ML19209D119

Interim Deficiency Rept Re Concrete Voids in Eighth Lift of Unit 1 Reactor Containment Bldg.Deficiency Will Be Closed Out by 800119.Final Rept Will Be Submitted within 30 Days

ML19209D119
Person / Time
Site:	South Texas
Issue date:	08/15/1979
From:	HOUSTON LIGHTING & POWER CO.
To:
Shared Package
ML19209D108	List: ML19209D107 ML19209D119
References
NUDOCS 7910190423
Download: ML19209D119 (12)

Text

{{#Wiki_filter:. INTERIM REPORT ON THE STPEGS RCB NO. 1 LIFT 8 CONTAINMENT VOIDS INTRODUCTION On June 5,1979, Houston Lighting & Power Company submitted a final report on the void deficiency that had occurred on the 15th lift of Unit 1 RCB Containment Shell. This report contained a description of the methods that were used to identify, analyze, and repair these voids. The report also contained information on those actions taken to preclude the recurrence of this deficiency. Prior to the preparation of this final report, information was obtained from site personnel which led to the concern that voids might exist in the 8th lif t of the Unit 1 RCB Contair. ment Guter Shell. Soundings were begun and it was determined by drilling that voids did indeed exist. On June 18, 1979, HL&P notitied the NRC that the condition was reportable under the requirements of 10CFR50.55(e). At this time, a stop work notice was issued for the placement of all concrete in the Unit 1 and Unit 2 RCB Containment Shells. At this time, a significant amount of investigation has been performed towards the resolution of this deficiency; however, the work has not been completed. Thus, this interim report will provide the status of this activity and will provide information on the work yet to be com-pleted, including an estimated schedule fc-the completion of these activities. INVESTIGATION The investigation of this deficiency was two-fold. One facet of the in-vestigation was directed toward determining the extent of the voids. The ~1173 334 m o nw ez.3

Interim Report Page 2 other facet of the investigation was directed toward determining the cause and providing sufficient corrective action so that the placing of concrete in the RCB Outer Shells could resume. A logic diagram was prepared so that this work could proceed in a planned and orderly manner. A copy of this logic diagram is contained in Figure 1. Initially, B&R Construction placed a 2' x 2' grid on the steel Containment liner from El. 57'0" to El. 67'0" for the full circumference of the Con-tainment. The liner was then sounded for the purpose of detecting potential void areas, using procedures that were developed during the investigation on Lift 15. All of this activity was conducted under Quality Control sur-veillance. This procedure involves the tapping of the liner using a metal hanner and identifying areas of "non-contact" between the liner plate and the concrete based upon the sounds as detected by the human ear. The areas of "non-contact" were physically marked on the liner plate and this informa-tion was then transferred to drawings and transmitted for evaluation. Draw-ings of the liner were prepared showing all penetration and liner stiffening systems. Based upon these drawings, direction was provided to drill holes in the liner plate to determine if the "non-contact" areas were indeed voids. A total of 158 holes were drilled and investigated. As the result of this investigation,12 areas were identified in which voids existed. The voids were then explored using probes and a fiber scope to determine the extent of "non-contact". These void areas are shown in Figure 2. The majority of the "non-contact" areas were attributed to temporary weldnents attached 1173 335

Interim Report Page 3 to the liner, normal concrete settlement / shrinkage, and liner movement. These findings were consistent with the conclusions obtained during the investigation of the Lif t 15 deficiency. The investigation to determine the cause of tnis deficiency and to provide recurrence control for future pours was conducted in the following manner. A review of the pour packages (which included inspection reports, test data, and non-conformance reports) which were applicable to Lift 8 was conducted. This investigation was performed for the purpose of identifying any un-expected conditions which may have occurred during the course of the place-ments and thus, could have contributed to the problem. The information obtained during this investigation was cnnbined with information obtained during interviews with construction and inspection personnel to provide a basis for assessing the proccdurcs being utilized to control the activities during these complex concrete pours. During the investigation to determine the location of the voids, it was asce/tained that the voids of significanca were located under the horizontal 8" channel and l" x 8" plate stiffeners in the vicinity of added reinforcing steel around penetrations. Such areas require an additional amount of attention and vibration during the consoli-dation of tha concrete. During this pour, these areas were at the approximate 5' mark of the 10' pour and their accessibility for inspection and vibration was poor. As the result of these investigations, it was determined tat recurrence could be affected by providing for better accessibility to those areas of congestion where additional inspection and vibration is required, 1175 336

Interim Report Page 4 and by strengthening the construction and quality control procedures. A list of recommendations for corrective action was prepared and was reviewed and approved by both Brown & Root and Houston Lighting & Power Companies. A summary of these recorrmendations is contained in Table 1. Construction and inspection procedures and engineering design documents are currently being revised to accommodate for the implementation of these recommendations. CONTINUING ACTIVITIES Based upon the information obtained during this investigation of the voids in Lif t 8, it'was concluded that other void areas could exist beneath pene-trations and the 8" channel and plate stiffeners where additional reinforcing steel is located. Therefore, additional soundings will be made in,three general penetration areas )f high stress regions and congestion:

1) the equipment hatch, 2) personnel air lock, and 3) the main steam and feedwater lines.

The current areas of investigation are shown in Figure 3.1 and 3.2. The logic diagram and plan for the completion of this activity is contained in Figure 3.3. The use of alternate methods of sounding the liner was investigated. This investigation consisted of reviewing utility reports to the NRC for similar occurrences on the Wolf Creek, Edward Hatch, and VC Summer nuclear power plants. These reports described similar problems and methods of detecting voids behind the liners. The narits and effectiveness of the alternate methods contained in these reports were discussed with industry personnel 1173 337

Interim Report Page 5 directly involved with their use. It was concluded that physically sounding the liner surface and selectively drilling holes to interpret and verify the soundings is as reliable as other more sophisticated techniques used for void detection. To properly interpret the soundings, the geometry of the liner stiffeners, penetrations, and a general configuration and congestion of this reinforcing steel must be considered. At the present time, activities are underway to resume the placement of concrete in the RCB Containment Shell. Construction and inspection procedures are being revised to upgrade the control of the concrete placement during the shell placements. In addition, design drawings are being revised to provide for additional accessibility to areas where additional inspection and vi-bration is required. The plan and logic diagram for this activity is also contained in Figure 3.3. It has been determined that the methods used to repair the voids observed on Lift 15 are appropriate and suitable for use to repair the voids found on Lift 8. Final evaluation of the material used in the repair of Lift 1.5 will be performed after all information relative to the actual Lift 8 voids is available. It is estimated that this deficiency, including repair, will be closed out on or before January 19, 1980. The final report will be submitted to the NRC within 30 days thereafter. 1173 338

TABLE I RCB SHELL CONCRETE PLACEMENT RECURRENCE CONTROL PROBLEM RECOMMENDED SOLUTION 1. Concrete-Uniformity A. Buy all produced concrete (batch 0 6"). B. Area Engineer to visually monitor slump consistency at hopper. C. Use of grout at penetrations as determined by Engineering. D. Aggregate Moisture - Control for coarse aggregate. 2. Preplacement Planning A. Drawing and meeting on each placement and document. B. Define workable section on placement plan. 3. Inspection A. Training of QC inspectors. B. Increase number of inspectors to 4 to 6 per pour. C. Advise foreman of inspectors' authority. D. Have specific vibrator inspector (s) on pour. 4. Equipment Breakdown A. Back-up equipment, one to one, located at the pour. B. Preventive Maintenance Progran identified and followed. 5. Access / Visibility Problem A. Reduce Lift #7 to approximately 6'-0, with channel at top; subsequent lif ts to be 10'-0. B. Selective shear bar relocation to increase accessibility (10'-0 c. to c.). C. Lighting available on the form. D. Engineering to review tie attechment at liner for lifts, at top of form. 6. Fatigue Start by 9:00 or scrap pour. 7. Vibration A. Crew deposit and vibrate simultaneously, responsible for each workable section. B. Pre-training of vibrator operators. C. Pencil vibrators at each work section for inside and outside face and at penetrations (2 pencil vibrators). D. Vibrators set-up for each section. E. Vibrator / Placement Method written by Construction, including assignment of vibrator operators to each section. 8. Training A. Vibrator-Placement Fecoman - one training placement program on technical aspects. I1 3 339 i

TABLE I Page 2 B. Vibrator training field class, demonstrating and explaining technique. C. Meeting with crews prior to placement after prepour meeting, Pour Card signed by the foreman. 9. Production Pressure At prepour meeting, inspector (s) explain "how" identified problems are to be interfaced and solved during the placement. 10. Records Document post-placement interviews. 1173 340

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