ML20207B119
| ML20207B119 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 07/14/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19292F604 | List: |
| References | |
| NUDOCS 8607170432 | |
| Download: ML20207B119 (19) | |
Text
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NUCLEAR REGULATORY COMMISSION
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E k.....o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.78 TO FACILITY OPERATING LICENSE NO. DPR-61 CONNECTICUT YANKEE ATOMIC POWER COMPANY HADDAM NECK PLANT DOCKET NO. 50-213
- 1. 0 INTRODUCTION By Tubes.Fee Paid|letter dated December 6,1985]] as modified January 7,1986, the Connecticut Yankee Atomic Power Company (CYAPC0) submitted a request for changes to the Haddam Neck Plant technical specifications.
The amendment permits the repair of degraded steam generator tubes by installing metal sleeves in the degraded tubes rather than removing them from service by plugging them; changes the definition of tube degradation; adds additional reporting requirements dealing with tube sleeving and renumbers existing technical specification pages.
A Notice of Consideration gf Issuance of Amendment to License and Proposed.
No Significant Hazards Congideration Determination and Opportunity for Hearing related to the requested action was published in the Federal Register on January 29, 1986 (51 FR 3713). No comments or requests for hearing were received.
2.0 BACKGROUND
By letter dated January 1986, CYAPCO, the utility for Connecticut Yankee (Haddam Neck) plant, submitted a Westinghouse Report WCAP-11008, Rev. 1 (Proprietary) describing the methodology, design and testing for the I
, 1 proposed sleeving of Haddam Neck steam generator tubes. The Connecticut 8607170432ADOCK860714 0500021.,
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Yankee plant is a four-loop Westinghouse designed pressurized water reactor rated at 1825 megawatts thermal. The steam is supplied by four vertical U-tube (Westinghouse Model 27 series) steam generators. They contain heat transfer tubes with dimensions of 0.750 inch nominal outer diameter and 0.055 inch nominal wall thickness.
Sleeving is a technique in which a slightly smaller diameter tube (a sleeve) is inserted into a degraded steam generator tube. The sleeve bridges and isolates the degraded section of the original tube and is joined to sound sections of the original tube at each end. As installed l
in the steam generators at Connecticut Yankee, this repair process will
! allow numerous tubes to remain in service therefore maintaining the life of the steam generator.
3.0 EVALUATION i
i The main design features of the sleeve are illustrated in Figure 1. The i
upper end consists of a section which is M .-
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- The lower end of the sleevd, shown in Figure 2, consists of a section which
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The upper joint is located so as to provide a length of free sleeve above it. This length is added so that if the existing tube were to become severed just above the upper edge of the mechanical joint, the tube would be restrained by the sleeve, and subsequent leakage, would be limited.
Lateral and axial motion would be restricted, protecting adjacent tubes from impact by the severed tube.
3.1 Design Verification Test Program The mechanical testing was conducted to (a) verify the leak resistance of the upper and lower sleeve-to-tube joints, (b) verify the structural strength of the sleeve under normal and accident conditions, (c) verify the
,. fatigue strength of the sleeved tube under transient loads representing
.the remaining design life of the plant, and (d) establish the parameters required to achieve satisfactory installation and performance.
The acceptance criteria used to evaluate the sleeve performance are leak rates based on the plant technical specifications. Testing encompassed static and cyclic pressures, temperatures, and loads. The testing in-
- g cluded evaluation of joints fabricated using Inconel 600 sleeves, Inconel 690 sleeves, and Inconel 690 sleeves with Inconel 625 cladding, in Inconel 600 tubes. While the bulk of the original qualification data is centered on Inconel 600 sleeves, a series of verification tests were run using Inconel 690 sleeves to demonstrate the effectiveness of the joint formation process an'ddesign with either material. Inconel Alloy 690, which contains (, higher chromium content (30 percent) than Inconel Alloy 600, has been shown to have a higher resistance to inter-granular stress corrosion cracking (IGSCC) when thermally treated in the carbide precipitation region. The stress corrosion cracking performance of thermally treated Inconel Alloys 600 and 690 in both off-chemistry secondary side and primary side environments has been extensively inves-tigated. Results have continually demonstrated the additional stress corrosion cracking resistance of thermally-treated Inconel Alloys 600 and 690 compared to mill annealed Inconel Alloy 600 material. Direct compari-son of thermally treated Inconel Alloys 600 and 690 has further indicated additionil margin of stress corrosion cracking (SCC) resistance for
thermally treated Inconel Alloy 690. A summary of corrosion comparison data for thermally treated Inconel Alloys 600 and 690, based on test results reported by the licensee, is as follows:
Thermally treated Inconel 600 tubing exhibits enhanced SCC and IGA resistance in both secondary-side and primary-side environments when compared to the mill annealed condition.
Thermally treated Inconel 690 tubing exhibits additional SCC resistance compared to thermal treated Inconel 600 in caustic, acid sulfate, and primary water environments.
The alloy composition of Inconel 690 along with a thermal treatment provides additional resistance to caustic induced. IGA.
The addition of 10 percent Cu0 to a 10 percent de-aerated Na0H environment reduces the SCC resistance of both thermal treated Incanel 600 and Inconel 690. Lower concentrations of either Cu0 or NaOH had no effect, nor did additions of Fe 0 and SiO .
34 2 Inconel 690 always performed equal to or better than Inconel 600.
Inconel Alloy 690 is less susceptible to sensitization than Inconel Alloy 600.
Inconel Alloy 600 and 690 have comparable pitting resistance with a slightadvantageofuhingInconel690insometestenvironments.
3.1.1 Residual Stress Verification Tests A corrosion verification test program was conducted to demonstrate that the residual stresses induced in the parent tubing by the expansion process does not degrade the integrity of the tubing. The expansion processes for both the lower and upper joints involve a combination of m . M
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enemaeusmausmesulate Confirmation that the OD stresses on the parent tubing are very low tensile or compressive was obtained by X-ray dif f raction analysis of an Inconel 600 tube expanded 30 mils and by the parting / layer removal technique These results show an excellent correlation with the MgCl 2
tests and the results of the X-ray measurements. The OD surface of the tube was in compression in the axial direct.i_on at all locations along the I
expansion transitions and was compressive on the ID surface of the tube 4
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except for one measurement in the unexpanded tube near the transition that was tensile (about 5 ksi). The OD surface of the sleeve was also in com-pression in both the axial an'd circumferential directions except for one measurement that was in tension (about 5 ksi) in the axial direction in the The ID surface of the sleeve had areas where the stresses were as high as about 25 ksi in either the axial or circumferential direction. Residual stresses of this magnitude should not affect the service performance of the special thermally treated sleeve material.
3.1.2 Verification Test for the Lower and Upper Joints The specimens were tested for leak rates at room temperature, 3110 psi and at 600 F, 1600 psi. These tests establish the leak rate after the sleeve has been installed in the steam generator and prior to long term operation.
The specimens were also leak tested at 3110 psi, room temperature, and at 1600 psi, 600 F after simulated normal operation for 5 years. The heat-up and cooldown cycles were simulated by thermal cycling of the specimens 25 times (in some cases 125 times) and fatigue loading for 30,000 cycles.
, In addition, push out and pull' out tests were also conducted. The test results for the joints indicated that:
For the lower joint, initial leak rates, both at room temperature and at 600*F were l
Initial leak rates for the upper hybrid expansion joint (HEJ) at room temperature and 600 F at pressures between 1485 and 3110 psi wereW Thermal cycling between 120 F and 600 F, for both lower and upper joints, had no detectable adverse influence on joint leak rate. The leak rate after testing remained at
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l l Fatigue tests of lower and upper HEJ had no discernable adverse effect on l l
- 8mmmeummusummuutub The push-out and pull-out tests showed that all joints tested exhibited i
loads for initial slip, above the effective axial loads that were applied !
during the fatigue tests. l The leak rates observed during a simulated steam line break and LOCA tests were well below the acceptance criteria.
r 3.2 Structural Verification The licensee has performed a structural analysis of the sleeve and tube assembly to demonstrate compliance with the requirements of the ASME Boiler and Pressure Vessel Code,Section III, Subsection NB, 1980 Edition. The analyses include primary stress intensity evaluations, maximum range of g stress intensity evaluations, and fatigue evaluations for various mechan-ical and thermal conditions. The critical portions of the sleeve-tube assembly are two joints, the upper and lower hybrid expansion joints (HEJ),
and straight sections of the sleeve and tube between the two joints. Past U
analytical experience indicates that upper joint stresses are more limiting than lower joint stresses.\qhe finite element model developed contains both upper and lower jointh. A detailed stress evaluation of the
$ sleeve was performed for the upper joint only. The tolerances used in developing the models were such that the maximum sleeve outside diameter was evaluated in combination with the minimum sleeve wall thickness. This allowed maximum stress levels to be developed in the roll transition regions.
The sleeve material is Inconel 690 covered by the ASME Code Case N-20. The tube material is Inconel 600.
All material properties used in the analyses were as specified in the ASME Boiler and Pressure Vessel code,Section III, Appendix 1 and related Code Cases. 1
The criteria for primary stress intensity evaluation of the sleeve and tube are as follows:
ALLOWABLE STRESS LIMITS CONDITIONS FORMULA VALUE (KSI)
Sleeve Tube DESIGN P, < S, P,< 26.60 23.3 l PL+PB < 1.5 5, PL+Pb < 39.90 34.95
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a) If pressure does not exceed design pressure Pg < 5, P,< 26.60 23.3 Py+Pb # 1* b b m Py+Pb < 39.90 34.95 UPSET b) If pressure exceeds design pressure P,<1.1S, P,< 29.26 25.63 P +Pb < 1.65 S, 38.45 L PL+PL+Pb < 43.89 FAULTED P,< 2.4 S, P,< 56.00 55.92 PL+Pb < 3.6 S , Pg+Pb < 84.00 83.88 2 ,
TEST P, < 0. 9 5 **. P,< 36.00 31.5 Pg+Pb < 1.35 S P'y' .+ Pb < 54.00 47.29
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Structural analysis of the sleeve-tube assembly includes finite element model development, thermal, pressure stress and thermal stress calcula-tions, primary and primary plus secondary stress evaluation, and fatigue evaluation for various mechanical and thermal conditions which envelop the loading conditions specified by the appropriate Design and Equipment Specifications. Two computer programs, WECAN and WECEVAL, are used in structural analysis of the sleeved tubes.
The WECAN program performs thermal and stress analyses of the primary struc-ture. Thermal analysis provides the temperature distribution required for thermal stress calculations. Thermal stress calculations are performed for fixed times under thermal transients. These times for the total pressure and thermal analysis are chosen for the anticipated maximum and minimum total stresses in critical regions of the structure. Total stress distri-bution is determined by combining the pressure and thermal stress results.
Total stress calculations as well as stress evaluations are carried out by the WECEVAL computer program, a multi purpose code, which performs ASME Code,Section III, Subsection NB stress evaluations.
At any given point or section of the model, the program WECEVAL was used to determine the total stress distribution per the Subsection NB requirements.
This stress was categorized into membrane, linear bending, and non-linear components which were compared to the Subsection NB allowables. In addi-tion, complete transient histories at given locations on the model were used to calculate the totahcumulative fatigue usage factor per ASME Code Paragraph NB-3216.2. For 'the fatigue evaluation, the effect of local dis-continuities was considered.
The following is a summary of the results of the analysis:
All primary stress intensities for the sleeved tube assembly are well within all allowable ASME Code limits.
The largest value of the ratio " Calculated Stress Intensity / Allowable
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l The requirements of the ASME Code Paragraph NB-3222.2 were met at all locations for the maximum range of stress intensity values for the sleeved I assemblies. Based on the sleeve design criteria, the fatigue analysis considered a design life objective of 30 years for the sleeved tube I assemblies.
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l Because of possible opening of the interface between the sleeve and the tube along the hydraulic expansion regions, the maximum fatigue strength reduction factor of 5.0 (NB-3222.4(3)) was applied in the radial direction at the " root" interface nodes of the hard roll region.
All of the cumulative usage factors are below the allowable value of 1.0 1
specified in the ASME Code. I i
3.3 Effect of Flow Slot Hourglassing Along the tube-lane, the tube support plate has several long rectangular flow slots that have the potential to deform into an hourglass shape with significant denting. The effect of flow-slot hourglassing is to move the neighboring tubes laterally inward to the tube lane from their initial positions. The maximum bending would occur on the inner most row of tubes Based on the results of a chustic corrosion test program on mill-annealed tubing,thebendingstresskagnitudeduetoflow-slothourglassingis 1
judged to have only a small effect, if any, on the SCC resistance margins. ,
Two long term modular model boiler tests have been conducted to address the effect of bending stresses on SCC. No SCC or IGA was detected by destructive examination. It is to be noted that thermally treated Inconel 690 has additional SCC resistance compared to mill annealed Inconel 600 tubing.
In addition to the above two considerations, the effect of the hourglassing induced bending stresses on maximum range of stress intensity and fatigue usage factor of the sleeve was also consider,ed. Taking into account the
hourglassing induced bending stress along with the transient pressure I thermal stress, the largest value of maximum stress intensity would be .
1 47.37 ksi (allowable 79.80 ksi), the fatigue usage factor is considered to be negligible.
l 3.4 Tube Vibration Analysis Analytical assessments have been performed to predict nodal natural frequencies and related dynamic bending stresses attributed to flow-induced vibration for sleeved tubes. The purpose of the assessment was to evaluate the effect on the natural frequencies, amplitude of vibration, and bending stress due to installation of various lengths of sleeves. It was found that none of these parameters is adversely affected.
Since the level of stress is significantly below the endurance limit for the tube material and higher natural frequencies result from the use of a sleeve / tube versus an unsleeved-tube, the sleeving modification does not contribute to cyclic fatigue.
3.5 Allowable Sleeve Degradation I
Minimum required sleeve wall thickness, t , to sustain normal and accident
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condition loads were calculated in accordance with the guidelines of Regulatory Guide 1.121. In this evaluation, the surrounding tube was assumed to be completely de' graded; that is, no design credit was taken for the residual strength of tig tube. The limiting sleeve wall thickness which would satisfy the requirements of Regulatory Guide 1.121 was deter-mined to be of the nominal wall thickness. This sleeve wall thickness is required to meet the factor of safety of three during normal operation.
The maximum primary-to-secondary pressure differential occurs during a postulated feedline break (FLB) accident. Because of the sleeve location, the SSE bending stresses are small. Thus, the governing stresses for the minimum wall thickness requirements are the. pressure membrane stresses, P,.
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l These stresses are limited to the smaller of 0.7 uS and 2.4 S, that is 63.4 ksi. A minimum of @ of the nominal wall is required to sat-isfy the above mentioned criterion.
The leak-before-break evaluation for the sleeve is based on leak rate and burst pressure test data obtained on 7/8 inch OD x 0.050 inch wall and )
11/16 inch OD x 0.040 inch wall cracked tubing with various amounts of uni-form thinning simulated by machining on the tube 00. The margins to burst during a postulated Steamline Break Accident (SLB) condition are a function of the mean radius to thickness ratio, based on a maximum permissible leak rate of 0.105 gpm due to a normal operating pressure differential of 1375 psi.
Using a mean radius to thickness factor of 8.1 for the nominal sleeve, the current technical specifications allowable leak rate of 0.105 gpm, a SLB pressure differential of 2560 psi, and the nominal leak and nominal burst curves, a 105 percent margin exists between the burst crack length and the leak crack length. For a sleeve thinned 60 percent through wall over a 1.0 inch axial length, a 77 percent margin to burst is demonstrated. Thus, i the leak-before-break behavior is confirmed for unthinned and thinned conditions.
3.6 EddyCurrentInspectib*os j Conventional eddy current techniques have been modified to incorporate the most recent technology in the inspection of the sleeve / tube assembly. The resultant inspection of the sleeve / tube assembly involves the use of a cross wound coil for the straight regions of the sleeve / tube assembly and I for the transition regions. While there is a significant improvement in the inspection of portions of the assembly using the cross-wound coil over conventional bobbin coils, efforts continue to advance the state-of-the-art in eddy current inspection techniques. As (mproved techniques are developed
and verified, they will be utilized. For the present, the cross-wound coil probe represents an inspection technique that provides additional sensiti-vity and support for eddy current techniques as a viable means of assessing the tube / sleeve assembly.
In order to determine the plugging limit for tubes with degradation in the sleeves, allowances due to eddy current uncertainty and corrosion between inspection intervals should be considered with the structural limit of 3.7 Summary Based on a review of mechanical tests and analytical results obtained by the licensee, the staff concludes that (a) the upper' and lower sleeve-to-tube joints have an acceptable leak resistance, (b) the structural strength of the sleeve under normal and accident conditions and the fatigue strength under transient loads art adequate, (c) the parameters required to achieve satisfactory installation and performance of the sleeve have been established, (d) the residual stresses induced in the parent tubing by the expansion process does not degrade the integrity of the tubing and affect the service performance of the special thermally treated sleeve material, (e) all primary stress intensities for the sleeved tube assembly are well within all allowable ASME Code limits and all the cumulative usage factors are below the allowable value of 1.0 specified in the ASME Code, and (f) the limiting sleeve waii. thickness which would satisfy the requirements of Regulatory Guide 1.121 ks determined to be of the nominal sleeve wall thickness. Allowances.due to eddy current uncer-tainty and corrosion between inspection intervals will be considered with the structural limit of 3.8 ALARA Considerations By letters dated January 7, 1986 and March 6, 1986, CYAPC0 indicated the measures taken to account for ALARA considerations for each of the activities involved in the proposed steam ge,nerator tube sleeving program at the Haddam Neck Plant. ALARA activities specifically directed to reduction of occupational radiation doses include decontamination of steam generator channel heads, special shielding to reduce exposure of personnel during channel head and tubesheet operations, a control ventilatwn system for the channel heads and other surrounding work areas, special remote and semi-remote tools designed for high radiation areas, remote control of the sleeving process, TV and audio surveillances of all platform and channel head operations, and personnel training in full size mock-ups. CYAPC0 has verified that the training program will be in accordance with Regulatory Guides 8.27, 8.29 and 8.13 or equivalent.
CYAPC0 and its sleeving contractor, Westinghouse will make extensive use of classroom and mock-up training for individuals who will perform the sleeving operation.
Various measures will be utilized to limit occupational doses. Administra-tive control of personnel exposures will be affected by planning of maintenance procedures for +he job, in order to minimize the number of personnel used to perform ue various tasks. Temporary nozzle covers will be placed in the reactor coolant piping to prevent the dropping of foreign objects into the reactor coolant loops during sleeving. This is an o effective ALARA measure because it averts the potentially time consuming and dose producing process which results form extracting accidently dropped objects into the coolant loops. An internal head platform will be installed and covered by lead blankets to further reduce time in the l channel head and personnel exposures by having standby platform workers at stations behind biologi2hl, shields in low radiation areas.
5 The station locations will be determined by radiation surveys prior to sleeving. In addition to the visual surveillance provided from the standby stations, TV surveillance of personnel during the various sleeving tasks will be used to further identify areas and activities i involving high exposures and to rapidly indicate dose reduction actions.
CYAPC0 has described provisions for special local ventilation associated with the steam generator sleeving program. One of the steam generator manways is fitted with a blower. The air exhausted from the area of the steam generator bowl passes through two separate prefilters, two separate HEPA filters and a charcoal filter before the blower and then into the containment atmosphere. Air is drawn into the bowl through the other open manway. This arrangement serves to reduce airborne radioactivity within the steam generator work area.
The major source of the radiation dose rate inside the steam generator head is tenacious oxide film which includes deposited activated corrosion products. In order to remove this deposited activity from the inside of the channel head and thereby reducing dose rates in this region, CYAPC0 will decontaminate the steam generator channel heads prior to J the tube sleeving. CYAPCO will accomplish the decontamination by use of a tube honing process. The honing of tubes removes the oxide filu 5 from tube surfaces in preparation for installing sleeves. Experience gained during the Millstone Unit 2 tube sleeving program *has been used to estimate occupational doses for the Haddam Neck program. In particular, CYAPC0 considered information on mechanisms used in prior decontamination activities and has provided information relevant to projected occupational radiation exposures based on radiation survey measurements for Haddam Neck.
By letter dated March 6,1986, CYAPCO provided estimates of occupational
. qf exposures for those workers involved in the following sleeving tasks:
Task Exposure (Man-Rem)
Han-Way Removal and Reinstallation 11 NozzleCoverInstallationindRemoval 50 Chemical Decontamination g' 65 Eddy Current Testing 103 l Sleeving 650 Tubes 369 i
Plugging 61 Tubes 31 Pulling 2 Tubes 40 Other Activities 3.5 Total 672.5 l
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Based on our review of the Haddam Neck submittal, we conclude that the projected activities and estimated person-rem doses for the steam generator tube sleeving program are rea'sonable, and will include activities which properly account for ALARA considerations to reduce occupational doses.
We, therefore, conclude that CYAPC0 will be able to maintain individual occupational radiation exposures within the applicable limits of 10 CFR Part 20, and maintain doses consistent with the ALARA guidelines of Regulatory Guide 8.8. Therefore, the proposed radiation protection aspects of this steam generator sleeving program are acceptable.
4.0 ENVIRONMENTAL CONSIDERATION
This amendment involves a change to a requirement with respect to the installation or use of facility components located within the restricted area as defined in 10 CFR Part 20 and changes to the surveillance requirements. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the j
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 proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, this 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 issessment need be prepared in connection with the issuance of this amendk nt.
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5.0 CONCLUSION
The staff 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, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security,or to the health and safety of the public.
1 6. 0 ACKNOWLEDGEMENT L
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This Safety Evaluation has been prepared by J. Rajan, Engineering Branch ,
] and I. Spickier, Plant, Electrical & Instrumentation Systems Branch.
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j Dated: July 14,1986 4
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Figure 1 Installed Sleeve with Hybrid Expansion Upper Joint Configuration pop PROPRIETARY
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's Figure 2, Sleeve Lower Joint Configuration pop EROPRIETARY
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