ML20083L531

Evaluation of Acceptability of Fddr 1E6AR-FDDR-001 for Shroud Repair Program at Quad Cities Unit 2

ML20083L531
Person / Time
Site:	Quad Cities
Issue date:	05/04/1995
From:	Gordon B, Potter M, Wolf S GENERAL ELECTRIC CO.
To:
Shared Package
ML20083L522	List: ML20083L520 ML20083L531
References
GENE-771-110-05, GENE-771-110-0595-R0, GENE-771-110-5, GENE-771-110-595-R, NUDOCS 9505180468
Download: ML20083L531 (10)

Text

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GENE 771 110-0595 Rev.0

. DRF B13-01740 l

Evaluation L of the Acceptability l of l

FDDR No.1E6AR-FDDR-001 for the Shroud Repair Program at Quad Cities Unit 2 May 4,1995

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I Prepared By: -

M. D. Potter

/N B. !(4. Gordon

-[WW 3 S. Wolf [/

Approved.By: M /7" ~

S. Ranganath" l l

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Quad Cities Unit 2 Shroud Hardware Installation FDDR Evaluation 1 0 9505180468 950511 PDR ADOCK 05000265

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GENE-771 110-0595 t Rev.0 '

DRF B13-01740 Abstract During the installation of the shroud repair hardware, pockets were cut in the shroud flange to accommodate the long upper supports. One of the pockets was cut too deep, and the cut went through the back of the shroud flange. This cut produced a steam bypass flow area. This document provides the evaluation of the disposition of FDDR Number 1E6AR-FDDR-001, which addresses this deviation for the shroud repair hardware installation at Quad Cities Unit 2.

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- l Executive Summary l l

i During the installation of the shroud repair hardware, pockets were cut in the shroud flange to accommodate the long upper supports. One of the pockets was cut too deep, and the cut went through the back of the shroud flange. This cut produced a steam bypass flow area. This document provides the evaluation of the disposition of FDDR Number IE6AR-FDDR-001, which addresses this deviation for the shroud repair hardware installation at Quad Cities Unit 2.

The areas covered in this report are:

Pressure forces on the long upper support Stresses in the shroud flange Bypass flow through the shroud flange Steam cutting / erosion IGSCC at fillet welds connecting the shroud flange and the steam dam The result of this report is that the final disposition of the FDDR," Accept-As-Is",is correct. Also, the report demonstrates that the fillet welds between the shroud flange and the steam dam do not need to be,lookea at for at least the next five years.

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I PROPRIETARYINFORMATION NOTICE Thia document contains proprietary infonnation of General Electric Nuclear -

Energy (GENE) and' is fumished to Commonwealth Edison (Comed) in confidence solely for the purpose orpurposes stated in the transmittalletter. No  :

cther use, direct or indirect of the document or the information it contains is authorized. The recipient shall not publish or otherwise disclose it or the information to others without written consent of GENE. and shall retum the l document at the request of GENE.  ;

IMPORTANT NOTICE REGARDING THE CONTENTS OF THIS REPORT The only underiskings of GENE rc5pacting information in this document are  ;

contained in the contract between Comed and GENE, and nothing contained in .

this document shall be construed as changirg the contract. The use of this information by anyone other than Comed, or for any purpose other than that for i which it in intended, is not authorized; and with respect to any unauthorized use, GENE makcc no representation or warranty and assumes no liability as to the l completeness, accuracy, or usefulness of the information contained in this  ;

document.

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. .. GENE.771 110-0595 l

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- DRF B13-01740 l Table of Contents __

Page 1.0 Introduction 6

' 2.0 Description 6 ,

3.0 Areas of Concern 6 .)

3.1 Pressure Force on Long Upper Support 6 i 3.2 Stresses in the Shroud E=ge 7 l 3.3 Bypass Flow Through the Shroud Flange 7 3.4 Steam Cutting / Erosion 8 3.5 IGSCC at the Fillet Welds Connection the Shroud .

Flange and the Steam Dam 9 3.5.1 Purpose of the Steam Dam 9 l 3.5.2 Intergranular Stress Corrosion Cracking Asse= ment 9 3.53 Lost Parts 10 l 4.0 Conclusion 10- 'l 5.0 Reference 10 l Figure 1, Leakage Paths Through Pockets in Shroud Flange 11 .

Figure 2, Shroud Head, Bolt IGSCC Trends 12 l Attachment 1, Modification Drawing 13 Attachment 2, FDDR 14 A!!achment 3, Shroud Drawing 15 Attachment 4, Long Upper Support Drawing 16 Attachment 5, Shroud Flange Stresses 17 Attachment 6, Shroud Head. Drawing 18 j

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1.0 Introduction Shroud repair hardware was described and evaluated as summarized in the previously issued 10CFR50.59 Safety Evaluation ( Reference 5.1). Installation of the shroud repair j hardware at the Quad Cities Unit 2 plant requires that pockets be cut into the shroud flange in order to install the long upper supports These pockets are cut at eight locations in the shroud flange. They are cut usmg the Electrical Discharge Machining (EDM) process. When the upper right hand position pocket at the 290 degree azimuth was being cut into the shroud flange, it was cut too deep, resulting in a burnthrough to the inside of the shroud flange

. The purpose of this report is to document the justification of the " Accept-As-Is" disposition of the FDDR 2.0 Description of Deviation The pockets in the shroud flange are supposed to be EDM'ed into the shroud flange as described in the Installation Drawing, leaving 1/2" of the shroud flange material at the'back of tne pocket. Instead, the EDM process cut all the way through the back of the shroud flange. This bemthrough resulted in a hole at the back of the shroud flange that will allow the saturated steam-water leakage from the core upper plenum to the annulus between the shroud and the RPV. The hole also could potentially create a crevice between the back of the shroud flange and the steam dam. This area was not previously exposed to reactor water because the steam dam was welded to the shroud flange at both the top and bottom by a 1/4" fillet weld (See Drawing 718E861, Attachment 3). The burnthrough did not go through the steam dam nor did it destroy the integrity cf the fillet welds themselves, but exposure of the space between the shroud flange and the steam dam to reactor water cannot be ruled out.

3.0 Areas of Concern This report looks at the following areas to assure the acceptability of the " Accept-As-Is" disposition of the FDDR.

3.1 Pressure Force l

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F 3.2 Stresses in the Shmud Flange A stress analysis was performed on the shroud utilizing the exi element model.

i This stress is directly under the long upper support. l The analysis utilized the bounding conservative loading condition o differential pressure under an MSLB combined with d thethe asymmetric recirculation line break and a design base earthquake. ll h way The stress a acceptability of the stresses in the shroud, even with the notches go -

through.

3.3 Bypass Flow Through the Shroud Flange The. current evaluation shows that a leakage path exists. The impact ofleakage ll as postulated leakage through the holes machmed m the shroud s hole as support plate, covers, wewas through the weld cracks (HI through H8) and the replacement acces oreviously evaluated (Reference 5.1).

msult in additionalleakage of about 0.21%

The leakage paths' When combined with of core flow at 100% rated power and 87 to 108% rated core flow.d the ac the leakage through the shroud support plate, the welds an ,

(Reference 5.1), the total leakage is about 0.44% of core flow. ,

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DRF B13-01740 These leakage flows are predicted based on applicable loss coefficients and reactor intemal pressure differences (RIPDs) across the applicable shroud components. Leakage bypasses the steam separators and dryers and is assumed to be two-phase fluid at the core exit quality. The steam portion of the leakage flows will contribute to increasing the total carryunder from the steam separators. Perfonnance impacts of leakage flows were previously discussed in Reference 5.1. This discussion concluded l that there is no impact on plant safety due to this evaluated leakage. The additional i

leakage impacts the performance results only for the steam separation system and the fuel cycle length as follows:

Steam Separation System - The leakage flow above the top guide support ring includes steam flow, which effectively increases the total carryunder in the downcomer by a maximum of about 0.03% at 100% rated power and 87 to 108%

rated core flow. The canyunder from the separators is based on the applicable separator test data at the lower limit of the operating water level range. The combined effective carryunder from the separators and from above the top guide support ring is about 0.18% and is bounded by the design value.

Fuel Cycle Length - The increased carryunder due to leakage flow above the top guide support ring results in a slight increas'e in the core inlet enthalpy, compared with the no-leakage condition. The combined impact of the reduced core inlet subcooling and the reduced core flow due to the leakage results in a minor effect

(-0.8 days) on fuel cycle length and is considered negligible.

The conclusion of the leakage assessment is that there is no impact on plant safety due to the additional leakage through the pockets in the shroud flange.

3.4 Steam Cutting / Erosion Because the velocities calculated above are relatively low compared to this, there will be no steam cutting or erosion.

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- * - Rev.0 DRF B13-01740 3.5 Crevice Between Shroud Flange and Shun Dam 3.5.1 Purpose of the Steam Dam The purpose of the steam dam is to create a water leg at the junction between the shroud flange and the shroud head flange. This water leg will keep the steam at this elevation away from the junction of the flanges. The steam dam is not a stmetural component as there is no pressure differential across it. Any loads are carried by the shroud flange and the shroud head flange.

3.5.2 Intergranular Stress Corrosion Cracking Assessment 1

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1 3.5.3 Lost Parts i

There is no concern at this time for SCC to cause the fillet welds between the steam dam and the shroud flange to fail and thus create any lost pans inside the reactor. Because the l potential for SCC is very low, there is no need to look at these welds for at least five  ;

years.

4.0 Conclusion The result of this study is that the Final Disposition of

" Accept-As-Is", is correct. Also,it is felt that the suscepuonnty of the fillet welds connecting the steam dam to the shroud flange to IGSCC is too small to be of concern for at least five years.

5.0 References -

t 5.1 10CFR50.59 Safety Evaluation, Mod M4-l&2-94-007, NEP 04-03 Attachment B.

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