ML20086P855

Criticality Safety Analysis for Palisades Spent Fuel Storage Pool NUS Racks

ML20086P855
Person / Time
Site:	Palisades
Issue date:	12/09/1991
From:	SIEMENS CORP.
To:
Shared Package
ML18057B434	List: ML18057B433 ML20086P855 ML20086P857
References
EMF-91-174(NP), NUDOCS 9112270224
Download: ML20086P855 (22)

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Siemens Nuclear Power Corporation EMF 91174(NP)

Issue Date:

12/09/91 CRTrAlfN SAFETY ANALYSIS FOR THE PALISADES SPENT FUEL STORAGE

c POOL NUS RACKS December 1991

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CUSTCWEM OISCLA!MER IMPCRTANT_NOT1Cf Mt0ARpjNO CONTENTS ANO VSE CP Wi$

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S.emens Nuocer Power Corporeton a warrantes and representaports concoming be subsect maner of this occurnent are base set %f1h in the Agreement between

$ semens Nuoneer Power Corporeton art to Customer pursuant to wnich r e document it issued Accerengy, esmeA as emerwise espressly provced in such Agrooment neeer S. omens Nuasar Power Corporaten nor any person ac1 ng on its bonell makes any werfenty or representanon, esoressed of impled eith toegect 10 be soeuracy, compoeteness, or veefuleets of Po eformanon conmned in P's document or that me use of try mformation apparatus. *ethod er process descoed in his occument wdl not inWinge petvale*y owned ngnts, or assurros any 4andees we respect to the wee of any m#ormauon. accaratus, metnod or procese osoceed in true document The inhaton contamed meron is W ee $oes use of to Cwstomer in orear to avoid impermont of ngnts of 8.emens Neew Power Corporation a paonte or mveneans eru

Page 6 1

32 Storece Pecks Ceseriction and Cl The Palisades spent fuel storage acks comprising the main pocl and tilt pit pool. The pool layout is shown 90 main pool consists of NUS and Westinghouse storage racks. The NUSlouth end cf the main poolin a 2 tx16 array. The NUS racks have a 2 inch wi'g them ficm the Westinghouse racks (Reference 2). The NUS racks in the m.9 ave 6.56 inch square ID stcrage cot!s and a 10.25 inch center to ceriter spacin,t pool consists of a ncrth to scuth rew of three storage racks. The center rack: rage rack. The NUS rack is designec to store control rods as well as fuel au k has a 9.0 inch storage cell ID anc c

cells are located on 10.69 x 11.25 inch out is also shown in Figure 1.

Re storage cells each consisi outer stainless steel can. The gap detween the inner and outer can is 25 8 two 02ns is a neutren abscrter c! ate.

The plate is composed of B C bendedt The plate is 0.21 inen thick anc 9 26 4

inches wide with a B 10 loading of 0.09/ Between each sterago cellis a aater gap with nominal thickness of 0.69 inciarrangement of the Main Peel Sterage Cellis shown in Figure 3.1.

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FIGURE 3.1 PAUSADEG MAIN POOL STORAGE CELL NOMINAL ARRANGEMENT

E MF.91 174 A p 3 Page3 i

4.0 CALCULATlONAL METHODS AND MAJOR ASSUMPTIONS 4.1

, Calculational Methods The methodology used included CASMO 3G (Reference 3) and KENO Va (Peterence 4).

Beth codes share wide acceptance for fuel analysis throughout the nuclear industry.

CASMO 30 was used to determine the small enanges in reactivity cue to uncerta:nttes in the design telerances of the fuel assembly and spent fuel storage racks.

KENO Va was used to model the fuel storage pool.

Hansen Roach 16 group cress socitons prepared by BONAMl/NITAWL are used with the KENO Va models. KENO va BCNAMi.

NITAWL and the cross section library used are all part of the SCALE 3 system and have ceen extensively benchmarked against data from entical expenmentf:. Supplemental tenenmatorg using data from cntical expenments with bundle arrays cor.t10nir.g boren-containing ciates s included in section 7.0.

4.2 Maior Assumotions The major assumptions made in this analysis are as follows:

Fuel enrichment is the bunale average in all rod locations.

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Fuel bundles contain no bumable poisons.

No soluble poisons are present in the water.

Spent fuel pool bulk water temperature is 20*C, B,C content in the neutron absorber plates is constant over time and tie plates contain no significant gaps or missing plates.

The frst four assumptions make the analysis cos:servative. The last is a limidng condittor As part of Facility Change Package FC 375 each storage cellwas weigned after aestreer plate leading and compared to a reference weight. Random sampling of cells with a neutren source was also done befort 't si approval cf FC 375. Had significant gaps been present. they would have ceen found by these two checks (Feference 5).

EMF.91 174(NP)

Page 9 5.0 UNCERTAINT1ES 1

i The effect of dimensional and material tolerances on the system k eff was determined j

usinq CASMO 30. CASMO 30 s a 2 0 transport code used extensively for fuel depletien calculations. CASMO delta 4 J.M e a6.3 referred over those from KENO Va with a Mente Carlo uncertainty The fuel was mor.oA 6%t burnable poison and with all rods at a bundle average U 235 enrichment of 4.0 M.%

The effect of various f tNMt,Un is detailed below.

Enrichment.YMm f, hts tiominal enrichment was incteased by 0.0$ wt.% U 235. the j

e K infinity incr0aud by 00215.

Poltet Densfff;.1M Mminal smear density is TD basod en a volume

% dish and A 70 pellet density. K4nt increased by.00182 with a T')

pellet densAy and a volume % dish.

E3,[lgtplameter incrossing all pellet diameters by inen produced a C0029 rise in k inf.

Ctaddino O. 0.. Decreasing cladding O. D. by inch produced a,C0186 rise in k-int, 0

Temeeratury,. Temperature of the fuel and moderator was decreased to 4 C which resul'ted in 6n.00206 increase in k4nf.

Inner Can Wall T'hicw33. The inner can wall thickness was decreased by with is resulting decrease in k int of.00101. The inner wall thickness was Increased by with an increase in k Inf of.00085.

Outer Cao,ypall Thickness. The value of _.

from the inner can thickness is used agadn for thr# outer can thickness.

The storage rack cell pitch was decreased by.04 inch to 10=21 l

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inches. The resulting increase in k4nf is.00476.

. The RMS sum of the nine uncertainties due to tolerances is.00631. Tne tolerance uncertainty is used with the bias uncertainty and the KENO standard deviation to prepare the 95/95 upper limit of k of?. Section 7.0 reports the bias to be 0.0035,,,.00368. The 95/95 ccer limit for k ett is calculated using the methodology presented in Reference 9.

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EMc 911NM Page10 6.0 NORMAUA8 NORMAL CONDITIONS AND RESULT Ai conditions were modeled using KENO.Va and were found to have an acceptac!e reactMty (k off) of 5. 95 after accounting for all uncertaintles ar d bias. The maximum k effective at the 95/95 confidence level for any credible abnormal condition is.9131. The assumption that the entire NUS spent fuel storage rack contains 15x15 fuel with 4.4 wt.% U 235 conservatively accounts for the presence and potentialintermixing of older and lower enriched fuel bundles.

6.1 Normal conditions The main spent fuel storage pool was shown to be more reactive than the north tilt pit

- poolin Reference 6. The 24x16 NUS spent fuel storage rack was modeled as both a finite and an infinite system. The resulting k ett and a descriptlen of each model used is listed in Tacle 2.

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EMF 91 174tNP)

P8ge 11 TABLE 6.1 K. EFFECTIVE FOR HORMAL CONDITIONS CaseID Description k off.95 Vi l

4.4bnclR A 15x15 fuel assembly modeled as infinitely long 8985 and reflected en four sides with 30 cm of water.

Modelis used for comparisons and to show a single dropped buncle has acceptable reactMty.

4.4tntR1 An inf. x Inf. array of Infinitely long fuel 9006 assemblies in infinitely long NUS fuel storage racks.

4.41nf zR An Inf. x inf. array of 335 cm long fuel assemblies

.9053 in fuel storage racks. The neutron absorter plate tength is 339 cm. The top and bottom of the array is reflected with 30 crn of water.

4.4 fin 2R2 A 24x16 array of 335 cm long fuel assemblies in 9C91 fuel storage boxes. The neutron absorber plate length is 339 cm, All sides of the array are reflected by 30 cm of water.

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EMF.9 m 14(Np)

Page 12 6.2 Interaction The NUS fuel storage racks and the Westinghouse fuel storage racks are separated by a 2.00 inch water gap. Therefore, potential neutron interaction between the two racks wps analyzed. This analysis included modeling the entire spent fuel storage pool. The NUS racks were modeled as described in case 4.4 fin 2R2. The Westinghouse racks were medeled at nominal conditlens containing 15x15 fuel bundles. All positlens in the 15x15 fuel bunctes Aere assumed to contain fuel with 1.5 wt.% U 235. The entire fuel pool with a 2.0 inen water ;ao between the two racks was shown to have k eff =.905310037. This same model Mth a 6.0 inch water gap which essentially isolates the two racks has K-eff =.904610036. The difference between the two is 0,0007 and demonstrates that interaction between the two racks is negligible.

6.3 Abnormal Conditions 6.3.1 Seacina Given the arrangement of the spent fuel storage rack and the size cf the fuel bunc:es t

'3 t'ot possible for fuel bundles to be accidently placed in the water channels between the %el storage racks or between the racks and the concrete pool Walls.

The only abnormal spacing condition results from eccentric pcsitioning of :ne fuel assemblies in the fuel storage boxes. In order to eccentrically space the fuel assemblies in the fuel boxes, the four aligning pins on the bottom of the lower tie plate must be placed on the steel floor of the fusi stcruge bcx. Normally, these aligning pins fit into four 0,88 inch diameter notes in the cottom of the fuel storage bores. This type of misplacement of the fuel assembly causes the assembly to be elevated 1.47 inches. Although the length of the poison plates only exceeds the length of the active rod Mngth by 2.2 inches, elevating the fuel assembly by 1.47 inches dees not give the active portion of the fuel assemblies a line of sight path to other fuel assemblies without passing through a neutron absorber plate.

The worst case model for eccentric spacing was an Infinite x Infinite array of eccentncally spaced fuel assemblies. The fuel assembly in this model was placed at the lower left cerner of the fuel storage box with specular reflection placed around the fuel assemoly, Geff for in:s arrangement is.9131 at the 95/95 Upper Umit.

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EMF 91 17ANPi Page 13 4

6.3.2 Shifted Peisen P!ates The poison plates in the NUS rack could be shifted to one side instead of being centerec in the poison plate channel. This condition was modeled by creating an inifinite array of fuel storage boxes. The polson plates for each storage box were shifted to provide the maximum possible gap between the cates at two clagonal corners. For this arrangement, the 95i95 upcer limit of k.eff is.9080, 6.3.3 Drceced Fuel Bundle A dropped fuel bundle during fuel handling operations is also considered a croc;cle abnormal event. If a fuel bundle were dropped into the spent fuel tack and lay hon:enta;ly across the top of the. fuel storage rack, this bundle would be approximately seven inches acove the active portion of the fuel assemblies in Morage. Seven inenes of water separation. vill decouple the fuelin storage and the fuelin the dropped bundle. A single fuel buncle ref!actea on all sides by 30 cm of water has a 95/95 upper limit k eff =.8985. Pack cesign prevents a vertical fuel bundle from being placed outside of the fuel storage racks.

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EMF 91 174;Nc3 Pago 14 7.0 VAUDATION OF CALCULAT10NAL METHODS Supplemental benchmarking of the methods employed in the analysis was perferrred using experimental data with boron poison sheets in arrays of bundles. The experittents are described in References 7 and 8. The benchmark data are in Table 3.

Using the methods in Peference 9, the weighted average k ett and the stancard ceviat.cn of the bias were calculated:

Weighted average kaff: t.0035 Blas Standard Deviation: 0.00368 The weight cf each k ett value is proportional to the reciprocal cf its variance.

EMF 91 17 t(NP)

Page 15 TABLE 7.1 BENCHMARK CALCULATION RESULTS KENO.Va WITH 16 GROUP CROSS SECTIONS CASE No.

MLCULATED K.EFF REFERENCE 7 EXPERIMENTS i

-2378 1.00395 0.00376

_1 2384 1.00037 A 0.00306 l

2388 0.99886 0.00341 i

2420 1.00038 0.00367 2396 0.99443 0.00360 2402 1.00694 0.002S3 2411 1.01223 0.00266 2407 1.00647 0.00332 2414 1.00967 i 0.00327 REFERENCE 8 EXPERIMENTS l

9 1.00092 1 0.00487 10 1.00181 1 0.00412 I

11 0.99786 i 0.00413 12 0.99885 1 0.00487 31 1.00442 2 0.00421

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Page 16

8.0 REFERENCES

1.

Principal Reload Fuel Design Parameters Palisados Reload M. ANF49-063(P).

2.

Pallsades Facility Change F4ckage #FC 860.

3.

'CASMO 3: A Fuel Assembly Bumup Program (Methodology),' Studsvik/NFA 86,9, Studsvik Energiteknik AB, Nykoping, Sweden, November 1986.

4.

' SCALE: A Modular Code System for Performing Standardized Computer Analyses fer Ucensing Evaluation,' NUREG/CR 0200.

5.

Palisades Facility Change Package #FQ 375.

6.

" Palisades Nuclear Generating Station Spent Fuel Storage Pool Criticality Safety REANALYSIS." XN NF 542, May 1980.

7.

Baldwin, M. N., et.al.," Critical Experiments Supporting Close Proximity Water Storage of Power Reactor Fuel, 'BAW 1484 7, July 1979.

8.

Bierman, S. R., Durst, B. M., and Clayton, E. D., 'Cntical Separation between Suber:tical Clusters of 4.31% Enriched UO Reds in Water with Fixed Neutron Poisons.." NUREG,CR.

2 0073. May 1978.

9.

W. Marshall, P. D. Clemson, G. Walker, ' Criticality Safety..iteria," ANS Trans. 35, 278 (1980).

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EMF 91174(NP)

Issue Date:

'. 2 / C 9 / 91 CRmCALITY SAFETY ANALYSIS FOR THE P'ALISADES SPENT FUEL STORAGE POOL NUS RACKS DISTRIBUTION Consumers Power (5)

J. W. Hulsman C. D. Manning T. C. Probasco Occument Control (5) h

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