ML18043B013
| ML18043B013 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 09/11/1979 |
| From: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7909130033 | |
| Download: ML18043B013 (8) | |
Text
consumers
.power company-
- Area Code 517 788-0550 September 11, 1979 Director, Nuclear Reactor Regulation Att Mr Dennis L Ziemann,, Chief Operating Reactors Branch No 2 US Nuclear Regulatory Commission Washington, DC 20555
- DOCKET 50-255 - LICENSE DPR PALISADES PLANT - TECHNICAL SPECIFICATION.S
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CHANGE RELATED TO STEAM GENERATOR TUBE SURVEILLANCE -
UPDATE Consumers Power Company submitted proposed Technical Specifications changes related to steam generator tube surveillance on July 26, 1979.
As a result of discussions with NRC staff, modifications to that request have been modi-fied arid revised.
Technical Specifications page cha.~ges are attached.
Discussion Consumers Power has concluded that the chai:ige from coordinated phosphate to volatile chemistry control has arrested previous corrosion.
This has also been demonstrated by other utilities making the same chemistry control conver-sion.
Since June 1974 no tubes have leaked, and since February 1976 mean wastage increase has been essentially zero which further confirms the sat-isfactory performance of the steam generators.
- The operating allowance for 1978 of 6% is considered applicable to all past and future data as long as the mean wastage increase for the previous cycle is less than _1%.
If a mean wastage increase equal to or greater than 1%
is cbserved, the operating allowance for the next cycle shall be determined by the licensee and approved by the NRC.
Current inspection requirements provide assurance that any tubes approaching the Maximum Allowable Degradation of 64% and any changes in mean wastage in-.
crease will be identified.
Additionally, significant radiation exposure (approximately 6 to 9 man-Rem) is involved in inspecting steam generator tubes which are obstruc.ted by eddy cur-rent test or sleeving equipment and redundant dam supports.
This added exposure to inspection personnel results from the multiple entries that must be made into l\\~'
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the steam generator's access and manually inspect.the 20 to 30 tubes obscured.
It should be noted that these obscured tubes, are located near the center stay1 (low corrosion region) and that alternate tubes in the proxiID.ityof obscured tubes will be selected for inspection.
Consumers Power has concluded that the increased personnel exposure is not in keeping with our ALARA policies and that the proposed inspection alternatives are acceptable.
~4{lJ,J David P Hof~~
Assistant Nuclear Licensing Administrator CC. JGKeppler, USNRC
4.14 Augmented Inservice Inspection Program for Steam Generators Applicability Applies to the tubes within both steam generators.
Objective To provide assurance of continued integrity of the steam generator tubes over their service lifetime.
Specification 4.14.1 Inspections will be made at a frequency not less than 12 nor more than 24 calendar months after the previous inspection.
Tube inspection requirements will include inspection of all unplugged tubes with an ECT indication of greater than or equal to 30% in either of the previous two inspection periods. If inspection of unplugged tubes with an ECT_ indication of greater than or equal to 30% (which are obstructed by ECT and repair equipment) leads to significant added personnel radiation exposure, alternate tubes may be selected for inspection.
In any event, unplugged tubes with ECT indications of greater than or equal to 30% will be inspected at a frequency not to exceed two intervals specified in 4.14.1 above.
The conventional, circumferentially wound ECT pull type probe shall be used to inspect unplugged tubes for which an ECT indication greater than or equal to 30% was noted in either of the two previous ECT in-spections.
In addition, a random sample of 2% of the tubes in the hot leg and 1% of the tubes in the cold leg of each steam generator will be inspected using the conventional, circumferentially wound ECT probe.
ECT = Eddy Current Test 4-68
For the purposes of ~his Technical Specificati<;m, "tubes" refers to that portion of the steam generator U-tube from the point of entry on the cold-leg side to the top support of the cold leg, or from the point of entry on the hot-leg side completely around the U-bend to the top support of the cold leg.
4.14.2 Inspection techniques, capable of detecting flaws in the presence of tube dents, shall be used to inspect all accessible tube/tube support plate intersections where an ECT indication was present during the last inspection which was greater than or equal to 45% but cannot be interpreted in the current inspection due to the presence of dents.
In addition, the following shall apply for areas which could not be inspected due to dents in the last inspection.
Additional intersections shall be selected for special examination to assure that all accessible previous ECT indications are inspected when their last recorded ECT reading plus the approp-riate operating allowance from Table 4.14.1 exceeds the Maximum Allowable Degradation specified in Table 4.14.2. If such indications, regardless of accessibility, are not inspected, the repair criteria of 4.14.3 shall apply for sleeving or plugging.
4.14.3 When inspection reveals that the tube degradation plus an NRC-approved appropriate operating allowance (for future degradation) is greater than the maximum allowable degradation specified in Table 4.14.2, the tube shall be declared to be defective and tube plugging or sleeving shall be performed.
. 4-68a
In determining that a defect exists at a given tube location, indications from several ECT's may be averaged during a given inspection, but such averaging shall be based on not less than three ECT's.
4.14.4 Operating allowances for future degradation are tabulated in Table 4.14.1.
4.14.5 Sleeves will be installed such that, considering the axial 4.14.6 Basis location tolerances, swaging does not take place in an area of known degradation.
A base line ECT inspection of all newly installed sleeves shall be performed.
In addition, all previously installed sleeves shall be inspected or plugged during subsequent steam generator tube inspections.
A steam generator inspection report shall be submitted to the NRC within 30 days of completion of the inspection and any re-quired repairs.
Consumers Power has concluded that the change from coordinated phosphate to volatile chemistry control for the secondary side of the steam gener-ators has reduced the previous corrosion rate to essentially zero.
Palisades has not observed any tube.leakage since June 1974.
Furthermore, mean wastage increase has been essentially zero since February 1976.
The continuing inspection program provides for verifying that the corrosion has been arrested.
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The inspection program is also consistent with current industry practices and includes appropriate,measures to identify additional degradation of the Palisades steam generators.
The operating allowance will be and the repair criteria has been developed based on comparative results between steam generator inspections with consideration given to defect type, location, past corrosion rate observed, etc.
Calculations have been performed to demonstrate that a tube uniformly thinned to 36% of its original nominal wall thickness (64% degradation) can withstand a differential pressure of 1380 psi.
Likewise, a sleeved tube can withstand the same differential pressure when the limits in Table 4.14.2 are observed.
Combustion Engineering, Inc Report No CEN-59(P) "Palisades Steam Generator Tube Repair by Sleeving," dated August 26, 1977, contains the analytical and test results of tube sleeving.
In dented regions wh~n the presence of a tube support plate tends to cause interference in the eddy current signals, the standard ECT inspection technique will not be able to detect flaws embedded in these regions.
However', there are several advanced inspection probes under development which have been shown to be effective in detecting flaws by screening out the interference signals caused by the presence of the tube support plates or dents.
4-68c
Affected Tubes Tubes Inspected During 1978(a:Q.d Future ECTs lJ Tubes Last Inspected D'liring 1976 ECT Tubes Last Inspected During 1975 ECT
- Not Applicable TABLE 4.14.1 Operating Allowances ECT Indications Other Than Multiple ECT Indications 6%
10%
20%
Multiple ECT Indications 35%
- NA
- NA (1) If the mean wastage increase over the period since the previous steam generator inspection is less th.an +l percent (essentially no wastage) the operating allowances listed above shall be applicable.
If the mean wastage increase is greater than or equal to +l percent, the NRC shall approve new operating allowances.
4-68d
Location
~nsleeved Sections Sleeved Section Region l(l)
Region 2( 2 )
Region 3( 3 )
Footnotes:
TABLE 4.14.2
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Maximum Allowable Degradation Maximum Allowable Degradation <5 )
Degradation = 64%
Sleeve degradation = 34% and tube degradation exceeding the maximum allowable degradation for an unsleeved section.(4)
Either (a) sleeve degradation = 25% when tube degradation in Region 1 exceeds the maximum allowable degradation for an unsleeved section; S?£. (b) tui;le _degradation t~ Region 2 equal to the maximum allowable degradation for an unsleeved tube.(4)
Tube degradation equal to the maximum allowable degradation for an unsleeved section.
. (l)The undeformed region of the tube/sleeve assembly containing the original imperfection requiring sleeving.
(2 )The region containing the expansion joint. Specifically, the region of __
the tube/sleeve assemblyboun~ed by lines approximately 1/4 inch and 2 inches inboard from the sleeve ends.
( 3)The region of the tube/sleeve assembly containing approximately 1/4 inch of each end of the assembly.
(4 )Degradation occurring in the parent tube at any location in a Region and degradation occurring in the sleeve at any location in the same Region that exceeds the applicable maximum allowable degradation will require tube-plugging-.------
(5)Subtracted from these Maximum Allowable Degradation values shall be an appropriate allowance for future degradation as approved by the NRC as identified in 4.14.3.
4-69 1
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