ML20203K806

Proposed Tech Spec Changes Allowing Steam Generator Tubes to Be Repaired by Utilizing NRC-approved Sleeving Method. Evaluation of Significant Hazards Consideration & Description & Justification Encl

ML20203K806
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	04/24/1986
From:	COMMONWEALTH EDISON CO.
To:
Shared Package
ML20203K792	List: ML20203K790 ML20203K806
References
1588K, NUDOCS 8605010047
Download: ML20203K806 (11)

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ATTACN ENT 1 9

PROPOSED ZION APPENDIX A TBCHNICAI, SPECIFICATION CHANGES TO i SECTION 4.3 -

)< REACTOR COOLANT GYSTEM A._

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LlHITING CONDITION FOR OPERATION SURVEILLANCE REQUIREMENT

1. Imperfection means an exception to the dimensions, finish or contour of a tube from that required by f abrication drawings or specifications. Eddy-current testing indica'tions below 20% of the nominal tube wall thickness, if detectable, may be considered as imperfections.

2. Degradation means a service induced cracking, wastage, wear or general corrosion occurring on either inside or outside of a tube.

3. _ Degraded Tube means a tube containing imperfections 2 20% of the nominal wall thickness caused by degradation.

4. % Degradation means the percentage of the tube wall thickness affected or removed by degradation.

5. Defect means an imperfection of such severity that it exceeds the Plugging or Repair Limit. A tube containing a defect is defective.

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LIMITING CONDITION FOR OPERATION SURVEILLANCE REQUIREMENT

6. Plugging or Repair Limit means the imperfection depth at or beyond which the tube shall be repaired ,

(ie. sleeving) or removed by plugging from service because it may become unserviceable prior to the next inspection and is > 40%

of the nominal tube wall thickness.

7. Unserviceable describes the '

condition of a tube if it leaks or contains a defect large enough to affect its structural integrity in the event of an Operating Basis i Earthquake, a loss-of-coolant accident, or a steam line or i feedwater line break as specified in 4.3.1.B.3.C above.

8. Tube Inspection means an inspection '

of the steam generator tube from the point of entry (hot leg side) t completely around the U-bend to the top support of the cold leg.

9. Repaired Tube means a tube that has undergone a process that re-establishes its serviceability.

The specific process for repair or re-repair shall be approved of by the NRC prior to use. The plugging limit and inspection frequency of the repaired tubes will be specified in the report that ,

describes the repair process.

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1 LIMITING COND1110N FOR OPERA 110N SURVEILLANCE REQUIREMENT

B. The steam generator shall be determined OPERABLE af ter completing the corresponding action (plug or repair all tubes exceeding plug or repair.

limit and all tubes containing I through-wall cracks) required by Table 4.3.B-2.

4.3.1.B.5 Reports -

1 A. Following each inservice inspection of 3

steam generator tubes, the number of

< tubes repaired or plugged in each steam generator shall be reported to the Commission within 15 days.

B. The completed results of the steam generator tube inservice inspection shall be included in the SPECIAL REPORT pursuant to Specification .

, 6.6.3.(c). The SPECIAL REPORT shall '

be submitted within 12 months following completion of the in;pection. This report shall include:

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1. Number and extent of tubes i inspected.

2. Location and percent of wall i

thickness penetration for each indication of an imperfection.

3. Identification of tubes repaired or plugged.

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4 LIhlTING CONDITION FOR OPERA 110N SURVEILLANCE REQUIREMENT' C. Results of steam generator tube

- inspections which fall in to category

C-3 and require prompt notification of the Commission shall be reported

< pursuant to Specification 6.6.2 prior-to resumption of plant operation. The written follow up of this report shall provide a description of investigation ,

conducted to determine the cause of the tube degradation and corrective

' measures taken to prevent recurrence.

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TABLE 4.3.B-2 .

STEAM GENERATOR TUBE INSPECTION IST SAMPLE INSPECTION 2ND SAMPLE INSPECTIOR 3RD SAMPLE INSPECTION C-1 None C -1 None C-1 None m C-2 Plug or repair C-2 Plug or repair C-2 Plug or repair defective tubes and defective tubes and -> defective tubes inspect additional 25

• inspect additional 4S tubes in this S.G. tubes in this S.G. -

II C-3 Inspect all tubes in k C-3 Perform action for C-3 C-3 Perform action for C-3 this S.G. plug or M result of first sample result of first sample repair defective tubes and inspect 2S tubes in each other S.G. j L Sample Size None All other S.G.'s A minimum of Prompt notification to are C-1 S. Tubes per NRC pursuant to S.G. Specification 6.6.2 Same S.G.'s C-2 Perform action for but no additional C-2 result of S.G. are C-3 second sample I I i k Additional S.G. Inspect all tubes is C -3 in each S.G. and plug or repair defective tubes.

Prompt notification to NRC pursuant to specification 6.6.2 S=3 N % Where N is the number of steam generators in the unit and n is the number of steam generators n inspected during an inspection 74j 09780/09790

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Bases:

3.3.1 Steam Generators 4.3.1 The Surveillance Requirements for inspection of primary-to-secondary leakage less than this limit.

the steam generator tubes ensure that the during operation will have an adequate margin of structural integrity of this portion of the RCS safety to withstand the loads imposed during normal will be maintained. The program for inservice operation and by postulated accidents. Operating inspection for steam generator tubes is based on plants have demonstrated that primary-to-secondary a modification of Regulatory Guide 1.83, leakage of 500 gallons per day per steam generators Revision 1. Inservice inspection of steam can readily be detected by radiation monitors of generator tubing is essential in order to steam generator blowdown. Leakage in excess of this maintain surveillance of the conditions of the limit will require plant shutdown and an unscheduled tubes in the event that there is evidence of inspection, during which the leaking tubes will be mechanical damage or progressive degradation due located and plugged.

ta design, manufacturing errors, or inservice conditions that lead to corrosion. Inservice Wastage-type defects are unlikely with proper inspection of steam generator tubing also chemistry treatment of the secondary coolant.

provides a means of characterizing the nature However, even if a defect should develop in service, and cause of any tube degradation so that it will be found during scheduled inservice steam corrective measures can be taken. generator tube examination. Plugging or repairs will be required for all tubes with imperfections The plant is expected to be operated in a manner exceeding the > 40% limit of the tube nominal wall such that the secondary coolant will be thickness. Steam generator tube inspections of maintained within those chemistry limits found operating plants have demonstrated the capability to to result in negligible corrosion of the steam reliably detect degradation that has penetrated 20%

generator tubes. If the secondary coolant of the original tube wall thickness.

chemistry is not maintained within these limits, localized corrosion may likely result in stress Whenever the results of any steam generator tubing corrosion cracking. Th3 extent of cracking inservice inspection fall into Category C-3, these l during plant operation would be limited by the results will be promptly reported to the Commission limitation of steam generator tube leakage pursuant to Specification 6.6.2 prior to resumption between the primary coolant system and the of plant operation. Such cases will be considered by secondary coolant system (primary-to-secondary the Commission on a case-by-case basis and may result leakage - 500 gallons per day per steam in a requirement for analysis, laboratory generator). Cracks having a examinations, tests, additional eddy-current inspection, and revision of the Technical Specifications, if necessary.

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I ATTACHMENT 2 DESCRIPTION AND JUSTIFICATION OF PROPOSED AMENDMENT The proposed change will create the option of repairing a steam generator tube that contains a pluggable defect. This repair is anticipated to take the form of sleeving the affected tubes. This change also specifically requires that any repair process be approved by the NRC.

The current Technical Specifications require that any steam generator tube that contains a defect of greater than 40% of nominal tube wall thickness be plugged. The act of placing a plug in both the hot and cold leg tube ends removes the tube from service by eliminating reactor coolant flow through the tube. The plugging of the tube is currently required even if the defect exists within the tube sheet region.

Sleeving is a process by which a smaller, shorter tube (sleeve) is placed inside of the existing steam generator tube. This sleeve extends throughout the tube sheet region and is sealed to the original tube, effect-ively forming a new barrier. Thus, if a defect were to exist in the tube sheet region, the sleeving process just described is a viable alternative to plugging the entire tube.

The obvious advantage to sleeving is that the tube will remain in service since reactor coolant would still be permitted to flow on the inside of the sleeve and throughout the remainder of the existing steam generator tube.

Zion Station has been experiencing some defects in the tube sheet region. Thus, the existence of the sleeving option will extend the life of Zion steam generators by allowing tubes who possess defects in the tube sheet region to remain in service.

As discussed above, the exact sleeving process to be utilized at Zion Station will be submitted and approved by the NRC prior to its use.

The proposed change transmitted with this document simply creates the option of utilizing a process that is yet to be submitted and approved. This change has no effect on the plugging process until an acceptable sleeving process has been approved by the NRC.

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I ATTACHMENT 3 EVALUATION OF SIGNIFICANT HAZARDS CONSIDERATION PROPOSED CHANGES TO ZION TECHNICAL SPECIFICATION APPENDIX A - SECTION 4.3 REACTOR COOLANT SYSTEM DESCRIPTION OF AMENDMENT REOUEST An amendment to the Zion Facility Operating License is proposed to allow the use of an NRC approved sleeving process to repair defective steam generator tubes.

BACKGROUND 10 CFR 50.92 states that a proposed amendment will involve a no significant hazards consideration if the proposed amendment does not:

(1) Involve a significant increase in the probability or consequences of an accident prev)ously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involve a significant reduction in a margin of safety.

In addition, the Commission has provided guidance in the practical applica-tion of these criteria by publishing eight examples in 48 FR 14870.

The discussion below addresses each of these three criteria and demonstrates that the proposed amendment involves a no significant hazards consideration.

BASIS FOR NO SIGNIFICANT HAZARDS CONSIDERATION DETERMINATION Does the proposed amendment (1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involve a significant reduction in a margin of safety?

DISCUSSION - ITEM #1 The creation of the option to utilize an NRC approved sleeving process to repair a defective steam generator tube has no effect on either the probability or consequences of any accident previously evaluated. The integrity of the steam generator tubes will be equivalent to that of an original tube. Thus, since the structural integrity of the tubes will not be affected by this change, there is no increase in the probability of any accident previously evaluated.

In addition, the steam generator will remain capable of performing its required heat transfer function. The act of placing a sleeve in the steam generator tube actually results in a more efficient steam generator relative to plugging the affected tubes. Thus, the consequences of any accident previously evaluated is unaffected because the heat transfer capability of the steam generators will not be significantly altered.

DISCUSSION - ITEM #2 As discussed above, both the structural integrity and the heat transfer capability of Zion steam generators will not be significantly affected by the use of an NRC approved sleeving process. In addition, the steam generator tube sleeves do not interact with any of Zion's systems.

Thus, there is no potential for a new or different kind of accident due to the use of a sleeving process to repair Zion steam generators.

DISCUSSION - ITEM #3 The heat transfer capabilities of Zion steam generators will be improved by utilizing the sleeving process rather than the currently required plugging. The sleeving process will allow a repaired steam generator tube to remain in service, rather than completely blocking the tube's flow with plugs. Since the structural integrity of the steam generators will be unaltered the net effect of utilizing a steam generator tube sleeving process rather than the currently required plugging procedure will be an increase in the margin of safety. This increase is due to the relatively improved heat transfer characteristics of the steam generator.

It should be noted that the proposed Technical Specifications represent new controls governing the repair of steam generator tubes. Thus, example (ii) is applicable to the proposed change.

L Example (ii) reads as follows:

(ii) A change that constitutes an additional limitation, restriction, or control not presently included in the technical specifications: for example, a more stringent surveillance requirement.

Therefore, since the application for amendment satisfies the criteria specified in 10 CFR 50.92 and is similar to examples for which no significant hazards consideration exists, comanonwealth Edison Company has made a determination that the application involves no signficant hazards consideration.

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