Nuclear fuel assembly

Claim 2

A fuel assembly for use with a plurality of fuel assemblies and a neutron moderator in a nuclear reactor core, said fuel assembly comprising: a plurality of elongated fuel elements arranged in spaced array, including a first group of a plurality of said fuel elements containing initial fissile plutonium and a second group of a plurality of said fuel elements wherein the initial fissile fuel therein consists of enriched fissile uranium; an elongated continuous hollow tube positioned within said first group of fuel elements; means for directing a flow of said moderator into said tube; means for discharging said moderator from said tube; a plurality of fuel element spacers in axially spaced positions for laterally supporting said fuel elements, and spacer capture means comprising a plurality of axially spaced lugs fixed to said tube for engaging said spacers to retain said spacers in said axially spaced positions.

Claim 3

The fuel assembly of claim 1 wherein said tube is of substantially the same outside diameter as said fuel elements.

Claim 4

The fuel assembly of claim 1 wherein said means for discharging said moderator from said tube consists of apertures in one-half the length of said tube.

Claim 5

The fuel assembly of claim 1 wherein said spacers are formed with passages for said lugs whereby said spacers are axially movable along said tube to said axially spaced positions when said tube is in a first angular position with respect to said spacers.

Claim 6

The fuel assembly of claim 4 further including releasable means to prevent rotation of said tube to retain said tube in a second angular position with respect to said spacers wherein said lugs engage said spacers to retain said spacers in said axially spaced positions.

Claim 7

A nuclear fuel assembly comprising: a plurality of nuclear fuel elements; a support means including an upper tie plate and a lower tie plate providing a plurality of support positions to support said fuel elements in spaced array; an elongated continuous hollow tube supported in one of said support positions; means for directing a flow of a neutron moderator into said tube; means for discharging said moderator from said tube; a plurality of axially spaced spacers for laterally supporting said fuel elements and said tube; spacer capture means fixed to said tube, said spacer capture means being effective in a first angular position of said tube with respect to said spacers to allow axial movement of said spacers along said tube and being effective in a second angular position of said tube with respect to said spacers to engage said spacers to prevent substantial axial displacement of said spacers along said tube; an end member fixed to one end of said tube; a cavity in one of said tie plates for receiving said end member; and means formed in said cavity for engaging said end member to retain said tube in said second angular position.

Claim 8

A nuclear fuel assembly comprising: a plurality of nuclear fuel elements; a support means including an upper tie plate and a lower tie plate providing a plurality of support positions to support said fuel elements in spaced array; an elongated continuous hollow tube supported in one of said support positions; means for directing a flow of a neutron moderator into said tube; means for discharging said moderator from said tube; a plurality of axially spaced spacers for laterally supporting said fuel elements and said tube; spacer capture means fixed to said tube, said spacer capture means being effective in a first angular position of said tube with respect to said spacers to allow axial movement of said spacers along said tube and being effective in a second angular position of said tube with respect to said spacers to engage said spacers to prevent substantial axial displacement of said spacers along said tube; an end member fixed to one end of said tube; a cavity in one of said tie plates for receiving said end member; and means formed in said cavity for engaging said end member to retain said tube in said second angular position.

Claim 9

The fuel assembly of claim 6 wherein said tube is of substantially the same outside diameter as said fuel elements.

Claim 10

The fuel assembly of claim 6 wherein said means for discharging said moderator from said tube comprises apertures in the upper half of said tube.

Claim 11

The fuel assembly of claim 6 wherein said spacer capture means includes a plurality of axially spaced lugs fixed to said tube for engaging said spacers.

Claim 12

The fuel assembly of claim 6 wherein said end member comprises an end plug of square cross section fixed to said tube and wherein said cavity is formed with a mating square socket.

Claim 13

The fuel assembly of claim 6 wherein said tube includes end plugs at each end and wherein said end plugs are formed with moderator passages for admitting moderator into and discharging moderator from said tube.

Claim 14

A fuel assembly for use with a plurality of fuel assemblies and a neutron moderator in a nuclear reactor core, said fuel assembly comprising: spaced upper and lower tie plates having fuel element support means forming a plurality of fuel element positions; a plurality of first fuel elements in central ones of said fuel element positions to form a central cluster, said first fuel elements containing initial fissile plutonium; a plurality of second fuel elements in fuel element positions surrounding said central cluster, the initial fissile fuel in said second fuel elements consisting of fissile uranium; an elongated continuous hollow tube in one of said fuel element positions within said central cluster; means forming an entrance for moderator into said tube; means forming an outlet for moderator from within said tube; a plurality of fuel element spacers at intermediate positions between said tie plates; and spacer capture means including a plurality of axially spaced lugs fixed to said tube for engaging said spacers to retain said spacers at said intermediate positions.

Claim 15

A fuel assembly for use with a plurality of fuel assemblies and a neutron moderator in a nuclear reactor core, said fuel assembly comprising: spaced upper and lower tie plates having fuel element support means forming a plurality of fuel element positions; a plurality of first fuel elements in central ones of said fuel element positions to form a central cluster, said first fuel elements containing initial fissile plutonium; a plurality of second fuel elements in fuel element positions surrounding said central cluster, the initial fissile fuel in said second fuel elements consisting of fissile uranium; an elongated continuous hollow tube in one of said fuel element positions within said central cluster; means forming an entrance for moderator into said tube; means forming an outlet for moderator from within said tube; a plurality of fuel element spacers at intermediate positions between said tie plates; and spacer capture means including a plurality of axially spaced lugs fixed to said tube for engaging said spacers to retain said spacers at said intermediate positions.

Claim 16

The fuel assembly of claim 12 wherein said tube is of substantially the same outside diameter as said fuel elements.

Claim 17

The fuel assembly of claim 12 including two of said hollow tubes within said cluster.

Claim 18

The fuel assembly of claim 14 wherein at least one of said tubes is interchangeable with at least some of said fuel elements in said support means.

Claim 19

The fuel assembly of claim 12 wherein one of said fuel elements contains a burnable poison.

Claim 20

The fuel assembly of claim 12 wherein said means forming an outlet for said moderator comprises apertures in the upper half of said tube.

Claim 21

The fuel assembly of claim 12 wherein a first plurality of said fuel elements are secured to said tie plates and wherein said hollow tube and a second plurality of said fuel elements are resiliently supported between said tie plates.

Claim 22

The fuel assembly of claim 12 wherein said spacer is formed with a passage for said lug whereby said spacer is axially movable along said tube to said intermediate position when said tube is in a first angular position with respect to said spacer.

Claim 23

The fuel assembly of claim 19 further including releasable anti rotation means to prevent rotation of said tube to retain said tube in a second angulAr position with respect to said spacer wherein said lug engages said spacer to retain said spacer in said intermediate position.

Claim 24

The fuel assembly of claim 20 wherein said anti rotation means includes a lower end plug of square cross section fixed to said tube and mating square socket in said lower tie plate.