ML20215N448

Application to Amend License NPF-1,incorporating License Change Application 146 to Revise Tech Specs 3.1.3.4 & 3.1.3.5,to Define Fully Withdrawn Rods as Greater than 225 Steps

ML20215N448
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	10/31/1986
From:	Withers B PORTLAND GENERAL ELECTRIC CO.
To:
Shared Package
ML20215N443	List: ML20215N442 ML20215N448 ML20215N450
References
TAC-63526, NUDOCS 8611050418
Download: ML20215N448 (4)

Text

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PORTLAND GENERAL ELECTRIC COMPANY EUGENE WATER & ELECTRIC BOARD AND PACIFIC POWER & LIGHT COMPANY Operating License NPF-1 Docket 50-344 License Change Application 146 This License Change Application requests modifications to Appendix A of Operating License NPF-1 for the Trojan Nuclear Plant to revise Trojan Technical Specifications (TTS) 3.1.3.4, " Shutdown Rod Insertion Limit", and TTS 3.1.3.5, " Control Rod Insertion Limit", to define fully withdrawn rods as >225 steps instead of 228 steps.

PORTLAND GENERAL ELECTRIC COMPANY By hm)

I Bart "D. Withers Vice President Nuclear Subscribed and sworn to before me this 31st day of October 1986.

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My Commission Expires: ef/w[ MM V

1050418 861031 p DOCK 05000344 PDR

o 0-LCA 146 Page 1 of 3 J'

DESCRIPTION OF CHANGE-This change revises Trojan Technical Specifications (TTS) 3.1.3.4,

" Shutdown Rod Insertion Limit", and TTS 3.1.3.5, " Control Rod Insertion Limit", to define fully withdrawn' rods as >225 steps as discussed below and shown in Attachment A.

! REASON FOR CHANGE 4 .

A study of control rod life was initiated by EPRI to evaluate rod clad-ding wear. Tha- study (Reference 1) revealed that rod cladding wear was of two types. The first type was stepping wear due to the axial motion of the rod _ clad passing through the uppor internals guide tube alignment cards (guide plates as shown in FSAR Figure 4.2-13). This type of wear was evidenced by a long continuous axial scar. The second type of wear was a fretting wear approximately 1-inch long at elevations corresponding

to the alignment cards. This type of wear was caused by the rods

< vibrating against the cards from reactor coolant flow dynamics in the upper reactor vessel.

1, Stepping wear is not considered to be a significant problem at Trojan because it is a utandard practice to rotate different rod cluster control assemblies (RCCAs) into the control bank D duty position. This minimizes i the amount of stepping wear experienced by any one RCCA.

Fretting wear, however, is a phenomenon to which Trojan is susceptible.

When a rod is fully withder.wn it is positioned at 228 steps, as implied by TTS 3.1.3.5, Figures 3~1-1 and 3.1-2.

. Over long periods of time in the fully withdrawn position, the same portion of the rod is subjected to rubbing against the alignment cards due to anticipated flow induced-vibration. This can result in fretting wear. Excessive wear could potentially result in the collapse or breach of the control rod cladding and could impair the free movement of the rod into the core.

! To minimize the likelihood of significant fretting wear, a revision to

the TTS is proposed to define fully withdrawn as >225 steps. This allows i inserting a rod to 226 steps for several years of operation. This will

! eliminate the concentrated fretting wear that can occur at 228 steps by

!- subjecting a'different portion of the rod to wear against the alignment i

card. This long-range planning can help to significantly extend the rod j life. As described in Reference 1, axial repositioning of the RCCAs can i distribute the wear and permit an additional 37,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> minimum of use i before replacement needs to be considered.

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LCA 146 Page 2 of 3 A similar change to the Point Beach Nuclear Plant technical specifica-tions was approved by the NRC in Reference 2.

SIGNIFICANT HAZARDS CONSIDERATION DETERMINATION This change does not involve a significant increase in the probability or consequences of an accident. Rod insertion is ilmited to ensure that: . (1) power distribution limits are met, and (2) minimum SHUTDOWN MARGIN is maintained. No change is proposed to either the power distribution related limits (TTS 3/4.2) or the minimum SHUTDOWN MARGIN (TTS 3.1.1.1). This change does not alter the conclusions of the reload safety evaluation performed for Cycle 9.

This change does not create a new or different kind of accident.

Changing the definition of." fully withdrawn" to >225 steps as opposed to 228 steps does not affect power distribution limits nor the minimum SHUTDOWN MARGIN. Since these limits are unaffected, a new or different kind of accident'is not created.

This change does not significantly reduce a margin of safety. Because of the low cod worth in the top region of the core, the proposed change has a negligible impact on power distribution. Similarly, the effect on shutdown margin is minimal, and can be accommodated by available excess shutdown margin. Sufficient peaking factors and DNB margin are available to. accommodate this small perturbation in power distribution. The cur-cent Cycle 9 reload safety evaluation (Reference 3) indicates that-there is no impact on the accident evaluation for Cycle 9 by inserting all control rods to 226 steps.

In the April 6, 1983 Federal Realster, the NRC published a list of exam-pies of amendments that are not likely to involve a significant hazards consideration. Example No. 6 of that list applies to the changes proposed herein and states:

"A change which either may result in some' increase to the probability or consequences of a previously analyzed accident or may reduce in some way a safety margin, but where the results of the change are clearly within all acceptable criteria with respect to the system or j component specified in the Standard Review Plan, eg, a change

resulting from the application of a small refinement of a previously

' used calculational model or design method."

L Based on the above evaluation, the proposed change does not pose a significant hazard.

k

. LCA 146 Page 3 of 3 4

REFERENCES

1. EPRI NP-4512 " Lifetime of PWR Silver-Indium-Cadmium Control Rods",

March 1986.

2. Letter, T. G. Colburn (NRC) to C. W. Fay (Wisconsin Electric Power Co.), Amendments 88 and 93 to Point Beach 1 and 2 operating licenses, March 7, 1985.

3. Letter, M. F. Meunks (W) to R. L. Steele-(PGE), Cycle 9 Reload Safety Evaluation, May 20, 1986.

BLK/djh 0864W.0586 i

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