ML19317D936
| ML19317D936 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 01/22/1975 |
| From: | Thies A DUKE POWER CO. |
| To: | Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| RO-750122, NUDOCS 7912100612 | |
| Download: ML19317D936 (3) | |
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Letter to N. C. Moseley from Duke Power Company dated January 22, 1975.
DISTRIFUTION:
50-269 H. D. Thorncurg, IE IE:HQS (5)
Office of Standards Development W/ Central Files Division of Reactor Licensing (13)
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January 22, 1975 Mr. Norman C. Moseley, Director Directorate of Regulatory Operations U. S. Atomic Energy Commission Region II - Suite 818 230 Peachtree Street, Northwest Atlanta, Georgia 30303 Re: Oconee Nuclear Station Unit 1 Docket No. 50-269
Dear Mr. Moseley:
On November 11, 1974, during refueling operations on Oconee Nuclear Station Unit 1, an irradiated bolt was found on the floor of the Oconee Units 1 and 2 Spent Fuel Pool.
An extensive investigation has been conducted by Duke Power Company personnel and personnel from the Babcock and Wilcox Company (B&W) to determine the origin of this bolt and to assess the effects thereof on past and future operations.
Examination determined that the bolt was three inches in length by approximately one-half inch in diameter, had a hexagonal head and had NC-13 threads on the lower lh inches of the shank. An identification mark "214/HT1-A" was observed on the head of the bolt. No indications of prior installation, such as thread deformation, head surface upset or locking weld, were visible. A uniform black oxide coloration and nonmagnetic property indicated that the bolt was a corrosion-resistant, austenitic material.
Radiation levels from the bolt were approximately 200 R/hr on contact.
From rhe above description, the bolt was identified as being an "MK-214" designation bolt used by B&W in two locations in the Oconee class reactor In the first location, 24 MK-214 bolts are installed, torqued internals.
and lock-welded to attach 12 shock pads to the lower grid flange bottom.
In the second location, two MK-214 bolts are installed, using a locking clip, in each of the three surveillance specimen holder tube bearings.
1972, 48 During the Oconee 1 and 2 reactor internals modifications in unmarked, previously shop installed, MK-214 bolts were removed with the shock pads in order to perform the lower grid / flow distributor rework
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Mr. Norman C. Moncity Page 2 January 22, 1975 operations. At that time, records indicate that 60 MK-214 bolts, marked "214/HT1-A" for material traceability, were received at Oconee for.use in the Oconee 1 and 2 internals. Of these marked bolts, 24 were subse-l quently used to reassemble the shock pads to the lower grid in both Oconee 1 and 2, i.e., a total of 48 marked bolts were installed.
It cen1d not be conclusively determined as to whether marked or unmarked hW-214 bolts were used in Oconee 1 and 2 to reassemble the surveillance specimen holder tube bearings to the core support assemblies (total of 12 bolts installed).
A radiation analysis was performed on the subject bolt and the results indicated that the bolt could have reached its observed activation level only by residing in or near the Oconee 1 core for the approximate length of time of the first core cycle. Oconee Unit 2 had not achieved sufficient core burnup to have provided the integral neutron exposure that the bolt had received.
Records from the Oconee 1 post-hot functional testing reactor internals inspection indicated that all MK-214 bolts and their lock welds or locking clips were visually inspected and verified to be intact, without evidence of distress or change, at the shock pad and surveillance tube bearing locations.
Because the subject bolt had no indication of lock welding, the 24 bolt locations in the lower grid are not considered as a possible source.
A remote visual examination of the Oconee Unit 1 surveillance tube bearing bolt heads was performed and all six bolts were found to be properly positioned.
Additionally, as stated above, 48 of the 60 marked MK-214 bolts shipped to Oconee have been verified as having been installed in the Oconee 1 and 2 internals.
Eleven of the remaining 12 marked bolts have been determined to be in the possession of B&W site personnel.
Based on the information available, and summarized herein, it is concluded that the subject bolt had not been installed in the Oconee 1 reactor I
internals, but rather, apparently inadvertently remained in the internals following reassembly of the internals on site.
Analyses have indicated l
that such c~ occurrence would have created no significant adverse effects, l
and it is concluded that there are no safety implications associated I
with this incident.
Very truly yours, A.
.M s.
l A. C. Thies l
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