ML20080B827

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Clarifies Topical Rept TR-008 Re Acceptability of Steam Generators to Return to Svc.Conclusion That Tubing Left in Svc Acceptable for Continued Use,Based on Results of Previously Conducted Eddy Current Insps
ML20080B827
Person / Time
Site: Three Mile Island Constellation icon.png
Issue date: 02/02/1984
From: Hukill H
GENERAL PUBLIC UTILITIES CORP.
To: Harold Denton
Office of Nuclear Reactor Regulation
References
5211-84-2026, NUDOCS 8402070291
Download: ML20080B827 (2)


Text

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GPU Nuclear Corporation g

4 Post Office Box 480

,,% Route 441 South Middletown, Pennsylvania 17057-0191 717 944-7621 TELEX 84-2386 Wnter's Direct Dial Number:

February 2, 1984 5211-84-2026 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Washington, DC 20555

Dear Mr. Denton:

SU9 JECT: Three Mile Island Nuclear Station, Unit 1 (TMI-1)

Operating License No. DPR-50 Docket No. 50-289 TMI-l Steam Generators During the GPU Nuclear Corporation (GPUN) management review of the acceptability of the steam generators to return to service, one aspect of GPUN Topical Report 008 was identified as potentially ambig-uous. In telephone conversations with C. McCracken and H. Silver of the NRC staff on January 3, 1984, it was established that no misunderstanding exists. This letter provides clarification of TR-008 to document this mutual understanding.

The conclusion in the Topical Repcit that tubing left in service is acceptable for continued use is based on already conducted eddy current inspections and those to be carried out during future shutdowns, the results of transient loadings during the OTSG hot test program, the confirmation in the lead corronion test program that no crack growth is anticipated due to chemical conditions, and the ability of leakage :1oni-toring to detect leakage changes due to any loads imposed during cooldown which are sufficient to contribute significantly to mechanical fatigue.

TR-008, pp. 84-89 discusses tube stability during the most severe normal transient loading permitted by procedure, a cooldown re-sulting in a 70 F differential temperature between the shell and tubes. All plant cooldcuns are, of course, not at this maximum rate and thus do not develop the maximum tube-to-shell delta T. As etated on page 88, "the OTSG 1eak rate will be monitored during each plant cooldown.

High leak rates would be investigated prior to restart". This evaluation of each cooldown will be based on the actual plant conditions. Fcr tubes experiencing lower loading during cooldown, the cooldown leakage, if any, is of significance since low loads may not be sufficient to assure that residual crack openings will remain after cooldown.

8402070291 840202 f DDI PDR ADOCK 05000289 P

l0 PDR GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation

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e Mr. Harold R. Denton Page 2 February 2,1984 For low tube-to-shell delta Ts, the maximum load on some tubes may be lies than or equal to that assumed for steady state in the TR-008 evaluation (200-500 lbs). Leakage through a hypothetical critical-sized crack in such a tube would not ce significant under these conditions.

However, each earlier cooldown at a higher delta T, such as those delib-erately co;. ducted during ' steam generator testing, will have shown that such cracks were not present and such low loads have been demonstrated not to significantly contribute to mechnical crack propagation (see TR-008, p.87). If a tube is loaded to an extent to contribute signifi-cantly to crack growth, leakage monitoring will show the presence of a critical-sized crack. If not, these particular tubes will be no different from a monitoring standpoint than all tubes during hot steady-state operations. The leakage monitoring performed during the previous transient which did generate significant loads is expected to remain representative of the condition of the tubes. Thus, the fact that some cooldowns result in a tube to shell delta T of less than or equal to 70*F is consistent with the previously discussed conclusions in TR-008.

Very truly yours, .

.A$

. D. kill Vice President / Director, TMI-l 0141d cc: H. Silver l

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