ML20249A183

SER Accepting Request for Temporary Relief from ASME Code,Section XI Requirements,To Repair Flaws in Essential Cooling Water Sys Piping

ML20249A183
Person / Time
Site:	South Texas
Issue date:	06/11/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20249A177	List: ML20249A176 ML20249A183
References
NUDOCS 9806160150
Download: ML20249A183 (5)

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4444

[  % UNITED STATES g

,y NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30086 4 001

\ ..... SAFETY /- EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE INSPECTION PROGRAM REQUEST FOR RELIEF FROM ASME CODE REPAIR REQUIREMENTS FOR ASME CODE CLASS 3 PIPING j STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT. UNIT 2 DOCKET NO. 50-499

1.0 INTRODUCTION

l 10 CFR 50.55a(g) requires nuclear power facility piping and components to meet the applicable requirements of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and '

Pressure Vessel Code (hereafter referred to as the Code).Section XI of the Code spec;fies Code-acceptable repair methods for flaws that exceed Code acceptance limits in piping that it 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 implementation of required Code (weld) repairs to ASME Code Class 1,2, or 3 systems is often impractical for nuclear licensees since the repairs normally require an isolation of the system requiring the repair, and often a shutdown of the nuclear power plant.

Technical Specification (TS) 4.0.5 says, in part, that inservice inspection of ASME Code Class 1, 2, and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable Addenda as required by 10 CFR Part 50, Section 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR Part 50, Section 50.55a(g)(6)(i).

Attematives to Code requirements may be used by nuclear licensees when authorized by the Commission if the proposed attematives to the requirements are such that they are shown to provide an acceptable level of quality and safety in lieu of the Code requirements (10 CFR 50.55a(s)(3){i)), or if compliance with the Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety [10 CFR 50.55a(a)(3)(ii)).

A licensee may also submit requests for relief from certain Code requirements when a licensee has determined that conformance with certain Code requirements is impractical for its facility

[10 CFR 50.55a(g)(5)(iii)]. Pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant such relief and may impose such attemative requirements as it determines is authorized by law and >

will not endanger life or property or the common defense and security and is 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.

ENCLOSURE 9806160150 990611 PDR ADOCK 05000499 P PDR

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Generic L'etter (GL) 90-05, entitled " Guidance for Performing Temporary Non-Codo Repair of ASME Code Class 1,2 and 3 Piping," and dated June 15,1990, provides guidance for the staff in evaluating relief requests submitted by licensees for temporary non-Code repairs of Code Class 3 piping. For the purpose of this generic letter, impracticality is defined to exist if the flaw detected during plant operation is in a section of Class 3 piping that cannot be isolated for completing a Code repair within the time period permitted by the limiting condition for operation of the affected system as specified in the plant TSs, and performance of Code repair necessitates a j plant shutdown.  !

2.0 BACKGROUND

During plant operation, members of the STP Nuclear Operating Company (the licensee) i discovered corrosion deposits on a ten-inch by ten-inch by six-inch cast tee in the Essential l Cooling Water System (ECWS) in Unit 2. The ECWS is a low pressure system with normal  !'

-operating pressures of approximately 50 psig and the design pressure is 120 psig. The flaw was located in Unit 2 piping spool 10"-EW-2306-KK and the flawed pipe material was identified to be l cast aluminum-bronze (ASME SB 271 CA 952 material). The corrosion deposits were located at the bottom side of the tee joint and the deposits indicated that dealloying is taking place in the l aluminum-bronze cast fitting. By letter dated February 10,1997, as supplemented by letter dated i March 26,1998, the licensee requested relief from the ASME Code,Section XI repair or i replacement requirements under the provisions of 10 CFR 50.55a(g). The licensee based its i request for relief on the results of a flaw evaluation that was performed by the licensee in l

. accordance with the guidelines and acceptance criteria contained in GL 90-05. .

3.0 LICENSEE'S RELIEF REQUEST 3.1 Components for Which Relief is Reauested ASME Code Class 3 essential cooling water system piping (one terdinch by ten-inch by six-inch cast pipe tee).

3.2 gegygn,XI Edition for South Texas Proiecf. Unit 2 1983 Edition including' Summer 1993 Addenda of the ASME Code,Section XI.

3.3 ASME Section XI Code Requirement i

The ASME Code Section XI requires that repairs or replacements of ASME Code Class components be performed in accordance with rules found in Articles IWA-4000 or IWA-7000, respectively. The intent of these rules serve to provide an acceptable means of restoring the structural integrity of a degraded Code Class system back to the original design requirements.

I 3.4 Content of the Relief Reouest Relief is sought from m: forming a repair or replacement of one ten-inch by ten-inch by six-inch cast pipe toe (Unit 2 ECW piping spool 10"-EW-2306-KK) per the requirements of Article IWA-4000 or IWA-7000, respectively. Relief is being sought until the next South Texas, Unit 2 k

3 scheduled outage which was scheduled to take place in February of 1997. At that time, the licensee performed a 1de repair to retum the system to compliance with the Code (the repair was completed on FeLa ary 10,1997).

3.5 Basis for Relief Request for relief has been submitted under the impracticality provisions of 10 CFR 50.55a(g).

The licensee stated that performance of a Code repair during power operations within the time frame permitted by the TS limiting condition for operation may not be practical due to potential for fit-up problems during repair, potential need for access to the inside surface, and extended time required for draining.

The licensee evaluated the flaw in accordance with the guidance provided in GL 90-05. Based upon the evaluation, it was established that the discovered flaw satisfies the criteria for non-Code repair as described in GL 90-05. Further, the licensee has also determined that the leakage can be detected before the flaw reaches a limiting size that would affect the operability of the ECWS (currently there is no leakage). Also, because there was no leak, there was no adverse effect on any safety-related equipment in the surrounding area.

3.6 Licensee's Attemative Proaram

1. Visualinspection of the affected areas to detect possible leakage or indications of dealloying including all castings was performed monthly.

2. Weekly inspections of the identified through-wall flaw were initiated to verify the slow rate of dealloying and measure any leakage.

3. The identical tees in the other five diesel generator trains were inspected for similar indications of through-wall dealloying.

4. Performing a Code repair during the next refueling outage (repair was completed on February 10,1997).

4.0 STAFF EVALUATION AND CONCLUSIONS 4.1 Operability Determination. Root Cause Analysis and Structural Intearity Evaluation The licensee determined that the flaw was located in the ECWS which is classified as ASME Code Class 3 system. The flaw was located in Unit 2 pipe spool 10"-EW-2306-KK. The flawed pipe material was identified to be cast aluminum-bronze which is inherently ductile material (ASME SB 271 CA 952 material). Upon discovery of the flaw, the licensee performed an evaluation of the flaw using the guidance provided in GL 90-05 and found that the flaw satisfies the through-wall criteria prescribed in GL 90-05 and that the flaw meets the criteria for a non-Code repair. The licensee determined that the operability of the system will not be impaired because there was no leak. Also, because there was no leak, no adverse effect on any other safety-related equipment in the surrounding area was found.

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4 The licensee performed a root cause analysis of the flaw, and determined that the degradation resulted from dealloying. The licensee believes that a preexisting flaw was present to enable initiation of the dealloying process. The dealloying process normally initiates from a crevice such as a backing ring, a fabrication-induced flaw, or a casting flaw Radiographic inspection of the Unit 2 6-inch tee to flange joint found no linear indications. Indications found were consistent with casting defects which most likely were the initiation point for dealloying. Previous examples of such flaws were found to have initiated from pre-existing flaws exposed to the ECWS cooling water. The problem of dealloying of castings has also been described in previous communications with the NRC.

4.2 Auamented Inspection The flaw was located in ten-inch by ten-inch by six-inch cast too. The flaw was visually and radiographically examined to assess the flaw. No further areas of degradation were observed and the flaws were determined to be localized and caused by dealloying. The ECWS was l visually inspected monthly for leaks or indications of dealloying including all castings.  !

4.3 Temoorary Non-Code Repair and Monitorina Provisions I The licensee had monitored the flawed area monthly. If a measurable leak were identified, a l quantitative assessment of the leak would have been performed. The flaw was discovered on February 3,1997, and it was weld repaired on February 10,1997.

4.4 Staff Conclusions The staff has determined that the licensee's flaw evaluation has been consistent with the guidelines and acceptance criteria of GL 90-05. The staff, therefore, finds the licensees' structural integrity and operability assessments to be acceptable. The licensee performed monthly visual inspections of the affected areas to detect possible leakage or indications of dealloying. In addition, weekly inspections of the identified through-wall flaw were initiated to verify the slow rate of dealloying and measure any leakage (the weekly inspections were terminated when the tee was replaced). The licensee's actions constituted an acceptable temporary attemative to the Code requirements.

Furthermore, the staff finds that performance of an immediate Code repair was impractical since ,

it would require isolation of the affected ECWS piping and a plant shutdown, since performance of a Code repair would take longer than allowed by the limiting condition for operation. This

. meets the GL 90-05 definition of impracticality. Such an isolation is not in the best interest of plant safety, given the magnitude of the flaw and the licensee's attemative program. Further, the licensee has also determined that the leakage can be detected before the flaw reaches a limiting size that would affect the operability of the ECWS (there was no leakage). Also, because there was no leak, no adverse effect on any safety-related equipment in the surrounding area was found. The licensee repaired the flawed piping on February 10,1997.

The staff, therefore, concludes that the Code requirements are impractical. Therefore, the licensee's request for relief is granted and the attemative is imposed pursuant to 10 CFR 50.55a(g)(6)(i) since the proposed altomative provides reasonable assurance of operating

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readiness of the ECWS. Pursuant to 10 CFR 50.55a(g)(6)(i), the attemative is imposed (retroactively) until the permanent Code repair was made during the last Unit 2 refueling outage, which tsegan on February 8,1997. The licensee repaired the flawed piping on February 10, 1997.

The relief granted is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the l

burden upon the licensee that could result if the requirements were imposed on the facility.

Principal Contributors: G. Georgiev T. McLellan T. Alexion l

i Data - June 11, 1998 l

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