ML20050B867
| ML20050B867 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 04/01/1982 |
| From: | Lentine F, Letine F COMMONWEALTH EDISON CO. |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| References | |
| 3771N, NUDOCS 8204070505 | |
| Download: ML20050B867 (5) | |
Text
,
/7N Commonwealth Edison
[ C ")) Address Rrply to: Post Ofhce Box 767
^
One First National Plaza. Chicago. Ilknots
-g(j Chicago, lilinois 60690 April 1, 1982 N
,p s N2 4
Mr. Darrell G.
Eisenhut, Director d'
,i "raygg Division o f Licensing f._
~*
1982S" jg U.S. Nuclear Regulatory Commission Washington, DC 20555 a4 APRo
% g mssamn:s mcn gam
/
Subject:
Zion Station Unit 1 p
Steam Generator Inspection and Repair NRC Docket No. 50-295 References (a):
March 10, 1982, letter from D.
Eisenhut to L. DelGeo rge.
(b):
March 17, 1982, letter from F.
Let tine to D.
Eisenhut.
Dear Mr. Eisenhut:
This letter is to document the recovery program planned for the damaged tube ends in the Zion 1D steam generator, as presented to members of your staf f on March 25, 1982.
Following receipt o f the NRC's verbal approval at the conclusion of that presentation, we have continued our preparations for the recovery program.
Our current schedule is shown in Table 1.
Commonwealth Edison hereby requests confirmation o f the NRC's approval prior to the start of the actual repair work, presently scheduled for April 8, 1982.
The recovery program is in two phases.
The first phase addresses the following work:
1.
Repair'afudamaged tube ends which could result in future tObe fragments.
2.
Restoration of tube ends of Row 1 and other tubes requiring plugs to accept tube plugs and the eddy current probe.
The first phase of the program will be accomplished using manual techniques.
The second pha:e will consist of restoring the remaining damaged tube ends using an automated system controlled from outside
.the steam generator lower plenum.
This system will greatly reduce the radiation exposure of the personnel. involved in the program.
0
,D e
m
D.
G. Eisenhut April 1, 1982 Approximately 200 tubes in the peripheral area will not be restored at this time.
They will be restored at a later date to allow future eddy current examination to be performed completely from the hot leg side.
These 200 tubes are outside the range of the automated system and will require manual work with the associated additional radiation exposure.
ihe repair / restoration process will consist of the following steps:
Repair process:
1.
Machine the tube end to a minimum of (9 tubes) 0.070 inches beyond the tube sheet.
This assures that any potential loose pieces will be removed and the tube-to-tube sheet weld will not be removed.
2.
Expand the tube end to the required diameter using a hard roller.
Restoration process:
1.
Light damaged tube ends - hard (Remaining tubes) roll with final size hard roller.
2.
Medium damaged tube ends - hard roll with several hard rolls of increasing size.
3.
Heavily damaged tube ends - use slide hammer to enlarge opening then hard roll with hard rollers of increasing size.
The initial. construction of the steam generator made use of an 80 inch-pound hardroll to a depth of 21/4" to 21/2" in addition to the 1/8" fillet weld at the tube-to-tubesheet juction.
No credit was taken for this initial hardroll in the stress analysis report.
All stresses were considered to be taken by the 1/8" fillet weld.
Tube end damage and weld integrity were evaluated visually by the use of direct visual observation, video tapes, and indexed, magnified still photographs.
All of these methods indicated no damage to the cladding on the tubesheet, plenum, or divider plate.
No tubc-to-tubesheet weld damage was observed.
Additionally, the observed degree o f tube end deformation would have no e ffect on the flow characteristics or heat transfer capability of the steam generator.
Independent verification of weld integrity was obtained through laborator'y testing designed to simulate the observed damage, and additional stress calculations to determine changes in the total fatigue usage factor.
The laboratory tests simulated both the damage observed and the repairs proposed.
Photographic, x-ray, and metallurgical sectioning inspections all revealed no cracking in the
o D. G. Eisenhut April 1, 1982 weld area and no tube wall thinning in excess o f the manufacturer's allowable tolerances.
The stress calculations revealed an increase in the total fatigue usage factor from 0.063 to 0.144.
This is well within the ASME Section III code allowable total fatigue usage f actor o f 1.0.
During the recovery program, an additional 120 inch-pound hardroll to a depth of 1 1/2" will be perfomed on tubes with damaged ends.
This hardroll is a code acceptable stress carrier, and Westinghouse reseach (WCAP 9960) has indicated that it is capable o f taking all of the required stresses without any structural weld being present.
However, as in the original stress analysis report, no credit is being taken for this hardroll.
All stresses are considered to be taken by the fillet weld.
Af ter completion of the recovery program, another complete set of high resolution photographs will be taken for use as a final inspection device.
The manually repaired / restored tuce ends will be dimensionally checked by a tube gage, and the tube ends restored by the automated process will be dimensionally checked by a plug gage check on the first and last tube ends restored by a specific hard roller.
Commonwealth Edison is currently evaluating the feasibility of performing additional checks to further verify the integrity o ?
the tube-to-tubesheet weld.
Upon completion of our evaluation, we will discuss this matter further with the NRC.
In our March 25 presentation, we also discussed the 28 bolts from the aluminum cover plate still remaining in the primary sytem.
Our program to search for these bolts is as follows:
1.
Inspect "D" hot leg piping, incuding the isolation valve.
This has been completed.
One bolt was found and recovered between the lower plenum and the isolation valve.
No bolts were found in the area of the isolation valve seat.
2.
Inspect the reactor upper internals after they are placed on the inspection stand.
A T.V. camera will be used for this work, concentrating on the area closest to the "B" and "D" ~ steam generator hot leg nozzles.
3.
Inspect the top of the fuel.
Due to dimensional considerations, the bolts will not fall into the fuel.
Therefore, any that have fallen through the upper intr rnals should be found on the top o f the fuel assemblies.
4.
Inspect the _ tubes of the lD steam generator by -
performing a 100% eddy current examination.
4 D. G. Eisenhut April 1, 1982 Should any loose parts remain unaccounted for at the completion of this program, a safety evaluation will be made to confirm the acceptability of _ continued operation with those parts remaining _in the system.
The location-of the aluminum in the primary system, resulting from the dissolution of the manway cover, is being pursued by the following program:
1.
Samples have been taken f-m the following locations:
CVCS Hold-up Tanks, Reacto r Coolant System, and the outlet of the Reactor Coolant filter.
Essentially no aluminum was found.
2.
Samples will be t aken from a CVCS letdown demineralizer that was in service during the last part o f the fuel cycle.
3.
Crud samples will be taken from several fuel assemb-i lies from each region of the core.
Following receipt of the results of the sample program, an evaluation of the effect of any contaminants on fuel performance will be made.
Additional information on the investigation and recovery program will be made available to the NRC staf f as it becomes avail-1 able.
Additional conference calls, meetings, and written submittals will be scheduled as appropriate.
Please address questions regarding these matters to this l
office.
Very truly yours, k
F.
G.
Lentine Nuclear Licensing Administrator 1m i
t 3771N J
y
- y. -,,
,.w
TABLE 1 ZION STATION "D" STEAM GENERATOR RECOVERY SCHEDULE April 1 2 3 4 5 6 7 8 9 lo 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
- 1. EC - H. & CL
- 2. He Test
- 3. Manual Operation
- 4. Auto Operator y
- 5. Cosplete EC
't
- 6. Plug Tubes
- 7. Install Manways Y
l