ML20050E230
| ML20050E230 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/08/1982 |
| From: | Barrett L, Fasano A, Young F Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| PNO-TMI-82-007, PNO-TMI-82-7, NUDOCS 8204130123 | |
| Download: ML20050E230 (1) | |
Text
50289-320407 l
April 8,1982 l
PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-TMI-82-07 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verifi-cation or evaluation and is basically all that is known by NRC staff on this date.
Facility:'GPU Nuclear Corporation Licensee Emergency Classification:
Three Mile Island, Unit I X
Not Applicable Docket. No. 50-289
Subject:
STEAM GENERATOR TUBE DEGRADATION GPU Nuclear management briefed NRC staff of their plans for repairing the TMI-l steam generators at a meeting on April 7,1982, at the NRC's offices in Bethesda, Maryland.
The repairs are expected to be completed by late summer or early fall of this year.
The repairs involve a technique of expanding and resealing the tube walls at points below where corrosion attacked the tubes. The work will be done using remote-controlled equipment that will expand the tube walls either hydraulically or mechanically to create a new seal. The repair operation will begin after the tube expansion technique is fully tested and qualified for the TMI-l application.
Licensee studies that have been made of the steam generators' history, since the discovery of small leaks in TMI-l tubes last November, have developed a probable explanation for how the corrosion occurred. The licensee is proceeding on the basis of that explanation, which is still being verified by further testing, that a species of sulfur, most likely sodium thiosulfate, was the active corrosive agent. The licensee reported that the corrosion apparently occurred through a complex interaction of equipment test sequences, materials properties, stresses and chemical conditions that occurred during the latter part of the three-year period in which THI-l has not been operating.
The most likely manner in which small amounts of sodium thiosulfate entered the primary system water is by leakage through valves downstream of the sodium thiosulfate tank during testing of the THI-l containment building spray pumps, and from there into the borated water storage tank (BWST) at TMI-l. Makeup water from the BWST was injected into the reactor coolant system during September 1981 hot functional testing (HFT). During HFT of the plant the chemical' form of the sulfate compound was changed to one which upon subsequent cooldown would be corrosive in combination with the "right" conditions of stress, metal structure and chemistry of the reactor system water.
Because of the unique " primary to secondary" nature of the corrosion, the licensee also plans to inspect internal components of the reactor itself for any evidence of corrosion.
This operation is scheduled to commence beginning the week of April 12,1982.
Media interest had occurred because the licensee issued a press release. The Commonwealth of Pennsylvania was informed.
T'his preliminary notification is issued for information only and the NRC plans to continue monitoring events as they occur.
This inforption as current as of 9:30 AM, today, j
N Of.
(l <f1 Contact :
F.
oun 590-1155 V. F sano 590-1123 arrett 590-1120 Distribution :
H. St.
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