ML20151E033
| ML20151E033 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 04/07/1988 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20151E030 | List: |
| References | |
| NUDOCS 8804150027 | |
| Download: ML20151E033 (5) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION
- l W ASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF FROM CERTAIN REOUIREMENTS OF SECTION XI 0F THE ASME CODE OMAPA PUBLIC POVER DISTRICT FORT CALHOUN STATION DOCKE1 NO. 50-285
1.0 INTRODUCTION
The Technical Specification for the Fort Calhoun Station requires that inservice examination of ASME Code Class 1, 2, and 3 corponents shall be perfomed in accordance with Section XI of the ASME Code as required by 10 CFR 50.55(g)(4) except where specific written relief has been granted by the Comissien.
Some plants were designed in confonnance to early editions of this Code Section, consequently certain requirements of later editions and addenda of Section XI are impractical to perforn because of the plant's design, component oeometry, and material of construction.
Paragraph 10 CFR 50.55e(g)(6)(i) authorizes the Comission to grant relief from those requirements upon making the r.ec+ssary findings.
In a letter deted June 10, 1986, the Omaha ?ublic Power District (OPPD),
the licensee, identified specific ASME Code requirements that OPPD deter-mined to be impractical to perform at the Fort Calhoun Station and requested relief from these requirements. The staff completed the evaluation in a letter dated November 10, 1986. The licensee submitted additional infcnta-tion related to this issue in a letter dated August 17, 1987. The objective of this Safety Evaluation is to review the supplemental infenration.
2.0 STAFF EVALUATION 2.1 Description and Function of the Piping System The licensee submitted inspectico isometiic drawings that identify the inaccessible welds. materials of construction, nominal diameter and nominal wall thickness or pipe schedule. The sub,iect welds are in the main steam and feedwater system outside of containment in Room 81 of the Fort Calhoun facility. A total of 35 welds (8 circumferential welds and 19 branch connection velds) in the main steam system and 8 circumferential welds in the feedwater system are inaccessible for inservice inspection.
2.2 ASME Code Requiremen_t Table IWC-2500-1, Examination Category C-F requires (1) a volumetric and surface examination of ASME Code Class 2 circumferential pressure s804150027 M be5 PDR ADOCK PDR P
retaining welds in piping greater than 1/2 inch nominal wall thickness and (2) a surface examination of pipe branch connections (1980 Edition including Addenda through Winter 1980).
Paragraph IWC-2430 requires additional examinations when flaw indica-tions are detected that exceed the acceptance standards of Article IWC-3000.
2.3 Licensee's Request The licensee requests Comission approval to exclude the inaccessible welds from the Inservice Inspection Program.
2.4 License 9's Pases for Relief 2.4.1 Protective Measures The protective erclosures in Room P.1 were designed to contain the steam or fluid from a large break to the extent that severe impingement of jets on safety-related equipment or structures cannot occur. The protective enclosures consist of a series of longitudinal flat steel bars placed around the outside of the pipe insulation and held in position by a series of independent loops of wire rope. At the main steam safety valves, the spacing of the wire rope is increased to clear the valve nozzles and their reinforcing plates. At these locations the longitudinal enclosure bars are thickened and reinforced with stiffener plate 5.
Tha wire rcpe size is increased cud the spacing imediately adjacent to the norrles is deereased to compensate for the increased spacing between wire rope loops in this area.
In order to maintain the configuration of the bars following pipe rupture, the individual bars are tightly fastened to the wire rope by reeans of wire rope clips. Each bar is fastened by clips at a spacing of approximately one foot. The protective enclosures around the feedwater lines are similar to those for the main steam line although the loads involved are far smaller.
The design criteria for the main steam and feedwater piping protective l
enclosures is in Attachment C to Appendix M of the updated Safety Analysis l
Report. These documents reflect the results of the "Fort Calhoun Unit 1 i
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Pipe Rupture Analysis of Feedwater and Main Steam Out-side of Centainment" l
by Nuclear Services Corporation (Campbell, California) done in 1973, and on file in the OPPD Nuclear QA/ Records Management System. Basically, the conclusion of this report is that the design of the protective enclosures is sufficient to assure the mitigation of a main steam line rupture or l
feedwater rupture in Room 81 so that all vital control capabilities will be maintained. Updated Safety Analysis Report Section 14.12. "Main Steam Line Break" assures us that the radiological consequences of a main steam line break, concurrent with steam generator tube rupture will not exceed the exposure limits of 10 CFR Part 100.
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3-2.4.2 Examination Requirements 2.4.2.1 Main Feedwater 16" Circumferential Pipe Welo.,
The subject pipe is constructed from schedule 80 carbon steel with a nominal wall thickness of 0.844 inches. During scheduled examinatiens a number of recordable surface indications were detected that resulted in an expansion of the exanination program to include 100% of the weld locations as required by paragraph IWC-2430. All accessible welds in the 16 inch feedwater system were examined in 1985. All of the weld locations with recordable surface indications were repaired per ASME and subsequently passed reexamination. The surface it fications that were found appeared to be confined to the surface scale of the pipe and did not degrade the pressure retaininc function. Two of the welds in the feedwater system, weld f7 on Figure B-7 and #11 on Figure B-8 were examined; however, these welds are located slightly inside of the bio-shield penetrations for the feedwater lines and only a linited examination of the welds were perfomed (approximately 40% of the total weld length). The interference caused by their physical location does not prevent a 1005 ene-sided ultrasonic examination. Because 100% of the weld volume can be covered with the UT examination, OPPD will, therefore, continue the surface examination to the extent possible, and do 100% of the required volumetric examination as scheduled in the nemal ISI Program. The other six welds are totally ccaered by the protective enclosures. The feedwater welds are monitored by the required IWA-5000 system leakage test.
2.4.2.2 Main Steam 28" Circumferential Pipe Welds The eight welds identified in the licensee's June 10, 1986 are inaccessible because of the cable wrapping. No examinations are scheduled for these locations throughout the 10-year interval; therefore, relief is not necessary. This grcuo of welds was included to infom the staff that these welds are not avai1able for inservice inspection.
2.4.2.3 Main Steam Branch Connections, 21 and 6" Lines Mineteen branch connections are covered by cable wrapping. Two of these locations were scheduled for examination in 1985. At least one more location is required to be examined during the 10-year interval. The licensee has detemined that these Code requirements are impractical to perform.
There are no locations of similar material, configuration, diameter, wall thickness and operating conditions at Fort Calhoun that are not covered by cable wrapping. The above system are pressure test every 40 months in accordance to paragraph IWC-5221 and a system hydrotest perfomed every 10-years in accordance with paragrah IWC-5222.
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. 3.0 EVALUATION AND CONCLUSION The staff completed the review of the licensee's letters dated June 10, 1986 and August 12, 1987 based on the provisions of 10 CFR 50.55a(g)(6)(1).
The staff detemined that the protective enclosures make inservice inspec-tien ir: practical to the extent required by ASME Section XI.
3.1 Main Feedwater 16" Circumferential Pipe Welds A partial examination can be perfomed on two (2) of the eight (8) welds subject to examination. The 1980 Edition including Addenda through Winter 1980 of ASME Section XI requires a volumetric and surface examination of piping greater than 1/2 inch thickness in order to detect a flaw in the lower 1/3 of the weld by volumetric examination techniques and the outside surface of the weld by surface examination techniques. Since welds #7 and ill are fabricated from carbon steel material, the staff agrees with the licensee that an ultrasonic examination of 100% of the weld volume and the limited surface examination perfomed during the 1985 outage should have detected any significant flaw, if there is one.
When the sarple is expanded to irclude 100% of the weld locations, as required by paragraph IWC-2430, some welds may be difficult or impossi-ble to examine. The staff evaluates the type of flaws detected versus the measures required to perform the examinaticns. The staff detemired that removsl of the protective enclosures to continue the examination cf additinnal welds based on the detection of surface scale is not warranted.
The 1;censee has examined all accessible welds and did not find u condition that resulted in degradation of the pressure retaining function cf the pipe.
The staff finds that relief may be granted as requested by the licensee to eliminate the examinations in the feedwater system walus as a result of this event.
The staff concludes that the design of protective enclosures to mitigate the effects of a pipe break and the system pressure tests provides an acceptable level of quality and safety.
3.2 Main Steam 28" Circumferential Pipe Welds Since no examinations are scheduled for these locations throughout the interval, relief is not necessary.
In the event that the identified welds are required to be examined based on IWC-7430, the staff will consider each event on a case-by-case besis.
3.3 Main Steam Branch Connections, 21 and 6" Lines Only a few of the nineteen inaccessible branch connection welds are actually subject to examination. ASME Section XI requires an examina-tion of a representative sample of welds in order to detect unantici-pated generic service-induced degradation in a piping system. The reculaticn and the ASME Code have provisions for the substitution of an alternative prcgran that is demonstrated to be equivalent or superior to the specified requirement. The staff considers an Inservice Inspection Program that raintains the size of the examination sample to be equivalent.
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. The staff concludes that relief being granted from the required inservice inspection of-the welds made inaccessible by the protective enclosures on the condition that:
the licensee selects for inservice inspection at least an equivalent number of accessible welds that are of similar naterials, configuration, nominal diameter, nominal wall thickness, and operating conditions. The licensee has the option of perforning an examinatien nf larger diameter branch cornections, with the corresponding or icwer pipe schedule, in the main stean systen to meet the condition described above.
In addition, the staff concludes, with the above condition, the relief being granted is authorized by law, vill not endanger life or property, or the conmor, defense ar.d security, and is otherwise in the public interest.
Dated:
April 7,1988 Principal Contributor:
M. Hum, EMTP i
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