ML19269B995
| ML19269B995 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 01/09/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19269B992 | List: |
| References | |
| NUDOCS 7901190188 | |
| Download: ML19269B995 (21) | |
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3/4.7.12, "SL T TLEFINT OF CL ASS ! LTPUCIUPLS" UF OPE'?ATING LICLNSE NPF-4-NCRTH ANNA POL lER STATION - UNIT 1 Docket No. 50-338
Background
Both Units 1 and 2 of the North 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 seismic Category 1 auxiliary service water system as a backup for the cooling function of the normai 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.
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 (VEPC0) identified and evaluated the significance of settlement effects on Unit 1 and proposed a technical specification for plant operation 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.
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-u average service water pu:tphouse settlen.ent be changed from 0.lE 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.
VEPCO's letter dated November 22, 1978, indicated that they were experiencing difficulty in completing the surveillance requirements of the Technical Specifications.
We met with VEPC0 on December 5 and discussed the details and significance of these difficulties.
1 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 f rom VEPCO's technical representatives.
Our evaluation of this information follows.
Evaluation In the following evaluation, the term total settlement refers to the measured vertical movement of a settlement monum'ent (SM) located on some structure or component. Average settlement refers to the arithmetic average
. of the vertical novement of two or more specific settlec.ent..:onurents.
Differential settlement refers to the difference in measured vertical movement between two settlement monuments, each located on a separate structure or component.
The present North Anna Unit 1 Technical Specification 3/4.7.17 sets the allowable additional average settlement of the service water pumphouse (SM-7, 8, 9 and 10) over the life of the plant at 0.15 feet since the base date of December of 1975.
VEPCO'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 wate pumphouse se tiement effects. These include:
(1) Differential movement and tilt of the pumphouse with ct to the buried pipelines that might exceed the design movement of the expansion joints installed in January of 1976 to cccommodate 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 flow.
. (4 ) Leakage of service water from the reservoir thrcugh 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 f rom the pumphouse to the spray dir.ribution system in the reservoir.
Item 1 With respect to the first concern, we have concluded that VEPCO'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.
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. kl? n 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. Thus, VEPC0's request to increase the average settlement limit of the pumphouse does not assure that the design limit for the expansion joint will not be exceeded.
To assure that the design limits
. 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 taking the average of the settlement measured at the fcur corners of the pumphouse. According to this specification, whenever the average additional settlement reaches 75 percent of the allowable given in Table 3
-5 (Page 2/4.7-12 of the specifications), an engineering review of field conditions and an evalu-ation of the cansequences 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 resulted from its engineering review and evaluation of settlement of the service water pumphouse. On the basis of this evaluation VEPC0 requested that the maximum allowable pansion joints are not exceecod, the dif ferential settler.ent en the pumphouse and the north sidt of the expansion joints at their ection with the buried service water lines must be limited.
It is r position that the differential settlement measured between SM-7 or M-10 and SM-15, SM-16, SM-17 or SM-18 should not exceed the revised proposed Technical Specification limit of 0.22 feet after July,1977, the date that markers SM-15,16,17, and 18 were first established. A required revision to Table 3.7-5 of the Technical Specification is presented in Enclosure 1 of this report.
The 75 percent Technical Spu "fication reporting criteria will continue to apply to this limit.
Item 2 The second concern, pumphouse tilting effects on the service water umps, is addressed in the rer7onse to question P3.6 of the Final Safety nalysis Report. The applicant has stated that the pumps will be shimmed, s necessary, te correct for any pumphouse tilt so that the pump alignment is within the 0.011 inches per foot recommended by the pump manufacturer.
his corresponds to a total allowable displacement of 0.29 inches for the 6-foot-long vertical pump.
The manufactJrer has also indicated that a otal displacement of 0.5 inches would not adversely affect pump operability.
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In addition, the applicant is cleasuring differential pressure, flow rate and vibration amplitude every 30 days as required by Article IWP-3000 of Section XI of the ASME Code.
These pump performance parameters are to be maintained within 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 f or.
Item 3 The stresses induced in the buried service water pipes, concern three, are addressed in VEPCO's letter of June 13, 1978.
VEPCO's analysis and our independent evaluation indicate that American Society of Mechanical Engineers Boiler and Pressure Vessel Code allowable pipe stress applicable 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 VEPCO'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 additional settlement of the exposed end of any of the buried pipes beyond that of August 3, 1978, will
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not be allowed to exceed 0.22 feet so as not to exceed American Society of Mechanical Engineers Boiler and Pressure Vessel Code allowable stress in accordance with NC 3652.3(b).
This can be 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 service water reservoir was lined with compacted cohesive soil to impede leakage of reservoir water into the underlying saprolite.
The pumphouse foundation s supported by the compacted 1.'ner material. As the pumphouse settles with respect to the liner, it punches into the liner material, as evidenced by the past relative movement 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 system and will change groundwater levels measured
f o-by piezometers.
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 monitoring as presently required by the Technical Specification is to be conducted monthly for the first five years after the issuance of the Unit 1 Operating License.
Adequate assurance that leakage will not be undetected and affect safe
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operation of the plant can be attained by changing Technica Specification 3/4.7.13 to require:
(a) measuring and recording the quantity of ground-water 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 punphouse structure due to future differential settlement across the structure, concern 5, is likely to be preceded by warping of the pumphouse foundation. Available measurer.ents and visual inspection by the applicant indicates that very little, if any, warping has occurred to date and that only nominal cracking is now evident.
Because of the relatively soft foundation provided by the clay liner and underlying saprolite and the stiffness of the pumphouse foundation slab, significant differential settlement across the structure is unlikely.
However, an out-of-plane distortion of any corner of the pumphouse foundation of about 0.06 feet would indicate the onset of additional cracking in the structure. The potential for crack development can be interpreted by analyzing measure-ments at settlement points SM-7, 8, 9, and 10.
We have concluded that the out-of-plane distortion of any corner of the pumphouse foundation should not exceed 0.06 feet in order to limit the width of cracks. 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 apply to this limit.
Item 6 The vulnerability of the spray piping connections at the service water pumphouse to further settlement of the pumphouse has been reviewed with 'EPC0'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 Langer and footing resting on the clay liner of the reservoir.
Settlement of the southeast corner of the pumphouse, 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 allowable stress in these pipes, the differential settlement (as calculated by VEPC0 and reviewed by the staff) between the southeast corner of the pumphouse and the hanger would need to be 0.175 feet. Accordingly, in order to assure that pipe stresses will not exceed Code allowable values, the differential settlement between ma ier SM-8 at the southeast corner of the pumphouse and markers H-569 and 's-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 of this report.
The 75 percent Technical Specification reporting criteria will apply to this limit.
Because the allowable settlement values of the service water pumphouse 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 VEPCO'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.
Inservice Testing of Auxiliary Service Water Pumps at Lake Anna The auxiliary service water pumps are currently not tested periodically as required in Section XI of the ASME code.
By letter dated Seotember 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.
These pumps were successfully tested during the pre-operational testing program.
On this basis, we have reasonable assurance that the pumps will operate satisfactorily during the 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 We 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 it 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 VEPCO's proposed values of allowable settlement, we do agree with VEPC0 that the existing technical specifi-cation 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 maxinum 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 consequences 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.
=r: ' c s,; e 1 REVISICN 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 settlement of each Class I structure or the differential settlement between Cla'ss I structures shall not exceed the allowable values 1
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 75% 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.
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b.
With the total settlement of any structure or the differential settlement of any two structures exceed-ing the allowable settlement value of Table 3.7-5, be in at least 30T 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 E
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.
h,c k s v er-2 i'evision 1 PLANT SYSTEMS 3/4.7.13 GROUNDWATER 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.
.r In addition, at the end of the 5 year surveillance period, a sum-I l
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 furti:er measurements of groundwater conditions.
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SUR'.'EILLAt:CE REQUIRE"Ei;TS 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 on 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
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5 year period.
4.7.13.2 Piezometer 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 RESERVOIR PIEZ0 METER PIEZ0 METER ALLOWABLE GROUNDWATER ELEVATION NO.
LOCATION Mean Sea Level (feet) 10 SE, toe 277 11 SWPH, (Units 1 & 2) crest 280 12 SWPH, (Units 1 & 2) toe 285 13 SWPH, (Units 1 & 2) crest 280
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14 SUPH, (Units 1 & 2) crest 280 15 SE, crest 280 17 SE, crest 280 L:
18 SWPH, (Units 3 & 4) 295 15 ALLOWABLE DRAIN FLOW RATE il DRAIN OUTLETS LOCATION (gallons per minute) i,2 1 through 6 Drainage Gallery Flow rate for any month shall not exceed bi 3 times the average annual flow rate.
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e
.i TABLE 3.7-5 (Revision 1)
ALLOWABLE TOTAL SET 1LEMENT OR DIFFERENTIAL SETTLEf1ENT FOR i
SETTLEMENT SETTLEMENT POINT CTRUCTURE POINT STRUCTURE / COMPONENT 130 Containment Unit 1 223 Fuel Building 130 Containment Unit 1 129 Auxiliary Building j
143 Containment Unit i 142 Unit 1 Safeguards Area 144 Containment Unit 1 145 Unit 1 Safeguards Area 149 Containment Unit 1 239 Unit 1 Main Steam Valve House 144 Containment Unit 1 243,199,132 Service Building
[a 146 Safeguards Unit 1 239 Unit 1 Main Steam Valve House 238 Unit 1 Main Steam Valve House 128 Auxiliary Building 129 Auxiliary Building 239 Unit 1 Main Steam Valve House
[
129 Auxiliary Building 223 Fuel Building kc 123 Auxiliary Building 224 Fuel Building Z
122 Auxiliary Building 119 Service Building Tunnel 1
7, or 10 Service Water Pump House 15, 16, 17, North Side of Expansion Joint or 18 at Service Water Piping,
' "l[
243, 132 Service Building (E-5, E-6) 238 Unit 1 Main Steam Valve House 117 Service Building (E-14) 113 Unit 2 Main Steam Valve House 222 Auxiliary Feedwater Pump House-Unit 1 248 Pipe Tunnel 9
15, 16, 17, North Side of Expansion Joint at 1
l or 18 Service Water Piping i
1 4
1 d
STRUCTURES ALLOWABLE ALLOWABLE TOTAL DIFFERENTIAL SETTLEMENT SETTLEf1ENT (FEET)
(FEET)
N/A 0.13 N/A 0.13 N/A 0.04 N/A 0.04 N/A 0.13 N/A 0.13 N/A 0.075 N/A 0.03 N/A 0.03 N/A 0.05 N/A 0.05 N/A 0.07 0.22 from N/A July, 1977 N/A 0.045 N/A 0.031 From April 1.
1977 N/A 0.125 0.22 From August N/A 1973 t
4 i
ALLOWABLE TOTAL SETTLEMENT OR DIFFERENTIAL SETTLEME i
SETTLEMENT SETTLEMENT STRUCTURE / COMPONENT POINT STRUCTURE POINT 249 Pipe Tunnel 231 Auxiliary Feedwater Pump House Unit 2 228 Decontamination Building 250 Pipe Tunnel 251 Pipe Tunnel 226 Fuel Building 8
Service Water Pumphouse H-569, H-584 Pipe Hanger in Reservoir 55 114 Service Building (E-17)
Ei x
>s 158
- Turbine Building (B-9-1/2) 245, 246 Fuel Oil Pump House
'q Ei
-p 206, 207 Boron Recovery Tank Dike 208, 209
_s 204 Intake Structure l,j{
7"
'M
- Note Category I Structure.
Settlements affects Category I pipeline, (a) As 14easured from "as-built" survey.
SETTLEMENT SETTLEMENT POINT STRUCTURE POINT STRUCTURE / COMPONENT 7, 8, 9, Service Water Pumphouse 7, 8, 9, 10 Service Water Pumphouse 10
/
t.
e 6
- TURES ALLOWABLE ALLOWABLE j
TOTAL DIFFERENTIAL SETTLEMENT SETTLEMI.f'T (FEET)
(FEET)_
N/A 0.125 ft/A 0.06 N/A 0.06 N/A 0.17 0.15 Avg.
N/A ofg From February 1977 0.15 (a)
N/A 0.54 from N/A May 1974 0,031 N/A 0.15 (a)
N/A o' I OWABLE OUT-0F-PLANE DIST0]1TICM 0.06 feet - any settlement point k
1 v
b
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