ML20052E418

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Interim Deficiency Rept Re Existence of Cracks in Borated Water Storage Tank Foundation.Portion of Valve Pit & Surrounding Area Surcharged.Reinforcing Ring Constructed Around Existing Ring Wall.Final Rept Expected by 820702
ML20052E418
Person / Time
Site: Midland
Issue date: 04/23/1982
From: Jackie Cook
CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To: James Keppler
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
10CFR-050.55E, 10CFR-50.55E, 16172, 81-03-#13, 81-3-#13, MCAR-48, NUDOCS 8205110089
Download: ML20052E418 (9)


Text

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  • Consumers Power James W Cook Company na nsu- - n+aanzinn,i s and Construction G*aal officos: 945 West Parnall Road, Jackson, MI 49201 e (517) 788-0453 81-03 #13 April 23, 1982 s x. r o, _. / /\,

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Office of Nuclear Reactor Regulation x! ia' i US Nuclear Regulatory Commission Washington, DC 20555 MIDLAND PROJECT -

DOCKET HOS 50-329 AND 50-330 BORATED WATER STORAGE TANK FOUNDATION OL DESIGN CALCULATIONS FILE: 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) report concerning the existence of cracks in the borated water storage tank foundation.

Attachment 1 provides a report of the analyses and corrective actions that have been or vill be taken as a result of the deficiency identified with these cracks.

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

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. Attachment 1 Serial 16172 81-03 #13 Bechtel Associates Professional Corporation U67174 067259

SUBJECT:

MCAR 48 (issued 1/29/81)

The Existence of Cracks in the Borated Water Storage Tank Foundation - Units 1 and 2 FINAL REPORT DATE: April 20,1982 PROJECT: Consumers Power Company Midland Plant Units 1 and 2 Bechtel Job 7220 Introduction This report addresses the existence of cracks in the borated water storage tank (BWST) foundations as described in 11 CAR 48 and three subsequent interim reports. This report is a final statement on the investigative analyses and all corrective actions that have been or will be 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 on a reinforced concrete ring wall and compacted, granular backfill material contained within the ring wall. On one side is an integral valve pit that houses connections and valves for the two 18-inch diameter pipelines that service each tank. Figure BWST-1 from the Atomic Safety and Licensing Board (ASLB) llearing Testimony of Alan J. Boos and Dr. Robert llanson regarding remedial measures for the BWST is attached for reference.

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

( structure exceed allowable moments. The foundation at these locations was j examined to verify whether visible signs of high strain in the reinforce-ment existed. Cracks.were found in the structure at those locations indicated by the analysis as having greater than allowable moments. The largest crack measured 0.063 inch. Subsequently, the Unit 2 tank founda-tion was also examined; similar cracks were found, and the largest crack measured 0.035 inch. The smaller bearing area of the Unit 2 valve pit partially explains why the cracks in the Unit 2 tank foundation are smaller than the cracks in the Unit 1 tank foundation.

.g Serial 16172 81-03 #13 Attachment 1: MCAR 48, Final Report , "The Existence of Cracks in the Borated Water Storage Tank Foundation - Units 1 and 2, dated April 20, 1982 CC: RJCook, Midland Resident Inspector Document Control Desk, NRC Washington, DC Atomic Safety & Licensing Appeal Board CBechhoefer, ASLB MMCherry, Esq FPCowan, ASLB RSDecker, ASLB DSHood, USNRC (2)

RHernan, USNRC JHarbour, ASLB JDKane, USNRC W0tto, US Army Corps of Engineers WHMarshall FRinaldi, USNRC HSingh, US Army Corps of Engineers MSinclair BStamiris SJPoulos, Geotech Eng, Inc L_ _

Bechtel Associates ProfessionalCorporation 067174 067259 MCAR 48 Final Report April 20, 1982 Page 2 Safety Implications As shown in Figure BWST-1, the tanks' outside shell is attached to the ring wall foundation by equally spaced anchor bolts that transfer induced forces from the anchor chair. Field observations indicated gaps between the anchor bolt nut and anchor chair in several locations around the periphery of the tank. In other locations, the anchor chairs were deflected, indicating high tensile stress in the bolts. This aachor bolt behavior results from the distortion of the foundation ring which is caused by differential settlement; this agrees with the conclusions of the modified structural analysis. The tension induced in the bolts is similar to the tension induced by a preload phenomenon and does not affect the ability of the bolts to resist design loads. Although the ring wall is cracked, it is capable of providing the necessary anchorage for the anchor bolts to resist tension due to externally applied forces.

The concrete ring wall confines the foundation material which is loaded by the tank; this confinement causes hoop tension in the ring wall.

Cracks equal in size to those observed in the ring wall expose the reinforcing steel to the groundwater and atmosphere. If the reinforcing steel 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, may occur, causing stress concentrations in the tank near anchor chairs.

Based on the foregoing discussion, it is concluded that the cracking of the ring beam does not create a present safety problem for the tank.

However, it could not be conclusively shown that the safety of future plant operations would not have been affected if the deficiency had go'e uncorrected. Therefore, the condition was treated as reportable under the provisions of 10 CFR 50.55(e).

Probable Cause Review of field observations and analytical investigations leads to an understanding of the probable cause. When the tank was loaded, the bearing pressure on the tank area was increased to approximately 2 ksf greater than the valve pit area; however, this 2 ksf differential was not accounted for in the calculation for ring beam reinforcing. As a result, the valve pit restrained the tank foundation from settling uniformly, causing bending at the ring wall / valve pit junction.

Bechtel Associates Professional Corporation MCAR 48

?inal Report April 20, 1982 ,

Page 3 Corrective Action To ensure that the BWSTs function properly in the future under all design 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 of A.J. Boos and Dr. R. Hanson details the surcharge program which was begun October 27, 1981, and completed March 19, 1982.

The surcharge operation has consolidated the fill beneath the valve pit, thereby reducing the amount of expected residual differential settlement of the foundation structure over the 40-year life of the plant. In addition, by reducing the differential settlement, the surcharging has reduced the ring wall distortion. However, the proposed remedial plan for the ring wall described below will not take credit for this reduced distortion, and, therefore, is con-servative.

2. A reinforcing ring beam will be constructed around the existing ring wall. The new ring beam is sized to resist all imposed load-ing from the tank, including additional future bending induced by the predicted residual differential settlement between the ring wall and the valve pit. Shear connectors transfer the shear force from the existing ring wall to the new ring beam. One end of the shear connectors will be installed in the existing ring wall by drilling and grouting. The other end will be cast in the new ring beam. All cracks in the existing ring wall that exceed 10 mils will be repaired by pressure grouting. The main reinforcing bars in the new ring beam that terminate at the valve pit are anchored in the roof or base slab of the valve pit by grouting them into drilled holes.

Construction of the new ring beam is scheduled to take place between 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.

r A detailed procedure has been developed to define a plan of action l to relevel BWST IT-60. This procedure is supported by an analysis which demonstrates that the tank will not be overstressed during this operation. Strain gaging of the tank will be used as a backup to this analysis. A brief summary of the procedure is provided below.

Bechtel Associates Professional Corporation 067174 067259 MCAR 48 Final Report April 20, 1982 Page 4

a. Drain and vent the tank
b. Mount strain gages
c. Attach 12 to 16 electromechanical jacks to the anchor bolt chairs
d. Lift the vessel approximately 3 feet. ( All jacks will be con-trolled from a central control panel and will lift at the same

, rate and time.)

e. Support tank with cribbing
f. Install Celotex cofferdam around the inner diameter of the ring 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 ring wall. Level to a common datum plane approximately 1-1/2 inches above the ring wall. Set shims t'o the following standard:
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 Celotex cofferdam 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

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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 the final safety analysis report (FSAR).

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Bechtel Associates Professional Corporation U67I74 0672;._9 MCAR 48 Final Report April 20, 1982 Page 5

4. After the new ring beam is constructed, two observation pits will be provided for each BWST foundation at the high stress locations.

The new ring beams will be monitored monthly for possible cracks under the service condition for 6 months af ter filling the tanks.

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

BWST foundation settlement will also be monitored as part of the foundation survey. Foundations are surveyed at 60-day intervals during construction and at 90-day intervals for the first year of plant operation. Subsequent survey frequency will be established after evaluating the data taken during the first year of plant operation. As a minimum, the rank foundation would be monitored annually for the next 5 years of operation and at 5 year intervals thereafter.

The critical areas of each foundation at the transition zone between the ring wall and the valve pit will be monitored using a strain gage system. This system will be monitored at the same frequency as the foundation survey using established acceptance criteria.

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

Submitted by:

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L.H. Curtis Pro ect ng ne ring Manager Concurrence by: '

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