ML20059H405
| ML20059H405 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 01/10/1994 |
| From: | Broughton T GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| C311-93-2174, NUDOCS 9401270222 | |
| Download: ML20059H405 (2) | |
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GPU Nuclear Corporation i
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Middletown, Pennsylvania 17057-0191 717 944 7621 TELEX 84 2386 Writer's Direct Dial Number:
(717) 948-8005 January 10, 1994 C311-93-2174 i
U. S. Nuclear Regulatory Commission Attn:
Document Control Desk Washington, DC 20555
Dear Sir:
l
Subject:
Three Mile Island Nuclear Station, Unit I (TMI-1) l Operating License No. DPR-50 Docket No. 50-289 Technical Specification Change Request (TSCR) No. 214 Once Through Steam Generator (OTSG) Primary-to-Secondary Leak Rate Limit - Supplemental Information Ref:
GPUN Letter C311-92-2036, dated 5/13/92 On July 1, 1993, GPUN met with the Staff to discuss No. TSCR 214.
- Briefly, TSCR No. 214 proposed a change (0.2 gpm) to the leakage limit above the baseline leak rate when the increased leakage is judged to be caused by leaking plugs or joints.
The TSCR also proposed the retention of the current leak rate limit (0.1 gpm) in license condition 2(c)(8)(2) for all other conditions.
The current license limit reflected a caution which was applied due to the occurrence of circumferential cracks on the inside tube diameter in the early 1980's. TMI-1 has since removed the sodium thiosulfate which was suspected as the source of this damage mechanism.
Based on the results of subsequent OTSG inspections and repairs which concluded that the damage mechanism has ceased (no active degradation), we proposed a higher leakage limit to account for plug leakage during the operating cycle.
With the completion of the 10R outage, we wish to update the Staff on the OTSG inspections and repairs. The 10R OTSG work scope included: (1) a drip test of i
the lower tubesheet to identify leaking tubes or plugs for repairs; (2) eddy current testing (ECT) of all of the Mark-1 B&W explosive plugs and any leaking Mark III explosive or leaky rolled plugs; (3) completion of the preventive tube sleeving program for each OTSG; (4) ECT of the remaining I-600 B&W plugs in the upper tube sheet; and (5) repair and/or replacement of any leaking plug or non-leaking plugs with pressure boundary ECT defects.
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We completed ECT for about ten percent of the tubes in Steam Generator "A" and about seven percent of the tubes in Steam Generator "B."
There were no leaking tubes found in the leak testing. The evaluation of 'the eddy current '
inspection results determined the need to repair one non-leaking defective tube in OTSG "A" by sleeving, and remove one non-leaking defective tube in l
OTSG "B" from service by. plugging. These two defective tubes were the result of slight changes in existing degradation indications (monitored each.
successive outage since 1985 Restart of TMI-1).
The defective tubes did not indicate active tube degradation as confirmed by the absence of new ECT indications or significant active growth in the tubes sampled in 10R, and by the absence of leaking unplugged tube locations on the 9R and 10R drip tests.
For the leaking explosive plugs, we installed a total.of 32 rolled plugs in the lower heads of OTSG A and B.
We also installed a total of 58 rolled plugs behind the non-leaking explosive-plugs as a preventive measure in the-lower heads of the OTSGs. We removed four non-leaking I-600 rolled plugs with ECT indications in the upper tube sheets and replugged with I-690 plugs.
As in 9R, the' 10R leak testing again revealed that the previously monitored increasing leakage was attributed to leaking plugs.
Since startup from 10R, the primary-secondary leak rate has been calculated at about 1.5 to 2.0 gal /hr.
GPUN believes that this leakage is from explosive plugged tubes and is preparing a 11R testing and preventive repair plan for the.approximately 508 remaining lower tubesheet explosive plugs.
In conclusion, the current 0.1 gpm leakage limit above baseline is. overly restrictive for TMI-1 operation. During the early 1980's, this leakage limit provided a level of caution to account for the uncertainties associated with kinetic expansion repairs for the circumferential tube cracks. With the benefit of the knowledge gained through the nearly ten years of 0TSG.
inspections and leak tests, we believe there is technical justification to increase this limit to minimize the potential for forced shutdowns during plant operation.
We again request that an amendment authorizing TSCR 214 be considered by the Staff, so that we may implement the change during this operating cycle.
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Sincerely, b
T. G. Bro ton Vice President.and Director, TMI-1 cc:
Administrator, Region I TMI Senior Project Manager TMI Senior Resident Inspector
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