# Nuclear Reactor Design

1. Aug 25, 2010

### 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?

2. Aug 25, 2010

### Astronuc

Staff Emeritus
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?

3. Aug 25, 2010

### 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

4. Aug 25, 2010

### Astronuc

Staff Emeritus
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 %).