ML19340E087
| ML19340E087 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 12/29/1980 |
| From: | Sylvia B VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Clark R, Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 1017, NUDOCS 8101060349 | |
| Download: ML19340E087 (20) | |
Text
i Vepco December 29, 1980 Mr. Harold R. Denton, Director Serial No. 1017 Office of Nuclear Reactor Regulation Attn:
Mr. Robert A. Clark, Chief Docket Nos. 50-338 50-339 Operating Reactors Branch No. 3 Divisicn of Licensing U. S. Nuclear Regulatory Commission License Nos. NPF-4
'Vashington, D. C.
20555 NFF-7 i
l
Dear Mr. Centon:
Enclosed are 40 ccoies of a report entitled " Evaluation of Direct i
Yeasurement of Differential Settlement Across Service Water Lines Expansion Joints, Virginia Electric and Power Compairy, North Anna Power Staticn - Units 1 and 2".
This report is submitted in response to a Division of Licensing request dated September 12, 1980.
If there are any cuestions, please call.
Very truly yours,
/.
B. R. Sy via nager - Nbclear Operations and Maintenance cc: Mr. Joe S. Youngblood, Chief Licensing Branch No. 1 Pr. Thomas M. Novak, Assistant Director for Operating Reactors Division of Licensing g
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l EVALUATION OF DIRECT MEASUREMENT OF DIFFERENTIAL SETTLEMENT ACROSS SERVICE WATER LINES EXPANSION JOINTS d
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION - UNITS 1 AND 2 j
Introduc tion In a letter dated September 12, 1980, the NRC Division of Licensing requested Vepco to " submit an analysis of the precision obtainable from a direct mea surement system for the service water pipe expansion joints as compared with the existing indirect system, and the cost estimate for implementing a direc t measurement system." As explained in the letter, the request was based on the decision of February 11, 1980, by the Atomic Safety and Licensing Appeal Board which included the belief by the Appeal Board that " direct monitoring of the expansion joints has advantages over surveying," even 3
though "the evidence of record establishes that surveying provides an adequate means of assuring that these joints remain within their design capa-bilities." The Appeal Board further concluded that "this being the case, we I
would not be justified in ordering direct monitoring, regardless of its feasi-bility. Nonetheless, if a more accurate monitoring method could be employed, we strongly urge the staff and applicant to consider its adoption."
i This report describes the problems, conceptual designs, accuracies, and coste of direct measurement systems against the background of the requirements for surveying both the pump house and the service water lines imposed by the technical specification.
Technical Specification Requirements Amendment No. 12 to the operating license for Unit I changed the limiting conditions for operation with respect to the pump house and the service water lines in Technical Specification 3/4.7.12.
The four limitations given in Table 3.7-5 are as follows:
l 1.
Total settlement of any of the four 36-in. service water lines north 4
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of the expansion joints (settlement-monitoring points 15,16, 17, l
and 18) not to exceed 0.22 ft since August 1978 i'
2.
Out-of plane distortion of any corner of the pump house (points 7, 8, 9, and 10) not to exceed 0.06 ft in any survey 3.
Differential settlement between (a) any of the four 36-in.. service water lines north of the expansion joints (points 15, 16, 17, and
- 18) and (b) either the northeast corner of the pump house (point 7) or the northwest corner (point 10) not to exceed 0.22 f t since July 1977 4.
Differential settlement between (a) either of the two easternmost hangers (H-569 and H-584) supporting the 24-in. service water lines just south of the pump house and (b) the. southeast corner of the pump house (point 8) not to exceed 0.17 ft since May 1976
2 The basis for Technical Specification 3/4.7.12 requires that compliance with these numerical limitations must be based on the elevations of the points as determined by " precise leveling with second order Class II accuracy." These determinations are being made on a monthly f requency by the surveying firm of Moore, Hardee & Carrouch Associates.
Even if a direct monitoring system across the expansion joints were adopted, the elevations of points 15, 16, 17, and 18 on the 36-in. service water lines and points 7, 8, 9, and 10 on the pump house, as well as hangers H-569 and H-584, would still have to be measured by Moore, Hardee & Carrouth Associates each month to comply with the present technical specification requirer. ants.
Record of Differential Settlement Since July 1977, the four service water lines have all settled more than the two northern corners of the pump house.
Thus, the di'.ferential settlements discussed herein are positive for the settlement of the lines north of the expansion joints with respect to the lines south of the expansion joints where they penetrate the north wall of the pump house.
Each month, the settlement of (a) each of the service water lines north of the expansion joints is compared to (b) each of the northern corners of the pump house; that is, a total of eight comparisons are made.
The record of one of these comparisons (between the next to the easternmost line and the northeast corner of the pump house) is shown in Figure 1 since this has been the largest differential settlement of the four lines over the past 2 years. Currently, the three easternmost lines have approximately the same differential settle-ment with respect to the northeast corner, whereas the differential settle-ment of the westernmost line is about 0.010 ft less.
(Since July 1977, the settlement of the nor thwe st corner has always been larger than that of the northeast cornet, so comparison to the northeast corner has always provided the larger diffe ential settlement.)
Whereas total se6tlement, as a rule, always increases with the passage of time, the differential settlement shown in Figure 1 can either increase or de c re a s e.
Such variation occurs whenever there is a change in the rate of settlement of either the service water lines or the pump house during some period of ti e.
Figu re 1 shows that, for the last year and a half, there has been very little increase in the differential settlement across the expansion joints; the l
l increase is not more than about 0.005 f t.
The absence of differential move-ment during this period of time is clearly discernible from the calculations based on the surveyor's measurements of elevations.
i l
t Accuracy of Surveyor's Measurements 1
In each monthly survey of the Service Water Reservoir, the surveying team runs a line of levels from Reference Monument "B," as their benchmark, around the entire crest of the dike and back to Reference Monument "B" for closure.
In the course of this traverse, they turr. on one or more corners of the concrete l
expansion joints enclosure and on nearby alignment-settlement marker ASM-5 in front of the pump house. Thus, the elevations of these points are calculated once the error of closure of the main traverse has been distributed among the turns.
Separate loops are then run (a) through the pump house to survey the
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i four corners and (b) through the expansion joints enclosure to survey the four lines. Each loop, typically, starts from one corner of the expansion joints enclosure and closes on another corner or on ASM-5.
When evaluating the accuracy of the surveyor's measurements, it may be helpful l
to know the procedure followed to determine the elevations of the four service j
water lines. With the level set up on the top of expansion joints enclosure, the rod (graduated in yards) is placed upon the brass marker at one corner of the enclosure and read by the three wires in the reticle of the level tele-scope. The rod is then placed on a turning point inside the enclosure so that i
the rod projects up through the manhole, and the telescope of the level is pointed to the rod and the three wires are read.
The level is carried down j
into the enclosure and set up on the underlying slab between the westernmost line and the west wall of the enclosure. From this position, the three wires are read on the rod that is still being held on the turning point Then the t
telescope is pointed to each of the lines where the lower section of a rod 3
graduated in feet is placed upon the settlement-monitoring point on each line.
This short rod is read once on each line with the cencer wire. The telescope is pointed back to the main rod which has been moved to a second turning point, and the three wires are read. Then the level is moved to a new position on the slab, the three wims are read on the main rod, and a second reading is taken on each of the lines using the short rod. From the new position of the level, the three wires are read on the main rod now moved back to the original turning point so that it again projects through the manhole.
The level is carried out through the manhole and again set up on top of the enclosure.
With the rod still on the turning point inside the enclosure, the three wires are read, and then the rod is carried out and placed on a different corner of the enclosure or on ASM-5 where the three wires are read to close the loop.
When the error of closure has been distributed among the turns, -two elevations j
are computed for each line, and the average is reported.
One evaluation of the accuracy of the surveying of differential settlement across the expansion joints would be the algebraic difference of the errors of closures of (a) the loop through the pump house and (b) the loop through the expansion joints enclosure.
(If both' errors are in the same direction, one offsets the other.) Over the period of monitoring by Moore, Hardee & Carrouth Associates, the differences in the errors of closure has been as large as
+0.011 ft to -0.009 ft, but the overwhelming number of surveys (and every survey over the past year) have had differences that varied from no more than
+0.004 ft to -0.004 ft.
Therefore, +0.004 ft is suggested as a reasonable accuracy for the surveyor's measurements of the differential settlement l
across the expansion joints.
Problems of Direct Measurements Figures 2, 3, and 4 are sketches showing recently measured dimensions of the j
service water lines inside the expansion joints enclosure, and these figures reveal a number of problems in making a direct measurement across each of the joints. Each pipe is 36 in. in diameter. The 12-in.-wide by 44-in.-diameter j
protective sheetmetal covers (also used for the leakage detection system) over the two sets of convolutions are separated by a space of 44 in.
South of the southern set of convolutions is ' the 2-in.-thick by 50-in.-wide flange plate that is connected ti the balancing end of the joint (over 16 ft to the i
north) by four 1-1/2-ir..-diameter tie rods. The tie rods run along the sides i
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l of each joint, blocking access to the sides and bottom of the joints and making it awkward to walk between adjacent joints. There is only about 3 in.
of clearance between the bottom of each convolution cover and the underlying
- oncrete slab.
The difficult physical conditions inside the expansion joints enclosure are further revealed in Figures 5 and 6, two recently taken photographs. Figure 5 is a northerly view along the west of the westernmost line showing the bend in the line where it enters the fill of the dike while the length of 24-in. pipe extends to support the balancing bellows.
This viev shows the closeness of the enclosure footing to the expension joint.
Overhead can be seen the condensation glittering on the bottom of the roof sisb. At the extreme right, beyond the second convolutions cover, is the square, white paint swatch atop the pipe around the punch mark where the surveyor's measurements are made.
Figure 6 is a view f rom the south of the expansion joints flange plates toward l
the north wall of the enclosure between the two central lines. The spacing of rungs on the ladder (used to enter the enclosure chrough the manhole) provides l
a scale to judge how closely spaced are the cie rods of adjacent expansion joints.
In the center, beyond the end of the floor slab, can be seen the electrical water indicator of the leakage detection system.
The measurement of differential settlement must be made between two points I
that are over 6 ft apart.
Since nothing could be fitted on the sides or the bottom of each pipe, the measuremenc would have to be made across the top of I
the exp ansi on joint.
However, any device must (a) clear the convolutions covers that stand about 4 in, above the top of the pipe and (b) not have any part standing more than about 16 in, above the top of the pipe lest it j
interfere with the surveyor's line of sight.
l There is no point of stable elevation for reference.
The enclosure, the underlying slab, and the pump house wall are all undergoing slight, though continuing, settlement and tilting.
It is not sufficient to fix a beam rigidly to one side of the expansion joint and have it span across the joint to a scale or displacement transducer on the other side. Such a device could not distinguish between the vertical movement to be measured and any angular movement across the joint.
Any installed device must be sufficiently strong or protected against being stepped on, kicked, or otherwise abused in order that damage might not result in an erroneous mea suremen t.
It would also have to be resistant to dust, moisture, and large temperature changes for many years.
One of the most bothersome problems is the vibration of the pipes.
The surveyor can see through his telescope that the amplitude of the steady state vibration to the north of the joint is about +0.005 f t, but he can select the mean value whereas a device might not be able to do this. Also, some vibra-tion, not necessarily in phase, must be assumed in the pipe to the south of the joint. Finally, as discussed earlier, the lines undergo periodic large-amplitude motions due to hydraulic transients. The ef fect of these vibrations and shocks (and the accompanying fatigue) on the behavior of any direct measurement device over a long period of time is difficult to predict.
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1 4
5 Conceptual Methods of Direct Measurements The methods of direct measurements discussed hereinaf ter are based on the following criteria:
1.
Vertical movement across the joints cannot be measured unless a horizontal datum plane is established, though the elevation of the plane is not impor t an t. This, of course, is precisely the basis of the surveyor's measurements.
She mea surement must be directly readable by anyone, without any need for numerical conversion from one unit to another.
In other words, a tilt measurement or the bending of a flexible beam would not be considered a direct measurement.
3.
The measurement system must provide an indication outside the enclosure of further differential settlement even if the measur-ement of such settlement requir;d entering the enclosure.
4.
Any installed device must not interfere with (a) the surveyor's measurements or (b) the expansion joints leakage detection system.
5.
Protection of the me surement system against physical damage, cor-rosion, or other deterioration is imperative.
The conceptual nature of the fo'. lowing methods deserves emphasis, for there has not been an opportunity decing the preparation of this report to fully establish the suitability of certain instruments to the expected conditions.
For instance, the ef fect of fatigue due to pipe vibration is a concern of some instrument suppliers. In other cases, field trials are considered necessary.
Nevertheless, the concept of each of these methods is believed to be sound.
l Of the many methods of direct measurements considered, the only two practical methods were found to be (a) a manually leveled beam spanning the two sets of convolutions with a direct reading scale and (b) a laser rounted on the north wall of the pump house with a detector manually placed on each pipe north ot 1
the expansion joints.
l Bean. As shown in Figure 7, a deep steel beam would span about 8 f t between supports across the top of each expansion joint, pivoted at the northern end and guided vertically between two steel plates at the southern end where a screw support would permit the beam to be manually leveled. A precision level vial would be mounted on the beam.
A scale would be attached to one of the guide plates at the southern end, and :his scale would be read with respect to a long horizontal scribe mark on the beam (to accommodate any axial movement).
The vertical position of the scale would be set to indicate the differential f
settlement across the joint between July 1977 and the time of installing the i
beam. To avoid welding on these pipes, the supports for the beam (and for the protec tive cover) would be attached with heavy (2-in.-wide by 0.050-in.
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-thick) steel straps; a se-ond strap would be placed over the first at each l
location.
The beam would be protected by a length of structural steel tubing with part of the bottom removed and the ends closed with steel plates.
This box-like
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cover would be piveted on horizontal pins at both sides of the expansion jcint to accept vertical movement and the southern pivot would be in a slot to accept axial movement.
The supports for the cover would provide lateral stiffness and would be strapped to the pipe independent of the supports for the beam. The pins providing the pivots would be upset after installation so that they could only be removed by cutting.
To permir access to the leveling screw and vial and to read the scale, an openirg 1d be cut in the side of the protective cover, as shown in Figure 7.
A hinged and lockable steel plate would close this opening.
In addition to the provision for manually leveling the beam and directly reading the dif ferential settlement, a remote indication of further vertical movement would be provided by a sensor to detect any departure of one of the four beams from a horizontal ;.osition. A departure from horizontal would be sensed by a tiltmeter (such as "Digitilt" Model 50322 made by Slope Indicator Company) attached to the side of the beam. Cables from the tiltmeter would be carried across the enclosure and into the pemp house inside extra heavy pipe.
This instrument embodies an accelerometer to measure the tilt, and the output would be electronically processed to activare a signal should the beam exceed a specific inclination. Under static conditions, instruments of this type are accurate to one minute of arc, though the accuracy under the vibratory con-ditions has yet to be determined.
It might be that the limits for the alert signal would have to be placed as wide as +10 minutes of arc (corresponding to a dif ferential settlement of about +0.02 ft across the 8 ft length of the beam). The signal could be an indicator light placed on the north wall of the pump house above the expansion joints enclosure. The tiltmeter system would be hard-wired and activated by a clearly marked switch next to the indicator light.
Laser. A self-leveling laser level (such as "LaserLevel SL" Model 944 made by Spectra-Physics) would be mounted on the north wall of the pump house with the elevation of the light beam about 14 in. above the tops of the pipes.
This instrument rapidly rotates the light beam to produce a very thin plane of light that is autonatically maintained horizontal.
The level would be enclosed in a heavy steel protective cover, as shown in Figure 8, with a horizontal slot at tne elevation of the beam.
Measurements would be made by placing a short laser-detecting rod into a holder mounted on the top of each pipe north of the expansion joint, as shown in Figure 8, and activating tha detector by pressing a button on the rod. The rod would automatically move the poin'ter on the scale to the elevation of the laser beam, and the scale would be read by estimating to the nearest 0.001 ft to determine the vertical distance between the laser beam and the top of the i
pipe. The vertical movement across each expansion joint would be obtained by subtracting from the measured vertical distance a reference vertical distance marked on the side of the rod holder. This reference distance would reflect the differential settlement across the expansion joint between July 1977 and the time of installing the laser.
The laser-detecting rod offers an important advantage in view of the vibration of the pipes. The first press of the activating button would move the pointer to the exact elevation of the laser beam and lock it at that height. But the vertical distance between the top of the pipe and the elevation of the laser
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7 beam would be continuously varying by the amplitude of the vertical vibration of the pipe. However, a second press of the button wou t a cause the pointer to remain at the elevation of the beam despite the vertical movement of the rod.
Thus, in this mode, the person reading the rod could see the pointer moving up and down over the amplitude of vibration and, like the surveyor, could sele t a mean value.
A remote indication of further vertical movement wou?d be provided by a la ser receiver (such as Model 9913 made by Spectra-Physics) attached to the tot of one of the pipes north of the expansion joints. As shown in Figure 8, a heavy steel cover with a vertical slot would be placed over the receiver and strapped to the pipe independent of the straps holding the receiver to the pipe. Cables f rom the receiver would be carried across the enclosure and into the pump house inside extra heavy pipe.
In operation, the receiver would locate the elevation of the laser beam within a series of dead bands of increasing vertical width and would identify each dead band on a remote display (such as Model 9965 made by Spectra-Physics) having a vertit al row of seven indicator lights. The green center light would indicate that the receiver is within +0.02 ft of its initial position in alignment with the laser beam; beyond the +0.02 ft distance, the next lights above and below the green light would give a flashing yellow indication.
These would signal until the receiver had moved +0.13 f t from its initial position; beyond that point, the next lights would show a continuous yellow indication. The top and bottom lights in the row would indicate a vertical movement greater than +0.33 ft from the initial position of the receiver.
This display could be mounted on the north wall of the pump house above the expansion joints enclosure.
The laser system would be hard-wired and activated by a clearly marked switch next to the display.
All components of the laser system described above are completely waterproof (they can operate under water), and the laser receiver and display are designed to be mounted on heavy construction equipment, so they can withstand endless vibration and sho Accuracy of Direct Measurements Beam.
There are two components to the accuracy of measurements made with a manually leveled beam:
(a) the accuracy of leveling the bear. and (b) the accuracy of reading the scale.
A 4-in-long level vial for a surveyor's transit would lend itself to mounting on the beam, and it can f.e obtained with a sensitivi* of 30 seconds of arc for each 2 mm of movement (between gradu-ations) of tue bubble in the vial. This corresponds to a vertical movement of 0.001 ft over the 8-ft span of the beam for each graduatian of the vial.
Considering the vibration and the possibility of parallax, the bubble position could probably not be read any finer than to the nearest graduation.
The greatest uncertainty is the response of the bubble to the vibration.
A vertical amplitude of f,005 ft at one end of the 8-ft beam is about +2 minutes of arc or +4 graduations on the vial.
Only a prototype test could determine exactly how the beam and the bubble would respond to this movement.
Perhaps there would be a rapid, cyclic horizontal movement of the bubble of, say, +2 graduations in addition to the vertical vibration of the vial. As a minimum, the beam could probably not be leveled to within +2 graduations, giving an a curacy no better than +0.002 f t.
8 Realistically, graduations on the direct-reading scale could not be scribed or stamped closer than +0.001 ft (about 0.01 in. ). Considering parallax (not present in optical surveying) and vibration, the scale could not be read with an assured accuracy of better than +0.003 f t.
Overall, the accuracy of measurements made with a manually leveled beam would not be better than +0.005 to +0.006 f t in the most favorable circumstances.
The accuracy would be much worse should components loosen due to the vibration, creer occur in the mountings, or other deterioration develop in the installation.
Laser. The laser beam can be considered accurate to +0.001 to +0.002 f t over the short distance in this case.
Parallax in reading the pointer on the laser-detecting rod and the ef fect of the vibration would limit the assured accuracy of readings to no better than +0.003 f t.
Thus, the overall accuracy of measurements made with a laser would not be better than +0.004 to +0.005 f t in the most favorable circumstances.
As indicated above, any creep or loosening of components would worsen the accuracy.
l The true accuracy in measurements made with either a beam or a laser cannot be fully assessed by the estbnates of mechanical and physical limitations given above but it must include human limitations. Unlike a crew of highly trained and experienced professional surveyors following practices that enforce continual verification of accuracy, the person making direct measurements would not be doing the work with an assurance of freedom from human error.
The s ligh'.est impatience in leveling the beam or carelessness in placing the laser-detecting rod on the pipe could easily worsen the accuracy of a measure-ment by 0.005 ft or more. Just the differences in how different people read the pointer on a scale or interpret the mean position of a bubble moving in a level vial would produce a variability among measurements.
Precise leveliag with second order Class II accuracy, as is presently periormed, minimizes che human factors.
Costs of Direct Measurement Systems Beam.
The cost of materials and labor to fabricate four beam assemblies and protective covers, as shown in Figure 7, is estimated to be $30,000.
Engi-neering cost, including detailed design, drawing preparation, procurement documentation, etc.,
is estimated to be $12,000.
Slope Indicator Company estimated that it could provide a tiltmeter and a remote indicator for about
$5,000; a similar estimate was obtained from Structural Behavior Engineering Laboratories, Inc. A less certain estimate is the labor required to install, align, and calibrate the beam assemolies and tiltmeter system, especially in view of the awkward physical conditions inside the expansion joints enclo-sure. (The recent installation of the leakage detection system was very time consuming.) The cost of this effort is estimated to exceed $8,000. Further-more, the addi* !on of this eccentric mass of about 800 lb to each service l
water line wilt cequire a new seismic analysis of the lines that is estimated to cost between $10,000 and $15,000. The total cost of providing this method of direct measurements, therefore, would be something in excess of $70,000.
(Not included in this total are the costs of travel to the plant site by engineers and instrumentation suppliere.)
l Laser.
Spectra-Physics could provide a laser level for $6400 and a laser-detecting rod for $1700. For the remote settlement indication, the receiver,
9 control box, and display could be provided by Spec tra-Physics for about $6000.
Engineering cost, including an analysis to assure that the protective cover over the laser level would not fall on a service water lina during a seismic event, is estimated to be S14,000.
Materials and labor to fabricate mount-ings, protective covers, and rod holders, as shown in Figure 8, are estimated to cost $8,000.
Installation, alignment, and calibration are estimated to cost at least $ 6,000.
Therefore, the total cost of providing this method of direct measurements would exceed $40,000.
Disadvantages of Direct Measurements Some of the more obvious disadvantages of (a) installing a system to permit direct measurements and (b) replacing the monthly comparisons of the surveyor 's measurements with such direct measurements are as follows:
1.
No feasible method of direct measurements would be as accurate as the surveyor's measurements.
2.
Direct measurements would not reduce the monthly surveying work by Moore, Hardee & Carrouth Associates since, under the present tech-nical specification require men t s,
not a
single settlement-monitoring point could be eliminated.
3.
Because of (a) the lack of assured quality in making direct measure-ments and (b) the possibility of mechanical problems developing in an installed device, dependence on direct measurements would risk the initiation of spurious reports or actions.
4.
Any heavy attachments to the lines would unfavorably alter their response to a seismic event.
5.
The installation of heavy attachments would require the removal of the 20-ton concrete cover in the roof ot the enclosure over the expansion joints; such exposure of the expansion joints would introduce the risk of their damage while placing a heavy attach-ment.
6.
Any attachments across the expansion joints would hinder removal of the covers over the convolutions to inspect their condition.
7.
The installation of a system to permit direct measurements would be very costly.
Conclusions At the time of the decision of the Atomic Safety and Licensing Appeal Board regarding pump house settlement on February 11, 1980, Vepco responded posi-tively to the belief expressed by the Appeal Board that a device should be installed to detect any leakage f rom the convolutions of the expansion joints.
A system has been installed, at a cost of over $10,000, that provides a visual alert signal in the event of any leakage.
At that t im e, Vepco also reviewed the belief expressed by the Appeal Board that a method of direct monitoring of differential settlement across the
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expansion joints should be considered. That review revealed that the safest, most accurate, and most reliable method of monitoring the differential set-tiement across the expansion joints is the metnod which has been employed comparison of measurements made by precise since July 1977, that is, a leveling. The current study of direct measurement systems, in response to the NRC request of September 12, 1980, has reinforced the earlier conclusion.
Furthermore, the record of diff erential settlement shows clearly that there is no realistic basis to anticipate any sudden increase in this differential settlement or to believe that the monthly monitoring is not adequately timely.
Devices could conceivably be installed, at considerable cost and risk, that would permit dire c t mea sure ment s, but they would provide no r al benefit to compensate for che several disadvantages listed above.
The monitoring pro-gram presently used to verify compliance with the limiting conditions for
,peration given in the technical specification is a well established and ac'quate program.
Installation of direct measurement devices would con-tribute only an uncertain redundancy to this program.
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