ML20052E725
| ML20052E725 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 05/04/1982 |
| From: | Lentine F COMMONWEALTH EDISON CO. |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| References | |
| 4027N, NUDOCS 8205110384 | |
| Download: ML20052E725 (4) | |
Text
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Commonwealth Edison
- ) one First Nationti Ptna Chicago, Illinois C ' J Addr:ss R:: ply 13: Post Offica Box 767
,Q Chicago, lltinois 60690 May 4, 1982 Mr. Darrell G. Eisenhut, Director rs, Division of Licensing
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Subject:
Zion Station Unit 1 h
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Inspection and Repair NRC Docket No. 50-295 D
A References (a):
Ma rch 10, 1982, letter from D.
G. Eisenhut to L. DelGeorge.
(b):
March 17, 1982, letter from F. Lentine to D.
G.
Eisenhut.
(c):
April 1, 1982, letter from F. Lentine to D. G.
Eisenhut.
Dear Mr. Eisenhut:
In accordance with your letter of reference (a), this is to document Commonwealth Edison's program for recovery o f the loose parts associated with the Zion 10 steam generator nozzle cover.
This information was presented verbally to members of your staf f in a conference call on April 8, 1982.
Summary The nozzle cover that was lef t in ID steam generator consisted of an aluminum cover with two stainless steel hinges and 36 stainless teel bolts, nuts and washers.
The nozzle cover is believed to have spent its entire lifetime in the ID s team generator hot leg channel head.
It was pressed against the hot leg tube sheet while the plant was operating, thus producing an approximate 4% flow reduction.
The aluminum plates were completely dissolved af ter about 25 days of operation (5/08/81).
During the dissolution, the two stainless steel hinges and the 36 bolt / nut / washer combinations were released in the 1D steam generator hot leg channel-head.
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- n D. G. Eisenhut May 4, 1982 The bolt / nut / washer combinations are capable of passing though the steam generator tubes, through the reactor coolant pump and cold leg piping and into the lower plenum of the reactor vessel.
The hinges are too large to pass through the tubes, and they remained in the channel head until after the end of the operating cycle.
On 2/16/82, lA and 10 reactor coolant pumps were shut off as part of a normal reactor shutdown /cooldown.
Since the 18 and 1C reactor coolant pumps were still operating, a reverse flow condition existed in loops A and D until 2/21/82 when the 18 and 1C pumps were shut o f f.
The reverse flow through loop D swept some of the remaining material out o f the -1D hot leg piping and into the upper head region.
The B and D hot legs are adjacent to each other.
Thus, as material was expelled from the D hot leg, it was drawn into the operating B hot leg.
The above history is consistent with the location of the loose parts found (1D steam generator hot leg channel head, 10 steam generator tubes, ID steam generator cold leg channel head, 1B steam generator hot leg channel head, and lower nozzle of fuel assemblies).
It is also consistent with the observed damage, flow / power anomalies, and loose parts monitoring system alarms observed during Cycle 6 operation.
Loose Parts Recovery Program Inspections of accessible portions of the primary system have been performed by visual observation and/or TV camera, as noted below.
(a) Steam Generators The channel heads of all steam generators were inspected.
One hinge was found intact in the 10 hot leg channel head.
Thre e pieces comprising essentially the entire second hinge were found in the IB hot leg channel head.
Of the material from the second hinge remaining unaccounted for, the maximum size piece would i
measure no more than 1" x 1/2" x
.060".
Five bolt / nut / washer combinations were found in the 10 hot leg channel head, and one bolt / nut / washer combination was found in the 1D cold leg channel head.
All have been removed.
The 1A, 18 and 1C steam generator tubes have been probed by performing eddy current examinations from the hot leg side through the seventh tube support plate on the cold leg side on all tubes.
At least 3% o f the tubes were checked full length.
One restriction was located in the U-bend region of a tube in IB steam generator.
Probe measurements from both ends of the tube indicate that the restriction is the approximate size o f a bolt / nut / waster combination, but there is no way to verify its identity.
The tube has been plugged.
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.D D. G.
Eisenhut May 3, 1982 The 10 steam generator has been probed from tube sheet to tube sheet for all tubes beyond row five.
Rows one through five have been probed from the cold leg side through the seventh tube support plate o f the hot leg side.
(The remaining portion o f the rows one through five tubes will be probed following repair o f the 1D hot leg tube ends. )
No restrictions were found.
Two bolt / nut / washer combinations were found lodged in hot leg tube ends.
The have been removed.
(b)
"D" Hot Leg Piping A TV camera was mounted on a skid and inserted through the channel head into the hot leg piping down to the loop insolation valve.
One bolt / nut / washer combination was located and removed from the piping.
Nothing was located in the valve seats.
The reactor nozzle area was also inspected visually a f ter the upper internals package was removed.
No bolts, washers or nuts were found.
(c) Upper Internals Subsequent to moving the upper internals package to its refueling storage location, a TV inspection was performed around the circumference of the upper core support plate.
The columns and other portions of the internals were inspected in the area o f the "B" and "D" hot leg nozzles.
No bolts, nuts, or washers were found.
(d) Top o f the Fuel Prior to movement o f any fuel in the core, a TV inspection was performed over the top o f the core.
No bolts, nuts, or washers attributed to the nozzle cover were fourid.
One nut was found, but it was determined that it had not come from the nozzle cover.
It was removed with a discharged assembly.
(e) Bottom o f the Fuel During the planned TV examination of selected fuel assemblies, one bolt / nut / washer combination and one bolt were found lodged in the bottom of the lower cast!.ng of a fuel assembly to be discharged.
Subsequent to that time, all lower castings of discharged fuel assemblies and fuel assemblies moved to the RCC change fixture in the containment were examined by TV.
One additional bolt / nut / washer combination was located in a discharged assembly lower casting.
Eighty-seven (87) o f the 193 assemblies present during the last cycle were examined.
With the completion o f the programs described above, all inspections have been performed which can reasonably be done with minimum risk to the fuel.
Based on the results of these inspections we believe that the remaining loose parts are located in the bottom
D. G. Eisenhut May 4, 1982 of the reactor vessel, where they are expected to remain throughout the next operating cycle.
Bolt / nut / washer combinations are too large to pass through the lower castings of the fuel assemblies, or to pass through the space between fuel assemblies.
Individual washers might be able to pass between fuel assemblies if oriented exactly parallel to them, but this is considered highly unlikely.
(It should be emphasized that all but one of the bolts that have been located have been found in bolt / nut / washer combinations.)
Commonwealth Edison will closely monitor the reassembly o f the vessel upper internals, installation of the incore instrumenta-tion thimbles, and testing of the rod control cluster assemblies (RCCA's), to ensure no adverse effects due to the presence of the remaining loose parts.
It should be emphasized that since the control rods are always at least partially inserted into the control rod guide tubes, there is no mechanism by which loose parts can prevent rod insertion into the core.
Westinghouse Electric Corpo-ration has been requested to analyze the e ffects o f the remaining parts on the fuel and components of the lower reactor vessel.
Upo n completion of this analysis, the results will be forwarded to the NRC.
In summary, Commonwealth Edison believes that with the completion of the loose parts recovery program described above and pending the results of the Westinghouse analysis, the unit may be safely returned to power operation.
The nex t re fueling outage,
presently scheduled for Fall, 1983, will include a total core o f f-load and removal of the reactor vessel lower internals for the ten-year inservice inspection program.
At that time, the lower vessel area will be inspected and, if possible, the remaining loose parts will be removed.
Please address any questions regarding this matter to this office.
Very truly yours, F.
G.
Lentine Nuclear Licensing Administrator 1m 4027N