ML20081J618
| ML20081J618 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 11/07/1983 |
| From: | Schroeder C COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 7583N, NUDOCS 8311090053 | |
| Download: ML20081J618 (3) | |
Text
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6, 1
O) one First Nationd Ptara. Chicago, Ilknois Commonwealth Edison O
O Address Reply to: Post Office Box 767 Chicago, Illinois 60690 November 7, 1983 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation i.
U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
LaSalle County Station Units 1 and 2 Intergranular Stress Corrosion Cracking (IGSCC)
NRC Docket Nos. 50-373 and 50-374
Dear Mr. Denton:
During :he October 7, 1983, Unit 2 Preoperational Readiness meeting with Mr. Purple, et. al., of your staf f at LaSalle County Station, it was requested that Commonwealth Edison Company provide you with a summary of the status of actions regarding IGSCC.
Attached please find " Revisions to the LaSalle County Station To Reduce The Potential For Intergranular Stress Corrosion Cracking."
To the best of my knowledge and belief the statements contained herein and in the attachment are true and correct.
In some respects these statements are not based on my personal knowledge but upon infor-mation furnished by other Commonwealth Edison employees and consultants.
Such information has been reviewed in accordance with Company practice and I believe it to be reliable.
i If there are any further questions in this matter, please contact this office.
Very truly yours, Cid M,.h/e3 C.
W.
Schroeder Nuclear Licensing Administrator im cc: _NRC Resident Inspector - LSCS Attachment 8311090053 831107 T
PDR ADOCK 05000373 p
PDR q
7583N I
3 ATTACHMENT Revisions To The LaSalle County Station To Reduce The Potential For Intergranular Stress Corrosion Cracking Beginning with the 1974 discovery of cracks in stainless steel piping, Commonwealth Edison's LaSalle Engineering Group has actively improved the LaSallle design and equipment installation to reduce intergranular stress corrosion cracking (IGSCC).
Both general and specific corrective actions are noted here to indicate the scope of changes at LaSalle since stainless steel cracking became an issue.
General Actions Pursued:
1.
Type 304 stainless steel has been replaced where cracking conditions have been.found or are expected based upon the three contributory causes:
overstress, sensitization, and high oxygen content in semi-stagnant flows.
Replacement materials were 304L, 316L, 316K or carbon steel in some places.
Crevices and stress amplification designs were avoided.
2.
Post fabrication solution annealing was used on shop fabricated assemblies and piping spools.
Sensitization temperatures (800-15000F) were avoided.
3.
Field welding utilized controlled heat inputs to. limit the heat affected zone. - Controlled deposition of weld cladding was needed in safe-end replacements.
4.
Grinding' was not allowed on reactor coolant wetted surfaces of pressure boundary equipment.
5.
Stagnant. lines and certain NRC " target lines" were evaluated for possible removal or rerouting.
6.
Where possible cold water sources (CST) were avoided and piping was rerouted to decrease thermal stresses.
7.
Where possible, highly oxygenated water was avoided when low
[
oxygen-content water could be used.
l Specific Actions Completed:
1.. The core spray lines, LPCI piping, and RWCU piping have been changed from stainless steel type 304 to carbon steel.
l 2.
The core spray safe-ends and transition spools have been replaced l
with carbon steel components.
l' i
l
\\
. 3.
-The CRD return line has been eliminated; nozzle N-10 capped; CRD pressure equalization equipment installed; and carbon steel eliminated from CRD service lines.
4.
CR0 drive water is now taken from the condensate system for a low oxygen source (14-200 PPB) of water, instead of the condensate storage tank.
5.
The collet retainer tube has been redesigned with colmonoy hardfacing; the index tube and piston tube now contain XM-19 alloy.
(Stainless) 6.
The recirculation system bypass lines (10 inch) have been eliminated.
7.
The jet pump riser assemblies were solution heat treated after assembly as were the entrance elbows and pipe spools.
8.
The feedwater sparger has been redesigned with new spray nozzles which decrease thermal cycle stresses.
9.
A leak detection system has been designed, installed and tested to the criteria defined in Regulatory Guide 1.45.
10.
Stress ratios have been determined for all Class I and II stainless piping on Unit 1.
Forty-two welds in Class I piping were found to have'high ratios and usage factors.
These welds will have augmeted ISI appliedd to them.
On Unit 2 twelve welds in Class I piping were found to have high ratios and usage factors; these are included in the Unit 2-ISI program.
11.
Surveys have been completed on the recirc system welds of both units for evaluation of the feasibility nf performing IHSI.
12.
IHSI has been completed on Unit 2.
83 welds were treated.
Three welds in the 24" recirc piping could not be done due to pipe whip restraint interference with IHSI coils.
Four sweepolet to pipe welds also could not be done due to phisical configuration of the welds.
Seven welds in the RHR and RWCU Systems were also not done because of coil unavailability and interference with structural steel.
The above welds are being evaluated for treatment by last pass heat sink welding.
If no treatment of a weld is possible, an augmented ISI Program would be specified.
This additional work is expected to be completed not later than startup following the first refueling outage on Unit 2.
13.
Proposals are being obtained to perform IHSI or last pass heat sink welding on all welds inside containment for Unit 1.
This work is expected to be completed not later than startup following the first refueling outage on Unit 1.
7583N