ML17229A754
| ML17229A754 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 06/01/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17229A753 | List: |
| References | |
| NUDOCS 9806040131 | |
| Download: ML17229A754 (12) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055&0001 S
FETY V LUATI N BY TH OFFICE 0 UCLEA RE R RE LATI N F
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The Technical Specifications (TS) for St. Lucie Nuclear Plant, Unit 1, state that the inservice inspection of the American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel (B&PV) 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 alternatives to the requirements of paragraph (g) may be used, when authorized by the U.S. Nuclear Regulatory Commission (NRC), if(i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficultywithout 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 pre-service examination requirements, syt forth in the ASME Code,Section XI, "Rules for Inservice 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 inservice 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 edition of Section XI of the ASME Code for the St. Lucie Plant, Unit 1, second 10-year inservice inspection (ISI) interval is the 1983 Edition through Summer 1983 Addenda.
Pursuant to 10 CFR 50.55a(g)(5), ifthe licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, 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 alternative requirements that are determined to be authorized by law, willnot endanger life, property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result ifthe requirements were imposed.
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Pursuant to 10 CFR 50.55a(g)(6)(ii)(A), a licensee must perform an augmented volumetric examination of essentially 100% of each of the Item B1.10 shell welds of the Reactor Pressure Vessel (RPV). Essentially 100% is defined as greater than 90% of the examination volume of each weld. The licensee may submit an alternative pursuant to 10 CFR 50.55a(g)(6)(ii)(A)(5) for welds that have not been inspected essentially 100%.
In addition, all previously granted requests for relief under f50.55a, to licensees for the extent of volumetric examination reactor pressure vessel (RPV) shell welds specified in Item B1.10 of Examination Category B-A "Pressure Retaining Weldsin RPV," in Table IWB-2500-1 of subsection IWB in applicable edition and addenda of Section XI, Division 1, of the ASME Boiler and Pressure Vessel Code, during the inservice inspection interval in effect on September 8, 1992 are revoked, subject to the specific modification in f50.55a(g)(6)(ii)(A)(3)(iv)for licensees that defer the augmented examination in accordance with f50.55a(g)(6)(ii)(A)(3).
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I By letter dated April27, 1995, Florida Power and Light company (licensee) submitted an alternative to 10 CFR 50.55a(g)(6)(ii)(A) Augmented RPV Examination for St. Lucie Nuclear Plant, Unit 1. In addition, the licensee provided additional information in its letter dated October 13, 1995.
As the basis for the licensee's request, it presented the results of the last (1983) RPV examination for St. Lucie, Unit 1. The weld examination coverage obtained on two of three circumferential RPV shell welds and two of nine longitudinal RPV shell welds did not meet the augmented examination requirements for "essentially 100%" coverage.
By Safety Evaluation (SE) dated October 13, 1995, the NRC authorized licensee's proposed alternative to the augmented RPV examination required by 10 CFR 50.55a(g)(6)(ii)(A). The SE concluded that the licensee should notify the NRC of the actual examination coverage obtained and that the licensee should obtain the same or greater coverage in 1996 as obtairied in the 1983 examinations.
By letter dated October 10, 1996, the licensee submitted a summary of the RPV examination and its results of its 1996 examination.
The staff has z Ialuated the subject su'. +ittal in tl ~
following section.
The NRC staff, with technical assistance from its contractor, the Idaho National Engineering and Environmental Laboratory (INEEL), has evaluated the information provided by the licensee in support of its alternative to 10 CFR 50.55a(g)(6)(ii)(A) Augmented Reactor Vessel Examination for St. Lucie Nuclear Plant, Unit 1. Based on th'e results of the review, the staff adopts the
.contractor's conclusions and recommendations presented in the Technical Letter Report (TLR) attached.
The licensee performed the alternative to the augmented RPV examination and has submitted the actual examination coverage obtained for NRC review, as required by the October 13, 1995 SE. The information provided by the licensee has been evaluated and the bases for disposition are documented below.
In addition, Table 1, in the TLR compares the 1996 coverage achieved in the previous examination.
Recent advances in ultrasonic examination techniques have raised questions regarding the effectiveness of the full-vee 45'hear wave examination to which the licensee earlier committed. The examination technique used at St. Lucie, Unit 1, for the 1996 alternative augmented RPV examination featured 45'nd 55'duplex" transducers.
This technique's flaw detection capability is superior to that of the full-vee 45'echnique because of its increased signal-to-noise ratios and higher examination sensitivity. The effectiveness of the ultrasonic examination techniques used at St. Lucie, Unit 1 were demonstrated in accordance with the rules of Appendix Villas implemented by the Performance Demonstration Initiative (PDI).
Although the calculated examination coverages are less in 1996 than in 1983 for three of the four welds that did not obtain "essentially 100%" coverage, the quality of the examination performed exceeds that of previous examinations.
The reduction in percent coverage is relatively insignificant for two of the three welds in question (from 86.8% to 80.5% for Weld 10-203 and from 91.6% to 91% for Weld 1-203A). For Weld 1-203B, 'the percent coverage dropped from 78.8% to 54%. The licensee attributes these reductions in coverage to differences in the calculation method, specifically, elimination of the perceived "extended reach" of the full-vee 45'xamination technique.
Further, the coverage obtained on other RPV shell welds actually increas'ed (see Table 1 in TLR).
4.0 STA ONCLU ION The licensee has performed the examinations to the maximum extent practical.
Based on the examination coverages obtained, the number of RPV welds receiving 100% volumetric examination, and the PDI-Qualified volumetric examination techniques being used, the staff concluded that the original conclusion reached in the NRC SE dated October 13, 1995 remains valid and that the licensee's proposed alternative provides an acceptable level of quality and safety. Therefore, the licensee's proposed alternative augmented RPV examination is authorized pursuant to 10 CFR 50.55a(a)(3)(i) and 10 CFR 50.55a(g)(6)(ii)(A)(5).
Principal Contributor: Tom i~/IcLellan, ECGB
Attachment:
INEEL TLR Date:
dune 1,
1998
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BE '3 By letter dated April27, 1995, Florida Power and Light Company (FPL) requested approval of alternative examination requirements for the augmented reactor pressure
.. vessel (RPV) weld inspection required by 10 CFR 50.55a(g)(6)(ii)(A): As the basis for their request, FPL presented the results of the last (1983) RPV examination for St. Lucie, Unit 1. The weld examination coverage obtained on two of three circumferential.RPV shell welds and two of nine longitudinal RPV shell welds did not meet the augmented examination requirements for "essentially 100%" coverage.
By Safety Evaluation Report (SER) dated October 13,1995, the Nuclear Regulatory Commission (NRC) authorized FPL's proposed alternative to the augmented RPV examination required by 10 CFR 50.55a(g)(6)(ii)(A). The SER concluded that the licensee should notify the NRC of the actual examination coverage obtained and that the licensee should obtain the same or greater coverage in 1996 as obtained in the 1983 examinations.
By letter dated October 10, 1996, FPL submitted a summary of the RPV examination and its results.
The Idaho National Engineering and Environmental Laboratory (INEEL) staff has evaluated the subject submittal in the following section.
2.0 The licensee performed the alternative to the augmented RPV examination and has submitted the actual examination coverage obtained for NRC review, as required by the October 13;.1995 SER. The information provided by the licensee has been evaluated and the bases for disposition are documented below.
(as stated):
Periodic system pressure tests per Category B-P, Table IWB-2500-1 have been performed.
"2.
Essentially 100% mechanized (automated) ultrasonic examinations have been conducted to the extent practical on all reactor pressure vessel welds from the inside surface.
"3.
A 50/70 bi-modal ultrasonic examination was conducted of the inner 25% vessel wall and the cladding-base metal inten'ace.
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"4.
Full-vee 45 degree shear wave examination was not performed because it was determined to be an inferior examination technique.
This technique has been shown to be effective only for large flaws. The newly devised techniques described below proved to be much more effective in terms of examination quality for the detection and sizing of smaller fiaws.
"5.
Special qualified single-side access examination techniques were selected to enhance coverage and quality over the 1983 methodology."
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i 'ni (as stated):
"Examination techniques designed to meet the requirements of ASME Section XI, Appendix Villwere used during the 1996 examination.
The vessel shell weld examination technique featured 45 and 55 degree 'duplex'ransducers which exhibit superior flaw detection capability. 'Duplex'ransducers demonstrated significant improvement of signal-to-noise ratios over previous designs which allow flaw discrimination at higher examination sensitivity.
"The inner 25% of the vessel wall was examined using 50/70 degree bi-modal transducers designed to enhance the ability to detect 'under-clad'laws.
These techniques represent state-of-the-art examination technology with the ability to provide increased weld coverage to effectively detect flaws from a single direction.
"Both techniques were qualified, for single side and two sided access, by demonstration in accordance with the rules of Appendix Villas implemented by the Performance Demonstration Initiative (PDI). The demonstration met the rules of ASME Section XI, IWA-2240 and was witnessed by representatives of both authorized nuclear In-Service-lnspection agencies.
"Flaw discrimination metho'ds,.independent of amplitude; eliminated the time consuming need for maintaining extremely tight signal amplitude controls on calibration and sc'arming gain settings.
This, together with the digital electronic calibration parameter storage capabilities of the advanced ultrasonic imaging system, provided a more efficient, yet qualified, examination process."
I'as stated):
Table 1'ompares the 1996 coverage with the coverage achieved in the previous examination.
Although limitations were overcome or reduced in several cases, three welds (10-203, 1-203A and 1-203B) actually show an apparent reduction in coverage.
This is a result of differences in the calculation methods.
In 1983, FPL included the perceived 'extended reach'f the full-vee path 45 degree ultrasonic beam.
Current Table 1 is paraphrased from the licensee's submittal.
ATTACHMENT
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'hinking dismisses the effectiveness of broadly divergent ultrasonic beams at such long beam paths.
The 1996 calculations represent more realistic values.
"The limitations noted in Table 1 are fixed geometric obstructions caused by permanent welded attachments on the interior of the vessel.
The outside of the vessel is inaccessible, as previously reported.
Further reduction of the limitations noted was not practical.
"Allindications detected during this examination were acceptable in accordance with ASME Section XIwithout analytical evaluation.
In addition, no new indications were found."
WELD NO.
TABLE 1
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t WELD DESCRIPTION "1983
""':. 1996
'PERCENT PERCENT 10-203 9-203 8-203 3-203A 3-203 B 3-203 C 2-203A 2-203 B
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2-203 C 1-203A 1-203 B Lower Shell-to-Lower Head Circumferential Intermediate Shell-to-Lower Shell Upper Shell-to-Intermediate Shell Lower Shell Longitudinal at 135 degrees Lower Shell Longitudinal at 255 degrees Lower Shell Longitudinal at 15 degrees Intermediate Shell Longitudinal at 15'ntermediate Shell Longitudinal at 135'ntermediate Shell Longitudinal at 255'pper Shell Longitudinal at 255 degrees Upper Shell Longitudinal at 15 degrees r
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i 86.8%
83 5%
100%
95%
94 2'5%
91.6%
91 6%
90 2%
91.6%
78.8%
80 5%
83.5%
100%'00%
100%
100%
1PP%
100%
1P0%
91 0%
54.p 3, ~ EvVI Recent advances in ultrasonic examination techniques have raised questions regarding the effectiveness of the full-vee 45'hear wave examination to which she licensee earlier ATTACHMENT
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P committed. The examination technique used at St. Lucie, Unit 1, for the 1996 alternative augmented RPV examination featured 45'nd 55'duplex" transducers.
This technique's flaw detection capability is superior to that of the full-vee 45'echnique because of its increased signal-to-noise ratios and higher examination sensitivity. The effectiveness of the ultrasonic examination techniques used at St. Lucie, Unit 1 were demonstrated in accordance with the rules of Appendix Villas implemented by the Performance Demonstration Initiative (PDI).
Although the calculated examination coverages are less in 1996 than in 1983 for three of the four welds that did not obtain "essentially 100%" coverage, the quality of the examination performed exceeds that of previous examinations.
The reduction in percent coverage is relatively insignificant for two of the three welds in question (from 86.8% to 80.5% for Weld 10-203 and from 91.6% to 91% for Weld 1-203A). For Weld 1-203B, the percent coverage dropped from 78.8% to 54%. The licensee attributes these reductions in coverage to differences in the calculation method, specifically, elimination ofthe perceived "extended reach" of the full-vee 45'xamination technique.
Further, the coverage obtained on other RPV shell welds actually increased (see Table 1).
4.0 I
The licensee has performed the examinations to the maximum extent practical.
Based on the examination coverages obtained, the number of RPV welds receiving 100% volumetric
, examination, and the PDI-Qualified volumetric examination techniques being used, it is determined that the original conclusion reached in the SER dated October 13, 1995 remains valid. Therefore, it is recommended that the licensee's alternative augmented RPV examination remain authorized in accordance with 10 CFR 50.55a(g)(6)(ii)(A)(5).
ATTACHMENT
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