Porous plenum spacer for dual-cooled fuel rod

A porous plenum spacer for a dual-cooled fuel rod, in which the porous plenum spacer and a plenum spring are inserted into a plenum of the dual-cooled fuel rod having concentric inner and outer cladding tubes, the porous plenum spacer comprising:

• a hollow cylindrical body inserted into an annular space between the inner and outer cladding tubes;
• and
• a plurality of through-holes formed in an outer circumference of the hollow cylindrical body,
• wherein the porous plenum spacer has a length subtracting a length of the plenum spring from a previously determined length of the plenum, and
• the plenum spring includes a coil spring having an effective number N of spring coils and satisfying a formula below:
• N
• =
• G
• 8
• ·
• D
• 3
• ·
• K
• ·
• d
• 4
• where G is the shear modulus, D is the average diameter of the spring, K is the spring constant, and d is the diameter of the spring wire.

A porous plenum spacer for a dual-cooled fuel rod, in which the porous plenum spacer and a plenum spring are inserted into a plenum of the dual-cooled fuel rod having concentric inner and outer cladding tubes, the porous plenum spacer comprising:

• a hollow cylindrical body inserted into an annular space between the inner and outer cladding tubes;
• and
• at least one groove formed in one of outer and inner circumferences of the hollow cylindrical body in a lengthwise direction of the hollow cylindrical body,
• wherein the porous plenum spacer has a length gotten by subtracting a length of the plenum spring from a previously determined length of the plenum, and
• the plenum spring includes a coil spring having an effective number N of spring coils and satisfying a formula below:
• N
• =
• G
• 8
• ·
• D
• 3
• ·
• K
• ·
• d
• 4
• where G is the shear modulus, D is the average diameter of the spring, K is the spring constant, and d is the diameter of the spring wire.

A porous plenum spacer for a dual-cooled fuel rod, in which the porous plenum spacer and a plenum spring are inserted into a plenum of the dual-cooled fuel rod having concentric inner and outer cladding tubes, the porous plenum spacer comprising:

• a hollow cylindrical body inserted into an annular space between the inner and outer cladding tubes;
• and
• a combination of at least one selected from a first unit spacer that has a plurality of through-holes formed in an outer circumference of a hollow cylindrical body thereof, a second unit spacer that has at least one groove formed in one of outer and inner circumferences of the hollow cylindrical body of the first unit spacer in a lengthwise direction, and a third unit spacer that has at least one groove in the outer or inner circumference of a hollow cylindrical body thereof in a lengthwise direction,
• wherein an overall length of the combination of the unit spacers is gotten by subtracting a length of the plenum spring from a previously determined length of the plenum, and
• the plenum spring includes a coil spring having an effective number N of spring coils and satisfying a formula below:
• N
• =
• G
• 8
• ·
• D
• 3
• ·
• K
• ·
• d
• 4
• where G is the shear modulus, D is the average diameter of the spring, K is the spring constant, and d is the diameter of the spring wire.