ML20217K717
| ML20217K717 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 04/20/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20217K693 | List: |
| References | |
| NUDOCS 9805040080 | |
| Download: ML20217K717 (7) | |
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, wAsMinof oN, D.C. 30seHo01 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THE REllEF REQUEST TO THE FIRST TEN YEAR INSPECTION INTERVAL COMMONWEALTH EDISON COMPANY BYRON STATION. UNITS 1 AND 2 DOCKET NUMBERS: 50-454 AND 50-455
1.0 INTRODUCTION
j The Technical Specifications for Byron Station, Units 1 and 2, state that the in service inspection (ISI) of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) Class 1,2 and 3 components shall be performed in accordance with Section XI of the '
. ASME Code and applicable addenda as required by 10 CFR 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). 10 CFR 50.55a(a)(3) states that attematives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed altematives would provide an acceptable level of quality and safety,' or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1,2 and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, " Rules for in service inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that in service examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b)
, 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The applicable ASME Code,Section XI, for Byron Station, Units 1 and 2, first 10-year ISI interval, is the 1983 Edition through the summer 1983 addendum. The components 3 (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b) subject to the limitations and modifications listed therein and subject to Commission approval.
l Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an i examination requirement of Section XI of the ASME Code is not practical for its facility, l information shall be submitted to the Commission in support of that determination and a request !
made for relief from the ASME Code requirement. After evaluation of the determination, !
pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose attemative ;
requirements that are determined to be authorized by law, will not endanger life, property, or the 1
9905040080 990420 PDR ADOCK 05000454 G PM ,
I common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed.
By letter dated August 5,1997, Commonwealth Edison Company, the licensee for Byron Station, Units 1 and 2, submitted to the NRC its requests for relief from the examination requirement of the applicable ASME Code,Section XI, for the first ISI interval examinations. The NRC staff has reviewed and evaluated the licensee's Relief Request Nos. NR-22 through NR-24 for the first 10-year ISI interval of Byron Station, Units 1 and 2.
2.0 DISCUSSION (REQUEST FOR RELIEF NO. NR 22) i COMPONENT IDENTIFICATION
- 1 Code Class: ASME Code,Section XI, Class 2 i
Reference:
IWC-2500-1 Examination Category: C-C ltem Numbers: C3.20
Description:
Altemative Rules for the in service inspection of inaccessible Welds on Welded Penetration integral Attachments Component Number (s): See Table 1 of relief request NR-22 CODE REQUIREMENT:
ASME Code,Section XI (1983 Edition with S83 Addendum), Table IWC- 2500-1, Examination Category C-C, item C3.20 requires surface examination of the integrally welded attachments to '
piping (Figure IWC-2500-5).
LICENSEE'S REQUESTED RELIEF:
Relief is requested from performance of surface examination of inaccessible welds on welded penetration integral attachments.
BASIS FOR RELIEF: ( As stated) <
Pursuant to 10 CFR 50.55a(a)(3)(ii), relief is requested on the basis that compliance with the Code requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Some penetrations at Byron were originally designed where one of the integral .
attachment welds is inside the penetration assembly, thus making the welds inaccessible for in service inspection (see Figure 1) [of relief request NR-22). Access from outside of the closed end of the penetration assembly for examiners is prohibited by the integral attachment. Access from the open end of the penetration is severely restrained due to the penetration geometry. See Figures 1,2, and 3 [of relief request) for penetration details. The integral attachment weld is set back some distance inside the penetration assembly and the clearance between the pipe and penetration sleeve is small. See Table 1 [of the relief request) for these dimensions.
To satisfy the Code requirement to perform a surface examination of this weld, modification to the penetration assembly and/or piping to allow access would be required.
3-Byron would incur significant engineering and installation costs to perform such a modification without a compensating increase in the level of quality and safety to justify such modifications.
The limited access to these welds, as described in this request, was later acknowledged in the 1995 Edition of the ASME Code. Paragraph IWC-1223 exempts from examination welds or portions of welds that are located inside a penetration.
LICENSEE'S PROPOSED ALTERNATE PROVISIONS: (As stated)
When a weld is scheduled for inspection, a surface examination of the accessible weld on the exposed outside surface of the penetration will be performed. In conjunction with the surface examination, the periodic VT 2 examinations in accordance with the requirements of ASME Section XI, Table IWC-2500-1, Examination Category C-H will provide reasonable assurance of continued structuralintegrity of the piping systems.
2.1 EVALUATION
The relief request involves piping penetration assemblies classified as Code Class 2 piping that penetrate primary containment. The penetration assembly has a flued head with a Tee-joint at the process pipe connection which has one weld inside the flued head and the other outside.
The surface area of the weld inside the flued head identified in the Code Figure IWC-2500-5(a),
is inaccessible to perform the Code required surface examination. Therefore, the requirement of the Code is impractical. The licensee needs to redesign and modify the penetration assembly to gain access to the inside of the Tee-joint weld of the penetration assembly to perform the Code-required surface examination. The licensee, however, proposes to perform a VT-2 visual examination around the annulus of the penetration assembly during the system pressure test of the piping to ensure that there is no service induced through-wall flaw emanating from the inside weld surface of the Tee-joint that penetrates into the piping pressure boundary. Nevertholess, if a service induced flaw were to originate at the inside weld surface and penetrate into the surface of the outside weld of the Tee-joint, such a flawis detectable upon surface examination of the outside weld which is currently in the scope of examination. Hence, the licensee's proposed attemative to perform a VT-2 visual examination of the annulus of the penetration assembly along with a surface examination of the outside weld, provides reasonable assurance of operational readiness.
2.2 CONCLUSION
The staff concludes that compliance with the requirement of the applicable Code to perform the surface examination of the inside weld of the penetration assembly having a Tee-joint ,
configuration is impractical. The licensee's proposed attemative to perform a surface l examination of the outside weld of the Tee-joint in conjunction with a VT-2 visual examination of the inside surface of the penetration assembly provides reasonable assurance of operational readiness. Therefore, the Relief Request No. NR-22 is granted pursuant to 10 CFR 50.55a(g)(6)(i) for the first 10-year inspection interval. The relief granted is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest given due consideration to the burden upon the licem,ee that could result if the requirements were imposed on the facility.
4 3.0 DISCUSSION- (REQUEST FOR RELIEF NO. NR 23)
COMPONENT IDENTIFICATION Code Class: ASME Code,Section XI, Class I !
Reference:
IWB-2500-1 Examination Category: B-H ltem Number: B8.20
Description:
Altemate Rules for the in service inspection of the Pressurizer Seismic Lug Welds. ,
Component Numbers: 1RY 01-S, PSL-01, PSL-02, PSL-03, PSL-04 '
2RY-01-S, PSL-01, PSL-02, PSL-03, PSL-04 CODE REQUIREMENT:
ASME Code,Section XI (1983 Edition with S83 Addendum), Table IWB-2500-1, Category B-H, j ltem B8.20 requires surface examination of integrally welded attachments to the pressurizer, '
Figure IWB-2500-15.
LICENSEE'S REQUESTED RELIEF:
Relief is requested from performing a surface examination of the inaccessible portion of the pressurizer seismic lug welds.
BASIS FOR RELIEF:
Pursuant to 10 CFR 50.55a(s)(3)(ii), relief is requested on the basis that compliance with the Code requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Byron Station, Units 1 and 2, pressurizer seismic lugs are welded to the pressurizer shell. There are four seismic lugs per unit, located 90 degrees apart. In order to perform examinations on the seismic lug welds, the outside surface of the lower vessel shell to lug area must be accessible.
The entire examination surface is not accessible since it is covered by the seismic lug restraint and lower pressurizer shellinsulation. In addition, the pressurizer coffin limits access to the seismic lugs. The burden of removing the seismic lug restraint, altering the pressurizer coffin and removing the lower shell insulation to comply with the Code requirement on the extent of the surface examination of the seismic lug wolds, would result in hardship and unusual difficulty without a compensating increase in the level of quality and safety.
LICENSEE'S PROPOSED ALTERNATE PROVISIONS:
For the First inspection interval, a surface examination was performed on those areas of the lug welds accessible from the 428' elevation slab (approximately 21.5 percent). This exam along with the periodic VT-2 examinations in accordance with the requirements of ASME Section XI, Table IWB-2500-1, Examination Category B-P, and applicable reactor coolant systems monitoring requirements specified in the Technical Specifications will provide reasonable assurance of continued structural integrity of the Pressurizer shell and seismic lugs.
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5 3.1 EVALUATION The applicable ASME Code,Section XI, Category B-H, item B8.20 requires surface examination of essentially 100 percent of the subject attachment welds of seismic lugs that are used to connect the pressurizer seismic restraint. Due to partial inaccessibility of the lug welds in a confined space of the pressurizer coffin (enclosure) and the obstruction imposed by the seismic restraird itself, the licensee maximized surface examination coverage of the lug welds to 21.5 percent. The staff noted from the Byron Station Updated Final Safety Analysis Report that these seismic restraints are designed to resist rotational and translational movements by providing lateral support during a seismic event. However, during normal operation, the seismic lugs are under minimal load and, hence, the potential for flaw initiation and growth is minimum.
Nevertheless, the limited examination did not identify any unacceptable flaw nor existence of any degradation mechanism. The staff also reviewed the industry data and found no evidence of failure of integral attachment welds in Class 1 components which are systematically made under procedural controls. Thus, this is assurance of structuralintegrity. To enhance surface examination coverage, the pressurizer coffin needs to be modified and also, the seismic restraint needs to be redesigned. The staff has, therefore, determined that compliance with the Code requirement would cause hardship or unusual difficulty without a compensating increase in the level of quality and safety.
3.2 CONCLUSION
The seismic lug welds on the pressurizer are partially inaccessible due to the pressurizer enclosure and are also obstructed by the seismic restraints. The licensee maximized surface examination coverage to 21.5 percent in the existing configuration and did not find any unacceptable flew in the welds. Further, the loading on the lug welds during normal operation being minimal, any initiation and puh of a flaw is unlikely. The staff has concluded that in order to comply with the Code reqeirement on the extent of surface examination coverage, the required modification of the Pressurizer enclosure and redesign of the seismic restraints, would cause hardship or unusual difficulty to the licensee without a compensating increase in the level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(s)(3)(ii), the licensee's proposed altemative is authorized for Byron Station, Units 1 and 2, during the first inspection interval.
4.0 DISCUSSION (REQUEST FOR REllEF NO. NR-24)
COMPONENT IDENTIFICATION:
Code Class: ASME Code,Section XI, Class 2
Reference:
IWC-2500 Examination Category: C-F Item Numbers: C5.31 and C5.32
Description:
Altemate Examination of Branch Pipe Connections with Reinforcement Saddles Component Numbers: See Table 1, for Unit 1, and Table 2, for Unit 2, of Relief Request No. NR-24 CODE REQUIREMENT:
ASME Code,Section XI (1983 Edition with S83 Addendum), Table IWC-2500-1, Examination Category C-F, items C5.31 and C5.32 require surface examination of the pressure retaining pipe branch connection welds as shown in Figure IWC-2500-13.
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6-LICENSEE'S REQUESTED RELIEF:
Relief is requested from performing a surface examination of the branch pipe to the main pipe circumferential weld and the portion of the branch pipe longitudinal weld, inaccessible due to welded reinforcement saddle.
BASIS FOR RELIEF (As stated)
Pursuant to 10 CFR 50.55a(g)(5)(iii), relief is requested on the basis that the conformance with the Code requirements is impractical.
The design of certain branch pipe connection welds call for the use of reinforcement saddles. These saddles are fillet welded cver the pressure retaining branch pipe to main pipe connection and the initial portion of the intersecting branch longitudinal weld. When in place, the saddle plate completely encases these welds as illustrated in Figure 1. This design precludes any type of surface examination from being performed on the two concealed we,'ds and adjacent base material surfaces.
Assurance of the continued integrity of these joints is afforded by the fact that the reinforcement saddle strengthens the joint and reduces the stresses on the obstructed circumferential branch-to-pipe weld and branch longitudinal piping welds.
Additional assurance of continued integrity of these joints is provided by the surface examinations performed under the High Energy Augmented Inspection Program. These examina00ns are performed on all branch connection saddle plate wolds in the Main Steam System that are included in the break exclusion areas.
Based on the above, Byron Station requests relief from the ASME Section XI requirements for the surface examination of Class 2 branch pipe connection welds that are designed with a reinforcement saddle.
LICENSEE'S PROPOSED ALTERNATE PROVISIONS: (As stated)
When the pressure retaining welds are made inaccessible due to the usa of a reinforcement saddle, Byron Station will perform an altomative surface examination of:
a) the saddle-to-branch pipe weld and adjoining base material (identified as Alt-A on Main Steam piping and Alt-B on Safety injection piping), and l b) the saddle-to-main pipe and adjoining base material * (identified as Alt-B on Main Steam piping and Alt-A on Safety injection piping), and c) the required 2.5T area of the branch longitudinal weld and adjoining base material will begin at the intersection of the longitudinal and saddle-to-branch welds and extend for 2.5T of the branch pipe nominal thickness. ;
i Additionally, a VT-2 visual examination of the area will be performed in conjunction with the required Class 2 System Pressure Tests.
- Note: The saddle-to-main pipe weld is part of the surface examination requirement of IWC-500-1, Figure 13. The two welds (saddle-to-branch pipe and saddle-to-main pipe) were scheduled separately and given different suffixes.
I u.
7 4.1 EVALUATION The ASME Code on design of piping requires that the main piping be reinforced for certain branch connections to reduce localized stresses at the joint. Typically, a saddle plate is welded to reinforce the main piping, thus, masking the circumferential weld between the main piping and the branch piping and also the initial portion of the longitudinal weld in the branch piping. Hence, it is impractical to perform a surface examination of the subject welds and the adjacent base material, in accordance with the requirements of the applicable ASME Code,Section XI.
The licensee has, therefore, proposed an altemative to perform a surface examination of the saddle-to-main pipe weld and the saddle-to-branch pipe weld including adjoining base material due to inaccessibility of the main pipe to the branch pipe weld. If the Code requirements were imposed, the licensee has to redesign the branch connection and replace the existing components which would cause undue burden on the licensee.
However, the welds on the saddle plate will be surface examined during the augmented inspection of the high energy piping to evaluate structuralintegrity of the branch connection.
Additionally, a VI'-2 visual examination of the area during the system pressure test will further provide reasonable assurance of operational readiness.
4.2 CONCLUSION
The main pipe-to branch pipe circ'Jmferential weld and the initial portion of the branch pipe longitudinal weld are tendered inaccessible for the Code-required surface examination due to masking by the reinforcement saddle on the main pipe. The licensee, however, has proposed an altemative 10 perform a surface examination of saddle-to-branch pipe weld and saddle-to-main pipe weld including the adjoining base material to evaluate structural integrity of the joint and also conduct a VT-2 visual examination during the system pressure test of the area to ensure operational readiness of the subject welds. The staff concludes that the requirements of the Code are impractical and the attemative examination provides assurance of operational readiness. Therefore, relief is granted pursuant to the provisions of 10 CFR 50.55a(g)(6)(i), for Byron, Units 1 and 2, during the first inspection interval.
The relief granted is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest given due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility, Principle Contributor: P. Patnaik i Date: April 20, 1998 l l
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