ML20058N379

Criticality Safety Analyses:BU-7 Shipping Container for Below 5.0% Enriched UO2 Powder

ML20058N379
Person / Time
Site:	07109019
Issue date:	11/29/1993
From:	GENERAL ELECTRIC CO.
To:
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ML20058N366	List: ML20058N363 ML20058N375 ML20058N379 ML20058N382 ML20058N385
References
NUDOCS 9312210363
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Text

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'I APPENDIX C i

" CRITICALITY SAFETY ANALYSES:

BU-7 SHIPPING CONTAINER FOR BELOW S.0% ENICHED 00 POWDER" 2

]

NOVEMBER 29, 1993 o

1 l

9 LICENSE SNM-1097 DATE 12/03/93 PAGE DOCKET 71-9019 REVISION O

C 9312210363 931203 E

PDR ADOCK 07109019 b

C PDR ks

l Page I of 21 November 29,1993

\\

O Criticality Safety Analysis:

BU7 Shipping Container for Below 5.0% Enriched UO Powder 2

I I. INTRODUCTION Model BU-7 shipping containers are used by the General Electric Company for the transponation of low-enriched, unirradiated uranium dioxide powder. The BU-7 container is a Fissile Class I shipping package which is currently licensed for a maximum 235U enrichment of 5.0 %. The containers are restricted to two 5 gallon pails or three 3 gallon pails which are limited i

in mass of UO2 Powder per package. Each package is also limited in the amount of hydrogenous I

moderation that may be present in the fuel.

In this analysis for UO2 Powder er.riched below 5.0 %, the BU-7 container is demonstrated to comply with Fissile Class I requirements for conditions in which the inner containment vessel prevents water flooding under hypothetical accident conditions as specified in '

10CFR71.57. Each container is restricted to two safe batches of UO as shown in Table 24 for 2

enrichments from 3.0% to 5.0%. Safe batches range from 89.0 kg to 36.2 kg UO f

2 or these enrichments. The normal case restriction of the fuel contents to a H/U atomic ratio of 0.45 still applies, but the contents must be limited so that the total mass of hydrogenous moderator in the inner containment vessel is no greater than 1.5 % of the weight of the uranium dioxide.

i i

n

+

i

)

Page 2 of 21 November 29.1993 II. ANALYSIS A. BU-7 Container The BU-7 shipping container consists of a 55 gallon DOT Specification 17H outer drum 3

constructed of at least 18 gauge steel. The outer dmm contains 7-9 lb/ft fire-retardant phenolic resin insulation sandwiched between it and a 13.75 to 14.05 inch diameter by nominal 27 inch high inner drum. The inner drum (also described as the " inner containment vessel"), has a gasket and is sealed with a bolted metal lid to insure water tightness, and normally holds two 5 gallon pails or three 3 gallon pails. Figure 1 depicts the container with a cutaway section showing the internal container.

B. General Requirements for Fissile Class I Shipping Containers As specified in Parts 71.55 and 71.57 of Reference 2, the criticality safety requirements for a Fissile Class I shipping container are that subcriticality be maintained for the following:

1. Single Containers - with the most reactive credible configuration of the package and contents, including moderation by water, and assuming close reflection by water on all sides.

2. Infinite Arrays of Containers - undamaged, in any arrangement with optimum interspersed hydrogenous moderation.

3. Arrays of Damaged Containers - two hundred and fifty " damaged" containers stacked together in any arrangement, closely reflected on all sides by water and with optimum h

interspersed hydrogenous moderation. " Damaged" means in the condition resulting from being subjected to the " Hypothetical Accident Conditions" specified in Part 71.73 of the Rules and Regidations.

The " hypothetical accident conditions" tests were conducted for the BU-7 container and are reported in Referencc 3. The results of the tests have demonstrated that the BU-7 shipping container remains dry undir hypothetical accident conditions, with no intrusion of water into the inner containment vessel [3J. All cases treated in this analysis, however, conservatively assume at least 0.015 weight fraction H O present in the UO2 Powder. Under the accident conditions, the 2

UO2 Powder is assumed to remain in this " dry" state (i.e., the 0.45 H/U ratio and hydrogenous mass limits apply for both normal and accident conditions). In contrast, optimum moderation in the single container case is analyzed by mixing UO and some amount of water within the pails 2

and closely reflecting the fuel regions by full density water in all remaining void spaces (including regions outside the container).

Interspersed hydrogenous moderation is applied to all regions outside the pails, including the inner container and phenolic foam insulation. The phenolic foam insulation will also be considered to absorb water and will be treated as a region containing interspersed water.This treatment will enhance "close reflectien by water," as described above. Interspersed water in the 3

phenolic foam will be allowed vary between G and 100% of full density (1 gm/cm ).

The three or five gallon pails retain their integrity under all circumstances for the purposes g

of this analysis. For simplicity in modelling, the three and/or five gallon pails are conservatively

.~

Page 3 of 21 l

November 29,1993 O

i modelled as a single cylinder inside the inner containment vessel. UO2 Powder is allowed to fill this cylinder from the bottom up (there is no constraint on contents per pail for the purposes of this analysis). This also eliminates the steel of the pails between the regions containing the powder.

C. UO Powder and Water Mixtures 2

i For the present analysis, the contents of the container are taken to be uranium dioxide l

powder enriched up to 5.0% in U235, which is restricted in moderation to a H/U atomic ratio of 0.45. The fuel is modelled as UO2 and water and therefore applies to all uranium dioxide 3

powders having theoretical densities no greater than 10.96 g/cm Mixtures of fuel and water have been analyzed in the following manner. The mixture components are considered to occupy the minimum volume possible and have a maximum density.

A volume balance for the mixture can be written as UUO +VH O = P*##

(l) 2 2

or UO, H0 mix 3

Rearranging (2) gives an expression for the mixture density

- O 1

.(l - W F,o)

W F,o u

g (3) p,,,, = <

+

Puo, Pn,o t

where "WF" refers to the weight fraction (or mass fraction)

"H 0 3

W F,o = m

~

(A) g

+mH.0 UO.3 3

Multiplying the mixture density by a weight fraction gives a component density of that constituent. In this context," component" refers to treating the molecules or atoms of a substance

[

as spread over the larger volume of the mixture. The component density of a substance within a mixture is always less than the constituent theoretical density since the same mass (e.g., UO or l

2 water)is dispersed ever more volume.

For example, the maximum density mixture corresponding to 1.5% water (i.e., WFH2O =

3 3

3 This 0.015)is that with pmix = 9.535 g/cm, pUO2 = 9.392 g/cm, and pH2O = 0.143 g/cm mixture has an H/U atomic ratio of 0.45. The constituent densities are pUO2 (theoretical)= 10.96 3

3 g/cm and pH2O (theoretical)= 1.0 g/cm.

i Material atom densities are calculated from the mixture density by the standard formula:

.N p*4 '

O "x =

(5)

I i

e I -

Page 4 of 21 November 29.1993 A s Avogadro's number and M is the molecular weight of"x" in gm/ mole. Selected h

i where N x

atom densities are presented in Table 1.

Table 1. Sample Atom Densities for Maximum Density Mixtures of UO and H O 2

2 Enrichment WFH2O NU235 NU238 No NH

(%)

(atoms / barn cm)

(atoms / barn cm)

(atoms / barn cm)

(atoms / barn cm) 0.015 6.3645E-04 2.0319E-02 4.6696E-02 9.5704E-03 0.10 3.3482E-04 1.0689E-02 4.0418E-02 3.6741E-02 3.00 0.20 1.9854E-04 6.3385E-03 3.7584E-02 4.9020E-02 0.25 1.5957E-04 5.0994E-03 3.6774E-02 5.2532E-02 0.27 1.4693E-04 4.6908E-03 3.6511E-02 5.3671E-02 0.015 1.0607E-03 1.9900E-02 4.6706E-02 9.5704E-03 0.35 1.7932E-04 3.3640E-02 3.5695E-02 5.7216E-02 5.00 0.40 1.4898E-04 2.7949E-03 3.5316E-02 5.8856E-02 0.45 1.2416E-04 2.3293E-03 3.5006E-02 6.0198E-02 0.50 1.0347E-04 1.9412E-03 3.4748E-02 6.1317E-02 For full density water (pH2O = 1.00 g/cm ) NH = 6.6743E-02 atoms / barn cm and No =

g 3

3.3372E-02 atoms / barn-cm.

Partial density " interspersed moderation" atom densities are determined by taking the appropriate fraction of these values.

D. Materials of Construction The major constituents of the BU-7 container are the carbon steel dnims and phenolic foam insulation. Carbon steel has a density of 7.82 g/cm3 and its component atom densities are 3.921E-03 atoms / barn-cm for carbon and 8.3491E-02 for iron. Stainless steel, if used for construction, is a better neutron absorber than carbon steel. Thus, this analysis applies to BU-7 containers constructed of stainless steel as well as those constructed of carbon steel.

3 The phenolic resin foam used as insulation has a minimum density specification of 7 lb/fl 3

3 Since the phenolic resin foam contains bound hydrogen, boron and a (0.1146 g/cm ) gm/cm f rt bas o cri ic ity safet. I th s ana ys s, the density s c nserv tive y t ken a 0 o of he 3

minimum specification value, 0.0688 gm/cm The SP-9 phenolic foam contains several j

compounds; the resulting atomic densities are as described in Table 2.

Note that one of the constituents is boron. Therefore, in addition to the reduction of density, a minimum amount of boron is included in the model in the normal condition case. The nominal amount of boron called for by the SP-9 specification is 3 2% of the phenolic foam density. For the purposes of this analysis, only a very small fraction of the boron is required for the infmite array calculations. Of this nominal amount only 5% of the nominal boron fraction is used in the calculation. Therefore, i

3 of boron is used, hl combined with the reduction of density of the foam, a total of 0.00011 g/cm

t Page 5 of 21 November 29,1993 i

O 3

compared to a nominal boron density of 0.0022 g/cm. For the accident array and single container cases, it is conservatively assumed that no portion of the phenolic foam is present, but is replaced by optimum interspersed water. For the case of the single container, optimum is actually l

full density water as a reflector.

Table 2. Constituents of 60% Density Phenolic Resin in the BU-7 Container l

r i

Nuclide Nuclide number Density q

(atom /b-cm) l Boron-10 1.29375E-06 l

Boron-11 4.70584E-06 Carbon 1.38300E-03 l

Nitrogen -

3.1734E-05 Hydrogen

• 1.8084E-03 Oxygen

• 1.2306E-03

• These figures are for the hydrogen and oxygen normally contained in the phenolic resin foam.

The interspersed water is in addition to the indicated values.

j O

E. Analytical Method Neutron multiplication factor calculations in this criticality analysis have been performed with the GEMER Monte Carlo code [4]. GEhfER is a modified version of the Battelle Northwest Laboratory's BMC Monte Carlo code which has been combined with the geometry handling subroutines in KENO IV. Cross section sets in GEMER are processed from the ENDF/B IV j

library in 190 broadgroup and resonance parameter formats except for thermal scattering in water which is represented by the Haywood Kernel in the ENDF/B library. In GEMER, the resonance

}

parameters describe the cross sections in the resonance energy range and Monte Carlo sampling in this range is done from the resonance kernels rather than from the broad group cross sections.

Thus, there is a single, unique cross section set associated with each available isotope and dependence is not placed on Dancoff(flux shadowing) correction factors or effective scattering cross sections. The cross section library includes fission, capture, elastic, inelastic and (n,2n) i reactions. Absorption is implicitly treated by applying the non absorption probability to neutron weights at each collision point.

l GEMER's bias has been determined (from an extensive validation against critical j

experiments) to vary from +0.006 to -0.014 over the range of moderation in the fuel mixtures considered in this analysis. For under moderated mixtures with H/U atomic ratios less than about 5, the bias is positive denoting that neutron multiplication factors are over predicted. The bias.

then decreases almost linearly to -0.015 at an H/U ratio of about 25. These values span the range O

c nsidered for the BU-7 container since the highest degree of moderation (that for the UO and 2

H O mixture with a WFH2O of 0.40) corresponds to an H/U ratio of about 20. Since the bias i 2

'l

- 1

Page 6 of 21 November 29,1993 positive for H/U ratios less than 5, it can be ignored for the array calculations v.here the weight fn etion of water is limited to 0.015.

F. Modeling of Geometry The geometry model used in this analysis of the BU-7 container is illustrated in Figure 2 and the GEMER geometry input is tabulated in Tables 4 through 6. Tables 4 through 6 give the geometry inputs for the single container, infinite array and accident array cases, respectively.

These inputs resemble KENO input cards; as noted in the previous section GEMER utilizes the KENO IV geometry handling routines.

For the Single Container case, the BU-7's outer 55 gallon drum is tightly reflected on all sides by at least 31 cm of full demity water. Water is assumed to leak into the inner conteinment vessel to the extent of optimum moderation within the container. The BU-7 is modeled weh the 28.74 cm diameter inner pail filled with UO2 and water to the appropriate height (t a accommodate the volume of the mixture) The heights are determined by dividing the appliceble UO + H O mass by the product of the maximum mixture density and the pail's inside area. Only 2

2 interspersed water which is assumed o leak into the insulation regions is included in the calculations. Actual constituents of.ne phenolic foam insulation are conservatively omitted from the single container analysis.

In the case of an infinite artay of normal containers, BU-7 containers are closely packed in a triangular pitch array. The effect of the triangular array as it compares to the normal rectangular a

array is also examined. The model in Figure 2 is spatially reflected on all sides with varying W

amounts of interspersed water in the phenolic foam and in the regions outside of the outer container. The fue! mixture density is varied between the maximum fuel density and the minimum allowed by " smearing" the fuel mixture throughout the region dermed by the pails.

For the accident case of an array of accident condition containers, the array is modeled as an 9 x 7 x 4 triangular pitch array of BU-7 containers. The array is tightly reflected on all six sides by at least 31 cm of water. The 9 x 7 x 4 triangular array is the one having a minimum of at least 250 units (252 units). The array dimensions are those closest to a cube, which has the minimum geometrical buckling (most reactive configuration). Each BU-7 was modeled as in Figure 2 but with only interspersed water in the regions normally occupied by phenolic foam insulation. The constituents of the foam itself are conservatively not included in the calculations. The effect of smearing the mixture in the pail region is examined as it was for the normal condition arrays. The effect of the triangular array versus the rectangular array is also investigated.

i O'

Page 7 of 21 November 29,1993 O

Table 4 GEMER Geometry Model for Single Containers (GEMER Inputs) 1)

CYLINDER 1 14.370 XX.XX *

-35.05 16*0.5 2)

CYLINDER 2 14.371 35.05

-35.05 16*0.5 3)

CYLINDER. 3 14.420 35.10

-35.10 16*0.5 4)

CYLINDER 2 17.700 35.10

-35.10 16*0.5 5)

CYLINDER 3 17.808 35.5763

-35.2087 16*0.5 6)

CYLINDER 5 23.495 35.5763

-42.8287 16*0.5 7)

CYLINDER 2 23.4955 36.688

-42.8287 16*0.5 8)

CYLINDER 5 28.575 44.308

-42.8287 16*0.5 9)

CYLINDER 3 28.5755 44.4167

-42.9374 16*0.5 10)

CYLINDER 2 28.576 45.3692

-44.8424 16*0.5 11)

CYLINDER 3 28.684 45.3692

-44.8424 16*0.5 12)

CUBOID 4

59.471 -59.471 59.471 -59.471 76.3692 -75.8424 16*0.5 Notes:

Numbers 1 through 12 noted on the left are for information only and are not part of geometry input.

• Determined from the height of the fuel mixture.

Materials:

1 UO + H O 2

2 Q

2 Interspersed Water (1.0 weight fraction, i.e., full density) 1 3 Carbon Steel 4 Water Reflector (full density water) 5 Interspersed water (Full density water) r t

I O

i l'

Page 8 af 21 November 29,1993 Table 5 GEMER Geometry Model for an Infinite Triangular Array of Containers 1)

-1.0 -1.0 -1.0 -1.0 -1.0 -1.0 2)

BOX TYPE 1

3)

CYLINDER 1 14.370 XX.XX *

-35.05 16*0.5 4)

CYLINDER 2 14.371 35.05

-35.05 16*0.5 5)

CYLINDER 3 14.420 35.10

-35.10 16*0.5 6)

CYLINDER 2 17.700 35.10

-35.10 16*0.5 7)

CYLINDER 3 17.808 35.5763

-35.2087 16*0.5 8)

CYLINDER 5 23.495 35.5763

-42.8287 16*0.5 9)

CYLINDER 2 23.4955 36.688

-42.8287 16*0.5 10)

CYLINDER 5 28.575 44.308

-42.8287 16*0.5 11)

CYLINDER 3 28.5755 44.4167

-42.9374 16*0.5 12)

CYLINDER 2 28.576 45.3692

-44.8424 16*0.5 13)

CYLINDER 3 28.684 45.3692

-44.8424 16*0.5 14)

BOX TYPE 2

15)

CUBOlO 2

28.685 -28.685 28.685 -28.685 45.3692 -44.8424 16*0.5 16) 2 111 111 111 1 17)

BEGIN COMPLEX j

18)

COMPLEX 21

-28.684 -24.875 0.0 211 57.37 0.00.0 J

f 19)

COMPLEX 21 0.0 24.875 0.0 111 0.0 0.00.0 e!

Notes:

i Numbers 1 through 19 noted on the left are for information only and are not part of geometry input.

• Determined from the height of the fuel mixture.

UO + 0.015 WF H O Materials:

1 2

2 2 Interspersed Water (0 to 1.0 weight fraction) 3 Carbon Steel l

4 Full Density Water Reflector (not used in this calculation) 5 Phenolic foam + interspersed water O

Page 9 of 21 November 29,1993 O

i Table 6 GEMER Geometry Model for a Triangular Array of Damaged Containers 1)

BOX TYPE 1

2)

CYLINDER 1 14.370 XX.XX *

-35.05 16*0.5 3)

CYLINDER 2 14.371 35.05

-35.05

-16*0.5 4)

CYLINDER 3 14.420 35.?9

-35.10 16*0.5 5)

CYLINDER 2 17.700 35.10

-35.10 16*0.5 6)

CYLINDER 3 17.808 35.5763

-35.2087 16*0.5 7)

CYLINDER 5 23.495 35.5763

-42.8287 16*0.5 8)

CYLINDER 2 23.4955 36.688

-42.8287 16*0.5 l

9)

CYLINDER 5 28.575 44.308

-42.8287 16*0.5 10)

CYLINDER 3 28.5755 44.4167

-42.9374 16*0.5 1I)

CYLINDER 2 28.576 45.3692

-44.8424 16*0.5 12)

CYLINDER 3 28.684 45.3692

-44.8424 16*0.5 13)

BOX TYPE 2 14)

CUBOID 2

215.15 -215.15 227.7 -227.7 45.3692 -44.8424 16*0.5 15)

CORE O

215.15 -215.15 227.7 -227.7 181.4768 -179.3696 16*0.5

{

16)

CUBOID 4

245.63 -245.63 258.18 -258.18 212.0 -210.0 16*0.5 17) 2 111 111 141 1 18)

BEGIN COMPLEX 19)

COMPLEX 2 1 -186.465 -199.015 0.0 751 57.37 99.50 0.0 O

2o) cour'ex 2 i -257 78 -149 266 o o 7 4 i 57.37 99 5o o o 4

Notes:

Numbers 1 through 20 noted on the left are for information only and are not part of geometry input.

• Determined from the height of the fuel mixture.

Materials:

1 UO + 0.015 WF H O 2

2 2 Interspersed Water (0 to 1.0 weight fraction) 3 Carbon Steel 4 Full Density Water Reflector 5 Interspersed water r

O h

Page 10 of 21 1

November 29,1993 III. CRITICALITY SAFETY ANALYSIS RESULTS The following sections summarize the results of the GEMER calculations performed for the fuel mixtures and geometry models described in Section II. The results are all sufliciently suberitical.

A. Single Containers Tables 7 through 11 show k-effective values for various weight fractions of modentor (within the fuel / water mixture). Each table of results corresponds to the limiting mass / enrichment pairs. All of the results are sufficiently suberitical. The largest k-effective values (corresponding to l

optimum moderation) appear in boldface. The far right column contains keft plus 2 o less any 1

235 ratio [4]. No model bias that must be considered. Note that the bias varies with the H/U credit is taken for positive bias.

Table 7. GEMER Resulta for Single BU-7 Containers 36.2 kg U(5.00)O and 11 0 2

2 k r+ 2c - Bias WFH2O keff a

Bias ef 0.25 0.8706 0.00367

-0.0032 0.8812 0.30 0.9094 0.00389

-0.0058 0.9230 0.35 0.92503 0.0036

-0.0085 0.9407 g

0.40 0.92924 0.00240

-3.0113 0.9453 W

0.45 0.92603 0.00316

-0.0142 0.9465 0.50 0.91614 0.00311

-0.0171 0.9394 0.53 "

0.89706 0.00307

-0.0188 0.9220

• Neutron multiplication factors based on the fission particle flux method.

• Full container (i.e., the UO2 and water mixture is within I cm of the top of the pail region).

Increasing the weight fraction of water in the mixture results in reduced UO mass.

2 Table 8. GEMER Resulta for Single BU-7 Containers 40.4 kg U(4.60)O and 110 2

2 WFH2O keft c

Bias k y+ 2c - Bias ef 0.25 0.87418 0.0035

-0.0040 0.8852 0.30 0.90591 0.0039

-0.0067 0.9204 0 35 0.92544 0.00336

-0.0095 0.9417 0.40 0.92615 0.00348

-0.0124 0.9455 0.45 0.91843 0.003

-0.0154 0.9398 0.50 0.89607 0.00295

-0.0183 0.9202

• Neutron multiplication factors based on the fission particle flux method.

O,

Page 11 of 21 November 29,1993 O

Table 9. GEMER Resulta for Single BU-7 Containers 51.4 kg U(4.00)O and H O l

2 2

WFH2O keft a

Bias kefT+ 2e - Bias 0.25 0.88915 0.0037

-0.0055 0.9020 0.30 0.91176 0.00326

-0.0084 0.9267 0.35 0.91906 0.00315

-0.0114 0.9368 0.44 *

• 0.89259 0.00}01

-0.0168 0.9154 0.45 0.89021 0.0038

-0.0174 0.9144

• Neutron multiplication factors based on the fission pardcle flux method.

• • Full container (i.e., the UO2 and wate mixture is within I cm of the top of the pail).

I Increasing the weight fraction of water in de mixto results in reduced UO2 mass for the calculation.

Table 10. GEMER Result

• for Single BU-7 Containers 62.2 kg U(3.60)O and II 0 2

2 k y + 2o - Bias WFH2O keft a

Bias ef 0.20 0.87004 0.00335

-0.0036 0.8804 0.25 0.89798 0.00362

-0.0066 0.9119 0-0.30 0.90556 0.00297

-0.0097 0.9212 0.35 0.90744 0.00288

-0.0129 0.9261 0.39'

• 0.89243 0.00313

-0.0153 0.9140

• Neutron multiplication factors based on the fission particle flux method.

• Full container (i.e., the UO and water mixture is within I cm of the top of the pail). Increasing 2

the weight fraction of water in the mixture results in reduced UO mass for the calculation.

2 Table 11. GEMER Resulta for Single BU -7 Containers l

89.0 kg U(3.00)O and H O 2

2 WFH2O keft a

Bias keff + 2o - Bias 0.15 0.83598 0.00367

-0.0021 0.8455 0.20 0.87675 0.00385

-0.0055 0.8899 0.25 0.88804 0.00353

-0.0088 0.9039 1

I 0.29 a

• 0.8917 0.00302

-0.0115 0.9093

• Neutron multiplication factors based on the fission particle flux method.

)

• Full container (i.e., the UO and water mixture is within I cm of the top of the pail). Increasing 2

the weight fraction of water in the mixture results in reduced UO mass for the calculation.

2 O

Page 12 of 21 November 29,1993 B. Iniinite Array of Undamaged Containers Trbles 12 through 16 give results for the infinite triangular pitch array of BU-7 containers.

Table 12 shows kr versus the fraction ofinterspersed water for the 3.00 % enriched UO2 case (which includes 0.015 WF H O in the fuel). The results demonstrate that the case with 0.0 %

2 interspersed water is the most reactive materials in the BU-7 are more effective as absorbers when the neutrons are slowed down outside the region containing fuel. The remaining Tables 13 through 16 gives kx versus interspersed moderator density for the limiting cases of various other enrichment / mass loading pairs. The etTect of smearing the fuel throughout the pail region is also sown in these tables compared to the maximum mixture density configuration. The fully smeared cases (i.e., fuel occupying the entire pail region) are the most reactive condition since this maximizes the amount ofinteraction between the containers. Note that the model bias is positive for these cases (due to the small H/U ratio). No credit is taken for a positive bias, i.e., the bias is conservatively assumed to be zero. In all cases, the array remains sufficiently suberitical.

Table 17 gives the results for the infmite rectangular pitch array of BU-7 containers for the 5.00% enrichment case. Comparison with Table 16 shows that the effect of triangular pitch on the normal condition containers is relatively small.

Table 12. GEMER Results* for an Infinite Triangular Array of BU-7 Containers 89.0 kg U(3.00)O and 0.015 WF H O 2

2 Maximum Density Smeared Density Enrich-W F inter-keft a

kp*2a keft

• o ky 2c ef ef ment spersed

-bias

-bias HO 2

0.00 0.7276 0.00201 0.73162 0.88768 0.00179 0.89126 0.02 0.6361 0.00233 0.64076 0.88159 0.00235 0.88629 3.00 0.05 0.57933 0.00239 0.58411 0.82606 0.0021 0.83026 0.10 0.54663 0.00237 0.55137 0.70841 0.00235 0.71311 0.20 0.51352 0.00267 0.51886 0.55071 0.00222 0.55515

• Neutron multiplication factors based on the fission particle flux method.

I O:

i

Page 13 of 21 November 29,1993 O

Table 13. GEMER Results* for an Infinite Triangular Array of BU-7 Containers 62.2 kg U(3.60)O and 0.015 WF II 0 2

2 Maximum Density Smeared Density ky

• c keff* 2c Enrich-WF Inter-keff

• c k g* 2c ef e

ment spersed

-bias

-bias HO i

2 0.00 0.70581 0.00236 0.71053 0.89494 0.00164 0.89822 0.02 0.59765 0.00225 0.60215 0.87626 0.00197 0.8802 3.60 0.05 0.53034 0.0025 0.53534 0.80837 0.00221 0.81279 i

0.10 0.50541 0.00259 0.51059 0.69633 0.00259 0.70151 0.20 0.48129 0.00296 0.48721 0.53095 0.00299 0.53693

• Neutron multiplication factors based on the fission particle flux method.

Table 14. GEMER Results* for an Infinite Triangular Array of BU-7 Containers 51.4 kg U(4.00)O and 0.015 WF II 0 2

2 Maximum Density Smeared Density Enrich-WFInter-ky a

keft 2c keft a

keft 2c ef ment spersed

-bias

-bias HO 2

0.00 0.68454 0.00223 0.689 0.88861 0.00159 0.89179 0.02 0.57521 0.00238 0.57997 0.87169 0.00205 0.87579 4.00 0.05 0.50568 0.00251 0.5107 0.8011 0.00221 0.80552 0.10 0.47943 0.00226 0.48395 0.68607 0.00267 0.69141 0.20

'0.4681 0.00271 0.47352 0.52378 0.00266 0.5291

• Neutron multiplication factors based on the fission particle flux method.

[

O

Page 14 of 21 November 29.1993 Table 15. GEMER Results* for an Infinite Triangular Array of BU-7 Containers h

40.4 kg U(4.60)O and 0.015 WF II 0 2

2 l

Maximum Density Smeared Density kr*2a keft a

k r 2c Enrich-W F Inter-keft

• c ef ef ment spersed

-bias

-bias HO 2

l 0.00 0.66826 0.00229 0.67284 0.88588 0.00173 0.88934 l

0.02 0.54838 0.00243 0.55324 0.85983 0.00183 0.86349 4.60 0.05 0.47891 0.00283 0.48457 0.7867 0.00203 0.79076 0.10 0.45495 0.00245 0.45985 0.67446 0.00242 0.6793 0.20 0.44397 0.00254 0.44905 0.50835 0.00269 0.51373

• Neutron multiplication factors based on the fission particle flux method.

j Table 16. GEMER Results* for an Infinite Triangular Array of BU-7 Containers 36.2 kg U(5.00)O and 0.015 WF 1I 0 l

2 2

Maximum Density Smeared Density kr a

ky 2c j g

kr

+c keff 2c Enrich-W F inter-ef ef ef ment spersed

-bias

-bias HO 2

0.00 0.66025 0.00227 0.66479 0.88849 0.00164 0.89177 0.02 0.86055 0.00193 0.86441 5.00 0.05 0.78984 0.0021 0.79404

{

0.10 0.67547 0.00243 0.68033 l

0.20 0.50979 0.00269 0.51517

• Neutron multiplication factors based on the fission particle Oux method.

O

i Page 15 of 21 November 29,1993 O

Table 17. GEMER Results* for an Infinite Rectangular Array of BU-7 Containers 36.2 kg U(5.00)O and 0.015 WF II 0 2

2 Maximum Density Smeared Density kr*20 kr a

kr*2a Enrich-WF Inter-keff a

ef ef ef ment spersed

-bias

-bias H,0 0[00 0.61234 0.00246 0.61726 0.85407 0.00182 0.85771 0.02 0.48964 0.00239 0.49442 0.81308 0.0018 0.81668

)

5.00 0.05 0.41707 0.00211 0.42129 0.72549 0.00227 0.73003 0.10 0.38724 0.00259 0.39242 0.59464 0.00251 0.59966 0.20 0.37697 0.00252 0.38201 0.43115 0.00216 0.43547

• Neutron multiplication factors based on the fission particle flux method.

O l

l l

i 1

I i

{

O i

Page 16 of 21 November 29,1993 C. Triangular Array of Damaged Containers The analysis for the accident array is identical to analysis given in the previous section, except that (1) there are a finite number of BU-7 containers, and (2) the array of containers is closely reflected on all six sides by at least 31 cm of full density water. The phenolic resin insulation is replaced by interspersed water for this case. The spacing (pitch) of the containers and the treatment ofinterspersed moderation is identical to the infinite array problem. One might expect that neutron leakage from the finite array would reduce the effective multiplication factor relative to the intinite array case. This is demonstrated in Tables 18 through 22, which show k y ef versus the weight fraction ofinterspersed water for the various UO enrichment cases. The effect 2

of smearing the fuel throughout the pail region is shown to be the most reactive configuration for the accident condition array, as it was for the normal array. The effect, owever, is substantially reduced due to the leakage involved in the accident array.

Intermediate smearings (those in which the fuel is smeared only partially in the pail region, with a fuel height less than the full height of the inner container) result in intermediate values for k y. Other enriclunent/ mass pairs, ef which are less reactive in the infinite array case, are also less reactive in the 9 x 7 x 4 array c" Also, as explained in the previous section, the bias for these calculations is conservatively talu

.s zero. In all cases, the array remains sufficiently suberitical.

Table 23 shows the results for the rectangular pitch accident condition array for the 5.00%

enrichment, 36.2 kg UO2 case. Once again, the effect is relatively small when compared to the results in Table 18.

9:

Table 18. GEMER Results* for a 9 x 7 x 4 Triangular Array of BU-7 Containers 36.2 kg U(5.00)O and 0.015 WF II 0 2

2 Maximum Density Smeared Density ky*2a k y 2c keff a

Enrich-WF Inter-keff a

ef ef ment spersed

-bias

-bias HO 2

0.00 0.3272 0.00209 0.33138 0.37796 0.00228 0.38252 0.02 0.47654 0.00244 0.48142 5.00 0.05 0.65633 0.00258 0.66149 0.10 0.54835 0.0026 0.55355 0.20 0.35156 0.00247 0.3565 0.50 0.34532 0.00256 0.35044 1.00 0.36696 0.00256 0.37208

• Neutron multiplication factors based on the fission particle flux method.

O

Page 17 of 21 1

November 29,1993 O

Table 19. GEMER Results* for a 9 x 7 x 4 Triangular Array of BU-7 Containers 40.4 kg U(4.60)O and 0.015 WF H O 2

2 Maximum Density Smeared Density I

k r* 20 -

keft

• o kefy* 2a Enrich-W F Inter-keft a

ef ment spersed

-bias

-bias HO 2

0.00 0.33784 0.00225 0.34234 0.38383 0.00211 0.38805 0.02 0.3949 0.00248 0.39986 0.49083 0.00253 0.49589 4.60 0.05 0.42208 0.00265 0.42738 0.61702 0.00248 0.62198 0.10 0.37467 0.00241 0.37949 0.66334 0.00325 0.66984 0.20 0.34086 0.00244 0.34574 0.54689 0.00254 0.55197

• Neutron multiplication factors based on the fission particle flux method.

i Table 20. GEMER Results* for a 9 x 7 x 4 Triangular Array of BU-7 Containers 51.4 kg U(4.00)O and 0.015 WF H O 2

2 Maximum Density Smeared Density kr*2a keft a

k rr 2a Enrich-WF Inter-keft c

ef e

ment spersed

-bias

-bias HO 2

0.00 0.36576 0.00201 0.36978 0.40297 0.00221 0.40739 0.50559 0.00278 0.51115 0.02 0.63967 0.00305 0.64577 4.00 0.05 0.67002 0.0027 0.67542 0.10 0.56024 0.00273 0.5657 0.20 0.36832 0.00238 0.37308 0.50 0.36696 0.00256 0.37208 1.00

• Neutron multiplication factors based on the fission particle flux method.

O

Page 18 of 21 November 29,1993 Table 21. GEMER Results* for a 9 x 7 x 4 Triangular Array of BU-7 Containers h

62.2 kg U(3.60)O and 0.015 WF H O 2

2 Maximum Density Smeared Density k r 2o kp*2a keft a

ky

• o Enrich-WFInter-ef ef ef ment spersed

-bias

-bias HO 2

0.00 0.38941 0.00209 0.39359 0.42242 0.00223 0.42688 0.02 0.44762 0 00255 0.45272 0.52551 0.00219 0.52989 3.60 0.05 0.4673 0.00262 0.47254 0.64386 0.00262 0.6491 0.10 0.42973 0.00229 0.43431 0.68045 0.0027 0.68585 0.20 0.37943 0.00252 0.38447 0.57298 0.00292 0.57882

• Neutron multiplication factors based on the fission particle flux method.

Table 22. GEMER Results* for a 9 x 7 x 4 Triangular Array of BU-7 Containers 89.0 kg U(3.00)O and 0.015 WF II 0 2

2 Maximum Density Smeared Density Enrich-W F Inter-kefT

+o kefT 2a kefT o

keff

• 2a ment spersed

-bias

-bias l I

HO 2

0.00 0.43807 0.00211 0.44229 0.45534 0.00241 0.46016 0.02 0.49361 0.00264 0.49889 0.55644 0.00226 0.56096 3.00 0.05 0.51614 0.00283 0.5218 0.67426 0.00302 0.6803 0.10 0.47595 0.00248 0.48091 0.70858 0.00266 0.7139 0.20 0.42825 0.00247 0.43319 0.58818 0.00282 0.59382

• Neutron multiplication factors based on the fission particle flux method.

9,

i Page 19 of 21 November 29,1993 O

Table 23. GEMER Results* for a 9 x 7 x 4 Rectangular Array of BU-7 Containers 36.2 kg U(5.00)O and 0.015 WF H O 2

2 Maximum Density Smeared Density kr*2a keft a

kr*2a Enrich-WFInter-keft a

ef ef ment spersed

-bias

-bias 14 0 2

0.00 0.32277 0.00204 0.32685 0.38455 0.00237 0.38929 0.02 0.48644 0.00274 0.49192 5.00 0.05 0.6064 0.00234 0.61108-

' O.10 0.625 0.00294 0.63088 0.20 0.49338 0.00236 0.4981

• Neutron multiplication factors based on the fission particle flux method.

D. Presence of Plastic Bags or Other Moderating Materials Around the UO (or UO2 2

Containers)

It is sometimes desirable to ship UO enclosed in plastic bags in the BU-7 container. The 2

O dess may be around the fuel either inside or outside of the three or five gallon pails. For the BU-7 container with the contents and assumptions described in the previous sections of this report, the presence of these bags is acceptable. Analyses for similar containers have demonstrated that the results are not affected by including the plastic bags in the mass of moderating materials [5]. These analyses show that there is no difference between including the amount of hydrogenous material within the fuel (as assumed in the present analysis) and distributing a portion of that materirJ around the periphery of the fuel region. There is no statistical difference between results which include the plastic bags as explicitly modeled moderating material regions and results that do not.

Therefore, as long as the total H/U ratio remains below 0.45, the presence of the plastic bags is acceptable.

IV.

SUMMARY

AND CONCLUSION The containers have been shown safe by restricting the mass loading of each caontainer to two safe batches for enrichments from 3.0% to 5.0%. Safe batch limits in this range are smoothly varying functions of enrichment. As shown in this analysis, the most reactive cases in the BU-7 configurations depend on the case being analyzed: 3.0% enrichment for the accident array and 5.0% enrichment for the single container case. The normal condition infinite array is relatively insensitive to the enrichment.

O

Page 20 of 21 November 29,1993 This analysis has demonstrated that the BU-7 shipping container meets the requirements of 10CFR71.55 and 57 for a Fissile Class I package with contents specified as follows:

Type and Form The BU-7 may contain uranium dioxide powder enriched to not more than 5.0 wt/o in the U-235 isotope with the maximum H/U atomic ratio not exceeding 0.45. The mass of moderating materials within the inner container when added to the total mass of hydrogenous moderator within the fuel shall not exceed 1.5% of the mass of the fuel and moderator.

Maximum Ouantity per Packace The maximum contents per package shall be as specified below (Table 24).

Table 24. UO Mass Limits Versus Enrichment 2

Maximum Allowable Maximum UO Mass Loading 2

Enrichment (%)

(kg) 3.00 89.0 3.20 77.8 3.40 69.2 3.60 62.2 3.80 56.6 4.00 51.4 4.20 47.4 4.40 43.8 4.60 40.4 4.80 38.2 5.00 36.2 1

)

I

^ Page 21 of 21 November 29,1993 O

V. REFERENCES i

1. "U.S. Nuclear Regulatory Commission "Cenificate of Compliance for Radioactive

. Materials Packages," Certificate Number 9019, Revision 19.

2. " Packaging and Transportation ofRadioactive Material," United States Nuclear Regulatory Conunission Rules and Regulations, Title 10, Chapter 1, Pan 71, Code of Federal Regulations.

3. " Test Report for Model BU-7 Bulk Uranium Shipping Container," 4/25/80.

4. GEMER/ MONTE CARLO (GEMER.4), User's Manual, November 1990.

5. " Criticality Safety Analysis: BU-7 Shipping Container for Below 5.0% Enriched UO2 Powder with failure of Containment and Moderation Control", August 31,1993.

i 1

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APPENDIX D THIS APPENDIX HAS BEEN LEFT BLANK INTENTIONALLY O

P W

LICENSE SNM-1097 DATE 12/03/93 PAGE DOCKET 71-9019 REVISION O

D