Time dependent surface temperature of a nuclear fuel rod

[nukapprentice]

I was wondering if anyone has any actual data on the surface temperature of a fuel rod as a function of time. I am really curious as I am trying out a model I found which uses the fractional calculus. Or if anyone could point in the right direction to find said data that would be great as well.

 

[Astronuc]

I was wondering if anyone has any actual data on the surface temperature of a fuel rod as a function of time. I am really curious as I am trying out a model I made using the fractional calculus. Or if anyone could point in the right direction to find said data that would be great as well.

BWR or PWR?

Unless one has a thermocouple on the surface, the temperature must be derived from validated models, and possibly with temperature measurements from core inlet and outlet thermocouples.

In a BWR, there is some subcooling at the inlet, but much of the coolant is at saturated conditions, but the local coolant condition may be subcooled, saturated liquid, saturated liquid with nucleate boiling or liquid+steam in bulk boiling.

In PWRs, the coolant inlet temperature varies (285 to 293°C) according to the particular reactor. The exit temperature may vary from 315 to 330°C depending on the rating of the fuel rod. The coolant mass flux can vary from about 3500 to 3800 kg/m²-s.

The coolant surface temperature depends on the coolant temperature (which is a function of the coolant inlet temperature and enthalpy rise in the subchannel) and the heat transfer coefficient. Ideally, the coolant surface temperature is not much more than 340°C for long periods of time, in order to minimize the corrosion of the cladding. But predicted temperatures can be on the order of 345 to 347°C, with nucleate boiling, and this may promote crud (metal (Fe,Ni,Cr) oxide) formation, in addition to the oxidation of the cladding surface. A key issue in control of activation products is the control of crud through pH control in the primary system, and possibly the use of Zn-injection in the primary system.

 

[nukapprentice]

Thanks for the reply Astronuc and hope all is going well. I guess I wanted recorded data on the surface temperature because I found a model,(derived by Meyer in 1960 for wind tunnels) which used the fractional calculus to find that the surface heat flux is proportional to the surface temperature divided by the square root of time plus an integral involving the temperature(dimensionally also comes out to being divided by t^1/2). This means that the flux decreases as time increases, meaning that it goes to zero at a long enough time. The only way I think that the flux would eventually go to zero is when the water temp becomes equal to the surface temp, i.e. there is no potential for heat to transfer from the rod to the coolant. However since the water is flowing past the surface, heat should be still transferring. Any insight or advice would be greatly appreciated, thanks.

 

[nukapprentice]

Sorry, also meant to say that this is for a PWR.