ML20138E623
| ML20138E623 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 10/16/1985 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20138E597 | List: |
| References | |
| TAC-52631, TAC-55523, TAC-55762, NUDOCS 8510250066 | |
| Download: ML20138E623 (7) | |
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ENCLOSURE MISSISSIPPI POWER AND LIGHT COMPANY GRAND GULF NUCLEAR STATION, UNIT NO. 1 DOCKET NUMBER 50-416 Safety Evaluation Related to the Preservice Inspection Requirements of 10 CFR 50, Paragraph 50.55a(g)(3), Amendment Number 2.
- 1. INTRODUCTION This evaluation is in addition to the staff review reported in Appendix D in SSER 2 and 4. In letters dated September 20, 1984, May 11, 1984 and August 25, 1983, the licensee requested relief from other American Society of Mechanical Engineers (ASME) Code preservice examination requirements that he determined to be impractical and provided a supporting technical justification pursuant to 10 CFR 50.55a(a)(3).* The staff review of the information in these letters is discussed in the following paragraphs of this report.
- 2. TECHNICAL EVALUATION CONSI3ERATIONS (This information was published in NUREG-0831, Supplement 2, Appendix D)
A. The Grand Gulf Nuclear Station, Unit No.1, received a construction permit on September 4, 1974 The preservice inspection is based on conformance with the ASME Code,Section XI, 1977 Edition, including Addenda through summer 1978. The ASME first published rules for inservice inspection in 1971 Edition of Section XI. No preservice inspection requirements existed before that date. Since the Grand Gulf, Unit No. I plant system designs and ordering of long lead time components were well underway by the time the Section XI rules became effective, full compliance with the access and inspectability require-ments was not always practical.
B. Verification of as-built structural integrity of the pridiary pressure boundary is not dependent on ,the Section XI preservice examination.~ The construction codes to which the Grand Gulf, Unit No.1 primary pressure boundary was fabricated contaih material, design, fabrication, examina-tion, and testing requirements which by themselves provide th'e necessary assurance that the pressure boundary components are capable of performing safely under all operating conditions reviewed in the FSAR and described in the plant design specification. As a part of these examinations, the primary pressure boundary full penetration welds were examined volumetri-cally (radiographed) and the system was subjected to hydrostatic pressure tests.
rff he 1984 Edition of 10 CFR 50, this paragraph was designated 50.55a (a)(2) t l
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.1 C. The intent of a preservice examination is to establish a reference or
, baseline before the initial operation of the facility. The results of subsequent inservice examination can then be compared to the original l condition to-determine if changes have occurred. If review of the i . inservice inspection results show no change from the original condition, i no action-is required. In the case where baseline data are not available, all indications must be treated as new indications and evaluated accord-ingly.Section XI.of the ASME Code contains acceptance standards which are used as the basis.for evaluating the acceptability of such_ indications.
Therefore, conservative disposition of defects. found during inservice
! -inspection'can be accomplished even though preservice information is not i- available.
. D. Other benefits of preservice examination include providing redundant or alternative volumetric inspection of the primary pressure boundary
, :using'a test method different from that employed during the component fabrication. Successful performance of a preservice examination also i demonstrates that the welds so examined are capable'of subsequent in--
i service examination'using a similar test method.
In the case of Grand Gulf, Unit-No.1, a large portion of the ASME 1
Code' required preservice examinations are being performed. The staff has concluded that failure to perform a 100 percent preservice examina-
, tion of the welds identified below will'not significantly affect the assurance of the initial structural integrity.
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- E. In some instances where the' required preservice; examinations were not l performed to the full-extent specified by the applicable ASME Code, the 4,
staff will require,that these or supplemental examinations be: conducted as a part of the-inservice inspection' program.' The staff has concluded
, that requiring these supplemental examinations to be'perfonned at this-3 time' (before plant startup) would result in hardships or unusual diffi-
- ~ , culties without'a compensating increase in the level of' quality or safety. . The performance of supplemental examinations. .such as-surface j
4-examinations, in areas where.. volumetric inspection is difficult will be more meaningful after a period of operation.. - Acceptable preoperational integrity has'already been established by similar Section III fabrication examinations.
In cases where parts of the. required examination areas cannot be effec-
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'tively examined because of.a combination of components design or current 3 . examination technique limitations,'the' staff will' continue to evaluate L
Lthe development of new or. improved volumetric' examination techniques. As'
.c . improvements in these areas.are achieved, the staff will require.that" these new techniques be made a part of the inservice examination require-
, - ments of those components or welds which received a limited _ preservice
- examinaticn..
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! 3. EVALUATION OF RELIEF REQUESTS i The licensee' requested relief from the preservice inspection requirements of performing the volumetric examination of one pipe weld, the visual examination of. the internal surfaces of certain valves and the volumetric examination of i
! .the nozzle inside radius section of a, specific heat exchanger. Based"on the
, information submitted by the licensee in the referenced letters:and the staff's 1 review of the design,Lgeometry, and materials of construction of the components, l the'preservice requirements of the ASME Boiler and Pressure Vessel Code, 1
.Section XI, have been determined to.be impractical.
!. -The licensee has' demonstrated that either.(1) the proposed alternatives pro-
! vide an acceptable level of quality and safety or (ii) imposing these require-l ments would result in hardships or unusua1' difficulties without a compensating increase in the level of quality and safety. Therefore, pursuant to 10 CFR l50.55a(a)(3).. conclusions that these preservice requirements are impractical are justified as follows. Unless otherwise stated, references to the Code refer to the ASME Code,Section XI,1977 Edition, including addenda through Sumer 1978.;
[ - Relief Request No.15, Examination Category B-J, Pressure Retaining Welds l In Piping j' Code Requirement:
4 Examination Category B-J requires a volumetric and surface examination of essentially 100% of the weld of all piping welds 4 inches nominal pipe size and greater.-
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. Relief Request:
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' Relief is requested from perfonning the. entire volumetric prese;vice examination of one 6" elbow to valve weld located in the reactor core isolation cooling system.
Reason for Request
- A portion of weld number _ 502 cannot be examined because of a physical obstruction due to the design. - The volumetric examination of approximately 75% of the weld j- was completed. The following nondestructive examinations'have been performed:
.1.. The entire weld was examined-by radiography and passed in accordance with:ASME Section III, Class 1 requirements.
-2. The entire' weld was surface. examined (liquid penetrant) and passed in accordance with ASME Section'III and/or.Section XI, Class 1 requirements.
- . 3. The weld was subjected _to a hydrostatic test and VT-2 examination-in
[ accordance with ASME Section XI, Class 1 requirements and no leaks were
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4 Continuous monitoring of leakage is provided for RCIC system. The unlikely failure of this weld would have no adverse effect on plant safety because there is isola:'on capability as part of the plant design. As an alternative test, the licensee proposes to perform a volumetric examination of the accessible portion of weld number 502 twice during the ten year inservice inspection interval.
Staff Evaluation:
The staff has determined that the volumetric examination of the subject weld to the extent required by the Code is impractical because of the design of the piping system. The licensee has conducted the preservice surface examination
- on this weld.Section XI of the Code requires " essentially 100%" of the weld be examined and the licensee estimated that approximately 75% of the weld was examined. The staff concludes that compliance with this rode requirement would require redesign of the piping system and would result in hardship and unusual difficulties. The staff also concludes that the limited Section XI ultrasonic examination, the volumetric examination performed during fabrication, and the hydrostatic test demonstrate an acceptable level of preservice structural i integrity.
1 Accordingly, the finding required by 10 CFR 50.55a(a)(3)(ii) has been demon-strated. The staff has determined that the proposal by the licensee to increase the frequency of volumetric inservice examination of the accessible portion of the weld is acceptable and will provide additional assurance of the continuing structural integrity.
Relief Reouest No.12, Examination Category B-M-2, Valve Body Internal Surfaces Code Requirement:
Examination Category B-M-2, Item B12.40, requires the visual examination of the internal surfaces of valve bodies exceeding 4 inches nominal pipe size.
Relief Request:
Relief is requested inspection from surfaces of the internal disassembling and performing)the of sixty-nine preservice (69 valves identified in thevisual licensee's letter dated May 11, 1984.
Reason For Request:
The bases for the licensee's request are as follows:
- 1. The valve body and parts are designed, fabricated, inspected, and tested as required by the ASME Code,Section III. All valves have been volumet-rically and surface examined in accordance with the requirements of ASME Section III, Subsection NB, Paragraph NB-2570. In addition, the valve materials, exclusive of seals and packing, are designed for a 40-year plant life under the environmental conditions applicable to the particular system.
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, 2. ' Valves have been' fully cycled at the vendor's shop before delivery to substantiate the vendor's guarantee that.they will operate-under the-- '
C design service conditions.:
- 3. All valves have been subjected to shop hydrostatic tests, seal. leakage' j: tests, and performance tests, if applicable. . >
- 4. Valves arrive at the plant completely assembled and code stamped.1
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- 5. After the valves are insta11ed in the Nuclear System, each valve is tested in accordance with the preoperational and startup test procedures.
<-* 6. All of the -valves, with the exception.ot- the safety relief. valves
- 7 Q1821F041, -F047 and -F051, were tested in the system as part of the- 1 ASME Section III, Class I hydrostatic test.
- 7. 'The safety relief valves have-been preservice bench tested and adjusted
- required by ASME Section XI,. Article IWV-3510.
Should any valve be required to be disassembled for maintenance or repair, the.-
L licensee will consider performing the visual examination at that time either as i an alternative examination or as an additional examination.. The licensee will
- also consider other alternative examinations based on the operating and mainte-nance history of each valve.
- Staff Evaluation
The staff concludes that the disassembly of the subject valves solely to perform i
the' required Section XI preservice visual examination of the-internal surface is
, impractical . The staff has also determined that the nondestructive examinations, l
installation verification, ~preoperational tests and-functional verification per- 4 formed to date significantly exceed the reoutrements of the Section XI visual examination and, therefore, these examinations and test.-are an acceptable
- alternative to the Code inspection requirements and provide an acceptable level of' quality and' safety. '
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! Accordingly, the finding required by 10 CFR 50.55a(a)(3)(1) has been demonstrated.
In the event that any valve' is- required to be disassembled for maintenance or
- repair, the licensee.should perfonn the visual ~ examination of the accessible
- l. surfaces at that time.
l ! Relief-Request No.14. Examination Category C-B, Pressure Retaining Nozzle
! Welds In Vessels- ~
L Code Requirement:
Exarination Category C-B, Item C2.20 requires a volumetric and surface examina--
- tion of nozzles :in. vessels over 1/2 inch in nominal thickness at terminal ~ ends of piping runs.
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Relief Request:
Relief is requested from performing the volumetric examination of the inside radius section of the N3 and N4 nozzles on the Residual Heat Removal (RHR) heat exchanger #1E12 B001A.
Reason For Request:
Approximately 1,160 man hours would be required to remove and replace already-installed insulation to perform the required volumetric examination. The bases for the licensee's requests are as follows:
- 1. Nozzle welds (N3 & N4) have been volumetrically examined by radiography and ultrasonics and passed in accordance with ASME Section III, Class 2 requirements.
- 2. Nozzle Welds (N3 & N4) were subject to, and passed, a design Hydrostatic Pressure Test during fabrication, in accordance with ASME Section III,
. Class 2 requirements.
- 3. All modes of RHR that require the use of the RHR Heat Exchangers function as two (2) separate streams with two'(2) heat exchangers in series per stream. While there are no provisions for the isolation of any one (1) heat exchangeri either one 3f the two streams can be isolated. The RHR system design criteria allow for the isolation of either stream without
, adversely affecting plant safety or the ability of the system to perform ,
its intended function.
Staff Evaluation:
The staff co1cludes that an expenditure of 1,160 man hnurs to remove and replace already installed insulation to perform the required examination is impractical. The staff has determined that the radiography and ultrasonic examinations performed during construction of the nozzle welds and the system hydrostatic test demonstrate an acceptable level of preservice structural integrity. Therefore, imposing these requirements vould result in hardships or unusual difficulties without a compensating increase in the level of quality and safety. Accordingly, the finding required by 10 CFR 50.55a(a)(3)(ii) has been demonstrated.
In the event the maintenance or repair during service results in removal of the insulation, the licensee should perform the volumetric examin'ation-of the inner radius section at that time.
IV. CONCLUSIONS Based on the foregoing, pursuant to 10 CFR 50.55a(a)(3), the staff has deter-mined that certain Section XI required preservice examinations are impractical.
The Applicant has demonstrated either (i) the proposed alternatives would l .
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.-: ' e provide an acceptable level of quality and safety or (ii) compliance with the requirements would result in hardships or unusual difficulties without a compensating increase in the level of quality and safety. The staff tech-nical evaluation has-not identified any practical method by which the existing Grand Gulf Unit I can meet all the specific preservice int nection requirements of Section XI of the ASME Code. Requiring coupliance with all the exact Section XI required inspections would delay the commercial opera-tion of the plant in order to redesign a number of plant system, disassemble installed components, and perform the preservice examination of these com-ponents. Examples of components that would require disassembly to meet the specific preservice examination provisions are a significant number of valves and a heat exchanger. Even after the redesign or disassembly efforts, complete compliance with_the preservice examination requirements probably could not be achieved. However, the as-built. structural integrity of the existing primary pressure boundary has already been established by the-construction code fabrication examinations.
i Based on the staff review and evaluation, it is concluded that the public interest is not served by imposing certain provisions of Section XI of the ASME Code that have been determined to be impractical and pursuant to
, 10 CFR 50.55a(a)(3), relief is allowed from these requirements discussed in this safety evaluation.
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