ML20128E766
| ML20128E766 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 01/26/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20128E740 | List: |
| References | |
| NUDOCS 9302110064 | |
| Download: ML20128E766 (5) | |
Text
y*3 KtGy
[" 3
'o,%
/
UNITED STATES NUCLE AR REGULATORY COMMISSION
'p WAsHINGT ON, D. C. 20555
\\...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0.142 TO FACILITY OPERATING LICENSE NO. NPF-6 ENTERGY OPERATIONS. INC..
ARKANSAS NUCLEAR ONE. UNIT NO. 2 DOCKET NO. 50-368 1.0 JNTRQQUCTION By [[letter::0CAN079208, Informs That,Per 10CFR50.71 & 10CFR50.59(a)(3),Amend 10 to Arkansas Nuclear One Units 1 & 2 & Rev 15 to QA Manual Operations Shipped Under Cover Ltr (1CAN079204, 2CAN079210 & 0CAN079210)|letter dated July 22, 1992]], as supplemented by letter dated September 11, 1992, Entergy Operations, Inc. (the licensee) submitted a request for changes to the Arkansas liuclear One, Unit No. 2 (ANO-2) Technical Specifications (TSs).
The requested changes would revise the surveillance requirements cf Technical Specification (TS) 4.4.5, " Steam Generators," to reference CEN-601-P, Revision 01-P (proprietary), "ANO-2 Steam Generator Tube Repair Using Leak Tight Sleeves," dated July 1992, to allow for the repair of defective steam generator (SG) tubes through the installation of SG tube repair sleeves of the type supplied by Combustion Engineering Nuclear Services (CENS).
The September 11, 1992, letter provided clarifying information that did not change the initial proposed no significant hazards consideration determination.
2.0 BACKGROUND
CENS will provide three types of sleeves for SG tube repair.
These are a straight tubesheet sleeve, an eggcrate support (ECS) sleeve, and an expansion transition zone (ETZ) sleeve. The straight tubesheet sleeve and the eggcrate support sleeve are welded to the SG parent tubes near each end of the sleeve.
The ETZ sleeve is hard-rolled into the tubesheet just below the expansion zone and welded to the parent tube above the tubesheet. After welding, the welded joints in all three types of sleeves are given a stress-relief heat treatment to improve their corrosion resistance.
The ETZ sleeve spans the expansion transition zone at the top of the tubesheet to above tho first eggerate, where it is welded to the parent tube. At the lower end there is a hard roll joint.
Analysis and testing were performed on the CENS sleeves and sleeve-to-tube joints to demonstrate that design criteria was satisfied under normal operating and postulated accident conditions. -The details of the sleeve qualifications are discussed in report CEN-601-P, "AN0-2 Steam Generator Tube
'9302110064 930126:
PDR-ADOOK 03000360 P
p, i,
Repair Using Leak Tight Sleeves," Revision 01-P, dated aly 1992 (proprietary).
3.0 DISCUSSION
+
For the CENS sleeving process, analytical verification was performed using design and operating transient parameters selected to envelope loads imposed during normal operating, upset, and accident conditions.
Fatigue and stress analysis of sleeved-tube assemblies were completed in accordance with the requirements of the ASME Boiler and Pressure Vessel Code,Section III. The results of the qualification testing, analyses, and plant operating experience were cited to demonstrate that the sleeving process is an acceptable means of maintaining SG tube integrity.
The sleeve assemblies can be inspected by current techniques in accordance with the recommendations of Regulatory Guide (RG) 1.83, " Inservice Inspection of Pressurized Water Reactor Steam Generator Tubes."
The function of the sleeves is to restore the integrity of the tube pressure boundary.
The sleeves have been shown not to be subject to-stress levels in excess of allowable-limits for normal and postulated accident loading conditions. The sleeves have been designed and analyzed in accordance with the applicable sections of the ASME Soiler and Pressure Vessel Code. To l
determine the basis for the sleeve plugging limits, the minimum wall. thickness of each of the sleeve designs was calculated in accordance with P.G 1.121,
" Bases for Plugging Degraded PWR Steam Generator Tubes."
The material of construction of the sleeves will be thermally treated (TT) nickel Alloy 690, which is widely accepted as an improvement over the Alloy 600 material used in the original SG tubing. Corrosion tests in primary and secondary side environments confirm improved corrosion resistance of TT Alloy 690 over that of Alloy 600. Alloy 690 is a Code approved material (ASME SB-163), covered by ASME Code Case N-20-3, and is acceptable to NRC _under RG 1.85, Rev. 28, April 1992, "Haterials Code Case Acceptability ASME Section III Division 1."
The NRC staff has approved use of TT Alloy 690 tubing in replacement SGs as well as previous sleeving applications.
i 4.0. EVALUATION The CEF-601-P report describes the CENS sleeve design and_ installation processes, the analytical methods, the laboratory testing programs, and the results that were used to verify the adequacy of their sleeving methodology for sleeving degraded or' defective SG tubes. The sleeve dimensions, materials, and joints were designed to the applicable ASME Boiler and Pressure -
Vessel Code. An extensive analysis and test program was undertaken to prove the adequacy of the sleeves. The program determined the effect of normal operating and postulated accident conditions on the sleeve-tube assembly, as well as the adequacy of the asseinbly to perform its intended function.
s m
l 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.
The hard-rolled expansion zone sleeve uses a special technique to improve the sealing of the sleeve to the parene tube and is designed to be a leak-tight sleeve.
Since the NRC has not required that sleeve repairs be leak-tight (only leak-limiting), the staff did not qualify the adequacy of the sleeve for 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 the licensee, the hard-rolled sleeve joint process is essentially the same as is used for the CENS 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 primary 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 stress-relief heat treatment after welding.
Basically, 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, attaching b
'lding or hard rolling, and inspection. The installation of the tube sleeve:
.11 be performed in a manner consistent with the applicable standards, will preserve the existing design bases, and will not advsrsely impact any plant systems.
The design, installation, and inspection of the sleeves will be done in accordance with ASME Boiler and Pressure Vessel Code criteria.
By adherence to industry standards, the pressure boundary integrity will be preserved.
Three types of nondestructive examinations are use during the. sleeving process.
They are as follows:
ultrasonic testing (UT), eddy current testing (ECT), and visual examination. Ultrasonic testing is used to confirm that there. is full fusion of the sleeve to the tube.
The licensee has stated that-a lack of fusion areas can be reliably detected. _The multi-frequency eddy current method-will be used to perform a baseline inspection of the installed-sleeves of all three designs for future reference.
An eddy current test technique has been qualiffed for the_ inspection of installed sleeves to detect flaws in the-pressure boundary..The pressure boundary 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-detecting the ASME calibration standard anywhere in the sleeve or tube including the weld region.
Laboratory tests have demonstrated the detection of actual corrosion defects _in.the parent tube.
These inspection capabilities are documented in Combustion Engineering Report-CEN-601-P.
The basis for the plugging limit of 32% 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
_ _ _. _. ~.
P examination system.
The lighting is supplied as an integral part of the visual examination system.
Each examination is recorded on videotape to provide a permanent record of each weld's condition.
The inspections are performed to ascertain the mechanical and structural condition of each weld.
Critical conditions which are checked include weld width and completeness and the absence of visibly noticeable indications such as cracks, pits, and burn-through.
The acceptability of the lower seal weld of the full-length tubesheet sleeve is based on the absence of any cracks or other visible imperfections that would be detrimental to the integrity of the weld as examined by a borescope or micro-camera system.
Acceptance of the expansion zone hard-rolled joint is based on the control and monitoring of the process parameters. The staff requested additional information on the details and quality control of the process and found it to be acceptable based on the response.
Because the sleeves introduce changes in geometry and wall thickness, they challenge the eddy current testing technique, and special techniques must be used.
The licensee has described a number of special techniques that have been demonstrated to give an adequate inspection of sleeved tubes.
The techniques are used to qualify the original installation, and the eddy current techniques can be applied to periodic inspections also.
The licensee has made a commitment, documented in the Bases section of the plant Technical Specifications, that the adequacy of systems used for periodic inservice inspections will be validated and that upgraded testing methods will be evaluated and appropriately implemented as better methods are developed and validated for commercial use.
5.0
SUMMARY
Based upon the results of the analytical and test program, the sleeve fulfills its intended function as a leak-limiting structural member and meets all the established design and operating criteria.
The staff finds that the proposed' sleeving repairs can be accomplished to produce a sleeved tube of acceptable metallurgical properties, strength and mechanical stability, leak-tightness and corrosion resistance. We also find that the pre-service integrity of the sleeved tubes can be assured by implementing the proposed sleeve installation examinations.
Based upon the review and evaluation of the information and data. presented in CEN-601-P, Revision 01-P, " Arkansas Nuclear One Unit 2 Steam Generator Tube Repair Using Leak Tight Sleeves," the staff finds that the request by the licensee for a proposed license amendment to modify the Technical l
Specifications to permit repair of SG tubes by installation of sleeves using the Combustion Engineering methodology, it acceptable.
l
6.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Arkansas State official was notified of the proposed issuance of the amendment.
The State official I
had no comments.
l
7.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in'10 CFR Part 20 and changes in surveillance requirements. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or ~ cumulative occupational radiation exposure.- The commission has previously issued a pro-posed finding that the amendment involves no significant_ hazards consideration, and there has been no public comment on such finding (57 FR-37567). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).. Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
8.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of,the public will not_ be endangered by operation in the-proposed manner, (2) such-activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or-to the health and safety of the public.
Principal Contributor:
H. Conrad Date:
1/26/93 4
1