RRFM 2009 Transactions - European Nuclear Society

and longer fuel cycle length for UMo core (8.5 gU tot /cc) in comparison to the reference load
with standard BR2 fuel with mixed absorbers.
A preliminary choice was made to lump the new burnable absorber in 36 Cd wires
in the Al stiffeners of the fuel element. The optimum diameter for the different fuel types is as
follows: D=0.55 mm for HEU (1.3 gU tot /cc); D=0.4 to 0.5 mm for fuel type UMo (8.5 gU tot /cc);
D=0.4 mm for UMo (7.5 gU tot /cc).
The preliminary calculations of the axial distributions of the neutron fluxes for the
UMo core have shown a significant impact on the performance goals: reduction of the
thermal fluxes in the axis of the fuel channels (30 to 35%) and about 10% in the experimental
positions in reflector channels, which needs future optimization studies.
3. Sheathed Cd wires design and manufacturing
3.1 Sheathed Cd wires design
Following the conclusions of SCK●CEN concerning the replacement of the current poisons,
mixed in the fuel core, by cadmium wires in the stiffeners, two options were investigated by
AREVA-CERCA: sheathed or not sheathed cadmium wires. BR2 early decided to eliminate
the use of not sheathed cadmium wire: (i) cadmium is soluble in acid environment, (ii) reactor
water pool pH is slightly acid, (iii) cadmium solubility increases with temperature.
AREVA-CERCA studied different methods to sheath the cadmium wires: by coating or by
cadmium wire insertion into an aluminium sheath. As regard to the specification, the second
technical principle was selected as the most appropriated. This solution is already used since
years by some other customers. AREVA-CERCA masters this manufacturing and has a long
experience feedback.
3.2 Sheathed Cd wires manufacturing
The cadmium wires are inserted into an aluminium alloy sheath. End plugs made of the
same aluminium alloy close the both extremities in Fig 2.
Figure 2: Sheathed cadmium wire
Various inspections are performed:
- Leak-tightness test
- Dimensional inspection.
- Dimensions as well as the positioning of the cadmium inside the sheath.
- Cadmium integrity
- Visual inspection.
4. BR2 fuel element design and mechanical studies
A design study was performed to insert the cadmium wires in the stiffeners. In order to avoid
any major change on the fuel assembly or plate design, the following criteria have been
*AREVA-CERCA, a subsidiary of AREVA NP, an AREVA an SIEMENS company
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