How can I accurately calculate the cooling effect of an AGR fuel pin?

[Freddy_uk]

Hello and here is my problematic 1st post.

I have a problem which i need help with, I'm an electrical engineer so my understanding on this subject is basic.

I need to calculate the cooling effect of a AGR fuel pin and I'm not sure were to start.
Here is some background on the question.

At work we have a facility were we process the used irradiated fuel, this facility can be considered as a pipe with a diameter slightly larger than the fuel diameter. The fuel is lowered into the facility which has a CO2 cooling circuit flowing down the fuel.

This facility was designed for larger decay heat levels than we operate at, i wish to calculate/model the effect on fuel temperatures based on a reduced flow rate.

How do i go about doing this, the only information i have to go off is the decay heat of the fuel (16kW), physical dimensions, i know the coolant is CO2 its present flow rate and pressure of the facility.

 

[Astronuc]

Hello and here is my problematic 1st post.

I have a problem which i need help with, I'm an electrical engineer so my understanding on this subject is basic.

I need to calculate the cooling effect of a AGR fuel pin and I'm not sure were to start.
Here is some background on the question.

At work we have a facility were we process the used irradiated fuel, this facility can be considered as a pipe with a diameter slightly larger than the fuel diameter. The fuel is lowered into the facility which has a CO2 cooling circuit flowing down the fuel.

This facility was designed for larger decay heat levels than we operate at, i wish to calculate/model the effect on fuel temperatures based on a reduced flow rate.

How do i go about doing this, the only information i have to go off is the decay heat of the fuel (16kW), physical dimensions, i know the coolant is CO2 its present flow rate and pressure of the facility.

Well, for steady-state, the heat from the fuel element would have to be transported to the coolant. One should know the enthalpy in, add the heat from the fuel element, and that should give one the enthalpy (and temperature out).

It has to be steady-state heat transfer, otherwise temperature would increase until it achieves equilibrium.

Reduce coolant mass flow would produce a greater exit temperature, and also a reduced heat transfer coefficient, so the fuel element temperatures would also be greater.

 

[Freddy_uk]

Astronuc,

Thanks for your reply to my question.
I have been making some progress (i think) and have determined that the pin temperature would be around 320degC based on h=250W/m.k for general forced convection with gases.

Im unsure if this is at all accurate as when i look at decay heat at around 70kw the pin temperatures are a couple of hundred degC greater than some other predictions i have. This data though includes the radiative heat transfer between pins and uses a calculated value for h.

Once i have some confidence in my answers i wish to build a model that determines the maximum heat of the pin and how long it takes to reach it based on a given flow rate.