ML17229A328
| ML17229A328 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 05/15/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17229A327 | List: |
| References | |
| NUDOCS 9705160184 | |
| Download: ML17229A328 (9) | |
Text
~S RK00 Cy A.
I 0O I
O Y.+~
~O
++*++
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RE VEST TO USE CODE CASE N-524 FOR FLORIDA POWER AND LIGHT COMPANY ST.
LUCIE PLANT UNIT 1 DOCKET'NO. 50-335 1.0, INTRODUCTION The Technical Specifications for St. Lucie Plant, Unit No. 1, state that the inservice inspection and testing 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 Code (ASME Code) and applicable Addenda as required by Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g),
except where specific written relief has been granted by the Commission (NRC), pursuant to 10 CFR 50.55a(g)(6)(i).
Section 50.55a(a)(3) states that alter'natives to the requirements of paragraph (g) may be used, when authorized by the Nuclear Regulatory Commission, 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 difficulty without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4),
ASHE Code Class 1, 2, and 3 components (including supports) shall meet the requirements that become effective subsequent to editions specified in 10 CFR 50.55a(g)(2) and (g)(3), except the design and access provisions and the preservice examination requirements, set forth in the ASHE 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 ASHE Code incorporated by reference in 10 CFR 50.55a(b) on the date 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
The 1983 Edition, with Summer 1983 Addenda, of Section XI is the applicable edition of the ASHE Code for St. Lucie Unit 1.
This is the Second 10-year Inservice Inspection (ISI)
Interval for St. Lucie Unit l.
Enclosure 9705i60i84 9705i5 PDR ADQCK 05000335 P
Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance
.with an examination requirement of Section XI of the ASHE 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 ASHE Code requirements.
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 and will not 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 if the requirements were imposed on the facility; In a letter dated March 5, 1997, the licensee, Florida Power and Light Company (FPL), proposed to implement Code Case N-524 dated August 9,
- 1993, "Alternative Examination Requirements for Longitudinal Welds in Class 1 and 2
Piping Section XI, Division 1," as an alternative to Code requirements for St.
Lucie, Unit l.
2.0 EVALUATION AND CONCLUSIONS 2.1 Licensee's Re uest This submittal is requesting approval pursuant to 10 CFR 50.55a(a)(3) for use of Code Case N-524, "Alternative Examination Requirements for Longitudinal Welds in Class 1 and 2 Piping Section XI, Division 1."
- 2. 1. 1 ASHE Code Requirements:
The 1983 Edition through Summer 1983 Addenda Table IWB-2500-1, Category B-J, Table IWC-2500-1,= Category C-F-1 and C-F-2, and Table IWC-2520, Category C-G, requires surface and volumetric examination of the longitudinal welds.
In
- addition, FPL has adopted Code Case N-408, Alternative Rules for Examination of Class 2 Piping,Section XI, Division 1, which was approved by ASHE on July 12,
- 1984, and endorsed by the NRC in Regulatory Guide (RG)
- 1. 147, for use during this inservice inspection interval.
Therefore, FPL uses the C-F-1 and C-F-2 requirements of Code Case N-408 'for determining which longitudinal welds to examine.
Code cases are periodically published by ASHE to,either clarify the intent of
'the Code rules or to provide alternatives to existing Code requirements.
Use of these nonmandatory Code.cases for inservice inspection is subject to general acceptance by the NRC staff and incorporation into RG 1. 147.
Pursuant to 10 CFR 50.55a, other Code cases may be used provided specific authorization is granted.
- 2. 1.2 Licensee's Basis for Requesting Relief (as stated):
The current requirement for Class 1 systems is to examine longitudinal welds for a distance of one pipe diameter but not more than 12 inches from the intersecting circumferential weld.
Often, additional scaffolding must be built and additional insulation removed to accomplish this examination.
Much of the reactor coolant system piping is carbon steel with cladding.
This
C
'U a
material requires increased weld cleaning and preparation time.
The additional preparation increases the overall radiation exposure
'and the potential.for personnel contaminations.
For Class 2 systems, the current requirement is to examine the longitudinal welds for a distance of two and one-half times the weld thickness from the intersecting circumferential weld.
Essentially the same prepar ation
'equirements and radiation concerns discussed above for Class I applications apply to Class 2 piping.
Longitudinal welds are not produced in the field or fabrication shops as is the case of a circumferential weld.
Longitudinal piping welds for Class I and 2 applications were made by the piping manufacturer under controlled conditions that produce higher quality welds and more uniform residual stress patterns.
These welds were examined by the appropriate American Society for Testing and Materials (ASTM) or ASME specifications.
The manufacturing controls specified by the appropriate ASTM or ASME specifications provide assurance of the structural integrity of the longitudinal welds at the time the piping is manufactured.
The preservice examination and initial inservice examinations have provided assurance of the structural integrity of the longitudinal welds during the service life of the plant to date.
Based on results of these inservice inspections, St. Lucie Unit I has not experienced degradation that would warrant conti'nued examination beyond the intersection area or volume bounded by this Code Case.
In addition, experiehce in the United States has been that ASME Code longitudinal welds have not experienced degradation that would warrant continued examination beyond the boundaries required to meet the circumferential weld examination requirements.
No significant loading conditions 'or known material degradation mechanisms have become evident to date which specifically relate to longitudinal seam welds in nuclear plant piping.
By using this Code Case, FPL will meet the intent of Section XI.
FPL will examine those areas of the longitudinal welds within the boundaries of the intersecting circumferential welds.
If the longitudinal weld cannot be seen, then FPL will perform the examination around the entire length of the circumferential weld according to the Code Case.
If any degradation associated with a longitudinal weld were to occur, it is expected that it would be found at the intersection with a circumferential weld.
This intersection will be inspected according to the provisions of Code Case N-524.
Since longitudinal welds will be examined within the boundaries of the intersecting circumferential welds, the total costs, examination time, and radiation exposure will be reduced. 'hen this Code Case is applied to the volumetric examination of ferritic welds, the volumetric examination of the circumferential welds will include scanning for reflectors transverse to the weld.
In addition to the above, there is significant accumulation of personnel radiation. exposure associated with the examination of longitudinal welds.
The radiation exposure associated with the examination of longitudinal welds is dependent on the time it would take to remove and reinstall the insulation and
interferences, prepare the weld for examination, and perform the examinations.
Based on the current examination scope for the upcoming Unit 1 refueling
- outage, exposure savings of approximately 1.5 to 2 man-REM could result from the approval to use Code Case N-524. Therefore,.the continued imposition -of the ASNE Code,Section XI examination requirements for longitudinal welds constitutes a hardship to St: Lucie Plant with no compensating increase in. the level of quality or safety.
- 2. 1.3 Licensee's Proposed Alternative Examination:
The licensee proposes to apply Code Case N-524 as alternative rules for the examination of longitudinal welds in Class 1 and 2 piping.
In addition to the elements of the Code Case, when this Code Case is applied to the volumetric examination of ferritic welds, FPL committed to include scanning for reflectors transverse to the weld.
- 2. 1.4 Evaluation:
The ASIDE Section XI Code (1989 Edition) requires one pipe diameter in length, but no more than 12 inches, be examined for Class 1 longitudinal piping welds.
Class 2 longitudinal piping welds are required to be examined for a length of 2.5t, where t is the thickness of the weld.
These lengths of weld are measured from the intersection of the circumferential weld and longitudinal weld.
The licensee's proposed alternati.ve, Code Case N-524, limits the volumetric and surface examination requirements of the longitudinal weld to the volume or area contained within the examination requirements of the intersecting circumferential weld.
Longitudinal welds are produced during the manufacturing process of the piping, not in the field as is the case for circumferential welds.
The Code contains requirements on characteristics and performance of materials and
- products, and specifies the examination requirements during the manufacturing of the subject longitudinal piping welds.
In addition, there are material,
- chemical, and tensile strength requirements in the Code.
The manufacturing process that is specified by the Code provides assurance of the structural integrity of the longitudinal welds at the time the piping is manufactured.
The preservice examination and initial inservice examinations have provided assurance of the structural integrity of the longitudinal welds during the service life of the plant to date.
The experience in the United States has been that ASHE Code longitudinal welds have not experienced degradation that would warrant continued examination beyond the boundaries required to meet the
'ircumferential weld examination requirements.,
No significant loading conditions or known material degradation mechanisms have become 'evident to date which specifically relate to longitudinal seam welds in nuclear plant
- piping.
~ V
'I
If any degradation associated with a longitudinal weld were to occur, it is expected that it would be located at the intersection with a circumferential weld.
Thi's intersection is inspected in accordance with the provisions of Code Case N-524.
- However, a possible error in use of this Code Case could occur if it were applied to ferritic welds where there is not normally a Code-required scan for reflectors located transverse to the circumferential welds.
The use of this Code Case is contingent on the volumetric examinations of the adjacent circumferential welds providing scanning for reflectors transverse to the weld.
The licensee, in its submittal, committed to provide scanning for reflectors transverse to the weld for ferritic welds.
Given the significant accumulation of man-rem associated with the examination of longitudinal welds, especially in Class 1 piping, and the adequacy of the proposed alter native assurance of weld integrity, to provide compliance with the Code would result in hardship without a compensating increase in the l,evel of quality and safety.
- 3. 0 CONCLUSION The staff concludes that the licensee's proposed alternative to use Code Case N-524 as an alternative to the Code requirements, with scanning for reflectors transverse to the weld for ferritic welds, is acceptable
- because, given the alternative
- proposed, compliance with the code would result in hardship or unusual difficulty without a compensating increase in level of quality and safety.
Therefore, the licensee's proposed alternative to use Code Case N-524 is authorized for St. Lucie, Unit 1 second 10-year interval pursuant to 10 CFR 50.55a(a)(3)(ii),
provided volumetric examinations of adjacent circumferential welds provide scanning for reflectors as previously stated.
The licensee is authorized to use Code Case N-524 until such time as the Code Case is included in a future revision of Regulatory Guide 1. 147.
At that time, the licensee is to follow all provisions in Code Case N-524, with limitations issued in Regulatory Guide 1.147, if any, if the licensee continues to implement this relief request.
Principal Contributor:
L. Wiens Date:
May i5, 1997
0 V
't P% r