ML20213G859

Part 21 Rept Re Degradation in Pressurizer Heater Sheaths Fabricated from Unannealed Inconel 600.Initially Reported on 870506.Unannealed Watlow Heaters Will Be Replaced Prior to Startup

ML20213G859
Person / Time
Site:	Arkansas Nuclear
Issue date:	05/11/1987
From:	Scherer A ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:	Murley T NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM), Office of Nuclear Reactor Regulation
References
REF-PT21-87-083-000 PT21-87-083-000, PT21-87-83, NUDOCS 8705180492
Download: ML20213G859 (5)

Text

m COMBUSTION ENGINEERINE May 11,1987 LD-87-024 Dr. T. E. Murley, Director Office of Nuclear Reactor Regulation Attn: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

ANO-2 Pressurizer Heater Sheath Degradation

Dear Mr. Murley:

This letter confirms my May 6,1987 verbal notification to Mr. J. Sniezek (NRC) reporting a potential safety concern related to degradation in pressurizer heater sheaths which were fabricated from unannealed Inconel 600.

Combustion Engineering (C-E) procured the subject pressurizer heaters from Watlow Electric Manufacturing Co. as replacements for original equipment heaters at Arkansas Power & Light Company's Arkansas Nuclear One Unit 2 (ANO-2) plant. Twenty three (23) of the ninety six (96) pressurizer heaters in operation were of the unannealed Inconel 600 Watlow design. An event that occurred at ANO-2 on April 24, 1987 indicates that failure r T a heater sheath (which could be due to pure water stress corrosio i cracking) can lead to a situation where a steam leak develops creating a small but unisolable primary system to containment leak. At ANO-2, the leakage rate of approximately 0.02 GPM was well within the plant's charging capacity and did not inhibit an orderly plant shutdown to investigate the problem. It is our understanding that the planned corrective action will involve the replacement of all unannealed Watlow heaters prior to plant startup.

Based on the information available at this time, we believe that ANO-2 is the only C-E designed NSSS with any of the suspect Watlow heaters installed. Further, we are not aware of any other incidents of pressurizer heater sleeve leakage observed at units having C-E supplied NSSSs. C-E has no knowledge, however, as to whether Watlow provided heaters of q

$ ' l SD 'Q ')

Power Systems 1000 Prospect Hill Road (203) 688-1911 Combustion Engineering. Inc. Post Office Box 500 Telex: 99297 Windsor, Connecticut 060954500 8705180492 PDR 870511 '

S ADOCK 05000368 PDR, j

Dr. T. E. Murley LD-87-024 May 11,1987 Page 2 similar design to other nuclear units. The attachment to this letter summarizes the information available to us at this time.

If you have any questions on the above, please feel free to contact me or Mr. C.M. Molnar of my staff at (203) 285-5205.

Very truly yours, COMBUSTION ENGINEERING, INC.

as, A. [Scherer Director Nuclear Licensing AES:ss Attachment xc: Dr. S. T. Brewer, C-E l

1

Attachment to LD-87-024 Page 1 of 3 (1) Name and address of the individual or individuals inferming the Commission.

Combustion Engineering, Inc.

1000 Prospect Hill Road Windsor, CT 06095 (1) Identification of the facility, the activity, or the basic component supplied for such facility or such activity within the United States which fails to comply or contains a defect.

Watlow low density pressurizer heater.

(iii) Identification of the firm constructing the facility or supplying the basic component which fails to comply or contains a defect.

Combustion Engineering (C-E) purchased the subject component from:

Watlow Electric Manufacturing Co.

12001 Lackland Road St. Louis, MO 63146 (iv) Nature of the defect or failure to comply and the safety hazard which is created or could be created by such defect or failure to comply.

Some pressurizer heater sheaths at Arkansas Nuclear One Unit 2 (ANO-2) are fabricated from unannealed Inconel 600.

(Unannealed Inconel 600 can be susceptible to pure water stress corrosion cracking.) Twenty three (23) such heaters out of a total of ninety six (96) were of this particular design. The event that occurred on April 24,1987 at ANO-2 indicated that a cracked heater sheath apparently led to a situation where a steam leak developed. (It is postulated that this resulted when primary water entered the cracked heater sheath.) Failure of the pressurizer heater, in turn, caused a heater sleeve split and "J" weld (sleeve to pressurizer ID cladding weld) failure.

! The potential safety concern created when using unannealed Inconel 600 in this application is the increased probability of stress corrosion cracking of the heater sheaths with the potential consequence of a small unisolable primary to containment leak between the heater sleeve and the pressurizer (the ANO-2 leak rate was approximately 0.02 GPM). Steam cutting of the pressurizer exterior wall was indicated at ANO-2 as a result of the steam leak.

l

Attachment. to LD-87-024 Page 2 of 3 (v) The date on which the information of such defect or failure to comply was obtained.

Initial C-E determination and notification to NRC - May 6,1987.

(vi) In the case of a basic component which contains a defect or fails to comply, the number and location of all such components in use at, supplied for, or being supplied for one or more facilities or activities subject to the regulations in this part.

The suspect heaters are Watlow low density heaters sheathed.

with unannealed Inconel 600. Information presently available leads us to believe that ANO-2 is the only C-E designed unit with any of the suspect Watlow heaters installed. Other units were supplied with either Wiegand low density or GE high density Inconel 600 heaters or Watlow high density stainless steel ,

heaters. (The other heaters at ANO-2 are GE low density heaters which have been heat treated.) ANO-2 is, therefore, the only identified unit (supplied by C-E) to be affected.

Combustion Engineering has no information as to whether Watlow

,- provided low density unannealed Inconel 600 pressurizer heaters to other nuclear units.

(vil) The corrective action which has been, is being, or will be taken; the name of the individual or organization responsible for the action; and the length of time that has been or will be taken to complete the action.

It is our understanding that all Watlow heaters will be removed from ANO-2 prior to plant startup.

(viii) Any advice related to the defect or failure to comply about the facility activity, or basic component that has been, is being, or will be given to purchasers or licensees.

Watlow has been made aware of the situation described herein and has been at the ANO-2 site assisting AP&L. A preliminary Network notification was sent to C-E supplied units on April 30, 1987 (copy attached) informing them of the situation at ANO-2.

. ..

• Attachment to LD-87-024 Page 3 of 3 AMANSAS I -

$ W ECT: REACTOR COOLANT SYSTEM PRESSURE 30U W ARY LIANAGE AT 5:20 P.M. (CDT). THE LICENSEE DISCOVERED A NON-ISOLA 8LE LEAK ON THE REACTOR COOLANT SYSTEM Af8 DECLAAED A NOTIFICATION 0F UNU$UAL EVENT. THE PLANT WAS SMUTOOW Alt COOLED 00 W , A N UPON ENTRY INTO MODE 5 AT 10:20 A.M. (CDT), ON AMIL 25, 1987. THE NOTIFICATION OF UNU$UAL EVENT SS TEMINATED. THE LEAK WAS APPN011MTELY 0.03 GM IN THE AREA 0F THE PRES $URIZER LOWER NEAD. THE LEAK 18 FADN A PRE 55URIZER HEATER ELEMENT 5LEEVE PGETRATION, GUT THE EXACT LOCATION OF THC DEFECT IS PRESENTLY UNENOW.

' THE LICENSEE ALSO FOUNO A $NALL AREA 0F DAMAGE TO THE OUTER SURFACE OF THE CARION STEEL PRES $URIZER VR$$tL LOWER NEAD. A80UT 1/2 INCH FROM THE LEAK!NG $LEEVE. THE QMAGEO AREA APPEAR $ TO BE A40UT 1 1/2 INCH IN DIAMETER AND APPRGIINATELT 1/2 TO 3/4 0F AN INCH IN DEPTH.

THEWA$TAGEMECHANISM(ERR 05!0NORCORROS!ON)HASNOTYE7BEEN DETEMINED. THE NS$$ V GOGR (CONSUSTION ENGINEER!NS) IS SENDING PERSONNEL TO THE SITE TO ASSIST IN DETEMINING THE CAUSE.

j 30 APR.87 14:35 PT

' OE 9822P PAGGEN (CE)OF PRES $URIZER LEAKAGE

Subject:

0ESCRIPTION To:A00Y, TERRY.CAROS$!NO. CARPENTER,CARR.FISICAR0, GREEN,HELGE50N,PA44EN, SAVAGE,$HAN V0REES, WILLIAMS. DANIEL,WOOCAA0

$USJECT: Arkansas 2 Desertptten of Pressurtaer Leakage.

Arkansas Nuclear One Unit 2 is a Combustten Engineering designed PWR rated at 2815 WT. The unit entered commercial operatten on 03 86 40.

On Friday. 04 24 87, while operating at 100E power and having been on Itne for 158 days, the unit expertenced reacter coolant leakage free the pressuriger. The leakage rate was determined to be less than one half gallen per einute. Investigattens fellowing a manual plant shutdoun reveal a single leak free the pressurtter vessel emanating -

near 1 of the 96 heater sleeves.

This sleeve is located on the peripheral row of heater l sleeves. As a result of this finding: the pressuriter has been drained, the heating element inside the sleeve l

is being removed, inspectten of the remaining 95 sleeves .

has shown no evidence of leaking, ne radietten has been released free the sentainment, and the NRC has been nettfied.

No prier incidents of pressuriter heater sleeve leakage had been observed free other C E PWR's. Addittenal informatten util be provided when it beceses available.

Infermetten contact: V. A. PASGEN (203) 295 4700 Information Centact:K. N6UYEN (203) 188 2308

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