ML20195J435
| ML20195J435 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 11/18/1998 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20195J440 | List: |
| References | |
| 98-650, NUDOCS 9811240288 | |
| Download: ML20195J435 (13) | |
Text
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. s, VIRGiNI A EimcTitic ANi> I'owrit CONII%NY RaciistoNii, Visu;is:A 2326:
November 18, 1998 U.S. Nuclear Regulatory Commission Serial No.98-650 Attention: Document Control Desk NL&OS/GSS/ETS R0 l Washington, D.C. 20555 Docket Nos. 50-338 !
50-339 )
License Nos. NPF-4 NPF-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY l NORTH ANNA POWER STATION UNITS 1 AND 2 I PROPOSED TECHNICAL SPECIFICATION CHANGES '
REVISIONS TO ALLOWABLE GROUNDWATER ELEVATIONS AND REMOVAL OF PIEZOMETER DEVICE NUMBERS ASSOCIATED WITH THE SERVICE WATER RESERVOIR l l
Pursuant to 10 CFR 50.90, Virginia Electric and Power Company requests amendments, in the form of changes to the Technical Specifications and to Facility Operating License Numbers NPF-4 and NPF-7 for North Anna Power Station Units 1 and 2, respectively. The proposed changes will raise the allowable Groundwater levels of the Service Water Reservoir dike and will eliminate the measuring device numbers assigned to piezometers. A discussion of the proposed Technical Specifications changes is provided in Attachment 1.
The proposed Technical Specifications changes have been reviewed and approved by I the Station Nuclear Safety and Operating Committee and the Management Safety i Review Committee. It has been determined that the proposed Technical Specifications changes do not involve an unreviewed safety question as defined in 10 CFR 50.59 or a significant hazards consideration as defined in 10 CFR 50.92. The proposed Technical Specifications changes are provided as a mark-up in Attachment 2 and a typed version in Attachment 3. The basb for our determination that the changes do not involve a significant hazards consideration is provided in Attachment 4.
If you have any further questions, please contact us. !
Very truly yours, c . . _ ,
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Zur% n o
James P. O'Hanlon Senior Vice President - Nuclear 9811240288 981118 PDR ADOCK 05000338 P PDR
Attachments
- 1. -Discussion of Changes
- 2. Mark-up of Technical Specifications Changes
- 3. Proposed Technical Specifications Changes
- 4. Significant Hazards Consideration Determination
! Commitments made in this letter:
- . 1. There are no commitments in this letter cc
- U.S. Nuclear Regulatory Commission Region ll Atlanta Federal Center -
61 Forsyth Street, SW
, Suite 23T85 Atlanta, Georgia 30303 Mr. M. J. Morgan NRC Senior Resident inspector
! North Anna Power Station l l
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. Commissioner )
Department of Radiological Health 1 Room 104A :
1500 East Main Street Richmond,VA 23219 i i
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COMMONWEALTH OF VIRGINIA )
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COUNTY OF HENRICO )
1 The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by D. A. Christian, who is Vice President -
Nuclear Operations, for J. P. O'Hanlon, who is Senior Vice President - Nuclear,
- of Virginia Electric and Power Company. He has affirmed before me that he is l duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of his knowledge and belief.
Acknowledged before me this dayof GoamboO .19 .
My Commission Expires: March 31,2000.
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- )0U ]1 ([Ollh!] l l { Notary Public l
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Attachment 1 Discussion of Changes l
North Anna Power Station Units 1 and 2 Virginia Electric and Power Company l
DISCUSSION OF CHANGES l Introduction Pursuant to 10 CFR 50.90, Virginia Electric and Power Company (Virg;nia Power) I requests to change Technical Specifications Surveillance requirement 4.7.13.1, Ground Water Level Surveillance Requirements and related Table 3.7-6 Allowable ,
Ground"ater Levels - Service Water Resen/oir (SWR). Presently, TS Surveillance l Requirement 4.7.13.1 identifies individual groundwater level measuring device numbers that have been assigned to each of the three designated Service Water Reservoir zones. Table 3.7-6 contains groundwater threshold levels that are overly restrictive and out-of-date, which require Special Reports to be developed whenever these limitations have been exceeded.
This change requests that measuring device numbers assigned to piezometers be l eliminated from TS Surveillance requirement 4.7.13.1 in order to avoid redundancy, l eliminate confusion as well as the need to initiate Technical Specifications changes j whenever new piezometers are added, older devices are replaced or abandoned in-place. Eliminating reference to individual piezometers is consistent with the TS Surveniance requirement that clearly states that " groundwater level shall be determined l by measurement from each zone. At a minimum, at least one measurement shall be l made at each zone listed below and the measurement shall be within the limits presented'in Table 3.7-6:" Similarly, the TS Bases states: "A minimum of one I measurement device in each of the three zones is required to be operable in order to monitor g jundwater levels." However, all the operative standpipe piezometers will be monitored in accordance with the Periodic Test Program.
The proposed change in groundwater threshold levels will raise the allowable l groundwater levels to those consistent with the allowable levels as verified in Calculation CE-1385, Stability of SWR Slope Under increased Phreatic Surface.
Changes in the groundwater threshold levels are acceptable since this was expected I and recommended in the original Cc,fety Analysis Report (SAR) as well as the current Upated Final Safety Analysis Report (U?SAR), Technical Specifications (TS) and TS Basos. Technical Specification Bases 3/4.7.13 requires that " groundwater levels be rev:ewed to determine whether a changing groundwater environment warranted a change in threshold levels." This request to change allowable SWR groundwater threshold levels is the first request made since the initial piezometers were installed in 1972.
An Engineering mview of the original design basis stability calculation performed in 1974 has concluded that increasing the allowable groundwater levels in the southeast section of the SWR dike will not lower the factor of safety with respect to the stability of the SWR as defined by the original design basis calculation. In addition, Engineering has determined that the slope in the original design basis calculation was assumed to be more than seven (7) feet higher than the actual, existing slope. The phreatic surface assumed in the original design base calculation was found to be 'oprox. 30 ft. higher than the highest actual recorded water level along the southeast section to-date. The Page 1 of 7
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proposed SW reservoir groundwater level is 15 ft lower than the level assumed in the L original design basis calculation. Therefore, the proposed SW reservoir groundwater level is conservative as compared to the original design basis calculation, which means i
the stability is greater than that calculated in the design' basis calculation. Thus it is
!. - safe to conclude that raising the allowable groundwater level in the southeast section of r the SW reservoir as well as removing reference to individual piezometer device 2
numbers in the T3 Surveillance requirement will not create an unreviewed safety j question and will have no effect on the safety-related Service Water System or any l other system, component or structure.
Backaround i Current Licensing Basis
- The current Licensing basis originated from the NRC's response to an April 29,1975 Report on the Settlement of the NAPS Unit 1/2 Service Water Pump House. In its Regulatuy Staff Position 3.6, " Settlement of Service Water Pump House and Dikes,"
.F dated August 15,1975, the NRC expressed concem that loss of service water due to
. ~ seepage /loakage through the SWR liner could undermine the stability of the SWR,' as defined by the original design ~ basis calculation. it requested that the following-j corrective actions be taken:
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- i. a) A SWR . leakage monitoring . program be developed to promptly detect large
[ increases in the pond leakage rate. 1 j; . b) Periodic checks on pond leakage rates be included in Technical Specifications.
c). Analyses of the consequences of cracks in the piping within the spray pond be !
made to determine whether the lining will be eroded sufficiently to affect roling l capability, pond leakage or spray piping inspections. ;
- To meet these requirements, Technical Specification 3/4.7.13, Groundwater Level - ;
Service Water Reservoir, was devt.vped to require the monitoring of groundwater '
measuring devices around the SWR to be performed "at least once per 31 days for 5 years following the date of issuance of the operating license." Should the groundwater level measured at any piezometer exceed the allowable groundwater elevation given in Table 3.7-6, a) an Engineering evaluation must be performed and b) a Special Report must be submitted to the Nuclear Regulatory Commission (NRC) containing the results of the evaluation.
Additionally, Regulatory Guido 1.127, Inspection of Water-Control Structures associated with Nuclear Plants is also applicable, since raising the allowable groundwater elevation levels of the SWR can affect' its stability and function.
Regulatory Guide 1.127 requires that " dams and associated facilities be maintained in good working condition throughout their lives. Operation and surveillance throughout the years.should be conducted in such a manner that any change in their structural, hydraulic and foundation conditions can be detected promptly and corrections be made."
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b.
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i Design Basis t
Raising the TS Table 3.7-6 allowable groundwater level elevation at the crest located in the southeast end of the reservoir from "280 feet" to "295 feet" and the toe from "277 feet" to "280 feet" was anticipated in the original SAR / UFSAR and recommended in Bases 3/4.7.13. TS Bases 3/4.7.13 requires that " groundwater levels be reviewed to determine whether a changing groundwater environment warranted a change in threshold levels." UFSAR Section 3E.2.2, Borings and Instrumentation, as well as 3E.2.4.1, Foundation Conditions, noted that during initial 1975 soils testing, the " ground water table was approximately 10 feet below the original ground surface at the dike centerline at both sections." Based on this, the same analysis predicted that "when the phreatic surface was fully developed under operating conditions, the water surface is expected to be approximately at elevation 287-290 feet under the dike at both sections, an increase of less than 10 feet." Calculation CE-1386, Stability of SWR Slope Under increased Phreatic Surface, filed 04-13-98, confirmed that the limiting water level or phreatic surface along the toe of the southeast dike section could be raised from elevation 277 ft. to 280 ft. and the level of the crest could be raisrj from 280 ft. to 295 ft. without compromising the safety of the slope or lowering the factor of Safety below the required 1.5, as defined by the original design basis calculation and industry '
standards. Ultimately, raising these allowable groundwater levels will also result in fewer T.S. 6.9.2 required Special Reports beii.< asued.
To meet the above-mentioned SWR requirements, one (1) operable pneumatic and seven (7) open-tube piezometers are currently used to measure pore water pressure.
During previous TS Change Requests, Design Change Packages, and Periodic Test Procedure revisions, inoperable pneumatic piezometers were deleted or identified as
" abandoned." During initial filling of the SWR, pneumatic piezometers were installed since open-tube piezometers were not well suited for measuring rapidly changing groundwater levels. Since filling the SWR and the installation of the horizontal drcins near the SWPH, groundwater levels have fluctuated slowly with seasonal variation in rainfall and a gradual general increase in the groundwater levels. Such slow fluctuations can be readily monitored by open-tube piezometers.
Virginia Power plans to continue to monitor all open-tube piezometers installed within the SWR even though their individual measurement device numbers will be removed from the Technical Specifications and applicable sections of the UFSAR. The Technical Specifications continue to require measurement of groundwater by SWR quadrant irrespective of monitor type or present location. A current list of all open-tube piezometers will be monitored in accordance with applicable Periodic Test Procedures in order to obtain as much information as possible about groundwater levels.
No codes, standards, or regulatory requirements govern the operatien of pneumatic or open-tube piezometers. Open tube piezometers require no power source.
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- Discussion 1
The Service Water (SW: System is a shared, closed-loop system common to Units 1/2 that uses the SWR as ik normal heat sink. In the event of a failure in the function of the SWR, the SW system has the ability to draw required water from Lake Anna.
Together, the SWR and Lake Anna form the station's ultimate heat sink. The maximum SWR temperature of 95 degrees F and minimum level of 313 feet above sea level were designed to provide for 30 days of operation without reservoir makeup and without exceeding 110 degrees F after a single unit design basis accident.
During normal plant operations, service water is supplied from the nine (9) acre SWR i
- which contains approximately 22.5 million gallons of emergency cooling water. Service I water is pumped from the reservoir located south of the plant to various safety-related systems and components via redundant return headers and ' spray systems. The maximum allowed SWR level is 315 feet above sea level which prevents overflowing i the two (2) foot thick impervious clay liner that can hold water up to an elevation of 318 feet during high winds. The SWR is surrounded by a zoned rock-fill type dike that has
, a minimum 3-ft, freeboard when the reservoir is at its maximum level. The dike has an 1
impervious compacted center that is separated from rock fill by layers of sand and l 4 gravel. Located in the reservoir is the SW Spray subsystem which cools the retuming SW. The SW Pump House and SW Valve House are located along the northem edge of the reservoir. Reservoir level indication is provided on the Safeguards panels in the l Main Control Room.
l In order to ensure that SWR seepage or elevated groundwater levels do not affect the i a
stability of the SWR embankment, nine (9) pneumatic-type piezometers were installed I in trenches during the original construction of the SWR in 1972. The tip elevations of these piezometers were based on the assumption that the phreatic surface would develop at a relatively high elevation within the core of the SWR dike after the reservoir l was filled. No water was ever encountered in these original piezometers since the water levels never rose above the tips of the piezometers. The original piezometers i were subsequently replaced with nine (9) other pneumatic piezometers which were installed in boreholes in the dike after construction of the SWR dike was completed.
- Monitoring of these devices. centinued through mid to late 1980's until their end-of-service life failure.
In late 1990, four (4) opsvtube piezometers were installed to replace pneumatic piezometers that had failed. Open standpipe-type piezometers were utilized because of their simplicity, dependability, and long operanng life. Open tube or standpipe piezometers consist of En open well with a porous well screen attached which is monitored manually by dropping a probe or tape down it to determine the water level.
In 1993, two (2) additional open standpipe piezometers were installed to provide redundancy so that two (2) open tube piezometers were now available per zone.
In 1998, three (3) more standpipe piezometers were instal!ed to replace one of the last operative pneumatic piezometers, and to better define the groundwater regime at the toe of slope along at the southeast section of the SWR dike. The two (2) additional Page 4 of 7
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open-standpipe piezometers were installed at the toe of slope to provide actual rather I than estimated water levels which could be used in stability calculations should these l calculations become necessary.
J Several factors appear to be contributing to higher groundwater levels. Record rainfall !
amounts that resulted in increased local groundwater levels and recharge from the l SWR. There has been above-average rainfall since 1996. While groundwater levels '
have fluctuated with the seasons, it is known to be higher in the winter and early spring due to lack of vegetation and reduced drying due to shorter days and colder I temperatures. Evapotranspiration is recognized to be lower under these conditions and little recharge occurs during summer months.
1 Groundwater levels for the area adjacent to the lake have risen significantly since the North Anna River was dammed to form Lake Anna. Prior to filling the lake, the North Anna River elevation was at approximately elevation 200 ft. Currently, the lake is being maintained at el. 250 ft, which, over time, has gradually contributed to increasing the groundwater table in the immediate vicinity of the lake by approx. 50 ft. This rise in water level causes a reduction in the gradient or the difference in head of water over length, which results in slightly less water being discharged from the area near the SWR and a gradual build-up of water at the SWR.
Since the SWR was constructed in a relatively high area above the plant on partially saturated residual soil having low permeability, it also acts as a recharge basin. While the SWR is lined with a two foot impermeable soil liner, slow seepage of water from the SWR still percolates down through the partially saturated residual soil to the groundwater table. In this way the SWR recharges the area through seepage, however, if the recharge occurs at a faster rate than the horizontal groundwater movement away from the reservoir, a mound in the groundwater table at the SWR is created. Estimates of recharge versus horizontal flow indicate the recharge rate to be greater than the rate of horizontal groundwater movement. Based on this, it is reasonable to expect that the mound or saturation would increase as it has in recent years and this explains why water levels in the piezometers along the southeast segment of the dike show a greater increase in water levels than piezometers on the northeast, up-gradient side.
Fv cults of conductivity tests performed on samples of water taken from the SWR, at piezometer P-22 which is located on the crest of slope along the southeast side, and a small pond located near the SWR, clearly indicate that the sample obtained from the piezometer is not seepage from the SWR. The water in the SWR is treated with chemicals to protect the service water piping which are easily identified by conductivity testing. Samples of water from the SWR showed conductivity ten (10) times as high as the samples taken from piezameter P-22 or the small ponded body of water. Therefore, the contribution of seepage to the rise of the water level at the SWR is thought to be minimal when compared to the natural rise in the groundwater table.
The proposed changes to the North Anna Unit 1/2 Technical Specifications 4.7.13.1 are needed in order to clarify and provide flexibility to the TS Surveillance Requirement.
Surveillance Requirement 4.7.13.1 states, in part, that "at a minimum, at least one Page 5 of 7
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ground water measurement shall be made at each zone listed below," but then lists all the measuring devico numbers assigned to each of the three zones. This is m~isleading to those unfamiliar with the monitoring process, particularly when these same identified
- pneumatic piezonieters have been classified as " inoperable" or abandoned in the i applicable Periodic Test procedure. Pneumatic piezometers respond more quickly to l changing groundwater levels, but following the initial filling of the SWR and stabilization
'f groundwater leve!s, the pneumatic measuring devices could be replaced with the simpler more dependable and longer lasting open tube type piezometers.
1 Specific Chances I
a) Identify " Zone 1" with Service Water Pump House, " Zone 2" with southeast end of )
the reservoir and " Zone 3" with Service Water Valve House."
b) Remove all reference to individual piezometer measuring device numbers assigned to the three SWR zones.
. 2.~ Table 3.7-6 Service Water Reservoir - Allowable Groundwater Levels ,
, Reformat Table _ to more accurately identify the requirements of TS 3/4.7.1, specifically:
a) " Device No." column replaced by " Zone" and the 3 zones listed below it, b) " Measurement Location" column revised to-limit its description to the actual location of each measuring' device in each zone.
c) Elevations at the " crest" located in the southeast end of the reservoir were raised from "280 ft." to "295 ft." and the " toe" from "277 ft. to 280 ft." under the
" Allowable Groundwater Elevation" level column.
d) Add " Total" to clarify statement conceming Allowable Drain Flow Rate
< . Safety Sionificance Virginia' Power has reviewed this proposed Technical Specification chango request against the requirements'of 10 CFR 50.92 and has determined that the proposed
- changes will not pose a significant hazards consideration. Specifically, operation of the 1 North Anna Power Station in accordance with the proposed Technical Specification change will not:
- 1. Involve a significant increase in the probability or consequences of an accident previously evaluated since:
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a) Removing non-safety related SWR piezometer device numbers from the Technical Specification and raising Technical Specification allowable groundwater surface threshold elevation levels in the southeast section of the SWR will have no effect on the way the safety-related Service Water System '
was designed to operate.
b) Periodic Test Procedures will continue to identify all piezometer device numbers and require that they be monitored in order to obtain as much information as possible regarding changing groundwater levels.
c) Sufficient redundancy will continue to exist since at least two (2) open tube (standpipe-type) piezometers, not subject to mechanical failure, have been installed in each of the three (3) SWR zones to meet the TS Surveillance l Requirement that "at least one measurement per zone be available." '
d) Recent calculations have confirmed what initial, pre-installation calculations predicted: that raising the allowable water level in the southeast section of the SWR will not affect the stability of the SWR dike.
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- 2. Create the possibility of a new or different kind of accident from any accident i previously evaluated since:
a) The frequency of piezometer monitoring and the intent of monitoring groundwater surface threshold elevations in order to maintain stability of the SWR slope have not changed.
b) No physical modification to the plant or new mode of plant operation is involved.
c) Changes are consistent with the assumptions made in the Safety Analyses and original design basis calculation.
d) Failure of the SWR dike and ensuing loss of service water was the most serious accident postulated and considered credible. Operation of the SWR is not being ;
changed Therefore, a new or different kind of accident is not created by the I change in groundwater level. In addition, since both the SWR and Lake Anna reservoir provide redundant sources of service water, failure of the SWR is not considered as a credible accident.
- 3. involve a significant reduction in the margin of safety since:
a) Increasing the allowable phreatic surface in the southeast section of the SWR dike will not lower the Factor of Safety with respect to the stability of the SWR as defined by the original design basis calculation.
b) The margin to failure of the SWR dike has been proven by calculation to have not been reduced as defined by the original design basis calculation.
c) Subject changes will not impact the performance of structures, systems or components relied upon for accident mitigation or any safety analysis assumptions.
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Attachment 2 Mark-up of Technical Specifications Changes i
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4 North Anna Power Station
'Jnits 1 and 2 Virginia Electric and Power Company
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l North Anna Power Station Units 1 and 2 -
Virginia Electric and Power Compsny
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