ML20078L900
| ML20078L900 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 02/05/1995 |
| From: | Broughton T GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| C311-95-2037, NUDOCS 9502130173 | |
| Download: ML20078L900 (4) | |
Text
d e
,g GPU Nuclear Corporation o Nuclear "n
'r*
Middletown, Pennsylvania 17057-0480 (717) 944-7621 Writer's Direct Dial Nurnber:
(717) 948-8005 February 5,1995 C311-95-2037 U. S. Nuclear Regulatory Commission Att: Document Control Desk Washington, DC 20555
Dear Sir:
Subject:
Three Mile Island Nuclear Station, Unit 1 (THI-1)
Operating License No. DPR 50 Docket No. 50-289 Request for NRC Review of the THI-1 OTSG Tube Inspection Plan for the Cycle 11 Refueling (11R) Outage During NRC Inspection 94-23 GPU Nuclear discussed plans for eddy current tests (ECT) of the Once Through Steam Generator (OTSG) tubes during the Cycle 11 Refueling (11R).
For future inspections, we have explored the option of testing a larger sample size of approximately 21%. We believe that establishing a sample size this large will provide a better data base of information on which to base conciusions regarding 0TSG tube integrity.
Inspection Report (IR) 94-23, dated January 10, 1995 concluded that the 10R OTSG tube inspections and GPU Nuclear's evaluation of the results met the Technical Specifications (TS) Requirements. The NRC Region I inspectors had no comments on GPU Nuclear plans for llR tube inspections. However, because of the differences resulting from the 21% sample size, it was suggested that we submit our TS interpretation for NRC review at this time to preclude the need for discussions related to TS compliance during or after the 11R Outage.
We believe that the approach described in the attached TS Interpretation remains in compliance with the existing TS requirements. NRC comments are requested by June 1995 to provide the time to resolve any comments regarding TS compliance prior to the 11R outage which is scheduled to begin in September 1995.
Sincerely, Ah %
pgg21386M 828383g T.G.Brouhhton U
PDR Vice President and Director, TMI Attachment MRK
/
cc:
Region I Administrator
/MO TMI-I Senior Project Manager TMI Senior Resident Inspector ILh l
GPU Nuclear Corporation is a subsidiary of General Pubhc Utilities Corporation
\\
l
-*t Technical Specification (TS) Interpretation
. TS 4.19 - 0TSG Inservice Inspection Sampling Requirements REQUIREMENT Assuming that both Once Through Steam Generators (OTSGs) are to be inspected, THI-l TS 4.19 requires that each OTSG inservice inspection begin with a sample of least 3% of the total number of tubes in each OYSG (15,531) and that tube selection be on a random basis except as specified in TS 4.19.2.
Examination results are classified as either Category C-1, C-2, or C-3 where:
1.
Category C-1 occurs when less than 5% of the total tubes inspected in a steam generator are degraded tubes and none of the inspected tubes are defective.
2.
Category C-2 occurs when one or more tubes, but not more than 1% of the total tubes inspected in a steam generator are defective, or between 5%
and 10% of the total tubes inspected are degraded tubes.
3.
Category C-3 occurs when more than 10% of the total tubes inspected in a steam generator are degraded tubes or more than 1% of the inspected tubes are defective.
Depending on the results classification, sampling may be required to escalate to a second or third sample beyond 3% and could require inspection of the entire OTSG.
BACKGROUND i
This interpretation is only concerned with the organization and sequencing of inspection samples in keeping with the objective of the OTSG inspections.
The escalations of inspections as required by TS Table 4.19-2 for Category C-1, C-2, or C-3 inspection results are unaffected by this interpretation.
Plans for llR will invo!ve programming a total inspection sample of 21% of the 15,531 tubes in each OTSG.
This total sample will be broken down into predesignated 3%, 6%, and 12% elements.
Predesignated subsamples will provide a means of categorizing the inspcction results for reporting purposes.
If l
category C-3 results were to be obtained, inspection of the entire OTSG would still be required per TS Table 4.19-2.
The predesignated 3% subsample will include all previously degraded tubes as required by TS 4.19.2 and the remainder will be randomly selected.
For inspection efficiency and to keep personnel exposures ALARA, the predesignated 6% and 12% subsamples will not be selected randomly. Tubes from each of the 3%, 6%, and 12% elements may be distributed throughout the total 21% sample i
and will likely not be inspected as discrete groups in succession.
Use of i
this sampling method over time, even without further escalation, would result in the inspection of 100% of the tubes in each OTSG.
INTERPRETATION 1.
In all cases, the initial random sample shall be greater than or equal to 3% and the following guidelines shall be applied:
)
a.
For the predesignated initial 3% sample, the selection requirements of l
TS 4.19.a 1-4 documenting the exceptions to a " random basis" shall be followed.
C311-95-2037 Page 2 of 3 b.
For the predesignated second and third sample (6% + 12%) portions of the 21% tube inspection sample, tube selection is not required to be from "those areas of the tubesheet array where tubes with imperfections were previously found" unless partial tube length inspections are elected under T.S. 4.19.2.b.
For the predesignated second and third samples, representative sampling of all areas of the tube bundle may be performed in lieu of purely random tube selection.
Such representative sampling should ordinarily be from the population of tubes which has not been inspected in the most recent tube inspections. Over several outages this sampling method would ensure that all tubes are inspected at least once.
Purely " random" sampling might reinspect the same tubes several times while ignoring other tubes.
2.
This TS interpretation is based on application of Table 4.19-2 in a cumulative manner. Selecting a programmed sample size beyond the minimum can provide for a better utilization of resources for the planning and execution of the OTSG inspections. TS compliance is accomplished by determining a programmed sample size which equals or exceeds the cumulative sample size which could result from the inspections performed per TS Table 4.19-2.
Sample groups are pre-designated before the outage to ensure compliance with C-3 escalation criteria; if C-3 escalation is not required, the minimum additional sampling required shall be those inservice tubes immediately adjacent to new defective tubes.
(It is recommended that adjacent tubes to new degraded tubes also be inspected).
3.
The derivation of a programmed sample size of 9% is as follows:
Assuming an initial sample of 3% and the results of this sample are C-2 (one defective tube but not more than 1% defective in a steam generator, or between 5%-10% are degraded), then an additional 6% random tube sample is required.
If the results of this second sample are C-1 (no defective tubes and less than 5% degraded tubes), then no additional samples are i
required.
The cumulative inspection size is 9% with <5 defective tubes and <47 degraded tubes allowed without further evaluation.
4.
The derivation of a programmed sample size of 21% is as follows:
Assuming an initial sample of 3% and the results of this sample are C-2 (second sample of F% is required) and the results of this second sample are also C-2 (additional sample of 12% is required).
The cumulative sample size is 21% and with each sample having C-2 results, up to 1%
i defective tubes (<5 tubes) and 5-10% degraded tubes <47 tubes) are allowed without further evaluation. A 21% sample is the minimum required in this instance.
1 5.
If 5 or more defective tubes (1% of 3% sample) or 47 or more degraded tubes (10% of 3% sample) result from 21% programmed inspection (or any j
other programmed sample size greater than 3%), then further results evaluation shall be done to ensure that more extensive tube inspections are not required by TS Table 4.19-2.
Example 1: For a 21% programmed sample, if 5 or more tubes are found defective (or 47 or more tubes are found degraded) in the initial 3%
portion of the sample (designated before the outage), then a C-3 condition is declared and all tubes in that OTSG plus 6% of the other OTSG must be inspected.
- C311-95-2037
. Page 3 of 3 Example 2: For a 21% programmed' sample, if 10 or more tubes are found defective (or 94 or more tubes.are found degraded) in the 6% portion of the sample (designated before the outage), then a C-3 condition is declared and all tubes in that OTSG plus 6% of the other OTSG must be inspected.
Example 3: For a 21% programmed sample, if 19 or more tubes are found defective (or 187 or more tubes are found degraded) in the 12% portion of the sample (designated before the outage), then a C-3 condition is
' declared and all tubes in that OTSG plus 6% of the other OTSG must be inspected.
6.
As discussed in Paragraphs 3 and 4 above, further evaluation of cumulative inspection results may be necessary if the results are not as straight-forward as the first three examples.
For the sake of simplicity, only defective tubes are considered below.
(A similar approach would apply the different categorization criteria totals for degraded tubes.)
Example 4: For a 21% programmed sample, if no tubes are defective in the initiaT 3% sample, and 1 to 9 (or 1 to 18) tubes are defective in either the predesignated 6% (or 12%) second (or third) samples respectively, then a C-2 condition is declared, but no additional inspections (beyond the
" adjacent to defective tubes" minimum allowed sempling of Paragraph 2 above) are required.
CONCLUSION:
This interpretation complies with the existing TS requirements because a 21%
inspection size satisfies the requirements resulting from inspection results up to and including C-2.
This interpretation provides for predesignation of 3, 6, and 12% samples in order to retain the TS required sample escalations beyond a 21% sample size for C-3 results and for the required reporting of C-3 results to the NRC.
i i
I i
m e-m