ML19325D896

Application for Amend to License NPF-1,consisting of License Change Application 181,changing Min Requirement for Number of Operable in-core Detector Thimbles from 75 to 50% for Cycle 12 Operation

ML19325D896
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	10/20/1989
From:	Walt T PORTLAND GENERAL ELECTRIC CO.
To:
Shared Package
ML19325D895	List: ML19325D894 ML19325D896 ML19325D927
References
NUDOCS 8910270126
Download: ML19325D896 (8)

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PORTLAND GENERAL ELECTRIC COMPANY EUGENE WATER & ELECTRIC BOARD AND PACIFIC POWER & LICHT COMPANY

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i Operating License NPF-1 i

I Docket 50-344 License Change Application 181 i

This License Change Application (LCA) requestr modifications to operating

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License NPF-1 for the Trojan Nuclear Plant to change the minimum require-ment for number of operable in-core detector thimbles from 75 percent to 50 percent for Cycle 12 operation.

PORTLAND GENERAL ELECTRIC COMPANY By T. D. Walt General Manager Technical Functions l

Acting for Vice President, Nuclear l

Subscribed and sworn to before me this 20th day of October 1989.

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Notary Public of Oregon i

Ny Commission Expires:

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6910270126 891020 L

f.DR ADocg o7999344 FDC

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LCA 181 Attachment A L

page 1 of 7 1

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Roperistion of Chenne Trojan Technical Specification (TTS) 3.3.3.2, " Movable Incore Detectors",

requires a minimum of 75 percent of the 58 in-core detector thimbles operable whenever that system is used for recalibration of the axial flux offset detection system (Quadrant power Tilt Ratio greater than 1.02),

nenitoring the Quadrant Power Tilt Ratio, or measurement of Fog and Fg(s). The proposed change will revise TTS 3.3.3.2 to require a minimum of 50 per-cent of the detector thimbles operable for the remainder of cycle 12 operation as opposed to the present 75 percent.

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Reason for Change I

The proposed change would allow an increase in plant operating flexi-bility while maintaining sufficient data collection capability to ensure that the plant is operated within licensed limits.

The flexibility is needed due to the number of thimbles which were declared inoperable as a result of eddy current inspections performed during the past refueling outage.

Details of that inspection have been provided in accordance with the reporting requirements contained in NRC Bulletin No. 88-09, " Thimble Tube Thinning in Westinghouse Reactors". There were 11 thimbles l

inoperable at the start of Cycle 12 and more flexibility is needed to l

accommodate future failures beyond the presently allowed 14.

The proposed change will allow in-core detector system operation with up to 29 thimbles inoperable (50 percent) for the remainder of cycle 12 L

operation. That percentage is consistent wit.. npprovals granted by WRC to other licensees for operation of their in-core detector systems.

i Determination of Significant Hasards Considerations f

In accordance with the requirements of Title 10. Code of Federal Regula-i l

tions, part 50.92, " Issuance of Amendment", this License Change Request l

1s judged to involve no significant hazards based upon the following

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information:

1.

Does the proposed license change involve a significant increase in I

the probability or consequences of an accident?

During the recent start-up of Cycle 12, a flux map was made with the in-core detector system. By doing so, we have confirmed that a misloaded core is not present for Cycle 12 operation.

Consequently, l

the probability of not detecting a misloaded core [ Final Safety I

Analysis Report (FSAR) Section 15.4.7] has not changed.

Likewise, l

the probability of occurrence of other FSAR Chapter 15 accidents have not changed, since the in-core detector system is not used for operational pl mt control.

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i LCA 183 3

Attachment A Page 2 of 7 i

i An analysis was performed to determine the impact of the proposed change upon predicted peaking factors relative to base cases. The consequences upon accident analysis will nrt be increased so long as the predicted peaking factors are conservative.

The base cases con-form to the current TTS requirement for number of thimbles operating and represent actual measurements taken during the previous cycle under both Beginning of Cycle (BOC) and End of Cycle (EOC) conditions.

We are required to verify compliance with TTS 3/4.2, " Power i

Distribution Limits", every 31 effective full-power days by use of flux traces obtained from in-core detector thimble locations. The data is taken and analyzed with the INCORE computor code. The measured power distribution values, including the heat flux hot channel factor Fq(s), and the enthalpy rise peaking factor, FA e are compared to TTS limits to verify compliance.

The H

measured Fq(z) is increased by 5 percent to allow for measurement uncertainty (and 3 percent for manufacturing tolerances) prior to comparison to the limit, and likewise the FAH value is increased by its measurement uncertainty of 4 percent.

In order to determine if the calculation of peaking factors using only 50 percent of the instrument thimbles significantly increases these measurement uncertainties, we have reanalyged our previous cycle full-power measurements using only 50 percent of the thimbles.

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Five randomly selected patterns of 29 thimbles, illustrated in Figure 1, were analyzed near BOC 11.

Five different randomly selected patterns of 29 thimbles, illustrated in Figure 2, were analyzed near EOC 11.

These figures depict the core location of instrument thimbles.

Operating thimbles are in black while th3 white circles depict inoperable thimbles.

Known locations of inoperable thimbles (i.e., those locations which failed the recent eddy current test) have been included for all test cases. Table 1 gives the results for the ten cases analyzed and compares the predicted value of F (z) and FAH to the value of the base cases. As shown, the Q

calculated peaking factors using only 29 of the 58 instrument thimbles were higher in all but one case. And for that case, the Fog was 0.4 percent lower than the base case and Fg(z) was O.7 percent lower than the base case.

Although the one case is judged insignificant, we propose to increase our measurement uncertainty by 1 percent to completely encon. pass all cases.

plant procedures will be revised to require that whenever less than 75 percent of the thimbles are operable, the measurement uncertainty for F (z) will Q

be increased from 5 percent to 6 percent and FoH will be increased from 4 percent to 5 percent.

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LCA 181 Attachiuent A page 3 of 7

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t Because the peaking factors are conservative relative to the base p

cases and additional measurement uncertainty is proposed for opera-tion with less than 75 percent thimbles operable, the consequences of an accident will not be increased due to the proposed change, he have also determined that there is no significant impact upon monitoring the Quadrant power Tilt Ratio, *ince the required minimum number.of thimbles per core quadrant is r n ehanged.

2.

Does the proposed license changa create

'.+a p;~: albility of a new or different kind of accident f rom any.vcicr:.c previously analyzed?

l The only change proposed is a reduction in the number of operable thimbles. This change does not introduce any saw equipment or methods into plant operation and thus cannot create an accident of a different type.

3.

Does t'.se proposed license change involve a significant reduction in a margin of safety?

The results from Table 1 show that with a reduceo number of thimbles the predicted peaking factors will increase.

Since all cases remala below the TTS peaking limits, the margin of safety has not been reducet.

'In the March 6, 1986 Federal derister, the NRC published a list of O

examples of amendments the*

oot likely to involve a significant l

hazards consideration.

f (71) from this list states:

"A change which either may result in some increase to the probability or consequences of a previously-analyzed acci-dent or may reduce in some way c safety margin, but where the results of the change are clearly within all acceptable criteria with respect to the system or component specified in the Standard Review plan, rg., a change resulting from the application of a small tafinement of a previously used calculational model or design method".

Our analysis shows that the results of the change are clearly viinin all acceptance criteria of the Standard Review p)an. Thereforc, the proposed change is similar to Example (VI) discussed abovt and does not inv;1ve a significant hazards conrideration.

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t, LCA 181 At'achment A Page 4 of 7 Safety / Environmental Evaluation Safety and environmental evaluations were performed as required by Title 10, Code'of Federal Regulations, Part 50, " Domestic LicL*.2ing of E

Production and Utilization Facilities", and the TTS. The review 5

determined that the proposed change does not create an unreviewed safety question, nor does it create an unreviewed environmental question.

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Schedule Considerations It is requested that'the effective dato of the amendment be 15 days after-issuance by the NRC.

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TABLE l' PEAKING FACTOR RESULTS FOR RANDOMLY SELECTED OPERATING THIMBLE PATTERNS

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1himble Pattern No. of Thimbles FAH

% Difference _

Fq

% Difference

-4 Base Case - BOC 49 1.4381 1.7912 Test Case 1 29 1,4528 1.7 1.8082 0.9 rest Case 2 29 1.4415 0.2 1.8198-1.6 Test Case 3 29 1.4587 1.4 1.8268 2.0 Test Case 4 29 1.4512-0.9

'1.8185 1.5 Test Case 5 29 1.4517 0.9 1.8191 1.6 Base Case - EOC 50 1.3740

-1.6038 Test Case 1 29 1.4096 2.6 1.6272 1.5 Test Case 2 29 1.3755 0.1 1.6055 0.1 Test Case 3 29 1.3680

-0.4 1.5919

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Test Case 4 29 1.4126 2.8 1.6304 1.7 Test Case 5 29 1.4116 2.7 1.6300 1.6

% Difference = Reanalyzed Case - Base Case x IOC Base Case DBO/bsh 3419W.1089 h

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LCA 181 i

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