ML20010F445

Interim Deficiency Rept Re Existence of Cracks in Borated Water Storage Tank Foundation,Originally Reported on 810220. Cause Not Stated.Spec Changes & Surcharge Program Should Resovle Concerns.Next Rept by 811005

ML20010F445
Person / Time
Site:	Midland
Issue date:	08/28/1981
From:	Jackie Cook CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Keepler J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
10CFR-050.55E, 10CFR-50.55E, 13653, NUDOCS 8109100211
Download: ML20010F445 (3)

Text

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e Consumers Dower James W Cook C0mpBHy = ~,uen, - w, rw-mn and Construction

'teneral offices: 1945 West Parnell Road, Jackson, MI 49201 * (517) 788 0453 August 28, 1981 81-03 #6 Mr J G Keppler, Regional Director # g Office of Inspection & Enforcement O US Nuclear Regulatory Commission of Region III 799 Roosevelt Road Q'

Glen Ellyn, IL 60137 q<, 0 0193g v9 ,

u.s MIDLAND PROJECT & .

SURCliARGE OF THE BORATED WATER O , .,

S STORAGE TANK FOUNDATION s FILE: 0485.16, 0.4.9.49 SERIAL: 13653

REFERENCES:

J W COOK LETTERS TO J G KEPPLER, SAME

SUBJECT:

(1) Serial 11201, dated February 20, 1981 (2) Serial 11528, dated April 3, 1981 (3) Serial 12015, dated June 12, 1981 (4) Serial 12799, dated June 26, 1981 (5) Serial 13352, dated July 21, 1981 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. The purpose of this letter is to summarize concerns expressed in telephone conferences on July 30 and August 12 and 14 and in meeting discussions held at the Midland Plant site on August 3 and 5. The companies involved were Bechtel, Consumers Power, Corps of Engineers and the NRC.

The concerns expressed by the NRC and the Corps of Engineers are summarized in the following paragraphs.

1. The NRC would like assurance that the benchmark will be unaffected by the plant fill. The stability of Permanent Survey Bench Mark (PBM-1) has been verified by researching past survey records which show that the elevation of PBM-1 has been stable within surveying accuracy since its installation. Available onsite survey data was examined by R Landsman of the Region III NRC office on August 4. On August 5, we summarized the survey data relative to PBM-1 and USGS control point 7C. Similarly, we summarized the data for Subsidence #9 and USGS 7C (these surveys were run by Owen Ayres) as to dates run, level of survey, accuracy of closure and differences with respect to established elevation. This summarization data was submitted to R J Cook, Resident Inspector of NRC Region III, on August 5 for transmittal to R Landsman at the Region III office. In addition, the elevation of PBM-1 will be checked against a bench mark founded away from the plant fill prior to commencement and at termination of the surcharge program.

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2. There has been some concern regarding the development of concrete

• cracking in the valve pits during the surcharge program. The intelyt of

• he surcharge program is to improve the condition of the borated water storage tank foundation ind thus reduce the current stresses. It is not anticipated that the existing cracks will widen or that significant new cracks will form. During the surcharge program and upon removal of the surcharge, any new or existing cracks in excess of 10 tils will be monitored and the results will be reported to the NRP. This approach was discussed thoroughly and agreed to with the StatZ oad your consultant over a series of meetings although it is somewhat different than our prior approach which was documented in our letter of July 21, 1981.

3. It was agreed in a meeting on August 5,1981 that the existing condition of the borated water tanks and the foundation surcharge and repair are separate issues. We are committed to analyze the tanks under both the current condition and the predicted condition for the 40-year design life after the tank foundations have been modified and the tanks leveled.

These tanks will be repaired if an unsafe condition is indicated by the analysis.

4. An NRC Staff interest was expressed in-the expected shear stress in the valve pit walls. The allowable shear stress for working stress conditions is 70 psi. At the junction of the east valve pit wall to the ring of the Unit 1 tank, there is a 20 mil crack which extends the full height of the wall. The results of the finite element analysis indicates a shear stress of 91 psi at that 'x cation for the prior dead load condition. This shear stress will be seduced to 83 psi with the application of the surcharge load. We plan to repair the crack as part of our remedial measures on the foundation structure and this will reduce the shear stress below the allowable stress. Elsewhere in the val 7e pit, the wall shear stress under dead and surcharge loads is less than 59 psi.

5. The Staff was concerned that a crack could form in the tension zone of the valve pit wall and propagate into the compression zone of the wall.

The neutral axis for the critical section of the valve pit wall measures 16.2 inches from the top of the valve pit roof slab in a location within the 18-inch roof slab. The expected height of the new crack propagation is conservatively set at 18 inches from the top of the valve pit roof slab, which is the soffit. The crack at the critical section is expected to stay below this 18-inch value. We don't believe that crack propagation into the compression zone will occur because the ultimate moment capacity of the valve pit wall is governed by the yf21 ding of the reinforcement steel.

6. The Staff requested that the specifications for the surcharge program be revised to include settlement monitoring of the ring wall and the tank.

The ring wall will be monitored at approximately every 30 degrees. The tars will be monitored for vertical movement from the outside of the tank in the proximity of the ring wall monitor locations.

7. The Staff was concerned that the tank would be overstressed due to the surcharge load on the valve pit. The specification for the surcharge program will be revised to require that all the nuts on the anchor bolts ocC381-0417a100

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will be loosened prior to the surcharge application. This will allow for vertical movement between the anchor bolts and anchor chairs.

These specification changes supplement the changes we discussed in our reference letter dated July 21, 1981. In the earlier letter we committed to perform a daily visual inspection for cracks in the BWST ring walls and valve pits during the surcharge period. We also planned to stop further loading if a max! mum 1/2-inch settlement is reached prior to full surcharge loading, so that we can make an engineering evaluation.

We believe these resolutions cover all the concerns raised by the NRC in recent discussions and meetings on the BWST. We therefore request NRR concurrence in our surcharge program so that we can proceed with the program as soon as possible.

Another report, either interim or final, will be sent on or before October 5, 1981, a n g. ds L JWC/WJC/cr CC Director, Office of Inspection & Enforcement Att Mr Victor Stello, US NRC (15)

Director, Office of Management, Information & Program Control, US NRC (1)

RJCook, US NRC Resident Inspector Midland Nuclear Plant HRDenton, NRR (4)

JDKane, NRR DHood, NRR (1)

CBechhoefer, ASLB Panel RSDecker, ASLB Panel FPCowan, ASLB Panel MMCherry, Esq MSinclair BStamiris HSingh, US Army Corps of Engineers RLandsman, US NRC Region III I&E oc0881-0417a100 1

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