ML20077C563
| ML20077C563 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 05/14/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20077C564 | List: |
| References | |
| NUDOCS 9105220130 | |
| Download: ML20077C563 (3) | |
Text
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NUCLEAR REGULATORY COMMISSION
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's SAFETY EVALUATION B) THE OFFICE OF NUCLEAR REACTOR REGULATION RiQUEST FOR RELIEF FROM ASME CODE CODE CLASS 3 pipif4G REPAIR REQUIREMENTS NORTHERN STATES p0WER COMPANY PRAIRIE ISLAND NUCLEAR STATION, UNITS 1 and 2 DOCKET NOS. 50-282 AND 50-306 1.
BACKGROUND Temporary Non-Code Repairs The Code of Federal Regulations 50.55a(g) requires nuclear power f acility piping and components to meet the applicable requirements of Section XI of the A!ME Boiler and Pressure Vessel Code (hereefter called the Code).
Section XI of the Code specifies code-acceptable repair methods for flows that exceed code dCceptance limits in piping that is in service. A code repair is required to restore the structural integrity of flawed code piping, independent of the operational mode of the plant when the flaw is detected.
Those repairs not in compliance with Section XI of the Code are non-code repairs. However, the required code repair may be impractical for a flaw detected during plant operation unless the facility is shut down.
Pursuantto10CFR50.55a(g)(6)(i),
the Commission will evaluate determinat ns of impracticality and may grant relief and may impose alternetive reqb., ntnis. Gtmeric Letter 90-05, entitled
" Guidance for Performing Temporary Hon-Code Repair of ASME Code Class 1, 2, and 3 Piping," dated June 15, 1990, provides guidance fcr the staff in evaluating relief requests submitted by licensees for temporery non-code repairs of Code Class 3 piping. The Commission may grant relief based on a staff evaluation considering the guidance in Generic Letter 90-05.
Licensee's Relief Request By letter dated February 27, 1991, Northern States Power Company (the licensee) requested relief from code repair requirements of certain Code Class 3 piping at Prairie Island Nuclear Generating Plant, Units 1 and 2.
A pinhole leak was detected in the Code Class 3 moderate energy Cooling Water System Loop A during plant operation and, subsequently, the licensee found indications of flaws below allowable minimum wall thickness in Cooling Water Loop B.
However, no leakage was identified in Loop B.
The licensee had determined that conformance with code repair requirements was impractical.
Pursuant to 10 CFR !0,55a(g)(5)(iii), the licensee submitted e relief request to the Commission. The subject piping is 24 inches in diameter, fabricated f rom ferritic steel ( ASTM A-106, Grade B). The licensee proposed not to apply d putch to the Loop A leaking pipe, and for Loops A and B the licensee will o105;;20130 910314 PDR ADOCK 05000282 P
2 monitor the leakage or the presence of leakages weekly, in accordance with Generic Letter 90-05, the integrity of the piping will be verified once per three months by nondestructive evaluation (NDE) and additional inspections will be performed.
EVALUATION OF RElf EF RE00EST Code Requirement Article IWA-4000 of Section XI of the Code specifies the Code repair procedures.
Code Relief Request Relief is requested from performing a code repair for the flaw detected during plant operation in Code Class 3 piping.
Basis for Relief Code repair requirements are impractical unless the f acility's Units 1 and 2 are shut down.
Proposed Alternative The licensee proposed to utilize the guidance in Generic Letter 90-05 to perform the.following:
LOOP A 1.
The structural integrity of the pipe has been verified by analysis.
No patch will be applied to the pipe. The leakage will be collected and routed to a nearby floor drain.
This allows continuous monitoring of tne leakage rate.
2.
A qualitative assessment of leakage will be performed weekly by a walkdown.
The integrity of the p(ipe will be verified once per three months by NDE (typically ultrasonic UT)), in accordance with Generic Letter 90-05.
This inspection was performed as scheduled on January 24, 1991. There was no detectable increase in any flaw size, 3.
Generic Letter 90-05 requires five additional inspections of areas that are both accessible and susceptible to microbiologically influenced corrosion (MIC). These inspections were completed. One additional area with indications below allowable minimum wall thickness was discovered.
LOOP B 1.
The structural integrity of the pipe has been verified by analysis. -No
-through wall leakage was identified.
2.
A qualitative assessment of leakage will be performed weekly by a walkdown. The integrity of the pipe will be verified once per three months by HDE (typically UT), in accordance with Generir Letter 90-05.
This inspection was performed as scheduled on January 24, 1991.
i i
3 3.
As described for Loop A, one of the five areas of the augmented inspection identified additional areas of MIC.
Five additional dreas (for a total of 10) were then inspected. None of these areas had indications below allowable minimum wall thickness.
Staff Evaluation and Conclusions The staff has determined that code repair requirements in this case are i
impractical, as defined in Generic Letter 90-05.
Compliance with the code j
repair requirernents would place a burden on the 11cusset because the applicable technical specification limiting condition for operation action statenient and the time necessary to complete the code repair will riecessiteit thut the facility is in a two-unit outage. Furthermore, the licensee has coornitted to the guidance provided in Generic Letter 90 05 which will reascnably assure structural integrity and protect public health and safety. Accordingly, the staff concludes that granting relief where code requirements are irnproctical und irc. posing alternatin s u,Litu.uin uic cuthoi tzed by low and will not enconge life or property or the contaon def st.su and steurity and are otherwise in the public interest, given due consideration to the burden upon the licensee end fccility that could result if the code requirements were irnposed on the facility.
Pursuantto10CFR50.55a(g)(6)(1)andconsistentwiththeguidance in Generic Letter 90-05, relief is granted until no 16tu than the scheduled 1992 two-unit refueling outage. During the outage as discussed above, the subject pipir,g must be code ripaired, t
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