ML20062A176

Draft Commission Paper Informing of Present Status of Gpu Program for Recovery from Steam Generator Tube Corrosion Problem & Describing NRC Intended Response to Gpu Re Need for Hearings

ML20062A176
Person / Time
Site:	Three Mile Island
Issue date:	07/19/1982
From:	Dircks W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
To:
References
NUDOCS 8208030088
Download: ML20062A176 (9)

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Docket File 50-289 JStolz Program Support Staff NRC PDR EDO Rdg. SECY L PDR WDircks OIE ORB #4 Rdg HDenton CMcCracken ORB #4 Comm. Paper File ECase ORB #4-RJacobs RPurple ORB #4-RIngram DEis enhut OCA-3 OELD

,5 g e py,334-AEOD Jg( 1 g jgg7 MBridgers For: The Conmissioners From: William J. Dircls Executive Director for Operations

Subject:

TMI-1 Steamr,enerator Recovery Progran

Purpose:

To provide the present status of GPU Nuclear's (GPUN's) progran fo recovery from the Dil-1 steam generator tube corrosion problem and to describe the staff's intended response :.0 GPUN's letter of April 30, 1982 regarding the

= need for Searings on the issue.

Discussion: As discut sed in SECY-82-35 dated January 27, 1982, the degradation of the THI-1 steam generator tubes was due to intergranClar stress corrosion initiated from the primary system tube surface and caused by sulfur contamination. .

The corrosion resulted in the formation of circunferential intercranular cracks. Approximately 95% of the cracks occurred in a 2-3 inch area at the upper end of the tubes

• uithin the upper tubesheet (UTS) near the roll transition ,

area and the heat affected zone of the upper seal weld. "

Af ter deternining that a significant number of tubes had defects (now estimated at 16,000-20,000 tubes of the total 31,000 tubes) the licensee decided to apply an explosive expansion repair technique to all tubes. Therefore, the i exact number of tubes with failures in the upper tube area noted above is likely to remain unknown. The purpose of the explosive expansion repair process, which kinetically expands the existing tube against the UTS hole, is to expand the tube r

with sufficient length below any defects to fora a new structurally sound and essentially leak tight joint. The licensee's repair objectives are to naintain the structural design ra gins specified in the licensing basis documents; and to liciit total primary-to-secondary leakage to about 1 pound per hour which would be as low as reasonably achievable and well within the limits of the Technical Specifications.

Co ntact. 8208030088 820719 PDR COMMS NRCC R. Jacobs, NRR CORRESPONDENCE PDR 49-27471

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y. w g G2 & i e.  %~ W Qualification testing involving perfecting the repair technique and conducting structural tests, thermal cycling, and leak tests are underway. GPUN estimates that the qualification testing will have sufficiently progressed to permit connencement of repairs on the Tiil-1 steam generators by August 1982. The licensee indicates, assuming no major delays, that the steam generators could be repaired and the plant available for operation by November 1982. The Staff considers this schedule somewhat optimistic.

The Staff is reviewing each of the major areas of 6 PUN's stean generator recovery program with consulting assistance from five organizations. GPUN has also established an independent third party review committee composed of industry and national laboratory experts to independently assess GPUH's program.

GPUN's April 30, 1982 letter requested Staff advice on the requirements for a hearing regarding the steaa generator recovery prior to return to operation. GPUH believes that the repair and return to service of the TMI-l steam generators does not involve an unreviewed safety question and would not involve a license amendment. A prelininary Staff position on this issue differs from GPUN regarding the unreviewed safety question and the need for a license amend-ment. However, the Staff has not identified anything to date in GPUN's recovery program that would preclude the return of the stean generators and the plant to service with the same design margins specified in the licensing basis documents. Therefore, at this time, the Staff's preliminary determination is that there are no significant hazards consideration involved in this program. A final determina-tion by the Staff on any matter involving a significant hazards consideration must await the completion of inspec-tion and investigation results. Since the Staff's position is that there are unreviewed safety questions on this matter, Staff approval of the repair nethods will be needed prior to the start of repairs; and a favorable Staff safety evaluation will be subsequently required prior to the return of the steam generators to service. Additionally, a license anend-ent on this natter will be necessary prior to the return to service.

k ' #ep W gg p r 4 4 Qualification testing involving perfecting the repair technique and conducting structural tests, thermal cycling, and leak tests are underway. GPUN estinates that the qualification testing will have sufficiently progressed to pemit commencenent of repairs on the TMI-l steam generators by August 1982. The licensee indicates, assuming no major delays, that the steam generators could be repaired and the plant available for operation by November 1987. The Staff considers this schedule sonewhat optimistic.

The Staff is ceviewing each of the major areas of GPUN's steam generator recovery program with consulting assistance from five organizations. GPUN has also established an independent third party review committee composed of industry and national laboratory experts to independently assess GPUf1's program.

GPUN in an April 30, 1982 letter requested written Staff advice on whether a hearing nay be required on the repair and return to service of the TM1-1 steam generators. GPUN believes that no unreviewed safety questions are involved and that no license anendment is necessary. The Staff dis-agrees but has nnt yet finally detemined whether the license amendment would involve a significant hazards consideration.

Although no such consideration has been identified to date, a final detemination must await our review of the results of inspections and evaluations not yet conpleted. The Staff intends to provide its views on whether a hearing may be required to GPUN by means of the enclosed letter (Enclosure 1).

A more detailed discussion of the steam generator recovery program is enclosed (Enclosure 2).

(Signed) T. A, nehm Willian J. Dircks Executive Director for Operations

Enclosures:

1. Ltr. to GPUH

2. Steam Generator Recovery Progran G /)

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'. A more detail discussion is enclosed.

William J. Dircks Executive Director for Operations

Enclosure:

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-S-would note, however, that until all inspection and investiga-tion results are co@ leted, the Staff would be unable to make a final determination.

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• V  % d Q w THI-1 STEAM GENERATOR RECOVERY PROGRAM EnclosureI ( ,

Source /Cause of Steam Generator Tube Cracking The licensee's failure analysis efforts involving metallo-graphic analysis of portions of 19 removed tubes have con-firmed that sulfur in reduced foms was the aggressive agent causing the corrosive attack. The primary source of the sulfur was thiosulfate from the reactor building spray systen which entered the prinary system at various times in 1981. The thiosulfate leaked past shut isolation valves in the spray system and entered the RCS during various systems testing which involved systen cross connection.

The licensee believes that the corrosive attack occurred at the end of or shortly after plant cooldown in September 1981 following hot functional testing, when the "right" conditions of susceptible material, aggressive chemical environment and high stress existed. The attack was rapid, occurred pri-marily in the area where the tubes were exposed to air when system water level was lowered, and probably terminated when the concentration of the aggressive sulfur species was reduced.

Sulfur levels at the time of the corrosion are believed to be on the order of several parts per million. Sulfur levels in the primary system now are less than 100 parts per billion and the thiosulfate tank has been drained and flushed. There is no evidence that the corrosion has continued since the corrosion was first discovered in late November 1981.

Repair Technique The licensee has decided to perfom an explosive expansion repair technique to all tubes. GPUN currently plans to explosively expand the top 14 inches of each tube within the 24 inch UTS thereby closing the crevice area between the UTS and the tube and establishing a seal between the primary and secondary fluid. Although qualification testing is still in the early stages it appears that an 8-inch seal area free of defects is optimum for ensuring that the seal has sufficient load carrying capability to carry axial loads induced under all normal and design basis accident scenarios. Accordingly, the

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Enclosure .f j the 8-inch seal, below the upper six inches of the tubes which contain most of the defects, would fom a new structurally sound and essentially leak tight joint. How-ever, tubes containing defects below the upper six inch area will not be considered repairable using the explosive expansion technique and will be removed from service by plugging. GPUN estimates that approximately 700 tubes will need plugging; approximately 200 tubes with defects below the UTS which have already been plugged, and almost 500 tubes with defects within the UTS below the upper six inch area.

It also appears likely that the repair will be perfomed using two explosive expansion steps; one to expand the tube and the second to establish an essentially leak tight seal.

Although it is unlikely that the repair will create a completely leak tight seal, the principal objective is to limit leakage to about 1 pound per hour total which would be within existing Technical Specification and Appendix I requirements.

GPUN has selected Foster Wheeler as the contractor to under-take the repair under GPUN and B&W supervision. Qualifica-tion testing involving axial load testing, thermal cycling, leak testing and pullout load testing is underway at Foster Wheeler and B&W laboratories. Additional testing will also be conducted on an actual B&W steam generator at Mount Vernon, Indiana.

Other Components Another major concern related to the stean generator problem was the propensity of the sulfur corrosion to attack other primary system materials. During a two week period beginning in late April 1982 GPUN removed the reactor vessel head and con-ducted an extensive progran of inspections of vessel internals as well as other potentially susceptible primary system con-ponents. The results of GPUN's failure analysis efforts indi-cated that in order for the attack to occur, specific conditions involving materials with high intergranular stress corrosion (IGSC) susceptibility, aggressive chemical environment, and

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.n y' y Enclosure j3 q stress must be present. The inspection program concentrated on components which may have met these conditions although many other materials were also inspected. Over 1000 items were inspected using various HDE techniques and a few com-ponents involving the most susceptible materials (i.e.,

Inconel 600, Inconel X750 and 304 SS) were destructively examined. Two unirradiated fuel assemblies were rerroved and those assemblies along with adjacent assemblies were visually inspected. No evidence of intergranular stress corrosion cracking was found. The Staff monitored the RCS inspection and although Staff review is not yet complete, no significant concerns have been identified to date.

Staff Review The Staff is reviewing each of the major areas of GPUN's overall program. These areas are the failure analysis of the steam generator tubes, RCS inspection, the repair tech-nique for the within tubesheet defective tubes, and the eddy current testing program to verify all tubes with defects below the UTS are identified and removed from service.

The Staff has retained consultants from five organizations to assist with the review of GPUN's steam generator recovery program. Three of tiie consultant organizations will be involved in actual hardware testing to independently assess the adequacy of GPUH's failure analysis efforts and the repair program. Arrangements have been nade to provide both defective and non-defective Tril-1 steam generator tubing to Pacific Northwest Laboratory (PHL) to pennit failure analysis testing and to provide single and 10-tube /

tubesheet mockups to Franklin Research Center for testing of the explosive expansion repair technique. If feasible, Franklin will actually conduct the expansion process. In addition to the Staf f's independent review effort, GPUN has established an independent third party review committee composed of industry and national laboratory experts to independently assess GPUM's program.

GPUN's Request Regarding The Need for Hearing By letter dated April 30, 1982, GPUN indicated that in their opinion, repair and return to service of the Tl11-1 stean generators does not involve an unreviewed safety question and Further, GPUN would not involve a license amendner.t.

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Enclosure 3 .g a license amendment be required. GPUH is referring to whether or not the proposed action involves a "significant _

hazards consideration" which would require prenoticing the action affording an opportunity for a hearing prior to return of THI-l to service.

The Staff's position on this issue [which the Staff plans to send to the licensee) is that there are unreviewed safety questions involved in that the corrosion mechanism and extent of corrosion in the steam generators is unique, the potential existed for this type of corrosion to attack other prinary system materials and the proposed repair method has not pre-viously been approved by the Staff as an acceptable nethod of repairing steam generator tubes. In addition, the Staff has concluded that a license amendment is required since the only method authorized by the Technical Specifications for repairing defective tubes is removal from service by plugging.

Hosiever, the Staff to date has not identified any concern that would preclude the return of the steam generators to service with the sane design margins specified in the licensing basis docunents, that would involve a significant increase in the probability or consequences of an accident previously evaluated, or that would create the possibility of an accident of a type different from any evaluated previously. Therefore, at this time, the Staff has not identified any matter which would involve a significant hazards consideration and thus require the Staff to prenotice actions involving approval of the repair method and amendnent of the license. The Staff would note, however, that until all inspection and investigation results are completed, the Staff will be unable to make a final deter-nination as to whether the action involves a significant hazards consideration.

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