ML19269F421
| ML19269F421 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 12/10/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19269F419 | List: |
| References | |
| NUDOCS 7912210009 | |
| Download: ML19269F421 (6) | |
Text
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ENCLOSURE Review of Foundation Construc+ ion and Water Control Measures Backcround On November 2 & 3, 1979, the site received heavy rainfall of 5 3/4 inches which caused severe erosion around and possibly under seismic Category I foundations of the control building, and containment units 1 and 2.
Other parts of the site also were. damaged.
On November 14, 1979, NRC became aware of the problems during a ;uutine site visit by J. Harris, I&E Region II inspector. As a result, backfilling and concreteplacement in affected areas were halted, as described by I&,E Region II in a Confirmation of Action Letter dated Nov. 15, 1979, from J. O'Rcilly, I&E, to J. H. Miller, GPC. Resumption of limited work was approved by I&E Region II on Nov. 13, 1979, in a Confirmation of Concurrence letter from J. O'Reilly, I&E, to J. H. Miller, GPC. Following a conference call between NRR and I&E on November 27, 1979, we requested that the limited work authori::ed should be modifiec to include restrictions on removal of disturbed material until subsurf ace water levels have been established.
Our observations of the water problems are described in the attached trip report.
We find that there are two, related problems:
surface water problems -- intermittent problems caused by inadequate gracing and drainage and which resulted in erosien damage after a heavy storm.
subsurface water problems -- ongoing problems along the nor:3 wall of the auxiliary building. The source of the water is not, at this time, known and no damage has resulted but construction has been delayed. The seepage uncer containment unit 2 may be a subsurface water problem and may have caused damage.
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Reccmiendations Based on our observations of the water problems at the site, we recommend that the design and construction of foundations should be carefully reviewed by NRR and 1&E.
1.
The. existing subsurface water conditions and future changes in these conditions must be determined -- probably frem piezametric installations.
The critical area extends north of the auxiliary building to the fill under the turbine' generator building, and encompasses containment units 1 and P, and the control building. The subsurface water study should be designed to show the probable source of water near the auxiliary building, within containment unit 1, and under containment unit 2 tendon gaF ery, i.e., whether the source is rainfall within the excavation or seepage across the perimeter drain (around the edges of the excavation).
2.
After the subsurface water conditions are understood, a method (s) for handling this water during construction must be developed by the licensee and submitted to NRC for review and approval.
3.
Surface grading and drainage must be corrected to handle rainfall and to mitigate any furtiier erosion.
4.
Foundations which possibly have been damaged must be evaluated to determine the extent of damage. Corrective measures must then be developed by the licensca and submitted to NRC for review and approval.
5.
Special attention must be given to monitoring the performance of foundations in the vicinity of the erosion damage. The monitoring settlements and piezcmetric levels should continue at least through the completion of construction.
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There are indications that the foundation detail may have been modified since the PSAR was submitted'in 1972. Since.. i.; likely that a temporary dewatering system will be needed in the vicinity of seismic Category I structures, any variances from the PSAR submittal will need to be updated and reviewed in conjunction with the review of the proposed dewatering system.
7.
We have informtlly notified Hydrology-Meteorology Branch, OSE, and Structural Engineering Branch, 055, of the recent events relating to foundations at the Vogtle plant. We recommend that these branches continue to be informed of developments and to perform reviews in their areas, as appropriate.
Recuests for Infomatien from the Licensee In order for us to proceed with our review of the s,afety of the foundations at the plant we need the following.information from the licensee.
1.
Submit the results of subsurface water level determinations as obtained from piezcmeter installations or other methods.
Include an interpretaticn of the source of water, and estimated direction and rate of flow.
2.
Provide details of criteria andmethod(s) proposed for handling subsurface water,to NRC for our review and approval before ccmmencing dewatering operations.
3.
Provide cross sections showing (as of mid-November, 1979) marl elevations, foundation elevaticns, existing ground surface elevations, estimated locations of disturbed materials, and subsurface water levels.
Include cross sections at least along the following lines.
A.
east-west extending beyond both containments a) at the wall north of auxiliary building b) at the centerline of containment units 1 and 2 c) at the toe of the slope on the south side of turbine generator buiiding d) at the top of the slope on the south side of turbine generator building 2166 041
B.
north south from turbine generai.or building to auxiliary building e) at centerline of containment unit i f) at centerline of. plast '
g) at centerline of containment unit 2 C.
oblique directions, as necessary to show details of potentially disturbed areas at the southwest corner of containment unit 1, southeast corner of control room electrical tunnel, northwest corner of containment unit 2, and northeast corner of centrol building.
These cross sections may also be used to show actual areas of disturbed materials as such information becomes available. The cross sections generally should have equal vertical and horizontal scales.
4 Provid a detailed foundation plan of the area bounded by the north side of the auxiliary building, east side of containment unit 1, west side of centainment unit 2, and east-west centerline of turbine generator building.
Show (as of mid November,1979) existing foundations, existing mud mats, contours
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at 1 ft an*.ervals, notes indicating in general tctms the extent of existing construction above the foundat'.ons, Lee enimated areal enen't or disturbed materials, location of settlement monuments, and location of piezometers (indicating which are temporary and which are permanent). This plan may also be used to show actual areas of disturbed materials as such infonnation becomes available.
5.
For foundation construction, identify all areas of departure frcm the details specified in the PSAR and amendments.
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Whenthesubsurfacewaterregimehasbeenestablished,prohidedetails of the corrective measures which will be adopted to replace or repair any damage to existing mud mats,or foundation soils.
Include the methods to be used to handle contingencies such as loose or disturbed materials extending close to or beicw foundation elevatier., and such as ground water closer than 2 ft to finn, suitable material remaining after removal of unsuitable soil. Describe in detail the inspection and testing procedures to be adopted as criteria for acceptance of: suitable material.
Include, in addition to visual inspection and field density / moisture testing, a method of probing or evaluating materials 3 to 4 ft below exposed suitable surfaces. Provide a comitment to notify NRC in advance of your intention to expose critical areas identified in request #3 above so that inspection can be made.
7.
For the area delineated in request #4, abohe, prohide.available results and de-tails of the settlement monuments and settlement measuring program.
Inicude the location and type of settlement monuments, frequency of measuring, program for analyzing settlement data and accuracy of readings.
8.
Provide details of the piezometer installations. Include the location and installation details of piezameters and their identification as temporary (in foundation areas) or permanent (outside foundation areas and thus unseable at least throughout construction).
Indicate the proposed frecuency of measuring piezometric levels and the program for analyzing piezcmetric data.
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9.
Provide a plan showing details of the surface water management program.
Explain how this program will channel surface water away from foundations and slopes so' as to preclude a recurrence of damaging erosion.
- 10. Provide the design basis for construction slopes arcund seismic Category I structures. Specify the minimum acceptable building set-back distances from the top of slopes and maximum acceptable sloces.
Include a discussion of the effects of lateral' strain near the face of slopes on the integrity of footings above slopes. Specify the minimum acceotable factor of safety for construction slopes and show that all construction slopes around seismic Category I structures have met and continue to meet these criteria.
- 11. Provide details of the perimeter drainage system around the edges of the main excavation and within the excavation. Shcw the locations of structures and their foundation elevations in relation to the drains. Describe the deccmmissicning proposed for temporary drains.
These requests for information are preliminary and we expect that additional information will be needed for us and for Hydrology-Meteorology and Structural Engineering branches.
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