I pipe and the sleeve through which it penetrates a well?
(2) Identify all those locations where a Category I pipe deriving l
suppo rt from plant fill penetrates an exterior concrete well.
Determine 4nd,
re port the vertical and horizontal rattlespace presently available and the siniaua required at each location and describe remedial actions planned as a i
result of conditions uncovered in the inspection.
It is anticipstod that the answer to Question (1) een be obtained without any significant additional exc avation.
If this is not the case, the decision regarding the necessity to obtain information at those locations requiring major excavation should be deferred untti che data from the other toestions have been examined.
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7MN 2CEED-T l
SU1 JECT:
Interagency Agreement No. NRC-03-79-167 Tasic No.1 - Midland Plant Units 1 and 2 Subtask No.1 - Letter Report C
(e) Provide details (thickness, type e' asterial etc.) of bedding or cradle placed beneath safety related piping, conduits, and supporting s tructures.
Provide profiles along piping, and conduits alignannts showing the properties of all supporting anterials to be adopted in the analysis of pipe stresses caused by settlement.
(f) The two reinforced concrete return pipes 141ch exit the Service Water Pump Structure, run along either side of the emergency cooling tater reservoir, and ultimately enter into the reservoir, are necessary for safe shu tdown. These pipes are buried within or near the crest of Category I slopes that form the sides of the emergen..y cooling water reservoir. There is no report on, or analysis of, the seismic stability of post earthquake residual displacement for these slopes.
While the limited data f rom this area do not raise the wcter of any probles, for an important element of the plant i
such as this, the earthquake stability should be examined by state-of-the-art methods.
Therefore, provide results of the seismic analysis of the slopes leading to an estimate of the perunnent deformation of the pipes.
Please provide the following (1) a plan showing the pipe location with respect to other nearby structures, slopes of the reservoir and the coordinate system; j
(2) eross-sections showing the pipes, norani pool levels, slopes, subsurface conditions as interpreted from borings and/or logs of excavations at (a) a location parallel to and about $0 f t from the southeast outside us11 of the service unter pipe structure and (b) a loca, tion where the cross section will include both discharge structures.
Actual boring logs should be shown on the profiles; their of fset from the profile noted, and soils should be described using the Unified Soil Classification Systes; (3) discussion of available sNar strength data and choice of strengthe used in stability analysis; (4) determination o~f static factor or safety, critical earthquake acceleration, and location of critical circle; (5) calculation of residual anvenent by the method presented by Newmark (1965) or Makdisi and Seed (1978); and (6) a determination of whether or act the pipes can function properly af ter such sovenants.
I h.
Cooling Pond.
(1) Emergency Cooling Pond.
In recognition that the type of embankment fill and the compaction control used to construct the retention dikas for the cooling pond were the saes as for the problem plant fill, we i
request reasonable assuranee that the slopes of the Category I Emergency Cooling Pond (baf fle dike and usin dike) are stable under both static and j
dynamic loadings.
We request a revised stability analysis for review, which will include identificacica of locations analyzed, adopted foundation and embankment conditions (stratification, seepage, etc.) and basis for selection, adopted soil properties, asthod of stability analysis used and resulting factor of safety with identification of sliding surfaces analyzed.
Plea se address any potential tapact on Category I pipes near the slopes, based on the results of this stability study.
Recommendations for location of new exploration and testing have been provided is a separate letter.
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I I I 7n90 Mt 511TCT: Intersseney Agreement No. NRC-03-79-167, Task so.1 - M.idland Plant Caits 1 and.2, Subcask No.1 - 1,etter Report (2) Operattag Cooline; Pood. A high level of safety should 5e required for the reesta.i.:g r.iopes of the Operating Cooling Pond unless it can be assured that a failure vill not: (a) endanger public health and pr:perties (b) result in as assault on environment, (c) impair needed enertexy access. Eecommermiations for locations of new botings and laboratory tests have been subettted is a separate letter.
These recommendations were unds on the assumptians that the stability of the operating ecoling pond dikes should be Jemonstrated.
1.
Site Dewtering Adequaey.
(1) In order to provide the necessary assurance of safety against liquef aectoa, it is necessary to demonstrate that the water vill not rise above elewtion 610 during morant operations or during a shutdown process.
The applicast has decided to accomplish this by pumping from wells at the ette.
In the ennt of a failure, partial fatiure, or degradation of the Jewstertsg system (and its heckup system) eaused by the earthquake or any other event such as equipment breakdown, the water levels will begin to rise.
Depending on the answer to Question (a) below concerning the normal aperating
.seter levels in the tsaediate vietnity of Category I structures and pipelines f wnded in slant f t:1, dif ferest amounts of time are availsble to secompitsh repair or s9utdown.
In res ponse t.) Nestian 24 (19 CFR 50.54f) the ap.alicant states "the operating gr aundwater level will be approx 1::ately el 595 f t*
(p44e 24-1).
On pase 24-1 the appiteant also states %erefore el (210' is to 5e used in the desig s of the dewatering syste.2 as the snainus persissible groundwater lemi elevation under SSE eenditions." ?n page 2'*-15 it is stated that *ne wells will fully penetrate the backfill sands sad underlying natural sands in chte area.
- The bottae of the natural sands is indleated to vary f ew elevat.on W5 ts 540 within the plant fill area according to Figure 2 a-12.
The applicant should discuss and f urnish response m the following tue s t ions :
(a) 13 the oorsal operating Jewatering plan to (1) punp swh that the weer Lewl in the w!1s bet,4 pumped is held at or below elevation 595 or (2)
- -) pump as necessary to hold the wa ter levels in all 3b=+rvation wells near
'ategory 1 Struetwes and Category I Pipelises supported on plant fill it or belaw elevation 595, { 3) es pump as secessary to :mid water.4evela in the
.aelis sentisned in (1) iNew at or below elevatisa e19, or (*) so mething else?
- f it is sowthing else, sna t is it?
(b) In the event the ater levels in observation wells ne,sr Categorv
- it ruett.res ir ?tpelines supoort tJ on plant fall ex eed those f o r n<a raal sperating conditions as cefined av fcur ins.eer to @estion (.1). tat setton 4111 ':e taken ? In the eve t t%: the dete. level in any.u these steer.ition sells eteteds elevatian 91), wnat setion stil be taxen?
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7 JUL 1990
.'ICEED-T SUMECT:
Interagency Agreemet t No. NRC-03-79-167 Task No.1
'tidiand Plant l'aits 1 and 2, Subtask so.1 - Letter Report (c) Where will the observation wells in the plant fill area be located that will be monitored during the plant lifetime? At what depths will the screened intervals be? Will the combination of (1) screened interval in cohesionless soil and (2) den 2nstration of timely response to changes in cooling pond level prior to drawdown be made s condition for selecting the observation wells? t'ader what conditions will the alarm mentioned on page 24-20 be triggered? What will be the response to the alars? A worst case test of the completed permanent dauntering and groundwater level monitoring systema could be conducted to deterMne whether or not the time required to accomplish shutdown and cooling is available. This could be done by shutting of f the entire dewatering system when the cooling pond is at elevation 627 and determining the water level versus time curve for each observation well. The test should be ceatinued until the unter level under Category I structure, whose foundations are potentially liquefiable, reaches elevation 610 (the normal water level) or the sua of the time intervals allotted for repair and the time interval needed to accomplish shutdown (should the repair prove unsuccessful) has been exceeded, whichever occurs first.
In view of the heterogeneity of the fill, the likely variation of its permeability and the necessity of making several assumptions in the analysis which was presented in the applicant's response to Question 24a, a full-scale test should give more reliable infor=ation on the available time.
In view of the above the applicant should f urnish his resposse to the following:
If a dewatering systes failure or degradation occurs, in order to assure that the plant is shutdown by the time water level reaches elevation 610, it is necessary to initiate shutdown earlier.
In the event of a failure of the dewatering system, what is the water level or condition at which shutdown will be initiated? How is that condition determined? An acceptable method vould be a full-scale worst-case test performed by SSueting of f the entire dewatering system with the cooling pond at elevation 627 to determine, at each Category I Structure deriving support from plant fill, the water level at which a suf ficient time window still remains to accomplish shutdown before the water rises to elevation 610.
En establishing the groundwater level or cundition that will trigger shutdown, it is necessary to account for normal Surf ace water inflow as well as groundwater recharge and to assume that any additional action taken to repair the dewatering system, beyond the point in time shen the trigger condition is first reached, is unsuccessful.
(2) As per applicant respcase to NRC Question 24 (10 CFR 50. 54f) the design of tne permanent dewatering systen is based upon two major findingst (1) the granular backfill,nterials are in hydraulic connecuton with an underlying discontinuous body of natural sand, and (2) seepage fron the cooling pond is restricted to the intake and puep structure area, since the plant fill south of Diesel Generater asilding is an ef fective barrier to the inflow of the cooling pond water. Mowever, soil profiles (Figure 24-2 in the
" Response to : RC Tequests Regarding Plant Fill'), pumping test tise-drawdown graphs (yigure 2+-14), and plotted :ones of influence (Figure 2.-15) indicate that south of 3tesel Generator Builling, the plant fill taterial adjacent to 12
4 7 AL ;380 Near3-T
SUBJECT:
Interagency Agresenat No. NEC-03-79-167 Task No.1 - Midland Plant
}
Units 1 and 2, Subtask No.1 - Letter Report the cooling pond 'is not se offective barrier to inflow of cooling pond eter.
1 The estiented permeability for the fill enterial as reported by the applicant is 8 feet / day and the transmissivities range from 29 to 102 square feet / day.
Evaluate and f urniah for review tLe recharge rate of seepage through the fill
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materials from the south side of the Diesel Generator Building on the perunnent dewatering system. This evolustion should espacially consider the f
recovery data from PD-3 and complete data from PD-5.
(3) The interceptor wells have been positioned along the northern side of the ilater Intake Structure and service meer pump structures.
The calculations estiasting the total grounheter inflow indicate the structures serve as a positive cutoff. However, en isopschs of the sand (Figures 24-9 and 24-10) indicate 5 to 10 feet of remaining natural sands below these st ructures. The soil profile (Figure 26-2) neither agrees nor disagrees with the isopache. The calculations for tot.a1 flow, which assumed positive cutoff, reduced the length of the line source of inflow by 2/3.
The calculations for the spacing and positioning of walls as.sumed this reduced total flow is l
applied along the entire length of the structures.
Clarify the existence of
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seepage below the structurss, present supporting data and calculations, and reposition wella accordisgly.
Include the supportirs data such as drawdown at I
the interceptor wells, at midumy location between any two consecutive wells, j
and the increase in the ater elevations downstream of the interceptor wells.
The presence of structures near the cooling pond appears to have created a situation of artesian flow through the sand layer.
Discuss why artesian flow was not considered in the design of the dowatering system.
W i
(4) Provide construction plans and specification of persanent dewatering system (location, depths, size and capacity of walls, 811terpack j
design) including required unitoring program. The information furnished in j
response of NRC Question 24 (10 CFR 50.5&f) is not adequate to evaluate the
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a !e tuacy of the system.
I (5) Discuss the ramifications of plugging or leaving open the weep holes in the retaining well at the Service Water Building.
(6)
Discuss La detail the maintenance plan for the dewatering system.
(7)
- hat are your plans for monitoring meer table in the control towe r area of the Auxiliary Building?
(8) What seasures will be required to prevent incrustaticn of the pipings of the dewatering systes.
Identify the controls to be required durins plant operation (measure of dissolved solids, chemical controla). Provide l
basis for established criteria in view of the results shown on Table 1, page i
23 of tab 147 i
9 -
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.e---~-w,-
nm --
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,,-,--w--~
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7 JUL 90 NCEED-T
SUBJECT:
Interagency Agreement No. NRC-03-79-167 Task No.1 - ?tidland Plant Units 1 and 2. Subtask No.1 - Letter Report (9) Upon reaching a steady state in devatering, a groundwater survey should be made to confira the position of the water table and to insure that no perched unter tables exist.
Dewatering of the site should be scheduled with a sufficient lead time before plant start up so that the additional settlement and its effects (especially on piping) can be studied.
Settlement should be closely monitored during this period.
J.
Liquefaction Potential.
An independent Seed-Idriss Simplified Analysis was performed for the fill area under the assunption that the groundwater table was at or below elevation 610.
For 0.19 g peak ground surface acceeleration, it was found that blow counts as follows were required for a factor of safety of 1.5:
Elevation Minimus SPT Blow Count *I ft For F.S. = 1.5 610 14 605 16 600 17 395 19 The analysis was considered conservative for the following reasons (a) no 4ccount was taken of the weight of any structure, (b) liquefaction criteria f or a magnitude 6 earthquake were used whereas an 'iRC 2enorandum of 17 l tar 30 considered nothing larSet than 5.5 for.in earthquake with the peak acceleration levet of ).19 3's, (c) unit wei; hts were raried over a range broad enough to cover any uncertainty and the tabulation above is based on the soet conservative set of assumptions. out of over 250 standard penetration test a on cohesionless plant fill or natural foundation seterial below elevation 610, the criteria given above are not satisfied in four tests in natural materials located below the plant fill and in 23 tests located in the plant till. These tests involve the following bort 1;s:
S'43, SU2, D'h13, M 13, AX a, AX 13, M 7,.c 5, C 11, 3C 19, X 13, DC 7, DG 3, ) 21, GT 1, 2.
So,e of the tests on natural nacerial were conJuctsj at lepths >2f at less than 19 f t before approximatoly 35 f t of fill was,ilaced over the location.
?tior to comp.trison eith the criteria these tests should be nutti? tied by i f tetor af about 2.3 to account for the increase in ef fective overbur.!en pressure that results from the placenent and future Jewatering )f the fill.
n.
I*F.ar :1 = 7. 5 blow c 2unts wou1J increase by M.
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E5
, 7 JUL 1080 J
scuro-r 3
SUBJECT:
Interagency Agreement No. NBC-03-79-167, Task No.1 - Midland Plant y
Units 1 and 2. Subtask No. 1 - I.etter Report
?j Of the 23 tests sa plant fill which fail to satisfy the criteria, most are J
near or under structures where remedial measures alleviating necessity for g
support from the fill are planned. Only 4 of the tests are under the Diesel Cenerator Building (which will still derive its support from the fill) and 3
.2 others are near it.
Because these locations dere low blow counts were i
recorded are well separated from one another and are not one continuous j
stratus but are localized pockets of loose material, no failure mechanise is present.
.j In view of the large member of borings in the plant fill area and the cons trvatism adopted is analysis, these few isolated pockets are no threat to plant safety.
The fill area is safe against liquefaction in a Magnitude 6.0 earthquake or san 11er sich produces a peak ground surface acceleration of f
0.19 g or less provided the groundwater elevation in the fill is kept at or l
below eierstion 610.
k.
Seismic analysis of structures on plant fill meterial.
.J (1) Category I Structures.
From Section 3.7.2.4 of the FSA2 it can
_t be ealeulated that an average V, of about 1350 f t/see was used in the g
original dynamic soil structure interaction analysis of the Category I structures. This is confirmed by one of the viewgraphs used in the 28
'[
February 3echtel presestation. Plant fill V is clearly auch lower than s
It is understood from the respon,se to Question 13 (10 CTR 50.54f) g this value.
a conee.ning plant fill that the analysis of several Category I structures are j
underw y using a lower bound average V = 500 f t/sec for sections supported i
on plant fill and that floor response, spectra and degian forces will be taken
)
as the most severe of those from the new and old analysis. The questions which follow are intended to aske certain if this is the case and gain an understanding of the impact of this parametric variation in foundation condi tions.
r (a) Discuss Wieh Category I structures have and/or will be c
reanalyzed for changes in seisnie soil structure interaction due to the change in plant fill stiffness fram that envisioned in the original design. Have any 4
. Category I structures deriving support from plant fill teen excludedJroe reanalysis? On dat basis?
(b) Tabu
- ate for each old analysis and each reanalysis, the foundation parameters (v,,V andP ) used and the equivalent spring and damping constants derived therefrom so the reviewer can gain an appreciation of the extent of parametric variation performed.
-L (e) Is it the intent t2 analyze the adequacy of the structures and their contents based upon the envelope of the results of tne old and new analyses? Tor eseh stracture analyzed, please show on the sane plot the old.
- new, nd revised envelqing floor response spectra so tSe etfeet of the 15
7 Jul1960 NCEED-T
SUBJECT:
Interagency Agreement No. NRC-03-79-167 Task No.1 - Midland Pla.t Units 1 and 2. Subtask No. 1 - Letter Report changed backfill on interior resmase spectra predicted by the various andels can be readily seen.
(2) Category I retainlag tan 11 near the southeast corner of the Service Water Structure. This unil is experiencias some dif ferential settlemmat. Boring inforancion la Figure 24-2 (Question 24. Volume 1 Responses to NRC Requests Regarding Plant Fill) suggests the well is founded on natural soils and backfilled with plant fill on the land side.
Please furnish details clarifying the followtag:
(a) Is there any plant fill underneath the unil? What additional data beyond that shown in Figure 24-2 sopport your answer?
(b) Have or should the destga seismic loads (FSAR Figure 2.5-45) be changed as a result of the changed backfill conditions?
(c) Have or should dynamic unter loadings in the reservoir be considered La the seismic design of this wall? Please explain the basis of your answer.
5.
M your response for the eousents and questions in paragraph 4 above, if you feel that suf ficiently detailed information already exists on the Midland docke t that any have been overlooked, please sake reference to that inforancion.
Resolution of issues and concerns will depend on the expeditious receipt of data sentioned above. Contact Mr. Neal Cehring at FTS 226-6793 regarding questions.
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P. McCAI. LISTER Chief. Engineering Division 16 1