ML20236P226

Forwards Response to Request for Addl Info Re Change to Interim Tech Spec 3/4.1.7, Reactivity Change W/Temp. FSAR Section 3.8.3.1 Will Be Revised at Next Annual Update to Be Consistent W/Other FSAR Sections on Reserve Shutdown Sys

ML20236P226
Person / Time
Site:	Fort Saint Vrain
Issue date:	11/12/1987
From:	Brey H PUBLIC SERVICE CO. OF COLORADO
To:	Calvo J NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM), Office of Nuclear Reactor Regulation
References
P-87396, TAC-65241, NUDOCS 8711170205
Download: ML20236P226 (6)

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2420.W. 26th Avenue, Suite 1000, Denver, Colorado 80211 November 12, 1987 Fort St. Vrain

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Unit No. 1 i . P-87396 U. S. Nuclear Regulatory Commission ,

ATTN: Document Control Desk Washington, D.C. 20555 I Attention: Mr. Jose A. Calvo Director, Project Directorate IV i

Docket No. 50-267

SUBJECT:

Interim Technical Specification 3/4.1.7, Additional Information

REFERENCE:

1. NRC letter Heitner to Williams, dated 7/20/87(G-87241)

2. PSC letter Williams to Berkow, dated 4/8/87 (P-87056)

Dear Mr. Calvo:

.. Attached is the additional information which the NRC requested in Reference 1. This information is in support of a change to interim Technical Specification 3/4.1.7, Reactivity Change with Temperature, which Public Service Company of Colorado proposed in Reference 2.

This proposal involved raising the maximum reactivity change with temperature from 0.056 to 0.065 delta k.

8711170205 871112 0 A gDR ADOCK0500g7 f

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P-87396 Page'2 ]

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If you have any questions regarding- the information provided j herewith, please contact Mr. M. H. Holmes at (303) 480--6960. .

j Very truly yours, m &n H. L. Brey, Manager Nuclear Licensing and Fuels 1 HLB /SWC/ lmb  ;

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Attachments j cc: Regicnal Administrator, Region IV '

ATTN: Mr. T. F. Westerman, Chief

. Project Section B l Mr. Robert Farrell Senior Resident Inspector Fort St. Vrain l

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Attachment to'P-87396 RESPONSE TO REQUEST.FOR ADDITIONAL INFORMATION~

.m l ' REGARDING TECH SPEC;3/4.1.7 t

PSC's responses ~ to the NRC's request for1 additional?information~are as follows:

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',NRC Question #1i '

.Has -the . previous : Technical Specification ;value .for ' the ' maximum

,, temperature defect ( .056" delta k) 'ever. been produced by: a measurement result; i.e., has a measurement result everl caused a plant shutdown?,

PSC' Response:

No. The,Lmaximum temperature defect of 0.056 delta k.has never been produced by a measurement result at FSV, nor has a measurement result -

ever caused a plant shutdown.

In the . initial' core,' a temperature defect of 0.059 delta k was.

predicted (FSAR Table 13.5-4). 'However, initial cycle- testing- was only. performed up to .1300 degrees F and the . highest measured.

temperature . defect- was 0.051 delta k. This higher. ~ predicted-temperature defect was balanced by-a higher RSS worth in the initial core,. 0.14 versus 0.13 delta k, . per FSAR Section'3.5.3.3.

In' all subsequent cycles, the predicted temperature defect has been steadily decreasing toward'the value for the equilibrium core, namely-0,044 delta k.

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-Attachment'to P-87396 1

.NRC Question #2:

From' Attachment .Three,-it appears that the calculated worth for the-f Lreserve-shutdown system (RSS) of ;13 delta k does not' allow for: the-

.J highest worth rod being stuck or in.the case of FSV the RSS poison

. balls failing to drop in the most worthy ~ channel . What is the basis 'f D

, 1: -for not taking an . allowance for the maximum worth Lunit being inoperable?..Is the analysis consistent with Section 3.2.3 of' the January'20,.1972' Safety Evaluation by the USAEC?

PSC Response:

The calculational methodology' that was used t'o determine a maximum temperature defect of 0.065 delta k,' based on an RSS' worth o f. 0.13 delta k, is the. .same. methodology that. was used in the: approved interim Tech Spec to determine a maximum temperature defect.of 0.056-

' delta , k,. based on .an RSS worth 'of 0.12 delta 'k. PSC proposed this change-to ensure consistency with the FSAR and to allow use of' the

-associated margins.

Although it was not stated in the explanation provided with the Tech Spec change request (P-87056)', the maximum temperature defect .of 0.065 ~ delta. k does, in fact, allow for the maximum worth unit.being inoperable.

The RSS would -assure subcriticality with the maximum worth hopper' inoperable, for two weeks of Pa decay, as follows:

Positive Reactivity - Delta k Maximum temperature defect 0.065 (from proposed LCO 3.1.7)

Full Xenon decay (FSAR Table 3.5-4) 0.032 Pa decay & Sm buildup (2 weeks)

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0.007 (Basis for. interim LCO 3.1.8/SR 4.1.8) 0.104 RSS Worth - 0.130 Maximum worth hopper inoperable ,

0.020 (FSAR 3.5.3.3)

- 0.110 i

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Attachment to'P-87396 n ,

f This_ tabulation does not . treat the effects of excess reactivity included in the' design of the core to allow for burnup. Throughout the cycle, this excess reactivity is matched by the rods that remain inserted in the core. Inadvertent withdrawal of all of these control reds. is considered incredible due to interlocks against withdrawing more than one rod pair at a time. Consequently, excess reactivity

~does not have to be considered in the calculation to demonstrate subcriticality using the. RSS with the maximum worth hopper 1 inoperable.

If the highest worth inserted control rod pair were inadvertently -

withdrawn, followed by failure of all control rod pairs to scram, the RSS would' be able to ensure subcriticality, but not with an inoperable RSS hopper. This condition would require multiple independent failures, however, and it is not part of the FSV design or licensing basis.

The 0.006 delta k margin between the positive reactivity (0.104 delta 1 k) and the RS3 worth (-0.110 delta k), allows for temperature defect-measurement uncertainties and still assures suberiticality.

Therefore, the RSS worth, with a single inoperable hopper, is sufficient to ensure subcriticality for the first-14 days, even with the maximum temperature defect of 0.065 delta k. Fourteen days is considered sufficient to repair or replace the inoperable RSS hopper.

This is consistent with updated FSAR Section 3.5.3.3 and interim LCO  :

3.1.8.

Tha FSAR section regarding RSS design (Section 3.8.3.1) currently refers to two inoperable RSS hoppers, as does the 1972 USAEC Safety Evaluation. The allowance for two inoperable hoppers'was based on the predicted temperature defect of 0.044 delta k for the equilibrium core. This was an expected value and is not appropriate for a Technical Specification upper limit. The selection of a suitable i higher limit, as discussed herein, does not allow for two inoperable hoppers. Therefore, interim Technical Specification 3/4.1.8 does not permit plant operation with more than one inoperable hopper. FSAR Section 3.8.3.1 will be revised at its next ennual update to be .

consistent with other FSAR Sections on the RSS that were previously  !

updated to refer to operation with one inoperable hopper.

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Attachment to P-87396

.e NRC Questfon:#3:  ;

The calculated' excess reactivity for the equilibrium core with a core average temperature of 220 degrees F., Xe-135 decayed, Sm-149 buildup, and two week Pa-233 decay is .102 delta k. Are these tne same conditions as assumed in the calculation of the RSS reactivity worth

(.13 delta k)?

PSC Response:

The core conditions were essentially the same as those indicated, but the control rod configuration was not.

The conditions assumed in both calculations are as follows:

Excess Reactivity kSS Worth Calculation Parameter Calculation Assumptions Assumptions Core Average 220 Deg. F 220 Deg. F Temperature Xe-135 Decay Full Full  ;

Sm-149 Buildup Full Full Pa-233 Decay 2 Weeks Full Control Rod Soma inserted to All Withdrawn Positions match excess reactivity The reactivity worth of the RSS was determined for the same core conditions as the excess reactivity calculations, except Pa was 3 conservatively assumed to be fully decayed. The excess reactivity

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calculation assumes some control rod pairs inserted, but the RSS  !

worth calculation assumes all control rod pairs withdrawn, as at end of cycle. This is conservative because any control rods that are ,

inserted in the core when the RSS is actuated will increase the- i reactivity worth of the overall control system, even though they may ]

decrease the worth of the RSS. j l

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