ML19267A324
| ML19267A324 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 12/22/1978 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19263B150 | List: |
| References | |
| NUDOCS 7901080064 | |
| Download: ML19267A324 (20) | |
Text
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SAFETY EVALUATIO:10F VIRGlilIA ELECTRIC AllD POWER C0:! patly'S (VEPC0'S) REQUEST TO REVISE TECIUlICAL SPECIFICATI0!iS OF SECTIO!1 3/4.7.12, "SETTLEMEllT TO CLASS I STRUCTURES" 0F OPERATIflG LICEllSE flPF-4-liORTH AtillA POWER STATI0il - UllIT 1 Docket flo. 50-338
Background
Both Units 1 and 2 of the florth Anna Power Station share the service water system which is the normal source of cooling water and is designed as seismic Category 1.
It consists of two full capacity redundant trains each of which supplies water to both units. The service water is supplied from the service water reservoir by means of four service water pumps housed in the service water pumphouse, any two of which are required during all operational modes, while all four are available for fast cooldown.
Units 1 and 2 are also provided with a full capacity seirmic Category 1 auxiliary service water system as a backup for the cooling funct10n of the normal service water system. This system obtains its water supply from an alternate source, Lake Anna.
The service water pumphouse for Units 1 and 2 of the North Anna plant is located within the dike that impounds the service water reservoir.
Since the completion of construction of the pumphouse, it has settled more than was anticipated at the time the design was established and the construction permit was issued. Prior to issuing the operating license for Unit 1, the Virginia Electric and Power Company (VEPCO) identified and evaluated the significance of settlement effects on Unit 1 and proposed a technical specification for plant operation 73010s coc,c[
to assure that the service water pumphouse and all other necessary related structures would perform their safety function.
We reviewed, approved and published the Technical Specifications.
Technical Specification 3/4.7.12, as published indicates the maximum allowable additional average settlement of the service water pumphouse since the base date of December 1975 is 0.15 feet for the life of the facility. This value is computed by takirg the average of the settlement measured at the four corners of the pumphouse. According to this specification, whenever the average additional settlement reaches 75 percent of the allowable given in Table 3.7-5 (Page 2/4.7-12 of the specifications), an engineering review of field conditions and an evalu-ation of the consequences of additional settlement are to be conducted and reported to the NRC within 60 days.
Since the average settlement of the service water pumphouse now exceeds 75 percent of the allowable settlement value given in Table 3.7-5 of the Technical Specifications, VEPC0, in accordance with Technical Specification 3/4.7.12 provided the required information to NRC in their letter of May 31, 1978.
In its letter of June 13,1978, VEPC0 requested an amendment to a
Technical Specification to Operating license NPF-4 of the North Anna Power Station, Unit 1.
The proposed change related specifically to Technical Specification 3/4.7.12, " Settlement of Class 1 Structures."
In its letter, VEPC0 stated that its request ress '.ed from its engineering review and evaluation of cettlement of the service water pumphouse. On the basis of this evaluation VEPC0 requested that the maximum allowable average service water pumphouse settlement be changed from 0.15 feet to 0.33 feet. As stated previously, the results of the evaluation were reported by VEPC0 in its letter of May 31, 1978 and Attachment 2 to its letter of June 13, 1978.
We reviewed the information presented in VEPCO's letters of May 31, 1978 and June 13, 1978. As a result of our review, we determined that additional information was required, and requested VEPC0 to provide the additional information set forth in our letters of June 30, 1978, July 19,1978 and July 26, 1978.
In letters dated August 2,1978 and September 8,1978, VEPC0 submitted its response to our requests. VEPC0's letter dated November 22, 1978, indicated that they were experiencing difficulty in completing the surveillance requirements of the Technical Speci fications. He met with VEPC0 on December 5 and discussed the details and significance of these difficulties.
In a letter dated December 6, 1978, VEPC0 clarified its November 22, 1978 letter with respect to survey points associated with the service water pumphouse. We have reviewed this information and have obtained supplemental clarification with VEPC0's technical representatives. Our evaluation of this information follows.
Eval uation The present North Anna Unit 1 Technical Specifications 3/4.7.12 and 3/4.7.13, settlement and groundwater levels, set the allowable additional average settlement over the life of the plant at 0.15 feet since the base date of December of 1975.
4-VEPC0's proposal to more than double the 0.15 feet allowable additional average settlement value to 0.33 feet (since the base date of December 1975) has required the staff to conduct a detailed evalu-ation, as the actual design and code limits of connections and piping are approached.
We have identified some items of concern with respect to service water pumphouse settlement effects. These include:
(1)
Differential movement and tilt of the pumphouse with respect to the buried pipelines that might exceed the design movement of the expansion joints installed in January of 1976 to accommodate past and future differential movement.
(2) Tilt of the pumphouse that could result in deterioration or malfunctioning of the service water pumps within the pumphouse.
(3)
Increased stress levels and possible large deformation of buried service water piping resulting from settlement of dike and fill material that could affect the functional capability of the service water piping system to deliver design required fl ow.
(4) Leakage of service water from the reservoir through shears in the clay liner along the periphery of the pumphouse foundation.
(5) Cracking of the pumphouse structure due to differential settlement across this structure.
(_6) Deformation of pipes leading from the pumphouse to the spray distribution system in the reservoir.
Item 1 With respect to the first concern, we have concluded that VEPC0's proposed plan, as discussed in its June 13, 1978 letter,to alleviate the effects of settlement is incomplete because it does not address the effects of pumphouse tilting.
The expansion joints connecting the pumphouse to the service water pipes had been designed for 0.25 feet of differential settlement. An additional settlement of 0.2 feet due to dike fill settlement could be accommodated by the buried service water piping without exceeding American Society of Mechanical Engineers Boiler and Pressure Vessel Code limits. Technical Specification 3/4.7.13, which gives the present groundwater level monitoring program and limiting groundwater levels in the vicinity of the service water reservoir is closely related to Technical Specification 3/4.7.12.
Groundwater moni-toring as presently required by the Technical Specification is to be conducted nonthly for the first five years after the issuance of the Unit 1 Operating License.
If the pumphouse tilted such that greater settlement occurred at settlement monument SM-10 (Northwest Corner of pumphouse) than at SM-7, 8 and 9, the design vertical movement of the expansion joint (0.25 feet) could be exceeded at service water pipe joints closest to SM-10. Ikn average pumphouse settlements were limited to 0.15 feet, the realization of this concern was unlikely; at a limit of 0.33 feet, this occurrence may be possible.
As discussed for item 3, the staff has modified VEPC0's request of 0.33 feet to 0.22 feet.
It is our position that the differ-ential settlement measured between SM-7 or SM-10 and SM-15, SM-16 and SM-17 or SM-18 should not exceed the design basis of 0.25 feet for the expansion joints.
The technical specification of 0.25 feet for the expansion joints remains the same. Table 3.7-5 of the Technical Speci-fication is presented in Enclosure 1 of this report. The 75 percent Technical Specification reporting criteria will continue to apply to this limit.
Item 2 The second concern, pumphouse tilting effects on the service water pumps, is addressed in the response to question P3.6 of the Final Safety Analysis Report. The applicant has stated that the pumps will be shimmed, as nect ssary, to correct for any pumphouse tilt so that the pump align-ment is within the 0.011 inches per foot recomended by the pump manu-facturer. This corresponds to a total allowable displacement of 0.29 inches for the 26-foot-long vertical pump.
The manufacturer has also indicated that a total displacement of 0.5 inches would not adversely affect pump operability.
In addition, the applicant is measuring differential pressure, flow rita ivr vibration amplitude every 30 days as required by Article IUP-3000 of Section XI of the ASME Code. These pump performance parameters are to be maintained witnin the tolerances specified in Table IWP 3100-2 of section XI, except that for the flow rate parameter, a tolerance of
+8 percent is acceptable.
If necessary, corrective action will be taken as required by paragraph IWP-3230 to assure the required pump performance.
Maintaining the pump performance parameters within the specified tolerances provides adequate assurance that the pump will maintain its operability and that any effects of tilt will be accounted for.
Item 3 The stresses induced in the buried service water pipes, concern three, are addressed in VEPC0's letter of June 13, 1978. VEPC0's analysis and our independent evaluation indicate that American Society of Mechanical Engineers Boiler and Pressure Vessel Code allowable pipe stress appli-cable to the effects of any single nonrepeated anchor movement
(_NC 3652.3(b); i.e. as could result from building settlement) could be reached if the dike settles another 0.2 to 0.3 feet since the last reported settlement measurement of August 3,1978 reported in VEPC0's letter of September 8,1978. Because of uncertainties and gaps in settlement measurement data for the buried pipes, we have concluded that the maximum average additional settlement of the exposed end of any of the buried pipes beyond that of August 3,1978, will not be allowed to exceed 0.22 feet so as not to exceed Aaerican Society of Mechanical Engineers Boiler and Pressure Vessel Code allowable stress in accordance with NC 3652.3(b).
This can ce established by limiting the absolute elevations of SM-15, SM-16, SM-17 and SM-18. A required revision to Table 3.7-5 of the Technical Specification is presented in Enclosure 1 of this report. The 75 percent Technical Specification reporting criteria will continue to apply to this limit.
Item 4 With respect to concern four, the Final Safety Analysis Report indicates that the bottom of the ser vice water reservoir was lined with compacted cohesive soil to impede lea'< age of reservoir water into the underlying saprolite. The pumphouse foundation is supported by the compacted liner material. As the pumphouse settles with respect to the liner, it punches into the liner material, as evidenced by the past relative movemalt of the pumphouse with respect to the wingwalls. The VEPC0 letter of September 8,1978, includes an analysis of reservoir leakage potential due to bending of the liner.
We have concluded that the lack of potential for leakage has not been demonstrated and would be difficult to demonstrate and, therefore, have conservatively postu-lated that leakage will occur during the plant lifetime. Leakage of the reservoir liner will contribute to the quantity of water collected by the underdrain systen and will change groundwater levels measured by piezometers. Adequate assurance that leakage will not be undetected and affect safe operation of the plant can be attained by changing Technical Specification 3/4.7.13 to require:
(a) measuring and recording the quantity of groundwater flowing from the underdrains on a monthly basis for five years; if flow rates for any month become more than three times the average annual flow rate, an engineering evaluation of the cause of the changed flow rates should be conducted and a report filed with the NRC, (b) monitoring and recording groundwater elevations on a monthly basis for a period of five years, (c) at the end of the five year period, an engineering report is to be filed by VEPC0 to determine if further measurements of groundwater levels are needed.
A required revision to Technical Specification 3/4.7.13 covering the above matters is presented in Enclosure 2 of this report.
Item 5 The potential for significant cracking of the reinforced concrete pumphouse structure due to future differential settlement across the structure, concern 5, is likely to be preceded by warping of the pumphouse foundation. Available measurements and visual inspection by the appli-cant indicates that very little, if any, warping has occurred to date and that only nominal cracking is now evident.
Because of the relatively soft foundaticr. provided by the clay liner and underlying saprolite and the stiffneos of the pumphouse foundation slab, significant differential settlement across the structure is unlikely.
Item 6 The vulnerability of the spray piping connections at the service water pumphouse to further settlement of the pumphouse has been reviewed with VEPC0's technical personnel and representatives of the Stone &
Webster Engineering Corporation. One end of the four 35-foot long pipes supplying the spray system was rigidly connected to the pumphouse wall with concrete above the reservoir bottom during the spring of 1975. During June of 1975, the other end of the 24-inch-diameter pipes was supported above the reservoir bottom by a hanger and footing resting on the clay liner of the reservoir. Settlement of the southeast corner of the pump-house, where the spray pipes are connected, has been about 0.095 feet since the spring of 1976. The hanger has settled an estimated 0.08 feet since June 1975. To reach the American Society of Mechanical Engineers Boiler and Pressure Vessel Code allowabie stress in these pipes the differential settlement (as calculated by VEPC0 and reviewed by the staff) between the southeast corner of the pumphouse end the hanger would need to be 0.175 feet. Accordingly, in order to assure that pipe stresses will not exceed Code allowable values, the differ-ential settlement between marker SM-8 at the southeast corner of the pumphouse and markers H-569 and H-584 at the pipe support hanger should not become greater than 0.175 feet since the hangers were installed in June,1975. To incorporate this limit, a revision to Table 3.7-5 of the Technical Specification is presented in Enclosure 1 of this report.
The 75 percent Technical Specification reporting criteria will apply to this limit.
Because the allowable settlement values of the service water pump-house in the service water reservoir would be set at the actual design and code limits for the affected items, additional assurance was sought on the availability of service water to the plant from Lake Anna through the auxiliary service water system to maintain levels of safety which were determined at the construction permit stage of review.
In a letter dated December 20,1978, VEPC0 indicated that the intake structure on Lake Anna has not experienced either settlement or tilt as evidenced by the agreement between construction specification elevations for this structure and actual elevations recently measured on this structure.
The staff has concluded that VEPC0's present program which monitors the vertical movement of only one point on the Lake Anna intake structure is adequate because the intake structure has not experienced any settlement or tilt.
However, the auxiliary service water pumps are currently not tested periodically as reqaired in Section XI of the ASME code.
By letter dated September 29,1977, VEPC0 requested relief from the Section XI pump testing requirements for the first 20 months of commercial plant operation.
In this letter, VEPC0 also committed to conduct a study of the feasibility of installing a pump test bypass loop as permitted by paragraph IWP 1400 of Section XI of the Code. We have previously granted relief to VEPC0 from testing for this initial 20-month period.
However, at the end of the 20-month period we will review the results of the study and we will require that the auxiliary service water pumps be tested in the same manner as the service water pumps, or require that VEPC0 provide an alternate test mechanism which will assure operational readiness of the pumps.
The assurance of operational readiness will be incorporated into a future Technical Specification.
Environmental Consideration lle have determined that the proposed amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact.
Having made this determination, we have further concluded that the proposed amendment involves an action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR Section 51.5(d)(4),
that an environmental statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this proposed amendment.
Conclusion On the basis of our review we have concluded that the North Anna plant can continue to operate with a reasonable assurance of a supply of water from the service water pumphouse in the reservoir. Although we have made some changes in VEPC0's proposed values of allowable settle-ment, we do agree with VEPC0 that the existing technical specification value can be safely modified.
In the event the specified maximum allowable values are reached, the plant can still be safely shut down since the needed service water can be provided from Lake Anna by the Category I auxiliary service water system which will be periodically tested after 20 months to demonstrate its availability.
We have also determined that the maximum allowable limits specified in the proposed amended technical specifications cannot be increased without modifications if any pumphouse settlement occurs beyond the limits herein specified.
Specifically, when 75 percent of any of the maximum allowable settlement values are reached, the proposed amended Technical Specifications require that VEPC0 submit for our review its proposal for structural and/or system modifications to correct any deficiencies related to the settlement of the service water pumphouse.
Therefore, we have concluded, based on the considerations discussed above, that:
(1) because the proposed amendment does not involve a significant increase in the probability or consequenct.- of accidents previously considered or a significant decrease in any safety margin, it does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of this proposed amendment will not be inimical to the common defense and security or to the health and safety of the public. Also, we reaffirm our conclusions as otherwise stated in our Safety Evaluation Report and its Supplements.
Enclosmre 1 REVISION 1 NORTH ANNA UNIT 1 - TECHNICAL SPECIFICATIONS PLANT SYSTEMS 3/4.7.12 SETTLEMENT OF CLASS 1 STRUCTURES LIMITING CONDITION FOR OPERATION 3.7.12.1 The total settlemant of each Class I structure or the differential settlement between Cla'ss I structures shall not exceed the allowable values of Table 3.7-5.
APPLICABILITY: All Modes a.
With either the total settlement of any structure or the differential settlement of any structures exceeding 757, of the allowable settlement value, conduct an engineering re-view of field conditions and evaluate the consequences of additional settlement.
Submit a special report to the Commission pursuant to Specification 6.9.2 within 60 days, containing the results of the investigation, the evaluation of existing and possible continued settlement and the re-medial action to be taken,if any, including the date of the next survey.
_2-b.
With the total settlement of any structure or the differential settlement of 'ny two structures exceed-ing the allowable settlement value of Table 3.7-5, be in at least HOT STANDBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
SURVEILLANCE REQUIREMENTS 4.7.12.1 The total settlement of each Class I structure or the differen-tial settlement between Class I structures listed in Table 3.7-5 shall be determined to the nearest 0.01 foot by measurement and calculation at least once per 6 months.
r ALLOWABLE TOTAL SETTLEMENT OF SETTLEMENT SETTLEMENT POINT STRUCTURE POINT 231 Auxiliary Feedwater Pump House 249 Unit 2 228 Decontamination Building 250 226 Fuel Building 251 8
Service Water Pumphouse H-569, H-:
5 114 Service Building (E-17)'
M
=
158
- Turbine Building (B-9-1/2)
Y 245, 246 Fuel Oil Pump House E
5 206, 207 Boron Recovery Tank Dike 208, 209 m
4 204 Intake Structure C
3 M
- Note Category I Structure.
Settlements affects Category I p (a) As Measured from "as-built" survey.
SETTLEMENT SETTLEMENT POINT STRUCTURE POINT 7, 8, 9, Service Water Pumphouse 7, 8, 9, 10 N
DIFFERENTIAL SETTLEMENT FOR CLASS 1 STRUCTURES ALLOWABLE ALLOWABLE TOTAL DIFFERENTIAL SETTLEMENT SETTLE 'ENT STRUCTURE /C0MPONENT (FEET)
(FEET)
Pipe Tunnel N/A 0.125 Pipe Tunnel N/A 0.06 Pipe Tunnel N/A 0.06 84 Pipe Hanger in Reservoir N/A 0.17 0.15 Avg.
N/A From February 1977 0.15 (a)
N/A 0.54 from N/A May 1974 0,031 N/A 0.15 (a)
N/A peline.
STRUCTURE / COMP 0NENT ALLOWABLE OUT-OF-PLANE DISTORTION 0
Service Water Pumphouse 0.05 feet - any settlement point O
ALLOWABLE TOTAL SETTLE:
SETTLEMEN SETTLEMENT POINT STRUCTURE POINT 130 Containment Unit 1 223 130 Containment Unit 1 129 143 Containment Unit 1 142 144 Containment Unit 1 145 149 Containment Unit 1 239 144 Containment Unit 1 243,199,13 146 Safeguards Unit 1 239 5
128 Auxiliary Building 238 129 Auxiliary Building 239 f
129 Auxiliary Building 223 c=
123 Auxiliary Building 224 5
122 Auxiliary Building 119
[
7, 8, 9, Service Water Pump House 2
10
[
243, 132 Service Building (E-5, E-6) 238 117 ServiceBuilding(E-14) 113
~
222 Auxiliary Feedwater Pump House-Unit 1 248 15, 16, 17, North Side of Expansion Joint 18 15, 16, 17, Service Water Piping 0 SWPH 18 s
\\
r I
~~
TABLE 3.7-5 (Revision 1)
'~' '~~
EilT OR DIFFERE?iTIAL SETTLEMENT FOR CLASS 1 STRUCTURES ALLOWABLE ALLOWABLE TOTAL DIFFERENTIAL SETTLEMENT SETTLEMEllT STRUCTURE / COMPONENT (FEET)
(FEET)
Fuel Building N/A 0.13 Auxiliary Building N/A 0.13 Unit 1 Safeguards Area il/A 0.04 Unit 1 Safeguards Area N/A 0.04 Unit 1 Main Steam Valve House N/A 0.13 Service Building N/A 0.13 Unit 1 Main Steam Valve House N/A 0.075 Unit 1 Main Steam Valve House N/A O.08 Unit 1 flain Steam Valve House N/A 0.08 Fuel Building il/A 0.05 Fuel Building N/A 0.05 Service Building Tunnel fi/A 0.07 0.22 Avg.
From July 1977 Unit 1 Main Steam Valve House N/A 0.045 Unit 2 Main Steam Valve House N/A 0.031 From April 1, 1977 Pipe Tunnel N/A 0.125 0.25 From August 1978 0.22 Avg.
From July 1977 a
)
5 A.
A
Revision 1 PLAf1T SYSTEMS 3/4.7.13 GROUNOWATER CONDITIONS - PUMPHOUSE AND SERVICE UATER RESERVOIR LIMITING CONDITION FOR OPERATION 3.7.13 The groundwater level of the service water reservoir shall not exceed the elevation at the locations listed in Table 3.7-6.
The flow of groundwater from the drains beneath the pumphouse shall not exceed the values given in Table 3.7-6.
APPLICABILITY: ALL MODES ACTION:
With the groundwater level of the service water reservoir or the ground-water flow rate exceeding any of the limits of Table 3.7-6, an engineer-ing evaluation shall be performed by a Licensed Civil Engineer to deter-mine the cause of the high ground water or flow rates and the influence on the stability of the service water reservoir and pumphouse. A Special Report shall be prepared and submitted to the Commission pursuant to Specification 6.9.2 within 90 days, containing the results of the evaluation and any corrective action determined to be necessary.
In addition, at the end of the 5 year surveillance period, a sum-mary report will be prepared and submitted to the Commission, within 90 days, illustrating the results of the groundwater monitoring program.
Based on this report, a determination will be made as to the need for further measurements of groundwater conditions.
, SURVEILLAf!CE REQUIREMEflTS 4.7.13.1 The groundwater level of the service water reservoir shall be determined to be within the limits by piezometer readings from at least 7 of the locations shown c.
Table 3.7-6.
The groundwater flow rates shall be determined by measurements at the drain outlet gallery. Readings shall be taken at least once per 31' days for 5 years following the date of issuance of the Operating License. The need for further surveillance will be determined at the end of the 5 year period.
4.7.13.2 Piezameter readings shall be taken from piezometers 10 thru 14, inclusive, at least once per 12 months for the time period following 5 years from the date of issuance of the Operating License.
The need for further surveillance will be determined at the end of the 5 year period.
TABLE 3.7-6 ALLOWABLE GROUNDWATER CONDITIONS - PUMPHOUSE - SERVICE WATER RE ALLOWABLE GROUNDWATER ELEVATION PIEZONSTER PIEZOMETER Mean Sea Level (feet)
NO.
LOCATION 277 10 SE, toe 280 SWPH, (Units 1 & 2) crest 11 235 SWPH, (Units 1 & 2) toe 12 280 SWPH, (Units 1 & 2) crest 13 280 SWPH, (Units 1 & 2) crest 14 E
280 15 SE, crest 280 17 SE, crest 295 SWPH, (Units 3 & 4) b; 18 s
ALLOWABLE DRAIN FLOW RATE I
(gallons per minute) f DRAIN OUTLETS LOCATION Flow rate for any month shall not exceed E!
1 through 6 Drainage Gallery 3 times the average annual flow rate.
l5 O e e