ML20199G933
| ML20199G933 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 01/28/1998 |
| From: | Kansler M VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 97-682, NUDOCS 9802040372 | |
| Download: ML20199G933 (19) | |
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VIHUINIA ELECTHIC AND POWHH COMi%NY HICitMOND,VIHUINIA 20061 January 28, 1998 United States Nuclear Regulatory Commission Serial No.97-682 Attention: Document Control Desk MPW/ETS R2 Washington, D.C. 20555 Docket Nos. 50-338,339 License Nos. NPF-4,7 Gentlemen:
Y1BGINIAfJ.ECIRlC_AND_P_QWEfLC.QMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 RESP _QMSE.IQ_IHE_ DAM _SAEEIY_AMD1I_RELAIED TO THE CATEGORY l SERVICE WATER RESERVOIR DAM AT NORTH ANNA Wa have reviewed your letters dated November 13,1997 and December 16, 1997, regarding findings and recommendations from the Safety Audit of the Service Water Reservoir (SWR) Dam. The purpose of this letter is to provide clarification for certain findings along with corrective actions. A corrective action plan is attached for each finding including, actions taken, actions planned, and completion dates.
As a result of actions already taken, several of the findings require no further action at this time.
Of specific importance, a water sample from piezometer P-22 clearly indicates that the suspected seepage is groundwater and is not emanating from the service water reservoir. In conjunction with our review of stability calculations, we conclude that the SWR remains stable under the highest recorded phreatic surface to date.
Should you have any questions regarding this letter, please contact us.
Very truly yours, if
/
gwI A
Mr
. anslar
'/ic -P' resident - Nuclear Operations Attachments Commitments made in this letter:
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cci U S. Nuclear Regulatory Commission.
Region ll
. Atlanta Federal Center -
61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. M. J, Morgan NRC Senior Resident inspector North Anna Power Station
. Mr Jerrold W. Gotzmer, Director Federal Energy Regulatory Commission Atlanta Regional Office Parkridge 65 North Building y
3125 Presidential Parkway - Suite 300 Atlante, Georgia 30340 x
i
Serial No.97-682 Dam Safety Audit SW Reservoir Page 1 of 9 s -.
CORRECTIVE ACTION PLAN RECOMMENDATIONS FROM THE SAFETY AUDIT OF THE SERVICE WATER RESERVOIR (SWR) DAM, NORTH ANNA POWER STATION, UNITS 1 AND 2 5
Serial No.97-682 -
1 Dam Safety Audit SW Reservoir -
Page 2 of 9 -
INTRODUCTION Virginia Power has evaluated the items identified in your_ letter of November 13,1997,.
- and will address them individually in the body.of this document. Additional tests and
~ inspections were conducted and the following overview concerning stability of the-j l Service Water. Reservoir (SWR) is provided in conjunction.with results of these tests and inspections.- A sketch showing the locations of current instrumentation and survey monuments is contained in Figure 1 in Attachmec 2.
4 o
- The original' design basis caiculations used an assumed geometry for the dike which was greater than seven feet higher than the existing as t,uilt maximum section with the
- same dike slopes. The phreatic surface used in the original design basis calculation in
- the steady _' state condition, was assumed to saturate the dike,- intersect the sand and -
4
~ gravel filter, exit the filter, and be located several feet below the toe of the slope. A i
sketch depic:ing the dike - section and phreatic surface used in the design basis
[
L calculation is provided in Figure 2 in Attachment 2.
[
The phreatic surface utilized in the design basis calculation, at the crest of the dike
(
corresponding to the location of P-21 and P-22, was located at elevation 310.
l
[
Monitoring of the plezometers along the Southeast section of the dike shows the t
maximum phreelic or groundwater surface to be near the 280 foot elevation, some 30 feet lower than assumed in the design basis calculation. The assumed phreatic surface g
. based on_ current piezometer data and the present as built geometry is shown in i
~ Attachment 2, Figure'3. The factor of safety (F.S.) against a failure of the slope at the
+
Southeast section of the SWR dike using the historically highest phreatic surface as depicted Jin Figure 3 would be greater than that obtained by the design basis calculation. It is estimated that the F.S. based on the phreatic surface in Figure 3 would p
. be 1.6 or slightly greater as compared to 1.5 obtained in the design basis calculation.
4 As suggested, plazometers P-21 and P-22 were bailed to within a foot of their tips. The
! water level rose to the elevation recorded before bailing within approximately 24 and 48
[
hours, respectively, indicating 1 that ~ both piezometers were operating properly.
- Pneumatic piezometer P-10 was also purged and subsequent readings were consistent -
~
. indicting that Pm10 is also functioning properly. A plot of the water levels including the
[
latest readings-obtained on January;12,r1998,-are provided=in Attachment 2. Details concoming the result of the hailing are contained in Table 1 of Attachment 2.
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Serial No.97-682 Dam Safety Audit SW Reservoir Page 3 of 9 INIRODUCTION (conlinued)
Water level in test wells 1, 2, and 3 located along the northeast section of the SWR were measured. These water levels were compared with the levels in the piezometers located in the vicinity of the wells (P-20 and P-14). There was close agreement between the wells and the respective piezometers. Water levels in the wells and piezometers are provided in Table 2 of Attachment 2.
A Special Report entitled " SWR Groundwater Level Evaluation," sent in a letter (Serial No.96-561 dated December 10, 1996), concluded that the elevated water levels encountered in piezometer P-22 was the result of an elevated groundwater level ano not seepage from the SWR. To provide verification of this conclusion, water samples were taken from three areas around the SWR on January 12, 1998 to measure
(
conductivity, These conductivity tests clearly indicate the water obtained from eiezometer P-22 and the drainage area did not originate from the reservoir and therefore are not the result of seepage from the reservoir.
IMMEDIATE ACTION FINDINGS 1.
Increase piezometer reading frequency from quarterly to monthly.
Action: Starting in January 1998, the scheduled frequency for piezometer reading was changed to monthly. This frequency will continue until it is determined by Virginia Power not to be necessary.
Readings from piezometers P-10, P-21, and P-22 have shown decreasing water levels since April 30,1997. Piezometer P-22 has decreased 1.1 feet and has not exceeded the Technical Specification limit since the September 30, 1997 reading, it is probable that the summer drought in 1997, has had an effect on the ground water level. (Attachment 2, Piezometer Trends)
- Due Date: Initial action complete.
Monthly readings ongoing.
2.
Using embankment survey monuments, perform a horizontal movement survey and compare with the previous readings.
Action: The SWR slope and toe are inspected by an Engineer in accordance with station procedures on a six month frequency. Additional inspections of the crest and toe of slope, performed in November and December 1997, showed no cracking, displacement, sloughing, or indications of movement. Review of the survey data obtained for the SWR monitoring points, which is performed to monitor vertical movement of the survey monuments in the crest show no
Serial No.97-682 Dam Safety Audit SW Reservoir Page 4 of 9 1MMEDJATE ACTION FINDINGS (continued) indication of abno. mal or excessive movement.
There is no indication of movement or distress that would warrant reactivating alignment survey of the
- monuments. As suci', this action is not considered necessary at the present time.
Due Date: Complete, no further actions required.
3.
Piezometers P-21 and P-22 should be read, bailed until the water level is 5 to 10 feet below the current level, and then read periodically during refilling to d'..armine if the piezometers are operative and if the current readings are correct.
Action: Piezometers P-21 and P-22 were read on January 12,1998. Each piezometer was bailed and read. Subsequently, the piezometers were read twice a day until the water level reached the pre-bailing height. Piezometer P-21 returned to its original level within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and P-22 within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. The results indicate satisfactory operation of both piezometers. (Attachment 2, Table 1)
Due Date: - Complete, no further actions required.
4.
Inclinometer SI-3, located at the toe of area 4, should be read and the results compared to the latest available reading.
Action: As discussed in Finding Response 2 above, there is no indication of any movement in the SWR dike. Furthermore, Virginia Power has not been able to locate the cable required to monitor angular movement in the inclinometer casing thereby rendering the inclinometer inoperative.
The equipment manufacturer was contacted and informed Virginia Power that the cable required for the model is no longer available as it has not been manufactured for 20 years.
Due Date: In our opinion, no further actions are required.
o
- Serial No.97-682.
Dam Safety Audit SW Reservoir-Page 5 of 9 1
SHORT TERM ACTlON FINDINGS 1.1 Clear the vicinity around the weir wall of vegetation and obstructions to enable flow measurements.
Action: Virginia Power submitted a report to the NRC in February 1983, titled " Report on Monitoring of Settlement and Groundwater Level at Service. Water
- Reservoir, North Anna Power Station, Units 1 and 2." The report identified that flow? rates were measured et the weir wall from October 1978 through
- Septemb'sr 1982. -The flows were the result of rainfall and snowmelt runoff rather _ than SWR seepage __ and therefore - monitoring was discontinued.
- Furthermore, based on the results of the water samples taken and the review of the stability calculations (see responses to Short Term Action Findings 4 &
- 7) measuring flow at the weir wall is not considered to be necessary. For the above reasons, clearing of this area is not presently warranted.
Due Date: No further actions are required or planned at this time.
2.
In the area between the weir wall and the access road, clear vegetation and maintain cleared for visual observation.
Note any wet spots and develop a recording procedure to identify the locations and monitor the extent.
Action: See response to Short Term Action Finding 1 above. In addition, this area has been determined, by Virginia Power Water Quality Department personnel,_to
- meet the hydrology, vegetation, and soils definition of a " wetland." Anything that would remotely " disturb" the wetland, would require notification of the Army
' Corps. Of Engineers (COE)i describing our intentions and request a jurisdictional determination.- Projects subject to COE interpretation include any mec'enized land clearing, ditching and draining, stream channelization, and any other activity involving excavation.
= Due Date: In our opinion, no further actions required,
- 3.-
- At the culvert that passes under the lower access road (dividing line between zone 3 and 4); clear the upstream and downstream sides of vegetation.
Action: The upstream and downstream sides of the culvert that passes under the lower
- access road ' are - part _of-the - routine cutting and clearing; that is-currently performed around the SWR.~ A more thorough clearing of the culvert area will be_ performed during future cutting activities.
'Due Date:' Cutting and clearing is a continual activity, no further actions required.
Serial No.97-682 Dam Safety Audit SW Reservoir Page 6 of 9 SHORTTERM ACTIONElNDINGS (continued) 4.
Virginia Power Corporate staff indicated that analysis of seepage water could determine whether seepage was from the SWR. Once the welts are operational, water samples should be taken to see if the water source is in fact the SWR.
Action: Water samples were taken from three areas around the SWR on January 12,
-1998 to measure conductivity. These included water from the service water reservoir, water from piezometer P-22 casing during bailing, and ponded water at the weir wall in the wet aret. below the SWR dike and adjacent roadway (Attachment 2, Figure 1).
Sample results are as fellows:
2 Piezometer P-22 99 micrombos Weir Wall 123 micrombos Service Water Reservoir 922 micrombos Conductivity is a measure of a solutions capacity to conduct electric current and depends on the presence of ions. The more dissolved salts / ions that are present in the solution the higher the conductivity that would be expected. The substantially higher conductivity values obtained from the SWR sample is due to the biocidal and other chemical treatment used in the reservoir.
These conductivity tests clearly indicate the water obtained from piezometer P-22 and the drainage area did not originate from the reservoir and therefore are not the result of seepage from the reservoir. As a comparison, the conductivity of distilled (de. ionized) water ranges from 0,05 to 2.0 micrombos.
Due Date: Complete, no further actions required.
- 5.
Reactivate weirs for flow measurements. Those that cannot be made functional should be removed and new weirs established.
Action: Results of the conductivity tests on a water sample taken from the weir wall which is located downstream or downgradient from the other weirs, clearly indicates that the water did not emanate from the reservoir.
Therefore, reactivating weir-flow measurements - would only measure runoff and groundwater movement which would provide extraneous data not pertaining to SWR seepage or stability, in our opinion, such effort is unwarranted.
- Due Date
- = No further actions required or planned at this time.
-5+-
iSerial No. 97-682:
Dam Safety _ Audit SW Reservoir
..Y Page 7 of 9l SHORT TERM ACTION FINDINGS (continued) 6.=
Prepare and submit for approval _ additional piezometer installation locations. In areas 3 and 4 and in the downstream vicinity.
Action:TThis action was previously identified and submitted to the NRC in Special Report, Serial No.- 96-561, dated December 10/-1996.
A-_ design change.-
package is under development for the installation'of three additional standpipe
- piezometers. Approval by the NRC is only required _if it is determined that an
- unreviewed safety question exists. _Two standpipe piezometers will be installed -
at the toe of the: slope below existing piezometers P-21_ and P-22.- A-third
- standpipe piezometer will be installed near existing' piezometer P-10, which is -
the last pneumatic piezometer. These three piezometers will be monitored for information only.
u The Technical: Specifications will _not -be revised-to -include these new piezometers! Attachment 2, Figure 1.contains a plan-view of the SWR indicating approximate piezometer locations.
Due Date: Piezometer installation will be completed in 1998.
Monitoring at a frequency consistent with other piezometers will continue until it is determined these additional locations are not necessary.
7.
Review stability calculations based on the latest piezometer readings.
- Action::The original design basis-calculations were reviewed.
The SWR remains stable under the highest phreatic surface to date Reference the introduction for specific detal!s.
_ Due Date: 1 Complete, no further actions required, t
8.
The pneumatic piezometer, P-10, should be carefully purged and reread.
L Action:_ On January 12,1998, P-10 was ; carefully purged in-accordance with the-manufacturers instruction manual. - The ground water: elevation reading _after purging was 276.1 feet which is consistent with previous readings.
Due'.Date! Complete, no further actions required.
s' 3
______.__m__m______.___m m__.___
. Serial No.97-682 Dam Safety Audit SW Reservoir Page 8 of 9 INTERMEDIATE ACTION FINDINGS
-1.
Determine if the test wells can be used to obtain water level measurements for comparison with P-11, P-14 (new), and P 20.
Action: The water levels in the test wells (TW) were measured on January 9 and 13, 1998. There is close agreement in the water level between the respective test wells and operating piezometers. Reference Table 2 in Attachment 2 for water level measurements. Piezometer P-11 has not recorded a water level since 1977, as the water level was lowered below the tip (elevation 275.4 feet) by installation of horizontal drains at the SWPH.
Due Date: Complete, no further actions required.
2.-
Install an additional settlement marker in the east portion of area 5.
Action: There is no indication of movement or distress that would indicate a need for installing an additional settlement marker in the east portion of area 5 (reference response to immediate Action Finding 2), in our opinion, this action is not necessary at the present time.
Due Date: No actions planned or required
.s 3.
Re-evaluate embankment stability Lased on the latest piezometer readings and survey results.
i Action: See response to Short Term Action Finding 7 and Introduction.
Due Date: Complete, no further action planned or required at this time.
4.
Continue tree and brush removal.
Action: Tree and brush removal will continue as is currently being performed during the growing season.
-Due Date:
Compide, no addi'.ional commitment required,
)
Serial No.97-682 Dam Safety Audit SW Reservoir 5
Page 9 of 9 lNTERMEDIATE ACTION FINDINGS (continued) 5.
Conduct quarterly flow measurements for the horizontal drains that extend beneath the Service Water Pump House and include a summary of readings in the annualinstrumentation report.
Action: The Technical Specification requirement is to verify that flow does not exceed 8.5 gpm at least once per six (6) months. In addition, the cl:.rity of the out flow from each drain is recorded. A review of five years flow data was made (1993 through 1997). During this period the highest flow recorded was 3.8 gpm with an average bi-annual reading of 2.6 gpm.
Of the 60 clarity inspections performed, 52 were identified as being clear with 8 noted as having slight turbidity commensurate with still lake water.
At this time, it is felt that there is little if any correlation between flow from the horizontal drains and water levels in the piezometers, especially piezometers located in the Southeast section of the dike. Therefore, it is our opinion that an enhanced frequency of monitoring is not justified.
Due Date: No further actions planned, 6.
Prepare a report for review documenting additional measures to be taken based on instrumentation data and predicted performance of the embankment.
Action: Virginia Power will review applicable data for inclusion in the periodic 5 Year ISI Report, due by the end of 1999, unless new or additional data warrants an interim report.
Due Date: No further actions at this time.
7.
FERC staff conduct follow-up inspection and project review.
Action: Not applicable to Virginia Power.
i Serial No.97-682 Dam Safety Audit SW Reservoir Page 1 of 8 SERVICE WATER RESERVOIR FIGURE 1 -INSTRUMENT LOCATIONS FIGURE 2 -DIKE SECTION FROM CALCULATION 11715-141 SWEC FIGURE 3 - EXISTING SWR PHREATIC SURFACE PIEZOMETER TRENDS (P-10, P-21, P-22).
TABLE 1 - PIEZOMETER 21 & 22 BAILING MEASUREMENTS TABLE 2'- TEST WELL LEVEL MEASUREMENTS l
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TABLE 1 Data Obtained From Balling Pierameters P.21 and P.22 Initial Water El. (Pre Balling) 262.9 279.9 Piezometer Tip El.
260.0 259.6 El. Water aRer Bailing 260.5 260.4 El. Water aRer approx. 24 hr, 263.0 277.5 El. Water aRer approx. 48 hr, 279.5 NOTE: Water elevations are in feet mean sea level.
TABLE 2 Water Levels in Test Wells and Pierometers Located in Area 2 TW/Pizo. No TW-1 TW.2 TW.3 P.20 P.14 El. Water. A.
276.0 276.3 273.8 276.6 273.6 NOTE: Locations of test wells and piezometers are provided in Figure 1.
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_ _ _ _ _ _ _ _ _ _. _. _. _.. _. _ _ _