ML031740114

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Leakage from Bottom Mounted Instrumentation Nozzles at South Texas Project, Meeting Attachment for 06/12/2003 Materials Meeting
ML031740114
Person / Time
Site: South Texas  STP Nuclear Operating Company icon.png
Issue date: 06/12/2003
From: Matthews L
Electric Power Research Institute, Southern Nuclear Operating Co
To:
Office of Nuclear Reactor Regulation
Birmingham J
Shared Package
ML031740003 List:
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Download: ML031740114 (11)


Text

Leakage from BMI Nozzles What do the findings from South Texas mean?

Larry Mathews, Chairman Alloy 600 ITG Southern Nuclear Alloy 600 Issue Task Group Materials Reliability Program

South Texas Project Unit 1 Inspections

  • Visual Examination
  • Volumetric Inspections

- Bare Metal Visual - 57 BMIs inspected via

  • UT from ID of nozzle to Nozzle 1 & 46
  • Enhanced visual

- Deposit Characterization examination of the

  • presence of boron, lithium, surface of J-groove weld and cesium - Nozzle 1 & 46

- No evidence of wastage

  • ET from tube ID and of J-
  • based on the lack of groove weld surface discoloration of the boric - 8 other nozzles acid deposits
  • ET from tube ID
  • the small amount of boric
  • ET of J-groove weld acid accumulation. surface 2 Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved.

South Texas Project Unit 1 Inspection Results

  • Nozzle 1

- 3 axial indications

  • One leak path (through wall)

- No crack-like indications on J-groove weld

- Visual grinding marks in side of tube

  • Nozzle 46

- Two axial indications

  • One leak path (through wall)

- No crack-like indications on J-groove weld 3 Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved.

STP-1 Planned Additional Testing & Repairs

  • Visually examine inside bore #1 and #46

- Perform after nozzle capped and separated

- Possibly detect irregularities

- Look for known through wall flaw in #1

  • ECT profilometry of #1 and #46
  • Metallurgical analyses of removed nozzle ends
  • Boat samples from #1 and #46 flaw zones
  • Nozzle #1 and #46 will be repaired with half nozzle repair
  • Volumetrically interrogate vessel base metal for wastage
  • Root Cause expected in October 2003

- Probable Cause in July 2003 4 Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved.

BMI Inspections in Industry

  • Approximately 12 plants perform visual inspections of BMIs every refueling outage.
  • 15 additional plants have performed visual inspection of BMIs either in the Fall or Spring refueling outages
  • MRP recommending that all plants with BMIs perform visual inspections for future refueling outages
  • EDF has performed 16 volumetric and surface inspections

(> 500 nozzles) at 12 units since 1992.

- No cracking has been discovered.

  • Some inspections have been performed at other units in Europe and Japan.

- One ID indication recently reported in Japan 5 Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved.

Industry Actions

  • MRP working with the Owners Groups to develop the strategy to address possible degradation of BMIs.

- Ensure safe operation of plants with BMIs

- Determine the appropriate inspection type and frequency for BMIs

- Possible elements: LOCA analysis, FMEA, Risk Assessment, Stress Analysis, etc.

6 Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved.

Current Recommendation from MRP

  • During the current or next refueling outage, a bare metal visual examination of any Alloy 600 nozzles penetrating the bottom head of the reactor vessel be performed.

- Plants whose design significantly impedes access to perform the recommended examinations should initiate expedited actions, up to and including physical modifications, to allow implementation of the recommendation at the earliest possible scheduled outage opportunity.

  • Non-visual NDE may ultimately be a prudent and necessary component in a comprehensive inspection plan to fully evaluate the condition of the BMI population of an RPV, particularly following visual detection of a leak.
  • Will re-evaluate these recommendations following issuance of root cause by STPNOC.

7 Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved.

Near- Term Owners Group Activities

  • WOG IRG has authorized Reasonable Assurance of Continued Operation for Westinghouse and CE Fleet

- Will be completed shortly

- complete 8 Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved.

IMI Nozzle SBLOCA Analyses for B&W-Designed Plants M. A. Schoppman 6/12/03

B&W Plant IMI SBLOCA Analyses

  • Framatome ANP performed two SBLOCA analyses for each plant type with a break area of

- Inside diameter of the IMI tube with incore ejected (0.0021 ft2), and

- The RV IMI nozzle vessel bore inside diameter with incore ejected and nozzle not obstructing the break flow area (0.0060 ft2).

10 Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved.

B&W Plant IMI SBLOCA Conclusions

  • Any break of a single IMI nozzle at a B&W-designed plant would produce results that remain within the 10 CFR 50.46 acceptance criteria.
  • Operator initiated steam generator cooldown improves ECCS delivery. SG depressurization also creates primary side condensate that augments the HPI flow. These contributions increase the minimum core mixture level (decrease PCT) for the largest IMI nozzle break.

11 Copyright © 2003 Electric Power Research Institute, Inc. All rights reserved.