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ConsumersPower James W CookCompany na nsu- - n+aanzinn,i s

and Construction

G*a''al officos: 945 West Parnall Road, Jackson, MI 49201 e (517) 788-0453 81-03 #13

April 23, 1982s x. r

// \,o, _. ._t_,y' NQ

/, \-Mr J G Keppler, Regional Administrator f- ,.r

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US Nuclear Regulatery Commission'a 07 6 h'

Region IIIg

i t..!.j799 Roosevelt Road f

d% yGlen Ellyn, IL 60137 \; if7

Mr H R Denton (25) ; g)-

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Office of Nuclear Reactor Regulation x! ia' iUS Nuclear Regulatory CommissionWashington, DC 20555

MIDLAND PROJECT -DOCKET HOS 50-329 AND 50-330BORATED WATER STORAGE TANK FOUNDATION OL DESIGN CALCULATIONSFILE: Oh85 16, 0.4.9.h9 SERIAL: 16172

References: J W Cook letters to J G Keppler:

(1) Serial 11201, dated February 20, 1981(2) Serial 11528, dated April 3,1981(3) Serial 12015, dated June 12, 1981(h) Serial 12799, dated June 26, 1981(5) Serial 13352, dated July 21, 1981(6) Serial 13653, dated August 28, 1981(7) Serial 14591, dated October 26, 1981(8) Serial lh339, dated November 13, 1981(o) Serial lh902, dated November 2h, 1981

(10) Serial 146h5, dated December 11, 1981(11) Serial lh66h, dated January 18, 1982(12) Serial 16127, dated March 15, 1982

This letter, as were the referenced letters, is an interim 50 55(e) reportconcerning the existence of cracks in the borated water storage tankfoundation.

Attachment 1 provides a report of the analyses and corrective actions thathave been or vill be taken as a result of the deficiency identified withthese cracks.

Another report , either interim or final, vill be sent on or before July 2,1982.

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{ EPA $8f$50hd 4 64 hf fIe

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Attachment 1.

Serial 16172'*

81-03 #13Bechtel Associates Professional Corporation

U67174 067259SUBJECT: MCAR 48 (issued 1/29/81)

The Existence of Cracks in the Borated WaterStorage Tank Foundation - Units 1 and 2

FINAL REPORT

DATE: April 20,1982

PROJECT: Consumers Power CompanyMidland Plant Units 1 and 2Bechtel Job 7220

Introduction

This report addresses the existence of cracks in the borated waterstorage tank (BWST) foundations as described in 11 CAR 48 and threesubsequent interim reports. This report is a final statement on theinvestigative analyses and all corrective actions that have been or willbe taken as a result of the deficiency identified with these cracks.

Description of Deficiency

The 52-foot diameter, stainless steel BWSTs are 32 feet high and rest ona reinforced concrete ring wall and compacted, granular backfill materialcontained within the ring wall. On one side is an integral valve pit thathouses connections and valves for the two 18-inch diameter pipelines thatservice each tank. Figure BWST-1 from the Atomic Safety and LicensingBoard (ASLB) llearing Testimony of Alan J. Boos and Dr. Robert llansonregarding remedial measures for the BWST is attached for reference.

During the load test on the Unit 1 tank (conducted in compliance with theresponse to 10 CFR 50.54(f), Question 4), a discrepancy was noted betweenmeasurements of settlements recorded at the jobsite and the computed dis-placements derived from the structural analysis used at that time. As aresult, the analysis was modified to include a finite-element model ofthe soil subgrade. A number of analyres were completed using variousvalues for the modulus of elasticity (E) of the soil. The results of theanalyses predicted that moments at several locations in the foundation

( structure exceed allowable moments. The foundation at these locations wasj examined to verify whether visible signs of high strain in the reinforce-

ment existed. Cracks.were found in the structure at those locationsindicated by the analysis as having greater than allowable moments. Thelargest crack measured 0.063 inch. Subsequently, the Unit 2 tank founda-tion was also examined; similar cracks were found, and the largest crackmeasured 0.035 inch. The smaller bearing area of the Unit 2 valve pitpartially explains why the cracks in the Unit 2 tank foundation aresmaller than the cracks in the Unit 1 tank foundation.

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Serial 1617281-03 #13

Attachment 1: MCAR 48, Final Report , "The Existence of Cracks in theBorated Water Storage Tank Foundation - Units 1 and 2,dated April 20, 1982

CC: RJCook, Midland Resident InspectorDocument Control Desk, NRC Washington, DCAtomic Safety & Licensing Appeal BoardCBechhoefer, ASLBMMCherry, EsqFPCowan, ASLBRSDecker, ASLBDSHood, USNRC (2)RHernan, USNRCJHarbour, ASLBJDKane, USNRCW0tto, US Army Corps of EngineersWHMarshallFRinaldi, USNRCHSingh, US Army Corps of EngineersMSinclairBStamirisSJPoulos, Geotech Eng, Inc

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Bechtel Associates ProfessionalCorporation067174 067259

MCAR 48Final ReportApril 20, 1982

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Page 2.

Safety Implications

'

As shown in Figure BWST-1, the tanks' outside shell is attached to thering wall foundation by equally spaced anchor bolts that transferinduced forces from the anchor chair. Field observations indicated gapsbetween the anchor bolt nut and anchor chair in several locations aroundthe periphery of the tank. In other locations, the anchor chairs weredeflected, indicating high tensile stress in the bolts. This aachorbolt behavior results from the distortion of the foundation ring whichis caused by differential settlement; this agrees with the conclusionsof the modified structural analysis. The tension induced in the boltsis similar to the tension induced by a preload phenomenon and does notaffect the ability of the bolts to resist design loads. Although thering wall is cracked, it is capable of providing the necessary anchoragefor the anchor bolts to resist tension due to externally applied forces.

The concrete ring wall confines the foundation material which is loadedby the tank; this confinement causes hoop tension in the ring wall.Cracks equal in size to those observed in the ring wall expose thereinforcing steel to the groundwater and atmosphere. If the reinforcingsteel carrying the hoop tension were to corrode significantly, the

'

ability of the ring wall to resist the hoop tensio.n would be reduced.Reduction of overall strength of the ring wall, combined with increased

,

displacements (both vertically and laterally) of the ring wall, mayoccur, causing stress concentrations in the tank near anchor chairs.

Based on the foregoing discussion, it is concluded that the cracking ofthe ring beam does not create a present safety problem for the tank.However, it could not be conclusively shown that the safety of futureplant operations would not have been affected if the deficiency had go'e;

uncorrected. Therefore, the condition was treated as reportable underthe provisions of 10 CFR 50.55(e).

Probable Cause

'Review of field observations and analytical investigations leads to anunderstanding of the probable cause. When the tank was loaded, thebearing pressure on the tank area was increased to approximately 2 ksfgreater than the valve pit area; however, this 2 ksf differential wasnot accounted for in the calculation for ring beam reinforcing. As aresult, the valve pit restrained the tank foundation from settlinguniformly, causing bending at the ring wall / valve pit junction.

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Bechtel Associates Professional Corporation

MCAR 48?inal ReportApril 20, 1982 ,

Page 3

Corrective Action

To ensure that the BWSTs function properly in the future under alldesign conditions, the following actions are being implemented.

1. A portion of the valve pit and its surrounding area has been sur-charged. Figure BWST-2 from the ASLB Hearing Testimony ofA.J. Boos and Dr. R. Hanson details the surcharge program which wasbegun October 27, 1981, and completed March 19, 1982.

The surcharge operation has consolidated the fill beneath the valvepit, thereby reducing the amount of expected residual differentialsettlement of the foundation structure over the 40-year life of theplant. In addition, by reducing the differential settlement, thesurcharging has reduced the ring wall distortion. However, theproposed remedial plan for the ring wall described below will nottake credit for this reduced distortion, and, therefore, is con-servative.

2. A reinforcing ring beam will be constructed around the existingring wall. The new ring beam is sized to resist all imposed load-ing from the tank, including additional future bending induced bythe predicted residual differential settlement between the ringwall and the valve pit. Shear connectors transfer the shear forcefrom the existing ring wall to the new ring beam. One end of theshear connectors will be installed in the existing ring wall bydrilling and grouting. The other end will be cast in the new ringbeam. All cracks in the existing ring wall that exceed 10 milswill be repaired by pressure grouting. The main reinforcing barsin the new ring beam that terminate at the valve pit are anchoredin the roof or base slab of the valve pit by grouting them intodrilled holes.

Construction of the new ring beam is scheduled to take placebetween May 10, 1982, and July 23, 1982.

3. After ring beam construction is complete, the Unit 1 tank (BWST IT-60) will be releveled. The Unit 2 tank (BWST 2T-60) need not be

j releved because the ring wall foundation is not severely distorted.!

A detailed procedure has been developed to define a plan of actionr

| to relevel BWST IT-60. This procedure is supported by an analysiswhich demonstrates that the tank will not be overstressed duringthis operation. Strain gaging of the tank will be used as a backupto this analysis. A brief summary of the procedure is providedbelow.

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Bechtel Associates Professional Corporation067174 067259

MCAR 48Final ReportApril 20, 1982Page 4-

.

a. Drain and vent the tank

b. Mount strain gages

c. Attach 12 to 16 electromechanical jacks to the anchor boltchairs

d. Lift the vessel approximately 3 feet. ( All jacks will be con-trolled from a central control panel and will lift at the samerate and time.),

e. Support tank with cribbing

f. Install Celotex cofferdam around the inner diameter of thering wall to contain grout placed in Step k below

g. Add and contour oil-impregnated sand

h. Clean the top surface of the ring wall

1. Place stainless steel shims on the original concrete ringwall. Level to a common datum plane approximately 1-1/2inches above the ring wall. Set shims t'o the followingstandard:

1) 1/8 inch within any 30 feet of circumference

2) 1/4 inch over total circumference

J. Remove cribbing and lower the tank

k. Add nonshrink grout under the tank bottom to the Celotexcofferdam and allow grout to set

1. Remove strain gages

! m. Tighten anchor bolt nuts!

This releveling of BWST IT-60 is scheduled to begin July 19, 1982, and,

( be completed September 17, 1982. At that time, the piping will be'

reconnected to the tanks, the tanks will be refilled, and by December 17,1982, the BWSTs will be in conformance with the requirements of thefinal safety analysis report (FSAR).

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Bechtel Associates Professional CorporationU67I74 0672;._9

MCAR 48Final ReportApril 20, 1982Page 5

4. After the new ring beam is constructed, two observation pits willbe provided for each BWST foundation at the high stress locations.The new ring beams will be monitored monthly for possible cracksunder the service condition for 6 months af ter filling the tanks.

At the end of the monitoring period, a report evaluating crackswill be submitted to the NRC. However, if during the monitoringperiod any cracks are noted to be 30 mils or larger, an engineeringevaluation will be conducted ~ to determine whether the tank shouldbe drained.

BWST foundation settlement will also be monitored as part of thefoundation survey. Foundations are surveyed at 60-day intervalsduring construction and at 90-day intervals for the first year ofplant operation. Subsequent survey frequency will be establishedafter evaluating the data taken during the first year of plantoperation. As a minimum, the rank foundation would be monitoredannually for the next 5 years of operation and at 5 year intervalsthereafter.

The critical areas of each foundation at the transition zonebetween the ring wall and the valve pit will be monitored using astrain gage system. This system will be monitored at the samefrequency as the foundation survey using established acceptancecriteria.

The construction period survey requirements are currently a partof project construction specifications (7220-C-76). The construc-tion period strain gage monitoring requirements will be incorporatedinto the project construction drawings of the new ring beam (7220-C-1153 and C-1154) by May 21, 1982. The long-term survey and straingage monitoring requirements will be incorporated in the FSAR tech-nical specifications by January 1, 1983.

,

ha .ISubmitted by: M,j,M/i /

'I; Q)Approved by: e l- @*'

L.H. CurtisPro ect ng ne ring Manager

Concurrence by: ' ' ~ MtE,H. Smith

! Engineering Manager!

Concurrence by: b/k M.A. Dietrich'

| Project Quality; Assurance Engineer

L

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___.

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