ML19331D038
| ML19331D038 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 07/07/1980 |
| From: | Mccallister P ARMY, DEPT. OF, CORPS OF ENGINEERS |
| To: | Rolonda Jackson Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19331D037 | List: |
| References | |
| CON-NRC-03-79-167, CON-NRC-3-79-167 NUDOCS 8008270160 | |
| Download: ML19331D038 (16) | |
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- iUBJECT : Interagen y Agreement No. NRC-03-79-167, Task No. 1 - Midland Plant Units 1 and 2, Subtask No. 1 - Letter Report I
THRU: Division Engineer, North Central ATTN: NCDED-G (James Simpson) i s; IF -
lL U.S. Nuclear Regulatory;Ccemission TO:
ATTN: Dr. Robert E. Jackson Division of Systems Safety Mail Stop P-314 Washington, D. C. 20555
- 1. The Detroit District hereby submits this letter report with regard to completion of subtask No.1 of the subject Interagency Agreement concerning the Midland Nuclear Plant, Units 1 and 2. The purpose of this report is to identify unresolved issues and rake recommendations on a course of action and/or cite additional inforration necessary to settle these matters prior to preparation of the Safety Evaluation Report.
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- 2. The Detroit District's team providing geotechnical engineering support the NRC to date has made a review of furnished documents concerning foundations for structures, has jointly participated in briefing meetings with the NRC staff, Conrumers Power Co:pany (theiapplicant) and personnel from North Central Division of the Corps of Engineers and has made detailed site inspections. The data reviewed includ;s all documents recef .ed through Revision 28 of the FSAR, Amendcent 78 to the cperating license request, Ravision 7 to the 10 CFR 50.54(f) requests and MCAR No. 24 through Interic Report No, 8. Generally, each structure within the cecrplex was studied as a separate entity.
- 3. A listing of specific problems in review of Midland Units 1 and 2 follows for Category I structures.
The issues are unresolved in many instances, because of inadequate or missing inforention. The structures to be addressed follow thc description of the problem.
- a. Inadequate presentation ci subsurface information from completed borings on meaningf ul profiles and sectional views. Au structures.
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- rJUL E C NCEED-T SUBJECT Intsreg;r.cy Agrac_ent No. NRC-03-79-167, Task No. 1 - Midlind Pl nt Units 1 and 2, Subtask Nc. 1 - Letter Report
- b. Discrepancies between soil descriptions and classifications on boring logs with submitted laborator'/ test results summries. Examples of such discrepancies are found in boring T-14 (Borated water tank) which shcus stiff to very stif f clay where laboratory tests indicate of t clay with shear strength of only 500 p.s.f. The log of boring T-15 shows stif f, s.* ty elay, -
while the lab tests shew soft, clayey sand with shear strength of ILO p.s.f.
All structures. .f
- c. Lsek of discussion about! he riteria used to select soil san,iles for lab testing. Also, identificat' ion of the basis for selecting specifit values for the various paraceters used in foundation design from the lab test re s ult s. All structures. '
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- d. The inability to co:pletely identify the soil behavior fros lab testing (prior to design and construction) of individual samples, because in general, only final test values I'n sumrary form have been provided. All s truc t ur es.
(1) Lack of site specific information in esticating allowable bearing pressures. Only textbook type inforration has been provided. If necessary, bearing capacity should be revised based on latest soils data.
All st uctures on, or partially on, fill.
(2) Additional infornition is needed to indicate the design rethods used, design assumptions and computations in estimating settlement for safety related structures and systems. All structures except Diesel Generator Building where surcharging was performed.
- e. A complet' detailed presentation of foundation design regarding remedial measures for structures undergoing distress is required. Areas of renedial measures except Diesel Generator Building.
- f. There are inconsistencies in presentation of seismic design inforr.ition as affected by changes due to poor co=paction of plant fill.
Response to NRC question 35 (10 CFR 30.54f) indicates that the lower bound of shear wave velocity is 500 feet per second. We understand that the sace velocity will be used to analy::e the dynamic response of structures built on fill. However, from inforration provided by the applicant at the site rreting on 27 and 28 February 1980, it was stated that, except for the Diesel Generator Building, higher shear wave velocities are being used to re-evaluate the dynamic response of the structures on fill catarial. Structures on fill or partially on fill except Diesel Generator Building.
- 4. A listing of specific issues and inforration necessary to resolve them.
3, . Reactor Building Foundation (1) Set tle:rn t/Consolida tion. Basis for settlement / consolidation of the reactor foundation as discussed in the FSAR asst =es the plant site would 2
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7 JUL 1980 NCEED-T S U3 JECT: Intaregt=cy Agrec:en No. Np.C-03-79-16 7, ' Task No. 1 - liidland Plant Units I and 2, Subtask No. 1 - Letter Report not be devatered. Discuss and furnish co:putation for settle:ent of the Reactor Buildings in respect to the changed water table level as the result of site dewatering. Inclufe the effects of beuyancy, which were used in previous calculations, and fit:ctuatiens in water table which could happen if the devatering sys te: beca:a inoperable.
(2) Eearing Capacity. Searing capacity cceputations should be provided and should include mathed used, fcundation design, design assumptions, adapted scil properties, and basis for selecting ultirate bearing capacity and resulting factor of. safety.
%, ' . Diesel Genera:c Euilding.
(1) Se t tleme n t/ Con solida t ion. - In the response to NRC Questic: 4 and 27, (10 CFR 50.54f), the applicant has furnished the results cf his ccepu:ed set:lements due to various kinds 'of loading conditions. Fro his explanation of the results, it appears that co:pressibility parameters obtained by the preload tests have been used to co=pute the static settlements. Info::a tion pertaining to dyna ic respense including the a:plitude of vibration cf generator pedestals have also been furnished. Ihe observed settlement pat:ern of the Diesel Generator Building indicates a direct correlation with soil types and properties within the backfill =2:erial. To verify the preload test settle ent predictions, cc pu:e set:le=ents based on test results en sa:ples fre new berings which we have requested in a separate =e=o and present :he r e s ult s. Reduced ground water levels resulting frc dewatering and diesel plus seis=ic vibration should *ce considered in set:le:ent and seis ic analysis. Furnish the ceeputation details for evaluating a:plitude of vibration for diesel generater pedestals including =agnitude of exciting forces, whether they are constant or frequency dependent.
(2) Searing Capacity. Applicant's response to XRC Questica 35 (10 CFR 50.54f) relative :o bearing capacity of soil is not satisfacto: 7 Figure 33-3, which has been the basis of selection of shear strength for cceputing bearing capacity dots act reflect the characteristics of the soils under the Diesel Generator 3utiding. A bearing capacity cceputation should be subtitted based on the test results of samples fro: new borings which we have requested in a separate ce=o. This i=for:atica should include method used, foundation design assu=ptiens, adepted soil proper:1es and basis for selection, ulti= ate bearing capacity and resulting factor of safety.
(3) Preload Effectiveness. The effectiveness of the prelcad should be studied with regard :o the noisture content of the fill at the time of preloading. The height cf the water table, its time duration at this level, and whether the plant fill was placed uet or dry of opti=us would be all impo rttn: censiderations.
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7 JUL . odd NCEED-T SUFJECT Intnreg:ncy Agreecnnt No NRC-03-79-167, Task No.1 - Midland Plant Units 1 and 2, Subtask No. 1 - Letter Report (a) Cracular Soils.
When sufficien: Icad is applied to granular soils it usually causes a reorientation of grains and novement of particles into more stable positions plus (at high stresses) fracturing of particles at their points of centact.
Reorientation and breakage creates a chain reaction anong these and adjacent particles resulting in settlenent. Reorientation is resisted by fric: ion between particles. Capillary tension would tend to increase this f riction. '
noisture increase causing saturation,!such as a rise in the water table as occurred here, would decrease ' capillary tension resulting in nore conpac:fon.
Present a discussion on the cater table and capillary water effect on the granular por:lon of the plant fill both above and below the water table during anf aftet the preload.
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(b) I= pervious and/or Clay Soils.
Clay fill placed dry of opltinu= vould no: conpact and voids could exis: be:ueen particles and/or chucks. In this situation SPI blos counts would give misleading inforration as :o strength. Discuss the raising c: the water table and deter =ine if the tine of saturation was long enough to saturate possible clay lunps so tha he consolidation could take place that vould preclude further settlerent.
Discuss the preload effect on clay soils lying above the water table (7 feet i) : hat were possib'y conpacted dry of
. op-'- - T-would appear only linited consolidation fro the preload could :ake place in this situation and the potential for f urther set:1enen: vould enis:.
Discuss the effect of the preload on clays placed wet of optinun. I:
vould appear consolida ion along with a gain in strength would take place.
Deter =ine if the new soil strength is adequa:e for bearing capacity.
Cor lu ion- S'sce .he ella .11* c' exi .it fil' an c ,sact' an ir orna ion i u .er* in .s - de- -' .e - id r tio 6:an .ar b I of s) ala#kvaditic der ity.a1nois b .iry ar am con te *_n: dens ' ry, con olid . ion , rop :i Covfred b y a d d s .en .h ori <ial :est v uld 2ppe r to e ' si oble .n or er : 6/30/go at' fa .or'1y sve. t're abe e c sti ns. or'.gs _houl be antipcou push Aeffee v' a .di .ur' -d c aesi" s .1 np1 ta? n.
(4) Mi scellane ous. A contour =ap, showing the settlenenn configuration of the Diesel Generator 3uilding, furnished by the applicant at the aeeting of 27 and 28 Febr.uary icSO indicates that the base of the building has varped due to differential settlenents. Additional snnesses will be induced in the varicus cenponents of the structure. The applicant should evaluate these stresses due :o the differential se::lenenn and furnish the co=puta: ions and results for review.
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.. . o o U 7 0 NCEED-I SU3 JECT: Interagency Agreement No. NRC-03-79-167, Task No.1 - Midland Lant Units 1 and 2, Subtask No. 1 - Letter Report N. . Service Water Euilding Fcundation. .
(1) Eearing Capacity. A detailed pile design based upon pertinent soil data should be developed in crder to ore effectively evaluate the proposed pile support syste: prior to load testing of res: piles. Provide adopted soil properties, reference to test data on whf ch they are based, and method and assu=ptions'used to esti= ate pile design capacity including ec putations. Provide esti=ated r.axi=u static and dyna =ic loads to be 1 posed and individual contributice (DL, LL, OEE, SSE) on the saxi=un loaded pile. Provide factor of safety agains: soil failure due to =aximu: pile load. (2) Settlerents. 7 l J (a) Discuss and provide l analysis evaluating possible differential set:lement that could occar bet: e'en the pile supported end and :he portien placed on filla.nd g la cl.sI till. ' o n r< fe f Msc vile Me mp< c t
- f failunJi*sel fuel behind cilstor<ge e tavs)y r (b) int 31scuss4se why Nr# Fea tures tai (e 97 e $bg vall adjacent to the intake structure is not required to beISeistic Category I structure. Evaluate the observed settle =ent of'both the service water pu=phouse re:aining walls and the intake structure retaining vall and the significance of the settle =en:
including fu:ure settle c: prediction on the safe operation of the Midland Nuclear ?lant. This cv4/vs tien xbov// s/dPerf a ctuel fs'recref induced b y shc SetfIcse,7 again ef a t/owa.ble stretter perm tfed by ayroved codes. r (3) Seismic Analysis. Provided the proposed 100 ton ul:i= ate pile 1 cad capacities are achieved and reasonable rargin of safety is available, the vertical pile support proposed for the overhang sec: ion of the Service Water Pump Structure will provide the supper: necessary for the structure under cc bined s:atic and seis=ic inertial loadings even if the soil under the overhang portion of the structure should lieuefy. There is no reason to think this won't be achieved at this tire, and the applicant has co==1::ed to a lead tes to der.onstrate the pile capacity. The dynanic response ci the structure, including the inertial loads for which the structure itself is designed and the techanical equip ent contained therein, vould change as a result cf the introduction of the piles. Tnerefere: (a) Please su_=ari:e or previde ccpies of reports on the dyna:ic analysis cf the structure in its old and proposed configuration. For the latter, provide detailed infor:ation en the stiffness assigned to the piles and the way in which the s:1ffnesses vere obtained and show the largest change in interior floor vertical response spectra resulting frc: the proposed l codification. If the proposed coniiguration has not yet been analy:ed, describe the analyses that are to be perf or:ed giving particular attention to the basis for calculetica or'selec:ica, of and the range of nacerical stiffness values assigned to the vertical piles. (b) Provide af ter cc=pletien cf the new pile foundation, in accordance with co: it ent No. 6, 1:e 125, Consu=ers Poser Company =emorandu: 5
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7 JUL $80 ECEED-T , StJ3JECTt Interag;ncy Agrecment No. NRC-03-79-167,* Tesk,No.1 - Mid1:nd Plant i' Units 1 and 2, Subtask No. 1 - Letter Report dated 13 March 1980, the results of measurenents 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 fness can be determined and compared to that used in the dynanic analysis. N. [ Auxiliary Building Electrical Penetration Areas and Feeduter Isolation Valve Pits. .,/ l ll I f (1) Se telement. Provide ' the assu=ptions, method, computation and estimate of expected allowable / lateral and vertical deflections under static and seismic loadin3s. (2) Provide the construction plans, and specifications for underpinning operations beneath' the Electrical Penetration Area and Feedvater Valve Pit. The requested inforrition to be sub=1tted should cover the following in sufficient details [for ' evaluation: ibe tempnery (a) Details of Adewatering system (locations, depth, size and capacity of wells) including the =onitoring program to be required, (for example,
- masuring drawdown, flow, frequency of observations, etc.) to evaluate the performance and adequacy of the installed systes.
(b) Location, sectional views and dimensions of access shaf t and drift to and below auxiliary building wings. , (c) Details of te=porary surface support system for the valve pits. 4$7- Dewatering before underpinning is recommended in order preclude differential settlement between pile and soil supported elements and negative drag forces. () Provide adopted soil properties rethod and assu=ptions used to esticate caisson and/or pile design capacities, and computational results. Provide estimted =aximum static and dyna =ic load (co=pression, uplif t and lateral) to be impoced and the individual c6ntribution (DL, LL, GBE, SSE) on
=aximum loaded caisson and/or pile. Provide f actor of safety against soil failure due to =aximum pile load. :
e (f) Discuss and furnish computations for settlement of the portion of the Auxiliary Building (valve pits, and electrical penetration area) in respe ct to changed water level as a result of the site dewatering. Include the effect of bouyancy, which was used in previous calculations, and fluctuations in water table which could happen, if devatering system becomes inoperable. ( ) Discuss protection :nasures to be required against corrosion, if piling is selected. 6 MWF-~Wy%3W$$@cggpff,g ummW+W ?:w.2rrm-@j
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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 (3) What will be effects of uplif t pressure on the stability of the tacks and the associated piping system if the dewatering system becomes inoperable?
% , [ Underground Utilities:
(1) Settlement (a) Inspect the interior of water circulation piping with video ca:: eras and sensing device to show pipe cross section, possible areas of crackings and openings, and slopes of piping following consolidation of the plant fill beneath the imposed surcharge loading. (b) The applicant has stated in his response to NRC Question 7 (10 CFR 50.54f) tnat if the duct banks re=ain 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 =ade, during the preload test, to determine the stability of the duct banks, wi h your discussion regarding their reliability to perform their design functions. (c) The response to Question 17 of " Responses to NRC Requests Regarding Plant Fill" states that "there is no reason to believe that the stresses in Seismic Category I piping syste:s will ever approach the Code allowable." We question the above statement based on the following: Profile 26" - ORBC-54 on Fig.19-1 shows a sudden drop of approx. 0.2 feet within a distance of only 20 feet. Using the procedure on p. 17-2, ( b = E(e) = E ( D2R) = E ( D 2) ( 85 } t2 p = 30000 ( 26 ) [ 8(0.2)(12) ] = 130.0 KSI _ 2 (20x12)' aj g//ud/, i rth: =:. , the :q. 10(o) of Artimle .;C-5652.5,-See. III, Li.i;icr '., of &
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to a' -: p cd ;;t tlu.cn :::::::;. Yet, Table 17-2 lists only 52.5 KS17 stress for this pipe. This matter requires f urther review. Please respond to th/s apparent discrepancy and also specify the location of each computed settlement stress at the pipeline stationing shown on the profiles. More than one critical stress location is possible along the same pipeline. (d) During the site visit on 19 February 1980, we observed three instances of 'inat appeared to be degradation of rattlespace at penetrations of Category I piping through concrete walls as follows: 8 4
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SUBJECT:
Intortgency Agrasmnt No. NRC-03-79-167 Tcsk No. 1 - Midicnd Plcat Units 1 and 2, Subtask No.1 - Letter Report West Sorated Water Tank - in the valve pit attached to the base of the structure, a large diameter c eel pipe extended through a steel sleeve placed in the wall. Because the sleeve was not cut flush with the wall, clearance between the sleeve and the pipe was very s=all. : j
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, visible) were actually bearing on the invert of the opening. The bottom surface of one of the steel pipes had stall surf ace irregularities around the edges of the area in contact with the 2 x 4. Whether these irregularities are nor=al canufacturing irregularities or the result of concentration of load on this te=porary support caused by the settlement of the fill, was not known.
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These instances are sufficient to warrant an examination of those penetrations where Category I pipe derives support fro: plant fill on one or both sides of a penetration. In view of the above facts, the following infor ntion is required. (1) What is the mini =us seis=ic ra:itlespace required bet:.reen a Category I pipe and the sleeve through which it penetrates a wall? (2) Identify all those locations where a Category I pipe deriving support from plant fill penetrates an exterior concrete wall. Determine and re port the vertical and horirental rattlespace presently available and the
=ini=un required at each location and describe remedial actions planned as a result of conditions uncovered in the inspection. ~ It is anticipated that the answer to Question (1) can be obtained without any significant additional excavation. If this is not the case, the decision regarding the necessity to obtain information at those locations requiring enjor excavation should be deferred until the data fren the other locations have been examined.
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r 7 jUL E30 NCIED-T SU3 JECT: lateragencv Agreement No. NRC-03-79-167, Task'No. 1 - Midland Plan: Units 1 anc 2, Subtask No. 1 - Le::ar Report (e) Frevide detaits ( hickness, type of =ateriai etc.) of bedding or cradle placed beneath safety related piping, cenduits, and suppor:ing s tructure s. Provide profiles along piping, and conduits align =ents showing the pro:erties of all supper:ing =aterials to be adopted in the analysis of pipe stresses caused by se :le:ent. (f) The two reinforced conc ete retur pipes which exit the Service
'Ja er Pu=p St ructure, run along either side of the ecergency cooling sa:er reservoir, a:d ultica:ely enter into the reservoir, are necessary for safe shutdev=. These pipes are buried within or near :he crest of Category I slepes that for: the sides cf the e:ergency cooling water reservoir. There is no report cc, or analysis of, the seis ic stability of pos: earthquake residual di'splace:en for these s,lepes. While the li ited data frc this area do 0o: raise the specter of any proble=, for an irportant element cf the plant such as this, :he earthquake stability should be exa ined by state-of-:he ar:
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ce:heds. Therefore, provide results of the seis=ic analysis of the slepes leading to an es izate cf the per:anen: defor=ation cf the pipes. Please provide the following: (1) a plan showing the pipe location with respect to other nearby structures, slepes of the reserveir and the coordinate syste=; (2) cross-see:1 cts shosing the pipes, nor:al pool levels, slopes, subsurface cceditions as interpreted frc: borings and/cr icgs cf excavations at (a) a location parallel :o and abou 50 ft f c: the scu:heast cu: side vall cf the service water pipe structure and (b) a location where the cross sectics vill include both discharge structures. Actual hering legs should be shev: 0 the p refiles; their offset frc: :he prcfile ceted, and soils should be described using the Unified Soil Classifica: ice Syste:; (3) discussion of available shear strength da:a and choi- cf strengths used in stability analysis; (1) deter:1:a:1cn cf static facts: cr safety, critical earthquake accelera:ic:, and locatics of critical circle; (5) calculation of residual move en: by the se: hod presented by New ark (1955) or Makdisi and Seed (1978); and (6) a deter inatics of whether or not the pipes can function properly af ter such covenents. j-h .. Ccoling Pond.
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(1) Ecergency Cooling ?::d. In reccgnitie that the type of e=back:ent fill and the cc pactica con:rci used to cc:struct the retentie: dikes for :he cooling pend vere the sa:e as for :he proble: plant fill, we req ue s: rease:able assurance tha: the slepes of :he Category I Energency Coeling Pond (baf fle dike and =ain dike) are stable c der both static and dyna ic leadin;s. *Je request a revised stability analysis for review, which vill include identifica: ice of Icca:icas analyzed, adopted foundation and e:ba nk=e n t c: ditices (strati _ fica: ice, seepage, e:c.) and basis for selec: ion,
- adepted soil properties, nethod of stability analysis used and resulting f acter of safe:y with identification of sliding surfaces analyzed. Please address any po:ential 1: pact c Category 1 pipes near the slopes, based c the results of :his stability study. Recccrenda: ions for location of new exploration and testing have been provided in a separate letter.
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SUBJECT:
Intereg;ncy Agrnment Ns. NRC-03-79-167, Task No. 1 - Midlsud Plcut Units 1 and 2, Subtask No.1 - Letter Report (2) Operating Cooling Pond. A high level of safety should be required for the remaining slopes of the Operathg Cooling Pond unless it can be assurgd khat a failure will not: (a) endanger public health and - properties, (b) result in an assault on environment, (c) impair needed energency access. Reco:nendations for locations of new borings and laboratory tests have been subtitted in a separate letter. These recommendations were cade on the assu=ptions that the stability ' of the opera'-ing cooling pond dikes should be demonstrated. / 'j I. Site Dewatering Adequacy,. i* (1) In order to provide ,the necessary assurance of safety against liquef action, it is necesaary to de=enstrate' that the water will not rise above elevation 610 during nor=al operations or during a shutdown process. The applicant has decided to acco plish this by pu: ping from wells at the site. In the event of a f ailure, / partial f ailure,'or degradation of the devatering system (and its backup system) caused by the earthquake or any other e7ent such as equipment breakdown, the water levels will begin to rise. Dependir.g on the answer to Question (a) below concerning the normal operating water Itvels in the immediate vicinity of Category I structures and pipelites founded on plant fill, dif ferent a=ounts of time are available to accccplish repair or shutdown. In response to Question 24 (10 CFR 50.54f) the applicant states "the cperating groundwater level will be approxicately el 595 f t" (page 24-1). On page 24-1 the applicant also states "Therefore el 610' is to be used in the designs of the dewatering system as the caxicum permissible groundwater level elevation under SSE conditions." On page 24-15 it is stated that "The wells will fully penetrate the backfill sands and underlying natural sands in this area." The bottom of the natural sands is indicated to vary fro: eleva tion 605 to 580 within the plant fill area according to Figure 24-12. The applicant should discuss and furnish rnsponse to the following questions: (a) Is the nor=al operating dewatering plan to (1) pu=p such that the water level in the wells being pu= ped is held at or below elevation 595 or (2) to pu=p as necessary to hold the water levels in all observation wells near Category 1 Structures and Category I Pipelines supported on plant fill at or be' < eleve : ion 595, (3) to pu=p as necessary to hold water levels in the wells tantioned in (2) above at or below elevation 610, or (4) something else? If li is sou thin; else, what is it? (b) In the event the water levels in observation wells near Category 1 Structures c r Pipelines supported on plant fill exceed those for nor=al operating conditions as defined by your answeer to ' Question (a) what action will be taken! In the event.that the water level in any of these observation wells exceeds elevation 610, what action will bc taken? 11
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( ECEED-T
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- SCRJECT: Intcreg:ncy Agrccment No. NRC-03-79-167, Tesk Nn.1 - Midland Plin:
Units 1 and 2, Subtask No.1 - Let:gr Report i (c) IThere will the observation wells in the plant fill area be located that will b. monitored during the plant lifeti=e? At what depths will the screened intervals be? Uill the combination of (1) screened interval in cohesionless soil and (2) deconstration of tinely response to changes in cooling pond level prior to drawdown be made a condition for selecting the
- bservation wells? Under what condi: ions will the alar = mentioned on page 24-20 be triggered? What will be the response to the alar =? A worst case test cf the conpleted pernanent dewatering and groundwater le"el acnitoring systens ca21d be conducted to deter =ine whether,or not the ti=e required to acce Flish shutdown and cooling is available. This could be done by shutting off the entire dewatering syste when the cooling pond is a: elevation 627 and face:ciaing the water level versus time curve for each obsersution well. The
- est s?.ould be continued until the water level under Category I structure, whose foundations are potentially liquefiable, reaches elevution 610 (thu nor al water level) or the su: cf the time in:crvals allotted for repair and
- he ti=e interval needed to accompl' ish shutdown (should the repair prove unsuccessful) has been enceeded, wy.ichever occurs first. In riev of the heterogeneity of the fill, the likely variation of its perreability and the necessity of caking several assumptions in the analysis which was presented in the applicant's response to Question 24e, a full-scale test should give = ore reliable infor:ation on :he available ti:e. In view of the above the applicant should furnish his response to the following:
If a dewatering systen failure or degradation occurs, in order to issure that the plant is shutdown by the time water level reaches elevation 510, it is necessary to ini:ia:e shutdown earlier. In the event of a failure
- f :he dewatering systen, what is the water level or condition at which shutdown will be initiated? How is that condition deter =ined? An acceptable
- e: hod would be a full-scale worst-case test perforced by shu::ing off the entire dewatering syste with the coolin; pond at elevation 627 to determine, at each Category 1 Structure deriving support fres plant fill, the water level 1: which a sufficient tine window still remains to accomplish shutdown before the water rises to eleva: ion 610. In establishing the groundwa:er level or condition that will trigger shutdown, it is necessary to account for nornal surface water inflow as well as groundwater recharge and to assume that any addi:ional action taken to repair the dewatering system, beyond the point in
- ine when the trigger condition is first reached, is unsuccessf ul.
(2) As per applicant response to NRC Question 24 (10 CFR 50.54f) the design of the permanent dewatering systen is based upon two =ajor findings: (1) the granular backfill naterials are in hydraulic conaection with an underlying discontinuous body of natural sand, and (2) seepage fro the co: ling pond is restricted to the intake and purp structure ares, since the plan: fill south of Diesel Generator Iuilding in an ef fective barrier to :he inflow of the cooling pond water. However, soil profiles (Figure 24-2 in the
'Rasponse to NRC Requests Regarding ?lsn Fill"), punping test tine-drawdown
;raphs (Figure 24-14), and plo::ed cones of influence (Figure 24-15) indicate that south of Diesel Genera:or Suilding, :he plan fill =aterial adjicent :o 12
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? M l280 NCEED-T
SUBJECT:
Interagency Agreement No. NRC-03-79-167, Task No. 1 - Midland Plant Unitr I and 2, Subtask No. ! - Letter Report the cooling pond is not an effective barrier to inflow of cooling pond water. The esti=ated perreability for the fill caterial as re. ported by the applicant is 8 feet / day and the transmissivities range from 29 to 102 square feet / day. Evaluate and furnish for review the recharge rate of seepage through the fill caterials from the south side of the/ Diesel Generator Building on the pernanent dewatering system. This. evaluation should especially consider the recuvery data from PD-3 and compl'ete l data from PD-5. [ fl . (?) The interceptor wells have been positioned along the northern
- side of the Water Intake Structtire' and service water pump structures. The calculations esticating the total / groundwater inflow indicate 'the structures serve as a positive cutoff. Ho'ever, v the isopachs of the sand (Figures 24-9 and 24-10) indicate 5 to 10 fee't 'of '
re=aining natt.ral sands below these structures. The soil profile (Figure 24'-2) neither agrees nor disagrees with the isopachs. The calculations for total' flow, Wich assumed positive cutof f, reduced the length cf the line source of inflow by 2/3. The calculations for the spacing and positioning of wells assumed this reduced total flew is applied along the entire length of the structures. Clarify the existence of seepage below the structures, present supporting data and calculations, and reposition wells accordingly. Include the supporting data such as draudown at the interceptor wells, at tidway location between any two consecutive wells, and the increase in the water elevations downstream of the interceptor wells. The presence of structures near the cooling pond appears to have created a situatica of artesian flow through the sand layer. Discuss why artesian flow was not considered in the design cf the devatering system. (4) Provide construction plans and specification of permanent dewatering system (location, depths, size and capacity of wells, filterpack design) including required ronitoring program. The information furnished in response of NRC Question 24 (10 CFR 50.54f) is not adequate to evaluate the adequacy of the system. , (5) Discuss the ra=ific tions of plugging or leaving open the weep holes in the retaining wall at the Service Water Building. (6) Discuss in detail the naintenance plan for the dewatering system. (7) What are your plans for monitoring water table in the control tower area of the Auxiliary Building? (8) What ceasures will be required to prevent incrustation of the pipings of the dewatering syste=. Identify the controls to be required during plant operation (neasure of dissolved solids, che=ical controls). Provide basis for established criteria in view of the results shown on Table 1, page 23 of tab 147. 13 Jxw.eim m- m m e , ~ ~ - ,
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j Intsres:.ncy Agre:mnt N;.1GC-03-19-167, Task N5.1 - Midland <n:
SUBJECT:
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- Units I cnd 2, Subtssk Ns. 1 - Latter R2 port (9) Upon rcaching a stcrdy stata in d; watering, c groundwstne surv;y should be made to confirm the position of the water table and to insure that no perched water tables exist.
Dewatering of the site should be scheduled with a suf ficient lead tire before plant start up so that the additional settlement end its effects (especially on piping) can be studied. Settlecent should be closely =enitored during this period. f'royjde your ,ola ns fck condecling Uis youndudn Su twey , Liquefaetion Potential. [\/[ J. I
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An independent Seed-Idriss :Sinplified Analysis was performed for the fill area under the assu=ption th'at the groundwater table was at or below elevation 610. For 0.19 g peak grlound surf ace accceleration, it was found that blow counts as fo11cws were' required for'.a factor of safety of 1.5: 1 Elevation ft / ' Minimum" For F.S. =SPT 1.5 Blow Count
- 610 14 605 16 600 17 595 19 The analysis was considered conservative for the foll'owing reasons (a) no account was taken of the weight of any structure, (b) liquefaction criteria f or a mgnitude 6 earthquake were used whereas an NRC memorandum of 17 Mar 30 considered nothing larger than 5.5 for an earthquake with the peak acceleration level of 0.19 g's, (c) unit weights were varied over a range broad enough to cover any Lacertainty and the tabulation above is based on the most conservative set of assu=ptions. Out of over 250 standcrd penetration tests on cohesionless plant fill or natural foundation caterial below elevation 610, the criteria given above are not satisfied in four tests in natural =aterials located below the plant fill and in 23 tests located in the plant fill. These tests involve the following borings:
SW3, SU2, DG-18, AX 13, AX 4, AX 15, AX 7, AX 5, AX 11, DG 19, DG 13, DG 7, DG 5, D 21, GT 1, 2. Some of the tests on natural meerial were condreted at depths of at lessPrior than 10 f t before approximately 35 f t of fill was p aced over the location. to co=parison with the cr'teria these tests should be cultiplied by a factor
- the increase in effective overburden pressure that of about 2.3 to account and future dewatering of the fill.
results from the placeaen.: 1*For M = 7.5, blow counts would ir. crease by 30%. 14
v* ,7 JUL ESO NCEED-T 5173 JECT: Interagency Agreenent No. NRC-03-79-167, Task No. 1 - Midicad Plant Units 1 and 2, Subtask No.1 - Letter Report of the 23 tests.on plant fill which fail to satisfy the criteria, nost are near or under structures where renedial measures alleviating necessity for support from the fill are planned. Only 4 of the tests are under the Diesel Generator Building (which will still derive its support from the fill) and 3 others are near it. Because these locations stere low blow counts were recorded are well separated from one another and are non one continuous stratus but are localized pockets of loose =aterial, no failure mechanism is present. In view of the large nu.:ber of borings in the plant fill area and the conservatis: adopted in analysis, these few isolated pockets are no threat to plant safety. The fill area is saf e against liquefaction in a' Magnitude 6.0 earthquake or snaller stich produces a peak ground surface acceleration of 0.19 s or less provided the groundwater elevation in the fill is kept at or below elevation 610. Seis=ic analysis of structures en plant fill material. (1) Catego:y I Structures. Fro: Section 3.7.2.4 of the FSAR it can be calculated that in average Vsof about 1350 f t/see was used in the original dyna =ic soil structure in:eraction analysis of the Gregory I s:ructures. Bis is confir:ed by one of the viewgraphs used in the 28 February Bechtel presentation. Plant fill Vs is clearly =uch lower than this value. It is understcod fren the response to Question 13 (10 CFR 50.54f) concerning plant fill that the analysis of several Category I structures are underway using a lower bound averages V = 500 f:/sec for sections supported on plant fill and that floor response spectra and design forces will be taken as the cost severe of those from the new and old analysis. The questions which follow are intended to make > ertain if this is the case and gain an cders:anding of the i= pact of this parare:ric variation in foundation conditions. been (a) Discuss stich Category I structures havegand/or will be reanalyred for changes in seis=ic soil structure interaction due to the change in plant fill stiffness from that envisioned in the original design. Have any Category I structures deriving support fres plant fill been excluded fren reanalysis? On ttat basis? (b) Tabulate for each old analysis and each reanalysis, the founda: ion parameters (v s ,') and P ) used and the equivalent spring and danping constan:s derived therefro so the reviewer can gain an appreciation of the extent of pararetric vsriation perfor=ed. , (c) Is i: :he intent to analyre the adequacy of the structures and their contents based upon the envelope of the results of the old and new analyses? For each structure analyzed, please show on the same plot the old, new, and revised enveloping floor response spectra so the effect of the 15
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NCEED-T Interagency Agreement No. NRC-03-79-167, Task No. 1 - Midlnnd Plant
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SU3 JECT: Units 1 and 2, Subtask No.1 - Letter Report l changed backfill on interior response spectra predicted by the various nr.,dels I can be readily seen. (2) Category I retaining wall near the southeast corner of the Service Water Structure. This vall is experiencing sone differential settlement. Boring informtion in Figure 24-2 (Question 24, Volune 1 Responses to NRC Requests Regarding Plant Fill) suggests the wall is founded on natural soils and backfilled with plant fill on the land side. Please furnish details clarifying tiie following: (a) Is there any plant fill underneath the wall? What additional data beyond that shown in Figure 24-2 support your answer? (b) Have or should the design seisnic loads (FSAR Figure 2.5-45) be changed as a result of the changed backfill conditions? (c) Have or should dynanic water loadings in the reservoir be considered in the seisnic design of this wall? Please explain the basis of your answer. ,
- 5. In your response for the concents and questions in paragraph 4 above, if you feel that suf ficiently detailed informtion already exists on the Midland docke t that may have been overlooked, please nahe reference to that information. Resolution of issues and concerns will depend on the expeditious receipt of data centioned above. Contact Mr. Neal Cehring at FTS 226-6793 regarding questions.
y;E ige EIZ2102 UFW A P. McCALLISTER Chief, Engineering Division 16
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