ML20136J038

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Proposed Tech Specs Section 5.6.1.2,revising Enrichment of Fuel for New Fuel Pit Storage Racks
ML20136J038
Person / Time
Site: Sequoyah  Tennessee Valley Authority icon.png
Issue date: 03/13/1997
From:
TENNESSEE VALLEY AUTHORITY
To:
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ML20136J029 List:
References
NUDOCS 9703190398
Download: ML20136J038 (19)
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, DESIGN FEATURES R171 5.6 FUEL STORAGE each other and from the inner Region 3 cells by at least one (1)

Region 2 spent fuel assembly (i.e., fuel of 50 MWD /Kgu burnup or equivalent).

2. . Region .1 fuel assemblies located .along the_ wide. water-gaps **

between storage modules must be isolated from each other and from the inner Region 3 cells by at least one (1) Region 2 spent fuel assembly (i.e., fuel of 50 MWD /Kgu assembly average burnup or equivalent).

3. Region 1 fuel assemblies located along the narrow water-gaps **

between storage modules must be isolated from each other by at least two (2) Region 2 spent fuel assemblies and from the inner Region 3 cells by at least one (1) Region 2 spent fuel assembly (i.e., fuel of 50 MWD /KgU assembly average burnup or equivalent).

4. A checkerboard pattern of fresh fuel and empty cells may be used throughout any storage module, or internal to any storage module in lieu of Region 3 fuel as shown in Figure 5.6-2.

Figure 5.6-1 shows a typical arrangement of regions. Figure 5.6-2 illustrates internal module checkerboarding of fresh fuel with empty cells in a portion of the fuel pool. Figure 5.6-3 illustrates the two burnup-enrichment equations (5.6.1.1.c.2 and 5.6.1.1.c.3) in graphical form.

e. Only spent fuel meeting the Region 3 burnup requirernents shall be stored in any module in the cask loading area of the cask pit.

CRITICALITY - NEW FUEL ~v-IMstrr ---*

5.5.1.2 The new fuel pit-storage-racks-are-designed-and-shall-be-ma4nt+ined-1

-with a nomina-1-2h0-inch-center-to-center-distence between new fuel-assembl4es-

-3uch that k,n wi44-not-exceed 0.90 when fuel having an enrichment--of 4.5 weight

-percent 4-2-35-is-in-place-and-opt 4 mum-achievabk-moder-ation 1: c::=ed. R148 DRAINAGE 5.6.2 The spent fuel pit is designed and shall be maintained to prevent inadvertent draining of the pool below elevation 722 ft.

9703190398 970313 PDR ADOCK 05000327 P pgg .

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    • The nominal gap (2-1/8 inches) running in the E-W direction between the  !

adjacent modules is referred to as the " wide gap." The N-S direction gap (1.5 inch) is referred to as the " narrow gap."  ;

i SEQUOYAH - UNIT 1 5-Sa Amendment No. 13, 60, 114, 144, 167 April 28, 1993

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5.6.1.2 The new fuel pit storage racks are designed for fuel enriched to 5.0 weight percent U-235 and shall be maintained with the arrangement of 146 storage locations

, shown in Figure 5.6-4. The remaining storage cells must remain empty (contain no fuel j assemblies). This configuration ensures k.n will remain less than or equal to 0.95

! when flooded with unborated water and less than or equal to 0.98 under optimum

moderation conditions.

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  1. $$-# Basic Cell 21 inch X 21 inch

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Empty Cell

9 - 4 X 5 Cell Racks 146 /180 Loading Pattern 1

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l Figure 5.6-4 Satt OYA H - (diotr l- 3'-Sf

DESIGN FEATURES R157 5.6 FUEL STORAGE each other and from the inner Region 3 cells by at least one (1)

Region 2 spent fuel assembly (i.e., fuel of 50 MWD /KgU burnup or equivalent).

2. Region 1 fuel assemblies located along the wide' water-gaps **  !

between storage modules must be isolated from each other and i from the inner Region 3 cells by at least one (1) Region 2 spent i fuel assembly (i.e., fuel of 50 MWD /KgU assembly average burnup or equivalent). '

3. Region 1 fuel assemblies located along the narrow water-gaps **

between storage modules must be isolated from each other by at least two (2) Region 2 spent fuel assemblies and from the inner Region 3 cells by at least one (1) Region 2 spent fuel assembly l (i.e., fuel of 50 MWD /KgU assembly average burnut or i equivalent). I

4. A checkerboard pattern of fresh fuel and empty cells may be used throughout any storage module, or internal to any storage module in lieu of Region 3 fuel as shown in Figure 5.6-2.

Figure 5.6-1 shows a typical arrangement of regions. Figure 5.6-2 illustrates internal module checkerboarding of fresh fuel with empty cells in a portion of the fuel pool. Figure 5.6-3 illustrates the two burnup-enrichment equations (5.6.1.1.c.2 and 5.6.1.1.c.3) in graphical form,

e. Only spent fuel meeting the Region 3 burnup requirements shall be stored in any module in the cask loading area of the cask pit.

CRITICALITY - NEW FUEL INsptr ->

0.1.2 The new fuel-pi-t-storage-racks-are-des 49ned-and-sham-be-maintained-

-with c nomtaal-2h0-inch-center-to-center-d4stanse-between-new-fuel-assembl4es--

auch that k percent U Odis-in-place-andapt4 wH-1-not-exceed-0AB-when-fuel-having-en-enr4ehment-of mum-achievable-moderat4sn is ass =cdr L 5 we R125

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DRAINAGE 5.6.2 The spent fuel storage pool is designed and shall be maintained to prevent inadvertent draining of the pool below elevation 722 ft.

    • The nominal gap (2-1/8 inches) running in the E-W direction between the adjacent modules is referred to as the " wide gap." The N-S direction gap (1.5 inch) is referred to as the " narrow gap."

SEQUOYAH - UNIT 2 5-Sa Amendment No. 4, 52, 125, 157 April 28, 1993

insert 5.6.1.2 The new fuel pit storage racks are designed for fuel enriched to 5.0 weight percent U-235 and shall be maintained with the arrangement of 146 storage locations shown in Figure 5.6-4. The remaining storage cells must remain empty (contain no fuel assemblies). This configuration ensures k.n will remain less than or equal to 0.95 when flooded with unborated water and less than or equal to 0.98 under optimum moderation conditions.

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I ENCLOSURE 2 '

. PROPOSED TECHNICAL SPECIFICATION (TS) CHANGE SEQUOYAH NUCLEAR PLANT (SON) UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 i

(TVA-SON-TS-97-01)

DESCRIPTION AND JUSTIFICATION FOR REVISION OF FUEL' ENRICHMENT FOR NEW FUEL STORAGE l

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Description of Change TVA proposes to modify the Sequoyah Nuclear Plant (SON) Units 1 and 2 technical specifications (TSs) by revising the allowed enrichment of fuel stored in the new fuel pit storage racks from 4.5 to 5.0 weight percent U 235. This revision also places limitations on fuel storage locations that can be utilaed in these racks. These i limitations are depicted in a new Figure 5.6-4 which is added to TS Section 5.6 for I fuel storage requirements. The revised TS Section 5.6.1.2 does not change the l requirements for k.n under optimum moderation conditions but does provide additional  ;

limits on k .n when flooded with unborated water.  !

Reason for Change '

TVA requested Westinghouse Electric Corporation to perform an analysis to support the storage of new fuelin the new fuel pit storage racks that exceeded 4.5 weight percent U-235 but would be bounded to no more than 5.0 weight percent U-235.

Westinghouse completed this analysis in 1990. A copy of this analysis is enclosed in this request. This analysis imposed limitations on the fuel storage locations that could l be utilized and still maintain the required k.nlimits. TVA has not used this analysis in the past because of the required storage limitations and because there has not been a need to use fuel with enrichments of greater than 4.5 weight percent U-235. For Unit 2 cycle nine operation, the required fuel enrichment will exceed the current limit with new fuel that is enriched to 4.6 weight percent U-235. For this reason, TVA is pursuing a TS change to support the cycle nine operation of SON Unit 2 and is implementing the more restrictive limitations on acceptable fuel storage locations as evaluated by Westinghouse.

Justification for Changes TS Section 5.6.1.2 provides k.n limits for new fuel such that the storage of this fuelin dry or flooded racks will remain below acceptable levels and prevent the fuel from becoming critical. Westinghouse Electric Corporation has performed an analysis to support the proposed revision of the acceptable fuel enrichment and the storage location limitations required to support this analysis. This analysis is provided in Enclosure 5 of this request. Since the development of this analysis by Westinghouse, two changes have occurred that require evaluation to ensure the validity and acceptability of this analysis at SON.

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' The first change involves the use of another fuel vendor. The fuel assembly modeled by Westinghouse in this analysis is a 17x17 STANDARD design. Since this analysis was performed, SON has changed fuel vendors and will be using the Mark-BW fuel design from Framatome Cogerma Fuels (FCF). A comparison of the fuel design parameters relevant to the criticality analysis was performed as follows:

Parameter W STD Mark-BW Change Effect on Reactivity UO2 pellet:

density (%) 96 96 None None diameter (in) 0.3225 0.3195 Decrease Decrease - Less UO2 loading Rod:

pellet / clad gap 0.00325 0.00325 None None (in) clad material zirc-4 zirc-4 None None clad thickness 0.0225 0.024 Increase Decrease More (in) material for neutron absorption outer diameter 0.374 0.374 None None (in) inner diameter 0.329 0.326 Decrease Decrease - Reduced (in) pellet diameter and UO2 loading pitch (in) 0.496 0.496 None None Guide Tube:

outer diameter 0.482 0.482 None None (in) inner diameter 0.450 0.450 None None (in)

The comparison showed that most of the relevant parameters were unchanged between the two designs. The few differences that exist are small and result in a less reactive Mark-BW design. Therefore, the analysis using the Westinghouse STD design is conservative with respect to the Mark-BW design.

The second change involved an industry change in the temperature assumed for analysis purposes. At the time this analysis was purchased, industry practice was to perform criticality analyses at 68 F. However, current analyses are performed at 4 C, since these have been proven to be achievable temperatures in storage areas.

Whereas the lower temperature results in a more reactive configuration for poisoned spent fuel storage configurations, this change is not significant for new fuel arrays and does not impact the validity of the Westinghouse analysis.

Temperature affects a fuel storage array by incrossing or decreasing the density of the water in the array and thus changing the hydrogen / uranium (H/U) ratio of the system

4 4 system (moderation). For spent fuel storage systems which are flooded and poisoned, decreasing temperature increases the density of the water, thus increasing the moderation of the system (H/U ratio) and making it more reactive. However, for dry, non-poisoned systems such as the new fuel storage racks being analyzed, optimum moderation occurs at water densities less than 1.0 gm/cc and thus would occur at higher temperatures. The Westinghouse analysis has already addressed the most reactive temperature by addressing the low density optimum moderation condition.

Based on the evaluations discussed above, the Westinghouse analysis is applicable to the current SQN conditions and fuel design. The Westinghouse evaluation provides the appropriate analysis to support the increase in fuel enrichment and storage in the new fuel pit storage racks. The storage rack loading limitations imposed by this TS change request and required to support the analysis ensures the criticality requirements are not increased from the current TS requirements. As an added measure, TVA will install physical barriers in the required cell locations to ensure that inadvertent loading of fuel assemblies into these locations will not occur. These barriers will be verified by procedure to be in place prior to initialloading of fuel in the new fuel storage racks and an inventory will be performed after receipt is completed to verify the location of fuel assemblies and barriers. Therefore, the proposed TS change does not increase the potential for criticality events as a result of storing new fuel that is enriched up to 5.0 weight percent U-235.

Environmental imoact Evaluation The proposed change does not involve an unreviewed environmental question because operation of SON Units 1 and 2 in accordance tvith this chango would not:

1. Result in a significant increase in any adverse environmental impact previously evaluated in the Final Environmental Statement (FES) as modified by NRC's testimony to the Atomic Safety and Licensing Board, supplements to the FES, environmentalimpact appraisals, or decisions of the Atomic Safety and Licensing Board.

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2. Result in a significant change in effluents or power levels, j
3. Result in matters not previously reviewed in the licensing basis for SON that may have a significant environmental impact.

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1 ENCLOSURE 3 PROPOSED TECHNICAL SPECIFICATION CHANGE SEQUOYAH NUCLEAR PLANT (SON) UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 (TVA-SON-TS-97-01)

DETERMINATION OF NO SIGNIFICANT HAZARDS CONSIDERATION

s Significant Hazards Evaluation i

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TVA has evaluated the proposed technical specification (TS) change and has determined that it does not represent a significant hazards consideration based on criteria established in 10 CFR 50.92(c). Operation of Sequoyah Nuclear Plant (SON) .

in accordanca with the proposed amendment will not:

i i 1. Involve a significant increase in the probability or consequences of an accident previously evaluated. '

f The proposed change to the allowed enrichment of new fuel stored in the neue

! fuel storage racks does not change the criticality potential with the proposed fuel

! arrangement requirements for the storage racks. The potential k ,,, values are maintained the same as the current TS requirements. In addition, the storage

! racks are not modified, other than the locations that can not be filled with fuel assemblies, and the processes for loading and unloading fuel in these racks and the controls for these racks remain the same. Since the k ,,, limits and operating processes are unchanged by the proposed revision, there is no incresce in the probability of an accident previously evaluated. Likewise, there is no impact to the consequences of an accident or increase in offsite dose limits as a result of the proposed TS change because the criticality requirements are unchanged and  ;

plant equipment will be utilized and operated without change considering the fuel storage location limits imposed by this request.

2.' Create the possibility of a new or different kind of accident from any previously analyzed.

As stated above, the plant equipment and operating processes will not be altered by the proposed TS change with the exception of allowed fuel storage locations in the new fuel storage racks. The limitations on acceptable fuel storage locations in the racks ensure that the k ,,, limits are maintained at the same limits as currently required. TVA has not postulated a criticality event at SON for the spent or new fuel storage locations because the design of the associated storage racks, potential moderation, and TS allowable fuel enrichments do not support the potential for this condition. Considering the physical barriers that will be installed and verified to be in place prior to initialloading of fuelin the new fuel storage racks, the new fuel storage rack physical limitations will continue to ensure that criticality events are not credible for the proposed change. Therefore, this change does not create the potential for a new accident from any previously analyzed.

3. Involve a significant reduction in a margin of safety.

The proposed TS change maintains the existing requirements for criticality by utilizing limited storage locations in the new fuel pit storage racks. There is no change to operating practices associated with the use and control of these racks except for the storage limitations. For these reasons, there will be no reduction l.

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2 ENCLOSURE 4 ,

PROPOSED TECHNICAL SPECIFICATION (TS) CHANGE . :1 SEQUOYAH NUCLEAR PLANT (SON) UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328 (TVA-SO N-TS-97-01 )

REVISED TS PAGES II l

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DESIGN FEATURES 5.6' FUEL STORAGE R171 each other and from the inner Region 3 cells by at least one (1)

Region 2 spent: fuel assembly (i.e., fuel of 50 MWD /KgU burnup or equivalent) .

2. Region 1 fuel assemblies located along the wide water-gaps ** between ,

storage modules must be isolated from each other and from tFs inner Region 3 cells by at least one (1) Region 2 spent fuel assembly (i.e., fuel of 50 MWD /KgU assembly average burnup or equivalent).

3. Region 1 fuel assemblies located along the narrow watar-gaps **

between storage modules must be isolated from each other by at least two (2) Region 2 spent fuel assemblies and from the inner Region 3 cells by at least one (1) Region 2 spent fuel assembly (i.e., fuel of' 50 MWD /KgU assembly average burnup or equivalent).

4. A checkerboard pattern of fresh fuel and empty cells may be used throughout any storage module, or internal to any storage module in lieu of Region 3 fuel as shown in Figure 5.6-2.

Figure 5.6-1 shows a typical arrangement of regions. Figure 5.6-2 illustrates internal module checkerboarding of fresh fuel with empty cells in a portion of the fuel pool. Figure 5.6-3 illustrates the two burnup-enrichment equations (5.6.1.1.c.2 and 5.6.1.1.c.3) in graphical form,

e. Only spent' fuel meeting the Region 3 burnup requirements shall be stored in any module in the' cask loading area of the cask pit.

CRITICALITY - NEW FUEL 5.6.1.2 The new fuel pit storage racks are designed for fuel enriched to 5.0 weight percent U-235 and shall be maintained with the arrangement of-146 storage locations shown in Figure 5.6-4. The remaining storage cells must remain empty (contain no fuel assemblies) . .This configuration ensures k ,will remain less than or equal to 0.95 when flooded with unborated water and less than or equal to 0.98 under optimum moderation conditions.

DRAINAGE 5.6.2 The spent fuel pit is designed and shall be maintained to prevent inadvertent draining of the pool below elevation 722 ft.

    • The nominal gap (2-1/8 inches) running in the E-W direction between the

-adjacent modules is referred to as the " wide gap." The N-S direction gap (1.5 inch) is referred to as the " narrow gap."

SEQUOYAH - UNIT 1 5-5a Amendment No. 13, 60, 114, 144, 167 l

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  1. ** Basic Cell 21 inch X 21 inch q Empty Cell 9 - 4 X 5 Cell Racks 146 /180 Loading Pattern Figure 5.6-4 New Fuel Pit Storage Rack Loading Pattern SEQUOYAH - UNIT 1 5-5f Amendment

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- DESIGN FEATURES  !

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5.6 -FUEL STORAGE  ;

i each other and from the innter Region 3 cell by at least one (1) i Region 2 spent fuel assembly (i.e., fuel of 50 MWD /KgU burnup or equivalent) .  ;

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2. Region 1 fuel assemblies located along the wide water-gaps **

between storage modules must be isolated from each other and

.i from the inner Region 3 cells by at least one (1) Region 2 spent

} fuel assembly (i.e. , fuel of 50 MWD /KgU assembly average burnup 7 or equivalent).

3. Region 1 fuel assemblies located along the narrow water-gaps **

5 between storage modules must be isolated from each other by at i least two (2) Region 2 spent fuel assemblies and from the inner R157 4 Region 3 cells by at least one (1) Region 2 spent fuel assembly  !

. (i.e., fuel of 50 MWD /KgU assembly average burnup or j equivalent) . I 3

. 4. A checkerboard pattern of fresh fuel and empty cells may be used i throughout any storage module, or internal to any storage module r I in lieu of Region 3 fuel as shown in Figure 5.6-2.

I Figure 5.6-1 shows a typical arrangement of regions. Figure 5.6-2 i- illustrates internal module checkerboarding of fresh fuel with empty i

cells in a portion of the fuel pool. Figure 5.6-3 illustrates the ,

two burnup-enrichment equations (5.6.1.1.c.2 and 5.6.1.1.c.3) in graphical form.

_' e. Only spent fuel meeting the Region 3 burnup requirements shall be

! stored in any module in the cask loading area of the cask pit. >

$ CRITICALITY - NEW FUEL

.; 5.6.1.2 The new fuel pit storage racks are designed for fuel enriched to (

5.0 weight percent U-235 and shall be maintained with the arrangement of 146 l storage locations shown in Figure 5.6-4. The remaining storage cells must j remain empty.(contain no fuel assemblies). .This configuration ensures k,n will

remain less than or equal to 0.95 when flooded with unborated water and less than or equal to 0.98 under optimum moderation conditions, j 1

DRAINAGE

! 5.6.2 The spent fuel storage pool is designed and shall be maintained to

] prevent inadvertent draining of the pool below elevation 722 ft. 'I t

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    • The nominal gap (2-1/8 inches) running in the E-W direction between the adjacent modules is referred to as the " wide gap." The N-S direction gap (1.5 inch) is referred to as the " narrow gap."

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SEQUOYAH - UNIT 2 5-Sa Amendment Nos. 4, 52, 125, 157

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  1. Basic Cell 21 inch X 21 inch i Empty Cell

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} 9 - 4 X 5 Cell Racks

! 146 /180 Loading Pattern Figure 5.6-4 l New Fuel Pit Storage Rack Loading Pattern SEQUOYAH - UNIT 2 5-5f Amendment I

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I- ENCLOSURE 5 I' l PROPOSED TECHNICAL SPECIFICATION (TS) CHANGE

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1 SEQUOYAH NUCLEAR PLANT (SON) UNITS 1 ANC 2 i l

l DOCKET.NOS. 50-327 AND 50-328 '

(TVA-SO N-TS-97-01 )

j; WESTINGHOUSE ELECTRIC CORPORATION CRITICALITY ANALYSIS OF THE SEQUOYAH UNITS 1 AND 2 FRESH FUEL RACKS l

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. Westinghouse Commercial Nuclear km3912 Electric Corporation Pittsburgh Pemsylvania 15230-3912 '

, Fuel Division July 17,1990 901V*-G-0077 -

Mr. T. A. Fays, Manager N

Fuel Fabrication and Utilization gY Tennessee Valley Authority A'C

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.1101 Market Street 8#

BR.6N 60A y: b Chattanooga, Tennessee 37401

Dear Mr. Feys:

'ITNNESSEE VAIIEY AUIHORITY SEQUOnH AND WA'ITS BAR NOCIEAR POWER PIANIS i SBJUOOH/WATIS BAR FRESH RACK CRITICATTV ANALYSIS s

Attached are five copies of the Sequoyah and Watts Bar Fresh Rack Critically rg;w.is. '!hese zwi.ai show that Westirv*vma 17X17 standard i fuel with enridu= ads up to 5.0 w/o can be safely stored in the Sequoyah and Watts Bar fresh fuel racks.

Should you have any questicos regarding this subject, please do not-hesitate to call or write.

Sincerely, N. R. Metcalf Project Engineer CNFD Projects ,

i NRM:mid Attachmnt cc: :C. R. Williamson RECEIVED-

_ Ncclce Fuel -

JUL 181990 Nuclear Fuel Supply Chattanooga

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