ML19289B283
| ML19289B283 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 02/20/1976 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Thornburg H NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| NUDOCS 8303110493 | |
| Download: ML19289B283 (2) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISs10N REGION V I
D SUITE 202. W ALNUT C REEK PLAZ A T
1990 N. C ALIFORNIA BOULEVARD W ALNUT CREEK. C ALIFORNI A 94596 FE6 2 : 1976 H. D. Thornburg, Acting Director, Division of Field Operations, IE:HQ MISCELLANE0US INFORMATION IN RESPONSE TO JCAE HEARINGS - HUMBOLDT BAY UNIT 3 DOCKET NO. 50-133 Attached is information relating to an occurrence at Humboldt Bay Unit 3, in response to a telephone request made by G. H. Smith of your staff this date.
The occurrence at the Humboldt Bay facility in 1974 is the only experience in Region V which meets the criteria of the request made by Mr. Smith, i.e., instances of safe-end cracks or cracks revealed in the vessel internals of operating power reactor facilities.
hNan eGS, R. H. Engelken Director cc:
K. V. Seyfrit, IE:HQ 8303110493 760220 PDRADOCK05000g'j S
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I/76 191
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February 20. 1976 Pacific Gas and Electric Company Humboldt Bay Unit No. 3 50-133 Failure of U-Bolts Securing Feedwater Sparger Description of Problem - During a routine visuel inspection of reactor internals on November 17, 1974, the licensee discovered the failure of five (5) of eight (8) U-bolts which secured the feedwater sparger in place.
In the case of three U-bolts both of the threaded legs had broken. A single leg was found broken on the remaining two.
The sparger itself was found to be shifted approximately 2 inches from its normal position, without impairment of its normal functional capability.
The U-bolt failures were attributed to high cycle fatique at the point where the U-bolt enters the lock nuts.
IE Followup Inspection - Region V inspectors examined the failed U-bolts (including specimens subjected to metalluru:ral examination) and confirmed the licensee's assessment of failure mode.
A review was made of the design of a modified sparger clamp device to replace the U-bolts.
Installation of the modified clamping devices was verified prior to the resumption of reactor operation.
Action by Licensee - A modified clamp was designed, fabricated and installed to replace the failed U-bolts.
These devices were examined visually during the refueling outage of 1975, with no adverse conditions revealed.
Enforcement Action by IE - No enforcement action was appropriate as a result of the occurrence.
Dissemination of Information by IE Regarding the Occurrence - The generic applicability of this occurrence was evaluated and the con-clusion was reached that the design of the feedwater sparger mounting and holddown device was unique to the Humboldt Bay reactor. Therefore, an IE Bulletin or similar notification to other licensees was determined to be inappropriate.