ML20028G030
| ML20028G030 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 02/03/1983 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML20028G029 | List: |
| References | |
| PROC-830203, NUDOCS 8302070334 | |
| Download: ML20028G030 (9) | |
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MCGUIRE NUCLEAR STATION - UNIT 1 STEAM GENEP.ATOR MONITORING PROGRAMS
1.0 INTRODUCTION
1ae purpose of this report is to outline the specific actions and sur-veillance programs relative to the McGuire - Unit 1 Model D2 steam gene-rator modification. The Design Review Panel (DRP) in its report and transmittal letter dated January 17, 1983 identified three specific items to be addressed by each utility. These items are as follows:
1)
Provisions should be made for initial monitoring of inlet pressure oscillations, 2)
Plant specific provisions for assuring feedwater flow and/or feedwater temperature restrictions are met should be described, where applicable, 3)
Inservice inspection, eddy current testing and tube vibration monitoring programs and sche.fules should be described, where applicable.
The means by which each of the above items will be implemented on McGuire - Unit I and the schedule for programs in item 3 are described in subsequent sections of this report.
2.0 INLET PRESSURE MONITORING In Section 5.2.13 of its report, the DRP recommended that the pressure oscillations in the feedline be initially monitored throughout the de-sign operating flow range. To accomplish this, piezoelectric transducer probes installed in the feedline near the inlet nozzle of each steam generator (see Figure 1) vill be used.
Data will be recorded from these transducers during the powar escalation period following installation of the preheater modification.
Monitoring will commence at 20% power and continue up to 100% power. As a minimum data will be recorded at 3% power increments. This monitoring will be performeo during the initial power escalation only.
Monitoring would be performed during subsequent periods if necessary to obtain additional data or missed data.
3.0 FEEDWATER SYSTEM CHANGES Analysis by Westinghouse established that one of the forward flushing transients produced unacceptable stresses on several manifold bolts.
The problem was related to a combination of low feedwater line purge flow and cold feedwater in the feedline between the isolation valve and the steam generator. The DRP recommended that each utility provide some plant specific method to alleviate this situation.
I 3302070334 830203 PDR ADOCK 05000369 P
i Feedwater system piping changes have been made at McGuire to eliminate this transient.
Instead of using forward purge flow to warm the feed-line, hot water from the steam generator is used.
This reverse flushing of the feedline eliminates the thermal transient on the manifold which results in overstressed bolts.
The piping changes are shown on Figure 2 with dashed lines.
4.0 INSPECTION, TESTING AND MONITORING The DRP recommended that each utility develop inspection, testing and monitoring programs specific to their plant (s). These programs will verify the hydraulic performance of the modification and give early indication of any structural problems with the manifold. On McGuire -
Unit I this verification will consist of visual inspection, tube vibra-i tion monitoring, eddy current testing (ECT) and loose parts monitoring.
The scope and frequency of each of these items is discussed below.
4.1 Visual Inspection To provide an early indication of any unexpected loss of structural integrity, a visual inspection of the accessible areas of the modifica-tion components will be performed.
Inspection access will be through the radiography port in the feedwater piping up3tream of the steam generator nozzle. The inspection will be performed using a fiber optics borescope and will be recorded by videotape or still photographs for future reference. Specific items to be inspected are delineated in Table 5.8-1 of the DRP report (attached). The results of the subsequent 1
inspection will be compared with the as-built condition of the manifold.
Any questionable or unusual visual indications will be evaluted to de-termine the need for corrective action.
If corrective. action is required a report detailing the problem and the corrective action will be sub-i mitted to the NRC staff prior to subsequent power operation.
The visual inspection described above will be performed following re-assembly of the feedwater piping af ter modification installation and again at the first refueling shutdown. The next scheduled inspecticn would be at the teu yese inservice inspection shutdown. Additional inspection would be performed on an "as necessary" basis, e.g., severe water hammer accompanied by indications of loose parts in a steam generator.
4.2 Tube Vibration Monitoring The DRP endorsed the Westinghouse recommendation for tube vibration monitoring for the first plants modified. Accordingly, four tubes in the 'A' steam generator in McGuire - Unit I will be instrumented with two accelerometers each to provide an early indication of manifold performance prior to eddy current testing.
Due to the uncertainty in the relationship between tube vibration and wear, no short term accep-tance criteria have been established. Ilowever, the results of these measurements are expected to be useful in assessing the long term po-tential of the manifold to reduce the wear rate to an acceptably small value.
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Figure 3 shows the location of the tubes which have or will have acceler-meters installed. Axial location of each accelerometer is given in Table 2.
Acceleration readings will be recorded for off-line analysis by Westing-house and Duke. Limited on-line analysis will be performed to verify the validity of the recorded data.
j Data will be recorded during power escalation following installation of l
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the modification. As a minimum, data will be recorded at the following power levels during steady state conditions; 40%, 50%, 60%, 70%, 75%,
80%, 85%, 90%, 95%, and 100%. Appropriate plant data will be recorded I
concurrent with the accelerometer data for correlation purposes.
In addition to measurements taken af ter startup, data from each of the
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accelerometers will be recorded at 100% power during the subsequent op-j erating period approximately halfway between startup and the first re-fueling shutdown. This data will be compared with the initial data to verify no significant change in tube behavior.
4.3 Eddy Current Testing The primary method for assessing the effectiveness of the steam generator modification in reducing the rate of tube wear will be eddy current testing (ECT). The same ECT methods will be used for testing after modi-fication installation that were used in previous ECT examinations to allow comparison of results. The first five rows (45 to 49) will be ex-amine'd. Although not specifically required, the peripheral tubes (tubes adjacent to the wrapper) will also be examined using the same techniques.
The above inspection will be performed af ter completion of the modifica-tion on each steam generator. This inspection will serve as the base-line inspection for the modified steam generator. A second ECT examina-tion will be performed during the first refueling shutdown. This second examination will include the same tubes examined during the initial ex-anination. Subsequent ECT examinations will be performed as required by the McGuire Technical Specifications (which uses Regulatory Guide 1.83 for determining inspection frequency).
4.4 Loose Parts Monitoring McGuire - Unit I has an installed loose parts monitoring system (LPMS).
This system includes a sensor on the lower head of each steam generator.
This system, although intended for detecting loose parts in the primary system, has high enough sensitivity to detect a loose manifold. Although extremely unlikely, if a signal is detected on the LPMS which indicates that one of the manifolds is loose, the unit will be shutdown, NRC will be notified and appropriate corrective action taken.
McGuire Technical Specifications will require that daily channel checks, monthly operational testa and 18 month calibrations be performed on the LPMS, Further, the technical specifications will require that the LPMS be operable. A report must be submitted to NRC if any channel is in-operable for more than thirty days.
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With the above technical specification requirements, there is sufficient i
assurance that the LPMS will be operable and a loose manifold could be detected.
In the event that the McGuire - Unit 1 Technical Specifications do not include requirements for the LPMS at the time that Unit 1 is re-turned to service, the above provisions will be included in the station operating or periodic test procedures.
5.0 PLUGGED TUBES Operation of McGuire Unit I steam generator in the unmodified condition resulted in the plugging of six tubes in November, 1982 (one tube which did not have significant wear was plugged in July,1982 due to misinter-pretation of the eddy current signal). These tubes cannot be monitored by eddy current technique directly.
Integrity of these six tubes will 4
be inferred from eddy current information on active tubes.
If ECT measure-ments show that some wear has occured over several inspection intervals, a wear rate for the plugged tubes will be estimated.
If a previously plugged tube is thus evaluated to'have reached a defect of 80 % through wall, a detailed structural evaluation will be performed to demonstrate its integrity prior to returning to service.
j In the consideration of the performance of previously plugged tubes, the experience at Ginna has been noted. The previously plugged tubes in Ginna which became loose parts did so only because of repeated in-teractica with a large foreign object. The subseqaent failure of an inservice tube due to wear from an adjacent unrestrained tube occurred i
af ter several years of such interaction. During that time, ECT using j
the method to be used at McGuire would have reliably detected the pre-f sence of the ongoing wear and caused investigation and corrective action.
We conclude that the probability of later undesirable consequences due to previously plugged tubes at McGuire is very small.
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TABLE 1 Sl201ARY OF STEAM GENERATOR MONITORING PROGRAMS L
Post-Power During First Subsequent Periodically Ten Year Modification Escalation Operation Refueling Operation During S/D ISI Visual Inspection X
X X Note 1 X
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- j Tube Vibration Monitoring X
X Inlet Pressure Oscillation Monitoring X
Loose Parts Monitoring X
X X
X X Note 2 Note 1: To ta done as necessary.
Note 2:
Intervals determined by Technical Specification.
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Table 2 Axial Location of Tube Mounted Accelerometers Row Column
- Elevation 49 31 N Halfway between plates 5 and 6 i
49 31 N Halfway between p!ates 6 and 7 49 40 W Halfway between plates 5 and 6 49 40 W At Plate 3 49 60 W Halfway between plates 5 and 6 49 60 W At Plat,. 7 2
49 71 N At Plate 3 49 71 N Halfway between plates 5 and 6 l
f W - window Tube N - Non-window Tube i
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Column numbers are those used by Westinghouse. Duke Power numbers columns as a mirror image during ECT.
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Figure 1 Piezoelectric Transducer Location (Typical)
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Figure 2 McGuire Nuclear Station Feedwater System Changes I
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