Calculating Fission Cross-Sections for Nuclear Reactor Fuel Designs

In summary, the 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 and a fuel rod OD of 0.916cm with a clad thickness of 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. Assuming no fuel-cladding gap and 4.5% enrichment, the reactor pressure and temperature conditions are 15.5MPa and 304C. To determine the fission cross-sections for each lattice design, one
  • #1
TebatsoM
2
0
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?
 
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  • #2
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
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
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 %).
 
  • #5


To determine the fission cross-sections for each lattice design, we can use the equation:

σ = Nσ₀ / N₀

Where σ is the fission cross-section, N is the number density of nuclei, σ₀ is the total nuclear cross-section, and N₀ is the number density of target nuclei.

First, we need to calculate the number density of nuclei for each fuel assembly design. This can be done by considering the fuel enrichment level and the dimensions of the fuel rods. Since both designs have the same fuel enrichment level of 4.5%, we can assume that the number density of nuclei is the same for both designs. However, we need to take into account the different dimensions of the fuel rods.

For the current design, the fuel rod pitch is 1.215cm and the fuel rod OD is 0.916cm. This means that the volume of each fuel rod is (π/4)*(0.916cm)^2*(1.215cm) = 0.998 cm³. Since the fuel is 4.5% enriched, the number density of nuclei is 0.045*6.022*10²³/0.998 = 2.71*10²¹ nuclei/cm³.

For the new design, the fuel rod pitch is 1.232cm and the fuel rod OD is 0.882cm. This means that the volume of each fuel rod is (π/4)*(0.882cm)^2*(1.232cm) = 0.966 cm³. Using the same calculation as before, the number density of nuclei for the new design is 2.60*10²¹ nuclei/cm³.

Next, we need to calculate the total nuclear cross-section (σ₀) for each design. This value can be obtained from nuclear data tables or calculated using nuclear models. It takes into account the probability of a fission reaction occurring when a neutron interacts with a nucleus.

Finally, we can use the equation mentioned above to calculate the fission cross-section for each design. This will give us a numerical value that represents the likelihood of a fission reaction occurring in each fuel assembly design. The higher the fission cross-section, the more efficient the fuel will be in producing energy in the reactor.

In conclusion, to determine the fission cross-sections for each lattice design, we need to calculate the number density of nuclei and the total nuclear cross
 

What is a nuclear reactor?

A nuclear reactor is a device that uses nuclear reactions to generate heat, which is then used to create steam that turns turbines to produce electricity.

What is the purpose of nuclear reactor design?

The purpose of nuclear reactor design is to create a safe, efficient, and reliable system for generating electricity through nuclear reactions.

What are the main components of a nuclear reactor?

The main components of a nuclear reactor include the fuel, control rods, coolant, moderator, and the reactor vessel. These components work together to sustain and control the nuclear reactions.

What safety measures are taken in nuclear reactor design?

Nuclear reactor design includes numerous safety measures such as multiple layers of containment, emergency shutdown systems, and strict regulations and protocols for operation and maintenance. These measures are in place to prevent any accidents or releases of radioactive materials.

What are the different types of nuclear reactors?

There are several types of nuclear reactors, including pressurized water reactors, boiling water reactors, and advanced reactors such as molten salt reactors and fast reactors. Each type has its own unique design and features.

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