Coolant Mass Flow Rate Through Subchannel in Nuclear Fuel Assembly

[a1234]

I am trying to find the mass flow rate of coolant through a channel within a hexagonal nuclear fuel assembly. I am given the specific heat of the fluid, the coolant inlet and outlet temperatures, the total power produced by a single fuel pin, the diameter of the fuel pin, the length of the fuel pin, and the fuel pitch. I am told that the power follows a cosine shape axially.

I am trying to incorporate this information into q = m*cp*deltaT, but the power "seen" by one coolant channel is not the same as the total power produced by one pin. How can I find the power that is part of one coolant channel (or one "unit cell") within a hexagonal assembly using the given information?

 

[Astronuc]

We, if the fuel rods have the same enrichment and neutron flux, then the power, or heat flux, would be the same at the same axial elevation. On the other hand, fuel assemblies can have substantial flux/power gradients laterally across a given axial elevation.

If one is modeling a hexagonal lattice, then one can look at a triangular control volume with 1/6 of a fuel rods at each vertex of the cell. Otherwise, one observes 6 subchannels around a given rod, not on the boundary (outside row) of the lattice/assembly.

If one has control rod guide tubes in the lattice, e.g., in VVER-1200 fuel assembly, then that is also a special case.

The guide tube issue is encountered in PWRs, e.g., in a 17x17 where most fuel rods are next to at least on guide tube, and some fuel rods are next to two guide tubes.

 

[raining Pete]

Hi there,

To find the power that is part of one coolant channel, you will need to consider the geometry of the hexagonal assembly. Since the power follows a cosine shape axially, this means that the power is not evenly distributed along the length of the fuel pin.

One way to approach this problem is to divide the fuel pin into smaller segments, each with its own power value based on the cosine shape. Then, you can calculate the total power for each segment and divide it by the number of coolant channels in that segment. This will give you the power per coolant channel in each segment.

Another approach is to use a heat transfer coefficient to account for the non-uniform distribution of power along the fuel pin. This coefficient takes into account the geometry of the assembly and can be used to calculate the power per coolant channel.

Once you have the power per coolant channel, you can then use the given information to calculate the mass flow rate using the formula q = m*cp*deltaT. Just make sure to use the power per coolant channel instead of the total power.

I hope this helps! Let me know if you have any further questions.