ML18033A501

Safety Evaluation Supporting Util Plan for Controlling & Mitigating Effects of IGSCC for Plant

ML18033A501
Person / Time
Site:	Browns Ferry
Issue date:	12/30/1988
From:	NRC OFFICE OF SPECIAL PROJECTS
To:
Shared Package
ML18033A500	List: ML18033A499 ML18033A501
References
GL-84-11, GL-88-01, GL-88-1, IEB-80-07, IEB-80-7, IEIN-88-003, IEIN-88-3, NUDOCS 8901040210
Download: ML18033A501 (8)

Text

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t UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF SPECIAL PROJECTS NUCLEAR PERFORMANCE PLAN, VOLUME 3, SECTION III.7.0 INTERGRANULAR STRESS CORROSION CRACKING TENNESSEE VALLEY AUTHORITY BRONNS FERRY NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-260

1.0 INTRODUCTION

The Tennessee Valley Authority (TVA or the licensee) has experienced inter-granular stress corrosion cracking (IGSCC) of several components in each of the three units at Browns Ferry.

IGSCC in the austenitic stainless steel piping systems for reactor coolant has been an identified problem for boiling water reactors (BMR) for about 12 years.

Extensive studies have identified the conditions favorable for IGSCC and developed mitigation methods for each of the conditions in austenitic steel piping systems.

For other systems and components, the items affected tend not to be made monolithic by welding, but are relatively small, discrete parts which can be replaced with materials not susceptible to IGSCC, or if they are weldments, they are relative small in size or number and can be monitored and replaced/repaired as necessary.

2.0 EVALUATION 2.1 IGSCC Status of Reactor Attached Pi in and Safe Ends TVA has utilized a number of mitigation methods in treating the 180 welds in the austenitic stainless steel reactor coolant piping over 4 inches in diameter which is exposed to reactor coolant over 200'F up to the second isolation valve refer to Generic Letter (GL) 84-11 and 88-01.

Of the 180 weld joints, there remain eleven welds in non-resistant material which have had no mitigation actions.

There are five untreated welds in 'non-resistant material within penetrations.

TVA plans to either remove the welds by design or overlay clad these welds on the inside surface which is exposed to reactor coolant.

There are six welds in the Core Spray System where the austenitic stainless steel piping has been replaced by carbon steel piping but austenitic stainless steel fittings are still in use and these bimetallic or dissimilar metal joints must undergo a mitigation action.

TVA has indicated that these particular joints will be induction heating stress improvement

( IHSI) treated by the conclusion of the next outage.

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TVA has not completed post-IHSI inspections of 71 welds which have been IHSI treated.

Because TVA had not performed sample expansion inspections under the terms stipulated in GL-84-11 and required in our letter of March 26, 1986 letter to them, the staff has previously concluded that all remaining post-IHSI inspections be performed before restart in its Safety Evaluation of TVA's response to GL-88-11 and GL-88-01 {December 8, 1988).

The stipulation was that if any crack indications were found after IHSI in the 25 percent sample inspected, another 25 percent of the welds IHSI treated that had exposure since original licensing would be inspected.

TVA has replaced recirculation inlet safe ends on Unit 2 due to IGSCC.

In addition, TVA has made arrangements to install hydrogen water chemistry treatment facilities to Browns Ferry Unit 2 and this may be activated during mid-cycle or by the end of the next refueling outage.

2.2 Jet Pum Hold Down Beams In response to IE Bulletin No. 80-07, TVA performed the required inspections and reported the results by letter dated October 20, 1980.

No cracks were found.

The failure mechanism was determined to be intergranular stress corrosion cracking.

General Electric (GE), the vendor, made replacement beam assemblies from material more IGSCC resistant.

TYA replaced all jet pump beam assemblies on Unit 2 as documented in Inspection Report 50-260/84-16.

2.3 Shroud Head Bolts Shroud head bolt cracking has been observed in several BMR plants.

The failure mechanism has been identified by GE-as IGSCC.

All 48 of these bolts have been inspected by GE using a special ultrasonic process developed for the specific geometry.

TVA reported 13 shroud head bolts cracked.

TVA plans to replace all of the cracked bolts'with new or borrowed bolts from another unit prior to restart.,

TVA also plans to establish a prog'ram for periodic reinspection of these shroud bolts.

2.4 Control Blade Crackin 1i This issue was identified recently, and the industry is presently in the process of gathering data.

The cracking mechanism has been identified by GE as stress corrosion cracking.

However, other factors such as weld configuration and water chemistry have been found to be of significance.

The influence of the various factors, rates of occurrence, means of mitigating or eliminating the cause of the cracking, and the regulatory approach remain to be determined.

TVA is participating in the industry s effort to build an experience data base.

Prior to restart, a selected number of control blades from Unit 2 will be inspected.

The inspection will be an in-core remote visual examination of the upper portion of the control blades while they are in the fully inserted position.

TVA s participation in the industry data base generation will provide TVA with current and definitive information which will allow them to make informed decisions in addressing the issue.

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2.5. Control Rod Drive Collet Tube Crackin Control rod drive collet retainer tube cracking has been observed in BWRs since 1975.

TVA has a control rod drive rebuild maintenance program in place which requires inspection of tubes on a periodic basis.

Tubes are liquid penetrant examined per the vendor's recommended criteria.

TVA has demonstrated an adequate approach in addressing this problem.

2.6 RHR Pum Wear Rin s All of the Unit 2 RHR pumps have had their upper and lower impeller wear rings replaced with original specification material.

Also, two of the crosstie RHR pumps to Unit 2 will have their wear rings replaced prior to Unit 2 restart.

The mitigation action of hydrogen water chemistry for the stainless steel piping along with well controlled water chemistry may provide the necessary environment to control this IGSCC problem along with the other IGSCC occurrences.

2.7 Shroud Access Cover Weld Crackin The NRC issued Information Notice No. 88-03 on February 2, 1988 titled, "Cracks in Shroud Support Access Hole Cover Welds."

The notice alerted boiling water reactor licensees of the potential for cracking in these welds.

TVA contracted with GE to perform a special ultrasonic inspection to determine if there was cracking in these welds.

The inspections were performed as reported in Inspection Reports 50-260/88-06 and 88-15.

No crack indications were found.

The mitigation action of hydrogen water chemistry for the stainless steel piping along with a well controlled water chemistry program may provide the necessary environment to control this IGSCC problem along with the other IGSCC occurrences.

3.0 CONCLUSION

S The staff's view of TVA's program for mitigation of IGSCC of BWR austenitic stainless steel piping was expressed in our SE of December 8, 1988.

There are 71 welds that have received the induction heat stress improvement (IHSI) treatment which have not been post-IHSI inspected.

The staff believes that there have been enough instances of IGSCC indications in the piping to require post-IHSI inspection of these 71 welds prior to restart to demonstrate that there are no significant IGSCC flaws present in these welds.

Our evaluation of your response wi 11 be covered under the review of GL 88-01.

The other instances of IGSCC in the various components have been addressed adequately by TVA.

Principal Contributor:

D. Smith Dated:

December 30, 1988

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1 Mr. Oliver D. Kingsley, Jr.

CC:

General Counsel Tennessee Valley Authority 400 West Summit Hill Drive Ell 833 Knoxville, Tennessee 37902 Mr. R. L. Gridley Tennessee Valley Authority 5N 1578 Lookout Place Chattanooga, Tennessee 37402-2801 Mr. C.

Mason Tennessee Valley Authority Browns Ferry Nuclear Plant P.O.

Box 2000

Decatur, Alabama 35602 Mr. P. Carier Tennessee Valley Authority Browns Ferry Nuclear Plant P.O.

Box 2000

Decatur, Alabama 35602 Mr. D. L. Williams Tennessee Valley Authority 400 West Summit Hill Drive W10 885 Knoxvi 1 le, Tennessee 37902

Chairman, Limestone County Commission P.O.

Box 188

Athens, Alabama 35611 Claude Earl Fox, M.D.

State Health Officer State Department of Public Health State Office Building Montgomery, Alabama 36130,Browns,Ferry Nuclear. Plant

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Regional Administrator, Region II U.S. Nuclear,'Regulatory Commission 101 Marietta, Street, N.W.

Atlanta, Georgia 30323 ';

Resident Inspector/Browns Ferry NP U.S. Nuclear Regulatory Commission Route 12, Box 637

Athens, Alabama 35611 Dr. Henry Myers, Science Advisor Committee on Interior and Insular Affairs U. S.

House of Representatives Washington, D.C.

20515 Tennessee Valley Authority Rockvi lie Office 11921 Rockville Pike Suite 402 Rockville, Maryland 20852

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