ML20034F483
| ML20034F483 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 02/23/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20034F484 | List: |
| References | |
| TAC-M84099, NUDOCS 9303030290 | |
| Download: ML20034F483 (1) | |
Text
t Since the straight tubesheet and ECS sleeves are welded at both ends to the tube being sleeved, this process should provide a leak-tight repair.
Thc hard-rolled expansion zone sleeve uses a special technique to improve the 3
sealing of t h sleeve to the parent tube and is designed to be a leak-tight sleeve.
Since the NRC has not required that sleeve repairs be leak-tight t
(only leak-limiting), the staff did not qualify the adequacy of the sleeve for 1
leak-tightness; it has only satisfied itself that the sleeve meets the requirements for a leak-limiting sleeve equivalent to other types of sleeves that do not have a metallurgically bonded (fusion welded) joint. According to l
the licensee, the hard-rolled sleeve joint process is essentially the same as is used for the CEN5 mechanical SG tube plug and is based on experience with over 7000 plugs, used in over 24 units. This favorable service experience, in addition to corrosion tests, is cited to qualify the rolled joint as not being susceptible to prieary or secondary side stress corrosion cracking. A post-weld stress relieving heat treatment has been developed that has been shown to increase the resistance of the welded joint to stress corrosion cracking.
The licensee has stated that the welded joints in all sleeves will be given a st r ess relief heat treatment after welding.
k u olly, the sleeving process consists of cleaning the tube to be sleeved at the areas of the welds, insertion of the sleeve, expansion in the seal area.
at t at hing by welding or hard rolling, and inspection.
The installation of tbo tre slee.es. vill be performed in a manner consistent with the applicable l
standards, will preserve the existing design bases, and will not adversely l
m att any plant systems The design, instaliation, and inspection of the l
h. ves will be done in accordance with ASME Boiler and Pressure Vessel Code c rit eria.
By adherenc e to industry standards, the pressure boundary integrity
-:11 be preserved.
N ec type, of nondestructive examinations are use during the sleeving 3
process.
They are as follows: ultrasonic te' ting (Ul), eddy current test ing l
j (IfT). and visual examination. Ultrasonic testing is used to confirm that l
}
there is full fusion of the sleeve to the tube.
The licensee has stated that lack of fusion areas can tie re!1obly detetted.
The multi-frequency eddy 3
a i
(urrent method will be used to perform a baseline inspection of the installed
, lee es of all three designs for future reference.
i 1
An eddy current test technique has been qualified for the inspection of j
installed sleeves to detect flaws in the pressure boundary.
The pressure tmundary is considered to be the sleeve up to and including both joints and the SG tube above and below the joint.
These techniques are capable of 4
I detecting the ASM[ calibration standard anywhere in the sleeve or tube including the weld region.
Laboratory tests have demonstrated the detection 4
i of actual corrosion defects in the parent tube.
These inspection capabilities 1
are documented in Combustion Engineering Report CEN-f>01-P.
]
lhe liter'see's calculation of the minimum acceptable wall thickness of the sleeve in accordance with Regulatory Guide 1.121, to establish the basis for removing the tube from service, was not based upon ASME Code minimum allowable materials properties.
The staff performed its own calculation of the plugging 1imit based on ASME Code material minimum allowable properties (Code Case N-20), the use of which is consistent with the basis that the sleeves have the same margins as the original tubes.
The staff has found that the licensee's proposed plugging limit of 34% is acceptable.
Visual examinations can be performed on the upper welds to support UT results and are performed on the lower welds to determine their integrity and acceptance.
The welds are examined using a camera system or a borescope 9303030290 930223 PDR ADOCK 05000368 P
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