ML19261E802
| ML19261E802 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 09/13/1979 |
| From: | Howell S CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| HOWE-250-79, NUDOCS 7909200370 | |
| Download: ML19261E802 (32) | |
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"~'"[ Stephen H. Howell Senior Vsce Pressdent
.w-General Offices: 1945 West Pernall Road, Jackson. Michigan 49201 * (517) 788 0453
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Sept emb er 13, 1979 c'1 Ecve 250-79 -7
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h US Nuclear Regulatcry Cot =ission 5 _ n Att Mr Harold ? Denton , --
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~1 Office of Nuclear Reactor Regulatien o -
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'4ashington, DC 20555 MIDLA:D FF0 JECT -
OCCKI'" No 50-329 A::D 50-330 -
FES?0NSE TO 10 CFR 50.5h EEQUEST ON PLANT FILL -
FILE ChS5.16 UFI 71*01 SERIAL 7572 Enclosed are ten (10) copies of Revision 3 to censumers Fever Ccepany's respense of April 2h,1979 to your 10 CFF 50 5h(f) request regarding plant fill dated March 21, 1979 ,
Revision 3 includes updated responses tc C,uestions U , lh and 15 A "Su=rar/- cf Revisions to the 10 CFR 50 5L(f) Responses" page identifies all changes included in Revision 3.
Ccnsumers Fcuer Cc pany Cated S ept ember 13, 1979 by '
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5tepheQ E vell, Senior Vice President Svern and subscribed to before se en this 13th day cf September 1979.
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RESPONSES TO THE NRC 10 CFR 50.54 (f) REQUEST REGARDING PLANT FILL FOR MIDLAND PLANT UNITS 1 and 2 CONSUMERS POWER COMPANY DOCKET NUMBERS 50-329 AND 50-330 Consisting of:
- 1. Preface
- 2. Completion Status of Each Response
- 3. Responses to the 22 Questions Report Date: April 24, 1979 Revision 1: May 31, 1979 Revision 2: July 9, 1979 Revision 3: September 13, 1979 2157 239
SUMMARY
OF REVISIONS TO THE 10 CFR 50. 54 (f) RESPONSE PREPARED ON SEPTEMBER 13, 1979 The following revisions have been incorporated into the responses previously submitted on April 24, May 31, and July 9, 1979:
- 1. Cover sheet: Added date of revision.
- 2. Completion status paga: Revised to reflect comple' tion of Question 15. Also revised to indicate a future revision of Questions 4 and 14 to provide the results of continuing analyses and evaluations.
- 3. Question 4:
a) Page 4-1: Revised date for providing residual settlement criteria and extent.
b) Page 4-2: Revised to include additional updated information on current status and plans for the preload prograra.
c) New page 4-3: Added page to accommodate Iten b.
- 4. Pages 6-1 and 6-2: Revised to include additional updated information on field exploration program and tank preloading.
- 5. Page 7-3: Revised date for availability of results of duct bank settlement survey.
- 6. Page 12-1: Revised MCAR reference to add Interim Report 7.
- 7. Table 12-1:
a) Page 1 of 5: Revised remedial measures for Items A.2 and A.3.
b) All pages: Page numbering revised.
2l57 240 Revision 3 h
9/79
- 8. Question 14:
a) Pages 14-1, 14-2, and 14-4: Revised to incorporate minor clarifications.
b) Page 14-3: Revised to incorporate updated crack mapping, c) New figures 14-4 through 14-11: Added figures (made from MCAR 24, Figures 76 through 79 and 84 thror.gh 87) showing crack mapping.
- 9. Question 15:
a) Page 15-2: Revised to include discussion of applicability of loading combination.
b) .'
age 15-3: Revised remedial actions for electrical penetration areas and auxiliary building railroad bay.
c) New Page 15-4: Added page to accommodate Items a and b, clarified preloading of piles, and added discussion of retaining wall.
2157 24I Revision 3 9/79
COMPLETION STATUS Date to Complete Response Question Question Status (If Applicable) Actions and/or Remarks 1 Complete Corrective actions are currently in process.
2 Complete 3 Complete 4 Interim December 1979 Provide acceptance criteria.
5 Complete 6 Complete 7 Complete 8 Complete 9 Complete 10 Complete 11 Complete 12 Complete Complete response submitted in Revision 1.
13 Complete 14 Interim December 1979 Provide analysis and evaluation.
15 Complete Complete response submitted in Revision 3.
16 Complete 17 Complete Complete response submitted in Revision 2.
18 Complete 19 Complete 20 Complete Complete response submitted in Revision 2.
21 Complete 22 Complete 2157 242 Revision 3 9/79
Question 4 Specify and justify the acceptance criteria which you will use to judge the acceptability of the fill, structures, and utilities upon conclusion of the preload program. Compare these criteria with that to which the material was to have been compacted by the original requirements set forth in the PSAR, The response should consider all areas where preloading is either planned or in progress (i.e., diesel generator building, borated water storage tanks, diesel fuel oil storage tanks, Unit 1 transformer, condensate storage tanks, and others still under evaluation). Describe how conformance to these criteria will result in assurance that unacceptable residual settlements cannot reasonably be expected to occur over the life of the plant. For each such area, state the extent of residual settlement which will be permitted and the basis for each limit.
Response
The criteria and the extent to which residual settlements will be permitted will be provided by December 1979. T. e l3 manner in which acceptability criteria for the fill will be developed is discussed in the following paragraphs. Accepta-bility of the structures and utilities will be determined based on their ability to accommodate the predicted fill settlements.
The compaction requirements set forth in the PSAR were ba; on the premise that significant engineering properties, strength, and compressibility are related to degree of compaction. Where the engineering properties can be estab-lished by other, more direct means, the degree of compaction beccmes irrelevant.
The surcharge and the completed portion of the diesel generator building will produce stresses in the fill that, at all depths, will exceed those that will prevail when the structure is operational. The surcharge will remain until excess pore pressures are essentially dissipated and the rate of residual settlement becomes small and can be pre-dicted conservatively by extrapolation. It can then be concluded with assurance that, after removal of the earthen surcharge, the rate of settlement will be considerab3y less than the aforementioned prediction. Because of the initial variability of the degree of compaction of the fill, it is unlikely that the compaction requirements of the PSAR will be satisfied at all points, but because of the ensured favorable settlement characteristics due to the surcharge, the design intent of the PSAR will be met.
Revision 3 9/79 4-1 2157 243
The preloading at any structure serves the following purposes:
- 1) A primary benefit of preloading a building is that most of the settlement and differential settlement occurs before the building is put into service. Connections to the building can then be made after most of the differential settlement has already taken place, which will ensure a reliable design for the connections affected by differential settlement.
- 2) The preload is also a full-scale load test of the foundation soils. Data obtained during preloading will provide a reliable relationship between settlement and load which will be used to predict residual settlements of the structure.
- 3) The preload consolidates soft areas of clay fill, resulting in improved and much more uniform engineering properties of the fill.
As a result of the improved, more uniform engineering properties of the fill and based on the full-scale load test characteris-tic of the preloaded fill, a reliable prediction of upper limits of residual settlement will be possible. This will provide the assurance needed that unacceptable settlements will not occur during the life of the plant.
The intent of the preload program for the diesel generator building has been achieved, and removal of the st rcharge was started on August 15, 1979,and completed on August 30, 1979.
At the July 18, 1979, meeting with the NRC, R.B. Peck summarized the adequacy of the surcharge program as follows:
The results of the preload procedure have been convincing. The observed pore pressures were smaller than actually anticipated, and they dis-sipated rapidly. Hence, primary consolidation was accomplished quickly, and the curve of settle-ment as a function of the logarithm of time became linear shortly after the completion of l3 placement of the fill. Therefore, it is possible to forecast the settlement that would occur at any future time by simple extrapolation, on the assumption that the surcharge will remain in place. Even this amount of settlement would be acceptable. However, the projected settlement determined on this basis is an upper bound !
because the surcharge will be removed, and the real settlements will certainly be smaller. l i
Based on the available settlement data, the preliminary estimate for the residual settlement for the diesel generator i building due to secondary compression of clay for the 40-year l plant life is on the order of 1 inch. :
Revision 3 9/79 4-2 2157 244
The tank preloading provides a full'-scale test of the foundation soils. The tanks will be filled with water, and settlement rates will be monitored. In the unlikely event that these tests indicate the need for any corrective action, this will be undertaken as discussed more fully in the response to Question 6.
The soil investigations in the area of the borated water storage tanks (BWSTs) indicate that the material below apprcximately the top 4 Jaet is satisfactcry. All unsuitable material, as determined by soil testing, in the tank farm area will be removed and replaced by suitable compacted fill. The BWSTs will then be preloaded by filling with water and monitored to perform a full-scale test of subsurface materials. Settlement observations will enable reasonable settlement predictions that take into account the actual subsurface conditions under actual loadings. While one tank is being preloaded, the other will be used for preoperational testing.
The emergency diesel fuel oil storage tanks are buried structures that have already been subjected to a full-scale loading by filling with water for the past 6 months. 3 Settlements under these test conditions were minima 2.
Actual settlement of the tanks will be associated primarily with settlement of the underlying and surrounding fill under its own weight. Because the tanks will be settling with the ,
fill, the differential movements between the tanks and the j surrounding soil and piping will i' minimal, and the connec-tions can be expected to settle appraximately equally with the tanks. Existing connection details have reasonable flexibility, and will accommodate such small differential movements. No further remedial action is planned.
The Unit 1 transformer is a non-Seismic Category I area, but has been preloaded with 5 feet of sand and monitored. The non-Seismic Category I condensate storage tanks will also be monitored, and the design includes a flexible connection detail which will allow relative mctement between the tanks and the attached piping.
The preloading will not significantly improve the quality of any loose sand. Loose sand indicates a potential for liquefaction during an earthquake. A permanent dewatering system has been selected as a positive solution co the liquefaction problem. In addition, the dewatering operation will substantially reduce seismic shakedown.
Following removal of the preload at the diesel generator building and other locations where preloading has been applied, dynamic moduli measurements will be made. The data from these measurements will be used to evaluate the seismic response of the structures supported by the fill to determine that they satisfy the commitment made in the PSAR.
Revision 3 9/79 4-2157 245
Question 6 You propose to fill the borated water storage tanks and measure the resulting structure settlements.
(a) On what basis do you conclude a surcharge no greater than the tank loading will achieve compac-tion to the extent intended by the criteria stated in the PSAR? What assurance is provided by the technique that residual settlement for the life of the plant will not be excessive?
(b) A similar procedure is proposed for other tanks, including the diesel fuel oil storage tanks, and should also be addressed.
(c) The borated water storage tanks have not yet been constructed and are to be located upon question-able plant fill of varying quality. Provide justifi-cation why these safety-related tanks should be constructed prior to assuring the foundation material is suitable for supporting these tanks for the life of the plant. For example, can the tanks be removed with reasonable effort without significant impact?
Response (to Question 6, Part a)
The field exploraticn program in the area of the horated water storage tanks (BUSTS) shows that the material below l approximately the tcp 4 feet is satisfactory. All unsuitable i material, as determined by soil testing, in the tank farm area will be removed and replaced by suitable compacted fill. The BWST foundations (bottom elevation !
629'-0") are underlain by suitable material. To confirm that the fill is satisfactory, the tanks will be constructed and filled with water in order to make a full-scale test of 3 the foundation soils. The tank filling will provide reliable information for predicting long-term settlement. Although the degree of compaction set forth in the PSAR may not be satisfied at all points, the PSAR design intent will be met because the fill will have been subjected to a full-scale load test, which will allow a reliable prediction of long-term settlement.
The full-scale load test provides direct and reliable assurance that unpredicted long-term settlements will not occur.
Because the piping connections will be made to allow startup flushing, filling, and testing of the tank, selected points on the piping between the borated water tank and the auxiliary building will be monitored for differential settlement and Revision 3 9/79 2157 246 6-1
evaluated in accordance with the procedure described in Question 17. .
Each borated water storage tank is constructed of 1/4-inch stainless steel plate. It is designed to have the tank bottom resting on the soil backfill inside the ring beam to transfer the vertical load directly to the soil. The tank bottom is flexible enough to accommodate the settlement of 3 supporting fill and maintain proper load transfer capability.
The stresses thus induced in the tank bottom are secondary l in nature, and would not affect the integrity of the tank. i l
Response (to Question 6, Part b)
The emergency diesel fuel oil storage tanks are buried structures which have a full weight approximately the same as that of the fill they replace, and are supported on medium to stiff sandy clay fill. The tanks are surrounded with backfill consisting of loose to dense sands and very soft to stiff clays. Locations of borings made in this area are shown in Figure 12-1.
These tanks have already been subjected to a full-scale loading by filling with water for the past 6 months. Settle-ments under these test conditions were minimal. Actual settlement of the tanks will be associated primarily with settlement of the underlying and surrounding fill under its ,
own weight. Because the tanks will be settling with the l 3 fill, the differential movements between the tanks and the j surrounding soil and piping will be minimal, and the connec- ~
tions can be expected to settle approximately equally with the tanks. Existing details have reasonable flexibility, and will accommodate small differential movements.
There are no Seismic Category I tanks supported on fill other than the borated water storage tanks and the diesel oil fuel tanks. However, the non-Seismic Category I conden-sate storage ' anks will also be monitored, and the design 3
includes a flexible connection detail for the associated piping.
Response (to Question 6, Part c)
As described in the response to Part a, the exploratory program in the area shows the materials to be suitable for support of the tanks. However, in order to provide justifi-cation for this conclusion, the tanks will be constructed and filled as a full-scale test of the soils beneath them.
A reliable estimate of long-term settlement will be determined based on the measured settlements of the loaded tanks. '3 Although removal of the tanks after construction would be both costly and require a schedule delay, the tanks are accessible, and removal remains a viable alternative if } } [# 7 2 /> 7 unanticipated settlements that require remedial action occur.
Fevision 3 9/79 6-2
The strains induced in the duct banks due to seismic effects are small (lec; unan 10% of the yield strain) and, when added to the possible strains from settlement, will have no further effect on the function of the duct banks. There-fore, if the duct banks are still intact and continuous with no obstructions after the diesel generator building load has been removed and if the duct banks remain intact after the preload program has been completed, they will be able to withstand all future operating loads.
All four duct banks were checked for continuity and obstruc-tions after they were isolated from the diesel generator building footings. This was accomplished by pulling a segmented, hard fiber composition rabbit through each conduit (see Figure 7-3). The rabbit was pulled through the conduit by hand. No obstruction was detected during the pulling of the rabbit. The continuity check will be performed again after the preload program is completed. The results of this check, along with the results of the duct bank settlement survey, will be available after November 1979. l3 In the event that any significant obstructions or discontin-uities are encountered, several alternatives will be consid-ered to correct this condition. If the obstructions are small, a router may be pulled through the conduit to remove the obstruction and provide a smooth transition through the conduit. Replacement and rerouting of the duct bank will be studied as alternatives in the event of large discontinuities of the duct bank.
2157 248 Revision 3 9/79 7-3
Question 12 Document the condition of soils under all safety-related structures and utilities founded on plant area fill or natural lacustrine deposits. Based on the results of in-vestigations, compare the properties and performance of existing foundation materials under all expected loading conditions with those which would have been attained using the criteria stated in the PSAR. If the foundation materials are found to be deficient, discuss measures that will be taken to upgrcie them to criteria stated in the PSAR.
Response
Soil conditions beneath safety-related structures and utilities and planned remedial measures are summarized on Table 12-1. The soil conditions described for each struc-ture are based on the borings completed to date. Figure 12-1 shows the boring locations. These borings were made from July 1978 to April 1979. One additional boring is planned in the middle of the diesel oil fuel tanks area and three mote borings are planned in the auxiliary building control tower area. Natural lacustrine deposits (sands) are addressed in the response to Question 2. Remedial measures will not necessarily result in densifying the fill to the degree of the PSAR compaction criteria, but support will be provided for the structures and utilities that will meet the intent of the PSAR in that settlement and structural response will be acceptable.
Subsequent to the above response submitted in April 1979, the boring program to document the condition of soils under and/or adjacent to safety-related structures has been completed.
The soil conditions observed during this boring work are summarized in Table 12-1. Boring logs for the borings listed in Table 12-1 have been included into the FSAR, Appendix 2A (Revision 21) .
This table also summarizes the planned remedial measures to correct any deficient foundation conditions. For a detailed description of the planned corrective actions, refer to '
Interim Reports 6 and 7 to MCAR 24, issued in June and August 1979, 3 respectively.
General areal dewatering of the power block area is planned to eliminate the liquefaction potential of any sand backfill.
The dewatering system will lower the piezometric level from the present elevation of approximately 627 feet to approx-imately elevation 600 feet.
Revision 3 9/79 2157 249 12-1
TABLE 12-1
SUMMARY
OF SUPPORTING SOIL CONDITIONS AND PLANNED REMEDIAL MEASURES FOR ALL SAFETY-RELATED STRUCTURES AND UTILITIES Borings Performed from 7-78 Structures to 5-79 Supporting Soil Conditions Planned Remedial Measures A. Auxiliary Buildingil )
AX-6, 9, 18 Medium dense to very dense sand backfill over Pressure grouting of void
- 1. Control below concrete mud mat as tower dense glacial till with the exception of possible local void under concrete mud mat elevation 590' needed.
to 589' at boring AX-9.
- 2. Unit 1 AX-7, 15 Generally dense to very dense sand backfill with Underpin with caissons.
electrical occasional layers of loose sand and soft clay. The penetration backfill is underlain by dense glacial till. Concrete area was also used as backfill. A layer of concrete was encountered from elevations 583.5' to 580.l' 3 at boring AX-7.
AX-8, 19 Medium dense to dense sand backfill with occasional Underpin with caissons.
- 3. Unit 2 electrical medium stiff clay layers over dense glacial till, penetration with the exception of very loose to loose sand area backfill pockets encountered between elevations 596.5' to 600.5' at boring AX-19. Concrete was also used as backfill.
10 Medium to very dense sand backfill over dense Areal dewatering to
- 4. Railroad AX-1, 2, bay north glacial till. Concrete was also used as backfill. eliminate liquefaction potential end) 4)
D. Feedwater Isolation Valve Pits
- 1. Unit 1 AX-5, 11 (adjacent) Loose to dense sand and medium stiff to very stiff Removal of unsuitable clay backfill with occasional soft zones over material and replacement dense glacial till. Concrete was also used as by lean concrete.
backfill.
IN3 2. Unit 2 AX-4, 3, & 12 Loose to dense sand and medium stiff to very stiff Removal of unsuitable
--' (adj acen t) clay backfill with occasional soft zones over dense material and replacement glacial till. Concrete was also used as backfill. by lean concrete.
(J7
~sa A layer of concrete was encountered from elevations 585.2' to 575.5' at boring AX-4.
N Page 1 of 5 LJ7 Revision 3 CE) 9/79 9
Table 12-1 (continued)
Borings Performed from 7-78 Structures to 5-79 Supporting Soil Conditions Planned Remedial Measures l1 C. Service SW-3 through 9 Soft to very stiff clay and loose to very dense sand Piles under the north wall Water Pump SW-5A, SW-1 backfill over medium dense to very dense sand over to support the vertical Structure glacial till, with the exception of 2.5 feet of load.
- Portion loose sand encountered between elevations 601.5' on Fill and 599.0' in boring SW-6.
i l D. Tanks l
- 1. Diesel DF-1 through 7 The tanks are supported on medium to stiff sandy clay Fill the tanks with water. I1 fuel oil backfill. Surrounding backfill consists of loose If limited recidual settle-1, storage to dense sands and very soft to stiff clay. The ments cannot be assured the tanks backfill is underlain by dense glacial till. tanks will be surcharged in excess of full weight or removed or reconstructed.
l 2. Borated T-14, 15, 16, 18 Medium to very stiff clay backfill with occasional Pull load test by filling water C-274, 276 medium to very dense sand layers over dense to of the tanks with water.
storage very dense sand.
tanks E. Seismic Borings made adjacent to the Seismic Category I Category I utilities indicate:
Utilities
- 1. Piping 1. None anticipated.
Discussed in detail in
- a. Service Q-1, 3 through 8 Soft to very stiff silty clay and loose to very the response to water SW-7, 9 dense sand backfill over very dense sand Question 13, Section Sa, line ser- SWL-3 through 8,8A and Question 17.
vice water T-9, 10 pump structure 1
to auxil-iary build-ing
- b. Service Q-2, 9 Medium dense to very dense sand and soft to hard water SW-7, 9 silty, sandy clay backfill over very dense sand line, SWL-1, 2, 3 PN) st ice DG-1 through 7,27
__. water pump y, structure to diesel Nd generator building N
LJ1 Page 2 of 5 Revision 3 9/79 ,.
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Table 12-1 (continued)
Borings Performed from 7-78 Structures to 5-79 Supporting Soil Conditions Planned Remedial Measures
- c. Emergency DC-1 through 6 Medium dense to very dense sand and soft to very diesel DF-4, 5, 6, 7 stiff silty clay backfill over very dense sand fuel oil Q-2 lines SWL-1
- d. Borated SWL-8, 8A Very loose to medium dense sand and medium stiff to water T-9, 10, 21 hard silty clay backfill over very dense sand lines
- 2. Electrical 2. None anticipated.
Duct Banks (2) Discussed in detail in response to Cuestion 13,
- a. Auxiliary Q-3 through 7, 10, Soft to very stiff silty clay and medium dense to Section Sa and Note 2.
building 11, 12 very dense sand backfill over very dense sand to the SNL-3, service SW-4, 7, 9 water pump structure
- b. Auxiliary AX-6, 9, 18 Medium to very dense sand backfill over concrete building DG-19, 9, 14, and hard glacial till based on borings AX-6, AX-9, to the 13, 32, 28, 31, and AX-18 diesel 29 l2 generator building
- c. Diesel CT-1, 5, 6, Medium dense to very dense sand and medium stiff to generator DP-4, 5, 7 very stiff silty clay backfill over very dense sand building DG-7, 27, 30 to the 0-2 emergency diesel fuel oil tanks and the service water valve pits pgj d. Auxiliary SWL-8,8A Very loose to mediun dense sand and medium stiff
__, building T-9, 10, 21 to hard silty clay backfill over very dense sand to the L II borated tar @ "3' O Q
) CJ e/ evJT1 dd. sk 22 rage 3 of s nevision 3 I'3 9/79 e
f
Table 12-1 (continued)
Borings Performed from 7-78 Stru^tures to 5-79 Supporting Soil Conditions Planned Remedial Measures
- 3. Service Wat 3. None anticipated.
Valve Pits (gr) Refer to Question 13, Section Sc, and Note 3.
- a. Unit 2 DG-7 Stiff to very stiff silty clay and medium dense sand pit backfill over hard glacial till 2
- b. Unit 1 DG-27 Stiff to very stiff silty, sandy clay and medium pit dense to dense sand backfill over dense silty sand.
P. Retaining W-4, SW-13 Eorings made adjacent to the structure indicate that None anticipated Wall Adja- supporting backfill below the foundation level cent to consist
- of stiff to very stiff clay. The backfill Service is underlain by medium denso to very dense sand.
Water Pump Structure G. Diesel DG-1 through 32 Very soft to very stiff clay with pockets and Surcharge for preconsolidation Generator layers of very loose to dense send backfill over and areal dewatering to eliminate liquefaction potential of sand 2 Dailding medium dense to very dense sand. Concrete was also and Asso- used as backfill. backfill ciated Utilities NOTES:
(1) The auxiliary building is partially founded on glacial till and partially supported on plant fill materials, as described in the above table. Iloweve r , for several areas intended to be founded on glacial till, construction activities necessitated local excavation of the glacial till material (e.g., construction slopes for lower elevation excavations). Lean concrete backfill was used locally as required.
This condition may occur beneath the foundation slabs adjacent to Area A (as shown on FSAR Figure 2.5-47),
including Areas B, C, 0, G, I, J, K, and L (as shown in the same figure) . (Reduced copy of FSAR Figure 2.5-47 l is attached.) l2 (2) The electrical duct banks are reinforced concrete elements enclosing PVC and rigid steel conduits thus providing a void for the cables. The following information generated during construction is being used to evaluate the adequacy of the Seismic Category I electrical duct banks in the plant area fill:
(a) A construction inspection with a rigid foam rabbit prior to cable pulling (b) The cable pulling records In addition, at least one conduit in each duct bank will have a continuity check made with a hard fiber IN3 composition rabbit prior to cable pulling. Existing spare conduits will be maintained as long as feasible to allow future continuity checks. At present, one spare exists for the electrical duct bank from the tj7 auxiliary buildiruj to the service water pump structure and one from the diesel generator building to the sa emergency diesel fuel oil tanks. At present, only the electrical duct bank from the auxiliary building to t h. service water utructure has hau cable pulled. !!owever, the remaining conduits in that duct bank have had tho continuity check nade with the solid rabbit. The information did not indicate that any section of the duct bank had abnormali ties or obstr actions in conunon.
U7 t,a Page 4 of 5 nevision 3
. */79 l,
4
Table 12-1 (continued)
NOTEJ (continued)
(3) The gaps between embedded sleeves and pipes entering the service water valve pits were reasured at the top, bottom, and each side. The measurements were taken before the surcharge was applied.
Additional measurements will be taken when the surcharge is removed. This information will be 9 coordinated with the profile data.
(4) Immediately west of the Railroad Bay is a valve pit area wi+h approximate dimensions of 24'-6" x 28'-0",
and the bottom of foundation slab is at elevation 610 (i.e., shown as Area II on FSAR Figure 2.5-47) . For purposes of the soils review, this area has been evaluated as part of the railroad bay.
N La N
N U1 4
Page 5 of 5 Revision 3
. 9/79 l
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Question 14 For all Seismic Category I structures (including, but not limited to, the diesel generator building) which are located on fill, provide the results of an evaluation showing which structure you predict may experience settlemen2s in excess of that originally intended, and provide an evaluation of the ability of these structures to withstand the increased differential settlement. For the diesel generator building and/or any Seismic Category I structure which exhibits cracking, evaluate the effects of the existing and/or anti-cipated cracks on the performance of the intended function of these buildings. The calculated stresses for Seismic Category I structures at critical locations should be tabulated and compared to that o; allowable stresses as stated in the appropriate ACI Coc.es.
Response
The Seismic Category I structures located completely or partially on fill are identified in Figure 14-1.
- 1) Predicted Settlement The present records indicate that the settlement of the diesel generator building exceeds the predicted settle-ment. Other Seismic Category I structures do not exceed the predicted maximum settlement. For structures founded on questionable fill, the planned remedial actions identified in Table 12-1 (attached to the response to Question 12) will restore the foundation media to a satisfactory condition or provide support that is not based on the fill material. Therefore, it is not anticipated that the settlement of Seismic Category I structures other than the diesel generator 3 building will exceed the ultimate settlement values shown in FSAR Figure 2.5-48.
For the borated water storage tanks, where no corrective action is required, the estimated settlement will be reviewed upon completion of the load test program discussed in the response to Question 6 and also identified in Table 12-1.
- 2) Effect of Differential Settlement The effects of differential settlement within a structure can be divided into two parts:
a) Tilting b) Curvature or distortion Revision 3 9/79 4-2157 255
Tilting is of concern in tall, narrow structures such as towers and stacks. The plant structures subjected to differential settlement do not belong to this class of structures. Tilting does not cause any additional stress in the structure, whereas a curvature or distortion will cause additional stresses. Because the stress due to curvature is strain-induced it is self-limiting in nature. Therefore, the ultimate strength of the structural member is not affected by differential settlement.
The distortion is also dependent upon the stiffness of the structure. For a rigid structure which cannot be deformed appreciably, the distortion will be reduced by redistribution of soil bearing pressures.
These observations are verified 'y the behavior of the diesel generator building exterior walls. The three solid walls at the north, east, and west sides of the building mainly show tilting, whereas the south wall, which is more flexible because of the presence of large openings, shows both tilting and arching.
As discussed in the interim 10 CFR 50.55(e) report dated August 10, 1979, the diesel generator building is being analyzed for variable foundation properties by a finite element model. The possible building distortion is simulated through the use of different support 3 stiffnesses. These stresses will be combined and evaluated in accordance with the criteria given in response to Question 15. The results will be available in December 1979.
It is also to be noted that no extensive cracking has been observed in any of these buildings, indicating no largc stress buildup in the structural members. In case the differential settlement is increased, the concrete may crack and the tensile stress will be carried by the reinforcing steel. Cracking of concrete will also reduce the stiffness of the members, and the forces and moments due to distortion will be redistributed.
- 3) Evaluation of Cracking The diesel generator building, the fill-supported portion of the service water building, and parts of the auxiliary building (railroad bay, electrical penetration rooms, and control tower trea) have been examined for cracks in the main structural elements. The identified cracks in the diesel generator building and service water building have been mapped. They are presented in Figtres 14-2 and 14-3. The majority of these cracks are shrinkage and temperature cracks, as evident from their widths and orientation.
2157 256 Revisien 3 14-2
The structural cracks in the diesel generator building are in the lower part of the structure and are located in the areas around the vertical electrical duct banks.
They were caused by the estimated 1,000 kips of load transmitted from the building to the duct bank. Since then, the concentrated load has been eliminated by isolating the duct bank from the building. For details, refer to the response to Question 7.
In the applicable portions of the service water pump structure, the structural cracks are probably caused by the partial cantilever action of the northern part of the structure. It is theorized that the cracks on the roof slab are due to the bending tension and the cracks on the walls are due to principal tension caused by shear.
The cracks in the auxiliary building, the feedwater isolation valve pits, and the borated water storage tank ring foundations are localized and their widths do 3 not exceed .020 inch. These cracks have been mapped and are presented in Figures 14-4 through 14-11.
A crack in concrete indicates that the tensile strength capacity of concrete has been exceeded. Because no reliance is placed on concrete tensile strength in designing for bending and axial tensile stress, the strength of the structure (to resist these forces) is not affected by the crack. The compressive forces can be transmitted through the crack by bearing and shear force by the uncracked concrete or concrete in compression and reinforcing bars. However, the stresses in these walls are small, and only a fraction of the member capacity in shear is utilized to resist loads.
The maximum crack width encountered to date is about
.030 inch. Wherever cracks are caused by loads not included in the original design (such as the cantilever action of a part of structure), their widths nay be reduced when the loads are released during the corrective action. Therefore, it is concluded that the structural integrity of the buildings has not been affected by cracking.
Revision 3 9/79 14-3 2kb
- 4) Comparision of Allowable versus Calculated Forces and Moments at Critical Sections In FSAR Tables 3.8-19, 3.8-22, and 3.8-27, the calculated forces and moments for critical load combinations for the auxiliary building foundations, service water pumphouse, and diesel generator building have been compared with the allowable forces and moments. Also, in FSAR Table 3.8-20, the amount of reinforcements required has been compared with the amount of reinforce-ments provided for representative walls in the auxiliary building.
These load combinations do not consider the effect of differential settlement. The settlement stresses and 3 the loading combinations for the diesel generator building are discussed in Part 2 of this response.
2157 258 Revision 3 9/79 14-4
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The cude requirement that the differential settlement effects are to be combined with dead and live loads recognizes that the differential settlements will add to the long-term applied live and dead loads. The additional cracking resulting from the combined effects of wind or earthquake loads with dead and live loads and the settlement effects will only be temporary during the event. The structure will return to its original condition after the event. The Midland project structural design criteria for Seismic Category I structures that are partially founded upon fill will be expanded to include the differential settlement effects by the addition of the following load combinations: Normal Operating Conditions U= 1.05D + 1.28L + 1.05T and U = 1.4D + 1.4T These loading combinations will ensure serviceability by combining the differential settlement effects with the long-term operating loads. Severe Environmental Conditions U = 1.0D + 1.0L + 1.0T + 1.0W and U= 1.0D + 1.0L + 1.0T + 1.0E These loading combinations consider the effects of operating loads and settlement combined with either the design wind or operating basis earthquake. These additional provisions are beyond the ACI 318-77 code requirements, and are included to maintain safety margins consistent with the nuclear industry criteria (see ACI 349) because the wind and operating basis earthquake loadings are considered to occur more than once in the life of the plant. Provisions will not be added for extreme loads such as tornado, safe shutdown earthquake, and pipe rupture because these are postulated one-time occurrences. The above criteria for normal operating and severe i environmental conditions are applicable to all Seismic , Category I structures subjected to differential settlement. ! Only the diesel generator building will be evaluated by 3 these criteria because the other Seistic Category I structures are either founded on adequate backfill or include corrective measures to transfer the loading directly to the glacial till. Revision 3 9/79 15-2 2i57 20/
- 3) The ground motions are small during a seismic event at the Midland site (0.06 g OBE and 0.12 g SSE), and the resulting strains from an earthquake will be small.
The calculations on all of the structures indicate that the structural foundations during a seismic event generate increases in bearing pressure which are well within the allowable pressures that the soils can withstand. The main loads on the structures are already present and are far greater than any increase in load due to a postulated seismic event. In order to give assurance that no loss of contact between the structural founda-tions and the supporting media is credible, the fol-lowing areas are discussed, a) The fill properties under the control tower of the auxiliary building were evaluated by soil borings during the investigation program. The investigation and subsequent studies indicate that the fill settlement leading to a loss of contact between the mat foundation and the fill is unlikely for the following reasons.
- 1. The fill material is clean sand and concrete.
The average value of the standard penetration resistance of the fill is approximately 90, based on borehole AX-6. Thus, the penetration resistance value indicates that the fill is very dense.
- 2. The fill has been loaded by the construction of the structures, and no appreciable settle-ments (0.3 inch as of March 20, 1979) have been observed or loss of ctntact under the control tower mat been found.
b) The electrical penetration areas of the auxiliary building will be underpinned with caissons. The fill material beneath the feedwater isolation valve pits will be replaced by concrete backfill 3 and will be utilized to resist the horizontal seismic force from the electrical penetration areas. c) The auxiliary building railroad bay is founded on medium to dense sand backfill. The backfill is adequate for supporting the structure and the 3 liquifaction potential has been eliminated by areal dewatering. Revision 3 9/79 2157 208 15-3
d) The portion of the service water pump structure foundation on fill will be modified as stated in
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the response to Question 12. Driven piles will be loaded by jacking against the existing structure l3 and will be founded in the natural till. e) The portion of the retaining wall adjacent to the service water pump structure which is not founded on original material is supported by stiff to very stiff clay backfill underlain by medium dense to 3 very dense sand. This backfill is adequate for supporting the structure, and no remedial measures are planned. , ,.. ~~' 21S7 269 Revision 3 9/79 15-4}}