Calculating Fission Cross-Sections for Nuclear Reactor Fuel Designs

[TebatsoM]

A utility is considering changing its fuel vendor and resulting fuel assembly design. The
current fuel in the reactor is standard Westinghouse 17x17 fuel with a fuel rod pitch of
1.215cm fuel rod OD of 0.916cm. The clad thickness is 0.055cm. The new fuel design has a
fuel rod pitch of 1.232cm and a fuel rod OD of 0.882cm with a clad thickness of 0.055cm. (Assume that there is no fuel-cladding gap).
Considering that the fuel for both designs is 4.5% enriched, and that the reactor pressure
and temperature conditions are 15.5MPa, and 304C

How to determine the fission cross-sections for each lattice design?

 

[Astronuc]

This seems like a homework problem.

The pitch of a standard 17x17 design is 1.26 cm (12.6 mm) or 0.496 inch - at room temperature, or about 1.263 cm at hot conditions.

How does one determine the cross-section of any lattice? What does the lattice cell look like?

Is the assembly envelope the same?

Is one accounting for guide (thimble) tubes?

 

[TebatsoM]

Given all this information how does one solve the problem and is it necessary to more assumptions if the info provided is not enough?

Yes this part of assignment

 

[Astronuc]

Presumably one's class notes and/or textbook would explain the methods used to determine cross-sections, which I take to mean either macroscopic cross-sections, or the weighted (equivalent, or adjsusted) microscopic cross-sections.

Self-shielding is an important factor, as is competition for neutrons among the different materials, as is the energy spectum of the neutrons.

Think about fuel-to-moderator ratio.

Consider infinite lattice, and whether or not one assumes homogenous or heterogeneous composition of the fuel-moderator. I expect one can assume Zircaloy-4 cladding (Zr-1.5Sn-0.24Fe-0.12Cr-0.125O, where the coefficients are in weight %).