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XYLENE POWER LTD.

FNR FUEL BUNDLE

By Charles Rhodes, P.Eng., Ph.D.

INTRODUCTION:
A Fast Neutron Reactor (FNR) is made modular and economic through the use of hundreds of identical truck transportable fuel bundles. A practical 1000 MWt fast neutron reactor is an assembly of 640 active fuel bundles which are surrounded on their outer perimeter by 446 passive fuel bundles for a total of 1086 fuel bundles. Each fuel bundle weighs several tonnes and an active fuel bundle is transported in a lead container weighing ~ 50 tonnes.

Each passive fuel bundle is a module 0.4 m long X 0.4 m wide X 9 m high. A passive fuel bundle contains a 0.4 m wide X 0.4 m deep X 6.0 m high assembly of vertical closed end 0.500 inch OD steel fuel tubes that is totally replaced when the contained fuel is reprocessed. Below the fuel tubes are 4 X ~3 m high corner support legs.

Each asseembled active fuel bundle is a module 0.4 m long X 0.4 m wide X 12 m high. A fuel bundle contains a 0.4 m wide X 0.4 m deep X 6.0 m high assembly of vertical closed end 0.500 inch OD steel fuel tubes that is totally replaced when the contained fuel is reprocessed. Above the fuel tubes is a 0.4 m long X 0.4 m wide X 3.0 m high square sheet metal chimney which also acts as an indicator tube guide. Below the fuel tubes are 4 X ~3 m high corner support legs. For ease of transportation the chimneys and indicator tubes are attached on the reactor site.

Spent active fuel bundles may serve as outer ring passive fuel bundles while they are held in liquid sodium storage to permit fission products to naturally decay.
 

CHIMNEY AND INDICATOR TUBE:
A fuel bundle chimney isolates an active fuel bundle's hot liquid sodium discharge from the surrounding cooler liquid sodium. This isolation enhances the vertical flow of liquid sodium through the active fuel bundle and assists in accurate measurement of an active fuel bundle's discharge temperature and gamma ray emission by stabilizing and guiding the indicator tube. The indicator tube has slightly positive buoyancy so that when part of it is projecting above the liquid sodium surface it maintians a firm connection to the active fuel bundle control portion.
 

FUEL BUNDLE LEGS:
The fuel bundle support legs maintain sufficient distance separation between the fuel bundle and the bottom of the sodium pool to ensure that there is no long term deterioration of the stainless steel pool bottom liner due to neutron absorption. These legs also maintain separation between the fuel tubes and the hydraulic actuator which extends the working life of the active fuel bundle hydraulic actuators. These legs also allow free circulation of liquid sodium beneath the fuel tubes.
 

FUEL TUBES:
The fuel tubes are positioned on a horizontal square grid which is (5 / 8) inch center to center. This grid is square to ensure sufficient primary liquid sodium natural circulation in the presence of 15% linear fuel tube swelling. The fuel tube height is set by FNR design calculations relating to the core height, blanket thickness and plenum height. The fuel tube OD and length are in part constrained by material availability. The fuel tube center to center distance in the fuel tube bundle was found by itterative liquid sodium flow and fuel reactivity calculations. The number of tubes in a fuel bundle is set by weight constraints relating to practical road transport of highly radioactive fuel bundles in lead containers of sufficient wall thickness for certain biosafety.

The fuel tube bottom plugs have tapered bottom tips for easy downward vertical fuel tube insertion into the fuel bundle. The fuel tube bottom plugs also have cross cuts for mating with the fuel bundle bottom grating. The fuel tube top plugs have indentations and faces to allow easy grasping for controlled insertion, rotation or withdrawal of each individual fuel tube.
 

MECHANICAL CONSIDERATIONS:
A major issue in fuel bundle design is mechanical stability and rigidity because the rigid fuel bundle assembly height (9 m) is much greater than its width (0.4 m). thr rigid portion of a fuel bundle is about 22X as high as it is wide or long. Hence, the mechanical engineering and stabilization of fuel bundles is important to ensure that during fabrication, transport, installation and operation they do not bend, warp or otherwise deform. Such bending or warping could cause a jam in the sliding of the active fuel bundle control portion within its surround portion.

A fuel bundle has outside corner girder extensions which serve as support legs, lifting points and chimney corner fastenings. On installation the corner girders are further stabilized at the junction with the chimneys by clips to adjacent fuel bundles and at the bottom by the fuel bundle support tubes. In operation part of an active fuel bundle's weight is borne by the hydraulic actuator that positions the fuel bundle control portion.

The fuel tube spacing is maintained using horizontal (1 / 16) inch diameter steel rods that run between the fuel tubes at about 0.8 m, 2.0 m, 4.0 m and 6.0 m from the fuel tube bottom. The (1 / 16) inch diameter east-west rods are sufficiently vertically separated from the (1 / 16) inch diameter north-south rods to avoid obstructing the upward primary liquid sodium flow.

The fuel bundle mechanical design must allow for longitudinal swelling of the steel components of the fuel bundle that are exposed to fast neutrons. For example the shroud sheets must be designed so that they can expand in overall width and length without buckling and without their edges going outside their supporting girder corners.
 

NUCLEAR DESCRIPTION:
A practical FNR consists of a 0.35 m high pancake shaped core completely surrounded by 1.6 m thick blanket. The Pu-239 fission chain reaction occurs in the core. Excess neutrons originating in the core are absorbed by U-238 in the blanket. The core and blanket vertical thicknesses are set by fuel rod lengths.

Each active fuel bundle consists of a control portion and a surround portion. A key issue in fuel bundle design is that every fuel bundle must remain subcritical, regardless of its control portion position, if its four nearest neighbour fuel bundles have their control portions fully withdrawn. This fuel bundle design constraint enables safe fuel bundle transport and safe reactor assembly/disassembly and ensures the independent operation of two fully redundant FNR shutdown systems.

An active fuel bundle contains 476 vertical active fuel tubes. Each active fuel tube contains one core fuel rod where nuclear fission occurs. Each active fuel tube also contains 3 X 0..533 m blanket fuel rods above the core fuel rod and 3 X 0.533 m blanket fuel rods below the core fuel rod. About 99.75% ???? of the excess neutrons emitted by the reactor core are by the reactor blanket.

A passive fuel bundle contains 556 vertical passive fuel tubes. Each passive fuel tube contains 7 X 0.533 m blanket fuel rods which absorb neutrons.
 

DEFINITIONS:
Active fuel tube: contains 6 X 0..533 m long blanket fuel rods plus 1 X 0.35 m long core fuel rod plus liquid sodium.

Passive fuel tube:
contains 7 X 0.533 m long blanket fuel rods plus liquid sodium

Active Fuel bundle:
Consists of a vertically sliding control portion with 244 active fuel tubes + fixed position surround portion with 232 active fuel tubes. The side walls of each portion are enclosed by (1 / 16) inch thick sheet steel shroud walls to exclude particulate matter.

Passive Fuel Bundle:
Contains a fixed position fuel bundle with 556 passive fuel tubes

Active fuel bundle control portion:
Is vertically sliding protion of an active fuel bundle which is used to set the fuel bundle discharge temperature. The control portion withdraws about 1.0 m below the fuel bundle to cause a reactor cold shutdown. The control portion consists of 244 active fuel tubes, 4 shroud panels, 4 corner girders about 6 m long, (1 / 16) inch diameter spacer rods, control portion bottom grating, control portion bottom filter, push rod assembly, indicator tube attachment.

Active fuel bundle surround portion:
Is fixed position portion of an active fuel bundle consisting of 232 active fuel tubes, four outside corner girders 9 m long, four inside corner girders 6 m long, 8 shroud panels, surround portion bottom grating, surround portion bottom filter, (1 / 16) inch diameter spacer rods

A control portion hydraulic actuator consists of a 1.4 m long hydraulic cylinder 10.75 inch OD + piston + 1.6 m push rod moves active fuel bundle control portion up and down, is located in bottom 1.4 m of the fuel bundle support tube.

Fuel bundle support tube:
12 inch X 12 inch X 2 m long square tube, supports either active fuel bundle surround portion or passive fuel bundle in correct fixed position and contains the hydraulic actuator for the active fuel bundle control portion. Has a fitting that mates the hydraulic actuator with the corresponding hydraulic pressure line.
 

FUEL BUNDLE DETAIL:
Each active fuel bundle consists of a central (16 tube position X 16 tube position) control portion of a (24 tube position X 24 tube position) fuel bundle. Each active fuel bundle has a dedicated control portion hydraulic actuator which can move the control portion up and down with respect to the surround portion over a travel distance of 1.2 m. Each active fuel bundle surround portion has a maximum outside horizontal length allocation including swelling and thermal expansion allowance of 0.400 m (15.748 inch) and a maximum horizontal width allocation of 0.400 m (15.748 inch).

The nuclear fission reactions take place within the core rods of the active fuel bundles. Each fuel bundle in plan view is square and contains:
24 X 24 = 576 potential fuel tube positions. The fuel tubes are positioned on a square grid with (5 / 8) inch center to center spacing. However the (4 X 5) = 20 outer corner fuel tube positions are required for the surround portion outer corner girders, and (4 X 3) fuel tube positions are required for control portion outer corner girders. The interior shrouds and slide space take up 68 tube positions between the two portions leaving:
576 - 20 - 68 - 12 = 476
actual active fuel tubes per active fuel bundle.

The nominal face to face size of a fuel bundle is:
(24 tubes X (5 / 8 ) inch / tube) + 4 (1 / 16) inch = 15.25 inch

Note that the maximum fuel bundle face to face dimension is:
0.400 m = 0.400 m / (.0254 m / inch) = 15.748 inch
so that there is:
15.748 inch - 15.250 inch = 0.498 inch
available to accommodate the combination of differential thermal expansion, material swelling and fabrication tolerances.

Note that the fuel bundle mounting rack on the bottom of the primary liquid sodium pool will also expand with increasing temperature. It is likely to be 100 degrees C cooler than the top of the fuel bundle. Hence the differential thermal expansion per fuel bundle is approximately:
20 ppm / deg C X 100 deg C X 15.25 inch = 30.5 X 10^-3 inch = 0.03 inch

The fuel tube bundles are designed so that individual fuel tubes can linearly swell without the external length or width of the fuel bundle materially changing. Fuel bundles are intended to be replaced after 15% linear swelling of the most intensely neutron irradiated fuel tube sections. The fuel tube array center-to-center spacing is established by the bottom grating and the (1 / 16) inch diameter spacer rods that are located out of the main fast neutron flux and hence are protected from fast neutron induced swelling.
 

ACTIVE FUEL BUNDLE PLAN VIEW:


 

INDICATOR TUBES:
Each active fuel bundle has an add-on indicator tube that projects 0.3 m to 1.5 m abouve the surface of the primary liquid sodium. The indicator tube and chimney are connected to the active fuel bundle while the fuel bundle is being installed and are removed before the fuel bundle is relocated.

The indicator tube is sufficiently buoyant to keep it upright, shows the actual vertical position of the the active fuel bundle control portion, allows measurement of gamma flux from the fuel bundle and allows measurement of fuel bundle discharge temperature. This temperature is indicated by a Bourdon tube. The Bourdon tube has an attached mirror that reflects a laser beam. The reflected beam forms a spot. The position of that spot moves with the internal pressure in the Bourdon tube. That pressure is the vapor pressure of the stable internal temperature sensing liquid such as mercury.
 

INDEPENDENT FUEL BUNDLES:
In plan view each fuel bundle is a 24 X 24 array containing 576 theoretical fuel tube positions. Inside the active fuel bundle surround portion is the sliding fuel bundle control portion which is a 16 X 16 array containing 256 theoretical fuel tube positions.

In plan view each active fuel bundle consists of a 15.25 inch X 15.25 inch fixed surround portion containing 232 active fuel tubes and a 10.25 inch X 10.25 inch square fuel bundle control portion containing 244 active fuel tubes. The reactivity and hence the discharge temperature of an active fuel bundle is determined by the distance of insertion of its control portion into its surround portion.

In plan view each passive fuel bundle is a 15.25 inch X 15.25 inch square containing:
576 - 4(5) = 556 passive fuel tubes. Since there is little heat released by the passive fuel tubes there is little liquid sodium natural circulation past these passive fuel tubes.

The outer corner girders of every fuel bundle extend downwards ~ 3 m below the bottom of the fuel bundle fixed support grid and are outside the 12 inch X 12 inch square fuel bundle support tubes. The upper corners of these same girders extend up a few inches to provide lifting points for fuel bundle installation and removal, to support the chimney corners and to allow up to four adjacent fuel bundles to be clipped together for mechanical stability.
 

PLAN VIEW CROSS SECTION:
At the outer corners of every fuel bundle are 4 outer corner girders, each of which occupies 5 fuel tube positions. At the inner corners of the fuel bundle surround portion are four inner corner girders each of which occupies 3 fuel tube positions within a lost ring of 68 theoretical fuel tube positions.

At the outer corners of the active fuel bundle control portion are 4 corner girders each of which occupies 3 fuel tube positions. Between the control portion and the surround portion is a ring of 68 lost fuel tube positions.

Hence the active fuel bundle surround portion contains:
576 - 4(5) - 68 - 256 = 232 real fuel tubes
and the active fuel bundle control portion contains:
256 - 4(3) = 244 real fuel tubes.

Thus the total number of fuel tubes per active fuel bundle is: (232 + 244) = 476

The outside of the fuel bundle control portion has dimensions of:
{[16 (5 / 8)] inch + 4 X (1 / 16) inch} X {[16 (5 / 8)] inch + 4 (1 / 16) inch} = 10.25 inch X 10.25 inch.

Supported by the outer corner girders of the fuel bundle surround portion is the shroud which has a thickness of (1 / 16) ????? inch. The shroud must have large filtered triangular openings in the reactor core region to allow for shroud material swelling due to the high fast neutron flux. The shroud sheets provide fuel bundle diagonal structural stability.

In normal reactor operation the fuel bundle control portions insert into the fuel bundle surround portions from the bottom of the surround portions. When all the fuel bundle control portions are fully inserted into the fuel bundle surround portions the reactor is at maximum power and should provide a liquid sodium discharge temperature of over 440 degrees C. When the fuel bundle control portions are 1.2 m withdrawn from the surround portions the reactor must be subcritical. The fuel bundle geometry limits the range of acceptable Pu concentrations in the fuel rods.

From a power control perspective each fuel bundle can almost be regarded as an independent FNR. Each fuel bundle has its own discharge temperature which is determined in part by the extent of insertion of the fuel bundle control portion into the fuel bundle surround portion. Under cold shutdown conditions gravity causes a fuel bundle control portion to withdraw 1.2 m with respect to its fuel bundle surround portion.

The outer corner girders on the fuel bundle control portion and the inner corner girders on the fuel bundle surround portion are each about 6 m long to act as slide guides for the fuel bundle control portion. There are mechanical stops that prevent the fuel bundle control portion travelling either too far up or too far down.

The outer corner girders of the fuel bundle surround portion transfer the weight of the fuel bundle onto the 12 inch X 12 inch X 0.5 inch X ~2 m tall support tubes. These support tubes stop 1 m below the tube bundle surround portion to allow liquid sodium to easily flow into the bottom of the fuel tube assembly and to prevent fast neutron damage to the fuel bundle support tubes.

When the fuel bundle control portions are fully inserted into the fuel bundle surround portions there is a ~1 m high nearly open space under the fuel bundle assembly that allows both horizontal and vertical liquid sodium circulation.

Inside the 12 inch X 12 inch X 0.50 inch support tube is a hydraulic actuator formed from a 1.5 m length of 10.75 inch OD steel pipe with an internal piston. This actuator has a permitted piston travel of 1.2 m and is used to position the active fuel bundle control portion within the active fuel bundle surround portion.

The extent of insertion of the active fuel bundle control portion into the corresponding surround portion is determined by the volume of liquid sodium inside the hydraulic actuator. There is fluid pressure feedback relating to the approximate fuel bundle control portion position due to the buoyancy of the indicator tube. The hydraulic fluid feed tube is routed through the 12 inch X 12 inch horizontal steel tube on the bottom of the primary sodium pool. Small holes are cut in this horizontal 12 inch X 12 inch steel tube to allow hydraulic tube connection to the hydraulic cylinders. In the event of a hydraulic cylinder jam an entire line of such hydraulic cylinders extending half way across the pool must be removed and replaced.

There is a 1.6 m high push rod from the piston to the bottom of the active fuel bundle control portion. The piston has sealing piston rings similar to those in a diesel engine.

At the bottom of the active fuel bundle control portion corner girders is a connection to the hydraulic cylinder piston push rod. The actuator piston has a tapered bottom for easy blind insertion into the 10.75 inch OD, 9.75 inch ID X 1.5 m high steel pipe that acts as a hydraulic cylinder. This hydraulic cylinder is located inside the 12 inch X 12 inch X 0.5 inch X 2 m square support tube. As the active fuel bundle control portion withdraws more than 1 m from the surround portion its corner girders sink into the 12 inch X 12 inch support tube. To cause the active fuel bundle control portion to insert into the surround portion liquid sodium at up to 60 psi is injected under the hydraulic piston which gives up to 4700 lb of lifting force to raise the fuel bundle control portion. If the piston lifts too high the high pressure liquid sodium behind the piston is released into the primary sodium pool via a vent hole in the hydraulic cylinder side wall. This arrangement acts as a certain upper limit to the piston travel. An orifice located on each high pressure sodium feed tube limits the rate at which an active fuel bundle control portion can insert into the corresponding surround portion. Note that the active fuel bundle emergency hydraulic drain valve is not orifice restricted.

The corners of the 12 inch X 12 inch X 0.5 inch X 2 m support tubes are fitted with slide guides that mate with a lower extensions of the fuel bundle outer corner girders. These slide guides are tapered at their tops to allow practical blind mating. These slide guides are vertically short to allow liquid sodium to easily circulate in the lower 2 m of height under the tube bundle.

The support tubes are welded to horizontal 14 inch X 6 inch X 0.625 inch horizontal structural steel tubes each of which supports a line of up to 18 12 inch X 12 inch X 2 m support tubes that are spaced at 0.400 m intervals. Of these 18 support tubes up to 14 of them support active fuel bundles. The horizontal 14 inch X 6 inch X 0.625 inch tubes are themselves spaced 0.400 m center to center. This center to center spacing is set by spacers between the horizontal tubes. The spacers must be securely fastened to give the whole assembly of fuel tubes structural stability in a earthquake. Of particular concern is torque about the axes of the horizontal 14 inch X 6 inch X 0.625 inch structural steel tubes.

There are 7.5 m high closed end indicator tubes field attached to the active fuel bundle control portions. The vertical position of each active fuel bundle control portion is indicated by the height of the top of its indicator tube.

The thermal power output from a fuel bundle is proportional to the gamma flux propagating up its closed end indicator tube.

The fuel bundle discharge temperature is indicated by the mercury vapor pressure inside the closed end indicator tube.
 

FUEL BUNDLE FILTERS:
At the bottom of each active fuel bundle are two filters, one for the control portion and one for the surround portion. The purpose of these filters is to prevent foreign particulate matter suspended in the primary liquid sodium from blocking the cooling flow channels between adjacent fuel tubes. These filters must completely block flow of any particulate matter with any dimension greater than (1 / 32) inch. Similar filters are installed at the bottom of passive fuel bundles. The perforated plate filter material is mounted at a 60 degree angle to increase its area and hence its open area. For the active fuel bundle control portion the diagonals from the push rod double as filter material supports.

Downstream from the filter material is a void space that allows redistribution of primary sodium flow in the event that a filter is partially obstructed. Every practical means should be used to keep foreign material out of the primary sodium pool. The bottom of the pool must be kept above 320 degrees C to prevent NaOH precipitation. In the event that a filter is partially plugged the liquid sodium circulation will decrease causing the fuel bundles gamma/neutron output to fall, while maintaining the fuel bundle discharge temperature, indicating a problem with flow obstruction of that fuel bundle.
 

FUEL TUBE BUNDLE DIMENSIONS:
The fuel tube bundle frame and shroud are fabricated from HT-9 steel (85% Fe, 12% Cr, 3% other, 0% C, 0% Ni).

The height allowances for the main fuel bundle components from bottom to top are: support tube (2.0 m), contained hydraulic actuator 1.5 m, active fuel bundle control portion travel = 1.2 m, bottom grating (0.1 m), fuel tubes (6 m), indicator tube (7.5m).

The active fuel bundle surround portion length and width are:
24 X (5 / 8) inch + 4 (1 / 16) inch = 15.25 inch

The fuel tube height of 6 m is limited by availability of 0.500 inch OD X 0.065 inch wall thickness steel tube

The fuel bundle length and width are limited by the weight of the lead shielded container needed to move a fuel bundle by truck. In that truck the fuel bundle and its transportation container are supported at an angle to ensure that the fuel rods and liquid sodium remain at the bottom of the fuel bundle. This bottom should be supported by the back wheels of the truck. It is contemplated that the truck trailer will have 3 rows of four back wheels so as to be rated for 3 axels X 4 wheels / axel X 5 tons per wheel = 60 tons. The truck trailer may have two additional forward wheels to assist with steering.
 

ACTIVE FUEL BUNDLE DESIGN:
Each fuel bundle surround portion is structurally stabilized by its rigid outer corner angle girders. These angle girders are each:
(15 / 8) inches X (15 / 8) inches X (3 / 8) inches X 9 m. The cross sectional area of each of these angle girders is:
[ 81 / 64] inch^2
Twenty outer corner fuel tube positions on the fuel bundle surround portion are lost due to the four outer corner girders.

Each active fuel bundle surround portion is further structurally stabilized by its rigid inner corner angle girders. These girders are each:
(17 / 16) inch X (17 / 16) inch X (1 / 4) inch X 6 m. The cross sectional area of each of these girders is:
(15 / 32) inch^2. The cross sectional area of each of these inner corner girders is:
(7 / 8) inch^2.
Sixty-eight fuel tube positions are lost to the four inner corner girders and the gap between the active fuel bundle surround portion and the active fuel bundle control portion.

Each active fuel bundle control portion is structurally stabilized by its rigid corner girders. These girders are each:
(5 / 4) inch X (5 / 4) inch X (3 / 8) inch. The cross sectional area of each of these girders is:
(51 / 64) inch^2.
Twelve fuel tube positions are lost to these four control portion girders.

Hence, each active fuel tube bundle actually contains:
24^2 - 4(5) - 68 - 4(3) = 576 - 100
= 476 real fuel tube positions
 

PASSIVE FUEL BUNDLES:
In order to achieve fuel bundle interchangability the passive fuel bundles are made and installed in the same manner as the active fuel bundles, except there is no middle portion cut out.

Each passive fuel tube bundle actually contains:
24^2 - 4(5) = 576 - 20
= 556 real fuel tube positions
 

FUEL BUNDLE SUPPORT GRATINGS:
The fuel tubes are held in position by the steel grating at the bottom of each fuel bundle. The gratings transfer the weight of the fuel tubes onto the fuel bundle outer corner girders. It is of paramount importance that the gratings and their support welds never structurally fail. Hence every fully fabricated grating must be tested at 3X its normal maximum load.

The bottom steel grating of a fuel bundle is composed of 48 pieces of .125 inch X 4.0 inch X 15.000 inch steel, for a total volume of:
48 pieces / bundle X .125 inch X 4.0 inch X 15.000 inch = 360.0 inch^3

Of this amount the grating metal volume used on the fuel bundle control portion is:
32 pieces / bundle X .125 inch X 4.0 inch X 10.000 inch = 160.0 inch^3

Hence the grating metal volume on the fuel bundle surround portion is:
360.0 inch^3 - 160.0 inch^3 = 200 inch^3

The mass of the active fuel bundle control portion grating is:
160.0 inch^3 X (0.0254 m / inch)^3 X 7.870 X 1000 kg / m^3 = 20.6345 kg

The mass of each active fuel bundle surround portion gratings is:
200 inch^3 X (0.0254 m / inch)^3 X 7.870 X 1000 kg / m^3 = 25.793 kg

The mass of each passive fuel bundle grating is:
360 inch^3 X (0.0254 m / inch)^3 X 7.870 X 1000 kg / m^3 = 46.428 kg

Between the active fuel bundle control portion and the active fuel bundle surround portion is a (3 / 8) inch gap that reduces to (1 / 8) inch gap at the corners to provide reliable sliding clearance.

Note that the passive fuel bundle bottom grating must transfer the weight of 556 loaded fuel tubes onto the outer corner girders.

The active fuel bundle control portion bottom grating must transfer the weight of 244 loaded fuel tubes onto its outer corner girders and hence to the actuator piston while still permiting unobstructed primary liquid sodium flow.

The diagonals connecting each indicator tube push connection to the corresponding active fuel bundle control portion corner girders must also allow easy primary liquid sodium flow.

The diagonals connecting the piston push rod to the active fuel bundle control portion must also allow easy primary liquid sodium flow.

The 12 inch X 12 inch X 0.5 inch X 2 m support tubes are welded to the steel floor frame. The 10.75 inch OD X 1.5 m hydraulic cylinder fits inside the bottom of the 12 inch X 12 inch X 2 m support tube. There are 8 tapered slide guides welded onto the outside corners of the 12 inch X 12 inch X 2 m support tube. The tapers assist in blind fuel bundle positioning. Each support tube also has 4 precisely positioned welded corner girder stops that support the entire weight of the fuel bundle. There is a backup steel plate that protects the primary sodium pool liner from being punched by a fuel bundle corner girder.

There is a piston that slides within the 10.75 inch OD X 1.5 m hydraulic cylinder to cause insertion of the active fuel bundle control portion into the corresponding surround portion.

Forming the outer shroud on the fuel bundle are 4 X ~ (1 / 16) inch thick steel sheets 15 inches X 240 inches for a volume of:
4 X 15 inch X 240 inch X (1 inch / 16) X (.0254 m / inch)^3 = 0.014748 m^3

The mass of this outer shroud cover per fuel bundle is:
+ (0.014748 m^3) X 7.870 X 1000 kg / m^3
= 116.06 kg

FIXED TO HERE CALCULATE THE WEIGHTS OF THE OTHER SHROUD PLATES

There are 4 fuel bundle surround portion outer corner angle girders, each with a cross sectional area of 9 (49) / 256 = 1.7266 inch^2:
4 X (1.7226 inch^2) X 12 m X (.0254 m / inch)^2 X 7.874 X 10^3 kg / m^3
= 420.05 kg

There are 4 fuel bundle surround portion inner corner angle girders each with a cross sectional area of (7 / 8) inch^2:
4 X (7 / 8) inch^2 X 6 m X (.0254 m / inch)^2 X 7.874 X 10^3 kg / m^3
= 106.68 kg

From FNR Fuel Tubes each active fuel tube has a mass of 6.53 kg.
 

CHIMNEY:
A chimney is 3 m high. It attaches to the four main corner girders by a sliding fit inside the tops of those girders. The chimney has four light corner girders and two sets of diagonal cross pieces that provide a sliding guides for the chimney's indicator tube. These guides keep the indicator tube centered in the chimney.

TOTAL FUEL BUNDLE SURROUND PORTION MASS
232 loaded fuel tubes + 1 surround bundle gratings + 4 fuel bundle surround portion outer corner girders + 4 fuel bundle surround portion inner corner girders + shroud outer cover + shroud inner cover
= 232 (6.53 kg) + 25.763 kg + 315.04 kg + 106.68 kg + 58.03 kg + 38.69 kg
= 1875.81 kgFIX
 

FUEL BUNDLE CONTROL PORTION:
Note that the buoyancy of the indicator tube must not be sufficient to lift the weight of the fuel bundle control portion when it is immersed in liquid sodium.
Indicator Tube: 5.563 inch OD X 0.258 inch wall X 4.5 m long
Mass = Pi X 5.563 inch X 0.258 inch X 4.5 m X (.0254 m / inch)^2 X 7.874 X 10^3 kg / m^3
= 103.074 kg

(Consider use of thinner wall material)

Control bundle corner girders:
4 X (7 / 8) inch^2 X 7 m X (0.0254 m / inch)^2 X 7.874 X 10^3 kg / m^3
= 124.46 kg
 

There are cross pieces that serve to move the Indicator Tube up and down. These cross pieces must be attached after fuel tube insertion. Indicator tube pushing cross pieces:
Volume = 4 X 0.5 inch^2 X 30 inch = 60 inch^3 ????

Mass of indicator tube diagonal connectors = 60.0 inch^3 X (0.0254 m / inch)^3 X 7.874 X 10^3 kg / m^3
= 7.742 kg ?????

Active fuel bundle control portion bottom plate:
10 inch X 10 inc X 0.5 inch X (.0254 m / inch)^3 X 7.874 X 10^3 kg / m^3 = 6.451 kg

Active fuel bundle piston rod (push pipe):
Pi X 5.563 inch OD X 0.258 inch wall X 1.0 m long X (0.0254 m / inch)^2 X 7.874 X 10^3 kg / m^3
= 22.905 kg
 

TOTAL MASS OF FUEL BUNDLE CONTROL PORTION:
244 loaded fuel tubes + 2 control portion gratings + 4 control bundle corner girders + indicator tube + indicator tube diagonals + control portion bottom plate + piston push rod
= 244 (6.53 kg) + 41.269 kg + 124.46 kg + 103.074 kg + 7.746 kg + 6.451 kg + 22.905 kg
= 1705.98 kg
FIX  

TOTAL ACTIVE FUEL BUNDLE MASS:
Surround bundle + control bundle
= 1875.81 kg + 1705.98 kg
= 3582.2 kg
FIX  

PASSIVE FUEL BUNDLES:
In order to achieve fuel bundle interchangability the passive fuel bundles are made and installed in the same manner as the active fuel bundles.
 

SUPPORT ASSEMBLY MASS:
The mass of each complete fuel bundle assembly is significant. The major mass components consist of:

Support Tube 12 inch X 12 inch X 0.500 inch wall X 2.0 m long
Mass = (12^2 - 11^2) inch^2 X 2.0 m X (.0254 m / inch)^2 X 7.874 X 10^3 kg / m^3
= 233.673 kg

Support tube wings:
Each support tube has 4 welded wings 3.74 inch long X 1.5 m high X 0.5 inch thick which stabilize the support tube against adjacent support tubes. The wings are located slightly off center so that adjacent wings overlap and are bolted together to give the assembly overall structure stability.

The minimum support tube wing mass is:
4 X 3.74 inch X 0.5 inch X 1.5 m X (0.0254 m / inch)^2 X 7.874 X 10^3 kg / m^3
= 56.997 kg

Guides:
There are 8 guides to contol the sliding fit of the surround bundle outer corner girders over the support tube. Each guide is an L shaped piece 1 inch thick X 2 inches X 3 inches.

Guide Mass = 8 X 3 inch^2 X 3 inch long X (.0254 m / inch)^3 X 7.874 X 10^3 kg / m^3
= 9.29 kg

Hydraulic Cylinder:
Mass = Pi (10.750^2 - 9.759^2) inch^2 / 4 X 1 m X (.0254 m / inch)^2 X 7.874 X 10^3 kg / m^3
= 81.79 kg

Hydraulic cylinder bottom disk:
Mass = Pi (9.750 inch / 2)^2 X 0.5 inch X (.0254 m / inch)^3 X 7.874 X 10^3 kg / m^3
= 4.8168 kg

Piston:
Piston Mass = Pi (9.750 inch / 2)^2 X 3 inch X (.0254 m / inch)^3 X 7.874 X 10^3 kg / m^3
= 28.91 kg
 

BASE:
The 12 inch X 12 inch X 0.5 inch support tubes are welded to a base made from 14 inch X 6 inch X 5 / 8 inch rectangular tube. Note that access holes are cut into the base material to allow running 14 hydraulic lines per base tube. The support tubes are spaced 0.400 m center to center using 1.748 inch spacers and connected to vertical members at the pool walls.

Base mass = 0.4 m X 40 inch X (5 / 8) inch X (.0254 m / inch)^2 X 7.874 X 10^3 kg / m^3
= 50.800 kg
 

OUTSIDE CORNER GIRDER STOPS:
The outside corner girder stops transfer the weight of the fuel bundle from the outside corner girders onto the horizontal 14 inch X 6 inch X (5 / 8) inch tubes.
 

SUPPORT SYSTEM MASS PER ACTIVE FUEL BUNDLE:
Mass of support = base + support tube + support tube wings + 8 guides + Hydraulic cylinder + hydraulic cylinder bottom + Piston + surround bundle girder stops
= 50.800 kg + 233.67 kg + 56.997 kg + 9.29 kg + 81.79 kg + 4.8168 kg + 28.91 kg kg + 7.45 kg + 10.83 kg
= 483.92 kg
 

TOTAL MASS PER FUEL BUNDLE OF CONTROL PORTION + SURROUND PORTION + SUPPORT:
Surround bundle + Control Bundle + support
= 1875.81 kg + 1683.486 kg + 483.92 kg
= 4043.216 kg FIX
 

The reactor floor load not including the liquid sodium is about:
[4043.216 kg X 1 pound /0.454 kg] / [14 inch X 15 inch] = 42.41 psi
 

FIX

ULTRASONIC IMAGING SYSTEM:
A very important accessory requird for installation and removal of fuel bundles is an ultrasonic imaging system that allows the gantry crane operator to "see" inside the liquid sodium pool. This imaging system is required to accurately position the fuel bundles, to seal the connection between the hydraulic line and the active fuel bundle control portion actuator, to add and remove the indicator tube, to hook onto the fuel bundle for lifting and to address other mechanical issues under the liquid sodium surface. When performing these operations the liquid sodium should be cooled to about 120 degrees C to minimize thermal stress on the ultrasonic imaging apparatus.
 

FUEL BUNDLE LIFTING:
The lifting points for a fuel bundle are loops attached to the outer corner girders of the surround portion.
 

INDICATOR TUBE ATTACHMENT:
Indicator tubes are attached to the control portion of a fuel bundle after it is installed and are removed before the fuel bundle is relocated. The attachment point is central between the control portion corner girders. Once an indicator tube is in place its corresponding square sliding float is slipped over it. The indicator tube should be thin wall to remain buoyant to keep it upright. The indicator tube diameter should be minimal to minimize obstruction of liquid sodium flow.
 

ACTIVE FUEL BUNDLE STEEL CROSS SECTIONAL AREA:
An important parameter is the steel cross sectional area in an active fuel bundle near the core zone. Fuel Tubes:
476 tubes X Pi (0.25^2 - (0.25 -0.062)^2) inch^2
= 476 tubes X Pi (0.0625 - 0.035344) inch^2
= 40.609 inch^2

Surround portion outer shroud:
4 X (1 / 16) inch X 15 inch = 3.75 inch^2

Surround Portion Inner shroud:
4 X (1 / 16) inch X 11.25 inch = 2.8125 inch^2

Control Portion outer shroud:
4 X (1 / 16) inch X 10 inch = 2.5 inch^2

Surround portion outer corner girders:
4 X 5 X (5 / 8) inch X (1 / 2) inch = 6.25 inch^2

Control portion outer corner girders:
4 X 3 X (5 / 8) inch X (1 / 2) inch = 3.75 inch^2

Corner guides:
8 X 9 X (1 / 8) X (1 / 8) = 1.125 inch^2
 

TOTAL STEEL CROSS SECTIONAL AREA IN CORE ZONE:
40.609 inch^2 + 3.75 inch^2 + 2.8125 inch^2 + 2.5 inch^2 + 6.25 inch^2 + 3.75 inch^2 + 1.125 inch^2
= 60.7965 in^2
= 0.03922347 m^2 = 24.51%
 

ACTIVE FUEL BUNDLE CORE FUEL CROSS SECTIONAL AREA:
476 core rods X Pi (4.04 mm)^2 X 1 m^2 / 10^6 mm^2 = 0.024407 m^2 = 15.25% core fuel area
 

TOTAL CROSS SECTIONAL AREA:
0.4 m X 0.4 m = 0.16 m^2 = 100% of fuel bundle area
 

ACTIVE FUEL BUNDLE SODIUM CROSS SECTIONAL AREA:
0.16 m^2 - 0.024407 m^2 - 0.03922347 m^2 = 0.09636953 m^2 = 60.23% liquid sodium area
 

These values are important in evaluating the nuclear reactivity in the core zone.

CALCULATE THE AVERAGE ELEMENTAL MASS / UNIT VOLUME IN BLANKET:
Na =
Fe =
Cr =
U =
Zr =

CALCULATE THE AVERAGE ELEMENTAL MASS / UNIT VOLUME IN ACTIVE FUEL BUNDLES:
Na =
Fe =
Cr =
U =
Zr =

This web page last updated December 26, 2018

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