ML20087H148

Forwards GE Repts on Metallographic Exam of Metal Samples Taken from Cracked Vent Header,Per NRC 840206 Meeting W/ Util,Bwr Regulatory Response Group & Ge.Vent Header Cracking Brittle Fracture Caused by Injection of Cold Nitrogen

ML20087H148
Person / Time
Site:	Hatch
Issue date:	03/13/1984
From:	Gucwa L GEORGIA POWER CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
NED-84-131, TAC-54150, NUDOCS 8403200262
Download: ML20087H148 (5)

Text

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Georgia Power Corr.pany 333 Piedmont Avenue At'anta, Georgia 30308 Vetephone 404 5266526 Ma!;ng Address.

Post Offer Box 4545 At!anta. Geregia 30302 h

Georgia Power L T. Gucwa IS ' of*w Mn c swem Manager Nuclear Engineering am Ch,ef Noctear Engineer NED-84-131 March 13, 1934 Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz, 011ef Operating Reactors Branch No. 4 Division of Licersing U. S. Nuclear Regulatory Comnission Washington, D. C.

20555 NRC DOCKET 50-366 OPERATING LICENSE, NPF-5 EIMIN I. HNICH NUCIEAR PLANT UNIT 2 VENT HEADER CRACK Gentlemen:

On February 6,1984, representatives of Georgia Power Capany (GPC), the BWR Regulatory Response Group, and General Electric Capany (GE) met with the NRC staff to discuss the cracked vent header at Plant Hatch Unit 2, which was discovered on February 3,1984.

At that meeting, GPC officials discussed a most probable cause of the cracking and stated that further metallurgical tests and evaluations would be conducted. Accordingly, GE has provided us a report (attached hereto) on the metallographic exmination of metal saples taken frm the cracked vent header.

We conclude that the vent header cracking was a brittle fracture, caused at cryogenic temperature, resulting fra the injection of cold nitrogen into the torus and impingement on the vent header.

Please let us know if you require additional information.

-Very truly yours,

/(&

1 L. T. Gucwa

/inb Enclosure xc:

J. T. Beckham, Jr.

H. C. Nix, Jr.

J. P. O'Reilly (NRC-Region II) 0!

8 Senior Resident Inspector -

I l 8403200262 540313 L

PDR ADOCK 05000366 P

PDR_

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GENERAL @ ELECTRIC NUCLEAR ENERGY ENGINEERING DMSON GENtRAL ELECTRIC COMPANY

• 175 CURTNER AVENUE e SAN JOSE, CALIFORNIA 95195 February ?4,1984 T.V. Greene, Deputy General Manager Edwin I. Hatch Nuclear Plant Ceorgia Power Company P.O. Box 439 Baxley, Georgia 31513

SUBJECT:

Status Report: Meta 11ographic Examination of Metal Samples of Vent Header Hatch-2

REFERENCE:

Status Report:

Letter Delwiche to Greene, Feb. 10, 1984.

This letter is a summary report of the materials testing performed to date at GE - Vallecitos Nuclear Center on sampics removed from the cracked regions of th( Hatch-2 Torus Vent header.

Work Plan The work plan that GE is following is outlined in ' Figure 11; The plan consists of three tasks; materials verification testing, fractere mechanics evaluation, and failure analyses. The goal of the test program is the identification of the cause of failure.

Summary of Previously Reported Information Scanning Electron Microscope (SEM) examination of the vent header sample transmitted to GE on February 6, 1984 has shown the cracking of The Plant Hatch Unit 2 torus vent header was caused by a " quasi-cleavage" brittle fracture. The fracture surface is characteristic of a single loading event fracture at a temperature below the Nil ductility transition temperature of the A516 gr 70 material.

Recently performed tests continue to support these early conclusions.

Status - Material Verification The material specified for the vent header was ASTM-A516 Grade 70, with the following requirements:

Chemistry o

.27 max carbon o.85/1.20 manganese o.035 max phosphorus o

.04 max sulfur o.15/.30 silicon Y

e'

GENERAL $ ELECTRIC T.V. Greene February 24, 1984 Page 2 Mech. Properties Tensile 70/90 ksi Yeild. min 38 ksi The test certification chemistry and mech, properties values for the heat of material used in the tent header are tabulated below.

For the purpose of comparison the independent laboratory

• verification of the chemistry and mechanical property values is also listed in the table.

U.S.S Corp Test CERT Anamet Verification Chemistry 0.23 carbon 0.26 carbcn 1.11 manganese 1.07 manganese

.005 phosphorus

.010 phosphorus

.022 sulfur

.023 sulfur

.22 silicon

.21 silicon Mech. Properties Tensile 81.3 ksi Tensile 77.4 ksi Yield 60.8 ksi Yield 53.2 ksi

% Elongation 22.0

% Elongation 29.7 Charpy V-notch impact toughness values were determined for the material per ASTM E-2g on subsg:e (5 X 10 X 55 mm) specimens over a range of temperatures from +40 F to -80 F. sThe Nil duct.ility.; transition: temperature was found to be approximately 450?F; Anamet Laboratories - Berkeley California Chemistry was determined by the emission spec. method, except for carbon which was determined by a LECO combustion method.

The microstructure and grain size was normal for this material and as o

expected for a fine grain material normalized at 1616 F as stated on the test certification.

These data verify, (A) That the material used in the Hatch-2 Torus Vent header meets the requirements of the ASTM-A516 gr. 70 specification, and (B) That the material is as identified in the U.S.S. Corp. Test certification.

Status - Failure Exami. nation i

GENERAL $ ELECTRIC T.V. Greene February 24, 1984 Page 3 Initiation

.- Macroscopic examination of the fracture surfaces and observation of the geometric features associated with the suspected point of fracture initiation suggest initiation occurred at the 12 0' clock (Top Center) position of the pipe on the inner surface of the pipe at the notch-like discontinunity of the fusion line of the butt weld.

Cause of Fracture Optical metallographic examination of three fracture samples has shown the vent pipe failure to be due to'transcrystalline;brittlelfracture;;7 characteristic of crack propagation at temperatures below the NDT temperature (ie. -60 F).

The fracture occurred along a single microplane, without plastic deformation. " Micro-branching", fatigue striations, and other features characteristic of a possible cyclic mechanism were 1.ot found.

SEM Fractography Some delay has been experienced in the completion of The Scanning Electron Microscope study due to a malfunction of the machine. As an alternate course of action replicas are being prepared of the fracture faces for study on an alternate machine an uncontrolled (radiation protectron) area. Completion expected by Tuesday Feb. 28th.

Conclusion Materials Testing on the Hatch Unit 2 Torus Vent header material has shown that the cracking was due to a brittle fracture as can be caused at cryogenic temperatures resulting from cold nitrogen injection into the torus and impingement on the vent header.

The properties of the header material has been found to be normal and within specification of ASTM-A516 gr 70.

If you have any questions, please contact me.

d' h

C Q trAJ r i ~P D. E. Delwiche Plant Materials Technology M/C 785 (408)925-4110 cc:

S. Koski Plant Hatch

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FIGURE 1 - WORK PLAN l Materials Test l Material Fracture Verification of Verification Mechanics Failure Mechanism o Chemical Analysis e Critical Flaw Size e Optical Microscopy SEM Fractography e Mechanical Properties e Stress Analysis e

Optical Macro-Examination e NDT/ Impact Toughness

- Residual e

e Microstructure

- Operational h

4 if Verification of Verification of Conditions st Probable Fracture Material Condition Required for Crack Initiation de And Propagation i r 7 pause Of Failurei '-

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