05000530/LER-2003-002, Re RCS Pressure Boundary Leakage Caused by Degraded Inconel Alloy 600 Components

Re RCS Pressure Boundary Leakage Caused by Degraded Inconel Alloy 600 Components

ML031540552
Person / Time
Site:	Palo Verde
Issue date:	05/27/2003
From:	Overbeck G Arizona Public Service Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
192-01121-GRO/SAB/REB LER 03-002-00
Download: ML031540552 (7)

LER-2003-002, Re RCS Pressure Boundary Leakage Caused by Degraded Inconel Alloy 600 Components

Event date:
Report date:
5302003002R00 - NRC Website

text

LAMJR Palo Verde Nuclear Generating Station Gregg R. Overbeck Senior Vice President Nuclear 1 OCFR50.73 Mail Station 7602 TEL (623) 393-5148 P.O. Box 52034 FAX (623) 393-6077 Phoenix, AZ 85072-2034 192-01121 -G RO/SAB/REB May 27, 2003 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P1-37 Washington, DC 20555-0001

Dear Sirs:

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unit 3 Docket No. STN 50-530 License No. NPF-74 Licensee Event Report 2003-002-00 Attached please find Licensee Event Report (LER) 50-530/2003-002-00 that has been prepared and submitted pursuant to 10CFR50.73. This LER reports the discovery and corrective actions taken as a result of reactor coolant system pressure boundary leakage caused by a degraded inconel alloy 600 hot leg instrument nozzle and a degraded inconel alloy 600 pressurizer heater sleeve.

The degraded nozzle and pressurizer heater sleeve were discovered prior to the Unit 3 tenth refueling outage and were repaired prior to Unit 3 resuming power operation.

The corrective actions described in this LER are not necessary to maintain compliance with regulations. Arizona Public Service Company makes no commitments in this letter.

In accordance with 10 CFR 50.73(d), copies of this LER are being forwarded to the NRC Regional Office, NRC Region IV and the Senior Resident Inspector. If you have questions regarding this submittal, please contact Daniel G. Marks, Section Leader, Regulatory Affairs, at (623) 393-6492.

Sincerely, G RO/SAB/DJS/kg Attachment cc:

Regional Administrator-NRC Region IV N. L. Salgado J. N. Donohew (all with attachment) f;-

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APPROVED BY OMB NO. 3150-0104 EXPIRES 7-31-2004

Abstract

On March 29, 2003 with Unit 3 operating in Mode 4, Hot Shutdown, and cooling down to Mode 5, Cold Shutdown, for a refueling outage, engineering personnel discovered boric acid on a reactor coolant system hot leg instrument nozzle and a pressurizer heater sleeve. The cause of the boric acid leakage was attributed to primary water stress corrosion cracking of alloy 600 Inconel material in the instrument nozzle and the pressurizer heater sleeve. The amount of boric acid found was small.

A second pressurizer heater sleeve was initially suspected to be leaking, but a subsequent VT-2 examination revealed no indication of leakage.

The instrument nozzle was replaced with an Alloy 690 nozzle and the pressurizer heater sleeve was repaired using a mechanical nozzle seal assembly (MNSA). As a conservative measure, the second suspected heater sleeve was repaired with a MNSA clamp.

Similar previous conditions were reported in LER 50-530/2001-003-00, LER 50-528/2001-001-00 and LER 50-528/1999-006-00.

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PREVIOUS SIMILAR EVENTS

Similar previous conditions were reported in LER 50-530/2001-003-00, LER 50-528/2001-001-00 and LER 50-528/1999-006-00, in which different hot leg instrument nozzles were found to have evidence of leakage (boric acid residue). Similarly, these conditions have been attributed to PWSCC and the nozzles were repaired using Alloy 690 instrument nozzles. The corrective actions to prevent recurrence from the previous conditions are the same as for the conditions reported in this LER.